To explore the influence of acid or alkali contamination on the shear strength of natural loess, the intact loess samples were first immersed in various concentrations of HCl and NaOH solutions. Then, triaxial shear tests, scanning electron microscopy tests, and mercury intrusion tests were carried out, and the soil chemical composition as well as liquid and plastic limits were measured, so as to assess the influence of acid or alkali contamination on the shear strength, microstructure, chemical composition and plasticity of loess. The results indicate that with the increase of the acid concentration, the peak of soil stress-strain curve attenuates, the shear strength deteriorates, the cohesion decreases exponentially, and the internal friction angle is relatively stable. As the alkali concentration increases, both the peak of soil stress-strain curve and the shear strength increase, the cohesion enhances markedly, and the internal friction angle enlarges slightly. Acid contamination breaks the soil particles, dissolves the cementing material, blurs the boundary between particles and pores, and increases the number and size of pores between skeleton particles and those between clay particles. Alkali contamination leads to the scaffold pore collapse of the soil, and the secondary cementation balances the local damage and strengthens the structural connection. Besides, the content and size of pores between skeleton particles decrease while more pores with a smaller size form between the clay particles. After soaking in acid solutions, the cation content in the soil increases notably, the calcium carbonate content decreases sharply, and the liquid and plastic limits are reduced. After soaking in alkaline solutions, both Al³⁺ and calcium carbonate in soil increase slightly, other cations decrease gently, and the liquid and plastic limits increase. Based on the analysis of test results, the microscopic mechanism of the evolution of the shear strength of loess contaminated by acid or alkali was summarized. Acid or alkali contamination resulted in mineral dissolution, ion exchange, and adjustment of particle and pore structure in the soil, destroying the initial structure of the soil and facilitating the formation of new structures. It is the damage of the initial structure or the new structure formation taking the dominance that decides the comprehensive effect improving or impairing the shear strength of the soil.

In order to study the mechanical behavior and permeability evolution law of coal in mining process, the mechanical and seepage experiments on raw coal under different loading and unloading conditions were carried out by using self-made thermal- hydro-mechanical (THM) coupling seepage servo testing system for gassy coal. The influence of loading and unloading stresses on coal deformation and seepage was analyzed and discussed. The relationship between dilatancy angle and plastic shear strain was obtained, and it was found that the dilatation angle changes sharply when the plastic shear strain is about 1.6%. According to the experimental phenomena and results, the structures of coal in elastic stage and yield damage stage were simplified by considering the influence of coal structure on permeability. Based on match stick model and seepage theory analysis, the influence of loading and unloading stresses on coal permeability was discussed from the perspective of strain, and two permeability models (i.e. in the elastic stage and damage stage) were established. Based on the permeability models in different stages and dilatancy angle law, the whole process of permeability model of coal was constructed. The permeability model constructed in this paper is in good agreement with the experimental results, which verifies the applicability of the expression and provides insights for the realization of coal and gas simultaneous extraction.

The salt cavern underground gas storages in China are mostly built in layered salt rock strata with varying permeability. Ensuring good airtightness of the salt cavern gas storages is important. To solve the problem that the “open-hole section” of the wellbore accidentally traverses the micro-permeable layer and causes the airtightness failure of gas storage, a grouting test platform for plugging the micro-permeable layer was independently developed and a feasibility test of grouting plugging was designed based on the geological leakage situation on site. After determining the proportion of slurry with fluidity and filling compactness, an experimental study on plugging cores with ultra-fine cement was conducted. The test results show that the ultra-fine cement can effectively fill the pore and reduce the core permeability. The porosity and permeability of the cores are decreased by about 16% and 95% after the grouting tests. The plugging test data show that the plugging range is in the power function relationship with the grouting time, and the grout flow pattern satisfies the power law flow instead of the Newtonian flow. This study can provide theoretical and experimental basis for the grouting method to plug the micro-permeable layer in salt cavern gas storage, and it is critical for the secondary utilization of similar airtightness failure of the wellbore.

It is of great theoretical and practical significance to study the mechanical characteristics and laws of fault-slip process for predicting the occurrence of fault rockburst. The test material is a kind of coarse-grained syenogranite, the characteristics of stick-slip instability in different fault dip are studied by biaxial loading method. The effects of loading rates of 0.5, 1 and 5 μm/s on the stick-slip instability of faults are studied under different lateral pressures. The results show that: The stress drop during the fault stick-slip instability decreases with the increase of loading speed. The critical shear stress during the fault stick-slip instability is the largest under a low loading speed and a high confining pressure, and the stress drop is the largest when the fault stick-slip occurs. The critical shear stress, the average stress drop and the average period of stick-slip increase when confining pressure increases. With loading rate decreases, average stress drop and average stick-slip period increase under the same confining pressure, and the influence of confining pressure on the average stick-slip period is more significant. The relationship between stick-slip period and loading speed is negative logarithmic linear, and it is not affected by lateral pressure. When the fault dip changes from 56º to 45º, the critical shear stress and the average stick-slip period increase, the average stress drop decreases under the same confining pressure. Fault dip has a significant influence on the stick-slip characteristics of faults. When the fault dip is 34º, the instantaneous instability of the fault occurs when the specimen stress reaches the peak stress, and the energy release increases with the increase of confining pressure. Mining speed has a direct impact on the occurrence of fault rockburst. Under a certain mining speed, fault rockburst is most likely to occur, and the released energy is also large, so the mining speed must be avoided in production.

The existing stability analysis of symmetrical fixed block of roof does not consider the influence of original rock holding force and structural plane fracture, which easily leads to inaccurate analysis results. Based on the relaxation analysis method, the stress situation of symmetrical fixed block under clamping force is analyzed, an equivalent stress formula of fixed surface under the fracture of structural plane is deduced, the joint stress distribution state of fixed surface under the joint influence of clamping force and structural plane frac-ture is discussed, and the analytical solution of the minimum fixed area of symmetrical fixed block is given. The symmetrical fixed block is simulated by PFC^2D software, the difference between the numerical solution of the minimum fixed area and the analytical solution is compared, and the field investigation is carried out on the roof breaking phenomenon of a roadway in the #105 orebody of Gaofeng mine in Guangxi. The results show that: (1) The minimum fixed area of symmetrical fixed block is positively correlated with the height of block and the angle between structural plane and vertical plane, respectively. (2) The numerical solution of the minimum fixed area is basically consistent with that of analytical solution, and the average relative error between them is 7.4%. (3) The clamped block is frac-tured and falls off, leaving visible minimum fixed area at the roof of roadway. The results are in good agreement with the results of nu-merical analysis. The research results show that the stability analysis of symmetrical fixed block of roof based on relaxation analysis method is scientific and reasonable.

Completely decomposed migmatitic granite（CDMG）is a kind of rock with special genesis, but there is little research on its mechanical properties and microstructure. In order to explore the relationship between macroscopic strength characteristics and microstructure of Lincang CDMG, triaxial tests and scanning electron microscopy tests were carried out on samples with different moisture contents, and the microstructure parameters that characterized the size, morphology and orientation of particles and pores were extracted and calculated. By investigating these microstructure parameters, the micro mechanism controlling the macroscopic strength characteristics of CDMG is revealed. The results show that with the increase of moisture content, the stress-strain curve of the sample exhibits a dissimilar hardening effect, the shear strength deteriorates significantly, the internal friction angle decreases linearly, and the cohesion fluctuates up and down. Under the condition of low moisture content, the samples are mainly characterized by micro and small pores, and the particle morphology is mostly angular and sub-angular strip with certain orientation. With the increase of moisture content, the pore content shows an upward trend, forming evenly distributed honeycomb medium and large pores, which are easier to be compressed under axial load. The shape of particles develops to be round, and the overall distribution is disorderly and poorly oriented. Comprehensive analysis of the above results shows that the mechanical properties of CDMG are essentially the result of the interaction between microscopic particles and pore structure. The increase of moisture content weakens the friction between coarse particles, resulting in uneven expansion of clay particles, which leads to pore connection and coarsening and damage of filling structure at the micro level, and then shows mechanical properties reduction at the macro level. The research results provide useful reference for the cognition of mechanical properties and microstructure damage evolution of CDMG.

The conventional triaxial compression test was carried out on the weathered rock in immersed tunnel section of the Shenzhen-Zhongshan Bridge in natural and water-soaked states to reveal the strength change law of the weathered rock after encountering water under different conditions. The strength of weathered rock will decrease significantly when it encounters water, showing obvious softening behavior. When other conditions are certain, the shear strength of the specimen with deviator stress consolidation is significantly lower than that with isotropic consolidation. With the increases of confining pressure and deviator stress, the strain softening phenomenon of weathered rock gradually weakens, and the peak strength and residual strength gradually converge. The elastic modulus of the rock mass before the peak strength is regarded as a constant, and the plastic internal variable when the internal friction angle and cohesive force reach the residual values is used as the variable. The fitting of the cohesive force and internal friction angle to the plastic internal variable is given. The functional relationship expression improves the constitutive model considering the strain softening of weathered rock after encountering water; through regression verification, the theoretical calculation and test results of the model are consistent, indicating that the model can describe the deformation characteristics of weathered rock softened by water. Based on this model, the softening modulus of the weathered rock is obtained, and the softening coefficient is proposed as a reference for the strength and stiffness reduction of the weathered rock when it encounters water, which can provide a theoretical basis for the design and construction of similar projects such as Shenzhen-Zhongshan bridge.

In order to study the tensile-shear behavior of rock discontinuities, the self-developed tension-shear device was used to carry out the direct shear test of the natural limestone bedding planes under normal tensile stresses, and the shear stress-displacement curves, the bedding plane fracture morphologies and strength characteristics were analyzed. The fracture surfaces have no friction crushing zone and local split under a tensile-shear stress. The shear strength decreases nonlinearly with the increase of normal tensile stress. Further, PFC simulation was used to study the influence of saw-tooth bedding plane undulation characteristics on its tensile-shear rupture and strength characteristics. As the normal tensile stress increases, the shear cracks decrease and the tensile cracks increase. When the undulation angle is small, cracks are generated along the saw-tooth bedding planes; when the undulation angle is large, cracks are generated along the saw-tooth bedding planes and saw-tooth. The saw-tooth bedding plane failure can be divided into three modes: tensile and shear ruptures along the saw-tooth planes, tensile and tensile-shear ruptures along the saw-tooth planes, and mixed saw-tooth plane and saw-tooth ruptures. And the damage evolution of each failure mode was analyzed. The shear strength of the saw-tooth bedding planes decreases first and then increases with the increase of the undulation angle, and the minimum is at 30º. It decreases almost linearly with the increase of the normal tensile stress, which can be described by the Mohr-Coulomb criterion. The friction angle and cohesive force decrease with the increase of the undulation angle. The variation of shear strength, friction angle and cohesion force with undulation angle is mainly controlled by the failure mode. With increasing levels of adhesive strength of bedding plane, the saw-tooth plane rupture is gradually converted into a mixed saw-tooth plane and saw-tooth ruptures. When the adhesive strength reaches a certain level, tensile-shear strength no longer increases, mainly controlled by the strength of the saw-tooth rock.

In order to investigate the influences of moisture content w, water cement ration W/C(W is water mass, C is cement mass) and cement content P_s on the thermal conductivity l of cement-bonded calcareous sand, thermal conductivity of cement-bonded calcareous sand under different test conditions were determined by thermal probe method. The change rule of thermal conductivity under the influence of various factors was analyzed, and the microcosmic mechanism of the change trend was explained by scanning electron microscope (SEM). On this basis, a calculation model of the thermal conductivity of cement-bonded calcareous sand, which takes into account the water content, water cement ratio and cement content, was proposed. The experimental results show that the thermal conductivity of cement-bonded calcareous sand is significantly higher than that of natural calcareous sand. The l value of former increases with increasing the cement content, but the increase rate decreases in turn. The l value of cement-bonded calcareous sand increases with increasing water content as positive correlation. However, a larger W/C leads to a smaller l. The results of SEM show that the macroscopic thermal conduction characteristics of cement-bonded sand depend on the variation of size and quantity of its micro-pores. The gel-like hydration product continuously fills the internal pores of the bonded sand, causing a reduction in porosity and thereby improving internal heat transfer of the sand sample. At macro level, the thermal conductivity increases with the increase of degree of cementation. Finally, the novel calculation model for the thermal conductivity of cement-bonded sand having a comprehensive consideration for P_s, w, and W/C has a good applicability, whose coefficient of determination R² is 0.916 4.

Electro-osmosis is frequently used in combination with surcharge loading in foundation treatment. Based on Fredlund’s three-dimensional consolidation theory of unsaturated soil, Esrig’s electro-osmosis consolidation theory and the equal-strain assumption, the governing equations of axisymmetric consolidation considering the radial-vertical flow and smear effect under the coupled electrical and flow field are derived. The semi-analytical solution in the time domain is obtained using Laplace transform, decoupling technology and Laplace inverse transform. Then, the solution of this paper is degraded to the two cases of considering the combined electro-osmotic and surcharge preloading in saturated soil and considering only the load in unsaturated soil respectively to compare with the existing solutions to verify the reliability of the solution in this study. Finally, the effects of the parameters such as effective voltage, electro-hydraulic permeability coefficient ratio, and smear coefficient on the axisymmetric consolidation characteristics of unsaturated soils are investigated by arithmetic examples. The results show that the negative pore pressure finally generated by excess pore-water pressure is proportional to the effective voltage; the consolidation of unsaturated soil under electro-osmosis and surcharge preloading can be divided into two stages, which are mainly affected by loading and electro-osmosis; the settlement of the foundation treated by electro-osmotic and surcharge preloading is the sum of the settlements when the two actions treat the foundation separately, and for the soil with low permeability, the consolidation rate will be significantly increased. Furthermore, the difference in the rate of excess pore-water pressure dissipation in the same interval of the smear coefficient after applying voltage is larger than that when voltage is not considered, and the smaller the smear coefficient is, the greater the negative pore-water pressure finally generates.

At present, the technology of fracturing coal by liquid nitrogen is a new type of anti-reflection technology of coal seam. Water content, coal rank and temperature gradient all affect the anti-reflection of liquid nitrogen. Among them, water content has a significant effect on the anti-reflection effect of liquid nitrogen cracking. In order to study the effect and mechanism of water content on liquid nitrogen cracking, four groups of coal samples with water contents of 0%, 2%, 4% and 6% were treated by liquid nitrogen leaching respectively, permeability tester is used to test gas phase permeability of coal samples, and the permeability and stress sensitivity of coal samples at different pressure points were discussed and analyzed. Some findings were obtained. (i) Under the same confining pressure, the variation trend of gas phase permeability with effective stress generally accords with negative exponential function k = ae^−bs + c, and the correlation indexes are all greater than 0.95. (ii) When the effective stress exceeds a certain critical value, the gas permeability of coal sample is affected by Klinkenberg effect and presents an upward trend with the increase of the effective stress. (iii) The increase of water content of coal sample can significantly promote the fracturing effect of liquid nitrogen. The most obvious is that when water content increases from 2% to 4%, the increase of permeability before and after fracturing increases from 92.88% to 357.12%. (iv) The normalized permeability of coal samples before and after liquid nitrogen fracturing is treated, and it is found that coal moisture has both a negative effect of blocking seepage and a promoting effect of improving the fracturing effect. The normalized permeability of coal samples before and after fracturing is complicated under the combined effect of moisture. (v) Under the same pore pressure, the effective stress sensitivity of coal decreases gradually with the increase of effective stress, and it can be significantly improved by liquid nitrogen fracturing.

The energy pile is a combination of load bearing and heat exchange. It bears the combined action of load and temperature. The bearing capacity of energy pile is very complex. Based on the energy pile engineering in Shanghai, the Brillouin optical time-domain reflectometry (BOTDR) distributed optical fiber sensing technology is used to monitor the axial force and temperature of energy pile. The axial force and side friction distribution curve of pile are obtained under the load, temperature and under the joint action of load and temperature. The bearing characteristics and load transfer characteristics of energy pile under load and temperature are analyzed. The results show that the bearing behavior of energy pile is different from the ordinary cast-in-place pile. The increase of pile temperature will cause pile deformation, and the axial force of pile will produce under the constraint of soil, which is basically linear with the change of pile temperature. Under the combined action of load and temperature, the axial force of pile is much larger than that under the action of a single factor, and the increment of axial force caused by the combined action of load and temperature can reach two times or more that of under the action of load alone. At the same time, the side negative friction of pile will be generated in a large range due to the influence of temperature rising, but the load action can obviously alleviate the generation of negative friction.

The concept of effective stress proposed by Terzaghi in 1922 is a cornerstone concept in soil mechanics, and its history has been a hundred years so far. On the occasion of the centenary of the birth of effective stress, it is worth summarizing and analyzing the origin, the physical meaning, the expression, and the mechanical effect of effective stress. The summary and analysis show that Terzaghi’s effective stress equation for saturated soil has been widely recognized, whereas the specific expressions for the Bishop-type effective stress equation for unsaturated soil have not been unified. The physical meanings of the stress variables in the effective stress equations for saturated and unsaturated soils have still been explained by different ways. Through further analysis, we find that the stresses existing on the soil skeleton can be divided into three types: the first one is the stress transmitted through the soil skeleton caused by the total stress, i.e., the effective stress; the second one is the stresses acting on the cross-section of soil particles and on the contact between soil particles induced by the pore fluid pressure, which are not transmitted through the soil skeleton; and the third one is the local stresses acting on the contact between soil particles induced by the van der Waals forces, diffuse double-layer forces, surface tension of water, and cementation forces, which are also not transmitted through the soil skeleton. Therefore, the contributions of these three types of stresses to the shear strength and volumetric strain of soils should be separately quantified.

To study the dynamic mechanical properties and damage evolution process of the cemented tailings backfill, a separate Hopkinson rod was used to perform impact loading tests on the cemented tailings backfill under different strain rates. The experiment results show that the dynamic compressive strength and the dynamic compressive strength enhancement factor of the backfill increases exponentially with the increase of the strain rate, and the strain rate effect of the backfill with a lower cement content is more significant. The pre-peak energy consumption density, post-peak energy consumption density, strain energy per unit volume, and total energy consumption density of the backfill all show an exponential function increasing law with the average strain rate increase, and the dynamic compressive strength has an obvious positive correlation with the post-peak dissipated energy density. Under the action of impact load, the deformation and failure of the backfill mainly experienced three stages: linear elastic deformation, yield failure and post-peak fracture. The energy is stored in the sample in the form of elastic strain energy in the linear elastic deformation and yield failure stage of the backfill, and the energy is mainly released by dissipated energy in the post-peak fracture stage. Under impact loading, the energy damage evolution process of the backfill is divided into three stages: the damage stable development stage, the damage acceleration stage and the damage destruction stage.

Microbial induced calcite precipitation (MICP) is a technique that can be a potential method to solve wetting swelling and drying shrinkage of expansive soils. With the bacteria concentration and urease activity as standards of measurement, the growth properties of Sporosarcina pasteurii in various conditions were studied, and the most favorable temperature, pH and vibration velocity were determined. Two different types of expansive soils were treated with MICP, and the effect of this method was studied by comparing expansive properties, cohesive force, internal friction angle and shear strength before and after the treatment. The mechanism of MICP treated expansive soils was explained through microstructure perspective. The results showed that the optimal culture conditions for the bacterial growth were as follows: the pH of 7, the vibration velocity of 200 r/min, and the temperature of 30 ℃. After treating with MICP, the free swelling ratio and unloaded swelling ratio were decreased significantly, while the cohesive force, internal friction angle and shear strength were increased. The calcium carbonate generated during MICP played the role of pore filling and soil particle cementation, and the replacement of low valence cations by calcium ions and the wrapping effect of calcium carbonate on soil particles improved the properties of expansive soils. The research can provide beneficial references for the technology and engineering applications of MICP treatment of expansive soils.

The acoustic emission (AE) test of sandstone rock sample under uniaxial multi-step loading compression were carried out, and the AE signals were observed. The relationship curves of time-stress-AE parameters were established, and the characteristics and evolution laws of AE during the entire loading were analyzed accordingly. With the aim to reveal the critical slowing down phenomenon of rock deformation and failure, the autocorrelation coefficient and variance of AE parameters versus time were analyzed in-depth. The results demonstrate that: (1) the rock produces obvious acoustic emission during the multi-step loading process, and the acoustic emission ringing count becomes higher and higher as the loading level increases, and reaches the highest at the moment of failure of the rock sample; (2) the characteristics of acoustic emission RA(rise time/peak amplitude)-AF(average frequency) indicate that the tensile cracking prevails in the whole loading process, and the shear cracking gradually increases in the later stage of loading; (3) the variance and autocorrelation coefficient of parameters such as AE ringing count, rise time, peak frequency, and RA suddenly increase before the catastrophic failure of rock sample, which indicates that the obvious critical slowing phenomenon appears before rock failure; (4) the variance of peak frequency and RA can be used as key precursor indicators of rock damage and failure. In view of this, applying the analysis of the critical slowing phenomenon to brittle failure process of rock has very important scientific value and practical significance for in-depth understanding of the damage state and the precursors of catastrophic failure of rocks.

By deforming and evolving the Weibull model formula, a gradation equation for quantitatively representing the continuous gradation distribution is obtained. The gradation equation can express three typical gradation distribution forms of hyperbola, approximate straight line and reversed S-shaped curve. The gradation distribution of silt, clay, sand, and coarse-grained soil is fitted, and the fitting results are all good. Considering the distribution range of the particle size, the value range of the gradation parameter is studied in detail with the method of theoretical deduction. By combining the actual fitting results with the theoretical derivation results, the final grading parameter range is obtained: c is 0.001−1.5, n is 0.065−4.8. Comparing the new gradation equation with Talbot fractal gradation equation and Wu Er-lu’s single-parameter gradation equation, it is found that the Talbot fractal gradation equation cannot reflect the reversed S-shaped gradation distribution, and the single-parameter gradation equation cannot reflect the uniform and narrow gradation distribution of particles, and the proposed gradation equation fits the above different gradation distributions well. The proposed gradation equation has wider applicability. In addition, the evolution of gradation parameters under the elimination method, similar gradation method, equivalent substitution method, and hybrid method is derived, and the quantitative expression of the gradation distribution before and after scaling is realized.

Wave propagation across rock masses containing structural planes has been an important subject of rock dynamics. The stresses of deep rock mass will affect the mechanical properties of rock structural plane, and then affect the stress wave propagation across rock mass. Based on the time domain recursive analysis method (TDRM), quantitative analysis for the interaction between stress wave and a nonlinear rock structural plane is carried out in this study, so as to deduce the wave propagation equation. The deformation of the rock structural plane is assumed to satisfy the Barton-Bandis model (B-B model) in the normal direction and satisfy the Coulomb slip model in the tangential direction. For some special cases, such as horizontal or vertical distribution of structural plane and horizontal distribution of wave front, the calculation model and wave propagation equation are simplified. Through comparison, it is found that the rock mass stresses have obvious influence on wave propagation characteristics. Parametric studies about the effects of rock mass stresses characteristics, joint characteristics and incident wave frequency on stress wave transmission and reflection coefficients are finally conducted.

Red mud is a solid waste residue from the production of alumina, which is highly alkaline and produced with huge amount. In this study, red mud was used as an alkaline activator combined with fly ash and ground granulated blast-furnace slag (GGBS) to solidify/stabilize cadmium contaminated soil. The unconfined compressive strength, shear characteristics, heavy metal leachability and microstructure of the samples cured for 7, 14 and 28 days were studied. The results show that: Cadmium ions in soil reduce the strength of soil, and the strength of soil increases after the addition of red mud, GGBS and fly ash; the initial concentration of cadmium ions affects the strength of red mud-based solidified soil. When the initial value is higher than the critical concentration value, the soil strength begins to decrease gradually; the increase of cadmium concentration in soil reduces the shear strength and cohesion of soil and increase the friction angle. Compared to red mud-fly ash, red mud-GGBS has higher unconfined compressive strength and lower heavy metal leaching concentration.

Based on the consolidation theory of unsaturated soils proposed by Fredlund and his co-workers (1984), by using Fourier series expansion and Laplace transform technique, semi-analytical solutions are proposed for the axisymmetric consolidation of the unsaturated foundation under the piece-wise cyclic load with the equal strain hypothesis in this paper. Firstly, based on the radial boundary conditions and equal strain hypothesis, the governing equations of axisymmetric unsaturated soil consolidation under piece-wise cyclic load are established. Afterward, the governing equations are solved by applying series expansion and Laplace transform, and the semi-analytical solutions of excess pore-air and pore-water pressures and the average degree of consolidation are given. Then, the correctness of the solutions and their results is verified by the degradation method and finite difference method. Finally, three specific segmental cyclic loads are introduced as the typical cases, the consolidation properties of unsaturated soil ground with the change of permeability coefficient ratio (k_a /k_w), model size (N), and load characteristic parameter (a) are analyzed. The conclusions drawn in this paper can give a strong theoretical support for the treatment of unsaturated soil ground.

With the typical saturated sandy gravel stratum in Beijing as the research object, the frost heave and thawing characteristics of saturated sandy gravel under different fine soil contents and load conditions are studied. The results show that there is a significant shrinkage phase at the initial stage of freezing of saturated sandy gravel specimens under loading conditions, and the shrinkage is 0.053% of the specimen height. Both the frost heave ratio and the thawing settlement coefficient have an obvious exponential correlation with time. Under the same condition of fine soil content, the thawing settlement coefficient of saturated sandy gravel (the content of fine soil is greater than 10%) and the frost heave ratio decrease with the increase of load, and the load has little effect on the thawing settlement coefficient of saturated sandy gravel with a fine soil content less than 10%. Under the same load condition, the frost heave ratio and thawing settlement coefficient of saturated sandy gravel increase with the increase of fine soil content. Load has the greatest influence on the frost heave rate, followed by the fine soil content. Unloaded saturated sandy gravel with a fine soil content less than 0.82% is a weak frost heave material. A prediction model for the frost heave ratio and thawing settlement coefficient of saturated sandy gravel considering the influence of fine soil content and load is established.

Soil-water characteristic curves（SWCCs）are one of the basic parameters in unsaturated soil mechanics, which is usually used to estimate the properties of unsaturated soils. However, the measurement of SWCC is time-consuming and laborious. In order to solve this problem, we used the one-point SWCC measurement and parameters of particle size distribution to estimate the three parameters of Van Genuchten equation for sandy soils. Parameters of the Van Genuchten model were correlated with the basic properties of 43 (No.1−43) types of sandy soils. Then we obtained two equations to estimate the three parameters. The values of the three parameters were calculated by the two equations and one-point SWCC measurement. The results show that the parameter av can be expressed as an exponential function of the combined parameter (P1 000/P500), and mv can be expressed as an exponential function of 1/nv. Sensitivity analysis shows that the one-point SWCC measurement locating in the range of 1 kPa and 10 kPa gave the most reliable estimated results. The proposed method was evaluated using a total of 4 (No.44−47) types of sandy soils. It shows that the proposed method has a good performance in estimating SWCC.

The pile foundation in high-steep rock slope has double functions, i.e., transferring loads from superstructure and bearing landslide thrust, and the mechanical behavior is very complex. In order to reduce the adverse effect of the pile friction to the slope stability, a steel casing coating pile (SCCP) is proposed, in which the isolation steel casing is set outside of the pile, and the inner of steel casing is coated by the asphalt. Based on the push-out test, the lateral friction distribution rule of pile and the isolation resistance-reducing effect of the asphalt coating are studied. The experimental results indicate that the shear stress of the concrete without asphalt coating is large at both ends and small in the middle, and the asphalt coating can effectively reduce the lateral friction of the pile, change the bonding mechanism between steel and concrete, and make upper loads transferred to deep rock mass. Based on numerical analysis, it is shown that the steel casing coating pile can reduce the upper friction of pile, and transfer the load to deep rock mass, and lessen the adverse effect of the pile lateral friction above the slope sliding surface to the stability of the high-steep slope.

The dispersity of dispersive clay in water is essential for the erosion and piping damage of dikes, channel slopes, and road slopes in dispersed land areas, and the discrimination of soil dispersion is prerequisite for engineering construction in dispersed land areas. In this paper, the tests such as pinhole test and crumb test are conducted to determine the dispersity of soil samples, then scanning electron microscope and X-ray diffraction are carried out to study the dispersion mechanism and microstructure of dispersive clay, and the primary and secondary influencing factors of soil dispersion are analyzed. Because of the strong linear relationship between the standard hygroscopic moisture content and the montmorillonite content of soil mineral composition, the distribution characteristics of montmorillonite content and pH value of typical dispersive clay are summarized by big data, a comprehensive discrimination method of soil dispersion based on the standard hygroscopic moisture content + pH value test is proposed, and the corresponding discrimination indices and discrimination procedures are given. Finally, it is verified with an engineering example. The results show that the existing environment with certain montmorillonite content and high pH value is the material basis and environmental guarantee for the dispersity of soil mass. If the requirements of montmorillonite content ≥ 10% and pH ≥ 8.5, the soil can be judged as dispersive clay; for soils out of this range, soil dispersity should be comprehensively judged in combination with the determination of dispersity of soil and field investigation results.

It is essential to expose the rock’s heterogeneous microstructure and micro-mechanical properties for understanding the macroscopic deformation and failure. In this paper, atomic force microscopy (AFM), combined with powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrum (EDS) techniques, is used to analyze the nanoscale mineral composition and microstructure of slate taken from Sichuan-Tibet railway tunnels. The spatial distribution of Young’s modulus is revealed at the microscale. The average Young’s modulus and probability of high, medium and low strength phases are determined by statistical deconvolution of more than 1.6 million test data using a mixed Gaussian model. The upscaling of Young’s modulus of slate is carried out based on the Mori-Tanaka model. A cross-scale characterization method of Young’s modulus is proposed based on the Mori-Tanaka model and micro-mechanical properties of minerals. The results show that: (1) The quartz embedded in the slate is a convex polygon block, the thin illite sheets are closely arranged with obvious stratification, and the chlorite is loosely distributed in the micro-pores as the matrix; (2) The adhesion of quartz, illite, chlorite and micro-pore to the probe increases in turn, and the Young’s modulus decreases; (3) The porosity of slate is 16.61%, and the equivalent Young’s modulus at the macroscale is 56.17 GPa. This approach can be used to determine the mechanical properties of fractured, small-size and arbitrary-shaped hard rock, which can overcome the difficulty of collecting large-size samples of engineering rock.

Sliding-bending failure is one of the common modes in bedding rock slopes. In this paper, we analyzed the geological origin of bedding rock slopes with slab-rent structure, and applied the theory of maximum tensile stress to the analysis of geomechanical models. According to the damage characteristics, the sliding-bending rock stratum was divided into two parts: the sliding section and the bending section. Then, the energy method, the Rayleigh-Ritz method, and the stationary value theory of total potential energy were used to simulate the equation of deflection curve approximatively. Besides, the formulae for calculating the maximum tensile stress and for the prediction model of potential failure location in bedding rock slopes with slab-rent structure were deduced based on the beam-plate theory. On this basis, the theoretical formula was programed and the approximate consistency between the theoretical prediction value and the accrual failure value was obtained through calculating the typical failure slope. Finally, the failure process of Shanyang landslide was analyzed by FLAC3_D numerical simulation software and the following conclusions were drawn: (1) The variation trend of the total displacement was characterized by obvious sliding-bending variation. (2) The numerical simulation results of the maximum tensile stress and the location of the tensile plastic zone were approximately consistent with the theoretical results.

Thermal deterioration of rock occurs in tunnel portal section due to temperature fluctuation of rock in high temperature environment in southern China. As heat conduction of fracture tip is nonlinear, a triangular heat source function of fractured rock mass is established based on Green’s function method and mirror image method. Temperature distribution of fracture tip is calculated, and influences of fracture shape parameters and multi-fracture interaction on temperature are analyzed. It is found that the internal temperature of fractured rock mass is higher than that of non-fractured rock mass during solar radiation period. For triangular fractures with the same length, the temperature varies greatly as apex angle of triangle is large. When spacing between parallel fractures or coplanar fractures is small, the superposition effect of temperature of fracture tip is strong, and the temperature value tends to that of single fracture with increase of spacing. The temperature of fractured rock mass transfers faster than that of non-fractured rock mass. Temperature isolines appear around fractures, and temperature around fractures increases significantly. The result provides theoretical basis for thermal stress analysis of fractured rock mass in tunnel portal section in high temperature environment.

In this work, the pseudo-dynamic method is introduced to evaluate the seismic stability of multi-level slopes reinforced with piles. Based on the kinematic limit analysis and the strength improvement technique, a horn failure mechanism is adopted to calculate the safety factors of the 3D complex slope reinforced by a row of piles. Comparisons between the solutions of pseudo-static method and the presented results show that the proposed technique is effective. Through parametric analysis, the influence law of each factor on the safety factor Fs is explored, and it is shown that multi-level slopes are safer than single-level slopes. In addition, in the seismic design of 3D complex slopes, piles can effectively improve the stability of slopes. Finally, the suggestions are provided for the seismic design of 3D complex slopes reinforced with piles.

The construction parameters of slurry shield in tunnel construction are mostly adjusted according to the field construction experience, and the systematic theoretical calculation model between the construction parameters and mud pressure of slurry shield is lacking. The relationship that each construction parameter needs to be met during the process of shield tunneling has been put forward through a detailed research and analysis on the type and working principle of slurry balance shield. The slurry pressure control model of the slurry chamber of the slurry shield and the calculation method of the directly quantified controllable construction parameters of the slurry shield to control the mud pressure are obtained. The requirement that the mud residue suspension and transportation capacity in shield construction of the slurry pressure in the slurry chamber needs to be met has been presented and the relationship between the tunneling speed of the slurry shield and the slurry flow is deduced. The result shows that the slurry pressure of the slurry chamber increases with the increases of the slurry flow and the shield tunneling speed, and decreases with the increase of slurry discharge flow. The effectiveness of the presented calculation model is verified through the slurry shield construction project in Changsha subway line 6 and numerical simulation. The research result provides a theoretical basis for the study on slurry pressure control in slurry chamber of slurry balance shield.

As an important mechanical index of rocks, brittleness is of great significance for deep rock mass behavior assessment and disaster prevention. The stress-strain curve of rock can well represent rock brittleness. Considering that most of the existing brittleness indicators based on stress-strain curves only analyze a part of the curve, and few indices can be accurately applied to the rock II type curve, lack of overall consideration may lead to the inadequate adaptability and reliability in engineering application. In order to solve those problems, such as the unclear physical meaning and the discontinuous relationship between the evaluation results and rock brittleness of the existing brittleness indices based on the complete stress-strain curve of rock, the influences of pre-peak stress rising rate, post-peak stress falling rate and peak strain on rock brittleness were analyzed, and a method of rock brittleness index with clear physical meaning, monotonous and continuous relationship between calculation results and rock brittleness was proposed. The commonly used brittleness indices were selected to compare the brittleness evaluation of the marble of Jinping II hydropower station and the granite, metamorphic sandstone and gneiss of a railway under uniaxial compression conditions, which verified the applicability of the index proposed. This novel brittleness index was further applied to the brittleness evaluation of marble under conventional triaxial test conditions. The results showed that this index could not only quantify and classify the brittleness characteristics of different rock types, but also characterize the confining pressure inhibition behaviors of rock brittleness.

The cylindrical cavity expansion theory is an effective method to analyze various geotechnical problems, such as pile installations and pressure meter tests. However, most of existing studies which assume that the soil is an infinite medium are not suitable for the case of finite medium. The critical state model is used to describe the stress-strain relationship of unsaturated soils and the constitutive model for water phase which represents the relationship between the specific volume and suction is introduced. With the boundary effects considered, the semi-analytical solutions for cylindrical cavity expansion in unsaturated soil under different drainage conditions are deduced. Intensive parametric studies have been conducted to analyze the effects of boundary, suction and drainage conditions on the results of cavity expansion. The results show that the cavity pressure increases continuously with the increase of cavity radius under the effects of boundary, which is different from the cavity pressure that tends to be a stable value in infinite medium. The greater cavity pressure is required to expand the same cavity radius for a smaller boundary size. In addition, the cavity pressure increases and variation of specific volume caused by the same stress increment decreases with the increase in initial suction, which can be attributed as the suction hardening effect. The saturation of soil at the same position around the cavity is higher, and the suction and effective stress components are lower in the case of undrained condition than drained condition. It is more obvious when the distance from the cavity wall decreases.

Analysis of the effects of sizes, shapes and wetting condition on crushing strength and modes of calcareous sand can be accomplished using a statistical method by subjecting particles with different sizes and shapes to single particle crushing tests through automatically uniaxial loading system and the crushing process, and modes of particles were observed and recorded with the help of microscopic probe. In addition, the micro-uniaxial loading device supported by in-situ X-ray μCT scan was used to scan the crushing process of two calcareous sand particles with high precision, and the effects of internal pore structure were deeply investigated by image processing and analysis technology. The results show that the characteristic strength of calcareous sand particles is decreased with increasing sizes. While for the particles with similar sizes, the characteristic strength of compact particles is the largest, followed by platy particles and bladed particles, and elongated particles are the least. The crushing process of calcareous sand particles can be summarized as three crack forms and three fracture patterns, which are single crack, cross crack, arch crack and patterns I, II, III, respectively. Finally, analysis results of μCT images show that the cracks caused by particle crushing concentrated mainly in the dense internal pores, which indicated that internal pore structure has an important influence on the crushing behavior of calcareous sand particle.

A series of drainage triaxial shear tests under different stress paths is carried out on calcareous sand in the South China Sea. The particle breakage and shear strength characteristics of calcareous sand under complex paths are systematically studied. The research shows that the mechanical properties of calcareous sand change regularly with the deflection of the shear loading direction. When the stress path is in the loading zone, with the clockwise deflection of shear path, the softening degree and shear strength increase; the dilatability, the peak internal friction angles decrease, and particle breakage increases. When the stress path is in the unloading zone, the calcareous sand breaks suddenly, and the particle breakage is relatively large. There is a "0 initial average effective stress" stress path boundary, and the effect of initial average effective stress on the volume change on both sides is completely opposite. Based on fractal theory, an empirical formula for predicting B_r value under different consolidations, shear paths and initial average effective stress is established, and the complex influence mechanism of stress path and particle fracture coupling on the shear behavior of calcareous sand is revealed. According to the test results, the generalized additive models (GAMs) are used to derive the strength envelope considering the effects of particle breakage and stress paths, which can be used as the basis for predicting the peak strength of calcareous sand under different stress paths.

The obvious particle size effect of the calcareous sand gravel with irregular particle shape and uneven particle grading is shown after loading. A series of shear tests on calcareous sand gravel under various particle sizes as well as dry and wet conditions was carried out. The relationship between shear stress and displacement of calcareous sand gravel under different shear modes was analyzed, and the particle size effect of shear strength and deformation of calcareous sand was studied. The results indicate that the peak strength of calcareous sand gravel first increases, then decreases and then increases, when the particle size increases from 0.075 mm to 60 mm. The inflection point of the peak strength change appears when the particle size is from 0.25 mm to 0.5 mm, and the calcareous sand particles generate more fragmentation under this particle size. Due to the influence of inflection point particle size, the internal friction angle shows the rule of increasing first and then decreasing with the increase of particle size. While the quasi cohesion shows the rule of increasing first, then decreasing and then increasing with the increase of particle size. The existence of water film effect makes the shear strength of calcareous sand under a certain water content lower than that under air drying. The quasi cohesion parameter obtained by direct shear test is larger than that by simple shear test, since the effective stress path and dilation angle under different shear methods have difference, and the deviation will increase with the growth of particle size.

A new idea that adopts a geotextile instead of a latex membrane to improve the performance of compaction-grouted soil nail, was proposed. Based on the self-developed device for testing geotextile’s filtration performance, a series of cement slurry filtration tests was carried out to study the influence of water-cement ratio, slurry volume and grouting pressure on the geotextile’s filtration performance. In addition, strength tests were carried out on cement blocks obtained from the slurry before and after filtration test. The main conclusions drawn are as follows. As the water-cement ratio increases, the final filtration mass of the slurry, the end time of the filtration and the mass flow rate increase accordingly, but the increment of the end time of filtration gradually decreases; the change in the volume of the slurry does not affect the mass flow rate. However, the end time of filtration linearly increases with the volume of the slurry. With the increase of the grouting pressure, the mass flow rate of the slurry gradually increases. At the same time, the increase rate of the expansion area of the geotextile is linearly increased with the grouting pressure. By adopting the geotextile, the water-cement ratio in the grout bulb is significantly reduced, which then largely improves the strength. This study is helpful for the application of the compaction-grouted soil nail by using geotextile.

The deep-sea rare earth-rich sediments are exploited in the Pacific district. In this study, the conventional physical properties are studied by analysis of laser particle size, test of liquid and plastic limit, and mineral compositions and microstructures are analyzed by X-ray diffraction(XRD) and scanning electronic microscope(SEM) method respectively. Test result shows that the deep-sea rare earth-rich sediments have high liquid limit, high plasticity, and their mineral compositions is mainly composed of primary minerals such as quartz, calcite, halite, feldspar, mica, and secondary minerals such as green stone. The microstructure is mainly composed of links structure and honeycomb-like sheet structure. In addition, the routine geotechnical experimental method can’t test the strength of this kind of deep-sea rare-earth-rich soft sediments，the sediment rheological tests under different temperatures and water contents are conducted by the Brookfield's RST rheometer, and the relevance of the undrained shear strength, yield stress and apparent viscosity with moisture content and temperature are analyzed according to the experimental results. Then, the Herschel-Bulkley model is introduced to discuss the rheological parameters. Further, the rheological characteristics and mechanisms of the deep-sea rare earth-rich sediments are analyzed by the phase transformation and the interparticle interaction. The results show that water content and temperature have a significant effect on the shear stress and apparent viscosity of the sediment. Compared with normal temperature conditions, the shear stress and apparent viscosity of the sediment are significantly increased in a low temperature environment. The apparent viscosity and the yield stress decrease as the moisture content of the sediment increases. This result can provide a scientific basis for the fluidized transportation of deep-sea rare earth-rich sediments.

The hydraulic characteristics of compacted loess are controlled by its microstructure, which depends on the sample preparation conditions. This study aims to explore the influence of sample preparation conditions on microstructure, saturated permeability coefficient and soil-water characteristic curve (SWCC) of compacted loess. The mercury intrusion porosimetry (MIP) tests, variable head tests and SWCC tests were carried out on the specimens prepared under different conditions to obtain the pore-size distribution curves, saturated permeability coefficients and their variations with the seepage times, and SWCCs. The results show that: (1) The molding water content affects the density of mesopores (2 000 nm < d ≤ 12 000 nm) and that of micropores (150 nm < d ≤ 2 000 nm) by affecting the sizes of aggregates; the higher the molding water content of the specimen is, the smaller the density of mesopores is, and the larger the density of micropores is. The compaction degree has a significant effect on the density of mesopores by affecting the arrangement of aggregates; the greater the compaction degree is, the tighter the arrangement of aggregates is, and the smaller the mesopores content is. (2) The initial saturated permeability coefficient reduces with the increases of compaction degree and molding water content of compacted loess. When the compaction degree is small (85%), the saturated permeability coefficient of compacted loess decreases with the increase in number of seepage, and it rises with increasing number of seepage when the compaction degree is high (90% and 94%). (3) The molding water content mainly affects air entrance vaule (AEV) and the slope of the transition zone. The greater the molding water content is, the smaller the AEV is, and the slope of the transition zone is. Compaction degree mainly affects AEV and saturated moisture of specimens. The higher the compaction degree is, the higher the AEV is, and the smaller the saturated water content is.

The effects of moisture content, dry density, temperature and volume deformation on the thermal conductivity of remodeled Nanning Tertiary expansive mudstone specimens were investigated by the thermal probe method. The research showed that the thermal conductivity of the remodeled expansive mudstone increased with the increase of moisture content and dry density, mainly because the increase of water content lowered the thermal resistance of the air in the mudstone and the increase in dry density brought the mudstone particles into closer contact with each other. The thermal conductivity increased by 135.7% when the water content increased from 10.4% to 21.9%, and thermal conductivity increased by 133.9% when the dry density increased from 1.50 g/cm3 to 2.00 g/cm3. Under the effect of latent heat transfer, the thermal conductivity of remodeled expansive mudstone increased with the growth of temperature and exhibited two different stages of slow growth and rapid growth. The particle size kept expanding and aggregating under the influence of temperature, which provided favorable conditions for latent heat transfer. The thermal conductivity of remodeled expansive mudstone decreased with the increase of the volume deformation rate. When the deformation rate increased from 0.5% to 5%, the thermal conductivity of expansive mudstone decreased by 5.7%−29.5%, due to the fact that the expansive mudstones are looser after water absorption and expansion.

At present, most studies on hydrate reservoir deformation do not consider the role of capillary force, and the hydrate pressure and fluid pressure in the reservoir are considered to be consistent. However, in the South China Sea, the hydrate reservoirs are mostly clayey silty with small pore size, thus the capillary effect is obvious. Based on poromechanics and hydrate phase equilibrium theory, a reservoir deformation model was established. In this model, the material in the pores is divided into two phases, i.e. the solid phase of the hydrate and the equivalent fluid phase consisting of discontinuous bubbles. The model focuses on the pressure difference between the hydrate solid and the equivalent fluid, known as capillary pressure. Finally, according to the data of Shenhu area in the South China Sea, the depressurization method and the thermal stimulation method of hydrate exploitation are analyzed in detail. The results show that the capillary effect has a great influence on the phase equilibrium condition of the hydrate and the reservoir deformation of the clayey silty reservoir in the South China Sea. For a given pressure, the melting point of the hydrate will decrease with the decrease of the aperture, which makes the phase equilibrium condition of the hydrate appear as a region rather than a curve in the pressure-temperature, and if the capillary effect is ignored, the reservoir deformation will be seriously underestimated.

Through the dynamic triaxial test of the saturated silt in the unloaded state of Hangzhou metro line 5, the dynamic characteristics of the lateral unloading saturated silt under long-term cyclic loading are studied, and the influence of unloading stress path on dynamic characteristics of such soil is summarized. The test results show that the saturated silt has critical dynamic stress under the lateral unloading, and the critical dynamic stress of the soil which is under the unloading and reloading stress path is the smallest. When the dynamic load does not reach the critical dynamic stress, the cumulative dynamic strain and cumulative dynamic pore pressure of the soil appear to be stable. When the dynamic load exceeds the critical dynamic stress, the cumulative dynamic strain of the soil appears to be a destructive type. However, in the single lateral unloading stress path, the cumulative dynamic pore pressure development curve of soil samples does not show a steep increase stage. The results show that when the soil sample is under the lateral unloading and reloading stress path, the increase of excess pore water pressure caused by the reloading process will produce larger dynamic pore pressure and accumulated dynamic deformation, and reduce the critical dynamic stress of the soil sample, which is also a risk factor for the settlement and vibration settlement of the soil around the subway tunnel.

According to the elastic-ideal plastic assumption and associated flow rule, the intermediate principal stress equation and the strength equation in plane strain condition are proposed on the basis of Lade-Duncan criterion. The shear strength parameter under plane strain condition is connected with that under conventional triaxial condition. Therefore, the equivalent internal friction angle and the cohesion in plane strain condition can be determined by a conventional triaxial test, which can effectively reflect the effect of intermediate principal stress on the increase of internal friction angle under plane strain condition. It is proved that the friction angle at the condition of strength failure of non-cohesive soil under plane strain is that of the maximum value of the equivalent friction angle, which is the mathematical meaning of the new strength equation. The mathematical meaning of the new strength equation is also shown by drawing the geometric relationship of three criteria on the π plane. The effectiveness of the strength equation is confirmed with experimental results of bearing capacity. In the calculation of plane strain using the standard method or the finite element method, the new strength equation can choose shear strength parameter more efficiently, considering the influence of the intermediate principal stress.

Current conventional primary thickness selection method of frozen wall is derived from the assumption of taking soil as a loose body, which is not applicable to clayey soil theoretically, hence the design of frozen wall thickness is always too conservative. As a result, it not only leads to a great waste of time and resources, but also causes many difficulties to the actual construction. In view of the above problems, based on the shear failure theory of clay stratum, this paper proposes and constructs a primary thickness selection method for the straight-wall arched frozen wall deeply buried in clay stratum. The rationality and applicability of the method are verified using numerical calculation and engineering application, and the superiority of the method proposed is further compared and analyzed in combination with the conventional design method. Research shows that: (1) Since the conventional design method cannot describe the failure mode of clay and calculate the supporting pressure of the frozen wall in an objectively and truly way, making it difficult to reasonably select the primary thickness of frozen wall. (2) Based on the shear failure theory of clay, this paper proposes and constructs a set of optimization methods suitable for the primary thickness selection of the straight-wall arched frozen wall deeply buried in clay stratum. It has been verified that the calculation result is effective and feasible as the primary selection plan. (3) Compared with the conventional method, the proposed method is theoretically closer to the engineering practice, and the frozen wall thickness obtained is obviously smaller than that calculated by the conventional method, which can effectively improve the economy of the artificial ground freezing construction on the premise of ensuring safety. (4) With the increases of cohesion and embedding depth, although the frozen wall thickness obtained by the proposed method shows a decreasing and increasing trend, respectively, they are significantly smaller than the design value of the conventional method under the same parameters. Besides, the increase of them has a positive correlation with the optimization of the frozen wall thickness. (5) The general formula and design process derived and constructed in this paper can provide necessary supplements to the existing specifications, and meanwhile, it could provide useful reference for both the design and construction phases when using the artificial ground freezing method in the similar projects in the future.

The Zhanjiang clay is a typical structured soil with high strength and sensitivity, and its mechanical properties are easily affected by sampling disturbance. Based on the self-boring pressuremeter tests (SBPT) and seismic dilatometer tests (SDMT) in the typical structured clay stratum, the in-situ stiffness decay curves are obtained. Furthermore, the Stokoe model is used to describe the normalized stiffness decay behaviors. Results show that the in-situ stiffness decay curve can be obtained by combining the tangential shear modulus G_t from SBPT with the small-strain shear modulus G₀ from seismic wave velocity V_s calculated by SDMT. The in-situ stiffness decay curves of structured clays at different depths have a declined trend with a hyperbolic type with the increasing strain levels, which proves that the mechanical properties of structured clays exhibit nonlinear characteristics. With the increase of depth, the in-situ stiffness parameters tend to increase under the condition of shear strain less than 10⁻³%, while they almost remain unchanged when the shear strain is larger than 1%. The normalized G-g decay curves obtained from the in-situ tests are in good agreement with the fitting curves from the Stokoe model, indicating that the numerical model could accurately describe the in-situ stiffness decay characteristics of structured clays. This study provides the design parameters for geotechnical engineering constructions of structured clays in Zhanjiang and an important reference for similar formations.

Accurately predicting and timely controlling the ground surface upheaval and settlement induced by rectangular pipe jacking in soft ground will effectively reduce the impacts on the adjacent constructed facilities. In this paper an analytical method for ground surface upheaval and settlement induced by rectangular pipe jacking is derived by combining Mindlin’s solutions and stochastic medium theory. The proposed method considers total influences of the additional excavation pressure due to the squeezing effect of cutter-head, softening and non-uniform distributed shield skin-soil frictions in soft soils, thixotropic mud affected friction resistances between pipe segments and surrounding soils, additional grouting pressure and soil loss considering convergence mode of excavation face. The predictions given by the proposed method are in good agreement with measurements from three field cases, indicating that the proposed can reasonably predict the ground upheaval and settlement caused by the rectangular pipe jacking in soft ground. It is also found that upheaval of ground surface is observed in front of the excavation face. As the excavation face moves away, the effects of fiction resistances and grouting pressure on the ground surface deformation gradually reduce and the ground surface settlement is mainly caused due to the soil loss. Moreover, the ground surface settlement is dominantly influenced by the convergence mode of excavation face.

Stability analysis is essential in the design of an embankment. A new limit equilibrium based method is proposed to calculate the factor of safety of a newly developed prestressed embankment. It consists of an analytical method for computing additional stresses on a sliding surface and a method for calculating inter-slice forces. First, analytical formulas are derived to approximately calculate the additional stress components on a potential sliding surface using the elastic theory, and the additional normal and shear stresses at any point of the sliding surface are obtained based on stress state analyses. Then, a limit equilibrium method combining the additional stress calculation method, slice method, inter-slice force calculation method, and the loading characteristics of railway subgrades is proposed to analyze the stability of a prestressed embankment. The proposed method is applicable to arbitrary shaped sliding surfaces, the calculation formulas are concise, and the analysis process does not need iteration trial calculations. Example analyses demonstrate that the additional stresses on the potential slip surface of an embankment resulted by the prestress are not all anti-slide, and there are sliding effects in small local areas. Compared with the traditional limit equilibrium method on treating the compressive prestress, the proposed method considers the continuous propagation effects of the prestress, and the analyzed safety factor is biased towards safety. Finally, numerical methods are used to further demonstrate the reliability of the proposed method.

The uncertainty analysis of the monitoring data in metro construction is significant for the decision-making and management of engineering. Statistical inference theory is employed frequently to analyze uncertainty. Three key issues must be ascertained in order to employ the theory scientifically. (1) What is the principle of monitoring data collection to ensure the statistical scientificity of monitoring data? (2) What are normally the statistical properties of monitoring data with statistical scientificity in practical cases? (3) How to test the statistical scientificity and properties of monitoring data in practical construction? The study on these issues is implemented by employing statistical theory and statistical test methods. Some conclusions achieved are that: (1) All the monitoring points selected to collect data must have similar engineering conditions to ensure that the data collected can comply with the demands of a random sample and statistical scientificity. (2) The monitoring data with statistical scientificity should follow Gaussian distributions because of the central limit theorem, therefore the normality assumption of practical analysis has a rationale. (3) The practical analysis should verify the statistical scientificity by employing run tests, and verify the normality of the monitoring data by probability plots and χ2 tests. These can ensure the scientificity and reliability of statistical inference by combining statistical theory and tests.

In recent years, tunnel engineering is developing towards super-long and deep, multi-field and multi-phase coupling, thus, which easily induce the structural instability during tunnel construction and operation. Aiming at the mountain tunnel, underwater tunnel and urban tunnel, this paper expounds the research status of structural model test system, and points out the existing issues. The results show that: mountain tunnel model test takes into account passing through the adverse geological rock, and the loading conditions such as high ground stress, high karst hydraulic pressure and high seismic intensity. However, it’s hard to simulate the high stress of surrounding rock due to the size limitation of the apparatus. The model test of mountain tunnel is mainly based on plane strain model, which lacks the simulation of active fault with various dislocation forms under large-scale true three-dimensional stress condition. The model test of underwater tunnel has achieved stable high water pressure loading, but it is still unable to simulate the true three-dimensional underwater environment of the coupled stress field and seepage field. Additionally, the visibility of the chamber is poor, the seepage of the tunnel is only be characterized by the water inflow at the entrance, which makes it difficult to obtain the deformation law of the surrounding rock. Urban tunnel is affected by train dynamic load, pavement load and adjacent construction disturbance. At present, the model test usually considers the vibration response of the tunnel under a single load, and often ignores the structural characteristics such as segment joints and cracks. Thus, it is necessary to design novel and efficient local loading device to analyze the ultimate deformation characteristics of weak parts of segment to ensure the safety of subway operation. Finally, the bottleneck issues of tunnel engineering model test are summarized, and the internal visualization of the apparatus needs to be improved based on transparent similar materials. Aiming at the adverse geological conditions under high geostress conditions, a three-dimensional static-dynamic coupled model test system with expandable size is developed. Combining with the micro low-power wireless monitoring sensors and 3D visualization results display platform, a tunnel engineering structure model test system suitable for complex environment is established.

Aiming at the difficult problems of the large deformation in deep and soft rock roadways, the reasons of large deformation are first analyzed for roadways in Panshan coal mine, Huainan, China. On this basis, step by step and combined supporting technique with steel grid frame for soft and fractured rock roadway, including steel grid + primary bolt and cable, initial shotcrete, shallow grouting, pre-stressed bolts, further shotcrete with thickness of 150 mm, deep grouting, and pre-stressed cables, was proposed for deep weak and fractured rock roadway. Furthermore, the control principle of grid arch support is analyzed, and the optimal support parameters (diameter of steel is 20 mm and space between frames is 700 mm) are determined by FLAC3D. The comparative analysis shows that both of the initial deformation rate and final convergence deformation of the steel grid technique are larger than that of the steel support, however, the roadway deformation can quickly converge after the addition of the secondary support was applied. The monitoring results showed that the reasonable period for applying pre-stressed bolt/cable is after about 10 days of shallow/deep grouting. The time between pre-stressed bolt and deep grouting that is set as 2 weeks will be better. Therefore, step by step and combined supporting technique with steel grid frame proposed here can provide an effective method for the soft rock roadway control in deep and soft coal mines.

In order to accurately calculate the settlement of rigid pile composite foundation under embankment load, an analysis method is provided based on vertically linear development model of friction coefficient between the inner and exterior soil columns in the embankment supported by the composite foundation, as well as distribution mode of pile-soil relative displacement and development coefficient of skin friction on the pile. Thus, considering soil arching effect in the embankment and coupling characteristics of vertical load transfer between the embankment and improved zone, pile-soil stress ratio, differential settlement between pile and soil, and settlement of the improved zone are all derived by the principle of static equilibrium of a microelement in the embankment-foundation system. The proposed method can quantitatively reflect the dominant influence factors, such as height of embankment, internal friction angle and cohesion of the filling and soft foundation soil, pile length, pile diameter and pile spacing. Analysis results of examples show that relative error between the calculated and measured values is less than 15%. Pile length has non-linear effect on the settlement of the improved zone, while area replacement ratio, cohesion and internal friction angle of the foundation soil have linearly negative effect on the settlement. Moreover, the settlement is more sensitive to internal friction angle than cohesion.

The emergence of blasting tight bottom seriously affects the effect of bench blasting and subsequent construction procedure. The dynamic analysis method of multi-degree of freedom system is applied to the structural stress analysis of bench blasting, and the influence mechanism of lithologic change on the formation of blasting tight bottom is analyzed based on the structural characteristics of the rock mass. The results indicate that 50% weakening of the lithology of the middle rocks could increase damage difficulty of bottom rock, because the shear force of rock mass at the bottom is reduced by 7.8% and the bending moment is reduced by 6.6%. And the weakening effect increases with the decrease of mechanical properties of rock mass. In addition, the strengthening of the lithology of the bottom rocks could increase the internal force of bottom rock slightly, but rock strength is greatly improved, which makes the bottom rock more difficult to break. Furthermore, the influence mechanism of different factors on the formation of blasting tight bottom is analyzed based on the rock mass structure failure criterion. It is found that the uneven distribution of lithology and the changes of structural stiffness and bottom stress conditions are the main reasons for the formation of bench foundation. Adjusting the initiation point below the bench can weaken the influence of weak-lithology segment. Increasing the stress conditions and reducing the structural stiffness of the bottom rock mass can also avoid the formation of blasting tight bottom. The relevant research results can provide reference for similar projects.

Forty-two case histories in which the laterally adjacent deep excavation affects the existing tunnel are collected. The typical stratum condition, size, relative position, structure deformation and control measures of deep excavation and tunnel in each case history are counted. By analyzing the influences of important factors on vertical and horizontal displacements of tunnel, the judging criterions of tunnel heave and settlement are clarified, and then the zoning of tunnel vertical displacement outside the deep excavation is given. The comprehensive prediction index of tunnel horizontal displacement is proposed, and the practical empirical prediction formulae of tunnel horizontal displacement under three categories of stratum conditions are given. Finally, relying on a specific case study, the deformation of tunnel is predicted using the obtained empirical formula before construction, and the rationality of the prediction formula is verified by comparing the prediction results with the field monitoring results. The results show that the horizontal displacement of tunnel is towards the pit, while the vertical displacement is in the form of heave or settlement, which is related to the buried depth of tunnel crown (H_t) and the distance between tunnel springline and deep excavation (L_t). It is obtained from statistics that the critical value of H_t is H_e+R and the critical value of L_t is H_e, and then considering the vertical displacement distribution characteristics of tunnel, the area outside the pit can be divided into settlement zone, transition area and heave zone. Horizontal displacement of retaining structure (ζ_hm), excavation depth (H_e), horizontal distance L_t between tunnel and deep excavation and longitudinal width b of deep excavation along tunnel are all important factors affecting horizontal displacement ζ_hm of tunnel. ζ_hm increases nonlinearly with the increases of d_hm and H_e; z_hm/δ_hm decreases with the increase of L_t as a power function relationship; ζ_hm has an increasing trend with the increase of b, which means multiple factors should be considered to scientifically predict the horizontal displacement of tunnel. ζ_hm and bH_e/L_t have a good linear relationship under three stratum conditions using bH_e/L_t as the prediction index of tunnel horizontal displacement, and the tunnel horizontal displacement prediction formula based on it can achieve good prediction effect proved by an actual engineering case.

During vertical jet grouting, the nozzle injects a large amount of fluid (cement slurry or water) into the surrounding soil, which leads to significant lateral ground displacements. Based on the analysis of the installation of a vertical jet grouting column, assuming that the lateral ground displacement caused by jet grouting is equal to that induced by cylindrical cavity expansion in infinite soil mass, a simplified calculation method of lateral displacement of subsoils caused by installing a vertical jet grouting column is proposed. With the analysis of the effect of installing the vertical jet grouting column on soil stress, a formula for calculating the soil stress at the elasto-plastic interface after construction is deduced. Taking installation of vertical jet grouting column with unit length as the research object and considering operational parameters and soil parameters, a formula of cylindrical cavity radius (key parameter for determining lateral displacements) is proposed based on the dimensionless principle. This method is applied to the engineering case of vertical jet grouting, and the comparison of prediction results and the observed data proves the reasonability of this method. By calculating with this method, the influence range of installing the vertical jet grouting column is approximately 7.5 times of the column diameter.

The problem of surrounding rock support of soft rock roadway in deep coal mining, especially the stability of surrounding rock of soft rock intersection roadway, has been concerned for a long time. From the analysis of the internal causes of the deformation and failure of the intersection, it is concluded that the roof and the rock pillar support system in the triangle area are the weak points of the instability and failure of the intersection. Based on the concept of ‘equivalent span’ and catastrophe theory, a cusp catastrophe model of the roof rock-column system at the intersection is established and the cusp catastrophe equation at the intersection and the necessary and sufficient judgment conditions for the instability and failure of the system are obtained. The effects of engineering geological factors (buried depth H and elastic modulus of rock column E), structural parameters of roadway intersection (intersection angle q and roadway height h) and support design parameters a on the stability of intersection are analyzed. It is concluded that the non-linear relationship between q, E, a and the control parameter v has a curvature change inflection point. When q <35º and E<16 GPa, the sensitivity order of control parameters to various factors is: q >E>a>h>H, that is, when the rock column is weak, the stability of the intersection is strongly affected by the strength of the rock column, and the design angle of the intersection should not be less than 35º. When q≥35º and E≥16 GPa, the order of sensitivity is: h>H>q >a>E, that is, when the strength of surrounding rock is high, the stability of intersection is significantly affected by structural parameters. Combined with the example of deep well soft rock engineering in Dingji mine, theoretical analysis is used to guide the optimization of design parameters of intersection. The ground pressure monitoring data show that the optimized support design effectively controls the surrounding rock deformation at the intersection of the west third track back link roadway, and verifies the correctness of the theoretical derivation.

In order to objectively obtain accurate and reliable rock quality evaluation results, a heterogeneous ensemble evaluation method based on improved D-S (Dempster-Shafer) evidence theory is proposed for the existing individual evaluation models which are prone to misjudgment and bias. Firstly, based on determining the rock mass quality evaluation standard and data set, 6 heterogeneous base classifiers are used to train the data set, and the preliminary rock mass quality evaluation results are obtained. Then, the result of each base classifier is taken as a piece of evidence, and the evidence is integrated through the improved D-S evidence theory to form a comprehensive evaluation result, to solve the inconsistency of the results of the existing evaluation methods. Based on 30 groups of samples, a heterogeneous ensemble evaluation model based on improved D-S evidence theory was constructed and applied to the rock mass quality evaluation of the Guangzhou water pumping and storage power station phase II project. The results show that the heterogeneous ensemble evaluation method based on the improved D-S evidence theory improves the accuracy and reliability of rock mass quality grade identification, avoids subjectivity and uncertainty in the evaluation process, and has high engineering practical value.

Based on the particle flow code platform, using image processing technology and Monte Carlo method, a discrete fracture network is generated. Combined with the grain-based model, the numerical modeling of the granite mesostructure is carried out. Then from a micro perspective, the effect of the discrete fracture network on rock strength and deformation properties and acoustic emission characteristics is described. The main conclusions are as follows: (1) The average length and density of the fractures affect the mechanical properties of the rock. The uniaxial compressive strength and elastic modulus of the rock decrease with the increase of the fracture density. (2) Rock failure under uniaxial compression is dominated by intergranular tensile cracks and intragranular tensile cracks. (3) The discrete fracture network is closely related to the acoustic emission events of the rock. With the increase of fracture density, the b value of acoustic emission and the D value of fractal dimension both show a downward trend. The sharp drop of b and D indicate that the rock instability failure. (4) The discrete fracture network has a certain influence on the magnitude of acoustic emission events. Acoustic emission events with high rupture intensity are prone to occur near discrete fracture networks. In summary, conclusions based on the mesoscopic rock fracture mechanism and acoustic emission phenomena obtained from the joint modeling of discrete fracture networks and grain-based models can effectively make up for the shortcomings of existing research methods in laboratory experiments and provide strong support for the stability evaluation and engineering construction of rock mass with more complex fracture network in the field.

How to make full use of the multi-source heterogeneous information of complex geology and engineering structure in the process of metro foundation pit construction to realize the construction digital fabrication is a difficult problem in metro engineering construction. In this paper, an idea of building information modeling (BIM) customization is proposed to solve this problem by effectively integrating engineering structure model and geological model, and establishing the foundation pit construction simulation method of dynamic coupling between earthwork excavation and retaining structure construction. Using industry foundation classes (IFC) standard, the geological body and engineering structure are extended and defined respectively, and the data system of foundation pit engineering based on IFC standard is constructed. Based on the Autodesk software platform, the foundation pit structure component library and parametric component modeling technology are developed to create a plug-in foundation pit structure modeling module. The three-dimensional (3D) geological modeling method based on borehole data is established, and a dynamic cutting method of geological model for the construction process simulation is established. The geological model is divided into 3D blocks at different excavation stages, and the 3D multi-phase geological model is formed. On this basis, the topology is reconstructed and the geological body and retaining structure are integrated; the multi-stage excavation BIM model is thus constructed. By dynamically loading construction schedule and time information on the integrated multi-stage model, the construction simulation method of metro foundation pit engineering based on BIM technology is then developed. Finally, the feasibility and effectiveness of the proposed simulation method are demonstrated through an engineering example.

In this paper, the full-scale test method is used to study the vibration isolation effect of different types of barriers (continuous and discontinuous) filled with different materials (ceramsite and sand). Meanwhile, to expand the experimental research, numerical research is supplemented. Therefore, to obtain the dynamic characteristics of the site as the basis of numerical research, the surface wave spectrum analysis (MASW) test was carried out on the original site before the experimental research. Then, to acquire the transfer function and attenuation decibels of the fixed point of the site by experimental research, the program is compiled to calculate the spatial distribution field of acceleration component through numerical method. After combining the above two methods, it is found that: Influence of vibration isolation material: at low frequency, the difference between them is not very obvious; at the intermediate frequency, the difference between the two begins to appear and the vibration isolation performance of ceramsite is close to that of open trench; at high frequency, the influence of material is difficult to show due to the obvious damping effect of soil. In conclusion, the vibration isolation effect of ceramsite is much better than that of sand, and the overall performance is close to the open trench. Influence of barrier type: when the frequency is 30 Hz, the barrier has little effect, and the spatial distribution of components takes the vibration source as the center, showing a circular distribution; When the frequency is 50 Hz, the annular distribution is broken by the barrier and its shape changes from annular to oval, while the short side points to the direction of the wave front, so that the component of a certain intensity is rejected in the rear area of the barrier; When the frequency is 80 Hz, the soil damping effect is obvious, so that the difference between them is not obvious. In conclusion, the vibration isolation effect of continuous barrier is much better than that of discontinuous barrier. Suggestions on the use of materials and barrier types: if general materials are used, both continuous and discontinuous barriers can be used considering factors such as cost. However, using high damping materials and considering the effect of vibration isolation, the continuous barrier is better.

Based on the Hertz-Mindlin contact model in EDEM, the relationship between contact radius and bond strength, and the influence of contact radius on tensile and compressive strengths of rock model were investigated. A method for establishing discrete element model of rock with high compressive-tensile strength ratio was suggested. According to the strength and geometric criteria of the contact model in EDEM, the concepts of “strong bond”, “weak bond” and critical contact radius coefficient were proposed. The formulae of critical contact radius when two particles in contact move along normal or tangential directions were derived. The rock uniaxial compression and tension simulation experiments were carried out with the contact radius coefficient α as an independent variable, and the results show that: the tensile strength shows a three-stage piecewise linear relationship with the change of α. At the interval of 1.000 0≤＜1.000 8, the slope of the curve is very large. At the interval of 1.000 8≤≤1.002 5, the slope of the curve is small. When ＞1.002 5, the tensile strength is almost constant. The compressive strength shows a two-stage piecewise linear relationship with the change of α. At the interval of 1.000 0≤ ≤1.000 2, the slope of the curve is very large, and after ＞1.000 2, the compressive strength is also almost constant. In the interval of 1.000 1≤≤1.000 3, the compressive-tensile strength ratio is about 6.5 to 14.0, and it can be used to reproduce the tensile and compressive properties of real rock, so as to construct the discrete element model of rock with high compressive-tensile strength ratio.

With the developments of geotechniques such as underground energy engineering, thermal foundation treatment, and nuclear waste treatment, the influence of thermo-mechanical coupling on soil has become one of the hot research topics in the field of geotechnical engineering. Based on the particle volume expansion method, the cyclic thermal consolidation experiment on loose particles (relative density D_r = 0.2) at different temperature changes (20 ℃, 40 ℃, and 60 ℃) is simulated by the PFC2D. From a macroscale point of view, it is found that the particles produce thermal consolidation during the temperature cycle, i.e. the process in which the void ratio of the sample cumulatively reduces as the number of temperature cycles increases. The studies have shown that the larger the amplitude of the temperature changes, the denser the granular material will be during the long-term temperature cycle, and the uneven distributions of void ratio, lateral stress, and vertical stress will appear. At the same time, the influences of temperature cycle and variable temperature amplitude on the number of contacts between particles, normal contact force, and tangential contact force are summarized by microscopic analysis. It is concluded that the amplitude of the temperature cycle in the thermal consolidation test has a greater impact on the anisotropy of the sample.

Taking the Bazimen landslide in the Three Gorges reservoir area as an example, a new landslide displacement prediction method is proposed to solve the problems of the static machine learning model in the periodic displacement prediction and the difficulty in the high-frequency random displacement prediction. Based on the idea of time series decomposition, particle swarm optimization (PSO) is used to optimize the parameters of variational mode decomposition (VMD), and the displacement time series is decomposed into trend term, periodic term and random term. The trend term is mainly affected by the internal factors of landslide, and the Fourier curve is used to fit and predict. The periodic term is caused by external factors. The causes are analyzed based on Granger causality test, and a nonlinear autoregressive neural network with exogenous inputs (NARX) with high sensitivity to the historical state of time series is introduced for prediction. The random term frequency is high and the influencing factors cannot be determined, thus one-dimensional gated recurrent unit (GRU) is used for prediction. Finally, the predicted displacement of each component is superimposed and reconstructed to realize the prediction of landslide cumulative displacement. The results show that the (PSO-VMD)-NARX-GRU landslide displacement dynamic prediction model has higher accuracy, and the prediction accuracy of each displacement component is obviously higher than that of BP neural network, support vector machine (SVM) and conventional autoregressive model ARIMA in static models, which can provide reference for step landslide displacement prediction.

There are a large number of cracks inside the rock mass. Due to the existence of fillers, the crack surface is closed in most cases, and friction will be generated when subjected to external forces, which will affect the crack initiation mode and propagation behavior of the rock mass cracks. Therefore, in order to study the crack initiation mode and propagation behavior of closed cracks, a rock-like material PMMA plexiglass plate was used to make pre-splitting specimens containing closed cracks, and uniaxial compression tests were performed on the specimens. Digital image correlation system (DIC) recorded the initiation and propagation characteristics of closed cracks. In addition, the extended finite element method (XFEM) was used to simulate the initiation and propagation of closed cracks, the failure process of the specimens with closed cracks was obtained through simulation, and the initiation and propagation characteristics of closed cracks were analyzed, which was in good agreement with the test results. The validity of the numerical simulation is verified. On this basis, the crack inclination angle and the friction coefficient of the crack surface are introduced as variables, and their influence on the crack initiation and propagation behavior of closed cracks is simulated. The research results show that the cracks generated under the condition of crack closure are airfoil tension cracks. Crack inclination and crack surface friction coefficient have a greater impact on the crack initiation mode and growth behavior of closed cracks. The larger the crack inclination angle is, the larger the crack initiation angle is. On the contrary, the larger the friction coefficient of the crack surface is, the smaller the crack initiation angle is. In addition, the friction coefficient of the crack surface has an inhibitory effect on the growth of closed cracks, and as the friction coefficient continues to increase, the inhibitory effect becomes more and more significant, and crack arrest occurs.

The risk status of a slope under rainfall conditions is closely related to the spatial variability of soil parameters. In order to efficiently evaluate the risk level of rainfall-induced landslides, this paper uses the modified Green-Ampt infiltration model combined with the infinite slope model to establish the limit state function, and combines the first-order reliability method (FORM) with the random field theory to study the probabilistic stability subjected to uncertain infiltration parameters with spatial variability. These calculation procedures are systematically realized in the Python platform. Finally, we make a probabilistic analysis of rainfall-induced landslides and establish a fragility curve of the slope in the case area. The research results show that: compared with traditional stability analysis methods, probabilistic analysis methods can more comprehensively reflect the risk status of slopes under different rainfall intensities and rainfall durations. When the rainfall intensity exceeds a certain level, the rainfall has little effect on the slope failure probability under the same rainfall duration. In a specific study area, when the rainfall intensity is known, the fragility curves can be used to clarify the failure time of the slope under allowable risk level and can provide an important reference for the disaster prevention and mitigation work for relevant departments.

The low efficiency of cover system generation is a bottleneck problem that restricts the application of 3D numerical manifold method in large-scale practical engineering. By improving the generation algorithm of 3D cover system, an improved algorithm of generating 3D cover system based on Boolean intersection operation is proposed, and the corresponding program with C++ is developed. According to the topological geometric relationship between mathematical mesh and physical domain, the manifold block is generated by the conventional Boolean intersection operation or the mathematical mesh directly. The manifold elements are generated when new blocks satisfy the validity, and then all preprocessing 3D cover systems are generated. Two simple examples and a slope engineering problem are selected to illustrate the feasibility of the present method and the correctness of the calculating program, and the calculating efficiency of the present method is also analyzed by comparison. The results show that the improved Boolean intersection operation is more efficient than the conventional Boolean intersection operation. With the increase of mesh density, the average generating time consumption of one element decreases gradually. With the increasing complexity of physical domain’s boundary, the computational efficiency of the present method is gradually reduced. It provides a foundation, with strong practical application value, for future structural analysis with the numerical manifold method.

The stability analysis of pile-anchor retaining structure is based on the searching method of the sliding surface and the calculating theory of the safety factor. During the process of analyzing anti-sliding moment, conventional slip circle method of slices has too many assumptions. At the same time, during the process of searching for the most dangerous sliding surface, there are some problems with the grid-search method. If the rough grid is applied, the result will be less accurate. However, if the fine grid is applied, the efficiency will be lower. To solve these problems, the soil strength redundancy method is proposed in order to analyze dynamic stability of foundation pit. Also, adaptive grid-search method is used to ensure accuracy and efficiency. Finally, this paper compareds the soil strength redundancy method, the sliding surface stress method and the slip circle method of slices. The results show that the sliding surface stress method overestimates the overall stability of the foundation pit and that the slip circle method of slices cannot consider the weakening effect on the shear strength of the soil behind the pile caused by excavation. Also, the soil strength redundancy method can reflect the overall stability of the foundation pit.

This paper is presented to investigate the theoretical calculation method for the inner-force and deformation analysis of batter piles. Firstly, the bearing mechanism and deformation characteristics of batter piles are reviewed on the basis of the existing studies. The simplified mechanical model of batter piles is proposed by assuming that external loads atop batter piles would be decomposed along axial and radial directions of piles, and then the determination method of the foundation resistance is proposed and the governing differential equation of batter piles is further derived. Secondly the conventional finite beam element method is modified to consider the effects of the second-order effect and pile-soil interaction, and a program is compiled for the analysis of the inner-force and deformation of batter piles based on the MATLAB platform. Finally, the proposed theoretical method is validated by a model test and a field test, and some conclusions are summarized. These above-mentioned analyses can provide references for engineering design of batter pile, which is of theoretical and engineering application value.

The morphological characteristics and deformation failure modes of weak structures in rock and soil mass under certain loading conditions are of great significance to the slope stability in geotechnical engineering, while the visual analysis of the inner weak structural planes and their feature description often lack effective field testing means. Therefore, a method for the visual analysis of weak structural planes based on the characteristics of multiple frequency ultrasound imaging is proposed. This method obtains the ultrasonic scanning image of the weak structures at different angles and frequencies under corresponding conditions using multiple frequency ultrasonic waves, analyzes the reflection attenuation feature and the gradient feature of the difference image statistically, and establishes the qualitative and quantitative analysis of the imaging features, so as to realize the visualization analysis of the weak structure in rock and soil mass. The method realizes the real-time imaging detection and visual monitoring of internal weak structure of the rock and soil mass, and solves the existing drawbacks that the in-situ imaging detection of internal weak structures cannot be achieved and the problem of the precise analysis of local structure planes for rock and soil. It provides a new technical approach for the instability mechanism research induced by the weak structures of rock and soil mass during the geotechnical engineering and geological investigation.

In view of the deficiency of deformation monitoring technology in transformer substation, a 220 kV substation in Zhaotong is selected to carry out research on deformation monitoring technology under strong electromagnetic condition. The field monitoring is performed by Beidou satellite positioning technology, laser ranging technology, inclinometer and rain gauge. The research results are described as follows: (1) Strong electromagnetic interference has a serious impact on the monitoring accuracy of global navigation satellite system (GNSS). If the influence of electromagnetic interference cannot be effectively reduced, the results of GNSS displacement monitoring cannot be used for monitoring and analysis of substation foundation deformation. (2) Based on the detection of substation electromagnetic field intensity, a monitoring point design and implementation method to improve the settlement monitoring accuracy of substation GNSS under strong electromagnetic field environment is proposed. The monitoring points with electronic components are arranged at the places with relatively weak electromagnetic field intensity to reduce electromagnetic interference and monitoring error. (3) For the first time, the low-cost and high-precision laser ranging technology is introduced into the substation horizontal displacement monitoring and successfully implemented. The research provides a new technical means for deformation monitoring of substation on soft foundation in mountainous area, which can improve the quality and management level of substation project.