In order to investigate the energy evolution and failure characteristics of single fissure carbonaceous shale under drying-wetting cycles, intact and fissure carbonaceous shale samples with fissure angles of 30°, 45°and 60° were fabricated respectively. MTS815 rock mechanical test system was used to conduct triaxial compression tests under different drying-wetting cycles. The influence of drying-wetting cycles on the strength, failure mode and energy evolution of single fissure carbonaceous shale were studied. The results show that the elastic energy and dissipated energy at crack initiation stress, damage stress and peak stress present exponential relationships with drying-wetting cycles. The elastic energy and dissipated energy at crack initiation stress and dissipated energy at damage stress are less sensitive to drying-wetting cycle, while the sensitivities of elastic energy at damage stress, and elastic energy and dissipated energy at peak stress are relatively high. The failure mode of carbonaceous shale is dominated by drying-wetting cycle and fissure angle, in which the drying-wetting cycle is the main controlling factor, and the fissure angle is the secondary controlling factor. It is found that tensile shear failure occurs in dry rock sample with fissure angle of 30°, while the dry rock sample with fissure angle of 45°and 60° are subjected to shear failure. With the increase of the number of drying-wetting cycles, the macroscopic length of the main crack increases, the density of secondary cracks increases, and the failure mode transforms to shear-tension composite failure. With the increase of the number of drying-wetting cycles, the energy storage level at crack initiation stress K_ci and the energy storage level at damage stress K_cd increase gradually. The higher the energy storage level at crack initiation and damage stress is, the more likely the crack initiation and rock damage occur. K_cd can be used as an warning indicator of rock failure. A larger K_cd indicates that the rock is more vulnerable to failure.

To improve the liquefaction resistance of calcareous sand foundations, microbially induced calcium carbonate precipitation (MICP) technology combined with fiber reinforcement technology was proposed to treat the calcareous sand in the South China Sea. Based on dynamic triaxial tests, the dynamic behaviors of MICP and fiber-treated calcareous sand were studied. The dynamic strain, dynamic pore pressure, cyclic stress-strain response and dynamic elastic modulus were analyzed. Then, the strengthening mechanism of MICP and fiber on the mechanical properties of the treated calcareous sand was explored from the microscopic point of view, based on the scanning electron microscope (SEM) test results. The results show that: (i) MICP could improve the deformation resistance and liquefaction resistance of calcareous sands. Compared with the untreated calcareous sand samples, the dynamic strain and dynamic pore pressure of calcareous sand treated by MICP decreased by 95.74% and 92.46%, respectively. (ii) The addition of fibers further improved the reinforcement effect of MICP. Compared to the MICP-treated samples, the dynamic strain and dynamic pore pressure of MICP and fiber-treated samples decreased by 74.32% and 74.18%, respectively. (iii) MICP and fiber reinforcement technologies improved the deformation resistance and liquefaction resistance of calcareous sand subjected to cyclic loading by reducing the cyclic activity strength and energy dissipation, increasing the dynamic elastic modulus and reducing the decay rate of the dynamic elastic modulus. (iv) The results of the SEM test showed that MICP and fiber reinforcement had a synergistic effect on the improvement of the mechanical properties of calcareous sands. The incorporation of fibers provided more spots for bacterial adhesion and promoted the formation of calcium carbonate crystals, which not only increased the bonding strength between sand particles, but also enhanced the restraint of fiber nets by fixing fibers and sand particles together.

Water vapor supply can induce frost heave of sand filler. Based on the self-developed moisture migration and frost heaving tester, the variations of sand moisture content, temperature and frost heave with freezing time under gaseous water recharge were studied. The change characteristics of sand microstructure during freezing were examined by stereomicroscope. By combining with the grey correlation theory, the correlation between the macroscopic index, i.e., frost heave and the microscopic parameters was analyzed. Notable frost heaving was observed under water vapor supply, and the frost heave reached 3.45 mm after 7 days of freezing. After sandy soil frost heaving, the proportion of large pore area increased and the proportions of small and medium micropore area decreased, and the change trend of pore number proportion was opposite to that of area proportion, while pore abundance value changed little, pore orientation angle distribution in each interval tended to be more uniform, the probability entropy of pore orientation present an overall upward trend of oscillation, and the pore fractal dimension showed a trend of decrease. In addition, the grey correlation theory is used to establish the correlation between the frost heave and the average pore size and other microscopic parameters, which provides an insight into the microscopic mechanism of sand frost heaving under water vapor supply.

In recent years, tunnel engineering is developing towards super-long and deep, multi-field and multi-phase coupling, thus, which easily induce the structural instability during tunnel construction and operation. Aiming at the mountain tunnel, underwater tunnel and urban tunnel, this paper expounds the research status of structural model test system, and points out the existing issues. The results show that: mountain tunnel model test takes into account passing through the adverse geological rock, and the loading conditions such as high ground stress, high karst hydraulic pressure and high seismic intensity. However, it’s hard to simulate the high stress of surrounding rock due to the size limitation of the apparatus. The model test of mountain tunnel is mainly based on plane strain model, which lacks the simulation of active fault with various dislocation forms under large-scale true three-dimensional stress condition. The model test of underwater tunnel has achieved stable high water pressure loading, but it is still unable to simulate the true three-dimensional underwater environment of the coupled stress field and seepage field. Additionally, the visibility of the chamber is poor, the seepage of the tunnel is only be characterized by the water inflow at the entrance, which makes it difficult to obtain the deformation law of the surrounding rock. Urban tunnel is affected by train dynamic load, pavement load and adjacent construction disturbance. At present, the model test usually considers the vibration response of the tunnel under a single load, and often ignores the structural characteristics such as segment joints and cracks. Thus, it is necessary to design novel and efficient local loading device to analyze the ultimate deformation characteristics of weak parts of segment to ensure the safety of subway operation. Finally, the bottleneck issues of tunnel engineering model test are summarized, and the internal visualization of the apparatus needs to be improved based on transparent similar materials. Aiming at the adverse geological conditions under high geostress conditions, a three-dimensional static-dynamic coupled model test system with expandable size is developed. Combining with the micro low-power wireless monitoring sensors and 3D visualization results display platform, a tunnel engineering structure model test system suitable for complex environment is established.

Soft rock engineering involves many important engineering fields such as mining, hydraulic engineering, transport and national defense. With the increase of mining depth and the development of tunnel engineering, a large number of tunnels and roadways need to pass through soft rock formations, in which the problems such as high geostress and broken and weak surrounding rocks are prominent. Large deformation disasters of soft rocks pose serious threats to engineering safety and cause enormeous economic losses. In this paper, the research progress on soft rock support in China is first reviewed, and the research status of technology for soft rock control for large deformation hazards is summarized in the following aspects. (1) Passive support methods represented by improved rigid support, retractable support and compound lining. (2) Reinforced active support technology using high-strength bolts and cables. (3) Soft rock modification technology dominated by grouting modification. (4) Soft rock reinforcement with pressure relief as the core idea. (5) Compound support methods. Furthermore, the development of different supporting technologies and methods are elaborated, and the applicable conditions, advantages and disadvantages of different supporting methods are analyzed. It is usually difficult to meet the demand of large deformation control of soft rock relying on a single support method. Therefore, it is urgent to solve the problems of the prevention and control of large deformation disaster of soft rock to realize the efficient collaborative control among different supporting measures and achieve the real-time accurate monitoring of deformation and stress fields. Finally, based on the above research results, the development tendency of support technology for soft rock with large deformation hazards is prospected and the countermeasures are proposed.

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.

To explore the influence of acid or alkali contamination on the shear strength of natural loess, the intact loess samples were first immersed in various concentrations of HCl and NaOH solutions. Then, triaxial shear tests, scanning electron microscopy tests, and mercury intrusion tests were carried out, and the soil chemical composition as well as liquid and plastic limits were measured, so as to assess the influence of acid or alkali contamination on the shear strength, microstructure, chemical composition and plasticity of loess. The results indicate that with the increase of the acid concentration, the peak of soil stress-strain curve attenuates, the shear strength deteriorates, the cohesion decreases exponentially, and the internal friction angle is relatively stable. As the alkali concentration increases, both the peak of soil stress-strain curve and the shear strength increase, the cohesion enhances markedly, and the internal friction angle enlarges slightly. Acid contamination breaks the soil particles, dissolves the cementing material, blurs the boundary between particles and pores, and increases the number and size of pores between skeleton particles and those between clay particles. Alkali contamination leads to the scaffold pore collapse of the soil, and the secondary cementation balances the local damage and strengthens the structural connection. Besides, the content and size of pores between skeleton particles decrease while more pores with a smaller size form between the clay particles. After soaking in acid solutions, the cation content in the soil increases notably, the calcium carbonate content decreases sharply, and the liquid and plastic limits are reduced. After soaking in alkaline solutions, both Al³⁺ and calcium carbonate in soil increase slightly, other cations decrease gently, and the liquid and plastic limits increase. Based on the analysis of test results, the microscopic mechanism of the evolution of the shear strength of loess contaminated by acid or alkali was summarized. Acid or alkali contamination resulted in mineral dissolution, ion exchange, and adjustment of particle and pore structure in the soil, destroying the initial structure of the soil and facilitating the formation of new structures. It is the damage of the initial structure or the new structure formation taking the dominance that decides the comprehensive effect improving or impairing the shear strength of the soil.

The line heat source method of soil moisture monitoring requires higher heating power. When the intensity of the heat source is unstable, the monitoring results are easily affected. To solve the shortcomings of the line heat source method, a mobile point heat source (PHS) method for soil moisture monitoring is developed in this study. This method uses the correlation between the thermal physical properties of soil and the moisture content to indirectly identify the moisture content by monitoring the cooling law of the PHS in the soil. Firstly, the heat transfer law of the PHS in the soil with evenly distributed moisture content was examined through numerical simulation. According to the characteristics of the cooling curves of the heat source, the moisture content discrimination index η was defined, and then the fitting relationship between the moisture content and the discrimination index was established. In addition, parameter analysis was carried out on the factors affecting the monitoring sensitivity. Then, numerical simulation of the PHS cooling law was carried out in the soil with unevenly distributed moisture content, and the moisture content discrimination index was calculated according to the time history curve at the cooling stage of the measuring point. After that, the moisture content distribution was inverted by the fitting formula of the moisture content and the discrimination index. The results show that the moisture content distribution inverted by the PHS method is in good agreement with the actual value, which verifies the theoretical feasibility of the method. Finally, the feasibility of the method is further verified by model tests.

Rainfall-induced landslides are the most common geological hazard in the world, and the effect of preferential flow infiltration has been neglected for a long time regarding the slope reliability analysis under rainfall infiltration. The preferential infiltration under rainfall conditions is solved numerically by Comsol Multiphysics, and the slope factor of safety is calculated using an infinite slope model. An improved Cholesky decomposition method is applied to generate spatially correlated random fields, and the slope reliability during rainfall is analyzed using the Monte Carlo method. Combining the deterministic and reliability results to compare the variation of slope factor of safety between the homogeneous infiltration and the preferential infiltration during rainfall, it can be found that: (1) the preferential infiltration model is safer when the rainfall intensity is low, while the homogeneous infiltration is more stable at higher rainfall intensity; (2) the spatial variability of infiltration parameters is the crucial factor of slope failure in homogeneous infiltration, while the slope instability of preferential infiltration is mainly caused by the rapid advance of the wetting front; (3) for the study of preferential infiltration model, the slope has a higher probability of failure when the hydraulic exchange intensity between the matrix domain and the preferential domain, while smaller hydraulic exchange intensity may affect the slope failure at the bottom.

To explore the environmental durability of heavy metal contaminated soil remediated by enzyme induced carbonate precipitation (EICP) technology, acid soaking, freeze-thaw tests, and rainfall tests were carried out on the zinc and lead contaminated soil after EICP remediation, respectively. The durability and influence of the zinc and lead contaminated soil remediated by EICP technique under different environmental conditions and the corresponding influence regularity were discussed in this paper. The results showed that under different concentrations and types of acid solutions, the leaching amount of heavy metal ions in exchangeable and carbonate bound forms in the zinc and lead contaminated soil after EICP remediation decreased with pH value, with the content of ions in carbonate bound forms decreasing and the content of ions in exchangeable forms gradually increasing. It was also found that the stability in sulfuric acid solution was greater than that in nitric acid solution. As the number of freeze-thaw cycles increased, the leaching amount of exchangeable ions in the zinc and lead contaminated soil remediated by EICP technique increased, while the content of ions in the carbonate bound form reduced. Under the condition of heavy rain, Zn²⁺ and Pb²⁺ were mainly released within the first 20 minutes and migrated from top to bottom. All the results demonstrate that the heavy metal contaminated soil remediated by EICP technology has a good durability under acid soaking, freeze-thaw cycles, and heavy rain.

Cement-based 3D printing technology is increasingly popularized in civil construction and rock-like physical simulation, yet its cement-based 3D printing materials not only is limited by the challenges in quality control such as liquidity, shrinkage, and processability, but also is lack in basic formula in concrete material. This paper firstly establishes a set of assessing system based on six indexes and corresponding quality classification method considering the whole process of solid model forming for cement-based 3D printing, including fluidity, extrusion, setting time, buildability, compactness and deformation rate. The quality evaluation of the 3D printing solid model is realized in three aspects: printing process, stacking process, and solid accuracy. Then, through the two-stage orthogonal design and printing test with different threshold ranges, the basic mix ratio of cement-based 3D printing materials, which is ideal in comprehensive printing performance, is obtained. Finally, the uniaxial compression test is carried out for the printed cement-based 3D solid model and its rock-like mechanical properties are evaluated, which can provide a new type of rock-like cement-based 3D printing material. The specific mix ratios lay the foundation for the civil construction and physical simulation test of rock engineering based on cement-based materials.

The pressure balance method is adopted in calculating the stability against the inrush of excavation in the current criterion. The effects of soil strength and excavation size are not considered in this method. Therefore, the method gives a conservative evaluation of the situation approaching the critical artesian pressure. Aiming at these problems, firstly, the safety factor is defined according to the principle of shear strength reduction in this paper. The existing method considering soil shear strength along slip surfaces is improved by adopting effective stress analysis and considering the passive zone of excavation. Then, a new calculation method for inrush resistance is proposed based on the elastic plate theory. Subsequently, the results of the finite-element method with reduced shear strength are compared with those of above calculation methods under the plane strain condition. And the effects of the excavation length-width ratio for the improved and proposed methods are further analyzed. Finally, the analysis of an engineering practice is carried out. The analysis shows that compared with the existing methods, the improved and proposed methods in this paper can better reveal the trends of excavation stability against inrush with the change of the artesian pressure and improve the economy on the premise of ensuring the safety of engineering practice.

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

The water softening of argillaceous sandstone in complex stress state will seriously reduce the bearing capacity of surrounding rock, resulting in the increase of failure range and deformation pressure of surrounding rock, and finally seriously threaten the safety of water tunnel during operation. To solve this problem, triaxial tests under different immersion time are carried out to investigate by using argillaceous sandstone from water delivery tunnel of Lanzhou water source project. The results are as follows. As the immersion time prolongs, the sensitivity of peak strength and residual strength to confining pressure decreases gradually. This may be attributed to the fact that the water reduces the sensitivity of peak strength and residual strength to confining pressure to a certain extent. In the early stage of immersion, the decreasing rate of residual strength with immersion time is significantly less than that of peak strength with immersion time, and the softening effect of water on the peak strength of argillaceous sandstone is more remarkable. The peak strength, residual strength and elastic modulus of argillaceous sandstone samples decrease with the increase of immersion time in a negative exponential relationship. With the increase of confining pressure, the influence of immersion time on elastic modulus gradually weakens, and the increase of confining pressure reduces the softening effect of water on the elastic modulus of argillaceous sandstone to a certain extent.

This study aims at revealing the deformation and evolution characteristics, formation mechanism and stability of slope under rainfall infiltration condition. A slope in the north stope of Taihe mine in Xichang city, Sichuan province was analyzed in detail as a research object by adopting various methods such as field geological survey and mapping, in-situ test, laboratory test and numerical simulation. The results show that: 1) Both landslides in 2018 and 2019 occurred in rainy season and stabilized again with the end of rainy season. 2) The formation of the landslide is the result of the comprehensive action of multiple factors: the fault provides the boundary for the formation of the landslide, which is the external condition; the diabase with high content of chlorite and montmorillonite is easy to soften and disintegrate when exposed to water, which is an internal condition; the mining and rainfall are the inducing factors. Mining forms an ultra-high slope and exposes the diabase rock layer, while rainwater infiltrates from the slope surface and fault to erode and soften the whole diabase rock layer, resulting in local sliding of the diabase layer under the action of high potential energy, and then pulling it to the overall sliding. 3) Rainfall greatly impacts on the factor of safety and failure mode of slope. The slope is in a stable state before rainfall, and the potential failure mode is overall sliding. After 5 days of rainfall, the factor of safety for the slope drops to 0.842, and two steps of local sliding occurs in the diabase layer. After that, the factor of safety continues to decrease, and the damage range further expands, which is confirmed by the actual observations.

The shear strength of the soil-rock mixture-bedrock interface is a key parameter for the stability of the slope and engineering design. In order to explore the influence of the block stone size on the shear mechanical behavior of the soil-rock mixture-bedrock interface, a series of large-scale laboratory shear tests of the soil-rock mixture-bedrock interface with different block stone sizes was carried out. The results show that the failure mode of the contact interface is not significantly affected by the size of the block stone and the normal pressure, and both are characterized by strain hardening. However, the normal pressure will weaken the impact of the block stone size effect. As the size of the block stone increases, the shear strength and the shear strength index (φ, c) first increased and then decreased. There are both a positive size effect and a negative size effect. The size effect has a limited influence on the angle of internal friction φ , which fluctuates around 29º. However, the size effect has a significant influence on the apparent cohesion c. The specimens with different block sizes show obvious shear contraction behavior under different normal pressures, and the normal pressure can enhance the shear contraction characteristics of the soil-rock mixture. The soil-rock mixture-bedrock interface is a weak potential slip surface. With the increase of the block size coefficient, the weak failure surface tends to transform into the soil-rock mixture.

Breakage-induced evolution of particle size distribution (PSD) has a significant impact on the physical and mechanical properties of soil. It is therefore of great practical significance to study the evolution of particle breakage. The gradation transition matrix provides an effective approach to describing the detailed particle breakage of granular soils. This paper presents a series of  one-dimensional compression tests on carbonate sands with different initial conditions (i.e., PSD, relative density) to establish the gradation transition matrix of sample with more detailed information on particle breakage of each size group. The breakage of each single-sized particles of soil samples with multi-sized particles under different initial conditions is explored based on the dyeing and PCAS image recognition technologies. The results show that the presence of small-sized particles plays a negative effect on the breakage of the large-sized particles, while the presence of large-sized particles promotes the breakage of the small-sized particles. The PSD of each single-sized particles of a carbonate sand sample evolves towards the fractal distribution, and the relative breakage index  B_ri  of each single size group is linear with the input work per unit volume W_in . Finally, the breakage transition matrices of both uniformly and non-uniformly graded carbonate sands are established with consideration of interactions between particles with different sizes, which demonstrates its satisfactory performance. The proposed method provides a new insight into the evolution of particle breakage of granular soils with more detailed information of each size group.

Pumping of confined water is one of the main problems faced by deep foundation pit engineering. And group well pumping test is the main method to reasonably analyze the drawdown of confined water and surface settlement around foundation pit engineering, which is of great significance. A large-scale deep foundation pit pumping test in the area of a terminal in Shanghai was selected as an example in this study. Combined with the engineering geology and hydrogeological conditions of the site, the confined water level change and surface settlement during the group well pumping tests were analyzed. The influence of the drawdown of confined water on soil layer compression and ground settlement were investigated. The results showed that within the monitoring range of 300 m, the maximum ground settlement was 104.9 mm, the maximum drawdown was 21.85 m, and the ground settlement caused by the drawdown per meter was about 5mm. The maximum compression of 7th soil layer was 68.4 mm, and the compression caused by one meter of drawdown was about 3 mm. The ratio of settlement to drawdown tended to decrease with the increase of distance, and within the range of 40−310 m from the center, the ratio of settlement to drawdown was 4.22−1.17 mm.

The gas in the seabed sediment exists in the seabed soil as discontinuous gas phase, existing theoretical studies seldom consider the gassy seabed environment, and there are few studies on the additional deformation of the tunnel lining caused by the seepage force induced by the wave dynamic pressure. Firstly, the control equation of gas-water mixed flow is obtained by Biot consolidation equation, and the pore water pressure response around the tunnel lining is obtained by combining with Stokes second-order nonlinear wave theory suitable for shallow water. Secondly, the superposition method is used to consider the oscillatory pore pressure and cumulative pore pressure in the seabed soil caused by waves, and the maximum pore water pressure and seepage force that may appear around the lining are taken as the most unfavorable load cases. The displacement variation law of the tunnel lining during service under the action of wave seepage force is obtained in combination with the exponential decay model to describe the lining deterioration effect. Finally, accuracy of the theoretical analysis in this paper is verified by the experimental monitoring data and numerical simulation. Parameter analyses are made on the wave period, water depth, seabed shear modulus, seabed gas content, tunnel radius, burial depth and lining deterioration. The cumulative effect of wave pressure propagating into the seabed and excess pore water pressure can be weakened when the seabed gas content increases. The extreme pore pressure around the tunnel lining decreases and the phase lag occurs with the increase of the gas content in the seabed. The external seepage force and the radial displacement of the lining decrease significantly with increasing the gas content in the seabed. Larger wave period and shallower seawater depth can significantly increase the wave pressure on the seabed surface, and induce greater seepage force around the tunnel lining, resulting in greater radial displacement. Reducing the radius and depth of the tunnel can effectively weaken the influence of the seepage force caused by the accumulated pore water pressure. When the lining deterioration coefficient is constant, the influence of excess pore water pressure caused by waves in the seabed with lower gas content is more significant, and the lining produces large radial displacement, which is not conducive to the normal service of the tunnel.

Tunnel roof collapse is a progressive failure process. In order to study the progressive collapse characteristics of deep tunnel roof with weak surrounding rock, we establish the three-dimensional progressive collapse mechanism of deep tunnel based on the limit analysis upper bound theorem and nonlinear Hoek-Brown failure criterion, derive the analytical solution of collapse surface in the whole process considering pore water pressure, and draw the three-dimensional surface diagram of roof progressive collapse. Furthermore, we analyze the morphological characteristics of the collapsed body when the relevant parameters are varied singularly, and the influence of each parameter on the collapsed body gravity and tunnel support force under different pore water pressures. The results show that the dimensionless parameters characterizing the rock mass, unit weight, pore water pressure and tensile stress have significant effects on the morphology, gravity and support force of progressive collapse. In the process of progressive collapse of deep tunnel, the physical and mechanical parameters of surrounding rock gradually weaken, which is mainly reflected in the gradual attenuation of the rock strength with the development of deformation up to a residual value. The attenuation of the strength of surrounding rock and the residual strength have a certain influence on the collapse gravity and tunnel support force. The theoretically calculated collapse shape of tunnel roof is basically consistent with the collapse range of tunnel roof in the F₃ fault fracture zone of actual tunnel engineering, which verifies the applicability of the theoretical results for predicting the collapse range of tunnel roof progressive collapse. The research results can provide a theoretical basis for the construction design and safety protection of deep tunnel with weak surrounding rock.

In order to explore the influence of the relative positional relationship between the dynamic load and the long axis of the elliptical  cavern on the characteristics of impact rockburst, a cuboid sample with an elliptical hole is prepared. With two positional relationships of disturbance direction parallel or perpendicular to the long axis of the elliptical cavern, the elliptical cavern impact rockburst experiments are carried out. With the aid of video recording device, the characteristics of the impact rockburst of the elliptical cavern are discussed in terms of damage process of rockburst ejection, ejection speed, failure mode and fragment size. The experimental results show that the rockburst processes of the two samples with different positional relationships are the same, and the rockburst pits are all V-shaped. The initial failure stress, rockburst stress, rockburst ejection velocity, rockburst pit size, fragment mass and proportion of coarse-grained fragments of the samples whose disturbance direction is perpendicular to the long axis of the ellipse are smaller than those of the samples whose disturbance direction is parallel to the long axis. The fragment characteristics of the samples whose disturbance direction is perpendicular to the long axis of the ellipse are mainly presented as thin stripes. The samples whose disturbance direction is parallel to the long axis of the ellipse can significantly improve the bearing capacity of the cavern structure. However, the rockburst phenomenon is more severe and its debris characteristics are mainly of thick plate.

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

Hydrogen is a low-carbon and clean energy source that can be produced from a wide range of sources, and the vigorous development of hydrogen energy industry is an important measure to achieve the dual-carbon goal and cope with the global energy transition. In the whole industry chain of "preparation–storage–transportation–application" of hydrogen energy, the difficulty of hydrogen storage has long been a constraint to the high-quality development of hydrogen energy industry. Salt cavern hydrogen storage has outstanding advantages such as low cost, large scale, high safety, and high hydrogen storage purity, which is an important development direction of large-scale hydrogen storage in the future, and also a major strategic demand during China's low-carbon energy transition. The current situations of hydrogen production industry and hydrogen energy consumption in China were comprehensively investigated, and the demand for salt cavern hydrogen storage in China was further analyzed. The technology and engineering status of using salt caverns to store natural gas and hydrogen in foreign countries were investigated, and the development and construction history of salt cavern storage in China were summarized. The similarities and differences of using salt caverns to store natural gas, helium, compressed air, and hydrogen were compared, and three major scientific and technological challenges that salt cavern hydrogen storage in Chin faces were proposed: hydrogen seepage and biochemical reaction in bedded salt rock, wellbore integrity control in salt cavern hydrogen storage, and pregnancy and prevention of disaster in hydrogen storage groups. The research results clearly define the rapid growth trend of hydrogen storage demand and the key research directions of large-scale salt cavern hydrogen storage in China.

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.

Sand-bearing rock is a special rock formed in the high-level key layer before water inrush and sand burst disaster. Its strength and mechanical properties are different from ordinary rock, which determines the stability of the high-level key layer. It is found that the fractured rock and sandy rock with different fracture angles have different characteristic stresses, and with the increase of fracture angle, the initiation stress, damage stress and peak stress of fractured rock and sandy rock increase, and the bimodal stress first increases and then decreases. The characteristic stresses of sandy rock under the same fracture angle are less than those of fractured rock, indicating that the sand body has a weakening effect on the characteristic stress of rock. From the perspective of failure form, the fractured rock is easy to show wing tensile fracture, the sandy rock is easy to form tensile fracture under the condition of low fracture angle (30º) and shear fracture under the condition of high fracture angle (60º), indicating that the sand body has shear effect on the rock after entering the rock fracture. At the same time, the mechanical model of sand filling is established, and it is pointed out that the reason why the strength of sandy rock is less than that of fractured rock is that the sand body reduces the friction coefficient of rock. Based on the cumulative acoustic emission ringing counts, the amount of rock damage is defined and the mechanism of sand-bearing rocks causing the disaster is analysed. The on-site sand-bursting disaster can be divided into four phases: 1) elastic deformation phase; 2) fracture expansion phase; 3) sand and energy storage phase; 4) sand-bursting energy release phase. Finally, PFC2D is used to verify the differences between fractured rocks and sandy rocks, and the energy evolution laws of different types of rocks are analyzed. The research results can be used as precursory information identification of water inrush and sand burst phenomenon in coal mine roof, and help to guide the safe production of water inrush and sand burst face.

The waste tire-faced retaining wall is an ideal way to effectively utilize waste tires. However, vertical modular waste tire-faced retaining walls cannot withstand high-intensity seismic action. Therefore, the geogrid striped-reinforced method is proposed to improve its seismic performances. According to the soil-structure dynamic similarity system, a shaking table test model of the geogrid striped-reinforced waste tire-faced retaining wall is designed. This test model can consider the influence of seismic intensity, seismic wave, length of geogrid reinforcement, spacing of geogrid reinforcement and the slope of the wall. The seismic response characteristics were analyzed, such as the tire-faced wall and the backfill acceleration, the lateral displacement of the wall, the settlement of the backfill on the top of the wall and the dynamic soil pressure on the back of the wall. In addition, the characteristics are compared with those of the shaking table test of the waste tire-faced retaining wall (unreinforced). The results show that geogrid striped-reinforced tire-faced retaining walls significantly improve the seismic response characteristics of unreinforced retaining walls, and improve the seismic performance of the tread retaining wall. Thus, the geogrid striped-reinforced vertical waste tire-faced retaining wall can be used as an ideal wall for engineering application.

Salt rock has been recognized as an ideal medium for energy storage or oil and gas storage because of its good creep characteristics and self-healing. Accurate characterization and prediction of the complex mechanical behaviour of salt rock is the basis for ensuring the safety of the underground space utilization project of salt caverns. Based on proposed parameters of hardening and other characteristic factors, in this study, a new creep fatigue constitutive model is developed for salt rock considering complex loading and unloading path. Based on the dislocation mechanism of salt rock deformation, hyperbolic damping elements are introduced as state variables to characterize the degree of rock hardening. The influence of loading and unloading history on the deformation behavior of salt rock is considered according to the evolution of hardening parameters. Based on the stress-strain relation of the classical Norton model, a basic mathematical relation is established for the creep fatigue constitutive model. By assuming the initial nucleation length and considering the material fracture toughness, the stress-strain relation is modified for the range of adjacent failure stage (accelerated deformation stage) based on a newly introduced crack growth factor. In this manner, the proposed model can well predict the plastic deformation characteristics under complex loading and unloading paths such as conventional creep, cyclic loading and unloading, lower limit interval cyclic loading and unloading, trapezoidal wave creep cyclic loading and unloading. The model can also better characterize the interaction between constant load creep and cyclic loading and unloading. Most of the model parameters have clear physical meanings in the new developed creep fatigue constitutive model. Parameter a represents the relation factor between stress and deformation rate in the steady-state deformation stage of salt rock, parameter b determines the relation factor in the first stage of deceleration deformation stage of salt rock, and parameters of  d₀  and μ_d  represent the initial crack nucleation amount and crack growth rate factor, respectively. The  d₀ and μ_d   jointly affect / modify the stress-strain relation at the critical failure stage of the model.

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

Buckling instability may occur when pile foundation passes through large caves, and the critical buckling load is the ultimate bearing capacity of pile foundation. To solve the buckling problem of pile foundation crossing single layer karst cave in karst area, a total potential energy equation of pile foundation crossing single layer karst cave is established according to the principle of energy method. According to the catastrophe characteristics of pile foundation buckling, the cusp catastrophe theory is introduced, and a cusp catastrophe model of pile foundation instability under the condition of elastic embedding at the top and fixity at the bottom is established. The bifurcation set equation of the system is derived, and then by analyzing its instability conditions, the method of calculation of buckling critical load of pile foundation crossing single-layer karst cave is developed. In order to verify the rationality of the proposed method, laboratory model tests of pile foundation crossing karst caves with different heights are carried out. Some conclusions are drawn. 1) The compression failure and buckling failure are main forms. When the height of the cave is less than 6d, the foundation pile fails due to material compression failure. When the height of the cave is greater than or equal to 6d, the buckling occurs in pile foundation. The maximum displacement point is observed to be located at the midpoint of the karst cave section. 2) The critical buckling load of pile foundation decreases linearly with the increase of cave height. The proposed method is suitable for the buckling of pile foundation, and it is in good agreement with the experimental results. 3) The small cave height, thick roof, great elastic modulus of the pile foundation, and rough pile-rock interface can result in a great critical buckling load, and not vice versa.

To study the fracture dynamic evolution process of grouting specimens under loading conditions, the graded gravel grouting specimen was periodically scanned during the uniaxial compression damage process using a CT scanning system. Based on the image reconstruction technique, the spatial visualization of the fracture structure inside the test grouting specimen block is achieved, and the structural characteristic parameters are characterized quantitatively such as the number and volume of fractures. The gray value and fractal dimension of the CT slices are calculated using Python programming to analyze the mesoscale damage extent at different loading stages of the grouting specimen. It is shown that the specimen’s internal fracture volume shows a trend of slow rise, slow fall, slow rise, and rapid rise. The fracture number shows a trend of increasing firstly and then decreasing during the whole compression stage. When the fracture expansion paths encounter gravel, most of the fractures expand around the gravel location and few fractures expand through the gravel. In addition, the fracture bifurcation expansion mostly appears at the interface between the cement matrix and gravel. The specimen damage process could be divided into four stages in terms of the fracture evolution process inside the specimen: initial defect expansion stage, internal crack compacting stage, fracture expansion stage, and fracture penetration stage. For the slice at the same loading stage of the test specimen, it is found that the value of the damage variable and fractal dimension shows a certain positive correlation, which is similar to the trends of the fracture volume evolution. The research results can provide a reference for the study of the failure process and fracture evolution law of the grouting body.

Roughness of rock fracture has a significant influence on the seepage characteristics of fracture. The point cloud data of rock fracture surface was collected by three-dimensional (3D) optical scanning system. The joint roughness coefficient (JRC) and surface roughness ratio (Rs) were calculated by SURFER and GEOMAGIC STUDIO, and the quantitative relationship between JRC and Rs was established. The effects of JRC and Rs on the fracture seepage characteristics in limestone were investigated by conducting seepage tests under the coupling effect of stress, seepage and chemical interaction. The results show that JRC is a logarithmic function of Rs, with the R-squared (R2) of 0.912 8. The maximum relative error (MRE), mean absolute error (MAE) and root mean square error (RMSE) between the proposed characterization formula and seepage test results are 6.93%, 0.34 and 0.27, respectively. JRC shows quadratic function and logarithmic function with the seepage flow and permeability at stable period, respectively. The fitted relationships of Rs and each parameter are consistent with that of JRC. The larger JRC is, the smaller the seepage flow and permeability are. The values of JRC and Rs of the fracture surface increase under the coupling effect of HMC (hydrological- mechanical-chemical) three fields. The characterization method proposed in this study can be used to estimate the surface roughness of rock fracture. Meanwhile, the value of JRC can be applied to predict the seepage flow and the permeability at stable seepage period.

In order to accurately obtain the vertical and horizontal saturated permeability coefficient of undisturbed Q3 loess, in-situ tests, laboratory tests and numerical tests were carried out, and the reliability of the saturated permeability coefficient measurement was verified by large-scale test pit immersion test. Firstly, the in-situ double ring infiltration tests with different inner diameter sizes were carried out to obtain vertical saturation coefficients and indoor tests were applied to test vertical and horizontal saturation coefficients and water holding curve. Then, COMSOL software was used to simulate the double-ring infiltration tests, the optimal values of vertical and horizontal saturated permeability coefficients were obtained by orthogonal tests, and the inversion results were used to simulate the test pit immersion test, and the simulated water infiltration was compared with the measured values. The results show that the saturated permeability coefficient obtained by selecting the double-ring with larger inner diameter is more rational in the field double-ring infiltration test. For the double-ring infiltration test, the optimal vertical saturated permeability coefficient obtained by numerical simulation inversion is close to the vertical saturated permeability coefficient obtained by in-situ test in the vertical direction, and close to the horizontal saturated permeability coefficient measured in the laboratory in the horizontal direction. The vertical saturated permeability coefficient affects the water infiltration process more significantly than the horizontal saturated permeability coefficient. The reliability of the optimal saturation permeability coefficient obtained from the inversion was tested by verifying the water infiltration in a large test pit.

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

To further explore the fracture initiation mechanism of fracture grouting in typical sandy mudstone from Huainan and Huaibei mining areas in China, a conventional triaxial fracture grouting test device was developed, and the model test of fracture initiation pressure of slurry fracturing in similar material of sandy mudstone was carried out. Based on the test results, the influences of rock strength and stress state on grouting fracture initiation pressure and fracture propagation pattern were analyzed, and the fracture initiation mechanism of fracture grouting in sandy mudstone was revealed. The results show that there is a positive correlation between the initiation pressure and the compressive strength of rock; the larger the compressive strength of the rock is, the more complex the fracturing path is. The sensitivity of fracture initiation pressure to confining pressure is much greater than that of axial pressure; the larger the stress difference Δσ = σ _V −σ _H is, the more regular the fracture shape is. Under the triaxial condition of pore pressure, the rock tensile strength determined by slurry fracturing method in sealed open hole section is approximately 2.5 times the uniaxial tensile strength. The research results can provide a reference for the design and construction of fracture grouting in similar rock strata in the future.

Mechanical properties of soft soil will change under freeze-thaw cycle with a certain confining pressure in artificial freezing engineering in coastal soft soil area. Therefore, it is of a great significance to study the influence of freeze-thaw cycle under different confining pressures on the mechanical properties of soft soil. This paper takes the typical muddy soil in Tianjin coastal area as the research object. Through a self-improved temperature controlled triaxial apparatus, the differences of mechanical properties of soft soil under conventional freeze-thaw without confining pressure and freeze-thaw with confining pressure are compared and analyzed. Furthermore, the effects of freezing temperature, number of freeze-thaw cycles and freezing-thawing confining pressure on excess pore pressure, stress-strain characteristics, strength and deformation index of soft soil are revealed. The influence mechanism of freeze-thaw confining pressure on the mechanical properties is explored by SEM. Then, the relationship of shear strength, reduction coefficient of elastic modulus of muddy soil and above influence factors is established by using an exponential function. The results show that the freezing and thawing confining pressure reduces the size and number of pores in the soil after freezing and thawing, which can weaken the damage of freezing and thawing to the soil structure to a certain extent. However, the freeze-thaw confining pressure has little effect on the stress-strain curve. With the decrease of freezing temperature and the increase of the number of freeze-thaw cycles, the strength and moduli of soil are greatly reduced. With the increase of freezing-thawing confining pressure, the freezing temperature and the decrease of the number of freeze-thaw cycles, the excess pore pressure decreases.

There are a large number of cracks inside the rock mass. Due to the existence of fillers, the crack surface is closed in most cases, and friction will be generated when subjected to external forces, which will affect the crack initiation mode and propagation behavior of the rock mass cracks. Therefore, in order to study the crack initiation mode and propagation behavior of closed cracks, a rock-like material PMMA plexiglass plate was used to make pre-splitting specimens containing closed cracks, and uniaxial compression tests were performed on the specimens. Digital image correlation system (DIC) recorded the initiation and propagation characteristics of closed cracks. In addition, the extended finite element method (XFEM) was used to simulate the initiation and propagation of closed cracks, the failure process of the specimens with closed cracks was obtained through simulation, and the initiation and propagation characteristics of closed cracks were analyzed, which was in good agreement with the test results. The validity of the numerical simulation is verified. On this basis, the crack inclination angle and the friction coefficient of the crack surface are introduced as variables, and their influence on the crack initiation and propagation behavior of closed cracks is simulated. The research results show that the cracks generated under the condition of crack closure are airfoil tension cracks. Crack inclination and crack surface friction coefficient have a greater impact on the crack initiation mode and growth behavior of closed cracks. The larger the crack inclination angle is, the larger the crack initiation angle is. On the contrary, the larger the friction coefficient of the crack surface is, the smaller the crack initiation angle is. In addition, the friction coefficient of the crack surface has an inhibitory effect on the growth of closed cracks, and as the friction coefficient continues to increase, the inhibitory effect becomes more and more significant, and crack arrest occurs.

Hashiguchi sub-loading surface constitutive model is one of the most influential constitutive models for over-consolidated soil. Therefore, this model is selected to analyze in terms of theoretical principle and construction method, and compare with the unified hardening(UH) model proposed by Yao et al. Through comparison, the Hashiguchi sub-loading surface model defines a single mathematical formula to fit the variation rule of the internal variables of the over-consolidated soil, and thus it can describe the stress-strain relationship of the over-consolidated soil. UH model holds the strength characteristics of over-consolidated soil, so it can describe the stress-strain relationship of over-consolidated soil more accurately and reasonably, which shows that the UH model is more advanced and complete in theory. At the same time, the comparison between the predictions of the two models and experimental data also verifies the correctness and superiority of UH model in numerical calculation.

The shield tunnel is typically simplified as an infinite beam with two free ends in existing analytical models, which are used to calculate the longitudinal deformation of the underlying shield tunnel induced by the excavation of a foundation pit. However, the applicability of those analytical models is limited due to the simplification. The current study is aimed at estimating analytically the longitudinal deformation of the underlying shield tunnel induced by the excavation of a foundation pit adjacent to the station (working shaft). The constraint on the shield tunnel generated by the joint between the station (working shaft) and the tunnel is treated as a rotation spring with the rotation stiffness of  K_θ  and a vertical rod support. The Winkler foundation – Timoshenko beam model for calculating the longitudinal deformation of the shield tunnel adjacent to the station (working shaft) induced by the foundation pit excavation is proposed. The finite difference solution of the proposed model is strictly derived based on the basic principles of the force method. The reliability and applicability of the proposed analytical model are verified via the comparison with the finite element numerical solution of one-dimensional elastic foundation beam model and the global finite element simulation results of the longitudinal deformation of the underlying tunnel induced by the excavation of a foundation pit adjacent to the station. The parametric studies indicate the following conclusions. (i) The longitudinal deformation and internal forces of the shield tunnel are significantly influenced by the rotation stiffness, K_θ , of the joint between the station (working shaft) and the tunnel. The internal forces and the longitudinal deformation (i.e. rotation angle) at the end of the tunnel increase and decreases nonlinearly with a increasing  K_θ , respectively. In addition, when the flexible connection is adopted at the joint between the station (working well) and tunnel, the working performance of the shield tunnel at the joint can be better guaranteed. (ii) The constraint effect of the joint on the end of the tunnel is non-negligible, when the distance from the center of the foundation pit to the station-tunnel joint ranges from 4 to 5 times the width of the pit along the tunnel axis. In this condition, the proposed analytical model should be adopted to evaluate the longitudinal working performance of the tunnel. (iii) The influence of the overlying foundation pit excavation on the underlying tunnel mainly exerts within 2 times the length of the pit perpendicular to the tunnel axis away from the center of the pit.

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

The concrete-granite combined body is a typical binary material in engineering, with mechanical response properties that differ from monomer under triaxial circumstances. Concrete monomer (CM), granite monomer (GM), and concrete-granite combination body (CGCB) were subjected to quasi-static compression tests under various confining pressures. To reveal the overall crack propagation and failure mechanism of the composite specimens, SEM was used to study the fracture and interface microstructure of CGCB, and RFPA was employed to simulate the failure process of CGCB. Finally, based on the Mohr-Coulomb strength criterion, a prediction model for composite triaxial compressive strength was developed. The results show that the uniaxial (triaxial) compressive strength of CGCB is affected by the material size effect and the interface constraint effect, and the failure condition of the combined body shifts from uniaxial "Y" splitting failure to shear failure of the concrete component when confining pressure is increased. Under various confining pressures, the concrete away from the contact and the granite near the interface are damaged in turn, and shear fractures occur progressively, resulting in the splitting failure of granite components, according to the numerical simulation findings. The strength prediction model can match experimental data and numerical simulations effectively, demonstrating the accuracy of the model. The findings of the study might serve as a scientific foundation for the excavation and support of deep subterranean engineering constructions.