Based on the continuous medium model and the pile-soil interaction, the horizontal seismic response of a single pile subjected to vertically propagating S waves was investigated by regarding the single pile as a one-dimensional linearly elastic beam. The time-harmonic displacement of bedrock was introduced as the vertically propagating S waves, and the horizontal dynamic impedance function of the soil was derived by the governing equations of the plane strain model. Analytical solutions for the seismic response of the single pile subjected to vertically propagating S waves were obtained by subsuming soil impedance into the governing equation of the single pile and considering the boundary conditions at pile top and toe. The solution was verified by comparing it to the results of existing studies. Furthermore, as pile-soil modulus ratio increases, the minimum value of the kinematic response factor decreases. The kinematic response factor is not particularly sensitive to the large pile slenderness ratio and the soil material damping. For the horizontal amplification factor at the pile top, the increase of the pile-soil modulus ratio only suppresses the amplification at high resonance frequency, and the large pile slenderness ratio has the trivial effect on it. As the soil material damping increases, the amplification at resonance frequency gets considerably suppressed. The seismic response of the pile is obviously affected by the pile-soil modulus ratio only when the pile slenderness ratio is small, and it decreases with the increase of the pile-soil modulus ratio.

Coralline soils are the emerging preferred geomaterial for island-reef engineering and harbor engineering in tropical regions, and wide gradation is the main feature of their structural composition. The liquefaction resistance of coralline soils is gaining attention due to the high seismic risk of related engineering projects. In order to investigate the liquefaction resistance of coralline soils containing fine grains, the saturated undrained dynamic strengths of three groups of representative graded samples with designed relative compaction of 0.4–0.8 and two groups of samples without fine grains were measured by large-scale dynamic triaxial liquefaction test based on an actual site of coralline soils in a tropical harbor engineering in the eastern Pacific Ocean. The test results indicated that the power function could simulate the relationship between the cyclic stress ratio and the number of cycles to cause liquefaction for coralline soils containing fine grains; the presence of fine grains and the increase of relative compaction did not significantly improve the liquefaction resistance of coralline soils; the excess pore water pressure development pattern of liquefaction process of coralline soils was similar to that of sandy soils, and the inverse sine model with two or three parameters could simulate the excess pore water pressure development of liquefaction process of coralline soils containing fine grains. The study revealed that the fine-grained coralline soils still belonged to liquefiable soils. Based on an actual engineering project, the same type of engineering project needed to consider the prevention of seismic liquefaction hazards in the design, construction and use stages, and this study provided technical support for the prevention and control of liquefaction for coralline soils.

The fractured rock mass in cold areas is damaged and deteriorated due to crevice-water frost heaving, which seriously threatens the safety of engineering construction in cold regions. In this study, freeze-thaw cycling tests were conducted on green sandstone, red sandstone and granite samples of different porosities. The strain changing with time and temperature of saturated fracture during freeze-thaw cycling under influences of fracture length, width and lithology were analyzed. The changing rules of the characteristic values of fracture strains and the failure mechanism of fractured rock were also studied. Experimental results show that the change rule of freeze-thaw strain of fractured rock mass with different fracture geometry parameters can be divided into seven stages: the cool shrinkage stage, the frost heave stage, the frost heave stabilization stage, the thermal expansion stage, the thaw shrinkage stage, the thaw shrinkage rebound stage, and the thaw shrinkage stabilization stage. The curve of freeze-thaw strain versus temperature of saturated fractured rock mass is an unclosed hysteresis loop. The phenomenon of “freeze-thaw hysteresis” occurs, and with the increase of freeze-thaw cycles, the hysteresis loop gradually moves up, leading to a gradual increase of the residual strain. Characteristic values of freeze-thaw strain of saturated fractured rock mass include: the maximum microstrain, the residual strain, the frost heave amplitude, and the thaw shrinkage amplitude. The characteristic value of strain is related to the fracture length, the width and lithology of rock mass, and the freeze-thaw failure of fractured rock mass is caused by gradual accumulation of the residual strain.

Wrinkles in geomembrane are common among anti-seepage engineering. However, the wrinkling effect has been neglected in most of the current studies on the interface shear properties of geomembrane. The composite liner consists of a textured geomembrane (GM) and a needle punched geosynthetic clay liner (GCL) was taken as the research object, and the hydration deformation tests confirmed that the two-step hydration method was effective in accelerating the hydration of the wrinkled GM+GCL composite liner. The shear properties of the wrinkled GM+GCL composite liner was studied by a large-scale temperature-controlled submerged direct shear apparatus. The shear characteristic of the wrinkled GM+GCL composite liner was analyzed compared to the shear results of the composite liner without GM wrinkle, and the influence mechanism of GM wrinkles on the shear characteristics of the composite liner was clarified. Experimental researches show that the existence of GM wrinkle will change the shear stress-displacement curve of the GM+GCL composite liner a lot, and the peak shear strength of the composite liner under low normal stress can be obviously reduced by the GM wrinkle. Significant progressive failure could be observed in the wrinkled GM+GCL composite liner. Besides, multiple failure modes can coexist inside the composite liner under unique normal stress as well.

Shear failure of bedding slope along weak zone is one of the main types of landslides. The seismic dynamic response and destabilization failure mode of rock slopes with laminated fractured structure were studied by a shaking table model of block masonry slope under the action of multi-dimensional and multi-parameter ground motion, meanwhile, considering the weakening process of mechanical parameters of slope under different working conditions of slopes. The results show that the ground shaking characteristics and geological structure of the slope are the decisive factors to determine the seismic dynamic stability and failure mode of the slope. The horizontal dynamic response of the slope has obvious elevation and slope surface amplification effects, and the elevation has less influence on the vertical dynamic response of the slope. Ground motion amplification effect is related to the mechanical strength of the structural surface, the waveform of seismic waves, and the spectral characteristics, and the sine wave has a more significant influence on the amplification effect of the slope than the natural wave. The slope cracks initiate and expand at the weakest part depending on the dominant structural surface and trace to the joint surface to form creep-slip and locking sections. The strength parameter of the joint surface weakens under the action of the external geological agents so that the potential slip zone appears to be differentiated between the forward failure mode of lap penetration from the rear edge to the front and the backward failure mode from the front to the rear edge, and accordingly the slip mass also evolves from shear exposure at high position to collapse failure.

Soda residue (SR) is a kind of solid wastes produced in the process of soda with the method of ammonia-soda. As a ground backfill soil, SR can effectively solve the problems of land occupation and pollution after appropriate reinforcement and treatment. However, because of the poor stability of physical and mechanical properties, the material strength of SR would be weaken obviously under the action of cyclic loading such as mobile machinery loading, which will reduce the bearing capacity of SR foundation. In this study, dynamic triaxial compression tests were performed on the undisturbed SR derived from Tianjin Port. Then, the cyclic cumulative pore pressure variation and undrained shear strength variation of SR under different stress conditions were discussed. Based on Yasuhara equivalent overconsolidation model, a cyclic strength weakening model of SR considering the influence of anisotropic consolidated ratio and dynamic stress ratio was established by using strength weakening coefficient β to quantify the weakening effect of cyclic loading on the strength of material. On this basis, a strength evolution model of SR considering the coupling effect of anisotropic consolidation process and cyclic loading process was established by using strength enhancement coefficient a to quantify the effect of anisotropic consolidation process on the strength of material. The accuracy of this model was validated by comparing the experimental measurements with the model calculation results.

To reveal the cyclic lateral characteristics of piles in sloping ground under the combined influence of slope effect and cyclic weakening effect, one-way cyclic lateral loading tests with different cycle numbers, load amplitudes and slope angles were carried out, and corresponding lateral static loading tests were conducted as a comparison. The variation trends of pile head deflection, bending moment and subgrade reaction were revealed. Then, the element stiffness matrix was improved by considering the second-order effect and pile-soil interaction to develop the finite beam element solution. Finally, the theoretical predicted curves were compared with measured curves and results calculated by the power series method to validate the finite beam element solution. The results show that the bending moments and pile deflections nonlinearly increase with cycle numbers, and the location of maximum bending moments gradually drops downwards from the non-dimensional depth z_a=1.25 to z_a=1.75. The relationship between the non-dimensional deflection y_0,a atop the pile and cycle number n satisfies the power function y _0,a= An ^0.11. When the load amplitude increases from 20 N to 40 N, the maximum non-dimensional bending moment increases from 0.010 to 0.029, but their locations remain near z_a =1.7. When the slope angle increases from 30° to 60°, the maximum non-dimensional bending moment increases from 0.011 (z_a =1) to 0.025 (z_a =2.5).

Desiccation cracking of soil affected by actions of climate is a common phenomenon in nature. The presence of cracks can dramatically weaken the engineering properties of soil and cause many geotechnical and geological engineering problems. A refined monitoring method of the dynamic process of soil desiccation cracking using electrical resistivity tomography (ERT) is proposed to determine the development of the cracking networks in clayey soil. The model test and in-situ test were carried out to monitor the process of soil cracking separately. Self-developed resistance measuring system was applied to continuously collect the current-potential difference data. The data were then processed and inverted using a self-developed system named FemERT (finite element method electrical resistivity tomography) to obtain spatial distribution characteristics of the cracking networks at different periods. The results show that: (1) ERT can achieve the refined monitoring of the soil cracking process and can monitor the geometrical morphology of three-dimensional crack networks. The identification accuracy of crack width and depth can reach millimeter level and centimeter level respectively. (2) The difference in sensitivity distribution of ERT can explain the influence of cracking on soil resistivity. The measured resistance curves show different features according to the position of the crack formatting. (3) The interpreted resistivity and its relative change rate (Rev) can directly describe the spatial geometric morphology of the cracking networks at different stages, highlighting the influence of the dynamic development process of cracking on the electrical conductivity of soils.

As a typical soft rock, the mechanical properties of salt rock are time-dependent significantly, so the accurate prediction and evaluation of the deformation and damage capacity of salt cavern gas storage during loading and unloading are related to the long-term safe and stable operation of energy reserves. In order to study the rate effect of salt rock, fatigue tests at different loading and unloading rates were conducted. Based on the existing creep constitutive model, the rate effect equation was established to distinguish the creep plastic deformation and loading plastic deformation during loading and unloading. The results show that: (1) The overall fatigue life of salt rock and the proportion of fatigue life in stable deformation stage (the second stage) increase with the increase of loading and unloading rate. (2) The proportion of fatigue life in decelerated deformation stage (the first stage) and the average residual strain of stable deformation stage decrease with the increase of load rate. (3) In the rate-coupled fatigue test, the residual strain decreases with the increase of loading and unloading rate. The creep plastic deformation decreases with the increase of loading and unloading rate. When the loading rate increases from 0.04 kN/s to 5 kN/s, the proportion of creep plastic deformation in the cycle decreases from 85% to 36%, showing a negative exponential relationship. (4) In the full cyclic loading and unloading process, the plastic deformation of loading and creep presents a U-shaped development trend, which corresponds to the three stages of fatigue process of salt rock. The results of this study can lay a foundation for further analysis of creep plasticity and loading plasticity of salt rock.

A tailing seepage failure testing instrument designed by the authors was used to simulate the whole process of tailing seepage failure under the condition of increasing upstream water level and continuous increase of hydraulic gradient. The evolution of the pore water pressure and flexural guided wave parameters, as well as the flexural guided wave signals' b-value and fractal dimension during the experiments, were analyzed. The evaluation criteria of tailing seepage failure level were proposed based on the change characteristics of pore water pressure and flexural guided wave characteristic parameters. The results show that: (1) During the tailing seepage failure process, the pore water pressure increases with the increase of hydraulic gradient, but when the hydraulic gradient increases to a certain degree, the pore water pressure will show a sudden drop. (2) Tailing seepage failure is a gradual process, and the flexural guided wave parameters in this process can be classified into four types: no signal, weak signals, strong signals, and violent signals. The four types of signals correspond to the ordinary operation stage, development stage, pre-damage and final seepage failure stage of tailings, respectively. (3) The b-value and fractal dimension of the guided waves are at a low level before the final seepage failure stage of the tailings and violently oscillate when the final seepage failure is approaching. (4) Through the analysis of the flexural guided wave parameters, the quantitative indices of the tailing seepage failure degree are proposed, and the tailing seepage failure is divided into four warning levels. The four warning colors of blue, yellow, orange and red represent the corresponding warning level.

The lifting mode is one of the failure modes of finite movable blocks proposed by block theory. Although direct collapse is the most common failure mode in underground engineering, there is still a lack of suitable quantitative stability analysis methods, resulting in the scarcity of necessary theoretical support for the excavation and reinforcement design of underground engineering. To this end, an improved stability analysis method for rock blocks considering progressive damage is proposed. Main improvements include: introducing overload base and overload direction to quantify the reserve load; proposing two options of overload base which are Tan and Scal; and setting the overload direction on the boundary sector of the joint pyramid. The example verification results show that the improved method is fully compatible with the existing safety factor algorithm for the wedge failure mode. It realizes the quantitative stability analysis of the lifting mode. Finally, the stiffness assignment method and its sensitivity are discussed.

For the plane strain problem of engineering construction in loess area, the plane strain shear tests on intact loess under different lateral consolidation pressures and moisture contents were carried out by using the transformational true triaxial apparatus of Xi’an University of Technology. The experimental measurements of angle of inclination for shear band at shear failure were obtained. The Mohr-Coulomb and Roscoe solutions to angle of inclination for shear band of were derived from the stress-strain curve. The changes of intact loess strength, failure mode and angle of inclination for shear band were analyzed. The study results show that the stress-strain curve vary from primary softening type to secondary hardening type wih the development of new structure when the water content and lateral consolidation pressure increase. The failure modes of shear band present single line-shaped, cone-shaped and X-shaped as the increase of lateral consolidation pressure. Along wih the increase of moisture content, decrease in the cohesion, internal friction angle leads to reduce the angle of inclination for shear band of Mohr-coulomb solution, while the enhanced dilatancy rising the Roscoe solution. With the increase of lateral consolidation pressure, both the dynamic internal friction angle and the dilatancy are increase, resulting in shear band inclination angles of Mohr-Coulomb and Roscoe solution increase.

Desiccation is the key factor causing the initiation and expansion of cracks in expansive soil. The evolution of cracks has an important influence on the integrity of soil structure and the long-term stability and safety of the foundation. In order to study the evolution characteristics of dry-shrinkage cracks in expansive soil, micro-CT scanning tests were carried out on undisturbed soil samples. The 2D/3D images and characteristic parameters of soil meso-cracks were obtained by using image processing technology, and the evolution of dry-shrinkage cracks was analyzed qualitatively and quantitatively. The results showed that the volume shrinkage characteristics of expansive soil in the desiccating process were restored by the 3D reconstructed digital model, which was in good agreement with the measured volume of samples. The quantitative indexes of meso-cracks, such as crack ratio, crack number, crack volume and crack structure characteristic parameters, can be extracted from micro-CT images. With the water content decreasing from 24.0% to 12.0%, the crack ratio and crack volume of expansive soil increased, while the number of cracks tended to decrease. According to the volume and geometric characteristics of cracks, cracks can be divided into connected cracks and independent cracks. During the desiccating process, the volume proportion of connected cracks increased significantly, while the number of independent cracks decreased continuously. The ‘ball-and-stick model’ effectively simulated the geometric characteristics of the cracks in expansive soil. The equivalent pore radius, throat radius, throat length and pore-throat coordination number all tended to increase during the desiccating process, and the connectivity of cracks was significantly enhanced. The SEM images showed that the connectivity of meso-cracks was closely related to the arrangement of clay particles and the development of the pores between particles.

The physical and chemical reactions between heavy metals in landfill leachate and soil may change the microstructure of soil, then the diffusion and migration of heavy metals and other toxic substances, threaten human health and surrounding environment. In order to investigate the effects of heavy metal contamination on macroscopic water retention and microstructure of loess, the soil-water characteristic curves of Pb-contaminated loess were measured by axial translation technique. Characterization of mesoscopic structure changes was clarified by scanning electron microscopy (SEM), mercury injection (MIP), X-ray diffraction (XRD) and Zeta potential. The results show that the air-entry values of Pb-contaminated loess decrease with the increase of Pb-concentration. When the lead pollution concentration increases from 0 mg/kg to 2 000 mg/kg, the air-entry values decrease from 19.18 kPa to 12.12 kPa, indicating that lead contamination lead to a decrease in water retention. On the contrary, the permeability increases with the increase of lead concentrations. The saturated permeability coefficient increases from 7.92×10–8 m/s to 3.73×10–7 m/s. The physicochemical reaction and reduction of Zeta potential caused by lead contamination produce flocculation structure, and the proportion of small pores decreases while that of medium pores increases. The microscale structural evolution has a good correspondence, induced by the lead contamination, with macroscopic water retention capacity and permeability. The results can provide important parameters for the study of unsaturated seepage and solute transport in heavy metal contaminated sites.

In view of the inadequacy of existing research on the bedding fracture propagation model of shale gas volume fracturing and its calculation method, the mechanical characteristic parameters of shale bedding were obtained by three-point bending (TPB) test combined with digital image method. A pseudo-three-dimensional (P3D) mathematical model of hydraulic fracture propagation in shale gas volume fracturing was established by the utilization of elastic mechanics and line spring model, which was verified by laboratory experiments. A calculation program for geometric parameters of shale bedding fractures was developed to calculated and analyzed the influence of bedding parameters and fracturing engineering parameters on the distribution of hydraulic fracture. The results show that the amount of shear slip reaches a maximum value and a minimum value when the bedding stiffness is less than  10 GPa/m and greater than 30 GPa/m, and keeps basically unchanged. And the bedding stiffness is linearly negatively correlated with the shear slip when the bedding stiffness is in the range of 10–30 GPa/m. The main fracture will communicate with more beddings when the bedding density is in the range of 5–7. The hydraulic fracture is easy to penetrate the bedding and can lead to the bedding shear slip when the bedding strength is in the range of 5–8 MPa, thereby generating a complex fracture network. Moreover, the hydraulic fracture is also inclined to pass through the bedding when the pumping rate and viscosity of fracturing fluid are in the range of 9–12 m³/min and 2.5–5 mPa·s, respectively, and finally a cross-shaped fracture is formed, which is conducive to the formation of complex fractures. This study has a certain guiding significance for understanding the mechanical properties of shale and its influence on the propagation regulation of hydraulic fracture.

Failure of buildings and structures due to the increase in pore water pressure (Uw) in soil is common in practice, and triaxial test under stress path of decreasing mean effective stress and constant deviator stress (CQT) is a frequently-used research method in related studies. However, to date experimental studies considering the influence of excavation-induced unloading during construction are rarely reported. In order to explore the effects of initial unloading on the mechanical response of granite residual soil during the increase in Uw, a stage of initial unloading was added in the conventional CQT and a series of modified CQTs were conducted, based on which the effects of initial unloading and unloading lag on the deformation characteristics, yielding behavior and strength properties of the soil were analyzed, and results of conventional and modified CQTs were compared to investigate the influence of initial stress path. The experiment results show that the deformation response to the increase in Uw can be divided into three different stages, negative increment of Uw emerges and mean effective stress increases instead as a result of rapid deformation and dilatation potential of the soil after yielding. The initial unloading brings about the degradation of the mechanical performance of the soil, which is manifested as the decrease in both stiffness and yielding strength with the increase in initial unloading degree. Compared with the conventional triaxial compression stress path, which is of “loading” type, initial unloading has a more significantly adverse effect. The degradation of soil performance intensifies as the unloading lag increases. The mobilized friction angle at yielding point decreases with the increase in the initial unloading degree, but is always greater than the mobilized friction angle at critical state.

Pillar burst is one of the most frequent dynamic disasters in deep mining, which poses a serious threat to safe and efficient mining. In this study, the failure mechanisms and precursors of pillar burst are investigated by active ultrasonic survey and passive acoustic emission (AE) monitoring in uniaxial compression tests on Zigong red sandstone. Combining active and passive AE monitoring data, a P-wave velocity tomography inversion is performed to analyse the temporal and spatial variations of P-wave velocity structure during the sample failure. Results show that the velocity structure of the sandstone sample is highly heterogeneous during loading, and a low-velocity zone emerges, within which most of the acoustic emission events are present. The dispersion of P-wave velocity reflects the global variations of P-wave velocity. It changes drastically during the peak stage, and increases with the ongoing loading. The AE events differ significantly between the pre-peak and post-peak stages. In the pre-peak stage, AE events are randomly distributed in the sample, while in the post-peak stage, clustered AE events are identified. In addition, it is found that using the homogeneous velocity structure for AE events location results in a higher positioning error. The decreasing b value before the eventual failure of the sample indicates that large-scale crack activities are intensified, leading to the increase of sample heterogeneity, which also proves the necessity of applying the heterogeneous velocity structure for AE events location. The research results can be further used for on-site pillar stability monitoring, and the periodic P-wave velocity tomography provides precursors for pillar bursts.

Cement-soil vertical cutoff wall is extensively applied to the remediation of industrial contaminated sites, but its impermeability needs to be improved and also the chemical compatibility under the effect of high concentration and toxic heavy metal contamination needs to be studied. Through laboratory tests, physical, strength and permeability properties of different cement-soil vertical cutoff wall samples based on different mixing ratios of GGBS (ground granulated blast furnace slag), bentonite, and curing agent were studied. Considering the quality of the vertical cutoff wall and economic cost, the curing agent dosage of 20% (the mixing ratios of PC, GGBS and bentonite are 8%, 8% and 4%, respectively) was validated as the optimal ratio for the amended cement-soil vertical cutoff wall. The chemical compatibility of cement-soil vertical cutoff wall materials under the effects of heavy metal zinc and lead pollution, in terms of hydraulic conductivity, is examined by a flexible-wall permeability test. The result shows that the decrease in the impermeability of the cement-soil vertical cutoff wall under the action of heavy metal solutions is jointly dominated by three factors, i.e., heavy metal species, the concentration of heavy metal, and the pH of pore solution. The adverse effect of the type of heavy metals on the impermeability of the samples is in this order: zinc nitrate-lead nitrate solution> zinc nitrate solution> lead nitrate solution. The hydraulic conductivities of the samples permeated with different heavy metal solutions are between 1.49 and 10.10 times that of sample permeated with tap water and increase with the increase of concentration of the heavy metal solution. Under the premise of meeting the requirement of hydraulic conductivity, the amended cement-soil vertical cutoff wall could barrier 50 mmol/L of zinc nitrate solution, 100 mmol/L of lead nitrate solution and 10 mmol/L of zinc nitrate-lead nitrate solution.

Discontinuities with different rock types are widely distributed on the Three Gorges reservoir area of Yangtze River, and the study of their peak shear strengths can provide a theoretical basis for the stability analysis and evaluation of rock masses. Three groups of rock-like specimens with different surface morphologies and upper and lower joint wall strengths were cast by high-strength gypsum, and then directly sheared under different constant normal stresses. The joint wall strength combination coefficient (λ ) is introduced to quantify the comprehensive influence of the compressive strength and basic friction angle of the discontinuity wall on the peak shear strength of discontinuities with different joint wall strengths. The smaller λ is, the greater the strength difference between the upper and lower discontinuity wall is. The peak shear strength of rock discontinuities with different joint wall strengths increases non-linearly with increasing λ , which is more significant at higher normal stress. Based on Barton criterion, an empirical criterion for estimating the peak shear strength of discontinuities with different joint wall strengths has been established by multiple regression analysis. The new criterion is further verified by the direct shear test results of the natural and artificial tooth-shaped discontinuities with different joint wall strengths, and tested shear strengths are in good agreement with predicted values by the new criterion. The application of the new criterion in the stability evaluation of soft and hard inter-bedded rock slopes is briefly analyzed. Finally, the applicability of Wu’s equation and the advantages and disadvantages of the new criterion are discussed.

Multi-disk anchor rod is a newly developed anchoring structure, which has excellent engineering characteristics compared with ordinary anchor rod. On the basis of the laboratory model test research of the multi-disk anchor, a theoretical calculation formula for the ultimate bearing capacity of the multi-disk anchor is deduced through the limit equilibrium theory. It’s validity is verified by the correspondence between the calculation result and the measured data. To further grasp the load transfer characteristics of the multi-disk anchor, an on-site slope anchoring prototype test is carried out. The data obtained from the on-site multi-disk anchor pull-out test are used to study the influence of the diameter of support disks, the spacing of support disks and the number of support disks on the ultimate bearing capacity and deformation control ability of multi-disk anchors. The test results show that in silty clay, when the distance between the support disks is greater than or equal to 4 times the diameter of the support disks, it can be considered that each support disk can work independently, giving full play to the bearing capacity of the multi-disk anchor; under the same conditions, compared with ordinary bolts, as the disk diameter increases from 300 mm to 500 mm and the number of disks increases from 1 to 3, the pull-out capacity of the multi-disk anchor increases significantly, and its deformation control ability is also greatly enhanced. The test results also show that the axial force transmission curve of the multi-disk anchor rod has a sudden change at the position of the support disk, presenting a steep drop, which fully reflects the contribution of the support disk in the uplift resistance. The research results have laid a good theoretical foundation for the engineering application of multi-disk anchor rods.

To study the influence of the spatial distribution characteristics of material composition on the deformation and failure of gravel soil slope under rainfall, four types of material composition spatial distribution gravel soil slopes and homogeneous slope model tests were conducted according to the characteristics of gravel soil slopes of different geneses. Results show that the role of spatial distribution of material composition played in the deformation and failure of gravel soil slope under rainfall depends on the directions of rainfall infiltration and stress adjustment. When the change direction of soil material intersects the rainfall infiltration direction at a large angle and is the same as the stress adjustment direction, the permeability of slope is actually the permeability of the constituent materials themselves, and the mechanical properties of slope approach the maximum value of the mechanical properties of soil materials that form the slope. When the change direction of soil material is the same as the rainfall infiltration direction and intersects the stress adjustment direction at a large angle, the slope permeability approaches the minimum value of the permeability of the constituent soil material, and the slope deformation and failure are controlled by the weak soil material. The deformation occurs in all parts of the slope under rainfall, and it adjusts to surroundings and thus affecting the surroundings. The fractured surface is more likely to occur in weak soil. Research contributes to the development of the slope disaster investigation, prediction, evaluation and prevention towards refinement.

In order to study the effect of shear rate on the shear mechanical properties of rock joints under different boundary conditions, RDS-200 rock joint shear test system was used to carry out direct shear tests with five different shear rates under two boundary conditions including constant normal stress and constant normal stiffness on artificially cast irregular rock-like joints with the same joint morphology. The experimental results are as follows. (1) Under the constant normal stress boundary condition and a same normal stress, the pre-peak shear stiffness of rock-like joints decreases with a decreasing rate, and the peak shear strength and residual shear strength decrease logarithmically with the increase of shear rate; in addition, the cohesion of rock-like joints increases, and the internal friction angle decreases logarithmically with the increase of shear rate. (2) Under the constant normal stiffness boundary condition and a same normal stress, the pre-peak shear stiffness of rock-like joints decreases with a decreasing rate, the peak shear strength decreases logarithmically, and the residual shear strength increases first and then decreases under higher normal stress with an increase of shear rate; moreover, the cohesion of rock-like joints decreases and the internal friction angle increases logarithmically with an increase of shear rate. (3) Compared with the constant normal stress boundary condition, the cohesion force of the rock-like joint increases by 115.85% on average, and the internal friction angle decreases by 8.44% on average under the constant stiffness boundary condition; the pre-peak shear stiffness, the peak shear strength and the residual shear strength of the rock-like joint increase by 11.96%, 19.47% and 32.32% on average, respectively, and the peak normal displacement decreases by 40.12% on average under the same initial normal stress and shear rate. The research results can provide some references for the shear instability evaluation of surface and underground engineering rock joints under different shear rates.

As urban rail transit construction increases year by year, conflicts between new tunnels and existed bridges become increasingly obvious. Aiming at the risk assessment problem of shield tunnel crossing the existing bridge construction, and based on the system idea, we introduce the C-V-T model to classify the engineering risk into consequence severity, which is called C; the vulnerability of the existing bridge system, which is called V; and the threat of the new tunnel system, which is referred to as T, so as to construct a three-system risk assessment process of disaster-causing, disaster-bearing and post-disaster. By introducing the two-factor catastrophe theory to establish a three-level index system, we obtain the catastrophe progression of the existing bridge to express its vulnerability. In order to improve the accuracy of T-value, we use the interaction matrix to measure the cross influence between the indicators of the new tunnel, and then give the indicator-system weight method. Finally, introducing the complex mapping relationship and transformation situation between the quantitative indicators and qualitative concepts to express multi-dimensional cloud and forward generator optimization algorithm objectively. Additionally, we clarify the consequence severity grading criteria, by which defining the direct economic loss, the surrounding environmental loss and human casualty, give the coupling method of the three system risk assessment results, and thus build a comprehensive assessment model for the construction risk of shield crossing existing bridges. We apply the proposed model to the risk assessment of Yixin Bridge Crossing Project of Kunming Metro Line 5, which shows that the evaluation results match with the actual situation of the project. The construction monitoring data also verifies the rationality, standardization and applicability of this model.

A series of geological disasters are observed in metal mines by sublevel caving method. In order to ensure safe production in mining areas, it is of great significance to carry out research on time-dependent strata movement behavior caused by sublevel caving method. The footwall of western area in the Chengchao Iron Mine was taken as the research case and more than 10 years of GPS monitoring data on the surface were collated and analyzed. By combining the monitoring data with in situ failure investigation and engineering geology, the time-dependent behaviour of strata movement under different zones was studied. The research results indicate that the time-dependent behaviour of strata movement is determined by deformation failure process, and its time-dependent behaviours are different in different zones. It can be further characterized by initial deformation, progressive deformation, accelerated deformation and residual deformation stages. The four time-dependent behaviours correspond to stable state, critical state, unstable state and post-mining creep state. The initial deformation stage corresponds to the initial creep process of the rock mass, and the progressive deformation stage reflects the process of resisting deformation. The accelerated deformation stage is related to the formation of through-going failure surface and the strong stress release. There is no space for the caved waste rock mass to flow after the mining activity is stopped, the strata movement is weakened due to the caved waste rock mass is compacted by surrounding rock mass. The residual deformation time is controlled by the creep characteristics of the rock mass and the compaction process of caved waste rock mass. A longer residual deformation time is observed in in the toppling-slipping zone due to an additional compaction process of caved waste rock mass.

Deformation control is essential when assessing the safety state of underground structures during construction. Due to the difficulty in quantifying the dynamic influence of underground construction, a deformation prediction model based on traction algorithm in control phases are proposed. The bidirectional long short-term memory (Bi-LSTM) is adopted to predict the time series of the monitoring data. The results of crucial construction stages obtained by numerical simulation are taken as traction points and are updated along with the stages according to the existing monitoring data. By using the attention mechanism combined with the bidirectional long short-term memory (Bi-LSTM-AM), the prediction results of the data-driven models in the control phases can thereafter be modified according to the updated traction points, achieving a more accurate and intelligent prediction of deformation during underground construction. Setting the traction relative weight allows the current reasonable traction degree to be adaptively determined, thereby realizing a valid fusion of Bi-LSTM and numerical simulation. The effectiveness of the traction prediction model is verified through relevant historical cases and data. Combined with the automatic monitoring case of Xi’an Metro Line 1 affected by the upper-span underpass of Fenghao third road in Xixian New District, the advantages and shortcomings of traction prediction are discussed. The results show that the traction effects improve the delay problem of data-driven prediction at the key construction stages, and the error is decreased by 24.34% on average. The continuously optimized traction points gradually approach the true values, which reduces the impact caused by the deviation of numerical simulation. The proposed model provides a fresh perspective on the deformation prediction during underground construction.

Piping was one of the main risks of dike engineering in China, thus it was vital to the flood control and rescue. However, in the practice of flood control and emergency rescue, the degree of damage caused by piping was different. It was difficult to take different measures to tackle the piping risks, which resulted in exaggeration or contempt for the rescue of piping. The main reason could be the lack of understanding of the piping damage degree. To this end, this paper presented the concept of collapsed piping based on the damage degree of piping to dike engineering, and developed a method for estimating piping damage degree using the analytic hierarchy process. And the quality of dike engineering, water head difference and piping risk characteristics were chosen as the main impact factors to evaluate the risk degree of piping. The results showed that the distance of piping to dike, with a weight value of 0.375 5, was the most important impact factor on the risk degree of piping, followed by the water level of outside dike with a weight value of 0.202 1, and piping scale had minimal effect with a weight value of 0.172 3. The risk degrees of 33 typical piping appeared in the Yangtze River, were assessed by using the analytic hierarchy process. Moreover, the two piping risks happened in Qingshan district of Wuhan city (2016) and Paizhouwan of Jiayu county, Hubei province (1998), were contrastively analyzed with the traditional empirical method and the analytic hierarchy process method, respectively, which showed that the analytic hierarchy process was more scientific and practical. The results can provide technical support for the classification of piping hazard and dike rescue.

Aiming at the non-limit active earth pressure distribution of sand under the rotating about the base (RB) mode of rigid retaining wall around the bottom of the wall, the active failure process of sand is analyzed by discrete element numerical simulation. The results show that in the non-limit active state, when the friction angle of the soil at different depths becomes the limit value, the horizontal displacement required at this point is approximately the same, which is about 0.03%H. When the soil-wall friction angle reaches the limit value, the horizontal displacement required at this point is approximately linear with the depth z, that is S_δ =0.12%z; and there are many parallel "quasi sliding surfaces" in the soil behind the wall in the process of retaining wall moving. According to the simulation results, this paper modifies the calculation formula of friction angle mobilization value proposed by Liu, takes the thin layer parallel to the sliding surface in the soil wedge behind the wall as the oblique differential element by using the oblique differential element method, establishes the static equilibrium equation of the element in the non-limit active state, and obtains the calculation formula of non-limit active earth pressure against different displacements of the retaining wall under RB mode. Finally, the calculation results are compared with the simulation results and the measured data of model test, which verifies the rationality of the theoretical formula proposed in this paper.