Soft rock engineering involves many important engineering fields such as mining, hydraulic engineering, transport and national defense. With the increase of mining depth and the development of tunnel engineering, a large number of tunnels and roadways need to pass through soft rock formations, in which the problems such as high geostress and broken and weak surrounding rocks are prominent. Large deformation disasters of soft rocks pose serious threats to engineering safety and cause enormeous economic losses. In this paper, the research progress on soft rock support in China is first reviewed, and the research status of technology for soft rock control for large deformation hazards is summarized in the following aspects. (1) Passive support methods represented by improved rigid support, retractable support and compound lining. (2) Reinforced active support technology using high-strength bolts and cables. (3) Soft rock modification technology dominated by grouting modification. (4) Soft rock reinforcement with pressure relief as the core idea. (5) Compound support methods. Furthermore, the development of different supporting technologies and methods are elaborated, and the applicable conditions, advantages and disadvantages of different supporting methods are analyzed. It is usually difficult to meet the demand of large deformation control of soft rock relying on a single support method. Therefore, it is urgent to solve the problems of the prevention and control of large deformation disaster of soft rock to realize the efficient collaborative control among different supporting measures and achieve the real-time accurate monitoring of deformation and stress fields. Finally, based on the above research results, the development tendency of support technology for soft rock with large deformation hazards is prospected and the countermeasures are proposed.

To explore the strength characteristics of anisotropic rocks caused by mineral directional arrangement during progressive failure process, biotite quartz schist was taken as an example, and triaxial compression tests were carried out on samples with schistosity angles of 0°, 45° and 90°. The macro and micro failure characteristics and progressive failure strength index of the specimens were analyzed, and the differences with other types of anisotropic rock were discussed. The results show that the failure characteristics of biotite quartz schist are closely related to its schistosity. With the schistosity angle increasing from 0° to 90°, the main macro and micro fracture modes of the specimens change from tensile to shear, and then to co-existence of tensile and shear. The strength characteristic values of biotite quartz schist show significant anisotropy. With the increase of schistosity angle, the strengthening effect caused by confining pressure increase on the strength characteristic values weakens, but the change of the strength value has a trend of acceleration. The anisotropic variation law of the ratio of strength characteristic value is not obvious, which gradually weakens and even disappears under high confining pressure. The fracture modes, variations of strength characteristic values and their ratios of anisotropic rocks with directional arrangement of minerals are different from those of rocks with stratified structure. A thorough understanding of the mechanical properties of rocks with directional arrangement of minerals will be helpful to guide the related engineering practice.

The siliceous and colloidal sandstone is common in Helan Mountains Rock Painting and Yungang Grottoes. The weighing test, ultrasonic test and uniaxial compression test were conducted on the rock subjected to freeze-thaw cycles at different temperature change rates to investigate the influences of temperature change rate on the physical and mechanical properties. The evolution and internal mechanism of crack propagation in rock after freeze-thaw cycles at different temperature change rates were revealed based on the features of acoustic emission and microseism during uniaxial compression loading process. As the temperature change rate increases, the micro-cracks increase and the joint force between particles decreases gradually, resulting in the lower peak strength and elastic modulus. Thus, the failure strain and damage parameters D_e、and  D_v  increase with the increase of temperature change rate.  During the loading process of rock, the micro-crack propagation progress shows an ‘initial compaction–propagation incubation–rapid propagation’ evolution feature, while the macro-crack propagation progress can be divided into two stages as ‘uniform propagation–rapid propagation’. And the rapid growth stage of the macro-crack also shows the wave-like development characteristic of ‘incubation–propagation–incubation–propagation’. The micro-crack and macro-crack propagation rate during the loading process increases with the temperature change rate. It is easier for micro-crack and macro-crack to enter each rapid propagation stage at a larger temperature change rate. When the temperature change rate increases to a certain value, the micro-crack and macro-crack propagate at a high rate from the beginning of loading progress to the failure of rock sample. The damage parameters  D_e and  D_v have a good fitting relationship with the relative growth rate of acoustic emission ring down count during the propagation incubation stage and the whole loading process for micro-crack, and the relative length and relative growth rate of microseism ring down count in the uniform propagation stage for macro-crack. These variables can be used to reflect the initial damage of rock induced by freeze-thaw cycles. The frost heaving force increases with the increase of temperature change rate, resulting in the different initial damage of frozen-thawed rock at different temperature change rates. It is the internal mechanism leading to the significant difference in crack propagation, acoustic emission feature and micro-seismic feature of frozen-thawed rocks during uniaxial compression loading process.

Based on the results of dynamic centrifugal model test with circular tunnel completed by the Engineering Department of Cambridge University, four different kinds of seismic waves EQ1-EQ4 from weak to strong were input at the base of the model under the condition of 80g gravity acceleration, and acceleration sensors were arranged at different positions in the laminated model box to measure the acceleration time history at different depths along the tunnel location. Using the traditional spectral ratio method considering destructive interference, the variation law of site amplification effect with depth under earthquake was analyzed and studied. The results show that under EQ1-EQ4, the ground motion amplification factor of each vibration mode decreases first and then increases from the base to the surface. According to the statistics, the probability that the value of ground motion amplification factor of high-order mode is larger than the first-order mode is 18.3%. The higher the mode, the greater the probability. The maximum value of ground motion amplification factor near the surface is mainly distributed in the middle frequency band of 4.20 – 8.63 Hz, rather than in the low frequency band.

A new three-dimensional curved solid failure model by combining semi-circular platform and partial sphere was proposed to calculate limit support force of shield tunnel excavation face. At present, wedge-shaped models were generally used to calculate the supporting force of excavation face by using limit equilibrium method, in which the lateral friction force of sliding face was estimated as a known quantity. However, it is difficult to estimate the lateral friction force accurately because the lateral friction force of sliding surface is affected by many factors. In this paper, the symmetry of the curved solid model was used to solve the support force of the excavation face, and the calculation accuracy was improved by avoiding the estimation of the lateral friction force of the sliding surface. Furthermore, the force acting on the semi-circular platform model above the tunnel vault was analyzed given consideration to the variation of the lateral pressure coefficient caused by the principal stress deflection, and the analytical solution of the vertical stress in the soil was derived considering soil arching effect when the sliding surface is a spatial curved surface. Then the rationality of the proposed model was verified through examples analysis. Examples analysis show that the proposed model is simple, effective and practical. It can be widely used in the stability analysis for shield tunnel excavation face.

We take red sandstone as the research object and apply the freeze-thaw cycles, CT scans and mechanical properties experiments. We use image processing technology combined with genetic algorithm optimization model to achieve the denoise, enhancement, segmentation and three-dimensional reconstruction of CT scan images after 0, 5, 10, 20, and 40 freeze-thaw cycles. With the damage identification and comparative study of the same object across scales, we established a prediction formula of elastic modulus deterioration based on mesoscopic damage. Therefore, the macroscopic mechanical behavior of freeze-thaw red sandstones can be interpreted from the physical nature of the material meso-structure. The results show that genetic algorithm based on image maximum entropy can quickly and accurately select the threshold for image segmentation, and achieve the recognition of matrix and defects in rock meso-structure. With the increase of freezing and thawing cycles, the porosity of rock increases, and the fractal dimension of pore decreases. On the meso-scale, the evolution shows that the pores expand and the number increases, but the structural complexity decreases. The macroscopic and mesoscopic damage variables defined by the traditional methods are based on the effective bearing area and elastic modulus, and they fail to fully consider the damage physical mechanism and the internal structure information of the material. The damage evolution curves are different. Based on the two physical mechanisms, we define the meso-damage variable and the macro-damage variable that considers the natural rock damage, which achieves the combination of macroscopic and mesoscopic damages. Finally, according to the relationship between meso-structure evolution and macroscopic mechanical response in the process of freeze-thaw cycles, we propose a prediction formula of elastic modulus degradation, and analyze the different dominant roles of pore size and pore structure morphology through the damage process. We interpret the mechanical mechanism of macroscopic sandstone freeze-thaw damage based on the meso-structure physical mechanisms.

Coral islands and reefs are always in a complex marine dynamic environment. Seepage deformation or even damage of foundation of embankment cofferdam, foundation pit and other structures on the island will increase the possibility of subsoil bearing capacity failure. In order to explore the permeability and consolidation of calcareous sand mixed with rubber fiber, constant head permeability test and consolidation test were used to study the permeability and consolidation deformation of calcareous sand with different fiber contents, and the control group containing fiber glass beads was set. Calcareous sand has extremely irregular particle shape, ultra-high non sphericity and abnormal rich edges and corners, further study was carried out by a high-speed dynamic image particle size analyzer to analyze the particle shape and size of the calcareous sand and glass bead. The test results show that the fiber content hardly affect the permeability of calcareous sand samples, but the permeability coefficient first increases and then decreases with the increase of fiber content in the glass beads containing fiber. To some extent, the addition of rubber fiber shortens the water passage in the calcareous sand sample. Calcareous sand sample has a pressure threshold of 800 kPa. When the pressure exceeds 800 kPa, the increase of compression modulus slows down. The e-lg p curve of the mixture sample with different fiber contents can be expressed by the Harris model. The material coefficient of the calcareous sand-rubber fiber mixture is C=5, and that of the glass bead-rubber fiber mixture is C=3. Meanwhile, there is a good linear relationship between material parameters a and b and fiber content.

In order to solve the failure of support structure of tunnel in high stress soft rock, based on the principle of reasonably releasing the stress in surrounding rocks and reducing the stress of support structure, a hydraulic tunnel graded yielding support structure is proposed. Considering the spatial effect of the excavation surface and the strain softening condition of the surrounding rocks, by analyzing the attenuation law of the virtual supporting force, the static balance equation of stress in the surrounding rocks, the virtual support force and the support reaction force is established. The synergy between the supporting structure and the surrounding rocks at each stage is studied to generate the relationship between the displacement and stress of the surrounding rocks in the whole deformation process of the support structure. The supporting effect of the proposed graded yielding support structure is revealed. The results show that the stress of surrounding rocks is significantly released at the two yielding stages and the deformation characteristics of surrounding rocks are consistent with the yielding characteristics of structure. The simulation results show the consistent variation trend with that of the theoretical values, which verifies the rationality of the theoretical analysis. The proposed yielding support structure can effectively release the stress in the surrounding rocks and reduce the stress of the supporting structure. It can avoid the yield failure of the support structure, solving the support problem of the tunnel in the soft rock with high stress, which can provide theoretical support for the application and development of the support structure.

Natural soils contain a certain amount of salt in the form of dissolved ions or electrically charged atoms, originated from the long-term erosion by acidic rainwater. The dissolved salt poses an extra osmotic water potential being normally neglected in laboratory measurements and numerical analyses. However, ignorance of salinity may result in overestimation of stability, and the design may not be as conservative as thought. Therefore, this research aims to first experimentally examine the influence of pore water salinity on water retention curve and saturated permeability of natural dispersive loess under saline and desalinated conditions. Second, the measured parameters are used for stability analyses of a railway embankment in an area subjected to regional rainfall incident. Eventually, a numerical parametric study is carried out to explore the significance of different rainfall schemes, construction patterns, and anisotropic permeability on the factor of safety. Results reveal that desalinization suppresses the water retention capability, which in turn results in a tremendous declination of unsaturated hydraulic conductivity. Despite the natural saline embankment, rainfall can hardly infiltrate into the desalinated embankment due to the lower conductivity. Therefore, the factor of safety for natural saline conditions drops notably, while only marginal changes occur in the case of the desalinated embankment.

The pile-soil stress and grid tensile force of each part of the geogrid reinforced pile supported embankment were detected through laboratory model tests under both dynamic and static loads, and the development and evolution mechanism of soil arching effect and the development characteristics of geogrid stretching effect were studied. The test results show that the distributions of pile-soil stress and grid tension are greater in the transverse direction of the subgrade than that in longitudinal extension direction, which is related to the design of the trapezoidal section of the subgrade; the spatial soil arching effect is stronger than the planar soil arching effect, and the limit state of the spatial soil arching effect when the pile-soil stress ratio is 3.8, the limit state of the plane soil arching effect appears when the pile-soil stress ratio is 2.2; the soil arching effect under dynamic load has a certain extent attenuation comapated with under static load, position with stronger soil arching effect under static load has a greater attenuation degree under dynamic load, the development trend of the soil pressure between the piles with the vibration frequency is similar to the N-type, which is exactly the opposite of the change trend of the soil pressure on the top of the pile.

In the past, grey materials such as cement were used to build and reinforce embankments in the Yellow River basin to prevent soil erosion, which caused serious damage to ecological environment. In response to the national strategy of ecological protection and high-quality development of the Yellow River basin, environment-friendly biopolymers were used to improve the typical silt in the Yellow River basin. In this paper, the water retention characteristics of biopolymer-improved silt are measured with WP4C instrument, and the mechanism of biopolymers to improve the water retention characteristics of silt is analyzed from a microscopic point of view. Compared with unimproved soil, the water content of biopolymer modified silt after saturation increases, the void ratio increases, and the water holding capacity is significantly improved. The water retention capacities of the silts modified by xanthan gum, gellan gum and guar gum increase with increasing the gum content, and the improved effect of gellan gum surpasses those of xanthan gum and guar gum. The improvement mechanism can be explained that the biomolymer particles form hydrogel through hydration, filling the pores between particles and increasing the adhesion between particles. In addition, pore space similar to honeycomb structure is formed in the improved silt by xanthan gum and gellan gum to provide water storage space, thus improving the water retention characteristics of the improved soil. The above research results can provide a scientific basis for the safe and scientific application of biopolymer in the prevention and control of soil erosion in the Yellow River basin.

For the geological disposal of high-level radioactive waste, the geological barrier system, as an important defense, is the last barrier for hazardous substances to enter the environment. Clayey rock, in virtue of its properties, such as low permeability, self-healing, and strong adsorption capacity, is considered a reasonable geological barrier for the disposal of high-level radioactive waste. In this study, the hydro-mechanical coupling mechanism and long-term rheological properties of a clayey rock were studied through a series of laboratory experiments. Triaxial tests show that the compression strength and excess pore water pressure have a positive relation with confining pressure. Permeability tests show the anisotropic hydraulic properties of the clayey rock and the permeability notably decreases under high confining pressure. Creep tests show that creep deformation and creep deformation rate are closely related to the load level. That is to say the larger the load is, the more significant the creep deformation is, the longer it takes for the creep deformation rate to reach stability, and the larger the corresponding steady-state creep rate is. According to the stress threshold and isochronal curve method, the long-term strength of the clayey rock is preliminarily determined to be 1.0-1.2 MPa. The results of this study will be of great significance to the geological disposal and safety assessment of high-level radioactive waste in clayey rock in China.

The shield tunnel is typically simplified as an infinite beam with two free ends in existing analytical models, which are used to calculate the longitudinal deformation of the underlying shield tunnel induced by the excavation of a foundation pit. However, the applicability of those analytical models is limited due to the simplification. The current study is aimed at estimating analytically the longitudinal deformation of the underlying shield tunnel induced by the excavation of a foundation pit adjacent to the station (working shaft). The constraint on the shield tunnel generated by the joint between the station (working shaft) and the tunnel is treated as a rotation spring with the rotation stiffness of  K_θ  and a vertical rod support. The Winkler foundation – Timoshenko beam model for calculating the longitudinal deformation of the shield tunnel adjacent to the station (working shaft) induced by the foundation pit excavation is proposed. The finite difference solution of the proposed model is strictly derived based on the basic principles of the force method. The reliability and applicability of the proposed analytical model are verified via the comparison with the finite element numerical solution of one-dimensional elastic foundation beam model and the global finite element simulation results of the longitudinal deformation of the underlying tunnel induced by the excavation of a foundation pit adjacent to the station. The parametric studies indicate the following conclusions. (i) The longitudinal deformation and internal forces of the shield tunnel are significantly influenced by the rotation stiffness, K_θ , of the joint between the station (working shaft) and the tunnel. The internal forces and the longitudinal deformation (i.e. rotation angle) at the end of the tunnel increase and decreases nonlinearly with a increasing  K_θ , respectively. In addition, when the flexible connection is adopted at the joint between the station (working well) and tunnel, the working performance of the shield tunnel at the joint can be better guaranteed. (ii) The constraint effect of the joint on the end of the tunnel is non-negligible, when the distance from the center of the foundation pit to the station-tunnel joint ranges from 4 to 5 times the width of the pit along the tunnel axis. In this condition, the proposed analytical model should be adopted to evaluate the longitudinal working performance of the tunnel. (iii) The influence of the overlying foundation pit excavation on the underlying tunnel mainly exerts within 2 times the length of the pit perpendicular to the tunnel axis away from the center of the pit.

In order to clarify the influence of fine-grained soil content on the salt expansion characteristics of coarse-grained sulfate saline soil embankment fill material, sand and gravel saline soils with sulfate salt contents 1% and 3% were investigated. A series of cooling and salt expansion tests was carried out to examine salt expansion characteristic of coarse-grained sulfate saline soil under conditions of increasing fines content. On this basis, PFC^3D discrete element method was adopted to simulate salt expansion of coarse-grained sulfate saline soil, and typical soil skeleton of coarse-grained saline soil during salt expansion process was analyzed combining microscope tests results. The result shows that with the increase of the content of fine-grained soil, the salt expansion/ frost heave of coarse-grained sulfate saline soil first increases, then decreases and increases finally. The boundary fines content varies with the salt content and soil type. Sand and gravel soil samples with 1% and 3% salt content would produce the largest salt expansion or frost heave at 15% and 10% fine-grained soil contents respectively. The initial expansion temperature of sand and gravel soil with 3% salt content is basically kept about 20℃. The initial expansion temperature of soil samples with 1% salt content varies greatly with the fines content and soil types, and there exists an obvious limit of fines content. When the content of fine-grained soil is lower than the limit value, the initial expansion temperature is about 0.5–2 ℃, when higher than the limit value, the initiation temperature is about 4–12 ℃. A typical state model of the coarse-grained soil skeleton in the salt-expansion state and the fines content limit of the coarse-grained sulfate saline soil as the embankment filler are given.

According to the cemented geological status of calcareous sand layers, a series of indoor model tests was performed to study the behaviors of the steel pipe pile in the cemented calcareous sand layers such as bearing capacity, the settlement, and compared with uncemented calcareous sand. The results show that the influence of relative density on bearing capacity of the pipe pile in cemented calcareous sand layers is obviously weakened compared with that in the uncemented layers. The bearing form of the pile still presents as an end-bearing pile, and the bearing ratio of pile tip resistance becomes higher and higher with the increase of cementation degree of calcareous sand. In highly cemented calcareous sand layers, there is an asynchronous process in the development of side friction of the pile. This is because when the pile foundation settles, the lower part of the pile shaft destroys the sand layer to form a tighter new contact surface, which is more sensitive to the radial expansion of the pile body. The side friction of the pile in cemented calcareous sand layers has no obvious hardening stage in the q_s-S_u  curve of pile in cemented calcareous sand, and different from the multi-segment broken line of the q_s-S_u  curve of the pile in uncemented calcareous sand, the  q_s-S_u  curve of the pile in cemented calcareous sand is closer to a hyperbolic curve.

Layered rock masses are often encountered in deep engineering. Due to the influence of high stress, rock mass hazards induced by layered structures often occur in engineering activities. This is closely related to the true three-dimensional high-stress environment and layered structures in deep engineering. For this reason, the test considering the orientation of schistosity was carried out under true triaxial compression based on a layered hard schist taken from a deep metal mine, and the deformation, strength and fracture characteristic of the samples with two schistosity loading orientations were obtained under different stress conditions. The results show that the mechanical properties of the hard schist are greatly affected by schistosity loading orientation and stress conditions. More specifically, when σ₂ is parallel to the strike of schistosity, the brittleness of the sample is stronger, and the smaller the σ₃, the stronger the brittleness. The strength of the sample is higher when σ₂ is perpendicular to the strike of schistosity, but the sensitivity of the increase in strength with the increase of  σ₃ is weaker. When σ₂ is parallel to the strike of schistosity, the shear failure along the schistosity prevails. When σ₂ is perpendicular to the strike of schistosity of the specimen, the tensile failure through the schistosity mainly occurs at a low σ₃ , and it transforms into shear failure along the schistosity at the high σ₃ . The test results have certain enlightenment significance for the stability evaluation of steep layered hard rock engineering: when the included angle between schistosity strike and tunnel axis is small, the normal stress release degree of schistosity of shallow rock is high, and brittle failure controlled by schistosity structure is easy to occur; on the contrary, the rock mass is relatively more stable when the included angle is large.

Breakage-induced evolution of particle size distribution (PSD) has a significant impact on the physical and mechanical properties of soil. It is therefore of great practical significance to study the evolution of particle breakage. The gradation transition matrix provides an effective approach to describing the detailed particle breakage of granular soils. This paper presents a series of  one-dimensional compression tests on carbonate sands with different initial conditions (i.e., PSD, relative density) to establish the gradation transition matrix of sample with more detailed information on particle breakage of each size group. The breakage of each single-sized particles of soil samples with multi-sized particles under different initial conditions is explored based on the dyeing and PCAS image recognition technologies. The results show that the presence of small-sized particles plays a negative effect on the breakage of the large-sized particles, while the presence of large-sized particles promotes the breakage of the small-sized particles. The PSD of each single-sized particles of a carbonate sand sample evolves towards the fractal distribution, and the relative breakage index  B_ri  of each single size group is linear with the input work per unit volume W_in . Finally, the breakage transition matrices of both uniformly and non-uniformly graded carbonate sands are established with consideration of interactions between particles with different sizes, which demonstrates its satisfactory performance. The proposed method provides a new insight into the evolution of particle breakage of granular soils with more detailed information of each size group.

Gassy soft soil is widely distributed in five continents in the world. The existence of a large number of discrete bubbles can strengthen or damage the undrained shear strength of soft soil. However, there is still a lack of analytical expression for undrained shear strength of gassy soil, which can comprehensively consider the competition mechanism between gas-phase strengthening and gas-phase damage. Combined with the theory of critical state soil mechanics and based on the yield function of gassy soil proposed by the author, this paper established the mathematical relationship between the intercept of critical state line and the gassy characteristics (u _{w 0},y ₀)  of soil in the  v-lnp¢  space, and then deduced the theoretical expression of undrained shear strength s_u of gassy soft soil in triaxial stress state. At the same time, using the deduced theoretical calculation formula of undrained shear strength of gassy soft soil, this paper compared the theoretical predictions and test results of undrained shear strength for three kinds of typical gassy soft soil under different gassy characteristics, including Malaysian kaolin silt, Combwich mud and kaolin clay. In addition, this study analyzed the predicted error percentage of four different theoretical calculation models for undrained shear strength of gassy soft soil, proving the rationality of the theoretical calculation formula of undrained shear strength based on the improved constitutive model of gassy soft soil. The proposed model can more accurately consider the dual effects of gas phase strengthening and gas phase damage of gassy soft soil simultaneously.

 Biomineralization of soil solidification methods is currently diversified, and different mineralization methods have their own limitations. The enzyme-induced carbonate precipitation (EICP) lacks nucleation sites, while the targeted activation of urease-producing microorganisms induced mineralization (biostimulation) has a longer solidification cycle and lower strength. Aiming at these problems, a mineralization method of biostimulation combined with EICP to reinforce soil is developed. In this paper,  reclaimed sea sand from Xiamen Xiang'an International Airport was investigated. Unconfined compressive strength tests (UCS), calcium carbonate production measurements, scanning electron microscope (SEM), X-ray diffraction (XRD), and microbial diversity testing were used to evaluate and analyze the solidification effect of the combined method. Some findings were observed.          1) Biostimulation combined with EICP mineralization can get a higher UCS, up to 2 300 kPa, which was greater than the sum of the UCS of the two separate mineralizations. 2) Biostimulation combined with EICP can promote the formation of calcium carbonate precipitation while improving its distribution uniformity, and optimize the crystal structure of calcium carbonate. 3) Microbial community analysis shows that biostimulation can highly stimulate urease-producing bacteria. EICP has a slight stimulating effect on some species. The species richness and uniformity of biostimulation combined with EICP are between those of EICP and biostimulation.

The structural abnormal response of underwater shield tunnel under operation is the prerequisite of structural abnormality early warning. Based on the monitoring segment strains of typical sections of the Wuhan Yangtze River tunnel during normal operation period (2013–2020), the distributions of strain increments, the relations of strain increment with temperature increment and water level increment, and relations of strain increments between adjacent segments (i.e. spatial effects) are thoroughly studied. An early warning method of structural abnormal response based on strain increment is proposed and the corresponding early warning threshold value is determined. Study results show that: 1) The distribution of strain increments does not obey the normal distribution but has a fat-tail. The exponential distribution can be used to describe the distribution of the absolute value of the strain increment. 2) The temporal strain increment is difficult to predict, but its variation range can be well determined through statistical analysis. Thus, an early warning method for structural abnormality is proposed based on the monitoring strain increment of a single measuring point, and its threshold value is determined. 3) There is a deformation mode of "one expand, the other contract" between adjacent segments during normal operation, which means the strain increases of one segment but decreases of the adjacent segment. This spatial effect constraints the average strain increments of adjacent segments in a relatively small variation range. Thus, another early warning method can be developed based on the monitoring strain increments of several adjacent measuring points, and its threshold value is determined.

In view of the existing unreasonable assumption on interslice shear forces involved in the horizontal slice limit equilibrium method for active earth pressure on rigid retaining walls, a mobilized coefficient of the interslice shear strength of the soil is proposed and its development mode is assumed to be 3 types of function including sine, linear, and hyperbolic patterns. A series of statistical values of the coefficient is given based on a great number of model test and in-situ observed results of the earth pressure. Further, static and seismic active earth pressure on rigid retaining walls can be determined using the horizontal slice method and pseudo-static approach with rationally considering the shear forces on interslice. Planar and log-spiral modes of potential slip surfaces of the retained soil are involved in the proposed method, which takes into account wall configuration, soil properties as well as external loads. It is found that the mobilized coefficient is not usually zero in the condition that wall-soil friction angle is equal to soil internal frictional angle or half of it, and the coefficient is greatly influenced by the wall-soil friction angle. The hyperbolic profile of the mobilized coefficient for wall translation and the sine mode for wall rotation about its heel are recommended because that the introduction of the mobilized coefficient can make the application points of the resultant of the active earth pressure relatively approach to the measured values. Internal friction angle of the soil, wall-soil cohesion, and vertical seismic factor have little effect on the application point of the resultant, while the soil cohesion, dip angle of the soil top surface, wall back inclination, wall-soil friction angle, and horizontal seismic factor have a greater influence. Some examples show that calculation results including the resultant and its application point of the active earth pressure using the proposed method are in good agreement with those monitored, and the maximum errors are less than about 10% and 7%, respectively.

The traditional strength reduction method (such as the unbalanced thrust method) is generally used in slope control design, and the design control force is based on unbalanced thrust, etc. Based on the analysis of the in-situ stress distribution along the sliding surface of slope, the three layout methods of control measures along the sliding surface are put forwards in this paper. Through the calculation and research on slope stability and anti-sliding design, the determination method of anti-sliding force under different boundary (or working) conditions is suggested. With the help of the multi-parameter space-time stability evaluation index of slope, a partial coefficient method for anti-sliding control design is developed, and the definitions of main sliding direction and slope failure are put forward. The proposed anti-sliding measure layout, anti-sliding force determination and partial coefficient design method in this paper are applied to the engineering (such as Budaiying slope in Shiyan city, Hubei province). The results demonstrate that the location selection of control measures, the determination of anti-sliding force and the partial coefficient design method of the slope are feasible after years of run.

For slopes that has failed or deformed significantly, the shear strength of rock and soil mass is frequently inversely estimated based on a factor of safety assumed. For the slope with a sliding surface passing through multi-layer rock and soil mass, it is unreasonable to achieve this goal by trial and error. To solve this issue, back propagation (BP) neural network is constructed using shear strength of multi-layer rock and soil mass as the input and the factor of safety of the slope, and the entry and exit positions of the sliding surface obtained by GeoSlope as the outputs. Then, based on the assumed factor of safety and the entry and exit positions measured in site, the shear strength is acquired by carrying out the “reverse back analysis-error check-sample correction” procedure repeatedly. The result of a case study verifies that the shear strength obtained by this method is reasonable and can be used as a reference when designing prevention measures for small-scale slopes. BP neural network usually considers the known information as the input, and the information to be determined as the output, which will induce a mathematical underdetermined problem when solving this issue. The proposed method avoids this demerit successfully, and has a lower requirement on the number of samples in the library and a higher precision compared to the classical BP neural network.

The retaining pile plus internal support structure has been widely used in foundation pit support engineering. Due to the complexity of geological condition, surrounding environment and earth excavation, however, it brings obstacles to the accurate design and calculation of foundation pit support system. This paper discusses the design and calculation method of single-layer internal support system under asymmetric load. Firstly, the difference of fixed point adjustment coefficient under articulated and fixed conditions between single-layer internal support and retaining pile is analyzed based on ultimate earth pressure method. Secondly, by using finite rod element method, the differences of pile shaft displacement, pile bending moment and pile shear estimated by two methods, i.e., earth pressure considering displacement by Terzaghi, and active earth pressure based on Chinese technical regulations for the support of building foundation pits. Due to the asymmetric load acting on the foundation pit support system, the displacement of the support piles on the side bearing large load and the side bearing small load are different, resulting in the different earth pressure on the support piles on the side bearing large load and the side bearing small load. The phenomenon of large difference in the internal force of the support pile shaft on the large and small sides should be paid attention to. The calculation methods of fixed point adjustment coefficient and displacement earth pressure proposed in this paper are more reasonable.

Rainfall-induced landslides are the most common geological hazard in the world, and the effect of preferential flow infiltration has been neglected for a long time regarding the slope reliability analysis under rainfall infiltration. The preferential infiltration under rainfall conditions is solved numerically by Comsol Multiphysics, and the slope factor of safety is calculated using an infinite slope model. An improved Cholesky decomposition method is applied to generate spatially correlated random fields, and the slope reliability during rainfall is analyzed using the Monte Carlo method. Combining the deterministic and reliability results to compare the variation of slope factor of safety between the homogeneous infiltration and the preferential infiltration during rainfall, it can be found that: (1) the preferential infiltration model is safer when the rainfall intensity is low, while the homogeneous infiltration is more stable at higher rainfall intensity; (2) the spatial variability of infiltration parameters is the crucial factor of slope failure in homogeneous infiltration, while the slope instability of preferential infiltration is mainly caused by the rapid advance of the wetting front; (3) for the study of preferential infiltration model, the slope has a higher probability of failure when the hydraulic exchange intensity between the matrix domain and the preferential domain, while smaller hydraulic exchange intensity may affect the slope failure at the bottom.

To improve the penetration rate of tunnel boring machine (TBM) in hard rock and reduce the cutter force, high pressure water jet assisted TBM rock breaking has been initially applied in industry. To investigate the rock breakage mechanism of disc cutter assisted by precutting kerfs, a 3D particle flow simulation was performed based on the indentation test of hard rock with hydraulic cutting kerfs. The variation of indentation force and indentation stiffness with kerf depth was studied. The evolution of crack propagation and contact force chain parallel and perpendicular to the cutter axis are revealed. The variation of tensile and shear cracks with kerf depth and kerf spacing and the corresponding failure mode and failure mechanism are discussed. The results show that the indentation stiffness and indentation force of the first indentation decrease linearly with the increase of kerf depth, and that of the second indentation are less than that of the first indentation. Moreover, the change of kerf spacing between 50 and 80 mm has no significant effect on the peak force. With the increase of kerf depth, the inclined boundary angle of the concentrated force chain under the cutter becomes larger. As a result, the failure tends to be inclined downward. When the kerf spacing increases, the failure mode changes from the inclined failure towards another kerf to inclined failure towards the middle rock ridge. The research results can provide some reference for the layout between TBM disc cutters and water jet nozzles and the selection of kerf depth.

To investigate the influence of temperature and humidity on the mechanical behavior of earth materials, a triaxial apparatus, which can accurately control the temperature and relative humidity of earth materials, was independently developed. Based on the conventional triaxial pressure chamber, a deformation measuring system was set up with the assistance of eddy-current type noncontact deformation sensor, thereby fulfilling the capture of continuous strain variation of earth specimen under the change of environmental condition. A series of cyclic loading-unloading triaxial tests was carried out on the earth material located in Lyon, France, while considering the effects of humidity, confining pressure and temperature. The failure strength, stress-strain curves and the volumetric change were measured through the aforementioned tests, and the Young’s modulus and residual strain under different stress levels were also studied by means of hysteresis loop occurred in the experimental results. Additionally, a vapor migration test of earth material under relative humidity action was also conducted. The results show that the new developed instrument can well control the environmental condition variation and simulate the real working state of earth specimen. The mechanical and environmental indexes are accurately measured, which preliminarily verifies the reliability and accuracy of this apparatus. The relevant research results can provide technical support for understanding the thermal-hydro-mechanical coupling deformation mechanism and constitutive modelling of unsaturated earth materials.