The performance-based seismic design requires engineers to design structures with desired seismic performance for a specific level of earthquake ground motions. One of the key factors is the determination of seismic effect, which depends on the local site condition. This paper collected 956 borehole profiles and shear-wave velocity profiles of soil lithology in Beijing, Suzhou and Tangshan urban areas, China. The correlations of the time-averaged shear-wave velocities VS20 and VS30 for the corresponding top 20 m and 30 m depths for sites are established. Cyclic triaxial tests were performed on typical samples of undisturbed soils at the depth of 105 m taken from Beijing urban area in this study, and the shear modulus reduction and damping increasing curves with increasing shear strain for various types of soils are given. Nonlinear site responses of soil column models for 170 borehole profiles in Beijing urban area were computed, and the site fundamental periods TS for each soil column model were estimated through the Nakamura’s HVSR method and the Chen’s weak-motion method. Subsequently, combined with the site classifications of the current seismic design codes at home and abroad and the recent research results of some scholars on site classification, two alternative seismic site classification schemes were proposed, namely the two-proxy method based on the H (soil depth from the surface to bedrock with shear-wave velocity ≥ 500 m/s) and VSE (time-averaged shear-wave velocity for the smaller value of both the upper 30 m and H), as well as the three-proxy method based on the H, VSE and TS. The two proposed site classification schemes in this study provide a beneficial reference to modify the site classification in the current seismic codes in China.

The fracture parallel plate seepage model has been widely applied to describe the processes and characteristics of fluid flow through fractures in rocks, while the actual flow field of the fracture seepage in rocks could be far more complicated than the assumption of rock matrix to be parallel plates. As a result, it draws lots of attentions on investigations on suitability and corrections of the fracture parallel plate seepage model. In this study, by taking the disc fracture model which is closer to the actual fracture shape than the parallel plate model, a physical model of a single disc fracture was constructed in the laboratory. By changing the aperture of the disc fracture in rocks and the sizes of the water inlets and outlets, the seepage experiments under different pressure gradients were conducted to investigate the laws of fluid flow in fractures. The experiment results show that the Forchheimer model fitted the relationship between the seepage flow and pressure gradient inside the disc fracture relatively well while the Darcy law model presents also a good fitting for the Non-Darcy flow regimes. It should be noticed that the calculation formulas of the parameters A and B in the Forchheimer model need to be modified as to the Forchheimer model. Furthermore, an approach has been recommended for those modifications and the corresponding modified calculation formulas with certain reliability have been given based on the experimental results. This study is expected to provide in certain degree theoretical foundations and methods for further investigation of fluid flow through a single fracture in rocks and the complex fracture networks.

Rock engineering may be subjected to high temperature environment. Different cooling methods of high-temperature rock often lead to significant changes in the physical and mechanical properties of the rock, which will have an important impact on the stability and permeability of rock engineering. Magnetic resonance imaging (MRI), scanning electron microscope (SEM) and uniaxial compression test were used to study the porosity, pore size distribution, peak strength, peak strain, stress-strain relationship and microstructure changes of five temperatures for sandstone samples at 100, 300, 500, 600 and 800℃ under two cooling methods (natural cooling and water cooling). The test results show that: (1) When the rock samples used the natural cooling method, the strength of high-temperature sandstone does not decrease continuously with the increasing of temperature. However, rock samples using water cooling method show continuous decrease of sandstone strength, and the decreasing extent is far greater than that of natural cooling; (2) 500℃ can be considered as the critical value of the influence of different cooling methods on the porosity of sandstone. When the temperature is above 500℃, the water cooling method will cause the rock porosity increase rapidly, and the proportion of pores with large pore diameter (Ф>10 μm) is also higher than that of the natural cooling method. In this consideration, in the field of high-temperature sandstone engineering, the possible seepage hazards should be fully considered when water cooling is used (i.e., fire extinguishing with water after a tunnel is on fire); (3) The SEM test results shows that when the temperature is above 500℃, water cooling promotes the widening and expansion of cracks. When the temperature reaches to 800℃, the pore size of water-cooled sandstone becomes larger, and the fracture is largely developed and connects into a network. This will lead to a substantial increase in water permeability. At the same time, it is one of the reasons for the sharp decrease in rock strength that caused by water cooling at this temperature.

Through the application of SHPB (split Hopkinson pressure bar) test, this research firstly analyzed the law of damage under the cyclical impact on grey sandstone samples with the condition of static load. After that, to obtain the sample failure mode and speculate the relationship between dynamic stress and strain, the static-dynamic loading experiments on pre-damaged rock samples were also performed. Finally, based on the principle of strain equivalence, the total damage variable under the condition of static-dynamic loading was analyzed to derive the damage evolution equation to explain the relation of damage constitutive. Based on above tests, the research suggests: (1) the damage variable of rock sample can be divided into three stages during the process of cyclical impact, which are rapid increase, low-speed development and high-speed development, meanwhile, a higher axial pressure will lead to a lower damage variable in the stage of low-speed development; (2) compared with pre-damaged sample, the effect of strain rate enhancement on intact samples is more significant under the same condition; (3) the joint impact of pre-damaged variable ( ) and static-load damage variable ( ) might be negative, which therefore explained the fact that the dynamic strength increases with the static pressure under the condition of static-dynamic loading; (4) the constructed constitutive relation is also in perfect agreement with the curve of test value, which can in turn show a consistency between the macro- and micro- damage of the rock and then reflect the nonlinear influence of cyclical impact and static loading on total damage development.

The fluid movement in rock mass is extremely complicated due to the existence of a large number of rough and irregular fractures. To address the difficulties such as concealment and non-repeatability of physical model in natural rough rock fissure seepage tests, a fissure channel with rough joint surface was constructed based on a three-dimensional Weierstrass-Mandelbrot fractal function. Using 3D printing technique, a transparent and refined fracture channel model was obtained, and the fracture seepage diffusion movements under different conditions were studied by using microfluidic control instruments. The relationships between the discharge of fracture channel and the pressure head, the fracture width and the fractal dimension were analyzed. The results show that in fractal fractures, the discharge of fracture channel is linear with the pressure head; the single-wide discharge is approximately cubic with the width of the fracture channel, which is similar to the parallel plate cubic law. Considering the influence of fractal dimension, the discharge through the fracture channel increases with the increase of fractal dimension. The cubic law of seepage in rough fractures can be modified by the power exponent function related to the fractal dimension.

The stress state of earth and rockfill dams is close to plane strain stress state or three-dimensional stress state, while the conventional triaxial test underestimates the mechanical properties of coarse granular material. The mechanical properties of coarse granular material under conventional triaxial stress state, plane strain stress state and true triaxial stress state( 0.25) were investigated by compression tests using large-scale true triaxial apparatus. The test results show that the relationship curves between the difference of major principal stress and minor principal stress and the strain in the direction of major principal stress become higher and steeper in sequence from conventional triaxial test, to plane strain test, to true triaxial test under the same minor principal stress. The volumetric strain increases with the increase of the spherical stress under a certain test loading condition, which shows a slow increase at the initial shearing stage and then increases linearly. The volumetric strain curves are close for different minor principal stresses. The strengths of plane strain stress state and true triaxial stress state are much greater than that of conventional triaxial stress state, and the percentage of strength increase under true triaxial stress state is larger than that of plane strain stress state. The initial elastic modulus increases linearly with the increase of the minor principal stress. In plane strain stress state, the coefficient of intermediate principal stress increases with the increase of the strain in the direction of major principal stress. The coefficient of intermediate principal stress increases slowly in the initial shearing stage and then increases linearly with the increase of the strain in the direction of major principle stress. From conventional triaxial stress state to plane strain stress state and then to true triaxial stress state, the strains in the direction of minor principal stress are all expansion deformations, and the expansion deformations increase successively under the same minor principal stress. The relationship curve between the ratio of deviatoric stress to spherical stress and deviatoric strain of small minor principal stress is located at the top for a certain test loading condition.

To explore the bearing characteristics of single pile under the combined action of torque (T) and vertical load (V) on the pile top in clay foundation, vertical load was applied after preloading the torque to pile top. Based on the results of laboratory model tests and combined with the boundary element method, a reasonable assumption was made for the vertical ultimate friction resistance of pile side under the T→V loading path. The nonlinear solution of single pile under the T→V loading path was obtained by MATLAB programming, and then the bearing capacity envelope was plotted. To facilitate its application in engineering design, the expression of the failure envelops for the bearing capacity of single pile under the T→V loading path was obtained by fitting the experimental data. The results show that the vertical bearing capacity decreases with the increase of torque on single pile, and the T-V combination effect becomes more obvious when the torque load exceeds one third of the limit value. Both the bearing capacity and the deforming resistance of single pile are strengthened with the increase of length-diameter ratio, and the deformation of pile shaft mainly occurs in the range of 0~0.6L. Therefore, the reinforcement of shallow foundation can effectively reduce the deformation. The vertical ultimate bearing capacity of single pile improved with the increase of elastic modulus of pile shaft under the T→V loading path. Nevertheless, the vertical ultimate bearing capacity was only increased by 26.74% when the elastic modulus of single pile increased by 10 times. Therefore, it is not advisable to improve the ultimate bearing capacity of pile-soil system by increasing the concrete grade.

Clay compacted at the dry side of optimal moisture content generally has a distinct double pore structure, inter-aggregate pore (also called macroscopic pore) and the intra-aggregate pore (also called microscopic pore). The significant difference of their influences on mechanical responses and water retention behaviors of soils leads to the discrepancy on the evolution rules of these two types of pores. The pore size distribution function of unsaturated soil with double pore structure is the bimodal pore size distribution form, which can be obtained by superposing the unimodal pore size distribution curves of macroscopic pores and microscopic pore. The evolution parameters of translation degree, scaling degree and dispersion degree, are adopted to describe the pore evolution rule of soils with double pore structure. Based on establishing the relationship between the evolution parameter and the porosity during mechanical and hydraulic loading and unloading, a model of the microstructural evolution of soils with dual-pore structure suitable for describing unsaturated compacted soils under variable suction was proposed. Based on the results of mercury intrusion tests on Guilin red clay and the test data of Minia Lubois expansive soil in the literature, the established model parameters were calibrated. The applicability and prediction accuracy of the model was verified by comparing the simulation results with test results.

The characteristics of sandstone localized deformation have been studied by visual triaxial compression servo control test system under different loading rates. By the use of the 3D-DIC (3 dimensional digital image correlation) test system, we obtain the axial and radial strain field nephogram, as well as the crack evolution process of sandstone under triaxial stress. The influence of loading rate on the localized deformation of sandstone has been analyzed. The results show that: before the peak strength, the surface deformation of sandstone is relatively uniform. The strain concentration phenomenon occurs at the peak strength, and it expands rapidly in the post-peak stage, and finally forms a deformation localized zone that penetrates the sample surface. As the load rate increases, the peak strength, elastic modulus, Poisson's ratio, peak axial strain and peak radial strain of sandstone all increase. When the loading rate increases from 1×10–6 s–1 to 1×10–3 s–1, the starting stress of localization of deformation also increases. Besides, the ratios and , which describe the levels of the starting stress of axial and radial deformation localization, have changed from 92.00% and 93.75% after the peak to 97.17% and 96.00% before the peak, respectively, indicating that the deformation localization of sandstone has relatively obvious loading rate effects.

Stability analysis is of great significance to the safety of slope engineering. In order to study the influence of seismic loads on slopes strengthened by prestressed anchor cables, firstly, the staged model of slope stability under seismic loads is analyzed based on the safety reserve characteristics of prestressed anchor cable, and secondly, the formulas of displacement, anchoring force and safety factor of bedding rock slope are derived by using the traditional Newmark’s displacement calculation method. At last, two examples are used to study the displacement behavior of prestressed slope under different cable models and seismic accumulations. It can be seen from the results that when the anchoring force is taken as a constant value, the calculated seismic slope displacement is larger and increases linearly with time. When considering the safety reserves of anchor cables, the growth rate of displacement gradually decreases with time and finally reaches a constant value. Different cable models have great influence on the calculated displacement, and the reserve effect of cable cannot be ignored. Seismic loads, meanwhile, have a permanent effect on the prestressed anchor slope. The critical threshold of slope sliding increases if the slope is re-disturbed seismically. Displacement growth rate is inversely exponential with the acceleration intensity of the last shaking. Finally, taking the slope of an open pit mining area as a case study, the optimum supporting scheme is determined under the seismic fortification standard.

Due to the lack of effective monitoring tools for the slurry flow and strength development of high stage cemented backfill in the metal mines, the conservative design of very high strength of in-situ backfill results in excessive filling costs. The self-designed stress monitoring system were buried horizontally at four sections to monitor the temporal and spatial evolution three-dimensional stresses during the full sequence period (filling, curing and bearing). The results indicated that the three-dimensional stresses increased during filling and bearing period but tended to stable during the curing period. Meanwhile, the vertical stress was higher than the horizontal stress at four sublevels. During the filling period, the 51%～65% of self-weight stress was transferred into horizontal stress by the arching effect. The vertical stress and mining distance show a polynomial relationship during the bearing stage. Combined with the second step mining operation process, the mechanism of arching effect and mining-induced stress-transfer was revealed. Based on the double-arch coupling effect of stress transfer, the internal stress prediction model of high stage cemented backfill in the stope was established, which can be used to accurately determine the required strength of backfill.

In view of the two typical modes of water inrush disasters, progressive fracturing of rock mass and seepage failure of filling structure, the mechanism of progressive fracturing of rock mass under the combined effects of dynamic disturbance, excavation unloading and high water pressure is described. The seepage failure mechanism of the variable strength-variable permeability-variable viscosity of the filling structure under osmotic pressure is also expounded. For the variable viscosity mechanism of water inrush caused by seepage failure of filling structure, a qualitative simulation study on the effect of fluid viscosity on seepage failure mechanism is carried out using the DEM-CFD coupled simulation method. The effects of fluid viscosity on the average contact force, flow rate (flow velocity), porosity, particle migration process, migration trajectory and critical hydraulic gradient of the simulation model are analyzed. The results show that the critical hydraulic gradient of fluid with low viscosity is smaller than that with high viscosity. In other words, seepage failure of filling structure is more likely to occur under the action of fluid flow with low viscosity; the average contact force is especially sensitive to the response of critical value of the hydraulic gradient, however it is difficult to be accurately reflected by the flow rate. Considering only the variable viscosity mechanism of water inrush due to seepage failure (regardless of the effect of increasing permeability), as the viscous medium flows into water, the fluid viscosity would increase, but the flow velocity would decrease, and the combined action of these two changes would actually hinder the development of seepage failure process. Finally, the phenomenon of water inrush process in engineering scale is simulated using DEM-CFD method, and the formation and expansion process of the dominant channel of water inrush is reproduced. The problems of parameter selection and quantitative analysis are identified to realize the simulation of water inrush mechanism.

The pore is the place where the seepage occurs in the porous medium, which is inevitably related to the permeability of the medium. Due to the special material source and formation process, coral sand has completely different pore characteristics compared with terrestrial sand. Through a series of microscopic studies, the reason for the special pore properties of coral sand in essence was revealed. It is found that it is reasonable to describe the properties of pores from the aspect of pore shape, pore throat size and global connectivity. Among them, pore shape is measured by the shape factor. Pore throat size includes pore radius and throat radius. Global connectivity in the porous media is described by coordination numbers. Particle shape and particle surface roughness are the main factors affecting pore shape, pore throat size and global connectivity. Particle shape mainly affects pore shape, throat size, pore throat size dispersion and the uniform distribution of connectivity in the medium. Particle surface roughness mainly affects pore shape, pore shape dispersion, pore size and global connectivity in the porous medium.

To investigate the effect of initial effective consolidation stress , void ratio e, and fines content FC on the small-strain shear modulus of saturated sandy soils, a series of isotropically consolidated bender element tests is performed on three saturated sandy soils with various physical properties. The test results show that the stress exponent n, reflecting the rate of increment due to the enhancement of , presents a soil-specific constant, and there is a good exponential correlation between n and the synthesizing grain size distribution parameter of sandy soils. Fitting parameter A of Hardin model decreases as FC increases, and an exponential correlation is found. But there is no obvious single correlation between fitted parameter d and FC. Combined with the test data of of three saturated sandy soils in the literature, it is found that the stress-corrected small-strain shear modulus /( /Pa)n for different types of sandy soils decreases monotonically with the increase of the equivalent skeleton void ratio , and a good power relationship between /( /Pa)n and is then obtained. Generalized Hardin model that allows unified characterization of values for different types of sandy soils with various , e and FC is established based on binary medium model.

To solve the problem of grout-rock interface relaxation due to self-shrinkage of cement-based material grouting in deep fractured rock masses, a bolt-grouting reinforcement method for deep fractured rock masses based on prestressed anchor and self-stress grouting was proposed. A self-stressed grouting reinforcement model and a new prestressed bolt-grouting reinforcement model for a single fractured rock mass were established. The mechanical characteristics of fractured sandstone specimens with ordinary and new bolt-grouting reinforcement were studied in physical experiments. The effectiveness of the new prestressed bolt-grouting reinforced rock mass was verified in engineering applications. Results showed that within a certain range, the greater the expansion restraint stress of the slurry stone is, the stronger the reinforcement effect on the fractured rock mass is. The expansion restraint stress of the slurry stone and the axial stress of bolt both contributed to the increase of the maximum principal stress of the fractured rock mass. The peak strength of the new prestressed bolt-grouting reinforced sandstone was 10% higher than that of the ordinary bolt-grouting reinforced sandstone. Its peak strain was slightly lower than that of the ordinary bolt-grouting reinforced sandstone. Moreover, the elastic deformation stage of the new prestressed anchor-grouting reinforced sandstone was shortened, and its reinforcement effect was enhanced. The surrounding rock of the substation roadway, which could not be well controlled by anchor-net support, U36 steel support or ordinary bolt-grouting reinforcement, was effectively controlled by new prestressed bolt-grouting reinforcement, and the maximum displacement of the surrounding rock on the roadway surface was 83 mm.

Seepage deformation is a phenomenon in which fine particles within the soil skeleton in granular materials are redistributed under the action of seepage, leading to the change in the internal fabric, hydraulic properties, and mechanical properties of soils. Seepage deformation has become one of the leading causes for the failure of sand-gravel foundation and embankment dams. The newly self-developed rigid wall permeameter was adopted to conduct the seepage test under the action of constant water head on gap-graded sand-gravel soils with different gradation and fines content. The spatial distribution of local hydraulic gradient along the specimen and the variation of vertical displacement were monitored during the seepage tests. The spatial distribution of soil particle size distribution was analyzed after the seepage test. The test results reveal that there appeared to be three kinds of packing state of fine particles, i.e., under-filled, filled, and over-filled state, and these packing state determined the different contact modes between the coarse particles and the fine particles then affecting the permeability. At the end of the penetration test, the spatial distribution of fine particle loss along the sample height can be divided into three areas, namely the top loss area, the middle uniform loss area and the bottom loss area. The rapid decrease in local hydraulic gradient, accompanied by an abrupt increase in vertical displacement, implied the onset of seepage deformation. The local hydraulic gradient at the start of seepage deformation was more substantial than the global hydraulic gradient, which proves the necessity of carrying out the seepage test on large scale specimens. Specimens with fine particles in the over-filled state are still susceptible to seepage deformation, leading to significant settlement deformation, which is worthy of further investigation.

Regarding the leakage of fractured limestone in the underground cavern of a hydropower station, the rock samples and reservoir water were collected on site, and two schemes of water-rock interaction tests which lasted 360 days were carried out. The scheme #1 regularly changed the soaking solution during the soaking process to simulate the long-term immersion and flow renewal phenomenon of groundwater, while the scheme #2 mainly simulates the long-term immersion process. Based on the micro-morphological characteristics of the fracture surface and the changes of ion concentration in soaking solution, the characteristics and mechanism of the seepage characteristics of fractured limestone under water-rock interactions were analyzed. The research results show that in the course of soaking, the permeability coefficient of the single-fractured limestone increases first sharply then gently. After 360 days of soaking, the permeability coefficients of the single-fractured limestone with 2.5 MPa, 3.0 MPa, 3.5 MPa, and 4.0 MPa confining stresses in the two schemes increased by 729.90%~384.17%、549.04%~297.45%, respectively. The smaller the confining stress is, the more obvious the permeability coefficient increases. Moreover, the growth trends of permeability coefficient stabilized after 120 days for scheme #1 and 90 days for scheme #2. In comparison, the permeability coefficient increase rate and amplitude of single-fractured limestone in scheme #1 are significantly higher, which is 1.34~2.07 times that of scheme #2. In scheme #1, the immersion reservoir water was periodically changed to maintain the disproportion of the immersion solution, which resulted in a large concentration gradient between the rock sample and the solution. This concentration gradient increased the reaction chemical potential, and accelerated the rate of mineral dissolution and erosion on fracture surface. In scheme #2, the long-term immersion facilitated the solution ion concentration to approach the equilibrium state gradually, leading to the dissolution and erosion rate of the minerals on fracture surface being significantly lower than that in the scheme #1. Long-term water-rock interaction weakens the roughness and fluctuation of fracture surface significantly accompanied with the progressively decrease of local slope and undulation, and the increase of overall erosion depth. Based on this, a seepage channel evolution model for single-fractured limestone under long-term water-rock interaction is established. The seepage channels of fractured rock samples gradually evolved to the direction of low anastomosis and large opening, which leads to significantly increases of equivalent hydraulic opening and permeability coefficient of fractured rock samples. The ideas and results of this study provide an excellent reference for the simulation of water-rock interaction in fractured rock masses.

Slab buckling rockburst is a common rockburst failure mode in high geostress areas. In view of the shortcomings of the existing mechanical models, such as neglecting the interaction between the split rock plates, a thin plate mechanical model of circular tunnel considering the horizontal stress between rock plates is established. The bending deflection of rock plate under load is calculated using the principle of the minimum potential energy, and compared with the ultimate deflection of tensile failure, thus the depth of rockburst failure is yielded. The research rationality is validated through the comparison between the calculation results of the new model and existing models by analyzing an engineering case. The results show that the rock plates around the tunnel are subjected to larger loads and smaller plates thickness. Moreover, the bending strain energy of rock plates is close to the work done by the longitudinal loads, and the buckling failure of the plates can be triggered by small inter-plate forces. With the increase of the distance from the tunnel wall, the thickness of rock plates increases and the stress decreases. The bending deflection of rock plate decreases faster than the ultimate deflection. After reaching a certain depth, the bending deflection becomes less than the ultimate deflection. As the buried depth increases, both the stress and bending deflection of each rock plate experience increase. The number of damaged rock plates also increases as well as the depth of rockburst.

Compared with the sampling on land, there are more disturbance factors on the sample in marine environment. Therefore, the quantitative evaluation of sample quality is of vital importance for marine geotechnical engineering. Based on the triaxial test of undrained unloading stress path and the bender element test, Hangzhou Bay marine fine sand was used to simulate the disturbance effect caused by stress release in the sampling process of marine water-soluble gas deposits. The change of shear wave velocity(Vs_lab/Vs_insitu) before and after unloading disturbance and its correlation with the rate of void ratio ( ) were investigated, and the feasibility of using the shear wave velocity method to quantitatively evaluate the quality of marine sediment samples was also discussed. The results show that the shear wave velocity of sand decreased significantly due to the unloading disturbance; and the change in void ratio of sand Δe presented a "S-shaped" curve with the increase of unloading amplitude. Moreover, the shear wave velocity ratio had a good relationship with the rate of void ratio before and after the unloading disturbance. The results of sample quality evaluation based on the shear wave velocity method are consistent with those from the method proposed by Lunne, which is based on the change rate of void ratio. This work provides a beneficial reference for the sample quality evaluation of sediments in the marine geotechnical engineering.

The liquefaction of small earth-rock dam slope under earthquakes is easy to cause serious consequences, such as instability and sliding of the dam slopes. Densification is one of the most commonly used anti-liquefaction methods. Two centrifuge shaking table tests were carried out to analyze the seismic response of small earth-rock dam slopes using two different densification methods, dam toe weight and dam shell compaction, respectively. The test results show that due to soil soften at the bottom of dam slope under the high water head, the acceleration amplification factor of the untreated dam slope decreased firstly and then increased along the elevation, while the acceleration amplification factor of the densified dam slope gradually increased along the elevation. There is a phenomenon of the surface amplification effect. The dam toe weight and dam shell compaction can increase the effective stress, reduce the excess pore pressure ratio caused by the earthquake, and effectively prevent the occurrence of liquefaction. Liquefaction occurred at the toe of the untreated dam slope under the earthquake peak acceleration of 0.24g, while the densified dam slope did not liquefy under the peak acceleration of 0.24g and 0.45g. The untreated dam slope had globally large lateral displacement, while the densified dam slope had mainly global vertical displacement under the peak acceleration of 0.24g after densification. The horizontal displacement of the dam toe in the dam toe weight area was significantly reduced, and the settlement of the dam slope crest in the dam shell compaction area was reduced by 50%. The test results verify the anti-liquefaction effect of dam toe weight and dam shell compaction, and provide references for seismic strengthening design of small earth-rock dams.

The dredged slurry has high water content and very low strength. It is generally considered that there will be no smear effect when the PVD is inserted. However, the dense "soil column" will be formed rapidly around the PVD under the vacuum pressure, which will greatly reduce the drainage capacity and fail to consolidate, i.e. clogging. The clogging effect of vacuum preloading on the dredged slurry is studied through laboratory tests. Based on the drainage volume and rate with consolidation time in the test, the formation time and the range of clogging zone are determined by the spatial and temporal distribution of the water content and permeability coefficient of soils. A vacuum transfer mode considering the clogging effect and the time effect is proposed. At the same time, considering the nonlinear relationship between the compressibility and the permeability of soils, an analysis model for analyzing the consolidation considering the clogging effect is established and the corresponding analytical solutions are obtained. The validity of the analytical solution is verified by comparing with the existing data and field test results. The influence of vacuum transfer mode, λ and c on the final settlement is analyzed by using the analytical solution in this work. The results show that the clogging effect obviously slows down the settlement rate and greatly reduces the final settlement of dredged slurry.

At present, the saturation line of a tailings pond is mostly solved by the method of numerical simulation or model experiment, and there are few analytical solutions reported in the literature. In view of this, a simplified calculation model of the saturation line of a tailings pond is established in this paper. Particularly, the differential equations of the saturation line are derived by using the energy equation and Darcy's law of permeability, and the upstream and downstream boundary condition equations are established. On this basis, the analytical solution to the saturation line of tailings pond is achieved (Note: due to the Dobby's assumption in the derivation of the solution, the analytical solution is mostly suitable for the tailings pond with slight slope). By comparing with the numerical simulation results, the analytical solution is verified. Considering the complexity of a tailings pond, the influence facts on the distribution of the saturation line of a tailings pond are analyzed, such as the tailing sand anisotropy, tailing sand stratification and bottom slope topography. The applicability of the analytical solution to complex tailings pond is discussed. Finally, the validity of the analytical solution in the paper is verified by the tailings pond example.

Lots of practical projects have revealed that the accurate calculation of lateral pressure at rest in the under-consolidation stratum plays a crucial role in the stability analysis and safety design. Therefore, this paper investigates the evolution of lateral pressure at rest during consolidation in detail by theoretical analysis and numerical simulation. The relationship between the lateral pressure at rest and the overconsolidation ratio (OCR) is established, and a new method for calculating the lateral pressure at rest in the under-consolidation stratum is proposed. A new concept of equivalent earth pressure coefficient at rest is introduced in consideration of OCR effects. The proposed method is validated by the results of numerical simulation and laboratory tests. Moreover, the proposed equivalent earth pressure coefficient achieves a unified method for calculating the lateral pressure at rest in the both under-consolidation and normal consolidation stratums. The results reveal that the lateral pressure at rest in the under-consolidation stratum decreases linearly with the increase of OCR, and such OCR effect becomes more obvious as the effective friction angle of soil increases. The results of this paper could technically support the calculation of earth pressure in the under-consolidation stratum.

The riverside groundwater level has a unique characteristic of low for long term working conditions but extremely high during flood seasons. This characteristic should be properly taken into account for designing a safe and economical anti-float scheme. For riverside underground structures, it will be dangerous when uplift piles or uplift anchors are adopted, taking the surface elevation as the anti-floating waterproof position. On the other hand, if uplift piles or uplift anchors are designed according to 50- or 100-years recurrence intervals, it is obviously uneconomical and the cost can be extremely high. Therefore, the definition of riverside underground structures and a new anti-float method on the combination of drainage corridors and uplift piles or anchors are proposed in this paper. Besides, considering the effect of leakage recharge, a simplified analytical approach of riverside drainage corridor based on circular pond formula is also put forward and verified by the finite element method. The drainage corridors are adopted to ensure the stability of water load on the underground structure and to eliminate the extreme water load caused by high water pressures during the flood season. In contrast, the conventional measures such as uplift anchors and piles will be adopted for anti-float during non-flood period. The drainage corridors only work during the flood season with high water levels, thus it will not cause environmental problems and its durability can also be easily guaranteed. In the end of this paper, an engineering application project adopting the proposed anti-float method is introduced.

In the process of static piling, there will be a strong soil squeezing effect, which will cause disturbance and deformation of the soil around the pile and the adjacent underground cable tunnel. If the deformation is too large, it may destroy the waterproof structure of the tunnel, causing leakage and seriously affecting the normal use and safety of the tunnel. Based on the theory of cylindrical hole expansion and the method of foundation bed coefficient, the theoretical calculation method of stress and horizontal displacement of surrounding strata and adjacent existing cable tunnels under the action of static piling in saturated soft soil areas are firstly studied. Secondly, considering the effect of group pile, the theoretical calculation method of horizontal displacement of adjacent existing cable tunnels caused by a single row of group piles construction is deduced, and the range of influence coefficient of group pile effect is studied. Finally, the theoretical calculation and numerical simulation of practical engineering problems are carried out. The results show that the method proposed in this paper can effectively calculate the horizontal displacement of adjacent existing cable tunnels, and the results are in good agreement with the numerical simulation results. The research can provide a reference for the prediction and protection of the disturbance to cable tunnels in the construction of adjacent pile foundations.

It has been realized that the points collected twice by the laser scanner for the same target do not coincide, and the landslide displacement cannot be quickly determined by direct comparison of the point cloud. Because the position of a single point cloud is uncertain and the density of regional point clouds is stable, the density of the point cloud can be used as the characterization of the deformation of the landslide surface. The article proposes a landslide displacement monitoring method based on point cloud density characteristics. First, the discrete three-dimensional point cloud is converted into a two-dimensional density image. Then, the particle image velocimetry technique is used to analyze the correlation between the two point cloud density images before and after displacement, thereby to calculate the relative displacement value of each subset in the raster image. When the entire displacements of each subset are calculated, the plane displacement field of the target area is obtained. The indoor block movement test shows that the calculation accuracy of this method is affected by the deformation gradient, which will produce a certain degree of error at the place where the ground surface changes drastically, and the subset correlation coefficient cannot reach 1.0. In the displacement monitoring of the Huangzangsi landslide, the method was used to identify the changing area of the slope, and the plane displacement field of the landslide was calculated. The calculation results intuitively reflect the deformation of the landslide surface, which verifies the practicability of the proposed method.

In order to study the formation and development mechanism of surface subsidence in Chaganaobao iron-zinc mine, Rongguan mining industry, Inner Mongolia, a detailed engineering geological survey was carried out in the mining area. The occurrence of structural planes of skarn and tuff were statistically analyzed by using software Dips. Based on the investigation results of subsidence pit and underground goaf, the formation and development mechanism of surface subsidence were analyzed in detail. The results show that: (1) there are three and four groups of dominant structural planes of skarn and tuff in the mining area, and the dip angles of structural planes vary from 77°to 81° and from 85°to 90° respectively. (2) The collapse pit forms a steep free face of rock mass on the three sides of the east-west and the south, which is mainly destroyed and collapsed in the form of dumping. Step type landslide is formed in the north side of the collapse pit, which is mainly destroyed in the form of arc-shaped landslide. (3) The formation mechanism of subsidence pit is mainly divided into four stages: natural stability stage - caving formation stage - caving extension stage - surface subsidence stage. The west, south and east sides of the collapse pit consist of three development stages: unloading rebound stage, fracture opening stage and fracture surface collapse stage. The development stages of the north side of the collapse pit include unloading rebound stage, compressive tensile crack bottom-up cracking stage and slip surface through slip stage. (4) A steep slope is formed at the footwall of the ore body, and a large number of fractures with different sizes and widths are generated along the strike of the ore body (NE30°), including some staggered fractures. The formation of surface subsidence is determined by multiple factors, among which the unique geological condition is the internal cause, whereas the underground mining activity acts as the inducement. The internal and external factors together account for the formation and development mechanism of the subsidence pit. (5) Subjected to the active toppling failure and passive traction of the surface soil arc landslide in the north side, the rock and soil masses in the northeast side of the collapse pit have experienced a special form of toppling failure. The findings of this paper provide references for mine safety production and collapse pit treatment.

Thermosyphon is one of the important measures for thermal protection of the embankment in permafrost region. But the design method of the thermosyphon embankment is not provided in relevant standards. Therefore, the design of the existing embankments with thermosyphon mainly depends on the past engineering experience. Through field monitoring and theoretical calculation, the characteristics of heat exchange balance for the embankment in frozen soil region were analyzed. It was found that the embankment absorbs heat in warm season, but releases heat in cold season, and it was in the endothermic state for the whole year. The essential reason of the embankment thawing settlement is that the heat absorption is greater than heat release. A new design method of thermosyphon embankment was proposed based on the theory of heat balance. Its basic principle is to ensure the thermosyphon annual heat transmission capacity which is not less than the embankment net heat absorption. Taking the highway engineering in permafrost region of Qinghai-Tibet Plateau as an example, the design method proposed in this paper was verified by field test. The results show that the settlement of the thermosyphon embankment designed using the proposed method was significantly less than that of the ordinary ones. The thermosyphon embankment has improved the stability of the underlying permafrost and mitigated the settlement of the foundation permafrost. That verified the correctness and rationality of the method proposed in this paper. This method has clear theory, simple parameter acquisition and strong engineering application value, which can be widely used in design of the thermosyphon embankment in permafrost region.

The high-bench dump of wide-graded waste rock formed by slope-to-the-bottom has obvious particle size grading characteristics. Traditional stability analysis methods usually simplify it to multi-layer isotropic homogeneous soil, and substantially ignore the uneven and random distribution of each particle group in the dump. This makes it difficult to obtain a reasonable conclusion about the slope stability. Relying on the high-bench dumping site of a copper mine in Jiangxi, with the help of self-edited cellular automata program EPOHHM, five groups of narrow-graded coarse-grained soils are used to characterize the particle size grading phenomenon of high-bench dump, and to simulate the non-uniformity and randomness of the granular media material in each particle group. The displacement field and plastic state of the dump site under different working conditions are analyzed, and the safety and stability of the dump site slope under different dumping modes are systematically discussed. A detailed analysis method for the stability of a high-step dump with wide-graded waste rock is proposed. The research results show that the “tension-shear” failure occurs in the dump; the middle-upper part of the soil has an arc-shaped landslide trend, the deformation of the lower part manifests as settlement, and the top platform produces tensile and shear cracks. Considering only the mechanical strength of the granular media material, increasing the content of coarse particles(d>100 mm) at the bottom plays a significant role in stabilizing the dump. The "full section height dump of single-step" dumping mode is more conducive to the safety and stability of the high-bench dump with wide graded waste rock than "full overlay dump of multi-step". The research results will provide guidance for ensuring the long-term safety and stability of the dump with obvious particle size grading, and also provide a reference for the future analysis of similar engineering problems.

Staggered zones have the properties of “multiple shear dislocation in history, wide range, easy to soften when exposed to water and low mechanical strength”, which cause rock masses with staggered zones to easily induce varying degrees of deformation and failure under excavation unloading. It seriously affects the stability of the underground caverns. In order to study the collapse of rock masses with staggered zones in the underground caverns on the right bank of Baihetan hydropower station, we adopted microseismic (MS) system to study the microseismicity in the process of collapse, including spatiotemporal evolution of MS events and distribution characteristics of magnitude and apparent stress. We analyzed the fracture mechanisms (tension, shear or mixed) of rock masses through moment tensor theory, and summarized the evolution process: surrounding rock tension fracture → fractures gradually extend deeper → fractures initiate and expand in the direction of staggered zones (mainly tensile fractures, accompanied by shear or mixed fractures) → the fractures merge with the staggered zones, then unstable wedges are cut → the rock masses with staggered zones collapse under the blasting vibration or gravity. This paper provides references for the excavation and support of rock masses with staggered zones in underground intersecting chambers under high geo-stress, and also provides guidance for the construction of similar projects.

Natural rock and soil have complex mesostructure and composition characteristics, and it is difficult to model geotechnical mesostructure, which has specific particle size, aspect ratio, dip angle, and plane distribution characteristics. For this reason, a method is introduced to use four connected arcs to approximate the shape of an ellipse, combining with improved advancing front method. A highly dense ellipse packing allowing any size, aspect ratio, orientation angle, and spatial distribution is generated by this method. Based on the ellipse packing generated, a complex geotechnical mesostructure with imposed elliptical particle size, aspect ratio, dip, and plane distribution characteristics is generated. A comparison between the proposed method and two traditional methods (optimized dropping and rolling method (ODR) and advancing layer algorithm (ALA)) shows that the ellipse packing generated by the proposed method has a higher density and faster speed than that generated by ALA and ODR, with a packing efficiency of 500-600 s in the MATLAB environment. Compared with the size distribution generated by GBM in modeling mesostructure of rock and soil, the method proposed in this paper can consider four factors (i.e., particle, size, long-to-short axis ratio, dip angle, and plane distribution). The method can construct a convex-based structure equivalent to real rock and soil. Two application cases show that the method proposed in this paper can improve the modeling accuracy and efficiency from the current geotechnical model.

The original discontinuous deformation analysis (DDA) takes the first-order approximation of the incremental displacement to update block configuration, deduces related sub-matrices, and directly superimposes the incremental strains calculated at different time steps, which generates significant errors when simulating large rotation of a block. In order to consider the coupling effect of block rotation and deformation, a modified incremental displacement formulation is introduced, which calculates the displacements caused by the strains before the rigid-body rotation term. The sub-matrix of the inertial force is then modified, and the centrifugal and Coriolis forces are added to the load matrix. In the calculation, the coordinate transformation is carried out for the strain components and its related variables, and the newly introduced displacement formulation is used to calculate the displacements of block vertices. After that, the post-adjustment and post-contact adjustment are used to update the block configuration. The numerical examples indicate that the modified DDA can eliminate the errors caused by large rotation, automatically consider the deformation caused by centrifugal and Coriolis forces of the rotating block, and the precision of strain calculation is higher than that of original DDA. The modified codes overcome the free volume expansion and strain distortion problems, and give a reasonable block strain.

The purpose of this study is to model the caisson in clay from a complete finite element analysis to a simplified microelement modeling. First, the finite element method is used to analyze the caisson foundation in clay under different monotonic combined loadings. To ensure the reliability of the simulation results, the hardened soil model (HS) is adopted to simulate the normally consolidated clay. The effectiveness of the finite element analysis using the HS model is verified through comparing with centrifugal tests, and the swipe tests with radial displacement control is further extended to the study of failure modes in V-H-M (vertical force-horizontal force-bending moment) space. A three-dimensional failure envelope formula for the caisson foundation in clay in V-H-M space is proposed. Then, using this three-dimensional failure envelope formula, a macroelement design model for the caisson foundation in clay is proposed using a hypoplastic framework. By comparing with the experimental results, the validity of the strength and deformation response of the caisson foundation under simulated monotonic and cyclic loading conditions are verified. The proposed macroelement based model is practically useful in marine geotechnical design.