In order to further explore the dynamic behaviors of outburst coal-gas two-phase flow under different roadway layouts, the self-developed multi-field coupled coal mine dynamic disaster large-scale simulation test system was used to carry out coal and gas outburst tests under the T-shaped roadway layout. The tests obtained the evolution law of impact force and static pressure during the migration of outburst coal-gas two-phase flow in the roadway. The results show that the impact force in the straight main roadway shows a trend of multi-peak oscillation and attenuation over time, reflecting the pulse characteristics of the outburst process. The closer to the outburst hole, the more impact force oscillation times. The impact force in the branch roads on both sides of the bifurcation has two evolutionary trends in the early stage. One is that it increases rapidly to the peak and then decreases slowly, and the other is that it increases slowly and then decreases slowly. Larger impact force values appear at 1 500 mm from the left side of the bifurcation structure and at 500 and 1 900 mm from the right side, indicating that these areas are severely dangerous. The whole process is divided into two stages of single-phase flow and two-phase flow by using the outburst motion image. In the single-phase flow stage, the impact force after the bifurcation structure firstly rises rapidly to the peak value. The impact force before the bifurcation structure rises to a peak point in the two-phase flow stage. There is a phenomenon that the peak value of the impact force after the bifurcation is higher than that before the bifurcation. During the outburst process, the static pressure value on the wall of the roadway is generally low. The static pressure fluctuates intermittently with time, and the peak value from near the coal seam to far first increases and then decreases. The time when the static pressure in the straight main roadway reaches the peak value is delayed with the increase of the distance from the outburst hole. The evolution of the static pressure on the left and right sides of the branch roadway is similar. As time progresses, the static pressure attenuation before and after the bifurcation structure gradually increases.

Considering the influence of soil thickness, the vertical vibration response of rigid strip footings on viscoelastic soil is theoretically investigated. Based on the assumptions for footing and foundation with rigid bedrock boundary condition, employing the method of Fourier transform, this mixed-boundary value problem is expressed as a pair of dual integral equations, which are transformed to a set of linear equations by means of Jacobi orthogonal polynomials and solved numerically. The solution in this study is compared with the solution of elastic half-space in the literature to verify its rationality. The results demonstrate that the attenuation of ground waves generated by the vibration of the footing, as well as the variation in dynamic compliance coefficient of the foundation, is sensitive to the thickness of the foundation soil layer. The numerical results suggest that considering the foundation soil as infinite half-space, as in existing solutions, is reasonable only in cases where the thickness of the top soil layer exceeds approximately fifty times the width of the footing.

The pore size structure of soil specimen can be divided into unimodal, bimodal and even multimodal pore size distribution. The soil specimens with bimodal pore size structure usually show bimodal soil-water characteristic curve (SWCC). Many existing bimodal SWCC models are obtained through the method of segmented or superimposed based on the unimodal SWCC model. It is often difficult to accurately determine the relevant parameters at the intersection of two SWCCs, and the influence of void ratio on water characteristics of bimodal soil is seldom considered. In this paper, the characteristic of unimodal SWCCs and bimodal SWCCs with different initial void ratios in a wide suction range are analyzed and discussed in detail. Secondly, based on the above analysis of soil water characteristics and the two different mechanisms of adsorbed water and capillary water, the adsorption term equation is derived in the form of exponential function with the combination of Kelvin equation, and the capillary term equation is based on the modified Fredlund and Xing SWCC model. Finally, a bimodal SWCC model considering the effect of initial void ratio is proposed, and the proposed model is applicable to various soil types ranging from sands to silt and clayey soils.

The concentrated solution sludge (CSS) produced by submersion combustion process has special characteristics, such as high water content, low organic matter and heavy metals content and extremely high salinity. In this study, sulfoaluminate cement (SAC) was used as the main curing agent, and two kinds of waste incineration fly ash and bottom ash were added as auxiliary curing agents to quantificationally investigate the influence of different curing agents on the solidification effectiveness of CSS, and various solidified CSS samples with a variety of curing agent combinations were prepared for a series of unconfined compressive strength tests, water stability tests and microscopic observation tests. The results show that the strength of CSS solidified with 10% SAC can meet the strength requirement (50 kPa) of landfill under the condition of 7 d curing age; the 28 d strength of the cement solidified samples meet the requirement of water stability as the SAC content exceeds 50%. The optimal dosages of fly ash and bottom ash of 28 d solidified samples are 5% (SAC content <40%) and 10% (SAC content ≥40%). Bottom ash is more effective than fly ash for improving water stability of solidified samples. The SEM and XRD results show that the formation of interlocked structure composed of hydration product of cement and ettringite crystal generated from the interaction between SAC and fly ash or bottom ash, is the major factor improving the water stability of solidified samples with a certain dosage of fly ash or bottom ash.

The critical state of structural loess is related to its initial void ratio, which causes the non-unique critical state line that can be described by an index “spacing ratio”. However, Modified Cam-clay model and its enhanced models show unique critical state line, which make it unable to capture the critical state and strain-softening of intact loess. To solve the issue, this paper conducts the investigation for the spacing ratio of intact loess and model prediction for the mechanical behaviors of intact loess. Firstly, the calculation method of the spacing ratio is given, and the values of the spacing ratio corresponding to different void ratios are calculated from triaxial undrained compression test results on intact loess. It was found that there exists an inversely proportional relationship between the spacing ratio and the void ratio. The physical meaning of the spacing ratio is also clarified. Secondly, a modified model is obtained by introducing a hardening parameter into a framework of structure bounding surface plasticity model considering spacing ratio. In the modified model, the various values of spacing ratio represent non-unique critical state line, and the structural decay of intact loess is accomplished by coupling the effect of plastic deviatoric strain and plastic volumetric strain. The modified model well predicts the critical state, strain-softening, stress paths, and pore pressure of intact loess. The above results show that the physical meaning of the spacing ratio is clear, and its role in predicting critical state is reliable. If the spacing ratio is considered in a constitutive model, it can well capture the critical state of intact loess. The conclusions have theoretical and practical meanings for numerical analysis of geotechnical engineering in loess area.

In order to study the erosion effect of in-situ leaching mother liquor on the receiving floor of ionic rare earth ore, an indoor leaching simulation test was carried out with the bedrock of ionic rare earth ore (semi/weakly weathered granite) as the research object. The stress-strain curves, peak stress, peak strain and elastic modulus of rock samples for different leaching durations are compared and analysed, the porosity and micro morphology characteristics of rock samples for different leaching durations are obtained, and the nonlinear crack characteristics of rock samples are described quantitatively by box dimension method. The results show that the effect of leaching erosion on the mechanical properties of the bedrock of the floor of ionic rare earth ore is mainly manifested in the first 150 days, and the failure form changes from penetration failure to the coexistence of penetration failure and flaky spalling. Under the erosion of ore leaching mother liquor, the mechanical properties of bedrock first decrease greatly and then rise sharply, and then fluctuate in a small range. About 60 days of ore leaching has the greatest impact on the mechanical properties of bedrock. The erosion of ore leaching mother liquor causes the growth of small pores in the bedrock, resulting in corrosion and holes on the surface. Different leaching durations will cause different microstructure changes of rocks.

Based on the upper bound limit analysis method, the three-dimensional seismic stability of inhomogeneous soil slope is investigated using the pseudo-dynamic approach, and the explicit expression of the factor of safety is obtained by gravity increase method (GIM). In addition, the genetic algorithm is used for optimization and the results are verified by comparing with other published data. Parametric studies are performed to investigate the effect of relevant parameters on stability of the slope. The results indicate that for the slope with the given height, the increase of width-height ratio and slope inclination angle, and the decrease of internal friction angle and inhomogeneous coefficient will lead to the reduction of factor of safety. The pseudo-static method yields a larger result compared with the pseudo-dynamic method, and the difference between the results of the two approaches increases with the increases of the horizontal seismic coefficient and the effective internal friction angle, but decreases with the increase of the slope inclination. The increasing of the soil amplification factor can lead to a significant decrease in the factor of safety of the slope, while changes in the period and velocity of the shear wave have little effect on the stability of the slope. The trace of the slip face is greatly influenced by the horizontal seismic coefficient, but less affected by the inhomogeneous coefficient.

Soil tends to have nonlinear compression characteristics, and the consolidation laws of soil are different under different compression characteristics. Considering the nonlinear characteristics of soil, variable load and continuous drainage boundary conditions, a one-dimensional consolidation equation is established. Its solutions are obtained by using the unconditionally stable finite difference method and semi-analytical method, and the reliability of the two methods is verified by the degradation of continuous drainage boundary condition and the comparison of the two solutions. Based on the solution of finite difference method, the influences of interface parameter, load parameters and nonlinear parameter on soil consolidation are analyzed in detail. The results show that, the larger the interface parameter of continuous drainage boundary, the greater the dissipation rate of excess pore water and the settlement rate of soil, while the interface parameter has no effect on the final settlement. The excess pore water pressure gradually increases at the loading stage and dissipates at the constant loading stage. With the increase of loading rate, both the peak value of excess pore water pressure and soil consolidation rate increase, indicating that extending the construction period is conducive to reducing the influence of excess pore water pressure. It is difficult to accurately predict the consolidation rate of soil in engineering. The accuracy of soil model, boundary conditions and soil calculation parameters should be ensured when the consolidation theory is used.

Composite pile refers to a new pile type generated by two different materials through a dual construction way. The composite pile is composed of two materials with different properties, which play a complementary and reinforcing role. Taking the composite ground improved by the concrete-cored sand-shell composite piles as the research object, the composite pile is transformed into an equivalent ring element based on the principle of constant cross-sectional area and perimeter. The core-pile ratio, i.e., the ratio of the concrete core and composite pile cross-sectional area was introduced, and the construction disturbance and the depth-dependent stress increment caused by time-varying surcharge loading was considered. A consolidation analytical model of the composite ground with composite piles was proposed based on the equal strain assumption and the Darcy’s law. Furthermore, explicit solutions under four different load conditions were obtained. Finally, the consolidation behaviors of the composite foundation were investigated by a series of parameter sensitivity analysis. The results show that the hollow ratio of the square section pile is the smallest and the excess pore water pressure dissipates fastest among the square piles with a certain circumference. The foundation consolidation rate is positively correlated to the core-shell compression modulus ratio and permeability coefficient ratio. With the increase in the top load, the consolidation rate gradually increases.

A coupling condition of cyclic major and intermediate principal stresses was applied to simulate the coupling of vertical cyclic normal stress with the horizontal cyclic normal stress parallel to the road direction under traffic load in three-dimensional stress space. A stress path with coupling of cyclic major and intermediate principal stresses was then proposed, and the coefficient of cyclic intermediate principal stress bcyc was defined as the characterization parameter of cyclic stress path. A series of undrained cyclic true triaxial tests under coupling of cyclic major and intermediate principal stresses was performed in normally consolidated saturated soft clay by GDS cyclic true triaxial apparatus. The effects of coefficient of cyclic intermediate principal stress and cyclic stress ratios on the long-term shakedown characteristics of normally consolidated soft clay under undrained conditions were analyzed. The experimental results show a significant increase of resilient modulus induced by increasing the coefficient of cyclic intermediate principal stress, which restrains the development of cumulative major principal strain. The cumulative major principal strain has a linear relationship with the coefficient of cyclic intermediate principal stress in the three-dimensional stress state. On the basis of the shakedown theory, the allowable cyclic stress ratios under coupling of cyclic major and intermediate principal stresses were determined, and it was also found that the allowable cyclic stress ratios increased with increasing the coefficient of cyclic intermediate principal stress.

To investigate the fracture mechanical behavior and failure mechanism of jointed rock mass under compression and shear load, shear tests were carried out on intact and discontinuous jointed granite. The macroscopic mechanical properties, acoustic emission signal characteristics and mesoscopic evolution law by particle flow simulation were analyzed through the experiment. A method predicting shear failure of granite was proposed by using the acoustic emission signal characteristics and its key information points. The results show that the rock integrity is damaged by the joint, and the shear modulus and peak shear strength of the rock are reduced. In addition, the existence of joints will affect the propagation path and failure mode of cracks, and the influence will be weakened with the increase of normal stress. The normal stress and joints have significant effects on the acoustic emission characteristic points. The slow growth of acoustic emission signal and the continuous decline of b value can be used as the precursor characteristics of rock shear failure. The acoustic emission signal characteristics and its key information points can be used to effectively predict the shear failure process of granite. The research results provide a reference for the shear failure mechanism analysis and stability prediction of jointed rock mass.

The anti-seepage performance of capillary barrier covers (CBCs) has been widely studied because of its importance in controlling leachate and mitigating pollution in the surrounding environment of landfills. However, the effect of rainfall pattern on the anti-seepage performance of CBCs has often been neglected in previous work because the constant rainfall intensity is usually used to simulate rainfall. Therefore, this study investigates the effect of rainfall patterns on the anti-seepage performance of CBCs and reveals its most unfavorable rainfall pattern under two types of rainfall conditions, namely short and heavy rainfall (SHR) and prolonged light rainfall (PLR), by using the self-developed soil column rainfall infiltration test system. In addition, the SEEP/W software was used to numerically simulate each test condition so that the simulation results and the test results could corroborate each other. The results show that the test results are basically consistent with the simulation results, and the maximum error is no more than 3%. The rainfall pattern only has a significant effect on the volumetric water content and pore water pressure in the upper part of the CBCs for SHR, while for PLR, the rainfall pattern has a significant effect on the volumetric water content and pore water pressure of the whole soil column. The rainfall pattern has an effect on both the breakthrough time and the leakage amount of the CBCs. The breakthrough time of the advanced rainfall is the shortest and the leakage amount is the largest, while the breakthrough time of the delayed rainfall is the longest and the leakage amount is the smallest. Advanced rainfall is the most unfavorable rainfall pattern, which is more likely to cause the CBCs breakthrough failure and produce large leakage. The research results can provide a reference for the design of CBCs.

The uneven distribution of organic matter in oil shale strata results in different mechanical response and failure mechanism. Uniaxial compression test, digital image correlation and infrared thermal imaging were used to study the deformation field, temperature field and energy evolution characteristics of oil shale during the whole loading process under different organic matter abundances, and to reveal the influence of organic matter abundance on mechanical properties and deformation and failure mechanism of oil shale. The results show that the stress-strain characteristics of oil shale present gradual attenuation as the organic matter abundance increases, while the ductility has improved significantly. The failure mode changes from splitting tensile failure to tension-shear compound failure, which is attributed to the fact that organic matter abundance affects the control degree of bedding planes on the macroscopic crack evolution. Moreover, the deformation field and temperature field exhibit obvious localized features during loading. With the increase of organic matter abundance, the surface deformation and infrared temperature increase, and the degree of differentiation of the two fields also intensifies. In addition, organic matter abundance also affects the energy transformation and distribution of oil shale. With the increase of organic matter abundance, the energy absorption, storage and release properties weaken, while the dissipation property enhances, causing a lower overall energy state. This is the essential reason for the differences in mechanical properties and deformation and failure laws of oil shale with different organic matter abundances.

Geotechnical site investigation may obtain the data of multiple soil parameters. These data for different soil parameters are cross-correlated and spatially correlated in the three-dimensional space. How to effectively use these site investigation data to quantify the uncertainties of soil parameters remains a challenging issue. To address this issue, this paper proposes a joint probability density function (PDF) estimation method of geotechnical parameters based on multi-source site investigation data with consideration of the three-dimensional spatial variability of these geotechnical parameters. The paper first briefly reviews the PDF estimation method based on multi-source investigation data at a single sounding that only considers the spatial variability in the vertical direction. The Gibbs sampler-based method is then proposed to estimate the joint PDF of geotechnical parameters based on multi-source site investigation data at multiple soundings by taking the three-dimensional spatial variability of these soil parameters into consideration. A simulated virtual site and a practical site at Texas USA are employed to demonstrate the performance of the proposed method. It is shown that the proposed method can provide an effective tool for uncertainty quantification with multi-source investigation data. Compared with the single sounding method, the proposed method can effectively reduce the statistical uncertainty.

For the problems existing in the traditional single discontinuity based clustering model, such as the risk of misclassification or omission and the inability to identify noise and isolated values, a dominant partitioning method of rock mass discontinuity based on selective clustering ensemble using density-based spatial clustering of applications with noise (DBSCAN) algorithm is proposed. Firstly, the spatial coordinate transformation is performed with the attitude of discontinuity, and the sine of the angle between the unit normal vectors is defined as similarity measurement. Then, a certain number of different base clusters are constructed based on the DBSCAN algorithm, with the selective clustering ensemble technology, some excellent base clusters are selected. Finally, the consistent ensemble technology is used to fuse these base clusters to generate a highly reliable selective clustering ensemble result. The DIPS software data set and the discontinuity survey result in the dam site area of Songta hydropower station are used to test the feasibility and effectiveness of the proposed method. The research results show that the clustering effect of the proposed method is significantly better than that of common clustering algorithms. The clustering results are objective and reasonable. It not only effectively identifies noise and isolated values, but also overcomes the shortcomings of over-segmentation or under-segmentation of the single discontinuity based clustering model. The research results are valuable in accurately determining the dominant group of discontinuity.

In recent years, seismic damage caused by sand liquefaction occurred frequently in earthquakes. Sand liquefaction has become the focus of earthquake engineering. It is of great significance to develop a method for evaluating liquefaction based on the cone penetration test (CPT) with good application prospects to prevent liquefaction damage. This paper tests the CPT liquefaction evaluation methods through the collected 171 sets of liquefaction data of 15 earthquakes, and analyzes the problems of these evaluation methods, and proposes a new liquefaction evaluation formula of hyperbolic model based on data regression optimization. Extracting 147 sets of liquefaction data of the 2011 New Zealand earthquake to test the new formula, the results show that the new formula has a high and balanced discriminant success rate for different seismic intensities and buried depth of sand, and also overcomes the disadvantages in the existing liquefaction evaluation methods. The new formula proposed in this paper has been adopted into the revised content of the latest The General Rule for Performance-based Seismic Design of Buildings and can provide theoretical basis and support for the revision of relevant specification and engineering applications in China in the future.

Material grading design, dam zoning and filling design criterion are the basis for dam material design and evaluation in gravel dam projects, which currently rely heavily on engineering experience. In this paper, the typical gradation envelope range of actual engineering dam sand and gravel materials are first analyzed based on the statistics on gravel grading envelope and field dry density from typical engineering dams. Then, the distribution intervals of key gradation characteristic parameters are given, and the influence of gravel gradation characteristics on compaction properties is studied. The results show that: i) The maximum particle size of typical dam-building sand-gravel grading is 400−600 mm; the gravel content of the common grading envelope is 70%−88%; the curvature coefficient is 1−10; the non-uniformity coefficient is more than 5; and the parameters b and m in the gradation equation range from 0 to 0.9 and 0.2 to 1.0, respectively. ii) The gradation of sand-gravel material that can obtain higher filling dry density should satisfy: the gravel content is 70%−85%; the curvature coefficient is 1−10; the inhomogeneity coefficient is greater than 5; and the b-value and m-value of the gradation equation parameters are 0.7−0.9 and 0.6−0.9, respectively. iii) Gravel content, curvature coefficient, inhomogeneity coefficient and maximum particle size all have significant influences on the dry density, and the degree of effect decreases in order.

In engineering practice simplified methods are essential to the seismic design of embedded earth retaining walls, as fully- dynamic numerical analyses are costly, time-consuming and require specific expertise. Recently developed pseudostatic methods provide earth stresses and internal forces, even in those cases in which the strength of the soil surrounding the structure is not entirely mobilised. Semiempirical correlations or Newmark sliding block method provide an estimate of earthquake-induced permanent displacements. However, the use of these methods is hindered by uncertainties in the evaluation of a few input parameters, affecting the reliability of the methods. This study uses 1D site response analyses and 2D fully-dynamic finite element analyses to show that simplified methods can provide a reasonable estimate of the maximum bending moment and permanent displacements for stiff cantilever walls embedded in uniform sand, providing that a few input parameters are evaluated through semiempirical correlations and a simple 1D site response analysis.

At present, the existing theoretical research on the seepage field around the subsea shield tunnel under the action of waves generally considered the lining as impermeable medium, and rarely studied the permeability of the tunnel lining, especially the influence of wave nonlinearity under the seabed slope terrain. Firstly, based on the dynamic boundary conditions of sloping seabed surface, the Biot’s consolidated pore water pressure response of free seabed under Stokes nonlinear wave is obtained. Secondly, the mirror image method is introduced to establish a governing equation of excess pore water pressure caused by the existence of tunnel, and the analytical solution of the equation is obtained by Fourier series expansion under the condition of continuous seepage between sand and lining. After that, the seepage response solution of the sand around the tunnel in the sloping seabed under the action of Stokes wave is obtained based on the superposition principle. Finally, the theoretical analytical solution is compared with the numerical results and the existing experimental results, and a good agreement is obtained. In addition, the influencing factors of wave sensitive parameters (wavelength, period and shape), seabed sensitive parameters (seabed permeability, shear modulus, saturation and slope) and tunnel sensitive parameters (lining thickness, permeability and buried depth) are analyzed. The results show that the excess pore water pressure outside the lining increases obviously with the increase of wave period and wavelength. As the water depth decreases along the seabed slope, the difference of wave pressure obtained by Airy wave and Stokes wave theory increases significantly within the applicable range (d/L＞0.125, where d is the water depth, and L is the wavelength), and the former will underestimate the excess pore water pressure around the tunnel. When the seabed permeability coefficient is large (k_s＞1×10⁻² m/s), the increase of wavelength and seabed saturation will increase the excess pore pressure outside the lining, while the increase of seabed shear modulus, seabed slope and tunnel buried depth will reduce the excess pore pressure outside the lining. Under the condition of inclined seabed with large slope angle, the excess pore pressure outside the tunnel lining shows an obvious asymmetric distribution. When the seabed permeability coefficient is small (k_s＜1×10⁻⁴ m/s), the excess pore water pressure around the tunnel is at a low level, and the influence of other sensitive parameters is not significant. When the permeability coefficient of tunnel lining is small (k_t＜1×10⁻⁶ m/s), the "blocking" effect of tunnel on the propagation of excess pore water pressure in sand is obvious, but when the permeability coefficient of lining is large (k_t＞1×10⁻⁴ m/s), and the excess pore water pressure in the sandy seabed around the tunnel is low. The influence of lining thickness on the distribution of excess pore water pressure outside the lining is not significant.

Limit analysis approach is one of the classical methods for the stability evaluation of geotechnical infrastructures. Low-order triangular elements with velocity discontinuities and special layout of mesh, or high-order triangular elements are usually used to overcome the volumetric locking problem encountered in the traditional finite-element upper bound limit analysis. However, the accuracy of this method depends heavily on the layout of discontinuities. In this study, a mixed constant stress-smoothed strain element is proposed to discretize the constrained functional of generalized variational principle, and a novel method of mixed constant stress-smoothed strain element limit analysis (MCSE-LA) is established for limit analysis. Following the associated flow rule and Mohr-Coulomb yield criterion, the novel MCSE-LA is finally converted to a second order cone programming (SOCP) that contains only stress variables and limit load multiplier. The MCSE-LA method has a simple representation form, and relatively few optimization variables, and in particular, there is no need for an explicit plastic internal energy dissipation function. Based on the duality of the convex optimization, the optimal velocity field and plastic multiplier can be solved in the dual problem simultaneously. Moreover, an adaptive mesh refinement algorithm is proposed based on the maximum plastic shear strain rate. This algorithm could refine the mesh in the plastic zone and significantly improve the computational efficiency and accuracy of the proposed method. Finally, by a comparative analysis of the slope stability problem, the proposed MCSE-LA method is verified to have higher computational accuracy and efficiency compared with the traditional finite-element limit analysis.

The new prestressed subgrade (PS) technology can be used to treat subgrade diseases or strengthen existing subgrades. It is of great significance to study the prestress loss law to ensure the long-term safety of PS project. Based on the elastic theory, an analytical method is developed to calculate the additional stresses on the horizontal path behind the center point of the lateral pressure plate-embankment slope interface. The analyzed results show that the horizontal additional stress on this feature path decreases with increasing the distance away from the center point in a good exponential relationship. According to the exponential diffusion law of the horizontal additional stress and the creep behavior of the subgrade soil, a formula is derived to calculate the creep deformation of the subgrade soil, and a prestress loss model and calculation method are then established for PS based on the deformation coordination of the embankment soil creep and steel bar contraction. Comparative analyses are consequently performed using the proposed method and FLAC3D numerical simulations. The results show that the theoretical prediction curves of the pre-tension loss of the steel bar is in good agreements with the numerical simulations with a deviation less than 5%, which indicates the effectiveness of the proposed prestress loss model of the PS. The pre-tension force of the steel bar stabilizes within 60 days after anchored, and the stable pre-tension force reaches 85%–90% of its initial value, which demonstrates that the new PS technology could provide considerable stable additional confining pressure for the subgrade soil, so as to strengthen subgrade by improving the stress state of the subgrade soil.

In homogenous half spaces, the wave-fields in the shallow depth are dominated by Rayleigh waves elicited by surface sources. When the forward Rayleigh waves encounter a shallow heterogeneity, the surface response spectrum over the heterogeneity is changed. When the length of the heterogeneity is significantly long compared to the wavelength of the forward Rayleigh waves, the effects of the stiffness contrast between the heterogeneity and the surrounding soil on the behavior of the diffracted waves are analyzed from the dispersion curves extracted from the spectrum performed on the surface response over the heterogeneity. Compared to Rayleigh waves in the half space containing the soft or hard soil layer, it can be found that the behavior of the diffracted waves is similar to that of Rayleigh waves. The spectral changes over the heterogeneity are related to the stiffness contrast. The phenomena of the spectral changes are explained using the displacement structure differences between the diffracted waves and the incident Rayleigh waves. It is shown from the results that the spectrum over the heterogeneity is obviously different from those in front of and behind the heterogeneity. In the offset-wavelength domain, compared to the spectrum in front of the heterogeneity, the spectral density decreases as a whole over a soft heterogeneity, while the spectral density increases over a hard heterogeneity. The location and the burial depth of a suspected heterogeneity can be estimated from the offsets and the wavelengths corresponding to the spectral changes, respectively. The type of the heterogeneity can be identified from the relative decrease or increase in the spectral density.

Cracking and fracturing of overlying strata are attributed to transformation of continuum medium into discontinuum medium or to evolution of discontinuum from the mechanical viewpoint. Accurate modeling of the motion process of overlying strata is especially important to control stability of strata and to predict and prevent some disasters. In the developed combined Lagragian-discrere element method (the continuum-discontinuum method), potential contact forces are reliable only if the normal stiffness coefficient is accurate. To model the mining process with long time and to solve the problem that assemblies composed of discrete elements of coal seams can still possess the excessive load-carrying capacity, a quasi-static calculation mode and a stress drop method were adopted. To accurately select the normal stiffness coefficient applicable to modeling of interactions of strata, the coefficient was firstly standardized to check errors due to the embedded amount between elements, then four groups (the upper relatively soft-lower relatively hard, the upper relatively soft-lower relatively soft, the upper relatively hard-lower relatively soft and the upper relatively hard-lower relatively hard) of numerical tests of contact and equilibrium processes of two rock blocks were designed, and one group as an example was analyzed in detail. Through examining evolution of the following quantities, such as the penetration of two blocks, the averaged stress at the lower end of the top block, and the duration from motion to equilibrium, a universal result was obtained, and the appropriate ratio of the normal stiffness coefficient to the elastic modulus was determined to be 15 m−1. In order to check reasonability of the suggested value for modeling the motion process of overlying strata in the stope, the working face 1141 in a coal mine was taken as an example. It is found that when the normal stiffness coefficient was selected as the suggested value, the calculation result is reasonable and the calculation efficiency is high.

The change of the soils around pile affected by scour is one of the major causes for the failure of structure of the partially-embedded single pile. The soil fields in engineering are mostly layered, and the research on the mechanical characteristics of pile foundation in layered soils has attracted increasing attention. In order to accurately reveal the effect of scour on the dynamic response of the partially-embedded single pile in layered soils, a dynamic model of the laterally loaded single pile in layered soils is established by employing Hamilton’s principle based on the modified Vlasov foundation model. Then, the finite difference method is used to solve the natural frequencies of the single pile affected by scour, and to achieve accurate modeling of the soil-structure interaction (SSI) system affected by scour. Analytical solution of the forced vibration of the single pile is obtained by Green’s function method. The effects of physical characteristics of the layered soils on the dynamic response of the partially-embedded single pile are studied by numerical calculation and parameter analysis. The results show that the dynamic model of the partially-embedded single pile in layered soils based on the modified Vlaosv foundation model can accurately predict the impact of scour on its dynamic characteristics. As the scour degree intensifies, the first-order natural frequencies of the single pile in layered soils decrease significantly, and the subgrade reaction coefficient of each layer of soils in the improved Vlasov foundation model decreases, and the shear coefficient increases. When the length of the non-embedded section of the pile satisfies ( is the pile length), the lateral instability of the partially embedded single pile is observed under the dynamic load. As the thickness of the underlying soil increases, the first-order natural frequencies of the single pile at each scour level increase. As the elastic modulus of the first layer of soil increases by about 0.43 times, 1.14 times, and 1.86 times, the first-order natural frequencies of the single pile at the scour level of 0 increase by about 8.9%, 19.5%, and 27.1%.

In view of the unreasonable setting of water injection pressure and poor water injection seepage effect in the process of coal seam water infusion and dust prevention, a three-dimensional meso non-uniform seepage damage numerical model which can characterize the internal pore and fracture structure of water injection coal and rock mass is constructed by using the method of CT scanning technology and RFPA software. Through the seepage damage simulation of coal rock model reconstructed by CT with different water injection pressures, the influence of water injection pressure on the seepage damage permeability, evolution and acoustic emission characteristics of coal rock sample was studied. The effect of coal rock size on seepage damage and acoustic emission of coal rock samples is studied by scaling the reconstructed coal rock model. The results show that in the process of micro fracture propagation of coal sample, with the increase of water injection pressure, the number of damage units, seepage movement distribution range of seepage field, permeability, acoustic emission number and energy of coal sample generally show an upward trend, and there are fluctuations in local area. The reason for the fluctuation is the critical reaction between the seepage field and the internal stress field of coal sample fracture, resulting in the change of the position of coal sample failure unit. The permeability of coal samples increases from 3.82×10−5 μm2 to 0.314 μm2, and the porosity increases from 5.45% to 48.45%, which reveals the influence law that the fractures of coal and rock mass continue to expand and penetrate with the increase of water injection pressure on the whole, and the expansion trend decreases with the increase of water injection pressure on the part. With the increase of coal sample size, the porosity of the coal sample after the water injection failure shows a trend of first decreasing and then gradually stabilizing, and the change trend of acoustic emission characteristic is just the opposite, indicating that the coal sample size has a significant impact on the water injection coal rock seepage failure. However, the impact of the coal sample size on the water injection coal rock seepage failure tends to be stable when the coal sample size exceeds 40 mm. The combination of CT scanning technology and RFPA software can effectively simulate the fracture seepage propagation behavior of water injection coal and rock.

Dynamic disturbance is an important influence factor that causes the sliding instability of rock discontinuity and then triggers strong dynamic geological disasters, such as earthquake and rock burst. In order to study the mechanical response and disaster-causing mechanism of rock discontinuity under dynamic disturbance loading, a multifunctional shear test apparatus for rock discontinuity under dynamic disturbance loading (DDST-1800) is independently developed. The test apparatus is composed of normal and shear loading units with quasi-static loading, varied normal boundary conditions, dynamic disturbance loading with complex and wide-frequency waveform (0.5−50 Hz), and wide-range shear velocity loading (0.000 1−10 mm/s) functions, pendulum impact system, cyclic shear box unit, data acquisition and control units. The servo-controlled apparatus DDST-1800 can conduct the following typical tests by programmed operations: monotonic or cyclic direct shear test of rock discontinuity under constant normal load (CNL), constant normal stiffness (CNS), unloading normal load (UNL), variable normal stiffness (VNS), and dynamic normal load (DNL) boundary conditions with different shear velocities, superimposed dynamic disturbance shear test, velocity and stress step tests, and pendulum hammer-driven impact test of rock discontinuity under pre-set normal and shear stress conditions. Preliminary experimental studies were carried out and the results verified the stability and accuracy of the new apparatus. The research and development of the new apparatus has important scientific significance and engineering value for clarifying the dynamic response characteristics of rock discontinuity under dynamic disturbance, and deeply understanding the triggering effect of activation instability of rock discontinuity and disaster-causing mechanism of geological disasters such as earthquake and rock burst.

Moment tensor inversion is an effective method to study the mechanism of deep rock mass failure, and station/sensor calibration is very important for obtaining accurate moment tensors. In order to obtain more accurate sensor calibration coefficients and moment tensors, a new sensor calibration method is developed: the search calibration method. The proposed method and the network calibration method are respectively applied to the microseismic monitoring data of the Geysers geothermal field in northern California. Then, based on the calibration results, a series of theoretical calculations and simulations are conducted to verify the effectiveness of the two different calibration methods. By comprehensively considering the influence of factors such as different focal mechanism parameters, preset calibration coefficients, noise addition methods and noise levels, the theoretical calculation and simulation analysis of the effectiveness comparison of calibration methods are carried out. The results show that both calibration methods can obtain stable coefficients from microseismic monitoring data, the components and stress state distribution of events are more concentrated after calibration; under all simulated conditions, the two calibration methods can effectively reduce the moment tensor errors; under low noise level condition, the moment tensor errors of two calibration methods are very small and similar; under mixed noise level and high noise level conditions, the accuracy and stability of the search calibration results are better than that of network calibration in most cases; based on the simulation results, the more reliable moment tensors of the Geysers microseismic data are selected. The research ideas and conclusions can provide further guidance for the study of microseismic moment tensor.