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.

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.

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.

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.

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.

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.

Expansive soil has strong swelling-shrinkage behavior. It swells and softens after absorbing water, and shrinks and cracks after losing water. These swelling-shrinkage behavior will seriously threaten engineering structures. In this study, the expansive soil was stabilized by rice husk ash (RHA) and ground granulated blast-furnace slag (GGBS). Through compaction test, unconfined compressive strength test, direct shear test, California bearing ratio (CBR) test, swelling test, scanning electron microscope test and X-ray diffraction (XRD) test, the mechanical strength, expansion characteristics and microscopic mechanism of solidified expansive soil were studied. Testing results show that the unconfined compressive strength of the stabilized soil with a ratio of RHA to GGBS of 6:4 and a 10% curing agent dosage is the highest among all stabilized soils. The mixture of rice husk ash-ground granulated blast furnace slag (RG) can reduce axial deformation and improve shear strength. With the increase of curing agent content, the cohesion of stabilized soil increases first and then decreases, and the internal friction angle increases gradually. Compared with the untreated expansive soil, the CBR value of the stabilized soil with RG can be increased to 7.9 times, and the mechanical strength of the soil has been significantly improved. RG can significantly reduce the swelling rate of expansive soil and the swelling force. The free swelling rate can be reduced from 11.4% to 0.5%, and the swelling rate with loading can be reduced from 1.1% to 0%. Additionally, the swelling force decreases between 12.1% and 62.8%. RG can promote the formation of flocculation, amorphous hydration products and a very small amount of ettringite (AFt), which are distributed on the surface of the soil and fill the pores so as to improve the strength of the soil and reduce the expansion of the soil. Meanwhile, RG can significantly diminish the hydrophilic minerals such as montmorillonite and illite in the soil and thus enhance the cementation between particles, thereby improving the strength and downgrading the swelling behavior of the expansive soil.

To study the dynamic response characteristics of soil under impact load, flat dynamic load tests (FDLT) with different load levels and loading rates were carried out on two typical soils (sand and clay) in Guangzhou University Town by using the self-developed additional excitation force-type FDLT system, obtaining three characteristic curves of load-time curve, displacement-time curve, and load-displacement curve, establishing the empirical formula of dynamic deformation modulus and loading rate, and comparing the effects of loading rate of the two soils under impact load. It shows that: (1) There is a threshold of charging voltage in the FDLT test of sand. During the impact test on this threshold, the loading rate has a great effect on the dynamic strength and deformation of sand, while it has no obvious effect on clay under the same conditions. (2) The same point of the loading rate on the displacement response of clay and sand is that the maximum load and maximum displacement of the two soils both increase with the increase of loading rate. The difference is that the time for clay to reach the peak displacement increases with the increase of loading rate while the time for sand to reach the peak displacement shows a pattern of increasing and then decreasing with the increase of loading rate. (3) The dynamic deformation modulus varies logarithmically with the loading rate. The results can provide a reference for soil dynamic characteristics study, dynamic and static parameter conversion and engineering design.

The abundance of fissures is one of the important characteristics for expansive soils. The inherent fissures and fissure propagation during the loading process have a significant impact on the mechanical behavior of the soil. In order to investigate the influence of fissures on the deformation and failure mode of expansive soil, with the help of an improved true triaxial instrument, the undisturbed expansive soils with different inclination angles of inherent fissures (type I - the long axis of the sample is perpendicular to the dominant fissure direction, type II - the long axis of the sample is 45º oblique to the dominant fissure direction, and type III - the long axis of the sample is parallel to the dominant fissure direction) were used to conduct the consolidated drained plane-strain shear test. Meanwhile, the deformation was analyzed using digital image correlation (DIC) technology, focusing on the local deformation characteristics controlled by fissures. The results show that under the same confining pressure, the peak stress of the type-II fissured soil sample is the smallest, the stress−strain curve is of strain softening type, and its failure type is sliding failure. The peak stress of the type-I fissured soil sample is the largest, and the stress−strain curve is strain hardening type. The failure type of the type-I fissured sample is compression-shear failure, and the type-III fissured sample presents different failure forms due to different confining pressures. Under the same confining pressure, the inclination angle of the shear zone produced in the type-I fissured samples is smaller than that of other fissure types and basically does not change with the confining pressure. The shear zone of the type-II fissured sample develops along the original fracture surface, and its dip angle has no obvious regularity with the confining pressure. The confining pressure affects the number of shear zones developed in the type-II fissured samples. For type-III fissured samples, the confining pressure affects the development type of the shear zone, and as the confining pressure increases, the dip angle of the main shear zone decreases. Based on Roscoe’s theory, the inclination angle of the shear zone in the samples with different fissure directions is more in line with the inclination angle of the shear zone when the sample is actually damaged. This test lays a foundation for studying the anisotropic mechanical properties of fissured expansive soil.

Rock mass disasters are caused by instability driven by energy within the rock mass. The excavation and unloading disturbance can lead to fractures and instability in the rock mass structure, which is a major cause of dynamic disasters such as water inrush in stopes. To understand the influence of excavation unloading on rock mass structure fractures and to clarify the degradation law of surrounding rock and the mechanism of dynamic disasters like water inrush, this study focuses on the characteristics of rock damage and the evolution of energy under stress-seepage coupling factors. Using the Rock Top multi-field coupling tester, the study investigates the rock damage characteristics and energy evolution under three stress paths: conventional triaxial compression (group C), conventional unloading confining pressure with different initial damage degrees (group W), and cyclic loading and unloading confining pressure (group X) under the influence of stress-seepage coupling. Based on the evolution characteristics of rock elastic strain energy, the stress-strain curve of rock under conventional triaxial compression (group C) is divided into five stages, and the characteristics of U₁, U₃, U_e, U_d and permeability change in each stage are explained in detail (U_e is the elastic strain energy, U_d is the dissipated energy, U₁ is the strain energy of the rock transformed by the positive work done by the axial stress on the rock, and U₃ is the strain energy released by the negative work). During the conventional confining pressure unloading process, the evolution law of U₁ and U₃ is similar to that of group C rock, but the negative growth of U₃ is more significant. The rock input energy gradually shifts from U_e to U_d, and the initial damage degree has no significant influence on the law. During the confining pressure unloading process, the permeability shows a fluctuating upward trend, and the confining pressure is negatively correlated with the permeability. In the process of cyclic loading and unloading confining pressure, the energy evolution law is similar to that of group W rock, with energy accumulation differing only due to time effects. On the whole, regardless of the stress path, the pre-peak rock is dominated by U_e, representing energy storage, while post-peak rock is dominated by energy release and dissipation. Axial stress loading is the main influencing factor for rapid accumulation of U_e, while the change in confining pressure is not enough to cause a large change in U_e. Axial load is the primary factor influencing engineering disasters. Furthermore, there is a significant negative correlation between rock damage variable and confining pressure. The larger the confining pressure is, the smaller the U_e release ratio of rock is, and the smaller the rock damage is. Confining pressure restraint effectively enhances the energy storage capacity of rock and inhibits the dissipation and release of rock energy.

This study aims to further reveal the deterioration mechanism of subgrade soil performance under the coupling of multiple factors. On the basis of previous work, CT scanning technology is adopted to analyze the mesoscopic structural characteristics of compacted silty clay under wetting-drying cycles sequentially coupled with dynamic loadings. By examining influences of the coupling effect on the three-dimensional spatial pore distribution, the statistical distribution of pore volume, and the statistical indicators of image grayscale, the relationship between the macroscopic performance and the mesoscopic structural characteristics of specimens is revealed. Results indicate that more large pores and through-cracks would be induced by wetting-drying cycles, while part of pores or cracks caused by wetting-drying cycles can be closed by dynamic loadings. With the sequential coupling of wetting-drying cycles and dynamic loadings, the number of small pores in the specimen tends to increase. Increasing of total pore volume can be caused by wetting-drying cycles, and decreasing of total pore volume can be caused by sequential dynamic loadings. The mesoscopic structural parameters can be used to explain the evolution of macroscopic performance of specimens.

Fluidized solidified mud can be used in foundation trench, road base and other casting projects, its mobility is an important factor to ensure the construction quality, but the lack of systematic research on the mobility of freshly mixed solidified muds with different liquid limits, it is of great practical significance to carry out the relevant research. In this study, flowability and viscosity tests were conducted on muds and freshly mixed fluidized solidified muds with six different liquid limits (w_L = 27.2%-62.0%), revealing the influence of curing material content, water content, and liquid limit on the rheological properties of muds and freshly mixed fluidized solidified muds, and methods for calculating the flowability and viscous shear force were developed. The study shows that: the adding of curing materials makes the fluidity of freshly mixed solidified mud decrease obviously, but the decrease slows down after the dosage exceeds 5%, and the fluidity basically stays unchanged after exceeding 10%; the larger the initial water content is, the better the fluidity of freshly mixed solidified mud is; the less change in fluidity were observed in the solidified mud when the water content is near w_L, and the fluidity of the solidified mud increases obviously after exceeding a certain number of times of w_L; the smaller the w_L is, the larger the value is; but when the water content exceeds a threshold, the growth rate of flowability slows down, and the flowability is positively correlated with the w_L. On this basis, a power function relationship between the flowability of mud/freshly-mixed solidified mud and w_L was proposed, and a hyperbolic model for computing shear force of freshly mixed solidified mud with different w_L was established. The results can provide a reference for the design and construction of freshly mixed solidified mud.

Microbially induced calcite precipitation (MICP) has been widely applied for soil reinforcement, but its applications in rock mass permeability reduction have been rarely reported. To explore the plugging mechanism of rock joints using MICP, artificial rock joint specimens made of transparent resin were prepared, and laboratory MICP plugging experiments under six various conditions considering MICP reaction influence factors were performed. Through the plugging experiments, evolution laws of rock joint transmissivity and hydraulic aperture, accompanied with corresponding CaCO₃ distribution images, during plugging processes were obtained. The experimental results showed that the hydraulic aperture of rock joint approximately decreases linearly with grouting cycles during MICP plugging process, and the decreasing rate is closely related to the CaCO₃ distribution that is significantly affected by grouting rate, injection time of fixation, bacterial, and reaction solutions, and standing time. Among the six experimental conditions, both the plugging efficiency and effect are optimal under the fourth experimental condition, where the grouting rate is high and the grouting and standing time is the longest. After only two grouting cycles under the fourth experimental condition, the rock joint transmissivity decreases from 40.51×10^–6 m²/s to 0.52×10^–6 m²/s with a decrease rate of 98.72%, and the hydraulic aperture decreases from 0.367 mm to 0.086 mm with a decrease rate of 76.6%. Furthermore, the CaCO₃ distribution on the upper and lower surfaces of rock joint specimens were observed, and CaCO₃ in rock joints produced by MICP reaction was found to bring cementation strength in a short time, which helps improve mechanical properties of rock joints while reducing rock joint permeability.

The variation of shear strength indices of unsaturated soil with the degree of saturation S_r is complicated. In order to describe the experimental phenomena, the existing literature on the variations of cohesion, internal friction angle and dilation angle with S_r is analyzed. The results show that: (1) When S_r decreases and the pore water gradually transits from capillary water to adsorbed water, the friction angle increases. The turning point can be defined as critical degree of saturation S_rc. When S_r is greater than S_rc, the value of the friction angle is constant; when S_r is less than S_rc, the friction angle increases linearly with the decreasing S_r, and the extended Mohr-Coulomb criterion is no longer applicable. (2) The “peak effect” exists in the process of cohesion changing with S_r, i.e. the cohesion first increases exponentially with the decrease of S_r and reaches its maximum when S_r reaches S_rv corresponding to the peak unsaturated strength, and then decreases, which is the main reason for the “peak effect”. (3) A linear model can describe how the dilation angle increases with the decrease of S_r and vertical load. In addition, an unsaturated shear strength model over a wide S_r range is proposed. The proposed model is verified by the comparisons between the published experimental data and the predicted results of the proposed and existing equations, which illustrate the superiority of the proposed model.

To explore the bearing mechanism and failure mode for rock layer of pile tip of bridge pile groups with underground karst cave, laboratory model tests of single pile and pile groups with different numbers of piles were carried out. The ultimate bearing capacity and failure modes for rock layer of pile tip of pile groups with different numbers of piles were captured. The failure surface was divided into two parts according to the characteristics of the failure mode for the rock layer with underground karst cave, and a calculation method for ultimate bearing capacity was developed by combining with limit analysis method. The theoretical calculation values match well with the experimental values, which verifies the rationality of the proposed method. Meanwhile, the relationship between the ultimate bearing capacity for the rock layer has been analyzed and it can provide reference for bridge pile foundation construction in karst area. The experimental and theoretical calculation results indicate that: (1) When the rock layer of pile tip of pile groups with underground karst cave is overall destroyed, the whole destroyed body can be regarded as a large pier foundation  similar to destroyed body of single pile. (2) When the pile spacing is smaller, the ultimate bearing capacity for the rock layer increases with the increase of the length of the outer envelope line of outer foundation pile. Furthermore, when the length of outer envelope lines are the same, the arrangement of internal foundation piles has no effect on the ultimate bearing capacity for the rock layer. (3) The coefficient of pile group effect increases with increasing the pile spacing, and the critical pile spacing is 5d−6d (d is the pile diameter).

Seismic active earth pressure is the primary load for retaining wall design in high earthquake-intensity areas. Based on the relative position relationship among water table, crack depth and wall heel, this study firstly presented three mechanical models of seismic active earth pressure on retaining walls in unsaturated soils with cracks, which corresponded separately to high/medium/low water tables. The pseudo-dynamic method was then employed to calculate the seismic effect of sliding soils behind a retaining wall. The solution of seismic active earth pressure on inclined retaining walls for changing water table was derived by adopting mechanical principles of unsaturated soils and the limit equilibrium method. The iterative steps to be easily conducted were provided, and the proposed solution was compared with the results of theoretical analysis and the shaking table test available in the literature. Finally, the influences of water table, crack depth and unsaturated soil characteristics on the seismic active earth pressure coefficient were discussed. The results show that the proposed solution well considers the effects of water table, crack depth and unsaturated soil characteristics, which can be degraded to the classical earth pressure equation. Additionally, it agrees well with the existing theoretical solution and measured data of the shaking table test. Consequently, the proposed solution has an important theoretical significance and good application prospect. The influences of water table, crack depth, matric suction, suction distribution and suction angle on the seismic active earth pressure are all apparent. In order to optimize the seismic design of a retaining wall, engineering measures should be taken to maintain stable existence of matric suction, suction distribution, low water table and small crack depth.

The red bedded mudstone, known for its expansive and water-sensitive nature, poses a long-term potential threat to the construction and post-construction deformation control of regional highways and high-speed railroads. In this study, an in-situ water infiltration response characteristics test was conducted on slightly-expansive mudstone foundations using a red mudstone road cut in Lanzhou, Gansu Province. The test aimed to analyze the spatial and temporal evolution of swelling deformation volume, swelling force, and volumetric water content of the mudstone foundations, as well as to compare the differences between laboratory tests and in-situ tests. The results reveal that the water infiltration forms in the red mudstone foundation include fissure flow and pore flow. The distribution of water in the rock mass exhibits significant spatial and temporal heterogeneity, with rock mass fissures promoting seepage and expansion. During the infiltration process, the water absorption and expansion of the mudstone exhibit significant time dependence. The expansion amount and expansion force of the in-situ foundation experience stages of rapid increase, slow growth, and eventually fail to converge. After reaching the infiltration peak, the surface of the mudstone gradually softens or even turns into mud, leading to a decrease in the bearing capacity of foundation. Additionally, through the analysis of macroscopic expansion time history variation characteristics and microscopic pore structure distribution laws of indoor and in-situ mudstone, it is found that laboratory tests provide limited characterization of the water infiltration response characteristics of in-situ soil.

This study aims to explore the seepage characteristics of fractured sandstone before and after grouting and the change rule of mechanical properties after grouting. Firstly, Rock Top multi-field coupling tester was used to conduct triaxial compression test on sandstone under different confining pressures at a constant rate of 0.02 mm/min to obtain fractured sandstone and conduct seepage test. Then, the self-developed grouting reinforcement system was used to reinforce the fractured sandstone, and the Rock Top multi-field coupling tester was used to conduct the triaxial compression seepage test on the fractured sandstone under different confining pressures. The results show that: (1) The permeability of fractured sandstone decreases significantly after grouting compared with that before grouting, with a decrease range of 24.26%-96.55%, but it is greater than the original rock permeability. (2) The permeability of fractured sandstone before and after grouting shows different periodic changes with the increase of hydrostatic pressure. When hydrostatic pressure reaches 40 MPa or above, the permeability difference within 5 MPa has a little effect on permeability, and the permeability curve tends to be horizontal. (3) After grouting, the fractured sandstone only exhibits brittle failure characteristics similar to the original rock only under 10 MPa confining pressure, but loses the brittle failure characteristics of the original rock under 20−60 MPa confining pressure, showing strong ductility failure and plastic flow phenomenon after the peak. (4) The peak strength and strain of the fractured sandstone after grouting both increase with the increase of confining pressure and show nonlinear variation characteristics satisfying the quadratic function relation. The peak strength ranges from 44% to 59% of the peak strength of the original rock. (5) The failure mode of fractured sandstone after grouting is mainly slip-shear failure, and new failure modes will appear under low confining pressure. With the increase of confining pressure, the failure effect weakens. (6) Scanning electron microscopy test on rock-slurry interface shows that ettringite and C-S-H (calcium silicate hydrate) gel are bonded to form stable hydration products, thus improving the bearing capacity of rock.

In subsurface engineering, grouting is an important measure to seal or strengthen fractured rock mass and reduce groundwater flow. Understanding the grout flow in rock fractures is significant to improve the grouting efficiency. The influence of grout material property on the grouting process in rock fractures saturated with a resident fluid is studied by visualized experiments. We present an experimental phase diagram of pattern formation and elucidate the relevant microscopic mechanisms. The experimental results show that the injection velocity and mass fraction in the grout significantly influence the displacement patterns in rough fractures, which is different from the displacement behavior with Newtonian fluid. During the displacement, the formation of different patterns is attributed to the local viscosity heterogeneity induced by the coupling effect of shear-thinning behavior and the spatial variability of fracture apertures. Decreasing injection velocity or increasing the mass fraction would stabilize the fluid-fluid interface and increase the area of initial stable region. The narrower aperture region of the fracture can only to be partially filled (with a low filling rate) by the polymer solution, except under the condition of very low flow rate and high mass fraction. The grout filling rate exhibits non-monotonicity with respect to flow rates. The displacement efficiency is significantly affected by displacement patterns, and thus we propose a theoretical model based on the interface stability analysis to elucidate the mechanisms behind the transition of displacement patterns. This work improves the fundamental understanding of grout flow in rough fractures and can provide a reference and technical guidance for evaluation and control of grouting efficiency in engineering practice.

The Central Plains are located in an area that experiences seasonal freeze-thaw cycles, which can have significant effects on the soil structure of soil relics. To determine if lime-metakaolin (L-MK) is a feasible alternative to natural hydraulic lime (NHL) for earth site restoration work, tests were conducted using lime, metakaolin and silty sand from the site as main raw materials. Mass loss, unconfined compressive strength and splitting tensile strength tests were carried out on L-MK improved silty sand soil undergoing different numbers of freeze-thaw cycles to study its strength characteristics in depth. X-ray diffraction (XRD) thermogravimetry (TG), and scanning electron microscope (SEM) microscopic tests were also performed on some samples to reveal the internal mechanism of strength deterioration law of L-MK improved soil. Results indicate that L-MK improved soil has better freeze-thaw cycle resistance than NHL improved soil under the experimental mix ratio. Increasing the content of metakaolin improves the strength of L-MK improved soil. As the number of freeze-thaw cycles increases, the strain softening characteristics of L-MK improved soil show a weakening trend, and unconfined compressive strength and tensile strength decrease monotonically. After 30 freeze-thaw cycles, the unconfined compressive strength and splitting tensile strength of L-MK improved soil are about 3.79 and 1.16 times higher than that of NHL improved soil, respectively. The variation of strength is consistent with hydration products such as CSH and C₄AH13 generated by hydration reaction under the influence of freeze-thaw cycle for L-MK and NHL improved soil.

To explore the variation of water retention capacity of expansive soil at different temperatures, the calibration curves of Whatman No.42 filter paper were measured by vapor equilibrium method at 5, 25, 40 ℃ and 60 ℃, and the bilinear calibration equation considering temperature effect was established. The results show that the water retention capacity of the filter paper decreases with the increase of temperature, and the effect on the high suction section of calibration curve is weaker than the low suction section. On this basis, Nanning expansive soil is taken as the research object, and the soil-water characteristic curves of Nanning expansive soil at different temperatures are measured by filter paper method. It is found that the water retention capacity of Nanning expansive soil decreases with the increase of temperature, but the influence of temperature depends on matric suction, especially when it is above 40 MPa, the water-retention capacity of Nanning expansive soil remains unchanged with temperatures. To probe into the microscopic mechanism of the change of water retention capacity of Nanning expansive soil under temperature, some samples were selected for mercury intrusion porosimetry test and adsorption bound water test. Based on the test results, the microscopic mechanism of water retention capacity change of Nanning expansive soil was analyzed from the physical mechanism of the interaction between each phase and each phase interface.

In this study, the variation characteristics of normal stress and normal closure of granite joints were studied. The effect of chemical solution with different pH values (1, 3, 7, 12), the corrosion time t (10, 30, 100 d) and various initial openings b on the evolution of the specific normal stiffness of the specimens were revealed through normal load compression tests taking into account constraint circumferential stiffness boundary conditions. The experimental results indicate that the normal stress-normal strain curves of specimens with mismatched joints are different from the intact specimens and specimens with matched joints. Due to the crushing of the asperity on the surface of the joints, the local stress drop phenomenon occurs during the overall growth process of the stress−strain curves. The normal closing curve of mismatched joints exhibit nonlinear characteristics, in which the increasing rate of normal displacement first increases and then decreases with the increment of normal stress. Under the same normal stress, both the normal displacement and the closing rate increase with the increment of the initial opening. By introducing several classical joint closure models, it is found that the normal stress and stiffness of joints are affected by the initial opening, pH value and corrosion days, among which the initial opening is the most import. When pH = 1 and t = 10 d, with an increase of normal displacement from 1−3 mm, the normal stress of the specimens with b = 1.65 mm increase by 46.26 %−149.46 %, compared with the specimens with b = 3.4 mm. The specific normal stiffness of the mismatched joints decreases with the reduction of pH value. The normal stiffness of joints in different chemical solutions decreases first and increases then as the corrosion time increases.

In this study, the “Xiaguiwa” landslide in Jinsha River Basin of Qinghai-Tibet Plateau is taken as a prototype, and the shaking table model test on bedding rock slope with weak interlayer is carried out. The dynamic response of bedding rock slope with weak interlayer under earthquake is studied from the aspects of peak ground acceleration (PGA) amplification factor and Hibert-Huang transform (HHT) time-frequency characteristics. The results show that the slope exhibits obvious “elevation effect” and “surface effect” under the action of input seismic waves. The PGA is larger at the 1/4 height of the slope surface from the bottom of the slope, the top of the slope, and the weak interlayer. With the increase of the intensity of the input seismic waves, the slope stiffness and natural vibration frequency decrease gradually. When the input wave amplitude reaches 0.7g, the slope cracking and structural deformation occur. When the input amplitudes are the same, the PGA amplification coefficient is positively correlated with the elevation, and decreases gradually with the increase of the input amplitudes at the same measuring point. The influences of different input wave types and time scale factors on the slope dynamic response are significantly different. The Hilbert spectrum shows that the elevation and weak interlayer amplify the energy of seismic waves, especially the high-frequency part. The Hilbert marginal spectrum shows that the weak interlayer could amplify the energy of the high-frequency part. The Hilbert marginal spectrum indicates that the cumulative energy of the high-frequency part is significantly amplified under the influence of soft interlayer, and the energy of the measuring point at the 1/4 height of the slope surface from the bottom of the slope suddenly increases, which is similar to the conclusion of the acceleration amplification effect. The results of Hilbert marginal spectrum shows that with the increase of the amplitude of the input seismic wave, the cumulative energy of the high-frequency part and the part representing the natural vibration frequency of the slope gradually decrease, and the energy of the main frequency part of the input seismic wave gradually dominates, indicating that the modal characteristics of the slope gradually disappear.

As transmission line projects continue to expand into the western mountainous regions of China, the need for more transmission tower foundations on steep hillsides has increased. However, research on the uplift bearing deformation characteristics of pile foundations under high-intensity wind and snow scenarios on sloped ground is lacking, and current specifications are insufficient. Therefore, laboratory model tests were conducted on rock-socketed uplift piles on both flat and sloped ground to investigate load-displacement curves, ground deformation and crack propagation, failure mode, axial force of pile, side friction of pile, and relative displacement between the pile and rock. ABAQUS numerical simulation results were compared to the model test results to validate the reliability of the numerical model and investigate the influence of steepness (slope angle) on the bearing capacity and deformation characteristics of rock-socketed uplift piles. The results demonstrate that the load-displacement curves for flat and sloped ground have similar steep shapes, and sloped ground can have an adverse impact on the bearing capacity and deformation characteristics of rock-socketed uplift piles. The decrease in pile bearing capacity is positively correlated to the steepness of the slope, with a decrease of 0%–12.8% for slopes of 0º–30º and up to 25.9% for a slope of 45º. Bedrock failure surfaces mainly occur in the downhill slope within a range of 3.2d(d is pile diameter), as well as within a fan-shaped range of 120º, while the failure range on adverse slopes is about 1d, which is different from symmetrical and composite failure on flat ground. When the load on the top of the pile reaches approximately 80% of its ultimate bearing capacity, visible cracks can be observed in flat or downhill areas of sloped ground. These research findings offer a scientific basis for improving the design and specifications of uplift resistance capacity in transmission tower foundations on sloped ground.

In the South-to-North Water Diversion Project, a large number of expansive soil slopes slid due to the long and gently inclined fissures. The micropiles had achieved good application in the rescue and reinforcement project of the expansive soil slopes. The study on the reinforcement mechanism and the influence of parameters of micropiles in reinforcing the soil slope with long and gently inclined fissures is of great significance for the design of such projects. Based on the actual project of reinforcing expansive soil slope with micropiles, the thrust was applied on the sliding body along the direction of the fissure surface, and the failure tests of the non-piled slope with different angles of the gently inclined fissure were carried out. After taking the pile length, row spacing and pile position as influence parameters, the model tests of micropile-reinforced soil slope with long and gently inclined fissures were carried out, the displacement characteristics of the slope and the stress characteristics and the reinforcement effect of the micropile were analyzed. The test results showed that the micropile had a good anti-slide reinforcement effect for the slope with gently inclined fissures, and could maintain the anti-slide resistance at a high level. The anti-slide resistance provided by micropiles increased with the increase of pile length (anchorage ratio), while the increase efficiency decreased with the increase of pile length. It was suggested that the anchorage ratio of micropiles should be 0.5 when the pile is arranged at upper 1/3 position of the slope, and less than 0.65 when it is arranged at lower 1/3 position of the slope. The distribution of bending moment and shear force of the piles was reversed S-shape, and the maximum values were located near the fissure surface. The double-row piles can enhance the toughness of the slope to resist damage. When the row spacing was 200 mm (10 times the pile diameter), the front and rear rows of piles can well coordinate, which could give full play to the anti-slide effect and greatly increased the anti-slide thrust of the slope.

Based on an ultra-deep circular shaft project in Shanghai, the field data of soil heave at the bottom of the pit during the construction were collected, and the vertical distribution pattern, evolution law and main influencing factors of soil heave at the bottom of the pit were summarized. An axisymmetric numerical model was then built and verified to investigate the effect of the excavation-induced unloading, dewatering, diaphragm wall and soil mechanical properties on the soil heave, then the mechanism of soil heave was revealed. Soil heave was the combined result of the soil mechanical response under the excavation-induced unloading, dewatering, and diaphragm wall restraint, in which the excavation-induced unloading and the deflection of the diaphragm wall caused the soil heave, and the dewatering and the negative frictional resistance inhibited the soil heave. Excavation-induced unloading had a prominent influence on the depth, and the unloading rebound mechanism dominated the soil heave within that depth, while the shear deformation controlled the soil heave beyond that depth range. Soil rheology and dissipation of negative pore water pressure jointly led to the time dependence of soil heave. The soil heave at the pit bottom of small-diameter ultra-deep shafts in soft soil areas decreased approximately linearly along the depth, and its maximum value was located at the center of the excavation face. The soil heave first increased slowly and then increased near linearly and rapidly with the increase of excavation depth. However, the soil heave tended to increase slowly with time in the non-excavation stage.

Based on the ideal fluid wave theory and Biot’s theory, an undersea tunnel model with imperfect interface is established by considering the imperfect contact relationship between the undersea tunnel and the surrounding seabed soil in engineering reality. The model also considers the dynamic interaction of seawater-seabed soil-undersea tunnel. The analytical solution of the imperfect contact interface effect between the undersea tunnel and the surrounding seabed soil under P₁ waves incidence is derived using the Hankel function integral transformation method and the wave function expansion method. Based on the analytical solution, the effects of imperfect contact conditions on the seismic dynamic response of the undersea tunnel are analyzed by numerical calculations. The calculation results show that the imperfect contact condition has a significant effect on the displacement response and stress response of the undersea tunnel; the displacement response and stress response of the undersea tunnel considering the imperfect contact condition at the tunnel-seabed soil interface are significantly higher than those at the interface with perfect conditions.

The existing Masing-type nonlinear soil constitutive models encounter the problem of relatively complex loading-unloading rules (eg, the "extended Masing" rule) to describe the soil stress-strain hysteresis curve under the irregular cyclic loadings such as earthquakes. It will lead to a large number of state variables during the solution, which is inconvenient to be implemented. At the same time, the existing (improved) models primarily match the shear modulus reduction curves with the damping ratio curves rarely being matched. In this paper, to overcome the above problems, a new irregular loading-unloading rule is proposed based on modified damping. The rule overcomes the "upper boundary rules", and only the current reversal point and historical maximum (minimum) point need to be stored, which greatly reduces memory. Meanwhile, it accounts for the effect of soil shear modulus and the damping ratio curve simultaneously to modify damping ratio. Then, a new nonlinear constitutive model is proposed and implemented into the Abaqus software based on the Matasovic back-bone curve and the proposed loading-unloading rule. The correctness of the proposed loading-unloading rule is verified by comparing numerical results of the site seismic response of Mississippi Bay with the results calculated by the Deepsoil software where the Davidenkov Chen Zhao (DCZ) model is adopted. To further validate the practical applicability of the proposed model, the seismic response analysis of KSRH10 site of Japan KiK-net is conducted and compared with the record of acceleration time history and spectral acceleration.

The research on the mechanical response of anti-slide piles has seldom considered the influence of intermittent heavy rainfall environment, and cannot reflect the multiple rainfall infiltration and solar radiation evaporation links, especially the nonlinear theoretical analysis method of anti-slide pile in the rainfall environment is relatively rare. Based on the improved Green-Ampt model, the mechanical response of anti-slide piles to intermittent heavy rainfall-induced landslides is investigated by introducing the nonlinear Pasternak foundation model. First, in consideration of the drying and wetting cycle and water evaporation theory, an improved Green-Ampt model for intermittent heavy rainfall is proposed to obtain landslide thrusts by taking the wetting front as a potential sliding surface and assuming the homogeneous landslide soils. Second, the pile-soil interaction is investigated based on the nonlinear Pasternak foundation model, and the Newton iterative difference method is used to obtain the mechanical response of anti-slide piles to intermittent heavy rainfall-induced landslides. Finally, the theoretical calculation results are compared with the field monitoring data, which shows a good agreement. In addition, the rainfall sensitivity parameters including the total number of intermittent rainfall events, intermittent duration, average temperature, slope inclination and rainfall intensity are focused to study their influences on the wetting front characteristics and the mechanical response pattern of the anti-slide pile. The results show that the displacement of the anti-slide pile increases by 43.15% when the temperature increases from 10 ℃ to 40 ℃, and by 116.82% when the rainfall intensity increases from 6 mm/h to 20 mm/h. The development of wetting front depth under intermittent rainfall exhibits a “step” upward trend, and there is an “unsaturated zone → saturated zone”. With the increase of the number of intermittent rainfall events, the wetting front of the slope soil keeps advancing downward and induces landslide when it reaches a certain position. The thickness of the sliding area and the landslide thrust increase simultaneously, the deformation and bending moment of the anti-slide pile also become larger and larger. Its development trend shows a gradual decrease to a specific value. The intermittent duration and the total number of intermittent rainfall events presents a negative correlation with the deformation and bending moment of the anti-slide pile, while the average temperature, slope inclination and rainfall intensity demonstrate a positive correlation.

Loose sand is highly susceptible to liquefaction, and small changes in stress state can affect its liquefaction characteristics. Based on multi-directional cyclic simple shear tests, this study conducted cyclic simple shear tests on loose sand under different magnitudes and directions of static shear stress, and complex shear paths. The cyclic simple shear characteristics of loose sand under complex initial stress states are studied. The main conclusions are drawn as follows: (1) As the static shear stress ratio increases, the peak shear stress of the specimen increases, the increment of pore water pressure in the first cycle increases, and the specimen is more prone to liquefaction. The effect of the magnitude of initial static shear stress on excess pore water pressure is more significant at the early stage of shearing. (2) With the increase of the angle between the initial static shear stress and the main direction of dynamic shear stress, the peak shear stress of the specimen in the X direction decreases, and the pore water pressure of the specimen accelerates to increase. In addition, the increment in pore water pressure in the first cycle and the last cycle increases, and the difference between the cycles increases. The specimen is more prone to sudden liquefaction. (3) The specimen with 8-shaped shear path has the largest area of stress−strain hysteresis loops, which consumes the most energy per cycle, followed by the specimen with the circular shear path, and the specimen with the straight shear path has the smallest area. Complex shear paths can induce a sudden increase in pore water pressure at the beginning of shearing, increasing the increment in pore water pressure in each cycle and making it more prone to liquefaction. (4) The sequence of factors affecting the liquefaction of loose sand is the angle between the initial static shear stress and the dynamic shear stress, the shear path, and the magnitude of the initial static shear stress.

In the area of deep soft soil, there are a large number of deep foundation pits conforming to the following characteristics: (1) insertion ratio of retaining wall is between 1:2.0 and 1:2.2; (2) excavation process goes smoothly; (3) basal heave stability does not meet the requirements of relevant standards. In order to reduce the inconsistency between theory and practice, based on the calculation formula of the existed foundation bearing capacity model, a basal heave stability analysis method for foundation pit considering soil stress state and shear capacity was developed by introducing the virtual foundation width. The critical width was defined as the virtual foundation width with the minimal basal heave stability in mathematics. In addition to the critical width, the width of the foundation pit and the thickness of the soft soil layer should also be considered in the selection of the virtual foundation width. A completed engineering example was given to compare the basal heave stabilities of the existed different analysis methods, and to analyze the influence of soft soil layer structure and internal friction angle on stability. The analysis results were closer to the actual situation, and showed that the influence of soil shear capacity was limited when the critical width was used as the virtual foundation width.

Expansive soils, known for their considerable swelling pressure upon wetting, have been identified as potential instigators of instabilities in retaining walls. The incorporation of expanded polystyrene geofoam (EPS) inclusions between the retaining wall and the backfilled expansive soil has been found to considerably mitigate the lateral pressure on the wall, which results from the water absorption and expansion of the expansive soil. This substantial reduction is due to the impressive compressibility of the EPS inclusion. To explore the implications of the EPS inclusion on the lateral pressure distribution on retaining walls, and to analyze the factors influencing this pressure, a comprehensive model test and a corresponding lateral pressure theoretical analysis were performed. The results show that (1) the total lateral pressure acting on the retaining wall was reduced by about 50% by the EPS inclusion with a density of 12 kg/m³ when the expansive soil is saturated in the model test; (2) in the absence of the EPS inclusion, the lateral pressure distribution acting on the retaining wall escalated along its depth, whereas with the EPS inclusion, it remained largely uniform throughout the wall’s depth; and (3) the lateral pressure reduction due to the EPS inclusion was enhanced with increasing thickness and decreasing density of the EPS inclusion.

To accurately evaluate the safety of foundation pit construction in soft soil area and its impact on the surroundings, the time and space influencing factors during excavation cannot be ignored. In this paper, based on the excavation of a deep foundation pit in the soft soil area of the Yangtze River floodplain, a 3D finite element model was established considering the combination of bottom-up and top-down constructions, and the calculated values of horizontal displacement of the diaphragm wall were compared with the measured values to verify the reliability of the finite element calculation. Based on theoretical analysis, numerical calculation and measured data, the influence coefficient of corner effect and equivalent horizontal resistance coefficient were used to measure the influence of spatio-temporal effect on the deformation of supporting wall, and the calculation method of the diaphragm wall deformation considering spatio-temporal effect was proposed. The necessity of the spatio-temporal effect and the rationality of the proposed method in the design of foundation pit in soft soil area were verified by engineering examples. The results can provide beneficial reference for the calculation of deep foundation pit deformation in soft soil area.

Underwater two-way vacuum preloading not only reduces more excess pore water pressure comparing to conventional vacuum preloading with vacuum acting only on the top face, but also has the advantage of utilizing the effective load from the overlying water. However, two-way vacuum preloading is currently only applied in the treatment of dredged soil, thus the mechanism and performance of consolidation of two-way vacuum preloading are hardly studied. To explore the consolidation characteristics and efficiency of underwater two-way vacuum preloading, centrifuge modelling has been performed to simulate soft soil subjected to underwater two-way vacuum preloading in collaboration with group sand drains and single sand drain. The finite element method is also used to analyze and compare the results with those from centrifuge modelling test. Variation of pore water pressure and development of deformation are compared. Meanwhile, changes in total head of pore water and stress path of soil element, as well as degree of consolidation are discussed and evaluated. It is found that more effective load can be obtained from underwater two-way vacuum preloading comparing to conventional vacuum preloading, and the rate of consolidation is larger and the ultimate settlement can be reduced in group sand drains zone comparing with single sand drain zone. The stresses for soil in the center of treated zone follow a path close to K₀ line. Under the combination effects of vacuum and gravity, the reduction of pore water pressure at the bottom layer is larger than that at the top layer, and it is found that a lower water head exists at the bottom at final consolidation stage in this experiment. These findings may enhance the understanding and practical application for two-way vacuum preloading.

The weakening of physical and mechanical properties of weathered granite often has a great impact on engineering stability. Therefore, it is of great significance to study the failure characteristics of granite with different weathering degrees. Combining the qualitative description of the core characteristics and the quantitative evaluation index of wave velocity ratio, the granite rocks collected from the reservoir area of Wuyue Pumped Storage Power Station in Henan Province were divided into three groups: slightly weathered granite, weakly weathered granite and strongly weathered granite. The fragments generated from granite rocks during uniaxial compression tests were collected, and their quality and scale characteristics were analyzed. Then, the corresponding relationship between fragment fractal dimension and wave velocity ratio was established. Meanwhile, the MATLAB software was employed to calculate the fractal dimension of the cracks on the main rupture surface. The results show that weathered granite rocks mainly produce coarse grain fragments and the proportion of fragments in coarse group gradually increases with the increase of weathering degree. Strongly weathered rocks produce blocky fragments in a small proportion and have a narrow range of the length-thickness ratio, indicating weak dynamic failure characteristics. Besides, their fragment shapes are single and mainly have plate-like structure. With the decrease of weathering degree, the proportions of blocky fragments increase and the dynamic failure characteristics become more apparent. The fractal dimensions of fragments have an increasing trend with the increase of the wave velocity ratio. Compared with the fragment quality, width and thickness, the fragment quantity and length are the main factors affecting the fractal dimension and are also the main parameters reflecting the fractal characteristics of granite with different weathering degrees. Moreover, the crack fractal dimensions of rupture surface for weakly and slightly weathered granite rocks increase significantly with the increase of wave velocity ratio, while for strongly weathered granite rocks there is no obvious change. It implies that the cracks of weakly and slightly weathered granite rocks have a higher degree of self-similarity, more complex structure and require more energy for their initiation and propagation

This study aims to investigate the problem that segment of shield tail is easy to float up in surrounding rock formation. Based on the self-developed gravity testing system of grouting, the nonlinear variation law of grouting buoyancy is obtained, and based on the equivalent continuous beam theory, a refined longitudinal uplift model of shield tail segment is established. The model can comprehensively consider the time-varying of grouting, the nonlinear distribution characteristics of grouting buoyancy and the cumulative effect of construction steps. The reliability of the model is verified by using the actual floating test results of shield construction in an underground pipe gallery in Guangzhou. The results show that with the increase of the pressure difference of the grouting and the permeability of the strata, the dissipation speed of the grouting buoyancy presents an increasing trend, and the uplift values of shield tail segment exhibits a decreasing trend. When the shield tunnels are in strongly weathered pebbly sandstone formation, the uplift characteristic curve follows the law of first increasing and then decreasing, and finally floating stably. Under an action of 20 kPa differential pressure, the maximum uplift value of segment is 151.74 mm, the value of which is 39.2 m away from the shield tail, and finally floating stably near 70 m away from the shield tail. At this time, the uplift value is 145.2 mm. The longitudinal model of segment upward movement further reveals the influence mechanism of grouting consolidation law on its uplift characteristics. The model has good reliability compared with the measured results. The results can be used to predict the uplift deformation of segment induced by grouting buoyancy and provide a theoretical basis for similar projects.

The seepage of sandy foundation would lead to the collapse of foundation and the destruction of engineering structure. A series of large-scale sand column seepage model experiments war carried out by microorganism-bentonite combined mineralization method. The discussion in-depth was conducted for the effects of sand particle size, slurry liquid-solid ratio and treatment cycles on the permeability, internal erosion characteristic and bentonite and calcium carbonate precipitation distribution of sand. Moreover, the stability of sealing and the microstructure were thoroughly investigated and the treatment effect of microorganism-bentonite combined mineralization method was evaluated. It was found that this method could improve the seepage prevention effect and the stability of sealing of sand, and the permeability coefficient of samples could be reduced by up to 4 orders of magnitude. In addition, the erosion rate during the permeation process was also reduced by several times and reached as low as 0.51 g/(s·m²). Based on the effect of bentonite and calcium carbonate precipitation on sand sealing, the anti-seepage mechanism of microorganism-bentonite combined mineralization method was analyzed. The results show that the microorganism-bentonite combined mineralization method is feasible and efficient in the seepage control of sand, which will provide an important reference for the application of microbial mineralization technology to engineering anti-seepage problems.

To clarify the creep damage mechanism of rock mass under the periodic variation of reservoir water level in the hydro-fluctuation belt, by considering the weakening effect of the water-rock interaction on the bond and the variation of material properties with time, we proposed a new discrete element method based on the parallel bond model in particle flow code (PFC) and implemented the creep simulation of water-rock interaction based on laboratory tests. The results indicate that under the failure stress level, the micro-crack growth behavior of the samples is similar to the creep strain and it consists of three stages: attenuation growth stage, stable growth stage, and accelerated growth stage. The ratio of the accelerated growth stage’s time to the total time of the micro-crack growth process increases with the period of the water-rock interaction. When the sandstone is damaged in the creep process, the proportion of shear cracks gradually increases with the period of the water-rock interaction and the distribution of inclination angles of micro-crack gradually scatters. The micro-cracks in the areas near the inclination angles of 65° and 115° increase, the tensile strength of the samples weakens and the shear strength increases. Under the water-rock interaction, the maximum cementation energy stored in the samples decreases and the strain with the same cementation energy stored in the samples increases, which is consistent with the rules observed in the field that the overall bearing capacity of the rock mass decreases and the deformation of rock mass increases. Because the method is feasible to simulate sandstone creep process under water-rock interaction, the study can provide theoretical support for the model study of reservoir bank slope rocks under the influence of reservoir water level fluctuation.

Conical polycrystalline diamond compact (PDC) cutter is a new type of PDC cutter with high impact and wear resistance, which has a very good drilling effect in hard, strong abrasion, and soft-hard interbedded formations. In order to reveal the hard-rock breaking mechanism of conical PDC cutters, the laboratory test and numerical simulation on the granite broken by the conical PDC cutter were carried out. The influence law of cutting depth and front rake angle on cutting force and rock breaking specific energy of the conical PDC cutter was analyzed. In the laboratory test, a high-speed camera and transparent K9 glass were used to observe the formation process of cuttings and the initiation and propagation of microcracks under the action of conical PDC cutters. The stress response and damage evolution characteristics during the rock breaking process were analyzed by numerical simulation. The surface morphology and fracture microscopic characteristics of cutting grooves and large-size cuttings were analyzed, and the mechanical model of conical PDC cutters to break granite was established. The results show that the granite breaking process can be divided into two stages: crushing and chipping. The effect of the front rake angle on the rock breaking process is relatively small, while the influence of cutting depth is significant. The cracks around the conical PDC cutter are mainly composed of compaction nucleation, longitudinal crack and transverse crack. The maximum propagation depth of the longitudinal and transverse cracks is 6.69 and 4.53 times the cutting depth, respectively. The compressive stress around the cutter tip is concentrated, the shear-compression failure occurs, an arc-shaped strip-like tensile stress zone is formed at the periphery of the compressive stress zone, and the tensile micro-cracks are induced at the boundary of the cutter tip and compressive stress zone. When the micro-crack propagates to the front of conical PDC cutters to form an arc-shaped tensile main crack, the block debris cracking occurs, which improves the rock breaking efficiency. Meanwhile, the tensile micro-cracks propagate to the rock inside and deteriorate rock strength, a bottom damaged area is formed, which improves the rock breakage efficiency of the subsequent cutting.