Expansive soil is a special kind of soil, which inevitably involves infrastructure construction such as roads and railways. However, the change of pore solution environment has a comparatively great impact on expansive soil. In this study, a cyclic load test on expansive soil in NaCl solution was carried out by using GDS true/dynamic triaxial instrument. The dynamic characteristics of expansive soil under the change of pore solution concentration were studied, and the cumulative deformation and damping ratio of expansive soil in NaCl solution with different concentrations under different dynamic stress amplitudes were analyzed. The results show that as the concentration of NaCl solution increases, the cumulative deformation of expansive soil decreases; and as the amplitude increases, the cumulative deformation gradually increases. According to the vibration frequency-accumulative deformation curve of expansive soil under different concentrations and amplitudes, a single exponential function is used to fit and judge it. The damping ratio curve of expansive soil under different NaCl solution concentrations gradually separates with the increase of the amplitude; the damping ratio gradually decreases with the increase of the concentration, and gradually increases with the increase of the amplitude. A model of the relationship between concentration and average damping ratio is established to provide reference for actual engineering.

Hashiguchi sub-loading surface constitutive model is one of the most influential constitutive models for over-consolidated soil. Therefore, this model is selected to analyze in terms of theoretical principle and construction method, and compare with the unified hardening(UH) model proposed by Yao et al. Through comparison, the Hashiguchi sub-loading surface model defines a single mathematical formula to fit the variation rule of the internal variables of the over-consolidated soil, and thus it can describe the stress-strain relationship of the over-consolidated soil. UH model holds the strength characteristics of over-consolidated soil, so it can describe the stress-strain relationship of over-consolidated soil more accurately and reasonably, which shows that the UH model is more advanced and complete in theory. At the same time, the comparison between the predictions of the two models and experimental data also verifies the correctness and superiority of UH model in numerical calculation.

The soil-water characteristic curve (SWCC) is an important characterization of the water-holding performance and water-vapor transport law of unsaturated soil. Due to its complicated testing process and many influencing factors, it is difficult to fully express it through a series of tests and mathematical models. The aim of this study is to explore the influences of soil type and physical state on SWCC. The abundant test data from worldwide research are collected as the database, and three characteristic values of SWCC (air-entry value, dehumidification rate and residual volumetric water content) are selected as the analytic target. Then, some data analyses are adopted to reveal the influence and sensitivity of different occurrence conditions on the characteristic values, and machine learning methods are employed to analyze the sensitivity. In the database，the material composition (particle gradation, particle size, plasticity index) and occurrence state (compactness, saturated water content, dry-wet cycle and ambient temperature) of the soil are common indicators that affect its water holding capacity. The influence mechanism of above factors presents some great differences but also obvious interrelation. The results of sensitivity analysis indicates that the plasticity index that reflects the clay content and the dry density that represents compactness) are two dominant factors influencing the water retention capacity of unsaturated soils. The distribution ranges of three characteristic values are also provided with considering the influences of two dominant factors, and can present most of test results and guide the engineering application.

In order to investigate the performance and mechanism of expansive soil slope with soilbags under the effect of raining-insolation cycles, a series of laboratory model tests on the expansive soil slope was conducted. The displacement of the reinforced slope, the slope erosion and rainfall infiltration were observed and analyzed, which were compared with expansive soil slope without reinforcement. The experimental results showed that under the action of raining-insolation cycles, the surface of expansive soil slope without reinforcement would develop cracks, which was further prone to soil loss. The soilbags performed well as a protection layer and a filter of soil particles, which could reduce the loss of soil in the bag and the underlying soil, and maintain the stability of the slope. In addition, soilbags had a good restraining effect on the expansive soil, which can effectively restrain its expansive deformation and reduce the possibility of slope instability. Furthermore, soilbags had a good drainage effect, so that rainwater could be quickly discharged through the gap between geotextile bags, and thus to ensure a relatively small increase of water content in the slope.

The microwave treatment effect of rocks is affected by many factors. Among them, water is a good absorbing medium, and it can improve the microwave absorbing ability of rocks. This study aims at exploring the effect of saturation on response characteristics of rock subjected to microwave irradiation. Tests of 3 kW power microwave irradiation were carried out on basalt samples with different saturations to examine the variations of the heating characteristics, wave speed, porosity change as well as dynamic tensile strength. The test data was analyzed from the meso and macro perspectives. Some findings identified. 1) The water affects the heating characteristics of the rock sample during microwave irradiation. Within the first 15 s of irradiation, the group with saturation lower than 75% obviously promotes the heating rate; when the saturation reaches 100%, the effect is opposite, and the heating rate is lower than that of the dry group；within 15−30 s, the heating rate of the water-containing sample decreases with the decrease of water content and the endothermic heat of evaporation; within 30−45 s, the water evaporation is completed, the heating rate of the water-bearing sample is close to that of the dry sample. 2) The difference in water saturation leads to varying degrees of wave velocity and porosity changes in basalt after microwave irradiation. The wave velocity reduction range is 8.18%−17%, and the porosity growth range is 18.71%−43.65%. The damage effect does not follow the saturation. 3) Under the same irradiation conditions, the 50% saturation group quickly reaches the strength limit under the combined action of steam pressure and thermal stress, and the samples are directly damaged. Obvious mesoscopic damage are not be observed in most of the other groups of samples, and the difference in final dynamic tensile strength is not distinct.

Cyclic shearing at low stress levels caused by microseism, engineering blasting has an important influence on the instability and failure of jointed rock mass engineering. In order to study the shear mechanical characteristics of rock joints under pre-peak cyclic shearing, the RDS-200 rock shear test system was used to carry out direct shear tests on artificial splitting yellow sandstone joints under the pre-peak cyclic shearing condition. Compared with the shear mechanical characteristics of rock joint without pre-peak cyclic shearing, the influences of pre-peak cyclic shear on the pre-peak shear stiffness, peak shear strength, peak shear displacement and residual shear strength are obtained. The results show that: (1) After pre-peak cyclic shearing, the pre-peak shear stiffness of rock joints increases when the normal stress is 2 MPa; but when the normal stress is 4−10 MPa, the pre-peak shear stiffness of rock joint within the cyclic shear stress amplitude increases, and the pre-peak shear stiffness of rock joint beyond the cyclic shear stress amplitude decreases. (2) After pre-peak cyclic shearing, the peak shear strength decreases by 10%−20%, and the decrease percentage increases logarithmically with the increase of normal stress. The peak shear displacement increases by 2%−40%, and the increase percentage decreases as a logarithmic function with the increase of normal stress. (3) After pre-peak cyclic shearing, the residual shear strength of rock joint doesn’t have a significant change, the difference between peak shear strength and residual shear strength decreases, and the loss percentage of work done by the post-peak shear stress also decreases.

In order to improve the rock damage constitutive model and parameter determination method under high temperature, based on the effective stress theory, the Weibull distribution function is introduced. Under the condition that the micro-element strength obeys the Hoek-brown criterion, the influence of residual strength is considered, the damage variables are modified, the damage correction coefficient is introduced, and a statistical constitutive model that can reflect the damage characteristics of rocks under high-temperature action is established. Considering the damage threshold factor in the rock damage process, the present constitutive model takes the form of a piecewise function. The conventional mechanical parameters are obtained by testing. Based on the process of solving the parameters of the constitutive model, the values of the constitutive model parameters are determined and the relationship between the values of the model parameters and the temperature is fitted. Finally, the theoretical curve of the model is verified. The results show that the theoretical curve of the proposed statistical damage constitutive model for high-temperature rocks has a good similarity with the test curve, and it is closer to the test curve and reflects the reasonableness of the constitutive model. At the same time, the theoretical curve of the model has a high degree of coincidence with the triaxial test curve, which indicates that the constitutive model can reflect the characteristics of the full stress-strain curve of the rock and can reflect the applicability of the model. The model provides a reference for rock strength estimation and rock thermal damage softening.

The planned high-speed railway in the Belt and Road area will frequently shuttle through salt desert areas, and it is difficult to find high-quality subgrade filler without salt along high-speed railway. To solve the technical problems faced by filling high-speed railway subgrade with coarse-grained saline soil, combined with the construction of Tehran-Isfahan high-speed railway in Iran, taking the coarse-grained saline soil subgrade filler obtained from on-site as the object, the test on water and salt migration and deformation response of compacted coarse-grained saline soil under temperature cycle was carried out. The results show that after each temperature cycle, the temperature wave amplitude is attenuated from superficial soil layer to deep soil layer. The temperature wave amplitude on closer to the surface of soil layers increases with the longer constant temperature time. The compacted coarse-grained saline soil with uniform distribution of water and salt gradually evolves into a non-uniform distribution after repeated temperature cycles. Water and salt migrate to the surface of soil layers, and the closer the position to the soil surface, the greater the increment of water and salt. In the first five temperature cycles, the plastic salt swelling or plastic thawing subsidence appears on the compacted coarse-grained saline soil. With the increase in number of temperature cycles, the plastic salt swelling or plastic thawing subsidence of saline soil decreases significantly or even disappears. The non-salted soil layer resting on coarse-grained saline soil layer has the functions of delaying salt migration up to the surface of soil layers, energy dissipation and expansion reduction. The structural layering technology should be adopted for the construction of high-speed railway subgrade with coarse-grained saline soil. The thickness of non-salted soil layer should not be less than the depth that significantly affected by the local temperature radiation. In the design of coarse-grained saline soil subgrade, the heterogeneous distribution of water and salt formed after repeated temperature cycles and the possible increase effect of salt swelling and thawing subsidence should be considered, and the degree of compaction of coarse-grained saline soil subgrade should not be too large. The research results will play a demonstration and reference role for the construction of high-speed railway subgrade engineering in saline soil areas.

Underconsolidated soil is the soil that has not finished consolidation under its self-weight. At present, there are two types of overconsolidation ratio for underconsolidated soil in literature, i.e., equal to 1 and less than 1 respectively, which may cause confusion or misusing problems. We have sorted out the relevant contents of overconsolidation ratio in the widely used soil mechanics textbooks and found that there are two different definitions for overconsolidation ratio, where the different denominators result in the difference of overconsolidation ratio for underconsolidated soil. Using knowledge graph method, we comprehensively analyze the conceptual meaning, historical origin and practical applications for overconsolidation ratio and underconsolidated soil. Results show that degree of consolidation or consolidation state parameters can be used as substitution for overconsolidation ratio while involved in the problems related to underconsolidated soil. Overconsolidation ratio should be defined as the ratio of preconsolidation stress to existing effective stress (OCR = p_c /p′₀, p_c is the effective consolidation pressure in the early stage, p′₀ is the vertical effective stress), which is consistent with the influence mechanism of stress history on soil behavior, as well as the historical origin meaning of the concept.

Large ground deformation such as faults, landslides and liquefaction may pose a serious threat to the structural safety of buried pipelines. This paper presents a series of three-dimensional numerical simulation of horizontal lateral pipe–soil interaction in medium dense sand, discusses the failure mechanisms of sand under different depth-diameter ratios, and examines the influence of depth-diameter ratio on the ultimate bearing capacity of sand. Moreover, a simplified analytical model is proposed based on the failure mechanism of soil around the pipe. According to the limit-state equilibrium theory, the analytical solution of the ultimate bearing capacity under horizontal lateral motion of the pipe is derived. The results show that, in the limit state, the soil around the shallowly buried pipeline forms a rupture surface extending to the ground surface with a failure shape approximately to a logarithmic spiral. The ultimate bearing capacity of sand increases with the burial depth-diameter ratio of the pipe, and finally reaches a constant value at the critical depth-diameter ratio. With the increase of depth-diameter ratio, the pipe displacement required for shear failure of soil also gradually increases. The difference in ultimate bearing capacity calculated by Chinese codes and foreign codes is due to the different empirical lateral bearing capacity coefficient. The analytical solution proposed in this paper can favorably predict the ultimate bearing capacity of soil under lateral horizontal movement of shallowly buried pipes in medium dense sand.

Stacked tunnels is a complex system involving the interaction between tunnels and between tunnel and soil, and its safety will seriously affect the construction of urban rail transit. At present, the research on shaking table test of stacked tunnels focuses on horizontal parallel and cross arrangements, unidirectional and bidirectional ground motion input. This paper uses a self-designed three-dimensional laminar shear soil container to implement a shaking table model test on seismic response of vertical parallel stacked tunnels under three-directional earthquake wave excitation. Its seismic response includes the dynamic characteristics of foundation soil-stacked tunnels model system, the acceleration of foundation soil and stacked tunnels, ground settlement, the pore pressure of foundation soil, and the dynamic soil pressure and the strain of stacked tunnels. The results show that with the increase of seismic wave peak ground acceleration (PGA), the natural frequency of foundation soil-stacked tunnels model system decreases and the damping ratio increases. The gradient difference of soil acceleration and pore pressure around the stacked tunnels increases with the increase of seismic wave PGA, and the gradient difference around the upper tunnel is larger than that around the lower tunnel. The amplification effect of the foundation soil on the acceleration decreases with the increase of the seismic wave PGA. Under the action of same seismic wave, the shape of the acceleration Fourier spectrum of stacked tunnels at the same position is similar, but the amplitude increases with the increase of the seismic wave PGA. Furthermore, compared with the crown and bottom positions, the frequency range of the acceleration Fourier spectrum at the waist position becomes wider, and the peak amplitude decreases. The peak value of ground settlement decreases with the increase of seismic wave PGA, and the peak value of ground settlement in the center is obviously smaller than that on both sides of the foundation soil. The type of seismic wave has little effect on the peak value of dynamic earth pressure and strain of stacked tunnels. For the peak dynamic earth pressure, in the upper tunnel, the maximum value of the two tunnels is at the waist position, while the minimum value of upper and lower tunnels is at the bottom and crown positions, respectively. The peak strains at the both waist positions in the upper tunnel are significantly larger than those at the top and bottom positions, while the peak strain does not differ much at the four positions in lower tunnel.

Based on improved PFC-FLAC numerical simulation method, this paper presents an improved particle flow acoustic emission (AE) model based on bilinear interpolation of nodal velocity in coupled region of FLAC model, and a method for judging the depth of rock mass failure zone according to the AE intensity. Both methods have been applied to studying the meso-mechanism of local rock damage and destructive characteristics for excavation surface of underground powerhouse cavern and contact surfaces of rock-anchored crane beams. The results show that the contact force chain of the shallow surrounding rocks is gradually sparse, and a large number of micro-cracks develop and merge into macro-cracks, and finally a shallow fracture zone appears, showing tensile fracture; with the increase of distance from the excavation surface, the surrounding rocks are damaged due to the large force at the early stage of excavation, and only a few micro-cracks are generated at the later stage, which correspond to the depth of rebound unloading zone. When the surrounding rocks deteriorate and crane beam is overloaded, numerous tensile and shear cracks will respectively develop on the vertical and inclined contact surfaces between the crane beam and surrounding rocks, which are macroscopically manifested as tensile fracture and slip failure. The above results are consistent with the three-dimensional finite element method. The proposed method also solves the problems of the finite element method that there is merely a single display method for surrounding rock damage and it is difficult to describe the changes of rock damage degree. This study provides a reference for investigating the macro- and meso-scopic characteristics and damage mechanism of large deformation and stress concentration areas of underground powerhouse caverns.

Rockburst must occur under the drive of energy. In this study, a mechanical model of coal-rock combined body was constructed to explore the accumulation layer of energy causing rockburst in coal-rock system, and a formula of pre-peak energy distribution of coal-rock combined body was deduced. The experiments of energy accumulation under five loading rates of fine sandstone-coal (FC), coarse sandstone-coal (GC) and fine sandstone-coal-coarse sandstone (FCG) were carried out. The failure characteristics, mechanical properties and energy accumulation law of the combined body were analyzed. The results showed that: 1) At a loading rate of 0.001 mm/s, the pre-peak energy of the combined body was mainly dissipated slowly in the form of primary crack propagation and coalescence, which belongs to complete plastic failure; and at the 0.1 mm/s loading rate, the pre-peak energy of the combined body was mainly released rapidly in the form of local ejection failure, which belongs to brittle incomplete failure. 2) The compressive strength, elastic modulus, pre-peak energy and impact energy index of the combined body have a logarithmic relationship with the loading rate. As the loading rate increases, the increases of compressive strength, elastic modulus and impact energy index decrease gradually, and the pre-peak energy growth rate shows a "low-high-low" trend. 3) The energy storage and energy share of coal components increase as the loading rate increases. At the 0.001−0.010 mm/s loading rate, the accumulated energy of coal components increases rapidly and at the 0.010－0.100 mm/s loading rate, the accumulated energy of coal components increases slowly. 4) At the same loading rate, the energy proportion of coal components is in the following order: FC combined body > FCG combined body > GC combined body. 5) The energy proportion of coal component in the combined body surpasses 50%, and the coal component is the main carrier of energy accumulation. Under the same stress condition, the energy accumulation ability of weak rock is stronger than that of hard rock. In other words, energy is more easily accumulated in weak rocks. The research results can provide an insight into determining the energy accumulation layer of rock burst and the work of energy release and impact reduction.

Enhancing coal seam water injection capacity is an urgent problem to be solved, and the difficulty of coal seam water injection lacks accurate criteria. By considering the characteristics of the seepage fractal structure of the pores and cracks of the coal and the chemical wetting characteristics under capillary action, a model of the seepage flow of coal seam water injection is established. Based on the methods of probability theory and mathematical statistics, a set-pair connection degree interval evaluation system is constructed, and the difficulty of water injection into the coal seam is divided. The results show that: 1) The effect of water injection is affected by the simplest parameters such as porosity, pore radius, contact angle, liquid density, surface tension, viscosity coefficient, gravitational acceleration and other seepage structural parameters as well as chemical wetting characteristics. The system model characterizes the relationship between the seepage structure and chemical wetting characteristics of coal and the seepage flow. 2) Under combined weighting, the porosity weight is 0.32, which has a greater contribution to the water injection effect, followed by the maximum pore throat radius and contact angle, and the minimum pore throat radius weight is 0.17, which has the least impact on the water injection effect. 3) The evaluation index values of coal samples X1, X2 and X5 are between (0, 0.25), which indicate that the coal seam belongs to the coal seam with difficult water injection; the evaluation index values of coal samples X3 and X4 are between (0.25, 0.50), which imply the coal seam belongs to the one relatively difficult to inject water.

To analyze the effect of various factors such as temperature, strength of alkali solution and dry density on the thermal conductivity of bentonite, thermal conductivity of MX80 bentonite in alkali-thermal environment was measured by a thermal probe method. Meanwhile, the X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests were carried out on selected samples to reveal the micro-mechanism of thermal conductivity evolution of MX80 bentonite under alkaline and thermal environment. The results show that the thermal conductivity of MX80 bentonite increases with the increase of alkali solution content and dry density. The thermal conductivity of bentonite increases with the increase of temperature under different content conditions, and the higher alkali solution content is, the more significant the temperature effect of thermal conductivity is. When the dry density is small, the influence of thermal conductivity λ of bentonite increases with the increase of temperature. The main reason is that temperature facilitates the latent heat transfer of water vapor inside the sample. At the same dry density and temperature, the thermal conductivity decreases with the increase of pH value, the higher the pH value is, the greater the decrease range of λ is. The main reason is that the strong alkali solution erodes the montmorillonite and quartz of bentonite, increases the porosity of bentonite, thereby reduces the thermal conductivity of bentonite, which is consistent with the XRD and SEM image results of the tested samples.

Freeze-thaw cycles destroy the structure of soil, resulting in a reduction in mechanical properties of soil. A series of tests on lime-soil and fiber reinforced lime-soil is completed, including freeze-thaw test, the unconfined compressive test, scanning election microscopy (SEM) test, and nuclear magnetic resonance (NMR) test. Based on the test results, the effect of freeze-thaw cycles on soil strength and microstructure index is discussed. The results show that the compressive strength of lime-soil and fiber reinforced lime-soil decrease with the increase of freeze-thaw number, and the four stages for soil strength variation are identified in soil failure process, i.e., large reduction, small reduction, slow reduction and stability. In the case of high moisture content and frequent freezing and thawing, it is more conducive to the reinforcement of soil by fibers. The addition of fiber delays the formation and development of cracks in soil, reducing the connection of cracks. With the increase of freeze-thaw number, the porosity and the pore diameter increase, as a result, a part of small pores connect into medium pores and large pores. The porosity and pore distributions of soil vary slightly under freeze-thaw cycles because of the spatial restraint effect of fiber on soil and the friction between fiber and soil, which result in the strength and freeze-thaw resistance of fiber reinforced lime-soil is better than that of lime-soil.

Heavy metal contaminated soils not only destroy environmental health, but also threaten the safety of geotechnical engineering. The control variable method was used to study the compaction characteristics evolution and active mechanisms of arsenic (As) and cadmium (Cd) single and composite contaminated soils with different concentrations through soil chemistry, microstructure and compaction tests. The results showed that in single contaminated soil, the As could enhance optimal moisture content by 5.90%, but decrease the maximum dry density by 1.02% through thickening diffusion double electric layer, promoting small pores and fine aggregates in flocculated structure. The effect of Cd on the soil particles is opposite. Cd compressed the diffused- double layer so that the number of small pores and fine aggregates were reduced. As a result, the optimal water content was declined by 8.03% and the maximum dry density is increased by 1.00% of Cd contaminated soil. Furthermore, the influence of Cd on the compaction characteristics of soil is greater than that of As. For the As and Cd co-contaminated soil, As and Cd had synergistic interaction on the optimal moisture content, while no interaction on maximum dry density. The correlation between macro- and micro-characteristics of contaminated soil was established by fitting the relationship between fractal dimension and the maximum dry density with a quadratic function. The results of this study can provide key parameters and theoretical support for mitigating the environmental and engineering disasters of heavy metal contaminated soils.

Apart from the effective restraint soils, soilbags have also a function of water filtration and soil conservation, so they can be used to resist foundation soil liquefaction. However, seldom studies have been made on the liquefaction resistance performance of soilbags. A series of shaking table tests was carried out on soilbags-stacked cushion to verify its liquefaction resistance performance and investigate the influence of the vibration acceleration, the layers and arrangements of soilbags on liquefaction resistance. The results show that soilbags have good liquefaction resistance effect, and the excess pore pressure ratio of soil in bags is less than that of the surrounding soil at the same depth. The drainage performance of soilbags is contributed to its good permeability, and the discharge of pore water along the interface between soilbags and foundation soil as well as the gaps among soilbags. Compared with the rigid impervious cushion, the surface of soilbag cushion basically keeps level during the process of vibration, showing better deformation coordination performance. The increase of soilbag layers and the staggered arrangement of soilbags are beneficial to anti-liquefaction.

Minimum void ratio is an effective physical index to determine the compactness and pore characteristics of soil mass. A fast and effective method to determine the minimum void ratio of soil mass can provide reliable parameters for soil consolidation and stability. Most of the model parameters corresponded to the ratio of fine-coarse particle size one by one, so it is difficult to estimate the minimum void ratio of fine-coarse mixed materials. By analyzing the grain size composition, deposition and consolidation stability of tailings, and combining with the minimum void ratio test results of tailings with 8 different grain sizes and 7−9 different fine grain contents, a power function of the minimum void ratio distribution model parameters of tailings with different grain size fractions was obtained. Based on the grain size fraction of mixed tailings, the exponent values to determine the power function relationship of parameters were given. Six groups of other soil materials grain size within the range of grain size fraction and three groups grain size without the range of grain size fraction were used to verify the model parameters. The results show that the model considering the influence of grain size fraction has simple parameters and high accuracy in estimating the minimum void ratio of different soil materials. The minimum void ratio given is reasonable, and it can provide a reliable calculation method for estimating the minimum void ratio in the field of geotechnical engineering.

The distribution and propagation characteristics of water pressure in water-bearing crack under blasting load are of great significance to the study of the initial crack propagation mechanism in water-bearing fractured rock mass. Through the laboratory blasting experimental in concrete with water-bearing crack, the water pressure in water-bearing crack was measured during blasting, and its loading characteristics and propagation law were analyzed, while the effects of crack aperture and blasting charge quantity on water pressure were studied. The experimental results show that the time-history distribution of water pressure in water-bearing crack presents multi-peak fluctuation distribution. And the sources of water pressure include the blasting load directly transmitted through the water and indirectly transmitted through the concrete; the main source of load is different for different crack lengths. Under the same charging condition, the water pressure in water-bearing crack attenuates rapidly with increase of distance from the detonation source, and the water pressure at the same position in crack is approximately inversely proportional to the crack aperture. The energy spectrum of water hammer wave in water-bearing cracks is mainly concentrated in 7.8−62.5 kHz during laboratory explosion test of concrete with water-bearing crack, which is a high frequency signal. Meanwhile, the energy distribution trends to concentrate in the low frequency range with increase of distance from the detonation source. The energy distribution characteristics of water hammer wave are affected by charge and crack aperture, and the explosion induced by emulsion explosive of the equivalent 4.5 gTNT charge can generate water hammer wave with more abundant high frequency information in comparison with the equivalent 8.1 gTNT emulsion explosive charge. For the same blasting charge quantity, the peak energy distribution of the water hammer wave frequency band tends to move to the middle band with the increase of crack aperture.

Application of cement-solidified mud to filling projects can mitigate the local scarcity of sand and gravel filling material and dispose of significant volumes of dredged mud. Nevertheless, when the dredged mud is at extra-high water content (>300%), the treatment efficiency of pure chemical solidification becomes very low. However, such problems can be effectively solved by treating mud slurry using the physicochemical composite method. As the quicklime has both the effect of flocculant and solidification agent, using quicklime to replace part of the cement may further increase the treatment efficiency. In this paper, the effect law of the replacement ratio of quicklime on physicochemical composite treatment of dredged mud slurries was studied via vane shear tests, and its solidification mechanism was revealed by XRD and FESEM tests. The results show that quicklime significantly impacts on the physicochemical composite treatment effect, and there is an optimal replacement ratio. Under this optimal replacement ratio, the quicklime can exert the dual effects of flocculation and solidification, which effectively increases the earlier and later strength of the treated mud specimens. From the microscopic test results, the treated mud samples at this optimal replacement ratio produce the highest amount of CSH/CAH/CASH, ettringite and other hydrated cementitious materials with the smallest pore gap. Therefore, quicklime can be used to replace part of the cement during the physicochemical composite treatment of dredged mud slurries in the actual project.

Porous structure of coral sand has a significant impact on its mechanical properties and permeability characteristics. In this study, computed tomography (CT) was used to scan the coral sand particles, and the three-dimensional pore structure model of the coral sand particles was established in combination with image processing technology. The diameter, volume, compactness, and sphericity of the pores were quantitatively analyzed. Numerical simulation methods were used to examine the permeability characteristics of the pore structure of loosely accumulated coral sand and single-particle coral sand. Experimental results show that the number of pores in the particles decreases significantly with the increase of the pore diameter, which is characterized by a large number of micropores and a small number of macropores. There is a power function relationship between the diameter of the pores and the tightness, and a linear relationship with the sphericity. Seepage analysis results show that the seepage capacity in the Z direction is significantly less than the seepage capacities in the X and Y directions, and the seepage capacity shows anisotropy. Porous seepage velocity in the inner pore of coral sand particles is slow, the seepage capacity gap between different particles is large. In addition, no seepage occurs in some particles, and the absolute permeability of the pores in the particles only accounts for 1.26% of the total absolute permeability.

To obtain the rock type-Ⅰ crack propagation process accurately, a simple crack directional propagation device was used to test the crack propagation of different rock types. The crack propagation process of rock is monitored with acoustic emission (AE) and digital image correlation method (DICM). A mechanical model of crack directional propagation was established. Then, AE and deformation field evolution laws during crack propagation process are analyzed, and a new crack propagation energy index (CE) is proposed to evaluate the difficulty of rock type-Ⅰ crack propagation and the crack initiation and propagation mechanism is discussed. The results show that, the simple crack directional propagation device can effectively realize the stable propagation of type-Ⅰ crack along the predetermined direction, the crack initiation angle is less than 10º, and the deviations between the peak strength of crack propagation calculated by simplified mechanical model and the tensile strength of Brazilian splitting are 22.76% and 7.53% for white sandstone and grey sandstone, respectively. According to the deformation field evolution law, the crack propagation can be divided into three stages: microcrack development (speckle deformation field is still uniform), main crack propagation (zone phenomenon appears in speckle deformation field) and main crack propagation. Four stages including quiet stage, slow increase stage, rapid increase stage and decreasing stage can be identified in the AE evolution process. Compared with white sandstone, the gray sandstone is denser and the main cracks are fully developed, resulting in a long quiet stage of AE, while the last three stages are short. The area ratio of pre-peak area to post-peak areaof load-displacement curve was defined as CE, the CE of gray sandstone and white sandstone are 13−16, 1−2, respectively, which shows that the CE can effectively evaluate the difficulty of type-I crack propagation. Rock type-I crack initiation and propagation mechanism can be summarized as follows: before the peak, the prefabricated crack tip is subjected to the maximum tensile stress, the elastic energy increases rapidly, and the dissipated energy increases slowly; nevertheless after the peak, elastic energy exceeds its energy storage limit and is released rapidly, most of the input energy is converted into dissipated energy, which results in a propagation rapid of crack. In the future, the crack directional propagation device will be optimized and improved, and it is expected to provide a new method for the study of crack propagation mechanism, rock fail precursor information and crack arrest principle, and to provide theoretical guidance for the optimization of coal strata directional blasting, fracturing, fracture arrest and other related technologies in the engineering site.

Based on the geometrical morphology of the columnar jointed rock mass at the dam foundation of Baihetan Hydropower Station, a water-soluble polyvinyl alcohol (PVA) material was introduced, and the columnar jointed rock mass network structure with different inclination angles was established. The columnar jointed rock mass samples were prepared by cement mortar as rock-like materials using 3D printing technology to study the anisotropic mechanical characteristics of the columnar jointed rock mass. The anisotropic mechanical characteristics of columnar jointed rock mass were analyzed by uniaxial compression test in a laboratory. The results show that the anisotropy of columnar jointed rock mass depends on the dip angle of the joint. Peak strength and modulus of columnar jointed rock mass show an approximate “U” shaped curve with the increase of joint dip angle. In the uniaxial compression test, the cleavage cracks perpendicular to the axial direction of the cylinder, the shear cracks along the longitudinal joint plane, and the tensile cracks parallel to the axial direction of the cylinder are mainly produced. According to the evaluation of mechanical anisotropy, it is found that the anisotropy degree of peak strength and residual strength are 0.68 and 0.52, and the anisotropy degree of elastic modulus and deformation modulus are 0.61 and 0.63. The research results provide a reference for the study of the anisotropic mechanical properties of columnar jointed rock mass.

Enzyme-induced calcite precipitation (EICP) is considered to be the cutting-edge technology with broad development in many fields of geotechnical engineering. However, there are limited studies focused on the mechanism affecting the calcite precipitation. This study conducts a series of test-tube experiments to examine the effects of different substrate concentrations, magnesium ion concentrations, and ammonium ion concentrations on the changes of conductivity, pH, calcium carbonate precipitation and precipitation rate during urease mineralization. In this way, the mechanism of urease mineralization strengthening and deterioration was revealed. The water absorption, air permeability and wind erosion tests were carried out on the brick specimens under the action of individual mechanisms. The results show that with the increase of substrate concentration, the conductivity gradually increases but the evolution trend of the curve remains basically unchanged, the pH value does not change significantly, the precipitation amount first increases and then decreases, and the precipitation rate gradually decreases, among which the urea hydrolysis rate and urease activity is the key to the conversion of carbonate and to increase the amount of precipitation and the rate of precipitation. With the increase of the concentration of magnesium chloride, the amount of precipitation increases first and then decreases, and the precipitation efficiency gradually increases. The ions have a positive effect on enhancing the urease activity to form the optimal mineralization effect. With the increase of the ammonium chloride concentration, the conductivity gradually increases and the pH value gradually decreases. Ammonium radical is the main reason for the deterioration of urease activity, precipitation amount and precipitation efficiency. The water-resisting ability of the produced calcite precipitation is further verified through the water absorption, air permeability, and wind erosion tests respectively. The findings of this study explore the potential use of the EICP technology for the protection of heritage buildings in north-west China

In seismic events, the occurrence of a rock landslide strongly depends on the dynamic mechanical properties of the rock mass materials of slope. In order to understand the characteristics of rock material under dynamic load, this study took phyllite, a representative rock mass developed in the Donghekou landslide area triggered by the Wenchuan earthquake in 2008, as the research object, to conduct a multi-stage cyclic loading and unloading test under triaxial compression. The confining pressure was 10 MPa, the loading frequency was 2 Hz, the loading waveform was sine wave, and 60 cycles were loaded at each level of stress. According to the axial stress-strain curve, the effects of cycle number and upper limit stress on elastic modulus, damping parameters and residual strain of phyllite samples were analyzed, and the evolution law of dissipated energy was also studied. The results are shown as follows: (1) The elastic modulus, damping ratio and damping coefficient of the samples decreased as the cycle number increased. When the upper limit stress was low, the internal structure of rock began to change significantly due to the closure of initial cracks and pores and formation of small new cracks, which caused the values of the parameters fluctuated greatly with a general increase as the cycle number increased. When the upper limit stress was high, the parameters demonstrated a slight change. (2) The cumulative residual strain showed an increasing trend as the cycle number and stress level increased, which was mainly related to the stress increase process (ramp loading stage) of rock samples. However, the relationship between the cumulative residual strain and the upper limit stress of rock samples at one stress level (cyclic loading stage) showed a W-type change. (3) The dissipated energy per unit volume also showed an overall increasing trend with the increase in cycle number and stress level. However, at lower upper limit stress level, the energy dissipation per unit volume changed slightly with the increase of cycles; at higher upper limit stress level, the energy dissipation increased in an “L” shape while in a “U” shape near failure. The research results can help to understand the mechanical behaviors of rock under dynamic cyclic loading, as well as to provide theoretical support for the formation mechanism analysis of large rock landslides under earthquake action from the perspective of rock mechanics in future work.

Geosynthetics are used in filtration and drainage engineering. The key issues closely related to the safety of the project are the filtration characteristics of the geotextile filter layer under the action of stress and seepage. In order to reveal the mechanism of nonwoven geotextile filtering clay, a self-developed gradient ratio permeameter test device that can apply normal compressive stress is used to determine the permeability coefficient kT of the clay-nonwoven geotextile system, the permeability kj of each layered soil, the gradient ratio RG and the mass change of geotextile before and after the test. The filtration characteristics of the nonwoven geotextile filtering clay under different hydraulic gradients and stress levels are studied. The results show that kT and RG decrease along with time and eventually tend to a stable value. Increasing the hydraulic gradient can improve the water permeability of clay-nonwoven geotextile filter layer. And increasing the stress level will reduce the permeability but improve the soil retention of filter layer. Under the action of seepage, the protected soil layer shows that the permeability coefficient of the bottom soil layer near the nonwoven geotextile is the smallest, while the permeability coefficient of the uppermost soil layer away from the nonwoven geotextile is the largest. The clogging coefficient  has an intrinsic relationship with kT and RG. There may be a critical clogging coefficient under a specific stress-seepage action. If the clogging coefficient is greater than the value, it may cause the failure of the nonwoven geotextile filter layer.

The long-term unsteady heat exchange of pile-soil makes the temperature of soil increase continuously. This phenomenon is called “heat accumulation effect” which affects the heat transfer efficiency of pile and soil, even make the energy pile system failure. In this paper, the composite phase change material was used to prepare the phase change concrete energy pile, and the thermal response model tests of the phase change pile and the ordinary pile were carried out on saturated silt. The temperature distribution around the pile, the stress and strain of the pile, the displacement of the pile top and the heat exchange efficiency of the pile were compared and anaylzed. The results show that the heat exchange direction of the phase change pile is mainly of radial exchange, and the influence area is within 2D, and the temperature change of the soil shows hysteresis effect. The change range of pile-soil temperature of phase change pile is smaller than that of ordinary pile, which can alleviate the thermal accumulation effect of soil around pile. During the temperature cycle, the phase change pile accumulates unrecoverable plastic strain. After several temperature cycles, the plastic cumulative displacement of phase change pile is smaller than that of ordinary pile. The heat transfer power of phase change pile is about 20% higher than that of ordinary pile in summer. The heat transfer power of both piles is basically the same in winter, and with the increase of operation time, the heat exchange efficiency of both piles is similar.

The reinforcement-soil interface in the reinforced soil structure not only suffers from the horizontal cyclic shear, but also the compression of the cyclic normal load. In this study, a large-scale direct shear apparatus was used to analyze the cyclic shear characteristics of the aggregate-geogrid interface under bidirectional cyclic loading. The influences of various cyclic normal load frequencies, horizontal cyclic shear frequencies and waveform of normal loading on the interface shear strength were investigated. The results showed that when the cyclic normal load frequency and the horizontal cyclic shear frequency were synchronized, the peak shear stress and the maximum vertical displacement increased with increasing the frequency, and the time shift between shear stress and the displacement curve at the front and back half cycle was the same. On the contrary, the relationship between shear stress-displacement and the vertical displacement showed two different morphological characteristics under bidirectional cyclic loading. The largest values of shear stress and vertical displacement were observed under the sinusoidal waveform of cyclic normal load. But the hysteresis loop and vertical displacement curve under harmonics and square waveform were different from those under the triangular and sinusoidal waveform. The shear stiffness increased with increasing the frequency of the bidirectional cyclic load. The interface shear stiffness is the largest under the sine wave and the smallest under the ramp wave.

The lithologic combination of the reservoir interlayers in a certain area of Xinjiang Oilfield is complex, showing prominent thin-interbedding occurrence characteristics. The study of the judgment conditions of combined and separated pressure is beneficial to improve the fracturing efficiency, enhance the production degree of the reservoir and the effect of post-pressure reconstruction. The behavior of hydraulic fracture penetration and fracture propagation in thin interbeds is affected by the geological characteristics of thin interbeds and fracturing operation parameters. Based on this, fracturing experiment on thin interbed physical model was carried out to study the influence of bedding interface cementation, rock layer distribution, rock layer thickness, fracturing fluid viscosity and injection volume on the vertical propagation of hydraulic fractures in thin interbeds. The experimental results show that the stratigraphic characteristics of thin interbeds, bedding interface cementation and rock distribution are the main controlling factors for the vertical propagation of hydraulic fractures. The influence of bedding interface cementation strength on fracture vertical propagation behavior is stronger than that of rock distribution. Due to the existence of weak cemented bedding interface, the direction of hydraulic fracture can be deflected when it propagates vertically through the bedding, which can inhibit the vertical propagation of fracture. The increase of fracturing fluid viscosity and injection volume is beneficial to the vertical propagation of hydraulic fractures in thin interbeds.

Microbial-induced carbonate precipitation is a novel green reinforcement technology in the geotechnical engineering field. To study the reinforcement effect of urease-producing bacteria extracted from the engineering environment in situ, a highly effective urease-producing bacteria was isolated from typical bank slope soil on the Three Gorges Reservoir and identified as Bacillus cereus. To analyze the reinforcement effect, the optimum culture conditions of Bacillus cereus were first determined by orthogonal optimization, and then the solidification tests on a sand column and fractured rock mass were carried out using Bacillus cereus and Sporosarcina pasteurii. The results showed that: (1) Compared with Sporosarcina pasteurii, the porosity of the sand column reinforced by Bacillus cereus was filled more densely, the impermeability was better, and the calcium carbonate engenderment was higher, thus designating that Bacillus cereus had better mineralization function. (2) The permeability coefficient of fractured rock samples reinforced by Bacillus cereus decreased by 3 orders of magnitude, and the internal friction angle and cohesion increased by 48.09% and 85.10% respectively，denoting that Bacillus cereus can efficaciously ameliorate the permeability and shear resistance of fractured rock, and compared with Sporosarcina pasteurii, it has a better reinforcement effect. Relevant research conceptions and results can provide a good reference for the green reinforcement of engineering rock mass.

In order to analyze the dynamic evolution process of the soil arch behind anti-slide pile, a novel type of soil mass relative deformation monitoring system was designed, and a series of physical model tests was conducted. Two dimensionless parameters were introduced based on the monitoring data in the tests, for characterizing the relative deformation degree and uneven deformation degree of sliding mass. Some findings were observed. The evolution process of soil arch can be divided into three stages based on the curve characteristics of soil arch deformation and lateral thrust behind piles: elastic formation stage, plastic development stage and failure stage. And significant three-dimensional failure characteristics were observed in failure stage: on the horizontal plane, the soil arch exhibited layered arch ring extrusion failure; on the vertical plane, the soil in the middle parts of sliding mass first cracked and collapsed, and then a catenary-shaped crack appeared on the top of sliding mass. The strength parameters of the sliding mass around piles were in a dynamic strengthening process in the sliding process with the change of relative deformation. As far as the degree of strengthening was concerned, cohesion was more sensitive than angle of internal friction. The relative deformation degree and parameter strengthening degree of the sliding mass relatively backward in the early stage were higher than those of the sliding mass relatively forward. Therefore, the cracks in the sliding mass around the piles gradually deflected towards the center line between the piles in the process of cracks developing backward, and formed a stable supported arch structure after the cracks coalesced.

Grouting reinforcement is one of the effective measures to solve the uneven settlement of calcareous sand ground. In term of the characteristics of calcareous sand, ultrafine portland cement was selected as the main grouting material, nano-silica sol, fly ash or calcium sulfate whisker were used as auxiliary materials. According to the requirements of single factor and orthogonal tests, grout with different proportions was prepared, and the setting time and compressive strength of grout and consolidated calcareous sand were tested respectively. Meanwhile, response surface method was used to simulate the test results to analyze the influence of each component on each performance index and to determine the optimal ratio of grouting materials. The results show that the compressive strength of consolidated body at different ages can be improved when the three kinds of excipients are added separately to the slurry in proper proportion. When the cement content is fixed, the water-cement ratio is the most important factor affecting the setting time of slurry and the strength of consolidated body. Compared with pure cement grout, the grouting grout prepared with the best proportion of additives can better fill into the intergranular space of calcareous sand, thus changing the compactness of the consolidated body and increasing its compressive strength significantly.

Improving the adsorption stability of petroleum pollutants in soil is the premise and key to the engineering reuse of contaminated soil. Relying on the disposal needs of oil contaminated saline soil in coastal areas, lime and fly ash that have solidification and adsorption function, were selected as solidifying materials. Solidification effect, contamination intensity and soil density were taken as variable parameters. The external environment was simulated with the help of pressure leaching. The control effect of solidification on the migration of pollutants in soil was evaluated by the residual oil content and oil seepage of soil. Results show that solidification can improve the adsorption stability of pollutants and control its migration. Under the action of pressure leaching, the change rate of oil contents in the solidified contaminated soil is only 1.52%−2.27%, and the oil seepage is 7.15−14.92 mg/L, which meet the class III standard of Integrated Wastewater Discharge Standard (GB 8978－1996) of China. Solidification can solve the large-scale migration problem of pollutants caused by the change of soil density and pollution intensity in unsolidified contaminated soil, and the oil content after leaching is close to the initial oil content. Solidification of lime and fly ash has a stable control effect on pollutants and has universal applicability in the disposal of petroleum contaminated soil.

In this study a centrifugal model test system was developed to explore the relationship between the face support pressure and ground deformation characteristics of shield tunnel in water rich sandy soil. Based on Wuhan Metro Line 8 large shield tunnel project, the influence of face support pressure on the face stability and ground deformation characteristics under different buried depths was investigated. The correlation curve between excavation face support pressure and surface deformation was obtained and the results show that: 1) When the cover of tunnel is shallow (<1.5D, where D is shield diameter), the influence of support pressure on surface deformation decreases with the increase of tunnel depth; when the tunnel is deep (>1.5D), no matter the support pressure is too small or too large, the influence of the excavation face support pressure on the ground deformation is difficult to extend to the surface. 2) When the support pressure is too high, the disturbance to the stratum takes on a “fishtail type”, which can be divided into compaction area, uplift area and settlement area induced by the jacking of excavation face as well as the settlement area. The settlement area is within 1D from the surface to the excavation surface, and the uplift area is within 1D−2D. 3) When the support pressure is too small, the main disturbance to the ground is settlement, and the influence range is about 1D in front of the excavation face. Additionally, the influence range will increase as the buried depth decreases. Based on centrifugal model test, the suggestion value of the range of support pressure premised on deformation control for different buried depths is obtained, which aims to provide guidance for the control of support pressure in practical engineering.

Pile runs often occur in the dynamic driving of steel pipe pile in ocean engineering, and it would bring about serious threat to the safety and to cause huge property losses to the engineering activities. Therefore it is of great significance to investigate the trigger mechanism of pile runs for the successful installation of pile foundation. Based on several project cases, this paper analyzed the popular strata condition and the mechanism for pile runs, and summarized the calculation methods for the dynamic skin friction of pile during pile running. It is found that, pile runs always occur in soft clayey soil layer, and can be classified into two categories. The first is hard layer puncture pile runs. In this case, the blow counts and the driving footage are relatively large before pile runs. The second is unstable equilibrium pile runs with less blow counts and driving footage. In either case, owing to the dynamic action in pile driving, the pore water pressure in the clayey layer increases constantly, resulting in a continuous decrease in the shear strength and a continuous loss in the structural strength of the clayey soil. When the soil resistance is not large enough, pile runs will be triggered. In the process of driving piles, the magnitude of the dynamic skin friction of pile will decide to a large extent whether pile drops or not. The dynamic skin friction of pile is often obtained by multiplying the static skin friction of pile by a reduction factor. This factor is closely related to the mechanical characteristics of the soil layer and the driving process, and is always located within [0.05, 0.5].

Compressive bearing and force transmission characteristics of granular backfill are of great significance to control the surface deformation in backfill mining. The compression tests were conducted on five types of granular materials including pebbles, gravel, mine tailings, river sand and tailings, and seven gradations pebbles under lateral confinement. The compaction process and the influence of particle size on deformation and bearing capacity were analyzed. Meanwhile, based on the numerical simulation test of the pebbles, the force transmission characteristics were revealed. The results indicate that the bearing process of granular backfill under lateral confinement can be divided into three stages, i.e. void compaction, particle crushing compaction and granular compaction consolidation. The type of granular material and particle size have no effect on its nonlinear compaction process, but have a remarkable effect on the process of internal structure reorganization. In the process of compression, there is a critical compactness that reverses the order of bearing capacity of pebbles with different gradations, and the average deformation modulus of pebbles and the characteristic factor of particle have a negative exponential relationship. Numerical simulation test of pebbles reveals the strength distribution of the force chain and the “pressure arch” inside granular materials. It confirms the facts that the vertical stress in granular backfill decreases along the loading direction, and lateral pressure first increases and then decreases throughout the filling height.

In order to investigate the influence of particle size on the micro-macro crack evolution mechanism of yellow sandstone, uniaxial compression acoustic emission tests on yellow sandstone with different particle sizes were carried out systematically. Based on acoustic emission monitoring technology and focal mechanism inversion method, the evolution mechanism of microcracks in the process of rock deformation and failure was studied. Meanwhile, the macroscopic morphology of surface cracks and the microscopic morphology characteristics of specimen fracture were analyzed by scanning electron microscope and geometric fractal theory. The test results show that the size of the particle size and the type of cement can affect the strength of the rock. The laboratory test shows that the peak stress of the yellow sandstone decreases with the gradual increase of the particle size. By comparing the bI values (improved b values) and average acoustic emission energy of different sizes of yellow sandstone specimen in the deformation damage process, it was found that before the peak failure of all specimens, the average acoustic emission energy rate had phenomenon of "surge" and "plunge", and the bI values dropped to the minimum value when the sandstone specimen reached the peak failure, this phenomenon could be regarded as a precursor of rock instability and failure. The failure mode of microcracks in the rock changed from tension-oriented to shear-oriented as the mineral particle size increased. After failure, the fractal dimension of macroscopic fractures on rock surface decreased with the increase of rock particle size, that is, particle size has a certain control effect on the evolution process of macroscopic fractures on rock surface.

The weakly cemented rock mass makes poor stability. Large deformation often occurs during coal mining or roadway excavation, which brings maintenance difficulties. To address the problems of the mechanical characteristics and deformation control of the surrounding rock of the weakly cemented siltstone, we performed the field survey, laboratory tests, theoretical analysis by selecting Linchang coalmine in Guangxi Province of China as the engineering background. On-site investigations show that the roof rock layer of roadway has poor self-supporting ability, high failure rate of supporting structure due to water effect; large floor heave occurs affected by water and mining. The point load test indicates that the uniaxial compressive strength is only 1.9−2.3 MPa. Scanning with an electron microscope reveals that the weakly cemented siltstone is based on coarse-grained minerals. According to Protodyakonov’s pressure arch theory, we derived the equations of ultimate bearing capacity of roof and two sides and put forward the key points of weakly cemented roadway surrounding rock control, including improving the overall strength and bearing capacity of roadway surrounding rock, determining reasonable bolt support parameters, designing roof anchor cable to strengthen support. Based on the results of experimental analysis and theoretical research, we proposed a control plan based on grouting reinforcement, combined with bolts and cables, and carried out industrial tests in Linchang coalmine. The monitoring data show that the designed support scheme can effectively control the deformation of the weakly cemented siltstone roadway.

This study aims at revealing the deformation and evolution characteristics, formation mechanism and stability of slope under rainfall infiltration condition. A slope in the north stope of Taihe mine in Xichang city, Sichuan province was analyzed in detail as a research object by adopting various methods such as field geological survey and mapping, in-situ test, laboratory test and numerical simulation. The results show that: 1) Both landslides in 2018 and 2019 occurred in rainy season and stabilized again with the end of rainy season. 2) The formation of the landslide is the result of the comprehensive action of multiple factors: the fault provides the boundary for the formation of the landslide, which is the external condition; the diabase with high content of chlorite and montmorillonite is easy to soften and disintegrate when exposed to water, which is an internal condition; the mining and rainfall are the inducing factors. Mining forms an ultra-high slope and exposes the diabase rock layer, while rainwater infiltrates from the slope surface and fault to erode and soften the whole diabase rock layer, resulting in local sliding of the diabase layer under the action of high potential energy, and then pulling it to the overall sliding. 3) Rainfall greatly impacts on the factor of safety and failure mode of slope. The slope is in a stable state before rainfall, and the potential failure mode is overall sliding. After 5 days of rainfall, the factor of safety for the slope drops to 0.842, and two steps of local sliding occurs in the diabase layer. After that, the factor of safety continues to decrease, and the damage range further expands, which is confirmed by the actual observations.

With the rapid development of China’s high-speed railway, some key lines will inevitably pass through the goaf site. Therefore, the “activation” classification of high-speed railway subgrade in goaf area needs to be solved first prior to a series of problems such as route selection of high-speed railway in goaf area. In this article, the underground goaf at the chainages DK259+135.95−DK259+710.00 of Taiyuan-Jiaozuo high-speed railway is taken as an example. A classification and evaluation model for "activation" of high-speed railway subgrade in goaf area is established using the basic principles of analytic hierarchy process and fuzzy mathematics. Firstly, five major factors and nineteen sub-factors affecting the classification of high-speed railway subgrade in goaf area are determined. On this basis, the classification standard of influence degree for “activation” classification factors of high-speed railway subgrade in goaf area is proposed, and the corresponding classification standard of “activation” of high-speed railway subgrade in goaf area is obtained by combining the influence degree of each major factor. By adopting the analytic hierarchy process, the weights of influencing factors and evaluation factors are determined, and the membership degrees of evaluation factors are obtained in combination with Delphi method, fuzzy statistics and membership function. Meanwhile, the typical characteristics of “activation” classification of high-speed railway subgrade in goaf area are preliminarily examined. Finally, the “activation” classification of the railway subgrade in goaf area is carried out using fuzzy comprehensive evaluation method, and the subgrade in this project is determined to be “necessarily activated”. The classification conclusion of the model is in line with the actual working conditions of the site, which provides a guiding significance for the later treatment of the subgrade in goaf area by grouting. After grouting treatment for the goaf area, another “activation” classification is carried out, and the subgrade in this project is determined to be “inactive”, which provides a scientific and reasonable demonstration for the safe operation of Taiyuan-Jiaozuo high-speed railway.

To ensure the construction safety of super-large rectangular pipe jacking shield tunnel adjacent to the high-speed railway, based on an actual railway related project, the safety of super-large rectangular pipe jacking shield close to high-speed railway in soft stratum is studied. The results show that the track settlement and pipe segment safety factor far exceed the control threshold during the construction, so the reinforcement scheme must be adopted. The track settlement can be reduced by 58.20% and the minimum safety factor of pipe segment can be increased to 1.35 by adopting advance grouting scheme. Using manually dug pile and D-shaped beam can reduce the track settlement by 63.05% and increase the minimum safety factor to 9.49. After adopting the pile-plate reinforcement scheme, the track settlement can be reduced by 70.90% and the minimum safety factor can be increased to 9.00. The reinforced effects of manually dug pile and D-shaped beam scheme and pile-plate scheme is significantly better than that of advance grouting. It is recommended to adopt the pile-plate scheme in the section under the high-speed railway to be built, and the manually dug pile and D-shaped beam scheme in the section under the existing high-speed railway. The on-site monitoring results show that the maximum surface settlement caused by pipe jacking tunneling is 3.25 mm after the super-large rectangular pipe jacking shield passes through the Fuzhou-Xiamen railway section to be built. After the manually dug pile and D-shaped beam is adopted for the existing Hangzhou-Shenzhen section, the maximum settlement of the high-speed railway track is only 1.65 mm. Both track settlement and surface settlement are far less than the settlement threshold. The super-large rectangular pipe jacking shield successfully crosses the Fuzhou-Xiamen Railway and Hangzhou-Shenzhen Railway. The research conclusion can provide reference for similar large-scale tunnel proximity engineering.

The influence mechanism of open caisson sinking in soft soil stratum is complex. The available theoretical research mainly focused on the mechanical characteristics of open caisson for analyzing the sinking process. The kinematic characteristics of open caisson during sinking process are lack of scientific and systematic interpretation. To this end, this paper establishes the mechanical model of open caisson sinking, deduces the kinematic equation of open caisson, and reveals the kinematic characteristics and the influence mechanism of the open caisson during sinking process. The rationality and correctness of the theoretical method is verified based on a practical project. The research results show that the sinking process of open caisson has obvious acceleration sinking stage and deceleration sinking stage. The initial unbalance force before sinking (F1) caused by sinking construction of open caisson is an important factor affecting the sinking characteristics, as well as the primary factor for controlling the sinking movement. Adjusting the parameter b1, which reflects the characteristics of soil layer and open caisson structure, is an effective method to prevent sudden sinking of open caisson.

Relying on the foundation engineering of the main tower caisson of Changtai Yangtze River Bridge, the variation of the soil pressure under the cutting edges of the caisson is modeled in the initial sinking stage by finite element method(FEM). In combination of the field measurements of the soil pressure, the variation trend of the soil pressure is analyzed along the cutting edges of the caisson during the excavation steps. The study shows that the numerical results are in agreement with the field measured soil pressures. The soil pressure will decrease in the region where the soil is excavated in caisson cells. It decreases more obviously while the excavation becomes deeper, and the soil pressure will increase in the cutting edges of the neighbouring caisson cells. In the process of excavation from internal caisson cells to outer ones, the soil pressure of the cutting edges of the outer bulkhead and skin of caisson accumulates. Finally, the soil reaches the bearing capacity and it develops into plastic state. The caisson sinks obviously. The work performed in the paper helps guide the smooth sinking of the similar caisson.

geotechnical engineering; building information model(BIM); integration; construction simulation; numerical simulation

In order to understand the research progress of rockburst risk prevention technology in deep hard rock mines, the relevant literature was summarized. Firstly, a general idea of rockburst risk prevention was proposed from three perspectives: avoiding rockburst before the occurrence, reducing the hazard of rockburst during the incident, and evading the damage of rockburst afterwards. Then, the types of rockburst prevention technology were summarized based on this idea. Additionally, the connotation of each technology and its prevention mechanism were analyzed in detail. Finally, the future development direction of rockburst risk prevention technology was prospected. The results show that the rockburst risk prevention technologies for deep hard rock mines can be summarized into five aspects: mining design, stress relief technology, alteration of rock formation properties, rock mass support and personnel exposure. Among them, the mining design includes mining methods, stope parameters, pillar retention, mining sequence, recovery rate, and goaf treatment. Stress relief technology includes distress blasting, stress relief slots, stress relief tunnels, stress relief holes and stress relief fissures. Alteration of rock formation properties includes hydraulic fracturing, confined blasting and water injection softening. Rock mass support includes surface support, internal support and combined support. Personnel exposure includes re-entry protocol, remote equipment and personnel protection. In the future, the prevention guidelines of rockburst risk in deep hard rock mines can be established from the construction of prevention systems for different types and risk levels of rockburst, research of new technologies, and evaluation of prevention time and effect.

It is difficult to accurately measure and quantitatively classify mountainous highway earth-rock mixed waste slag caused by their complexity and man-made accumulation characteristics. Standard and threshold values for quantitative classification are presented by big data for engineering. Subdivision of waste slag is conducive to scientific design and safe protection. Depending on measured particle composition and angle of repose of the multi-phase, multi-position waste slag at several key slag sites in mountainous highway areas, the big data base of earth-rock mixed waste slag is formed. Subgroup features of mountainous highway waste slag composition and angle of repose are statistically analyzed by these engineering data. Main conclusions are drawn as follows: 1) The big data for engineering prove that mountainous highway waste slag has obvious subgrouping characteristics. Using coarse-fine ratio k, the waste slag is divided into three types such as earth-type waste slag, whose k is less than 0.3, earth-rock mixed one, whose k is larger than 0.3 and less than 1.4, and rock-type one, whose k is larger than 1.4. 2) Fine particle proportion of mountainous highway waste slag is less and the coarse particles are the dominant. Probability distribution of waste slag’s coarse-to-fine ratio is N(0.85, 0.338 9), and that of waste slag’s natural angle of repose is N(37.64, 3.057 8). The angle of repose of earth-type waste slag is less than 32.6º, that of earth-rock mixed one is larger than 32.6º and less than 42.7º, that of rock-type one is larger than 42.7º. The classification solves problems of sampling and test results’ representativeness. 3) The controlled slope ratios for different types of waste slag are obtained using the formula of safety factor for cohesionless slope, classification and safety factor for different grade slag sites. The controlled slope ratio of earth-type waste slag is less than or equal to 1:2, that of earth-rock mixed one is less than or equal to 1:1.75, and that of rock-type one is less than or equal to 1:1.5. It is found that medium and long stability of the slope can be ensured under these slope ratios suggested. The above conclusions can present basic parameters for dynamic design of mountainous highway waste slag engineering, has remarkable engineering analogy value, and is conducive to forming regional experiences.

Under the influences of the geological conditions of landslide and external periodic and random factors, the evolution process of the landslide has typical abrupt characteristics. The conventional deep learning model based on gating mechanism has insufficient ability to predict step mutation sequence, while by mining the potential information of time series data with different scales, multi-head self-attention can adaptively find the alteration trend of sequences and improve the prediction ability of landslide sequence. Based on variational mode decomposition, the cumulative displacement of landslide was decomposed into trend displacement, periodic displacement and stochastic displacement. Dynamic time warping algorithm was used to analyze the correlation between each component and influencing factors. These displacement components were dynamically predicted by a modified model integrated with long short-term memory (LSTM) neural network and multi-head self-attention mechanism, and the predicted values of each component were added to obtain the cumulative displacement prediction result. The monitoring point ZG118 of Baishuihe landslide in the Three Gorges Reservoir area was taken as an example to predict the cumulative displacement in this paper. The monitoring points ZG93 and XD01 were used for model adaptability verification. The results show that the new model can greatly improve the prediction accuracy for the step data mutation caused by the changes of rainfall and reservoir water level, providing a new idea for the prediction of landslide displacement in the Three Gorges Reservoir area.

The distribution form of contact stress between the bottom of pile shoe and foundation has a significant effect on the penetration depth of pile, and the magnitude and distribution form of contact stress are associated with the tapered tip type of the pile shoe. Therefore, taking the pile penetration project in Qidong, Jiangsu province, as an example, the relationship between the tapered tip type of pile shoe and the penetration depth of pile has been discussed. Based on the field monitoring data of contact stress under different pile shoes, the penetration depth of pile has been calculated by empirical formulae recommended in the engineering specifications at home and abroad and numerical simulation method, respectively. The results demonstrate that the contact stress in the middle area is greater than that at the edge of the pile shoe with different cone end forms. The characteristic of stress distribution is similar to that of flexible plates. When the penetration depth of pile shoe is predicted according to the empirical formulae recommended in the engineering specifications, the effect of the shape of pile shoe on penetration depth can be ignored, and the calculated value is basically consistent with the field measured one. The penetration depth of pile predicted by small deformation finite element numerical method is satisfactory. The conclusions of this paper can provide reference for similar engineering practice.

The expansion stress of swelling rock in the contact with water has an adverse effect on the long-term safety of the subway tunnel structure. Previous studies mainly considered the volume expansion of swelling rock, but lacked the consideration of the softening effect during the expansion process. For this reason, through laboratory tests, the material components, softening characteristics, and expansion parameters of swelling rock are obtained, and the elastic softening effect of swelling rock in the expansion process is revealed. An equivalent simulation method of humidity and temperature expansion considering elastic softening is proposed based on the recognition that the volume expansion caused by humidity and temperature are similar. The determination methods of elastic softening parameters, expansion equivalent temperature boundary conditions, and expansion zone are given. The simulation procedure has been established. The above method is applied to the long-term safety assessment of the sandy mudstone section of the interval tunnel of Chongqing Metro Line 18, and the results show that the expansion stress calculated by the new method is closer to reality than the classical equivalent simulation result of humidity and temperature. Finally, the thickness of the expansion zone and the degree of elastic softening that affect the calculation results are discussed. Recommendations for the disposal of the swelling tunnel section are also put forward. This work can be used as a reference for long-term safety evaluation of swelling rock tunnels, and has a certain guiding role in preventing and controlling swelling disasters of underground engineering.

For the tunnel excavated in layered rock mass, the failure mechanism of surrounding rocks is different from that of isotropic surrounding rocks. For unsupported tunnel, the failure mode can be summarized into mixed failure, V-shaped notch breakout failure and spalling of bedding. The failure modes are controlled by multiple factors such as the physico-mechanical properties of the rock mass, in situ stress, and the shape of the tunnel. In this study, the combined finite-discrete element method (FDEM) is used to understand the failure mechanism of horizontally layered rock mass, including the influences of strength parameters (such as cohesion, internal friction coefficient and tensile strength), deformation parameters (such as Young’s modulus), in situ stress and tunnel span. The study results show that the mixed failure is the basic failure mode of the layered rock mass, and its failure mechanism is the conjugate shear fractures F3 generated by the horizontally concentrated stress continuously propagate into the surrounding rocks near the centerline of tunnel; at the same time, shear-slip fractures F1 parallel to the bedding plane are generated, resulting in slab-like rock fragments. The tensile fractures F2 perpendicular to the bedding plane are generated due to the contact squeezing effect between the left and right slab-like rock fragments and thus flip to the tunnel. With the increase of the rock mass strength, the increase of the lateral pressure coefficient or the decrease of the tunnel span, the fractures F1 disappear, and the fractures F2 are oblique to the bedding plane, resulting in V-shaped notch breakout. When the rock mass strength or the lateral pressure coefficient is further increased, the fractures F3 are blocked at the junction of the bedding planes, resulting in spalling of bedding.

Most engineers and even scholars can not fully understand advanced constitutive models, which brings great difficulties to the integration of theory with practice. In this paper, the elastoplastic model SIMSAND for granular material is taken as an example of constitutive models to develop a simple tool for modeling soil tests. Firstly, the development environment of MATLAB GUI is briefly introduced, and then the steps of interface development are described step by step such as overall layout design, control parameter input design, tick box design, result display design, control button design, error or warning prompt design. In order to study and train the readers, three cases are selected to study the conventional undrained triaxial test, the conventional triaxial drained test and the triaxial drained test with constant mean stress. Starting from the plastic multiplier, three key formulas with pseudo codes are derived and presented with modifications. The detailed development process and key source program of this tool platform will help readers to imitate and train, and provide examples and support for research and teaching in practice of constitutive modeling.

Compared with the Cosserat theory, the complexity of the numerical framework can be reduced in the couple stress theory to some extent, and it has been gradually applied to the geotechnical strain localization analysis. However, the C¹ continuity should be satisfied in the straight-forward couple stress finite element method, that is, the continuity of the strain inside the elements and on the interface of the elements should be satisfied. To avoid developing more complicated C¹ couple stress elements, within the framework of Cosserat continuum theory, the approximate solution of the couple stress theory can be obtained by relaxing the C¹ continuity with the aid of the penalty function method, and the penalty-based couple stress finite element method (named PCS-FEM) is developed. The effectiveness of the PCS-FEM is verified by the stress concentration problem of an elastic circular hole under plane strain condition, and it is further applied to the strain localization analysis of soil mass. Based on the numerical simulation of the plane strain experiment of Ottawa sand, it is found that the stress-strain curve and the failure form of shear band obtained by the PCS-FEM method are basically consistent with the test results, and the ill-conditioned mesh sensitivity problem of the classical continuum theory can be avoided by the PCS-FEM so that the well-posedness of the strain localization problem can be ensured. Based on the strain localization analysis of the soil slope subject to the eccentric load, it is found that the mesh sensitivity problem in the strain-softening stage of the soil slope can also be avoided, and the progressive failure process of the slope can be captured by the PCS-FEM.

Based on the Zhujiajian landslide in Zhoushan Islands, this paper developed a large-scale water tank-like physical model test device for investigating the influence of waves on the instability and failure of offshore submarine slopes, and built a wave division multiplexing technology-based fiber inspection system. The model test of the offshore submarine landslide under the action of waves was carried out, the variation law of pore water pressure and displacement in the slope model caused by waves was revealed, and the variation law of the surface velocity of the slope model was analyzed. Based on the SPH numerical simulation, the research on the sliding accumulation characteristics of the submarine slope under the action of waves was carried out to understand the catastrophic evolution process of the submarine landslide. Results showed that under the continuous action of waves, the bottom of the submarine slope was the first to be damaged, and then the slope became unstable and was damaged with the time elapsed. When a submarine landslide occurred, the displacement in the middle location of the slope and below changed abruptly, while the slip distance at the top of the slope was relatively small; waves affected the displacement and pore water pressure of the submarine slope simultaneously. When the slope was destabilized and damaged, the slope displacement and the pore water pressure changed suddenly, but the time of the sudden change of pore water pressure was slightly earlier than that of the displacement. Meanwhile, based on the landslide simulation of Zhujiajian geological profile I, the sliding accumulation characteristics of Zhujiajian offshore submarine landslides were preliminarily obtained. A set of test techniques and methods suitable for offshore submarine landslides under the action of waves has been established, which provides important guiding significance and reference values for the field research of offshore submarine landslides.

Based on the scaled boundary coordinate transformation of scaling splicing lines, an improved scaled boundary finite element method is proposed to accurately model the layered half-space, and a high-precision analysis model for the scattering field response of a complex layered site is established in the frequency domain. This method adopts the splicing lines as scaling center, which overcomes the difficulty due to the scaling requirements, and extends the scope of application of the scaled boundary element method to horizontal and inclined layered sites. Furthermore, based on the modified scaled boundary element method, a solution model for the complex layered half-space scattering field is established. In this model, the substructure method is used to transform the scattering problem with complex boundary conditions into the soil-structure interaction problem, which reduces the complexity of the seismic wave scattering problem. This transformation is strictly true in linearly elastic range. The accuracy of the proposed model is verified by comparing with the reference examples. In addition, the scattering field response of the canyon-underground cavity system in horizontally layered site is conducted. The results show that, compared with the case of no cavity under the canyon, the underground cavity will amplify the scattering displacement amplitude of the canyon surface, and this amplification effect is more obvious for the square cavity.

Compared with other soil layers, the risk of shield tunneling in water-rich sand is greater, but the mechanism of sand deformation caused by shield tunneling is currently unclear. Relying on an electric power tunnel project in Guangzhou, this paper selects a typical water-rich sandy stratum section for high-frequency, close-range monitoring of stratum deformation caused by shield tunnel construction. The following understandings are obtained, which can be used as reference for similar projects. 1) In a water-rich environment, compared to in a homogeneous sand layer, in a combination of fine and coarse sands, the tunnel is more prone to seepage failure. Under this circumstance, the fine sand layer bears greater seepage force while being strongly supplied with water from the coarse sand layer, and the fine sand layer is thus very easy to be eroded or even hollowed out. 2) The ground deformation caused by uniform volume loss and local concentrated loss is quite different. In the case of uniform loss, because the arching effect is not as strong as the local loss, the disturbance range, surface settlement and horizontal displacement are all larger. The location of the maximum horizontal displacement is also closely related to the heterogeneity of the formation loss. When the formation loss is uniform, the maximum horizontal displacement on both sides of the tunnel occurs within the tunnel elevation range; but when the uneven loss (partial collapse of the tunnel top) occurs, the location of the maximum horizontal displacement will move up significantly. 3) The seepage force expands the range of stratum disturbance. 4) The stratum loss rate is severely affected by grouting. The vicinity of the tunnel is large, the ground surface is the smallest, and the soil above the tunnel tends to loosen.

Safety monitoring and numerical simulation are two significant tools for assessing the slope stability. However, how to determine the slope critical failure state according to the monitoring data and numerical simulation results has always been the focus of the slope engineering. In this study, the Euclidean distances among the slope monitoring points of different types of state variables are calculated based on the hierarchical clustering method, and the effective monitoring points of slope are selected according to the distance. Then, the entropy weight of time series of effective monitoring points of the same type of state variables is calculated, and the entropy weight fusion method is used to perform data layer fusion for effective monitoring points of the same type of state variables, and the fusion monitoring index curves corresponding to different types of state variables are obtained. After that, principal component analysis method is adopted to perform feature level fusion for various fusion monitoring index curves, and a comprehensive monitoring information curve that can reflect the information characteristics of all state variables is obtained, and then an information mining and fusion framework for different monitoring variables in the process of slope progressive instability is constructed by using a variety of mathematical and statistical methods. Finally, a change point search method of graded curve is proposed to search the abrupt change point of slope state gradual evolution (i.e. slope critical failure state). The proposed method is applied to determining the critical instability of a highway slope. The results show that the cumulative value and change rate of a single monitoring point or a single fusion index are not unique as the criterion of slope instability. The comprehensive monitoring information sequence established by integrating multiple monitoring data can better reflect the evolution characteristics of slope state and avoid misjudgment of slope state by data of a single monitoring point with a single state variable, which verifies the feasibility and applicability of the proposed method.

Based on the particle flow code (PFC), the Brazilian splitting of sandstone treated at 25−1 000 ℃ under different contact angles (2a = 6º−30º) was carried out to study the stress distribution and fracture mode, and the Brazilian splitting was compared with the direct tensile test. The results show that: 1) The surface contact loading can reduce the end effect in Brazilian splitting. During the loading process, tensile cracks appear in the middle of the disc firstly. With the increase of the load, the tensile cracks converge and connect at the central part of the disc, and then extend to the end of the disc. 2) The tensile strength measured by Brazilian splitting at point contact of flat plate is less than that of direct tensile strength. The correction coefficient k of the tensile strength calculation formula decreases linearly with the increase of temperature T, satisfying k = −3.303×10⁻⁴T+1.468. With the increase of the contact angle, the tensile strength of the Brazilian disc increases after heat treatment of different temperatures. 3) When 2a≥18º, the Brazilian disc can guarantee to have a central crack initiation. When 2a = 18º−24º, the fracture mode of the disk keeps unchanged at different temperatures. The disk will develop an inclined crack at a lower temperature (≤600 ℃) when the contact angle is too large (2a = 30º). 4) Combined with the correction coefficient and the fracture mode analysis, the contact angle is recommended to be 18º−24º and the correction coefficient is between 0.802 6 and 0.856 0. It can ensure the center crack initiation and the stability of the fracture mode at different temperatures.

The low attenuation of high-frequency guided waves (greater than 1 MHz) in anchoring bolts makes it of great potential application value. However, the complexity of numerical calculation of high-frequency guided waves makes it very difficult to determine its propagation characteristics. It is not realistic to rely only on experiments to determine the optimal excitation wave in different anchorage bolts, so it is of great significance to establish a numerical model of high-frequency guided wave propagation. In this study, we first used the finite element software to construct a numerical model of the steel rod to examine the influence of the radial and axial element mesh density and material damping on the propagation process of high-frequency guided waves. And then, we employed the amplitude superposition and sum of all cross-section nodes as well as empirical mode decomposition (EMD) method to process data. Finally, we obtained the basic propagation characteristics of high-frequency guided waves in steel rods that are consistent with the theoretical results in the literature and experimental test results. The research results show that the element grid density, the setting of material damping value, and the vibration superposition of particles at different positions are the keys to reproducing the basic propagation characteristics of high-frequency guided waves.

In the rock slope stability analysis methods, the strength reduction method based on nonlinear Hoek-Brown criterion has some problems, such as the disunity of reduction schemes or the complexity of calculation. To solve this problem, a generalized Hoek-Brown criterion strength reduction method based on the compressive strength of rock mass is developed, which can better reflect the physical significance of strength attenuation than the direct reduction of material parameters. Based on the uniaxial compressive strength of rock mass, the uniaxial compressive strength of intact rock s_ci and the parameters’ combination s^a (s and a are empirical parameters of rock mass) are reduced by the same ratio, the reduction ratios of shear strength and the tensile strength are analyzed, and the factor of safety is defined based on the average shear strength. The proposed method is applied to the stability analysis of two classical slope examples, and the factor of safety and critical sliding surface obtained are compared with the local linearized strength reduction method and the limit equilibrium method. The results show that the factor of safety obtained by the proposed method is close to that obtained by the other two methods for two examples, and the relative error is less than 2%. In example 1, the location of the critical sliding surface obtained by the proposed method is in good agreement with the results of the other two methods. In example 2, the critical sliding surface of the proposed method is closer to that of the local linearization method, and can reflect both shear and tensile failures. The above results verify the reliability and rationality of the proposed strength reduction scheme and the definition method for factor of safety.

Based on the development experience of soil containers for shaking table tests, a multidirectional laminar shear model container with variable stiffness is designed to meet the needs of shaking table tests in geotechnical engineering under different site conditions. The container is constructed with a stack of annular steel frames, and supported by ball bearings and bolts. Its height can be adjusted according to the test conditions. By adjusting the stiffness, the number, and the arrangement of bolts, the stiffness of the container can be changed. The stiffness-variable characteristic of the container is verified by analyzing the characteristic frequencies of various combined model boxes in ABAQUS. Then a free-field shaking table test employing the container is performed. The test results are discussed in terms of the acceleration time histories and the corresponding response spectra at various heights and distances. A 2-norm deviation index is also used to quantify the boundary effects. The result shows that the developed laminar shear container does not impose significant boundary effect and is able to maintain the in-plane free-field response.

Argillaceous sandstone shows the typical characteristics of water-weakening due to the high content of clays. Tunnelling in argillaceous sandstone stratum with rich (trapped) water is a challenging issue for underground engineering. This study examined the stability and supporting time for a water conveyance tunnel in the argillaceous sandstone stratum with weakened and un-weakened conditions. Firstly, the water-weakened mechanical test results of argillaceous sandstone were presented. Then, to evaluate the mechanical parameters of the argillaceous sandstone in both water-weakening and un-weakening conditions, the rock mass evaluation method on basis of the Hoek-Brown strength criterion was adopted. Next, Lanzhou water source tunnel project was taken as the research object, and the stability of surrounding rock mass for the tunnel in argillaceous sandstone in both conditions was analyzed by a numerical modelling method. The researches indicate that the water-weakening of argillaceous sandstone significantly influenced tunnel safety. Finally, the convergence confinement approach was utilized to analyze the necessary supporting time to ensure tunnel safety during construction. The results indicate that if the argillaceous sandstone does not weaken, early support measures for the tunnel surrounding rock mass can be considered at the distance of 4 to 5 meters away from the excavation face. However, in the case of argillaceous sandstone water-weakening, early support measures should be employed immediately when the tunnel face is excavated. The research findings can provide the foundation for the safe construction of tunnels in a weak surrounding rock mass with water-weakened conditions.

Combined with the dynamic testing of pile foundation in a wind tunnel construction project, three-dimensional finite difference simulation software FLAC^3D is used to simulate the double-pile model foundation. The numerical results are in good agreement with the experimental data, which verifies the rationality of numerical method based on the pile-soil-structure interaction to solve the dynamic response of the pile foundation under the equipment load. The post-grouting model of cast-in-place pile is further established to explore the influence of different lateral resistance and tip resistance enhancement coefficients on the dynamic characteristics of the pile foundation. The results show that the post-grouting of cast-in-place pile has no influence on the resonance frequency of the vertical vibration. The post-grouting of cast-in-place pile has slight influence on the resonance frequency of the horizontal rotary vibration, the maximum amplitude, the shear stiffness coefficient of the foundation, and the first mode damping ratio of the horizontal turning of the foundation. The post-grouting of cast-in-place pile can improve the compressive stiffness and reduce the maximum amplitude of the pile foundation, but its effect is limited compared with the non-grouting pile.