The rock-breaking effect of high-pressure water jet is very important in the rock-breaking technology of high-pressure water jet assisted tunnel boring machine (TBM). In order to improve the efficiency of high-pressure water jet assisted rock-breaking under the working condition of TBM, rock-breaking tests of ultra-high pressure water jet at high linear speed were carried out, and the influences of nozzle moving linear speed, jet pressure and nozzle diameter on the rock-breaking effect were analyzed. The effects of adding abrasive and jet form on the rock-breaking effect were also investigated. The test results show that the cutting depth and cutting width of high-pressure water jet decrease approximately linearly with the increase of nozzle moving linear speed. With the increase of jet pressure, the cutting depth increases approximately linearly, and the pressure is increased from 200 MPa to 280 MPa, the cutting depth is increased by 72%−82%. As the nozzle diameter is increased from 0.35 mm to 0.60 mm, and the cutting depth is increased by 60%−85%. At a high linear speed, the jet flow becomes divergent after adding abrasive. So the cutting depth of adding abrasive is less than that of pure water, and the cutting width of adding abrasive is greater than that of pure water. The cutting depth of sand tube beam is 35%−42% greater than that of long-line jet, and the cutting width of sand tube beam is 78%−85% greater than that of long-line jet. Based on the Crow’s cutting rock theory and regression analysis of test data, a semi-theoretical and semi-empirical prediction model for the cutting depth of ultra-high pressure water jet at high linear speed is obtained, which can provide a reference for the optimization of jet parameters in the rock-breaking technology of high-pressure water jet assisted TBM. The research results are of great significance for improving the efficiency of high-pressure water jet assisted rock-breaking under the working condition of TBM.

To study the long-term creep mechanical properties of surrounding rock in the deep roadway under the action of groundwater, a self-developed five-joint rheological experimental system was used to carry out uniaxial compression tests and uniaxial creep tests on sandstone with different water contents (0%, 0.8%, 1.6%, 2.4%, and 3.3%) under water absorption and softening conditions. Some experimental findings were revealed. The uniaxial compressive strength, elastic modulus, and creep failure stress of sandstone decrease exponentially with water content, and the ratio of creep failure stress to uniaxial compressive strength ranges from 0.76 to 0.84. The attenuation creep time of sandstone decreases with the increase of water content and increases with the increase of stress level. The radial strain enters the steady-state creep stage earlier than the axial strain, and the accelerated creep stage of the radial strain under the damage stress starts earlier than the axial strain. The long-term strength of the sandstone is determined based on the steady-state creep rate curve, and the value of steady creep rate in the radial direction is slightly less than the axial one, and the long-term strength satisfies a negative exponential relationship with the water content. The ratio of radial strain to axial strain in the creep test is defined as μ_c, μ_c value is independent of water content, and a method for determining the long-term strength of rock based on μ_c value is proposed. For the sandstone samples used in this study, it can be considered that accelerated creep failure will occur in a particular period of time when the ratio surpasses 0.3. As the water content increases, failure pattern of samples gradually change from single inclined plane shear failure to X-shaped conjugate inclined plane shear failure. The research results provide a reliable theoretical basis for long-term stability analysis and early prediction of roadway creep failure under groundwa

The shaking table model test with a geometric similarity ratio of 1:100 was constructed to investigate the stability of the typical dangerous rock slope in the Three Gorges Reservoir area under the influence of rock mass deterioration and reservoir-induced earthquakes. The whole process of dynamic cumulative damage, instability failure, and the response law of the dangerous rock slope including deteriorated rock mass in the hydro-fluctuation belt were discussed. The results demonstrated that the whole process can be described as the cumulative damage in the slope → the cracks development → the penetration of secondary joints and deep large cracks → the instability toppling. At the same time, the rock mass on the surface of the hydro-fluctuation belt begins to loosen and fall, resulting in the formation of a seepage network, seepage channels, and cavities within the slope. As ground motion continues, the dynamic response of the dangerous rock mass exhibits a typical "elevation effect" and “surface effect”. The cumulative displacement on the dangerous rock slope surface increases continuously, while the pore water pressure within the hydro-fluctuation belt increases overall. The horizontal and vertical earth pressure of the dangerous rock slope initially increase and then decrease, and the natural frequency and the damping ratio of slope decrease and increase, respectively, throughout the entire stage. Before the end of the small earthquake stages and at the strong earthquake stages, the damage degree curve of the dangerous rock slope follows an "S" type distribution and an exponential distribution.

In order to explore the influence of particle shape on the particle fragmentation and strength characteristics of granular materials, this paper proposes a new parameter to quantify the particle shape of granular materials, designs an artificial sample preparation method considering the three-dimensional particle shape feature information, then conducts a conventional triaxial compression test for these prepared samples, and analyzes the particle local breakage law and strength characteristics, finally derives a binary medium strength criterion. Some research results are drawn as follow. Quantitative parameter of particle shape—spherical modulus G_M is proposed. On this basis, five different shapes of triaxial specimens of crushable granular materials were prepared, and it is found that the spherical modulus affects the triaxial compressive strength characteristics of granular materials. The particle breakage of the sample is determined by sieving method, and the evolution law and critical state of the sample particle breakage is discussed, and particle shape is found to control the nonlinear evolutionary characteristics of macroscopic strength by influencing the particle fragmentation pattern. Based on the binary medium theory, the strength criterion of crushable granular materials considering the particle shape is established, and its applicability is verified by experiments results from conventional triaxial condition.

To study the shear characteristics of rubber-sand mixtures, the effects of four rubber-sand mixtures gradations (one type of gap gradation, two types of continuous gradations, and one type of open gradation), three rubber contents (10%, 30%, and 60%), and three vertical stresses (30 kPa, 60 kPa, and 90 kPa) on the strength characteristics and volumetric change characteristics of rubber-sand mixtures were investigated by using a laboratory large-scale direct shear apparatus; and based on the laboratory direct shear test, the discrete element numerical models of pure sand and rubber-sand mixtures were established according to the same gradation and rubber content. The intrinsic mechanical mechanism of rubber-sand mixtures was explored from the perspective of particle contact state and displacement. The results show that the shear stress curve of rubber-sand mixtures is the same as that of pure sand at low rubber content, but its shear strength is lower than that of pure sand; the shear stress of rubber-sand mixtures increases with the increase of vertical stress, and the shear strength of continuous gradation SR2 is the highest among the four gradations of rubber-sand mixtures; the admixture of rubber particles can effectively inhibit the dilatancy of sandy soil, among which the gap grade SR1 has the best effect on inhibiting soil dilatancy, and the dilatancyis reduced by 37% compared with that of pure sand. The internal friction angle of rubber-sand mixtures decreases with the increase of rubber content, and the internal friction angle of continuous gradation SR2 is the largest under the same rubber content; rubber particles mainly participate in the formation of weak force chain in the rubber-sand mixtures force chain network, and the shear zone width of rubber-sand mixtures is smaller than that of pure sand.

The vertical cyclic loading device designed in-house was used to study the bearing characteristics of monopiles in sand and the deformation mechanism of the soil around the pile by laboratory model tests. According to the test results, the cumulative settlement of the pile can be divided into three regions: the non-developing region, the gradually developing region and the damaging region; the envelope area of the hysteresis loop of the hysteresis curve shows a trend of gradual decrease with the increase of the number of cycles, the hysteresis curve develops from non-closed to closed curve, and the deformation of soil around the pile gradually changes from elastic-plastic deformation to elastic deformation. The particle image velocimetry (PIV) technique is used to measure the soil deformation around the pile in real-time under the cyclic load, and the complete displacement field and shear strain field of the soil around the pile are obtained. The results show that the cyclic period, amplitude, and compactness are the main factors influencing the soil deformation around the pile. The shear damage zone shows an inward trend close to the soil surface, and the sheer damage surface is nearly parallel to the pile-soil interface as the increase of the cyclic period. The larger the cyclic load amplitude is, the more the surface soil tends to be compacted under the cyclic load, the lateral earth pressure increases, the displacement influence area decreases, the corresponding shear strain field shows an “ear” distribution, and the amplitude is more likely to cause the soil around the pile to sink than the cyclic period. The cumulative settlement of the pile in different densities of sands shows different characteristics with cyclic period. The displacement field of the soil around the pile shows an inverted truncated cone in loose sand, while dense sand shows a cylindrical shape.

South China Sea coral mud is a calcareous ooze of marine rock and soil formed by the accumulation of bones and debris after the death of coral groups, which has special engineering properties. It is significant to investigate its time dependent long-term nonlinear deformation under load for the construction and long-term stability analysis of dredger fill islands and reefs. Three groups of one-dimensional consolidation compression tests of coral mud with different loading and unloading schemes were carried out, and the influence of stress history on its long-term deformation properties was explored by changing the loading time and loading-unloading loops. According to the three-stage law of coral mud’s instantaneous deformation, delayed attenuation deformation and delayed stable deformation under loading and unloading test conditions, the improved Burgers model was used to fit ε-t curves under different vertical stresses, which has high fitting accuracy. Meanwhile, after analyzing the model parameters, it was found that the instantaneous strain increment and its growth rate decrease with the increase of graded loading time, the duration of delayed attenuation under the final load decreases, and the delayed stable strain rate and the total strain increment under the final load decrease. In the same loading-unloading loops, the instantaneous strain increment in the unloading stage is smaller than that in the loading stage under the same vertical stresses. With the increase of loading-unloading loops, the instantaneous strain increment in each stage of loading and unloading decreases and is close to each other, the duration of delayed attenuation deformation, the delayed stable strain rate and total strain increment under the final load decrease. The effects of graded loading time and loading and unloading cycles on the long-term deformation properties of coral mud were studied to provide theoretical basis for surcharge preloading scheme in island reef construction.

Soil deformation caused by karst collapse and tunnel excavation often causes uneven settlement, ground collapse and cracking of foundation construction and foundation structure. Development of approaches to determine the distribution of loose earth pressure at the top of soil structure and analyze the relationship between soil deformation and soil arching effect accurately is of much importance. A series of classical trapdoor tests with different H/B ratios were conducted to reveal the variation law of soil deformation and settlement on the loose earth pressure at the top of the structure. Based on the test results, a mathematical model is proposed to analyze the loose earth pressure with triangle as the mechanical model under different slip surfaces. The relationship among the slip surface angle, soil deformation and principal stress deflection is considered. The principal stress deflection of any horizontal differential soil layer in the slip surface is analyzed and the stress equilibrium differential equation is established. The theoretical formula of loose earth pressure is solved according to the boundary conditions under different slip surfaces. The rationality of the theoretical formula is verified by comparing with the trapdoor tests results. The main parameters (e.g. slip surface angle, coefficient of lateral earth pressure and internal friction angle) were analyzed. The results reveal that when the displacement-width ratio (1%− 3%) is smaller, the stress rapidly transfers and redistributes, and the angle of initial slip surface is slightly smaller than π/4+φ /2. With the increase of H/B, the vertical stress increases slowly and finally tends to be stable; loose earth pressure of closed triangular slip surface in foundation is related to the displacement-width ratio and internal friction angle; the increase of internal friction angle makes full use of soil arching effect, strengthens stress transfer and reduces vertical stress; the increase of internal friction angle brings a remarkable reduction in the horizontal stress component, thereby reducing the lateral earth pressure coefficient.

The heat and mass transfer, pore fluid phase transition process and salt frost heave deformation of sulfate saline soil under water and salt supply conditions were studied theoretically and experimentally. Based on unsaturated soil mechanics and thermoelastic continuum theory, a mathematical model of water-thermal-salt-force coupling in unsaturated sulfate-saline soil was established, in which the influence of phase transformation in pores on thermodynamic and hydraulic parameters was considered. The variation process of temperature field, water field, salt field and stress field in soil under unidirectional freezing condition of open system was analyzed by numerical simulation, and the validity of the theoretical model was verified by indoor cooling test. The results show that the latent heat released by salt during crystallization directly affects the process of water freezing into ice. Under the influence of the unidirectional freezing condition of the open system, the concentration of soil pore solution first increases rapidly to the peak value and then decreases gradually over time, and finally tends to be stable. Under the influence of negative temperature, the water phase inside the soil becomes ice, and gradually forms the freezing front. With the downward movement of the freezing front, the degree of salt frost heave is increasing.

The mechanism and prevention of coal burst is an important issue in the study of coal mine dynamic disasters. The disturbance of surrounding rocks can trigger the quasi-resonance phenomena of roadway roof support system in close proximity to its resonant state, ultimately inducing impact disasters. This is manifested in three strong quasi-resonant responses, including roof displacement, velocity and acceleration. Based on the support instability and plastic buckling criteria, three safety factors and the corresponding dangerous disturbance frequency ratio interval for the dynamic failure of support are proposed, and the support damping control strategy is given, aiming at the impact disasters induced by the quasi-resonance of the roof support system. The results show that when the amplitude of disturbing force is lower than the critical failure force of the support under static loads, the quasi-resonant phenomena of roof support system is the main reason for the dynamic failure of support. The frequency ratio range of quasi-resonant dangerous disturbance for support failure is related to the damping ratio and force amplitude ratio of roof support system. With the increasing damping ratio, the displacement, velocity and acceleration response amplitudes at the roof quasi-resonance will decrease. The support damping is a controlling factor sensitive to these three types of quasi-resonant responses. When the damping ratio in the roof support system increases or the force amplitude ratio (the ratio between the amplitude of external disturbance and the critical load for static support failure) decreases, the dangerous disturbance frequency ratio interval of the support will narrow or even disappear. When the damping ratio and force amplitude ratio are small, the dangerous disturbance frequency ratio intervals of the roof support system under three quasi-resonant conditions are close. This study will enrich the understanding of the mechanism behind coal bursts and provide valuable insights for the design of support control.

The first phase of water supply project in northern Xinjiang crossed the expansive soil area, and the mechanical properties of expansive soil are seriously weakened after repeated drying-wetting-freezing-thawing cycles, which cause local shallow landslide and frost heave damage of the canal slope. To further explore the deterioration mechanism of expansive soil canal slope, the changes of compression and permeability indexes are analyzed from macro-, meso-, and micro-perspectives through the compression test, the permeability test, and the SEM microscopic scanning test under drying-wetting-freezing-thawing cycles. The overall compressibility of expansive soil increases with the increase of drying-wetting-freezing-thawing cycles, and its compression curve can be divided into pseudo-elastic section and pseudo-plastic section. With the increase in the number of cycles, the rebound index shows a fluctuation tendency. The compression index is exponentially positively correlated with the number of cycles, and it is linearly correlated with the meso-micro cracks. Under the action of drying-wetting-freezing-thawing cycle, clay particles form a loose temporary structure of 'aggregates-pores-filled particles', flocculation structure increases, and anisotropy decreases. When the soil sample is subjected to vertical pressure, the pore spacing of expansive soil decreases, and the compressibility is large. When the pressure exceeds the consolidation yield stress, the aggregate particles become flat, the polar angular frequency increases, the pores are compacted, and the compressibility is gradually stabilized. Three stages i.e., slow, rapid, and stable stages, are identified in variation of permeability coefficient in the cycle process. The permeability coefficient changes greatly in the fifth cycle, and gradually stabilizes after 7 cycles, which is positively correlated with the number of cycles and surface fracture rate. The grey correlation degrees between the permeability coefficient and microscopic parameters are greater than 0.65, and microscopic porosity is the most important influencing factor. Under cyclic action, the microscopic pores develop obviously and form new seepage channels. The permeability coefficient is linearly and positively correlated with the microscopic porosity.

Based on the engineering environment of the wellbore surrounding rocks in the energy storage areas during deep geothermal energy mining, the methods of high temperature heating, water immersion at different temperatures, heating-cycle times and radial impact loading were used to simulate the physical and mechanical conditions of wellbore surrounding rocks, such as dynamic disturbance caused by high temperature, water encounter, cyclic heat extraction and thermal impact. Meanwhile, the concentric perforated rock samples with different inner-hole diameters were used to simulate deep geothermal wells, and the dynamic mechanical tests of concentric perforated granite samples under the thermal-hydro-mechanical coupling were carried out by SHPB test system. VIC-3D non-contact strain measurement and numerical simulation analysis technology were used to monitor the history of fracture initiation and formation and the surface strain evolution law of concentric perforated granite samples during the impact process so as to reveal the dynamic damage mechanism of concentric perforated granite under the thermal-hydro-mechanical coupling. The results showed that the concentric perforated granite under radial impact load experienced three typical stages, i.e., elastic deformation, plastic deformation and structural instability failure successively. The four factors of inner hole diameter, heating temperature, immersion temperature and the number of heating-soaking cycles all weakened the ability of concentric perforated granite to resist external loads, but did not change its overall deformation evolution law. The failure mode of concentric perforated granite samples was dynamic tensile failure. Firstly, from inner hole wall to outer wall of rock samples along the impact direction, and then from outer wall of rock sample to inner hole wall in perpendicular impact direction, cracks initiate and coalesce, forming two sets of vertical fracture surfaces nearly perpendicular to each other. Finally, based on the damage deformation characteristics and history of the concentric perforated granite, a dynamic damage structure model was established on the basis of certain assumptions, the structure equations were deduced, and the parameters of the equations were determined by combining the test results. Comparative analysis demonstrated that the theoretical fitted curve was in good agreement with the tested curve, which verified the constructed dynamic damage structure model of concentric perforated granite was reasonable. The results not only reveal the damage and failure mechanism of concentric perforated rock samples, but also provide theoretical reference for predicting the damage and deformation law of geothermal wellbore surrounding rock in deep energy storage areas, which have certain scientific and engineering practical significance.

As a simple and applicable theoretical tool, cavity expansion theory has been widely used in the research of geotechnical engineering problems such as tunnel, geotechnical in-situ test, bearing capacity design of pile foundation and anchor plate. The existing expansion theory cannot consider the size effect of soil with small radius expansion. This paper takes the expansion of cylindrical and spherical cavity in sand as the research object to investigate this issue. Based on the strain gradient plasticity theory, this paper introduces and explains the mechanical parameter that can consider the size effect of soil, i.e., soil characteristic length l; meanwhile, considering the large deformation characteristics of soil, a closed solution of cavity expansion that can take the size effect of soil microstructure into account is derived. The correctness of the theoretical solution in this paper is verified by reducing the normalized characteristic length of soil l /α₀ (α₀ is the initial radius of circular hole) to 0 (i.e., without considering the size effect), and thus the solution is reduced to the classical expansion solution without considering the size effect. Then, the effects of normalized characteristic length, friction coefficient, dilatancy coefficient and shape coefficient of soil on pressure expansion relationship, stress distribution around hole, strain gradient around hole and ultimate expansion stress are discussed in detail. Finally, the theoretical solution proposed in this paper is applied to the practical problems such as micro cone penetration test (MCPT), and the formula for calculating the penetration resistance of MCPT is proposed. By comparing with the existing test results, the applicability of this solution is verified.

This paper aims to reveal the rockburst mechanism of sandstone under cyclic disturbance and high temperature. The uniaxial compression tests and CT scan tests on sandstone after different cyclic amplitudes and temperatures were conducted to investigate the mechanical properties, rockburst tendency and failure characteristics of sandstone specimens. The rockburst tendency and failure characteristics of specimen were analyzed. Results showed that the effects of high temperature and cyclic disturbance on the mechanical properties and rockburst tendency of sandstone were significant. The compressive strength, elastic modulus and rockburst tendency of specimens without cyclic disturbances tended to first increase and then decrease as temperature increased, and the threshold temperature was 200 ℃; while those with cyclic disturbances decreased as temperature increased, and the mechanical properties and rockburst tendency of sandstone decreased with increasing the cyclic stress amplitude. The uniaxial compression failure mode shifted from splitting failure to shear failure with the increase of cyclic amplitude and temperature, and the rockburst tendency had a good negative relationship with the three-dimensional fractal dimension of fracture. In addition, the effect of high temperature on the mechanical properties, rockburst tendency and failure degree of sandstone was stronger than that of cyclic disturbance. The research results can provide theoretical basis and engineering reference for the prevention and control of rockburst in high temperature engineering.

This article aims to study the micromechanism of hydration instability of rock-anchorage agent structure. Based on the SEM test and nanoindentation test of anchored mudstone specimen, the evolution of micromechanical properties of rock-anchorage agent structure under different moisture contents was analyzed. The results show that the structural integrity of rock-anchorage agent structure is good under dry conditions, and the interface is a bonding area with a certain width. With increasing the moisture content, dissolution holes and cracks occur in the structure, the range of bonding area is reduced. As a result, the rock-anchorage agent structure debonding failure appears at saturated moisture content. At low moisture content, the indentation data is discrete due to the difference in mechanical properties among the components, and at high moisture content, the cementation ability of each component deteriorates, the overall mechanical properties of the structure decrease, and the data dispersion becomes small. The aggravation of hydration-induced damage makes the cementation structure of mudstone failed and leads to macroscopic damage, while the anchorage agent will fill the micropores generated at the interface under hydration so that the mechanical properties of the interface will be improved relative to the rock part. Therefore, the attenuation range of the microscopic parameters of the interface is smaller than that of the mudstone part.

The prestressed reinforced soil structure was proposed to solve the problem of large-area depressions of soil highways under rockfall impacts in remote mountain areas. Comparative model tests for prestressed reinforced soil embankment and traditional soil embankment were conducted to explore the deformation performance, mechanical response, and load transmission mechanism of both embankments under rockfall impacts. The results show that the size of pits formed in prestressed reinforced soil embankment is significantly smaller than that in traditional soil embankment, which reflects the good impact deformation resistance of prestressed reinforced soil embankment. The embankment stiffness increases with the increase of impact times, resulting in the change of the time history of impact-induced additional stress in the embankment from “parabolic single peak” to “double peak”, and the “double peak” in the prestressed reinforced soil embankment occurs earlier than that in the traditional soil embankment. The duration of rockfall impact on the prestressed reinforced soil embankment is less than that on the traditional soil embankment, and the distribution of the impact on the prestressed reinforced soil embankment is more uniform, indicating that the prestressed reinforced soil embankment is more conducive to the impact diffusion. In addition, the internal impact load transmission ratio for prestressed reinforced soil embankment increases first and then decreases with the increase of impact times, which is consistent with the deformation law of reinforcement structure. The pit sizes corresponding to various impact times are predicted by the Levenberg-Marquardt optimization algorithm, which can provide reference for the engineering application of prestressed reinforced soil embankment and early warning in collapse disaster prone areas.

The pile foundation of bridges and subgrades in high-speed railway engineering are frequently suffered from train-induced vibration. The train-induced vibration under a speed of 350 km/h reaches approximately 40 Hz, while a higher speed may do harm to the bearing capacity of the pile foundation. The soil-structure interface plays an important role in force and deformation transformation in pile-soil interaction, largely determining ultimate strength and long-term settlement. However, understanding of the behavior of soil-structure interfaces under high-frequency vibration is still very limited. Using a self-designed interface shear apparatus, which can achieve coupled vibration and high-frequency vibration, the critical state strength of the granular material-structure interface is investigated. The influences of vibration acceleration, frequency, normal stress, particle shape and surface roughness are studied. Test results show that vibrations lower the strength of interfaces. The shear strength under certain vibration conditions is even lower than half of that under static conditions. The weakening degree of interface strength under vibration increases with vibration acceleration and frequency, while decreases with normal stress. Based on Mohr-Coulomb strength theory, the strength criterion of the granular material-structure interface under vibration is built.

Previous studies on the dynamic characteristics of calcareous sand mostly focused on the saturated calcareous sand, and sine waves were often applied to replace seismic loads in the test process. In order to overcome this defect, a dynamic triaxial seismic load input method is proposed to convert the acceleration time history of seismic load into stress time history. Dynamic triaxial test on calcareous sand in the South China Sea is conducted to study the dynamic characteristics of unsaturated calcareous sand in single and multiple seismic load durations. The test results show that the strain and pore water pressure of calcareous sand develop in a stepwise manner under the seismic load, and the failure strain has both positive and negative values, that is, the failure type has both tensile failure and compression failure, which is different from the development laws of dynamic pore water pressure and dynamic strain under sinusoidal load; with the increase of matrix suction, the maximum dynamic pore pressure shows an decreasing trend, but the maximum pore pressure of calcareous sand samples does not reach the effective confining pressure.

Permeability prediction during hydrocarbon production is a rather important problem. The decrease in permeability due to depletion reserves and the drop in reservoir pressure (increase in effective pressure) leads to an increase in the time of oil or gas production. A large number of works have been devoted to the problem of permeability reduction due to effective pressure. Establishment of permeability models is carried out by various methods including coreflooding tests and field well tests. The results of previous studies have shown that permeability has a power-law or exponential dependence on effective pressure, however, the difficulty in predicting permeability is due to hysteresis, the causes of which remain not fully understood. To model permeability, as well as explain the causes of hysteresis, some authors use mechanical models of the reservoir, which cannot be applied with small fluctuations in effective pressures in the initial period of hydrocarbon production. In this work, we analyzed data from well tests at one of the fields in the north of the Perm region and came to the conclusion that in the initial period of production, the permeability of the reservoirs largely depends on the amount of fluid produced. Based on the well test data of the terrigenous reservoir, a model was obtained that describes the change in permeability in the initial period of oil production. To confirm the model, coreflooding tests of samples of the terrigenous reservoir were carried out according to a specially developed program. Coreflooding results showed high convergence of the model obtained from well test data. With computed tomography (CT) and scanning electron microscope (SEM), the properties and structure of the pore space of the cores were studied and it was found that the main reason for the decrease in the permeability of low-clay rocks in the initial period of production is the migration of natural colloids.

The prefabricated recyclable support structure provides a new green support system with economic security, functional coordination and sustainable development for the development of underground space. The physical model test of the foundation pit of a pipe-jacking working well in Zhengzhou city is carried out based on the similarity theory. A three-dimensional fluid-solid coupling model that can differentiate the deformation difference between rigid and flexible members in the support system is established by using the ABAQUS software. The stress and deformation characteristics of supporting structure in the process of dewatering and excavation are analyzed. The influences of dewatering and excavation on the deformation characteristics of foundation pit are also studied. Results show that in the processes of dewatering and excavation, both the stress and deformation of the main supporting structural members are all less than those of the design values, but the steel panels are prone to local yield at the position connected with the waist beams. The increment mode of horizontal displacement of retaining pile varies greatly with the processes of dewatering and excavation. With the progress of the dewatering and excavation of the foundation pit, the deformation of the supporting structure is less affected by dewatering, and the main factor affecting the deformation of the supporting structure is gradually changing from foundation pit dewatering to foundation pit excavation. The influence of foundation pit dewatering on the surface settlement is greater than that of foundation pit excavation. The surface settlement increases rapidly during the first level of dewatering, with the maximum settlement increment accounting for 44.6%.

In order to study the deformation characteristics of the undisturbed loess considering the change of the intermediate principal stress under high confining pressure conditions, equal b and equal p (p is the spherical stress) shear tests with controlled consolidation confining pressure and medium principal b values were conducted on undisturbed loess using a true triaxial instrument of Xi’an University of Technology. The relationships between the principal strains under high confining pressure were given, and the influence law of the failure strain and different b-value stages was revealed under different high confining pressure conditions. The results show that under the condition of high confining pressure, 3 of all b-value stages is expansion deformation, b = 0.2 is the critical point of intermediate principal strain deformation; 0≤b＜0.2 is the intermediate principal strain expansion deformation, and 0.2＜b≤1.0 is the intermediate principal strain compression deformation. In the high confining pressure state, the influence of the b value on the strain is much greater than the influence of the confining pressure on the strain. The degree of influence of b-value increment on strain is defined as b-value sensitivity K(ε), and b-value sensitivities K(ε2), K(ε3) and K(εs) all present an increasing trend when b-value lies between 0 and 0.7, are less affected by change in b-value between 0.7 and 0.9, and most affected by change in b-value between 0.9 and 1.0. K(εv) mostly falls in the range of 0 to 5, indicating that the failure volumetric strains in intermediate principal stress stages are less affected by the change of b-value.

In order to explore the dynamic interaction of the soil-pile group foundation-bridge structure system in overlaying water-saturated sand fields, a physical similarity model of the straight (oblique) pile group foundation-bridge structure was designed and fabricated. Centrifuge shaking table tests with seismic wave inputs of different ground motion intensities and characteristics were conducted. The dynamic characteristics indexes of pile group foundation-bridge structure were analyzed, and the development of excess pore water pressure in the overlaying water-saturated sand foundation and the dynamic response characteristics of pile-soil interaction was also investigated. The results indicated that the presence of overlaying water had little influence on the basic cycle and damping of the foundation soil-bridge structure system, but caused a 20% increase in the vibration amplitude of the straight pile group foundation-bridge structure system and a 10% decrease in the vibration amplitude of the oblique pile group foundation-bridge structure system. The damping ratio of the oblique pile group foundation model was twice as high as that of the straight pile group foundation model. The overlaying water caused the saturated sand foundation to change from a larger liquefaction depth under low-frequency vibration to a larger liquefaction depth under high-frequency vibration, meanwhile, it led to promote the development of excess pore water pressure under small earthquakes and vice versa under large earthquakes. Furthermore, the overlaying water would lead to an increase in the dynamic response of the bridge superstructure and the pile bending moment. The above research results could provide an essential reference for the seismic design of bridge engineering in overlaying water sand fields.

In order to predict the rock burst disasters of coal roadway, the coal with bump tendency is regarded as a perfectly elastic-brittle material, and the mechanical model of circular coal roadway is established to analyze the distribution characteristics of stress and deformation energy density of surrounding rock of coal roadway, and then the rock burst prediction model of coal roadway is established to predict the rock burst disaster of coal roadway. The results show that the tangential stress and deformation energy density of the surrounding rock of elastic-brittle coal roadway jump at the interface between the elastic zone and the failure zone. The damage degree of the strength and in-situ stress of coal increase, and the radius of failure area also increases. As a result, the jump height of the tangential stress and deformation energy density of the surrounding rock of the coal roadway increases. The tangential stress jumping provides a force for the instability and failure of coal roadway, and the deformation energy density jumping provides an energy for the rock burst. The higher the tangential stress and deformation energy density jump, the easier the instability and rock burst of coal become. Based on the jumping of tangential stress and deformation energy density, the analytical prediction model of rock burst in coal roadway is established, and the prediction results are consistent with the actual situation of rock burst in the field, thus providing a new method for predicting rock burst in brittle coal roadway.

The construction of islands and reefs in the South China Sea is progressing smoothly under the strengthening of China’s maritime development. The ground source heat pump technology and energy pile etc., which take shallow reef flat as medium, are essentially a process of energy exchange with reef sand medium, so it is necessary to further grasp the evolution law of thermal conductivity of coral sand. In this paper, coral fine sand of South China Sea reef was examined. Three thermophysical parameters including thermal conductivity, volumetric heat capacity, and thermal diffusivity, were measured, and the influence of dry density and water content on the thermophysical parameters were analyzed. The predicted data by 12 thermophysical parameter models for sand soil were compared with the measured data for analogical analysis. On this basis, an empirical model suitable for predicting the thermal conductivity of coral fine sand was developed. The results show that the thermal conductivity, volumetric heat capacity and thermal diffusivity of coral sand are positively correlated with dry density, and the correlation coefficients of thermal conductivity and volumetric heat capacity with water content are higher than that of dry density, while the correlation coefficient of thermal diffusivity with water content has a “convex” growth relationship, and the correlation coefficient with dry density is much higher than that of water content. The Cote & Konrad model and the Gangadhara Rao model were amended through the linear regression analysis of the measured data. The prediction accuracy of thermal conductivity of coral fine sand by the model was significantly improved. The difference between the predicted and measured values of the volumetric heat capacity of coral sand was significantly reduced by the linear correction of the De Vries model and the Xu model. Based on the binary fitting analysis of the correlation coefficient of Dai model, a prediction model characterizing the thermal diffusivity of coral fine sand was established to provide reference for the design of insulation and temperature control engineering of island reefs as well as the study of thermophysical properties of coral sand.

There was no systematic study on the development law of soil deformation and excess pore pressure caused by multi row hole grouting in soft soil area to date, which limits the deepening development of active control strategy of grouting deformation. In this study, field tests of multi-row grouting were carried out to systematically examine the variation and superposition law of soil horizontal displacement and excess pore pressure caused by single-row hole-by-hole grouting and multi-row row-by-row grouting. The research shows that the excess pore pressure caused by grouting decreases rapidly with distance, and the variation law can be expressed by a power function. It is recommended that the grouting is about 3 m or closer to the object. At this time, the grouting correction effect is the best. The excess pore pressure caused by grouting dissipated rapidly in Tianjin, which is conducive to the rapid stability of the deformation controlled by grouting. The dissipation law of excess pore pressure over time can be expressed by an exponential function, and an empirical formula for calculating excess pore pressure caused by grouting is put forward. When multiple rows of holes are grouted row by row, the wall formed by prior grouting has reaction force effect and shielding effect on the soil deformation on one side and the other side of the subsequent grouting respectively. When controlling the deformation of existing buildings and structures, the principle of “far before near” row by row grouting shall be followed so as to improve the effect of deformation control.

The application of 2.5D finite element method in the research on railway subgrade dynamic response is becoming more and more widespread. In order to solve the inefficient problem for calculating the dynamic response of subgrade under the random irregularity, a framework for fast calculation of dynamic response of subgrade based on reduced 2D Hermite interpolation is established. The interpolation principle is determined based on the characteristics of the dynamic response of subgrade in the frequency-wavenumber domain. Moreover, the influence of the distribution and number of interpolation points on the interpolation accuracy is discussed. The results indicates that the reduced 2D Hermite interpolation can greatly improve the computational efficiency in the calculation of subgrade dynamic response under the random irregularity. Compared with non-uniform distribution principle of interpolation points, uniform distribution principle can take into account both amplitude and phase interpolation accuracies and therefore is more suitable for 2.5D finite element method. Additionally, the computational efficiency of the present method is only related to the number of interpolation points, and is not affected by the number of random irregularity harmonics. It has obvious advantages in simulating the dynamic response of railway subgrade with random irregularity of track.

Based on the theory of elastic wave propagation in frozen saturated porous media and single-phase elastic media, the reflection and transmission of plane P wave on the interface between saturated frozen soil media and single-phase elastic media are studied. According to the Helmholtz vector decomposition theorem and the boundary conditions of the interface, theoretical expressions of transmission amplitude ratio and reflection amplitude ratio of plane P wave from single-phase elastic media to saturated frozen soil media are derived. Through numerical calculation, the relationships between the transmission amplitude ratio/ reflection amplitude ratio of elastic wave and incident angle are analyzed under different incident frequencies, cementation parameters, porosities, saturations and contact parameters. The results show that only the reflected P wave and three types of transmitted P waves are generated when the P wave is incident vertically from a single-phase elastic medium to the interface of the saturated frozen soil medium. When the grazing incidence occurs, only reflection occurs without transmission. The incident frequency, cementation parameters, porosity, saturation and contact parameters have significant influence on the amplitude ratios of reflected wave and transmitted wave.