Directional drilling technology (DDT) originated from oil drilling industry. After many years of development, DDT has been extended to geological investigation and disaster management for tunnel engineering, aquifer reconstruction at the bottom of coal mines, pumping channel construction for power storage stations, municipal pipeline laying and other fields. Combined with the advantages of DDT for long-distance accurate crossing, ground grouting technology can achieve safe and efficient management of underground engineering disasters, and has a broad application prospect. This paper systematically reviews the development history, research status and key technologies of DDT. Firstly, the development history of DDT is introduced. Secondly, the scientific research plan, academic paper publication, relevant patent authorization, and application exploration of DDT are analysed. The analysis results show that the DDT in China has reached an internationally advanced level of technological independence and broad-range application, but there are still some core technical problems that need to be resolved, such as thousand-meter long-distance fast drilling, accurate drilling guidance in complex geological conditions, and accurate grouting in underground engineering. Focusing on the construction requirements of strategic major projects, this paper proposes four functional modules, i.e., forecasting, drilling, grouting and detecting, and analyses and discusses six aspects of ultra-long directional drilling and grouting (i.e., sensing prediction while drilling, rapid drilling and sticking prediction, precision guidance technology, remote gel controllable grouting material, pressure stabilizing and controlling sectional grouting process, and detection system with drilling). This paper can provide reference for the development of DDT, and for the prevention and control of disasters in underground engineering.

In view of the mechanical properties of coarse-grained materials, such as strain softening and dilatancy, a generalized shear damage mechanical model with wide applicability was established in this study by considering the strain localization phenomenon marked by shear band. This damage model adopted the mathematical simplification of shear band in the envelope theory, and the stress-strain relationship equation of coarse-grained material was derived based on the strain equivalence principle and Weibull distribution. A nonlinear functional relationship between axial and volumetric plastic strain was proposed to describe the weakening of dilatancy based on the mechanism of dilatancy. Combined with the servo process of coarse-grained materials in triaxial compression tests, a method to determine the parameters of damage model was proposed based on genetic algorithm. By conducting a series of triaxial compression tests under different confining pressures, the shear damage mechanical model was validated, and the effects of the evolution of shear band parameters on the strength and deformation characteristics of coarse-grained materials were further analyzed. The results indicate that the proposed shear damage mechanical model considering the strain localization characteristics can accurately simulate the strain-softening and dilatancy characteristics of coarse-grained materials, and effectively reveal the influence mechanism of the internal deformation of the shear band on the overall macroscopic deformation of the coarse-grained sample. The evolution of the shear band parameters with the surrounding confining pressures in the model was consistent with the mesoscopic mechanism of coarse-grained materials. The strength composition calculated by this model was in good agreement with the micro mechanism, such as the breakage and reorganization of coarse-grained particles.

Solidification treatment of highly cohesive tailings is one of the important means for resource utilization. Highly cohesive iron tailings were taken as the object to carry out strength characteristic experiments of solidified tailings using high-calcium geopolymer to analyze the impacts of different dosages of chopped basalt fiber and dry-wet cycles. The micro-cementation behavior, unconfined compressive strength, and the response parameters after dry-wet cycles (strength, mass loss, and electrochemical properties) of the fiber-reinforced solidified materials were discussed. It is concluded that: 1) Adding fiber increased the strength. 0.5% was the optimal dosage (strength increased by 29.1%), which is equivalent to reducing the dosage of geopolymer by about 2%. 2) Fiber, hydration products and tailings were bonded by cementation and frictional occlusion. An appropriate amount of fiber could reduce pore connectivity and increase the capillary water holding capacity. 3) The dry-wet cycles destroyed the cementation, and the damage was stable after the sixth cycle. The fiber has no obvious advantage in improving the dry-wet durability of the solidified materials. The above results provide theoretical support and method reference for clarifying the strength characteristics and durability of solidified tailings.

In mining engineering geology, there are often faults and goafs. The law of the microseismic signal propagation through faults and goafs is bound to change, so it is important to study the propagation law of the microseismic signal in special geological structures. Based on the Huygens principle, the wave surface equation of microseismic waves in non-uniform medium conditions is established by considering the different propagation velocities of microseismic waves in different layered rock masses. Then the relationship between the wave surface radius and the incident angle is obtained. By combining with indoor similar material model experiment, the applicability of the wave surface equation is verified, and the influence characteristics of faults and goafs on the propagation of the microseismic signal are also summarized. The results show that the microseismic signal takes longer to cross the fault, and the presence of the fault causes a larger attenuation of the signal energy (maximum vibration velocity). The microseismic signal will continue to propagate at the original velocity after passing through the fault, and the attenuation of the signal energy does not lead to the attenuation of the propagation velocity of the microseismic signal. The larger the incident angle of the microseismic wave passing through the fault, the longer the time to pass through the fault, and the more the attenuation of the signal energy. The existence of the goaf gives rise to the attenuation of the propagation velocity of the microseismic signal, and the closer the distance between the seismic source and the monitoring point, the greater the influence of the goaf on the relative propagation velocity of the microseismic signal.

Groundwater inundation as a consequence of sea level rise triggers significant risks for building foundations in coastal areas. This paper presents a framework to model the resilience of coastal-building foundations in the presence of soil strength deterioration due to water intrusion. The resilience model is mathematically based on the integration of the time-variant performance function within a reference period of interest. A strip foundation is considered, whose ultimate bearing capacity is modeled by the Terzaghi trinomial formula. The rise of groundwater table reduces the strength of soils, and the impact of climate change on groundwater level rise is incorporated in the resilience assessment. An example is presented to demonstrate the applicability of the proposed framework. It is shown that ignoring the effect of groundwater level rise in a changing climate would result in a non-conservative estimate of structural resilience. The life-time resilience is also dependent on the selection of the maintenance strategies, through which the performance function is restored to an enhanced state. Future studies should also consider the joint impact of other factors (e.g., corrosion) on the deterioration of coastal-building foundations.

A rock burst experiment of granite with prefabricated single crack under the true-triaxial stress condition with a free face was carried out in this paper, and the rock burst process was monitored by high-speed camera system and acoustic emission (AE) system. The failure mode, strength, deformation and AE evolution characteristics of the rocks with different orientations of cracks were investigated. The relationships between crack orientation and rock burst process and ejection kinetic energy was analyzed. The rock burst mechanisms of the rocks with prefabricated single crack and the intact rocks were compared. The analysis of mechanical properties shows that, with the decrease of crack dip angle, the failure mode of rock samples generally changes from "internal shear and external splitting" to "Z-type oblique shear", and the weakening effect of cracks on rock strength is increasing. When the crack dip angle is less than 30°, the peak stress of rock is generally only about half that of the intact rock samples. The larger the length of the small-dip-angle crack is, the more obvious the splitting phenomenon of the rock slab will be, the slightly larger the rock burst pit will be, the larger the strength reduction amplitude will be, and the smaller the peak axial strain will be. The crack close to the free surface of rock samples will aggravate the splitting effect of the rock slab, large deformation and numerous cracks will occur in the plastic stage generally. When the crack is exposed and cuts off the free surface, it will be difficult to form rock burst pits. The analysis of rock burst process and ejection kinetic energy shows that, with the decrease of crack dip angle, the ejection kinetic energy of rock samples decreases significantly first and then increases slightly, the dip angle of 30° is the turning point of transformation. The closer the internal cracks of the rock sample are to the free surface, the smaller the ejection kinetic energy of the rock sample will be. The resin-filled crack greatly increases the ejection kinetic energy of rock sample, but not when cement fills cracks. The analysis of AE characteristics shows that, the longer length and the smaller dip angle of the crack are, the larger the time proportion of "quiet period" to rock burst process is, and the smaller the absolute energy proportion of rock burst in the post-peak stage is. If the crack is close to rock free surface, two "quiet periods" generally appear, and one more sudden rise will also appear in the AE absolute energy evolution curve. With the increase of crack dip angle, the duration of the initial fluctuation stage of b value of rock samples with crack becomes longer, the decrease rate of decline stage becomes larger, and the minimum b value point is closer to the rock burst time. In general, the mechanism of strain-type rock burst in rocks with cracks differs from that in intact rocks. The mechanism of strain-type rock burst in rocks with cracks can be classified into two types: shear-fracture type and tension-slabbing type. The research results provide a scientific basis for the mechanism analysis of rock burst disaster of fractured rocks and the early-warning by using AE technology.

When the shield machine is driving along a curve alignment or during deviation correction, the asymmetrical thrust will generate an additional bending moment on the head of the tunnel ring, which will cause longitudinal deformation of the shield tunnel. Current analytical methods commonly simplify the existing tunnel as an equivalent continuous beam, which will overlook the weakening of the circumferential joint. In this study, a simplified longitudinal beam-spring shield tunnel model (SLBSM) is established, which can simultaneously consider the opening and dislocation between segmental rings. Then, the shield tunnel under construction is simplified as a SLBSM resting on the Winkler foundation. The shield tunnel longitudinal deformation subjected to the shield tail asymmetric thrust is solved using the state space method; the reliability and applicability of the proposed method are verified by comparing with the results from finite element analysis and two existing continuous beam model. The parametric analysis is further performed to investigate the influences of some parameters on the deformation of shield tunnel. The results show that the longitudinal displacement of shield tunnel based on the continuous beam model exhibits continuous characteristics. While the longitudinal displacement predicted by the proposed method exhibits discontinuous characteristics, “gaps” appear at the joints between adjacent rings. Through the parametric analyses, it is found that increasing the rotation stiffness of the circumferential joint will effectively reduce the tunnel heave and opening of joint; increasing the shearing stiffness of the circumferential joint will effectively lead to the decrease of dislocation between adjacent rings, but it will increase the tunnel heave and shear force; improving the foundation stiffness will effectively reduce the tunnel heave and opening of joint, but it will result in the increase of the dislocation between adjacent rings. The effect of the axial force at the beginning of the segment on the longitudinal deformation of the tunnel cannot be ignored. Increasing the axial force will effectively reduce the tunnel heave, opening of joint, and dislocation between adjacent rings.

Magnesium lithium phyllosilicate (MLPS) transparent soil is used to build a double-layered soil model with upper hard and lower soft. The gas source generated in the sedimentary layer is simulated by pinhole gas injection. Based on the image recognition technology, the experimental researches on the shape change of gas and the uplift deformation of the upper soil in the process of gas accumulation in the formation are carried out. The results show that: (1) The gas presents different forms in the process of accumulation, and the time and shape of the gas breakthrough are determined by the strength and height of the upper soil. (2) The change of gas shape, volume and pressure can be roughly divided into two stages. In the first stage, the gas volume and width increase linearly, while the gas height decreases gradually due to the contraction of the bottom, and the gas pressure increases slowly; in the second stage, the increase of gas width is slowed down, the expansion speed of gas volume is accelerated, the height of gas begins to increase significantly, and the gas pressure decreases rapidly from the highest point. The height and width of the uplift of the upper soil begin to increase significantly in the second stage. (3) The width and volume of the gas before breakthrough and the uplift width and height of the upper soil have a good fitting relationship with the yield strength and height of the upper transparent soil. (4) The thin plate theory can reasonably explain the mechanism of upper soil deformation caused by gas accumulation, while medium thick plate theory is not applicable.

Among the existing literature on shear mechanical properties of rock discontinuities, there are more researches on simple discontinuities than those on natural discontinuities, and more researches on mechanical properties evolution than those on geometric evolution. In this study, rock discontinuities in nearly natural forms are prepared through the Brazilian splitting test, and the splitting samples are produced with simulated materials. Then under cyclic loading, the shear property evolution laws and influencing factors of rock discontinuities are studied. The influences of normal stress, number of shear cycles, rock wall strength and roughness of rock discontinuity surface on mechanical properties and morphology of rock discontinuities under cyclic shearing are analyzed. Finally, by introducing the negative exponential deterioration parameter related to the number of shear cycles (Nd) into the adhesion theory of friction-Barton empirical formula, a formula for cyclic shear strength of rock discontinuities is proposed. The results show that with the increases of normal stress, rock wall strength and roughness of rock discontinuity surface, the maximum shear stress of rock discontinuities increases; with the increases of normal stress, number of shear cycles and roughness of rock discontinuity surface, the rock wall strength decreases and thus the normalized roughness parameters of rock discontinuities reduce. The proposed cyclic shear strength formula verifies the test results and provides a theoretical reference for engineering safety design.

High-fill culverts placed in valley topography have a complex earth pressure distribution law due to their locations around culverts in various valley topography conditions. In order to investigate the influence of valley topography on the earth pressure around the culvert of high-fill arch culverts, a interaction model of "topography-culvert-fill" was established by using centrifugal model test and numerical simulation method. Additionally, the distribution laws of earth pressure around the arch culverts and earth pressure concentration coefficient K_s at the top of the culvert under different valley widths B and valley slopes a were analyzed and were compared with the latest Chinese culvert design code. Furthermore, the mechanism of earth pressure formation of high-fill arch culverts under valley topography was presented. The research findings are as follows: (1) The influence of the valley width B on the earth pressure concentration coefficient K_s at the top of the culvert is significant, and the increment of the earth pressure concentration coefficient K_s at the top of the culvert is larger when B is 4D−6D（D is the clear span of arch culvert）. (2) When B is less than 4D, the topography would play the role of load reduction to the culvert. (3) With valley slopes ranging from 45° to 60°, the earth pressure at the tops and K_s would be affected dramatically. (4) When fill height is 20 m with a >70°, K_s≤1; and when 40 m fill height with a >50°, K_s≤1. (5) The K_s recommended by the latest Chinese culvert design code differs to some extent from those by centrifugal model test and numerical simulation. In the case of a =45° with a small B value, the earth pressure concentration coefficient K_s at the top of a culvert of the code is more conservative. (6) K_s of high-fill arch culvert in valley is related to the formation of arch top compaction area and isobaric surface. The arch top compaction area can cause the earth pressure concentration on the top of the arch culvert, and cause the vertical earth pressure of the soil around the compaction area to be arched. At a certain depth approaching the surface of the fill, the arch distribution gradually transits to the horizontal distribution, thus forming an isobaric surface. The upper load of the isobaric surface will be dispersed on the valley slope, so the unloading effect of the valley topography can be exerted.

Based on the actual situation of excavation disturbance in underground rock engineering, it is of theoretical significance and engineering application value to carry out rock joints shear tests that consider the continuous excavation effect and fully reflect the stress adjustment process of the rock joints. In this paper, the shear tests under conventional stress path and continuous excavation effect were conducted on the rock joints prepared by artificial splitting method, and the shear mechanical properties, acoustic emission (AE) characteristics and energy evolution of rock joints under two conditions were systematically studied. The research results show that the greater the intensity of excavation disturbance load, the larger the overall shear stress drop when shear damage occurs at the rock joints, but the maximum value of shear stress drop under continuous excavation effect is only 48.57% of the shear stress drop under conventional stress path. The AE activity in the shearing process of rock joints considering the continuous excavation effect is mainly concentrated when the rock joints is failed by shear and the shear stress drop is generated, the intensity of AE activity is positively correlated with the intensity of excavation disturbance, and the extremum of the change rate of AE count is significantly smaller than the counterpart under conventional stress path. The intensity of crack development, the wear area and failure degree of rock joints in the specimens under the continuous excavation effect increase with the intensity of excavation disturbance, but the intensity of crack development and the failure degree of rock joints in the specimens are less than those under conventional stress path. The elastic strain energy at the shear failure of rock joints considering the continuous excavation effect increases with increasing disturbance load and is lower than that under conventional stress path. The continuous excavation effect reduces the shear strength of the rock joints, but is more likely to trigger shear failure of the rock joints.

In order to investigate the dynamic behaviors of coal and its deterioration law under different initial gas pressures, this study conducted impact compression experiments on gas-bearing coal by using the self-developed visualized gas-bearing coal rock dynamic and static combined loading test system, analyzed the expansion and evolution law of internal fracture in gas-bearing coal by combining with CT scanning system. Moreover, this study also quantitatively characterized the mesoscopic damage degree based on the increment of internal fracture rate of coal samples impacted under different initial gas pressures, and explored the deterioration law of macroscopic mechanical parameters of gas-bearing coal under the impact load. Some conclusions are drawn. (1) The dynamic stress-strain curves of gas-bearing coal under impact loading, which can be divided into linear elastic phase, plastic hardening phase and damage phase, have no obvious compaction phase. And it is found that the peak strength, peak strain and elastic modulus of impacted coal samples deteriorate with the increase of initial gas pressure. (2) Gas aggravates the expansion and coalescence of fractures inside the coal. CT scanning results indicate that the impact damage mode of gas-bearing coal is mainly splitting and stratified splitting damages, and the more significant the two damage modes are with the increase of initial gas pressure, so does the number of fractures and their damage degree inside the coal, which makes the spatial fracture network more complex. (3) The damage variables are defined on a mesoscopic level, and the values of damage variables show a rise of quadratic function with the increase of initial gas pressure. The comparison of the dynamic strength of coal under impact load with the theoretical strength obtained by defining the degree of damage by fracture rate increment verified the rationality of the damage variables defined by fracture rate increment of coal at the mesoscopic level. The intrinsic connection was constructed between the mesoscopic deterioration of gas-bearing coal and the loss of macroscopic parameters. The research results enrich the basic theory of gas-bearing coal dynamics and provide a theoretical reference for the prevention and control of coal-rock-gas composite dynamical hazards in mines.

Massive developed discontinuities are the salient geological features of unconventional oil and gas reservoirs, and the hydraulic fractures’ capabilities of crossing the discontinuities concern the stimulation effects of hydraulic fracturing. To study the development of the fracture process zone (FPZ) when the hydraulic fracture propagates through an orthogonal discontinuity, the self-designed visualization fracturing equipment was adopted to carry out hydraulic fracturing tests on sandstone plates with a prefabricated unbounded friction interface. Based on the digital image correlation method, the displacement and strain characteristics during the hydraulic fracture propagation across the orthogonal interface were monitored in real time. The test results show that the FPZ has developed across the interface before the hydraulic fracture extends across the interface. Whether the fracture can propagate through the interface is predetermined at the initial developmental stage of the FPZ and is not affected by the stress-softening process in the FPZ. Based on the Renshaw-Pollard criterion, a criterion considering the FPZ boundary was established for estimating the fracture propagation across the friction interface, and it was verified by test data and existing results. In comparison, the improved criterion considers a more accurate application scope of elastic fracture mechanics at the fracture front. The aspect ratio of the FPZ has a significant effect on the improved criterion, and the lower limit of friction coefficient required for the fracture propagation orthogonally across the interface declines as the aspect ratio of the FPZ rises under the same conditions.

Uniaxial compression behavior of fissured loess after vibration was investigated by small-scale shaking table and uniaxial compression test. The test results show that the failure modes of fissured loess can be classified as four types, i.e. fracture failure, slip failure, coupled slip-fracture failure and compression-shear failure. The failure modes of fissured loess in uniaxial compression test are less affected by vibration, while it mainly controlled by fissure angle. Furthermore, vibration has little influence on the type and characteristic of the stress-strain curves, which constantly presents characteristics of strain softening. It is worth noting that the curves of loess samples with fissure angle of 45° show bimodal variation, and the second peak strength is generally larger than the first counterpart. The uniaxial compressive strength (UCS) approximately decreases linearly with growing vibration amplitude and frequency. With the increase of fissure angle, the UCS exhibits "double V" changes regardless of vibration parameters. A binary medium model is finally established, and it can well predict the stress-strain behavior and UCS of fissured loess after vibration.

The phenomenon that the well resistance changes with both time and depth (i.e., the decrease of drainage capacity caused by silting and bending) has been widely concerned during the consolidation of soft soils with vertical drains. Moreover, the influence of variable well resistance on consolidation rate of soft soils with vertical drains cannot be ignored. However, there are few analytical solutions for consolidation which can consider the time-dependent loading and the variation of well resistance with time and depth at the same time. Considering the evolution process of time-and depth-dependent well resistance, a consolidation model of soft soils with vertical drains is developed by incorporating a single stage loading or a multistage loading which is widely adopted in practice, and the analytical solution of the consolidation model is obtained by using the separation of variables method. The correctness of the model is fully verified by comparison with the existing analytical solutions, finite difference solutions and engineering measured values. Finally, the influences of variable well resistance parameters on consolidation behavior of soft soils with vertical drains are analyzed through a lot of calculations. The results show that the consolidation rate of soft soils with vertical drains increases with an increase in the final drainage capacity of vertical drains, and decreases with an increase in the value of depth resistance parameters and time resistance parameters, and influences of time resistance parameters on the rate of consolidation are more significant.

In order to accurately predict the thermal conductivity of unsaturated frozen soil, the characteristic structure identification method and reconstruction method of unsaturated frozen soil were proposed based on the soil microstructure images, and the prediction model of the thermal conductivity of unsaturated frozen soil was established by combining these methods and the conventional finite element method. Through scanning electron microscope (SEM) images, the content, size and distribution probability of each component were identified by antidromic quartet structure generation set (AQSGS) method. A multi-element quartet structure generation set method considering soil, water, ice and gas (MQSGS method) was proposed to improve the conventional quartet structure generation set (QSGS) method. Based on the established unsaturated frozen soil model, the thermal conductivity of unsaturated frozen soil was obtained through Monte Carlo method, and compared with the thermal conductivity of frozen soil in the specification, which verified the rationality of the prediction model (average error <4%). The influences of porosity, particle size, soil particle thermal conductivity, degree of saturation and freezing rate on the thermal conductivity of unsaturated frozen soil were studied by multi-factor analysis. The correlation coefficients between each influencing factor and thermal conductivity were −0.352, −0.098, 0.641, 0.52 and 0.06, respectively. The influence sequences were soil particle thermal conductivity > degree of saturation > porosity > soil particle size > freezing rate. The effects of various influencing factors on the thermal conductivity of unsaturated frozen soil can be summarized as the influences on the density, width, connectivity, heat flow capacity of "thermal chain" formed by heat flux and "thermal bridge" flux.

Natural structural soil is susceptible to various types of construction disturbance. The disturbance results in the change of the physical and mechanical properties of soil, which in turn the engineering stability, deformation and adjacent environment. In this paper, triaxial tests and one-dimensional compression tests were carried out on undisturbed soil, lightly disturbed soil, heavily disturbed soil and remolded soil of two typical soils in Ningbo. The influence of disturbance degree on the main parameters of HSS model was analyzed, the influence laws were applied to a foundation pit project in Ningbo City. The horizontal displacement of the foundation pit was analyzed with Plaxis3D considering the influence of surrounding soil disturbance. The results show that disturbance has adverse effects on the strength and stiffness of soil. For mucky clay, the reference tangent modulus E^ref_oed, reference secant modulus E^ref₅₀ and reference loading/unloading modulus E^ref_ur of lightly disturbed samples are respectively reduced by 14%, 10% and 2%, the above parameters of the heavily disturbed sample are reduced by 43%, 14% and 15% respectively, and similar decreasing laws can also observed in silty clay. Considering the influence of soil disturbance, the maximum calculated horizontal displacement of the two inclined holes around the foundation pit increases by 13% and 15% respectively, which is closer to the measured values. The research results can provide a guidance for HSS model parameter selection and foundation pit engineering analysis and calculation considering disturbance effect.

Based on the propagation theory of elastic waves in unsaturated porous medium and single-phase elastic medium, considering that a composite multilayer wave impeding block(WIB) with a certain thickness is set in unsaturated soil (composite multilayer wave impeding block with three layers as an example), analytical solutions of transmitted/reflected amplitude ratio of S-wave passing through a composite multilayer wave impeding block in unsaturated soil foundation are derived by using Helmholtz vector decomposition theorem. The influences of physical and mechanical parameters such as shear modulus and density of interlayer wave impeding block on the propagation characteristics of S-wave passing through composite multilayer wave impeding block in unsaturated soil are analyzed by numerical examples. The results show that the shear modulus and the density of interlayer wave impeding block material have significant influences on the transmission/reflection coefficient. Therefore, the composite multilayer wave impeding block is an effective vibration isolation barrier, and a better vibration isolation performance can be obtained by strictly controlling the shear modulus and density of interlayer wave impeding block, which provides theoretical guidance for the application of composite multilayer wave impeding block in the field of foundation vibration control.

With the increasing of current installed capacity of offshore wind power, super-large diameter steel pipe pile foundation has been widely used. The increase of pile diameter changes the pile-soil interaction mode, thus the applicability of the method for calculating inner frictional resistance of steel pipe piles in the current code is open to question. In this study, centrifugal model tests are carried out to reveal the behavior of earth pressure and internal frictional resistance in clay with different pile diameters by using double-walled pile and pipe pile models. By using finite element numerical analysis method, the factors influencing the inner frictional resistance are analyzed, and a method for calculation of inner frictional resistance of steel pipe piles is developed. The proposed method is verified by comparison with the centrifuge test results. The results show that, with the increase of pile diameter, the inner wall earth pressure increases, and the inner frictional resistance also increases. The inner frictional resistance is exponentially distributed along the pile depth, and it is available within 5 times the pile diameter from the pile tip. The proposed calculation method of inner wall frictional resistance is found to be in good agreement with centrifuge test results.

Rainfall-induced instability of loess slopes is very common. Based on the governing equation for unsaturated seepage, a computational model of the seepage field of loess slope is established. The VG function and Gardner function are used to describe the soil-water characteristic curve and permeability function, respectively. The analytical solution of rainfall infiltration is derived by using traveling wave approximation and series expansion method. The validity of the analytical solution is demonstrated by fitting the model test data to the soil-water parameters using the numerical inversion method. By comparing and analyzing the distribution law of volumetric water content between the experimental value and the analytical solution under different working conditions, it is found that the test values of volumetric water content at shallow measurement points in the slope test model are closer to the analytical solution, and the peak volumetric water content reached during the downward movement of the wetting front is smaller compared to the analytical solution; the test value of volumetric water content of deep measurement points in the slope test model has some error with the analytical solution in the early stage, and the analytical solution of volumetric water content of deep measurement points grows faster in the early stage compared with the test value, which is mainly attributed to the hysteresis of wetting front in deeper soil layers.

In order to study the interaction mechanism between liquid-phase suction and solid-phase ice pressure in frozen soil / rock, the theoretical ice pressure equations under different boundary conditions are first unified according to the fundamental thermodynamics. Then, by combining the generalized Clapeyron equation and the Gibbs-Thomson equation, the freezing temperature equation of liquid phase water at curved interface is given on the basis of interpretation of the physical significance of liquid-phase suction and solid-phase ice pressure. Finally, the freezing temperature equation is introduced into the frozen capillary model, and the liquid-phase suction equation is substituted into Darcy's law to verify the action mechanism of solid-phase ice pressure and liquid-phase suction respectively. The results show that: 1) The theoretical ice pressure in equilibrium state is only linearly related to temperature and has nothing to do with the boundary conditions. 2) The liquid-phase suction stems from the difference between the theoretical suction and the offset factor of solid-phase ice pressure, and it is the unified driving force for water migration, and when the solid-phase ice pressure approaches the theoretical ice pressure, the liquid-phase suction tends to zero. 3) The solid-phase ice pressure is an absolute pressure, which can offset the liquid-phase suction, while the liquid-phase suction is a relative suction and cannot offset the solid-phase ice pressure. 4) The total pressure in the pores is only the solid-phase ice pressure and it can reach the theoretical ice pressure in equilibrium when the capillary is frozen, so it follows the formation mechanism of segregation ice by "ice pressure method". This research reveals the interaction mechanism between liquid-phase suction and solid-phase ice pressure in frozen soil / rock, which has high theoretical value and scientific significance for improving the existing frost heave theory.

Determining the characteristics of gas pressure distribution during aeration in landfills can provide key technical and theoretical support for aerobic ventilation engineering. Relying on the field single well aeration test and based on the theory of seepage mechanics, this study conducted gas pressure distribution monitoring tests under different aeration intensity conditions, analyzed the temporal and spatial distribution characteristics of the gas pressure during the aeration process, and deduced an one-dimensional steady-state analytical solution (AGPP model) of the gas pressure distribution in the garbage soil under the aeration conditions. By combining with the on-site gas pressure monitoring results, a gas pressure prediction model (EGPP model) with aeration intensity as the core parameter was constructed. The test results show that a low-pressure aeration intensity can also achieve aeration effect, and the gas is filled around the gas injection well in a short time. The reliability of the two models is preliminarily verified by comparing the field monitoring data with the AGPP model and the EGPP model. This study provides a new method for predicting and evaluating landfill gas pressure distribution during aerobic ventilation.

 In order to study the water infiltration and self-weight collapse deformation characteristics of Jingyuan loess with large thickness under the condition of immersion, a field immersion test without water injection holes was carried out in the self-weight collapse loess site of Jingyuan North Station along the Zhongwei-Lanzhou Railway. The surface and underground collapsible deformation, cracks, water content and vertical stress in the soil around the test pit were monitored and analyzed. The water diffusion, self-weight collapsible characteristics and vertical stress in the soil were studied, and the regional correction coefficient β₀ value and wetting angle were discussed. The results showed that: the change of volumetric water content was divided into four stages: immersion stability (2), rapid increase (1) and slow increase (1). In the immersion process, the vertical infiltration of water was accelerated and the radial diffusion was slowed down at 21 m, and the final shape of the wetting front was presented as elliptical. According to the water content test results of exploratory wells and boreholes, the maximum wetting angle was calculated to be 41°. The self-weight collapse process of loess in the site went through three stages: severe collapsibility, slow collapsibility and consolidation stabilization. At the end of the test, a total of 13 ring cracks were developed, and the farthest point of the cracks was  26 m from the edge of the test pit. According to the indoor test and field test results, it was suggested that the regional correction coefficient should be corrected along the depth of the soil layer, and the β₀ value was taken as 1.05 within 0−10 m and 0.95 within 10−27 m. In the depth range from the surface to 21 m, the foundation soil was saturated and fully collapsed. The vertical stress in the soil increased linearly along the depth, and the vertical stress in the soil was close to the saturated self-weight stress. The foundation soil below 21 m failed to collapse entirely, and the vertical stress in the soil decreased gradually. The research results could be applied to the later construction of Zhongwei-Lanzhou Railway and provide a reference for other regional engineering projects.

Field data from liquefaction case histories are important basis for the development, calibration, and validation of the liquefaction evaluation methods, and major standard for the validation of current liquefaction theories. Collecting liquefaction data from ChiChi, Bachu and Songyuan earthquakes, the Chinese standard penetration test (SPT)-based liquefaction database significantly increases from 121 to 465 in number. The dataset is used to validate the reliability of four liquefaction evaluation methods based on standard penetration test (SPT), i.e., the Chinese seismic design of building code method (code method), two hyperbolic models, and the cyclic stress ratio (CSR) simplified method. The results indicate that the two hyperbolic models can satisfactorily distinguish the liquefaction data from the non-liquefaction data, with success rates higher than 85% for both liquefaction data and non-liquefaction data. The code method and the simplified CSR method exhibit disadvantages for liquefaction evaluation. The predicted results are not satisfactory for all four methods for seismic intensity of 7, as the liquefaction data are mixed with the non-liquefaction data for this intensity. The overall success rates of the four methods are high for the data from seismic intensities of 8 and 9. A new probabilistic liquefaction evaluation formula based on the CSR method is proposed by regression analysis of the new liquefaction dataset. The predicted critical liquefaction lines are in reasonable agreement with reported probabilistic formula, even though the datasets ever adopted are different. The Chinese code method has obvious limitation with conservative results for soil layers at depth greater than 10 m. The analytical results provide reference for improving the liquefaction evaluation method in Chinese code.

The roadside roof cutting interrupts the continuity between the roadway and the lower roof, promoting the collapse of the lower roof to form a gravel gang. It is of great significance to study the influence mechanism of roof cutting on the caving characteristics of lower stope strata. In this paper, the stope support load was analyzed, the mechanical modeling of the overlying strata was carried out, and the relationship between the movement of the overlying strata and the stope support load characteristics at typical positions was clarified. On this basis, the load data of supports at typical positions were given for six working faces with roadway side roof cutting, so as to analyze the influence mechanism of the roadside roof cutting on the collapse characteristics of the lower strata in the stope. Meanwhile, a numerical model was established, taking into account the different starting positions of roof cutting and the strength of the lower roof, and further analyzed the effect of roadside roof cutting on the collapse of the lower strata. The results show that the "caving line" of the 121 method has a symmetrical arc boundary, the "caving line" of the 110 method is entirely moved to the working face on the roof cutting side, and the N00 method is between the above two. In addition, there are differences in the effect of roof cutting under different roof cutting starting positions and roof strength conditions. The research results are conducive to further deepening the understanding of the effect of roadside roof cutting on the caving characteristics of the lower stope strata.

The long-term creep deformation of soft and hard rock strata may be very uncoordinated, which poses a great threat to the safety and stability of excavation engineering. A series of creep tests and numerical simulations were carried out on two types of rocks (i.e., sandy mudstones and argillaceous sandstones) with large differences of hardness in the same excavation section of diversion tunnel of a hydropower station under unloading conditions. Results show that under the condition of unloading confining pressure, the lateral creep deformation of the specimen develops more rapidly than the axial deformation and a significant lateral expansion occurs. The specimen under a higher initial confining pressure exhibited a greater lateral expansion effect in the unloading creep failure. The deformation rate of argillaceous sandstone in the steady creep stage was slower than that of the sandy mudstone. Meanwhile, the strain values of argillaceous sandstone in the creep failure were smaller than those of the sandy mudstone with weaker signs. Based on the Burgers model, damage variables were introduced to establish a creep damage constitutive model. The model curve well described the linear creep characteristics of rocks before the failure deviatoric stress level and the nonlinear accelerated creep characteristics under the failure deviatoric stress level. The numerical simulations of creep deformation of soft and hard rock strata show that at the early stage, the deformation difference between soft and hard rock contact points was not large. With the increase of time, interlayer dislocation occurs at the interface, which is very unfavorable to the overall stability of surrounding rock and should deserve sufficient attention in the engineering practice.

The frost heave of subgrade has an important effect on the operation of high-speed railway in cold regions, while the ice-water phase transition is the key to understanding the mechanism of frost heave. The lattice Boltzmann method is applied in this study, which is a mesoscale numerical method. The modified freezing temperature algorithm of pore water is combined with the enthalpy-based lattice Boltzmann phase transition model. Two freezing processes including the freezing of suspended droplets and the formation of pore water into ice in frozen soil are investigated, which aim to reveal the mesoscopic mechanism of the ice-water phase transition in free state and pore-bound state, respectively. The numerical results show that the process of ice crystals growing from the inside to the outside in the pores is completely opposite to the freezing process of droplets suspended in the air, and the pore water has a lower freezing temperature when it is closer to the surface of the soil particles. The soil freezing characteristic curves (SFCCs) differ obviously for the particles with the same size but in different particle arrangements. Meanwhile, the morphology of SFCC becomes steeper with increasing soil particle size, and the residual water content gradually decreases. The numerical results of the ice-water phase transition process are validated by measured data in the literature, which indicate that the lattice Boltzmann method can provide a new tool to study the water-gas migration and phase transformation process in porous media in mesoscale.