As terrestrial resources and energy become increasingly scarce and advancements in deep space exploration technology progress, numerous countries have initiated plans for deep space missions targeting celestial bodies such as the Moon, Mars, and asteroids. Securing a leading position in deep space exploration technology is critical, and ensuring the successful completion of these missions is of paramount importance. This paper reviews the timelines, objectives, and associated geotechnical and engineering challenges of recent deep space exploration missions from various countries. Extraterrestrial geotechnical materials exist in unique environments characterized by special gravity, temperature, radiation, and atmospheric conditions, and are subject to disturbances such as meteoroid impacts. These factors contribute to significant differences from terrestrial geotechnical materials. Based on a thorough literature review, this paper investigates the transformation of geomechanical properties of extraterrestrial geological materials due to the distinctive environmental conditions, referred to as the "four unique characteristics and one disturbance", and their distinct formation processes. Considering current deep space mission plans, the paper summarizes the geotechnical challenges and research advancements addressing specific mission requirements. These include unmanned exploration and in-situ mechanical testing, construction of extreme environment test platforms, the mechanical properties of geotechnical materials under extreme conditions, the interaction between engineering equipment and geotechnical materials, and the in-situ utilization of extraterrestrial geotechnical resources. The goal is to support the successful execution of China’s deep space exploration missions and to promote the development of geomechanics towards extraterrestrial geomechanics.

It is extremely important to understand the mechanism of pile-soil interaction during pile installation for accurately predicting its bearing capacity. This paper presents a large-scale (1:10) model test to investigate this interaction specifically for open-ended pile penetrating sandy soil. The study focuses on pile with a diameter of 0.273 m penetrating sandy soil having a relative density of approximately 40%. Advanced monitoring techniques, including fibre Bragg grating (FBG) strain sensors and thin-film pressure sensors, were employed to meticulously analyze changes in soil plug height, strain, axial force, shaft resistance, and pile-soil interfacial stress throughout the cyclic penetration process. Following pile installation, vertical compressive static load tests were conducted with intervals of 10 and 30 days, respectively, to assess the long-term performance of the piles. Subsequently, the ICP-05 method and UWA-05 method, which are based on CPT to predict the vertical bearing capacity of piles, were compared with the bearing capacity measured by static load test. The results indicate the following: Firstly, the soil plug effect of open-ended pipe piles gradually increases during cyclic penetration, and the soil plug is partially occluded at the end of penetration. Secondly, as the depth of penetration increases, an “inverse point” of strain near the pile tip emerges. Specifically, the compressive strain at the final stage of penetration changes to a tensile strain during static stabilization, while the strain at the pile tip remains tensile at both stages. Thirdly, the radial stress of the pile body peaks at the pile tip and gradually tapers off as the h/R (h is the height from the sensor to the pile tip, R is the radius of the pile) ratio increases, indicating a significant h/R effect. Fourthly, the bearing capacity of the pile increased by approximately 12%, from 289 kN after 10 days to 323 kN after 30 days, demonstrating a notable time effect. Finally, both the ICP-05 and UWA-05 methods underestimate the shaft resistance near the pile tip, while their predictions above the pile tip align closely with measured values. Overall, the predicted pile bearing capacity using both methods is conservative, with the UWA-05 method yielding closer results to the measured values.

In order to further study the precursor temporal signals of damage in water-saturated and dry sandstones, as well as the dynamic sensi-tivity changes of acoustic and thermal signals, uniaxial compression tests were conducted on sandstones with different water content states, with real-time monitoring of internal acoustic emission (AE) signals and surface thermal infrared (TIR) signals. Research has shown that during the damage process of water-saturated and dry sandstones, TIR anomalies appear first, followed by AE anomalies. The time lag between the first appearances of TIR and AE anomalies in water-saturated sandstone is shorter than that in dry sandstone, indicating the detrimental effect of water. This time lag is of great significance for determining the degree of internal and external damage and the precursor of instability failure in rock samples. The order of sensitivity indicators for acoustic and thermal signals in wa-ter-saturated sandstone is as follows: combined acoustic-thermal signal > TIR signal > AE signal; for dry sandstone, it is: combined acoustic-thermal signal > AE signal > TIR signal. The sensitivity of the combined acoustic-thermal signal is significantly higher than that of individual acoustic or thermal signals. Therefore, in practical engineering, it is necessary to analyze the coupling of acoustic and thermal signals when analyzing the precursors of instability. K

Considering fabric evolution effects is crucial for accurately describing the macroscopic mechanical behavior of cohesionless soil under cyclic loading. Building upon the nonlinear dilatancy equation established for sand-gravel composites under monotonic loading, a fabric-dilatancy internal variable, which accounts for fabric evolution during the dilatancy stage under cyclic loading, is introduced. An elastoplastic constitutive model based on the generalized plasticity framework is proposed to capture the full range of mechanical behaviors of sand-gravel composites under both static and liquefaction conditions. By comparing the liquefaction deformation, stress paths, and excess pore water pressure development of sand-gravel composites before and after considering fabric evolution effects, the significance of fabric evolution effects in simulating the liquefaction response of sand-gravel composites is demonstrated. The model's performance is validated through a series of large-scale triaxial tests on sand-gravel composites under both static and dynamic loading conditions, as well as by comparing with test results from relevant literature. The results show that the model generally provides a reasonable representation of the stress-strain-volume behavior of sand-gravel composites under static drained conditions, as well as the accumulation and dissipation of excess pore water pressure, stress path evolution, and liquefaction deformation during liquefaction. This model can serve as a powerful tool for numerical simulation in sand-gravel composites engineering.

The large distribution of desertified land is one of the significant causes of frequent sand and dust weather. To effectively prevent and stabilize sand, two key challenges need to be addressed: one is to stabilize the sand and prevent it from flying up, and the other is to enhance the effectiveness and longevity of sand stabilization techniques. Biomineralization technology, as an innovative approach, has been studied to address the challenge of long-term sand fixation. Laboratory and field tests have proven the feasibility and applicability of bio-mineralization technology for long-term sand fixation. The study encompasses tests such as urease activity tests, calcification tests, and wind erosion tests. The effects of urease activity, gelation solution concentration, pH value, perfusion times, perfusion volume, and temperature on sand fixation by the bio-mineralization method were analyzed. Based on these tests, a combined sand fixation technology system of biomineralization-plant-fence is proposed. The longevity and effectiveness of sand fixation using this combined technology system have been validated through wind tunnel experiments and field engineering sand fixation tests. The effect of the biomineralization solidified sand on sunny days is the best in the field and can be more favorable to achieve long effect of the solidified sand.

Damage to the overlying soil caused by fault misalignment poses a significant threat to the structural safety of buried pipelines crossing faults, which is a non-negligible factor in the design of underground pipelines in complex environments. Existing research rarely involves analytical solutions for the force and deformation of pipeline structures under normal and reverse fault movements, and theoretical studies on fault-pipeline interactions often treat the pipeline structure as continuous, with little consideration for the influence of pipeline joints. Firstly, soil displacement curves for both normal and reverse faults are derived using the erf and erfc functions, based on a simplified SSR (stationary zone, shearing zone, rigid body zone) soil deformation model. Secondly, the deformation and internal force of the buried pipeline structure are solved using the two-parameter Pasternak foundation model and the finite difference method. Finally, the theoretical analytical solution is compared with existing experimental and 3D numerical simulation results, showing good agreement. In addition, sensitivity analyses are conducted for key physical parameters, including fault dip, fault-pipeline intersection location, and joint rotation stiffness. The results show that fault dip will change the position of the pipeline displacement curve and axial stress curve, but the maximum displacement and maximum axial stress are basically identical. The intersection of the fault and the pipeline will not only change the shape of the pipeline displacement curve and axial stress curve, but also alter the maximum axial stress. With the increase of joint rotation stiffness, the maximum axial stress value of the pipeline increases. When the joint rotation stiffness is large enough, the jointed pipeline can be calculated as if it is continuous.

The analysis of slope stability under a nonlinear strength criterion presents significant challenges due to the coupling of slope failure modes, stress distribution on the slip surface, and soil strength parameters. In this study, these challenges are addressed by employing a stress-based calculation mode for the slip surface, as opposed to the assumption of inter-slice forces under the slice division. Additionally, the nonlinear Mohr-Coulomb (M-C) strength criterion is incorporated, and stress constraint conditions at both ends of the slip surface are introduced. This, along with the global mechanical equilibrium conditions of the sliding body, establishes a limit equilibrium solution for slope stability with nonlinear failure characteristics using the stress-based calculation model for the slip surface. Furthermore, the slip surface is generalized to a curve represented by the polar diameter and polar angle under the rotating center point, creating a generalized generation model of the slip surface. For layered slopes, a rational connection mode for the inter-layer slip surfaces is proposed based on the most unfavorable shear direction under continuous stress. To integrate the limit equilibrium solution of slope stability under the stress-based calculation mode for the slip surface and the generalized generation of the slip surface, a joint iterative method for the polar diameter, stress, and strength of the slip surface is adopted. Through the comparison and analysis of several slope cases, the feasibility of the present method is verified, and the current work has the potential to contribute to a deeper understanding of slope failure mechanisms under the nonlinear strength criterion.

The rate effect of cavity expansion is not only related to the drainage conditions of the soil surrounding the cavity, but also closely associated with the rate-dependent mechanical properties of the soil. Most existing cavity expansion theories primarily focus on the rate effect caused by partial drainage conditions, with little attention given to the combined influence of drainage conditions and the rate-dependent mechanical behavior of soil. By employing numerical analysis and utilizing the overstress elasto-viscoplastic (EVP) model, the study focuses on the partial drainage conditions during cylindrical cavity expansion. The analysis indicates that when only the effect of partial drainage conditions is considered, the total radial stress and shear stress decrease monotonically as the expansion velocity increases, and the expansion velocity ranging from 10⁻⁴ to 10⁻¹ mm/s has a small impact on the total radial stress during the initial expansion stage. When the effect of partial drainage conditions and rate-dependent behavior is considered simultaneously, the total radial stress and shear stress gradually increase with the increase of expansion velocity during initial expansion stage, which is consistent with the results of in-situ self-boring pressuremeter tests conducted on the Burswood clay and Zhanjiang clay. With the cavity expansion, the radial total stress and shear stress show a pattern of first decreasing and then increasing with the increase of expansion velocity. Sensitivity analysis of the soil's viscoplastic parameters (γ ^vp and η ) reveals that, for a given expansion velocity, the total radial stress, shear strength, and initial shear modulus gradually decrease as γ ^vp or η  increase, with the rate of decrease diminishing over time. The expansion velocity, permeability coefficient, and overconsolidation ratio of the soil significantly impact the drainage conditions at the cavity wall, while the influence of γ ^vp and η  is relatively minor. The drainage conditions of the soil can be assessed using a dimensionless velocity V, with values of V corresponding to partial drainage conditions ranging from 0.04 to 250. It is suggested that the time-dependent mechanical behavior should be considered when applying cylindrical cavity expansion theory to analyze geotechnical problems related to cohesive soils.

In order to study the effect of moisture content on ultrasonic wave velocity and failure characteristics of soft coal, the mechanical testing & simulation (MTS) rock mechanics experimental machine, ultrasonic detector, and digital image correlation (DIC) processing technology were employed to conduct monitoring experiments on the wave velocity and surface morphology of briquette samples with different moisture contents under uniaxial compression. The evolution characteristics of wave velocity and deformation were analyzed. The computed tomography (CT) scanning test system was used to observe the meso-structure of failed coal, and the three-dimensional fissure distribution and characteristic parameters were obtained. The change laws of initial wave velocity and wave velocity of failed coal with moisture content were explored. The results show that: (1) With the increase of axial strain, the wave velocity of coal under different moisture contents exhibits four stages: steady, slowly decreasing, sharply decreasing, and then becoming steady again. As moisture content increases, the onset of the slowly decreasing, sharply decreasing, and then becoming steady stages of wave velocity change is delayed. (2) The initial wave velocity and post-failure wave velocity of coal increase and then decrease with the increase of moisture content, and the decrease in coal wave velocity after loading is linearly related to the moisture content. (3) As moisture content increases, the surface area, volume, and three-dimensional fractal dimension of internal fissures in the damaged coal show a linear increasing trend, and the failure mode of coal transitions from shear failure to tensile failure. (4) The microstructure is the main reason for the difference in initial wave velocity of coal under different moisture contents, while the wave velocity of the damaged coal is determined by both the microstructure and the distribution of meso-fissures. The research results can provide an experimental basis for revealing the acoustic-mechanical response characteristics of water-injected coal and for preventing and controlling instability disasters.

Heated pipeline transportation is one of the most economical and effective methods for long-distance transportation of oil and gas resources. Among them, the interaction mechanism between high-temperature pipelines and soft soil foundations is the key to analyzing their service stability. During the long-term service of the heated pipeline, heat is transferred to the surrounding soft soil, triggering complex hydro-thermal-mechanical coupling behavior. This, in turn, alters the bearing capacity of the foundation, significantly affecting the stability of the pipeline in service. A model test system has been developed to simulate the interaction between high-temperature pipelines and soft soil foundations, capable of replicating temperature variations in the pipeline. Focusing on the cyclic temperature loading experienced during the start-up, shutdown, and operation of high-temperature pipelines, model tests were conducted under various conditions, including different pre-compression stresses in the foundation, pipeline heating powers, and heating methods. These tests aimed to explore the evolution of temperature and pore pressure in the soil surrounding the pipeline during its service life under cyclic temperatures. Furthermore, the study investigated the development of restraint forces in the surrounding soil and the changing bearing characteristics of the foundation. The test results indicate that during continuous heating, the pore pressure around the pipeline increases, peaking before significantly decreasing, and may even reach negative values. This phase is beneficial for pipeline stability. When subjected to cyclic temperature loading, fluctuations in temperature induce corresponding variations in the pore pressure of the foundation. It’s worth noting that the amplitude of pore pressure fluctuations is smaller at the sides of the pipeline compared to the top and bottom. In tests simulating pipeline uplift, the foundation reaches its ultimate bearing capacity when the displacement reaches approximately 1.2 times the diameter of the pipe. Additionally, a higher pre-consolidation pressure offers greater bearing capacity, although there is little difference in uplift capacity between super-consolidated and normally consolidated foundation soils. T-bar tests conducted on the foundation revealed a significant enhancement in foundation strength during the high-temperature phase maintained by a single heating cycle. Moreover, an increase in foundation strength was observed even after the heating was stopped.

Saturated silt is prone to liquefaction and deformation under earthquake action, which can lead to severe damage to structures built on it. In natural conditions, saturated silt often experiences initial static shear stress  τ_s . To explore the impact of initial shear stress on the liquefaction characteristics of saturated silt, a series of cyclic torsional shear tests were conducted on liquefied silt, treating it as a fluid. The experimental results showed that the initial shear stress τ_s had a significant impact on the relationship curve of the shear stress-strain rate of saturated silt. When the initial shear stress  τ_s  equals zero, the pattern of the relationship curve transitions from the shape of an ellipse to the shape of a dumbbell as the number of loading cycles N increases. The pattern of the relationship curve successively appears as the shape of a sickle, ellipse, and hammer with increasing initial shear stress  τ_s . Meanwhile, the initial shear stress  τ_s  has a significant influence on the development of the apparent viscosity  η and the average flow coefficient κ⁻  of the saturated silt. As the initial shear stress increased, theκ⁻-N curve decreased first and then increased, while the development speed of the η -N curve showed a trend from fast to slow. Additionally, the excess pore water pressure ratio r_uth  at the solid-liquid phase transformation state first decreased and then increased as the initial shear stress increased. When the initial shear stress reached 5 kPa, the excess pore water pressure ratio of the saturated silt was the lowest.

Considering the impact of the subgrade water level and freeze-thaw cycles, experiments were conducted on ballast track subgrade mud pumping. The study analyzed the migration of water and fine particles, as well as the characteristics of mud formation during the mud pumping process of the ballast track subgrade under cyclic loading. The research findings indicate that, during the initial loading stage at ambient temperature, moisture migrates upwards from the bottom. As dynamic loading is continuously applied, the internal pore water pressure in the subgrade soil gradually dissipates, resulting in a decrease in the pore water pressure gradient and a stabilization of the moisture content in each soil layer. When the water level is positioned in the middle of the subgrade, the upper soil is in an unsaturated state with a relatively low volumetric water content of approximately 26%. Fine particle migration does not occur, and the effective stress at the subgrade surface is much greater than zero, thus preventing mud pumping. When the water level is at the top of the subgrade, particle migration is more pronounced. The effective stress at the subgrade surface rapidly decreases to below 0 under the action of the load, resulting in mud pumping phenomena. Compared to unidirectional freezing, freeze-thaw loading results in a slower descent rate of the freezing front and a greater amount of moisture migration. Under thawing conditions, the upper soil layer of the subgrade melts before the lower soil layer, forming a frozen soil interlayer. Due to the isolation effect of the frozen soil interlayer, the upper soil layer retains a higher moisture content. Under the action of the load, the effective stress at the subgrade surface rapidly develops into negative values, making it more susceptible to mud pumping.

Using a typical four-lane highway tunnel as a prototype, we conducted static pushover tests on a scaled-down model to examine the variations in ground displacement, ground pressure, and ground cracking with pushover distance. Compared with the test results of two-lane tunnel, the test results indicate that the ground is displaced reversely from the arching line and then cracked. Therefore, the location of fracture point should be modified from the bottom of the side wall to the arching line. The test results also show that the ground slides smoothly along the tunnel circumferential direction with a large inclination angle, so the potential slip planes should be modified from constant vertical to linear inclination. According to these test results, the applicability of surrounding ground pressure calculation model assumption in the four-lane tunnel is discussed, and a modified ground pressure calculation model suitable for the four-lane highway tunnels is proposed. These researches can provide experimental basis and technical support for the seismic calculation/checking of the four-lane highway tunnel, and provide reference for further improvement of surrounding ground pressure calculation model.

High water content in dredged silt leads to elevated costs for drying and solidification. By fully utilizing the porous water absorption of Expanded Perlite (EP), we can locally separate free water from the silt, resulting in an uneven water distribution and creating a “silt-water separation” solidification environment. Experimental results indicate that incorporating EP with silt can effectively enhance the unconfined compressive strength (UCS) of the solidified silt, but the method of incorporation affects the rate of strength increase and pore distribution. The stewing method, which involves pre-mixing EP into the silt and then adding cement after 24 hours, proves most favorable for promoting the solidification effect. After 28 days of curing, the strength of the stewing sample is 1.56 times that of the sample directly solidified with cement after EP incorporation, and 2.15 times that of the sample solidified with cement only. This indicates that the local "silt-water separation" effect facilitated by EP can effectively enhance the strength of the solidified silt. Meanwhile, hydration heat test results show that EP promotes cement hydration. According to the pore distribution curve and surface morphology images of EP-silt-solidified soil, while EP introduces porosity, it also provides growth space for hydration products, resulting in an embedded bond that forms a solidified soil skeleton between the interface of silt and EP. The method of regulating water content using EP is a physical one, which is convenient and efficient, differing from energy-intensive methods like machinery. Additionally, as a high-silica lightweight aggregate, EP exhibits good compatibility with silt and is environmentally friendly.

When movement occurs in active faults, tunnels crossing these faults may sustain varying degrees of damage. Most previous studies failed to consider the impact of tunnel depth and high in-situ stress on tunnels crossing active faults, resulting in findings that are not entirely practical. In this paper, the necessity of solving the anti-dislocation problem of deeply buried tunnels is systematically discussed. Through model tests of tunnels crossing active faults, the differences in failures between deeply buried and shallowly buried tunnels were compared. Additionally, a dislocation test of deeply buried segmented tunnels was conducted to analyze the external stress changes, lining strains, and failure modes of the tunnels. The results are as follows: (1) The overall deformation of both deeply and shallowly buried tunnels exhibits an S-shaped pattern. The most severe damage is concentrated in the fault zone. The failure mode of deeply buried tunnels is primarily characterized by shear and tensile failure, resulting in significant compressive deformation and a larger damaged area. In contrast, shallowly buried tunnels mainly experience shear failure, with the tunnel being sheared apart at the fault crossing. (2) After implementing the hinged design for the deeply buried tunnel, the S-shaped deformation pattern is transformed into a ladder pattern, reducing the strain on the tunnel and the peak stress of the external rock mass, thereby significantly mitigating damages. (3) Through the analysis of the distribution of cracks in the tunnel lining, it is found that the tunnel without a hinged design has suffered from penetrating failure, with cracks affecting the entire lining. The cracks in the hinged tunnel affect approximately 66.6% of the total tunnel length, while those in the tunnel with shorter hinged segments affect only about 33.3% of the total length. Therefore, a deeply buried tunnel with shorter hinged segments can yield a better anti-dislocation effect. (4) By comparing previous studies on shallowly buried hinged tunnels, it is concluded that shallowly buried hinged tunnels will also suffer from deformation outside the fault zone, while the damages to the deeply buried hinged tunnel are concentrated mainly in the fault zone. Therefore, the anti-dislocation protection measures for deeply buried tunnels should be concentrated mainly in the fault zone. These findings can provide theoretical guidance and technical support for the design and reinforcement of tunnels crossing active faults under high stress conditions.

Most of the landslide rock and soil masses undergo cutting and fragmentation during movement, and the entry of the fragmented sliding mass into the river significantly affects the characteristics of the resulting impulse waves. The wave-making effect of the fragmented sliding mass still needs further exploration. Based on large-scale three-dimensional landslide impulse wave scale physical experiments, physical experiments were conducted to investigate the generation of impulse waves from landslides under varying degrees of sliding mass fragmentation, and the wave-making effect of the fragmented sliding mass was analyzed. The results indicate that as the degree of fragmentation of the sliding mass increases, the first peak, maximum wave height, and propagation velocity of the impulse wave all exhibit a decreasing trend. Specifically, as the degree of fragmentation increases, the maximum amplitude of the impulse wave decreases by 8.84% and 19.75%, respectively, and the maximum wave height of the first wave decreases by 12.49% and 21.13%, respectively. Through experimental observations, it is evident that the degree of fragmentation of the sliding mass primarily influences the characteristics of the impulse wave by controlling the velocity of the sliding mass and the interaction process between the sliding mass and the water body. Based on the sliding mass-water interaction, three mechanisms are proposed: sliding mass structure reorganization, seepage flow, and impulse wave attenuation. These new insights reveal the characteristics of landslide movement, fragmentation, and wave-making, and deepen our understanding of the formation mechanism of landslide impulse waves.

The rockburst disaster triggered by the nonlinear large-deformation characteristics of deep rock masses has been a worldwide problem in geotechnical engineering, severely constraining construction progress and safety in engineering projects. Therefore, it is imperative to intensify in-depth research on rockburst prevention measures. Based on the principle of steel pipe compressive deformation, a novel steel pipe shrinkable energy-absorbing bolt constant-resistance large-deformation bolt was proposed, which can provide a high constant resistance while accommodating a substantial amount of deformation. Building on previous research, the impact resistance of the steel pipe shrinkable energy-absorbing bolt constant-resistance large-deformation bolt was investigated through drop hammer impact tests. The test results indicate that: during the impact process, the working resistance of the steel pipe shrinkable energy-absorbing bolt constant-resistance large-deformation bolt remains stable within the range of 150 kN to 180 kN, demonstrating notable constant-resistance characteristics; the bolt absorbs a significant amount of energy with high efficiency, capable of absorbing up to 53 kJ of impact energy in a single instance; throughout the impact, the compression rate of the specimen only decreased by 0.54% to 1.43%, indicating relatively stable deformation. The steel pipe shrinkable energy-absorbing bolt constant-resistance large-deformation bolt exhibits excellent impact resistance, providing robust technical support for the prevention and control of rockburst disasters during underground engineering construction.

In order to address the issues of settlement and collapse of coral sand foundations on island reefs caused by rainfall infiltration, this study conducted top-down unidirectional penetration tests on gap-graded coral sand with varying D₁₅/d₈₅ ratios (D₁₅ represents the particle size corresponding to a cumulative percentage of 15% for soil particles smaller than a certain size in the coarse-grained group, while d₈₅ represents the particle size corresponding to a cumulative percentage of 85% for soil particles smaller than a certain size in the fine-grained group.) and fine particle contents using a self-designed permeameter. It identified the migration characteristics and fundamental conditions for fine particle loss, revealed the patterns of permeability change in coral sand, and analyzed the underlying mechanisms through microscopic methods. The results show that: (1) For coral sand with a soil skeleton particle size ranging from 2 mm to 10 mm, particles measuring 0.25 mm to 0.50 mm are critical for ensuring stable seepage erosion. (2) Coral sand foundations with a D₁₅/d₈₅ ratio below 10 and a fine particle content between 20% and 30% exhibit better stability against infiltration erosion. (3) Compared to quartz sand, the unique mineral composition and particle morphology of coral sand contribute to its increased resistance to particle migration and stronger resilience against seepage erosion. (4) In engineering applications, measures such as improving relative density, optimizing particle gradation, or implementing grouting consolidation can enhance the stability of foundations against seepage erosion. The research findings provide a scientific basis for the design of coral reef foundations with resistance to seepage erosion.

Assessing the risk of earthquake-induced liquefaction in gravelly soils is a new challenge faced by earthquake prevention and disaster reduction efforts in China's engineering sector. In situ shear wave velocity testing is a universally applicable technical method; however, existing methods are not suitable for China. This study establishes a new method for calculating the liquefaction probability of gravelly soils based on shear wave velocity under the Chinese model, and compared it with the CYY (Cao, Youd and Yuan) method, which is based on the CSR (cyclic stress ratio) theory. The comparative analysis using measured data as well as different probability liquefaction threshold models indicates that the proposed Chinese model for calculating the liquefaction probability of gravelly soils based on shear wave velocity can solve the problem of CYY method unsuitable for China and is more advanced than the CYY method. It overcomes the shortcomings of the CYY method, which struggles to simultaneously consider different burial depths of gravelly soil layers and the effects of varying seismic intensities. Both in the deterministic discrimination with a probability of 0.5 and in the reliability of liquefaction probability calculation under measured data, the method proposed in this paper outperforms the CYY method. The proposed formula in this paper has been adopted in the revised version of the General Rules for Performance-Based Seismic Design of Buildings, serving as a model for China, and can provide guidance and technical support for related specifications and engineering applications.

The strength parameters of geotechnical bodies in strata formed under natural conditions often exhibit spatial variability. Predicting the run-out distance of potential large-scale landslides using limited strength data is challenging as it may not comprehensively reflect the range of changes in sliding distance. Therefore, it is necessary to conduct stochastic analyses of landslide sliding distance by combining statistical characteristics and distribution laws of strength parameters, providing a reference for the prevention and control of landslide disasters. This study presents a smooth particle hydrodynamics (SPH) method for modeling the large-deformation sliding process of landslides, based on the Bingham model, equivalent viscosity, and Mohr-Coulomb failure criterion. The mid-point method is used to generate random field samples of the internal friction angle. Monte Carlo simulations were conducted for stochastic analysis of the sliding distance, thereby obtaining the distribution characteristics of the run-out distance for large-scale landslides. The Yangbaodi landslide was chosen as a study case to verify the feasibility of the SPH method. The accuracy of the discretization of the internal friction angle random field was verified by establishing and analyzing geological models with different random field parameters, and the simulation parameters were calibrated. On this basis, the range and distribution pattern of landslide sliding distance under different conditions were analyzed by varying the coefficient of variation of the internal friction angle, as well as the vertical and horizontal scales of fluctuation. The results show that an increase in the coefficient of variation leads to an increase in the range of the landslide distance, with the sliding distance showing stronger discreteness; an increase in the vertical fluctuation range increases the size of the intensity parameter distribution clusters, which in turn increases the range of the landslide distance; both the horizontal and vertical fluctuation ranges, as well as the coefficient of variation, show a positive correlation with the standard deviation of the sliding distance, with the horizontal fluctuation range having the least impact.

The monitoring and forecasting of slope dangerous rock mass collapses have always been a critical yet underdeveloped area in geological disaster prevention research. An automatic sensing mechanism was devised for capturing, computing, and transmitting minor tilt angles and strong vibration accelerations of tension-cracking dangerous rock masses. A micro-core-pile geological disasters monitoring sensor has been devised, enabling low-power long-term monitoring. Through on-site monitoring and analysis of tension-cracking rock mass collapses, it was found that these rock masses exhibit a precursor of collapse characterized by accelerated tilt deformation accompanied by an increase in the frequency and amplitude of strong vibrations. It was revealed that there is a significant exponential relationship between the cumulative tilt deformation and the tilt deformation rate during the accelerated tilt phase immediately preceding collapse, and a linear correlation exists between the reciprocal of the tilt rate and the remaining time before collapse. Subsequently, a ‘reciprocal tilt rate method’ was established for predicting the time to collapse, and an algorithm for real-time application of the prediction model based on MEMS tilt angle sensor data characteristics was developed. These research findings can have a positive promoting effect on the monitoring and early warning of collapse disasters.

Piezocone penetration tests are widely used to determine the engineering properties of in situ soils. Continuous penetration of the probe in cohesive soils leads to the accumulation of excess pore pressure, which gradually dissipates after the penetration is stopped. In structured silt-clay, clayey silt or silty soils, partially drained may occur during the penetration process, leading to more complex pore pressure dissipation responses following penetration compared to those under undrained conditions. To simulate the entire “penetration-dissipation” process during piezocone penetration and dissipation tests in structured soil, Structured Cam-Clay model is incorporated into the large deformation finite element method within the framework of effective stress analysis. A normalised expression for the dissipation of excess pore pressure after partially drainage or undrained penetration is obtained. The reliability of the large deformation method is verified by comparing with the existing centrifuge tests. A large number of parametric studies have revealed that the effects of soil type, initial soil structure and dissipation depth can be reasonably neglected on the normalised dissipation curve, which can be used to determine the operative consolidation coefficient and subsequently predict the conventional consolidation coefficient.

In order to understand the mechanical characteristics of tree roots and their mechanical effects on slopes, the landslide in Wuping high vegetation coverage area of Fujian province was selected as the research site, and the root tensile mechanical properties of typical tree roots in the study area were tested after classification by diameter class. Furthermore, in-situ direct shear tests of root-soil composites under different root cross-sectional area ratios (RAR) and moisture content were conducted at the landslide site, and investigations were made into the distribution characteristics of roots in the profile to explore the mechanical effects of roots on shallow landslides. The results showed as follows: (1) The tensile force of Pinus massoniana and Cunninghamia lanceolata ranged from 12.45−673.09 N in 1−7 diameter class, and the tensile force was positively correlated with the root diameter by power function; The tensile strength ranges from 7.16 MPa to 60.95 MPa, and the tensile strength is negatively correlated with the root diameter as a power function. The average tensile force and tensile strength of Cunninghamia lanceolata root were higher than those of Pinus massoniana. (2) Tree roots significantly improved the shear strength of soil, and the additional cohesion provided by roots to soil was significantly positively correlated with the shear plane RAR. The root structure of Cunninghamia lanceolata is closer to R type, and that of Pinus massoniana is VH type. Under similar RAR, Cunninghamia lanceolata roots has a better reinforcing effect on the soil than Pinus massoniana. (3) With the increase in moisture content, the shear strength of the root-soil composites of Pinus massoniana and Cunninghamia lanceolata significantly decreases, as water infiltration diminishes the additional cohesion provided by the root systems to the soil. (4) Based on the Wu model, considering the influence of moisture content on soil cohesion and additional root cohesion, an estimation model for the shear strength value of root-soil composites considering moisture content was established. Upon verification, the accuracy of this model proved to be higher than that of the Wu model, and the results were reasonable. (5) Although the root system has a reinforcement effect on shallow landslides, its contribution to the stability of shallow landslides under heavy rainfall is limited due to the influence of root distribution depth, density and water infiltration.

The protruding part of the high slope at the bridge site in the deep canyon area has typical geological and geomorphic characteristics of three faces exposed to the air and multiple unloading faces. Studying the seismic terrain amplification effect of the protruding slope is crucial for ensuring the safety and stability of the bridge site. This study investigated the seismic amplification effects and deformation mechanisms of the slope’s protruding parts at the large bridge site and optimized the positioning of piers and abutments. The research results indicate: (1) Field investigation and numerical simulation comprehensively confirm the development of debris flow at the top of the slope bulge and the instability of the rock mass at the lower part of the main pier. These conditions have been significantly affected by historical earthquakes. The acceleration exhibits a nonlinear amplification pattern that is influenced by the slope height, and excavation exacerbates the acceleration amplification effect in the excavation area. The maximum amplification factor is at the waist and top of the bulge (ridge), and the maximum acceleration amplification factor (MPGA) reaching 3.2. (2) The acceleration Fourier spectrum amplitude of the high-frequency part of the slope ridge (5-12 Hz) generally exceeds that of the slope valley. Excavation leads to a decrease in the peak value of the Fourier amplitude of the upper slope of the pier and abutment, while the lower slope experiences an increase. The peak value of the Fourier spectrum amplitude near the excavation location initially increases and then decreases with the increase of peak acceleration. (3) The maximum slope height and the extreme value of amplification factor are limited in the seismic design code for buildings, potentially leading to an underestimation of the dynamic amplification effect of the bulge and resulting in a more hazardous seismic stability evaluation of the bulge. (4) To ensure the seismic stability of the bridge site slope, the optimal distance between the outer edge of the pier and abutment and the slope surface is determined to be 22-26 m. The research findings can provide valuable guidance for the seismic stability evaluation of high slopes with protrusions and the optimal design of pier and abutment locations.

Due to the heterogeneity and low permeability of most CO₂ reservoirs in China, CO₂ storage within a single reservoir is difficult to meet the demand for emission reduction. To achieve large-scale CO2 geological storage, multi-formation injection technology has been proposed to increase the amount of CO₂ geological storage. To explore the main influencing factors on the caprock sealing performance under the condition of multi-formation CO2 injection, the seepage-stress coupling simulation analysis was carried out. Pore pressure, displacement, and incremental Coulomb failure stress (ΔCFS) are used as the basis for evaluating the caprock sealing performance. The tornado analysis method was used for sensitivity analysis to select the factors that have a significant impact on the caprock sealing performance. The research results indicate that the more injection layers, the smaller the displacement, pore pressure, and ΔCFS of the caprock, and the better the caprock sealing performance. However, if the number of layers exceeds 3, the efficiency increase brought by the number of layers will no longer be significant; The main controlling factors for the sealing performance of the caprock include the Poisson’s ratio and Young’s modulus of the caprock, thickness and permeability coefficient of the reservoir, and injection rate; When the thickest caprock is located at the topmost part of the entire formation, the caprock sealing performance is the best, producing the smallest vertical displacement, pore pressure, and ΔCFS.

Dynamic properties of sandy soil under medium-high strain rates are of great significance for protection engineering, pile penetration, ship anchoring, aircraft landing, and so on. This paper reviews the current research status of split Hopkinson pressure bar (SHPB) impact tests and numerical simulations on sandy soil. The key issues in the research of sandy soil impact characteristics are summarized as follows: (1) The SHPB test still faces uncertainties for granular materials, such as the lack of standardized test sample size, difficulties in controlling boundary conditions, and the immaturity of triaxial testing methods. Future triaxial SHPB tests need to address issues related to measuring radial deformation of the samples and maintaining consistent confining pressure. (2) Due to uncertainties in gas and water discharge under test conditions and the presence of inertial effects, the accurate determination of strain rate effects becomes challenging. (3) The impact characteristics of granular materials are influenced by moisture content, which is correlated with changes in pore water pressure and pore air pressure. However, measuring these related variables is difficult, making it challenging to analyze the results. It is necessary to develop a device that completely eliminates the effects of gas and water discharge to mitigate the influence of boundary conditions. (4) To study the impact characteristics of sandy soils, it is necessary to overcome computational limitations and establish numerical models that account for complex mechanisms such as water content and particle fragmentation. Existing methods such as the finite element method, discrete element method, and coupled methods are unable to uniformly simulate the continuity of wave propagation and particle fragmentation. (5) It is crucial to develop constitutive models that consider the strain rate effects and can simulate complex mechanisms such as water content and particle fragmentation. This will help refine the theoretical framework of soil mechanics at medium to high strain rates.

As a commonly used pile foundation, tubular piles are widely used in practical engineering, and their dynamic response analysis has important research value. Based on the principle of elastic dynamics and viscoelastic saturated soil model, the dynamic characteristics of large-diameter tubular piles in fractional-order viscoelastic saturated soil under vertical dynamic load are investigated by taking into account the immobile viscosity of the soil skeleton and the lateral inertia effect of the tubular piles. Firstly, the fluctuation equations of fractional-order viscoelastic saturated soil in column coordinate system were established based on Biot's dynamic consolidation theory and fractional-order standard linear solid (FSLS) model. Secondly, based on the Rayleigh-Love rod model and considering the lateral inertia effect of the tubular piles, the analytical solution of the pile top dynamic impedance of the tubular piles is derived. Finally, the effects of fractional order model parameters, lateral inertia effect of tubular piles, pile length and soil permeability on the dynamic impedance of pile top of tubular piles are investigated by example analysis. The results show that: the increase of fractional order and strain relaxation time and the decrease of stress relaxation time in the FSLS model parameters of saturated soil skeleton increase the dynamic impedance at the top of the pile; the transverse inertia effect of tubular piles is especially obvious in the high-frequency section to reduce the dynamic impedance at the top of the pile; and the reduction of the outer radius of tubular piles and enlargement of the inner radius of tubular piles, as well as the increase of the pile length and decrease of the permeability of the soil body all help to improve the dynamic impedance at the top of the pile.