In the natural environment and engineering scenarios, there are not only bare unsaturated soils but also unsaturated soils covered by vegetation (i.e., unsaturated vegetated soils). For the unsaturated vegetated soil with a uniform root architecture, on the basis of considering the effects of roots on the hydrological properties, the linearized governing equations for one-dimensional transient seepage of water are acquired by some simplifying assumptions and variable substitution. The analytical solution for one-dimensional transient seepage of water in the unsaturated vegetated soil is obtained through the methods of separation of variable and series transformation. Subsequently, the computational results of this analytical solution have been compared with those of the existing analytical solution and the corresponding finite-difference solution to verify its reasonableness. Finally, a simple vegetated cover is taken as an example to analyze the influences of root-related parameters on its effectiveness in blocking rainwater infiltration. The results show that the cumulative leakage CQ_b at the bottom zone of a vegetated cover under the same rainfall scenario is smaller than that of a single cover without vegetation, and an increase in the rooted soil thickness l_g enhances the effectiveness of the vegetated cover in blocking rainwater leakage. The increase of the transpiration rate T_p significantly reduces the leakage rate at the bottom zone of the vegetated cover under the rainfall scenario, and the cumulative leakage CQ_b tends to decrease linearly with an increase in T_p. Compared with the extreme case where the root volume ratio R_v is zero and the effects of roots on the hydrological properties of soil are ignored, the effectiveness of the vegetated cover in blocking rainwater leakage is enhanced when the saturated permeability coefficient of the rooted soil decreases due to the value R_v, and conversely, it is weakened. Overall, this study could provide scientific guidance for engineering practices related to water infiltration in unsaturated vegetated soils.

Evaluating the compaction quality of rock-filled subgrades rapidly and accurately poses a pressing challenge in highway engineering. To address this, this study establishes a discrete element-finite difference coupling model to simulate the response of rock-filled subgrades under impact loading. The primary parameters of the model are calibrated using indoor large-scale triaxial tests, and the model’s accuracy is verified through comparisons between calculated and field data. Furthermore, this study conducts an in-depth analysis of the dynamic response results of five commonly used gradations of rock-filled subgrades under varying degrees of compaction, discussing the influence of gradation fractal dimension and porosity on subgrade deformation response. The findings are as follows: (1) A good exponential relationship between subgrade porosity and resilient modulus is identified, and the concept of settlement ratio is introduced, with a linear relationship between settlement ratio and subgrade porosity being verified. It is suggested that both resilient modulus and settlement ratio should be used as control indicators when evaluating subgrade compaction quality. (2) A prediction function for subgrade resilient modulus considering fill gradation and porosity is obtained, revealing that particle gradation has a significant impact on resilient modulus. Specifically, as the gradation fractal dimension approaches 2.31, the resilient modulus increases more rapidly with decreasing porosity. (3) A settlement ratio of zero corresponds to the ideal compaction state of the subgrade. This study establishes a prediction model for the critical resilient modulus of the subgrade in its ideal state, considering fill gradation, and finds that the critical modulus first increases and then decreases with increasing fractal dimension D, reaching a maximum when D=2.34. These findings aim to provide new methods and theories for evaluating the compaction quality of rock-filled subgrades in engineering.

In order to investigate the influence of rock interface roughness on the characteristics of the charge induction signal during fault slip, the time-frequency characteristics of the multi-channel charge induction signal waveforms, the cumulative velocity of charge, the fractal dimension, and the primary and secondary frequency zones of the rock assemblage structure with different roughness during the slip process in the double-sided shear test under different vertical loads were investigated. The results show that: (1) The localized micro-rupture nucleation in the elastic deformation stage leads to multiple charge induction clusters with maximum values, which increase with the increase of interface roughness and vertical load, and then become dense and small-amplitude signals when entering into the start-slip stage. (2) With the increase of interface roughness and vertical load, the fluctuation of the accumulated charge velocity and fractal dimension are more obvious and highly correlated with the change of the waveform of the charge induction signal. In the elastic deformation stage, the accumulated charge velocity shows “slow increase in the main body and sudden increase in multiple points”, and each charge induction cluster is accompanied by the phenomenon of “first ascending and then descending” of the fractal dimension, with the main frequency area located in the low-frequency domain and the sub-main frequency area located in the high-frequency domain. In the start-slip stage, the accumulated charge velocity changes to an overall rapid increase and the fractal dimension fluctuates more obviously with the increase of fault interface roughness and vertical loading. During the start-slip stage, the charge accumulation rate changes to an overall rapid increase, and the fractal dimension is continuously downgraded, and the primary and secondary frequency regions show the phenomenon of “translational interchange”, with the primary frequency region shifted right to the high-frequency domain, and the secondary frequency region shifted left to the low-frequency domain, and the primary frequency of the charge signals at each slip stage falls into the frequency aliasing domain common to the whole process of slipping. (3) Comparing the time-frequency resolution and time-frequency focusing of the three time-frequency transform methods, wavelet transform, short-time Fourier transform and S transform, it is found that the wavelet transform performs the best in the low-frequency domain, the short-time Fourier transform the second, and the S transform the worst, while in the high-frequency domain, the S transform performs the best, the wavelet transform the second, and the short-time Fourier transform the worst. (4) Differences in charge signals of sensors at different locations during fault slip destabilization are mainly related to the aggregation of charges in specific regions caused by locally concentrated micro-ruptures before the start-slip phase, and are mainly caused by the change of misalignment of the relative positions between the slip surface and the sensors after the start-slip phase.

Based on the dynamic theory of elastic media, the horizontal vibration of end-bearing piles embedded in a transversely isotropic soil is studied via an analytical scheme. By introducing displacement potential functions, the governing equations of the soil are decoupled, and the general solutions for the displacement and stress fields around the pile are derived using the method of separation of variables. Applying the continuity conditions at the pile–soil interface, the horizontal complex impedance of the surrounding soil is incorporated into the motion equation of the pile, leading to analytical solutions for the displacement, rotation angle, bending moment, and shear force of the pile. In addition, explicit expressions for the horizontal, rocking, and coupled horizontal–rocking dynamic impedances at the pile head are derived. Comparison with existing theoretical solutions confirms the accuracy and reliability of the proposed method. Furthermore, the influence of soil anisotropy parameters on the horizontal vibration characteristics of the pile is systematically analyzed. The results indicate that the anisotropic modulus ratio has a significant impact on the dynamic impedance at the pile head, as well as on the distribution of horizontal displacement, rotation angle, bending moment, and shear force along the pile depth.

A widely distributed salinized silt in Northwest China exhibits the physical characteristics of both low-liquid-limit silt and saline soil, yet its long-term deformation behavior remains insufficiently understood. A series of uniaxial creep tests were conducted to investigate its creep properties under varying conditions of salt content, dry density, moisture content, and overburden stress. Test results indicate that, compared to salt-free soil, the creep rate of salinized silt accelerates significantly with increasing salt content, demonstrating more pronounced nonlinear creep characteristics. The final strain of the salt-washed soil was 10%, which increased to 14% at a salt content of 6.4%. To more accurately characterize the soil’s creep behavior, the classical creep models were modified, leading to the proposal of two new models: an integer-order model and a fractional-order model. Comparative analysis between the experimental data and the improved models shows that both proposed models describe the actual deformation characteristics more accurately than the classical creep model. However, the integer-order model lacks refinement in describing the decay creep stage, whereas the fractional-order model demonstrates superior accuracy in capturing the detailed features of all creep stages and is therefore recommended for effectively predicting the creep behavior of salinized silt.

 The energy development projects in western China require the construction of a large number of vertical shafts in weakly cemented gravel layers with poor stability. Anchor rod support is an important means of controlling the deformation of surrounding rock. However, most of the current theories on anchor reinforcement have overlooked the lagging support of anchor rods. Therefore, based on the spatial constraint effect of the working face, elastic-plastic theory, and the anchor rod stress uniform distribution method, this study proposes a semi-analytical calculation method for the deformation and stress of the surrounding rock of vertical shaft anchor bolts considering the lag support of anchor bolts. The correctness of this method was verified by finite element method. Based on the proposed semi analytical solution, the influence of anchor parameters was further explored. The research results show that the larger the lag distance of the anchor rod, the greater the deformation of the surrounding rock, and the smaller the surrounding rock pressure borne by the anchor rod and other supporting structures. When the lag distance x_gs of the anchor rod is less than 1.5r_A (r_A represents the excavation radius of the vertical shaft), the deformation u_r(r=r_A) and safety factor s of the surrounding rock change greatly. When the lag distance x_gs of the anchor rod is greater than 3.0r_A, the deformation u_r(r=r_A) and safety factor s of the surrounding rock remain basically unchanged. Increasing the diameter of the anchor rod improves the shear strength, but the impact gradually decreases. When the length of the anchor rod L is less than 1.0r_A, the deformation of the surrounding rock u_r(r=r_A) and the safety factor s change greatly. When the length of the anchor rod L is greater than 1.0r_A, the change is slow, so it is not recommended to excessively use long anchor rods. Research suggests that when selecting support parameters, consideration should be given to the support lag distance to ensure the stability of the surrounding rock. This study successfully applied this theory to the vertical shaft engineering of pressure pipelines, and the research results provide a solid theoretical basis for the design of anchor rod support for the surrounding rock of the vertical shaft.

The microbially induced calcite precipitation (MICP) technique can effectively enhance the mechanical properties of coral sand. To investigate the small-strain dynamic characteristics of MICP-treated coral sand, resonant column tests were conducted on specimens with varying biocementation cycles N_b and effective confining pressures σ₀ and the development laws of dynamic shear modulus G and damping ratio γ were comparatively analyzed. The test results reveal that: at small strains, the dynamic shear modulus G increases significantly with both N_b and σ₀. The maximum dynamic shear modulus G_max exhibits a linear correlation with N_b and a power-law correlation with σ₀. A significant power-law relationship exists between G_max and unconfined compressive strength (q_ucs). As N_b increases, the reference strain γ₀  decreases gradually while the G/G_max-γ_d curves shift downward, indicating enhanced nonlinearity. Both minimum and maximum damping ratios increase, with the γ-γ_d curve moving upward and characterized by greater energy dissipation. In contrast, increasing σ₀ produces opposite trends in both G/G_max-γ_d and γ-γ_d curves, exhibiting reduced nonlinearity and energy dissipation. Empirical relationships are established to quantify the nonlinear dynamic behavior and energy dissipation characteristics of MICP-treated coral sand. Scanning electron microscope (SEM) observations reveal that stiffness improvement primarily results from three mechanisms: contact cementation between sand grains, grain coating by calcite precipitates, and matrix supporting through pore filling.

Current research on rock freeze-thaw damage mainly focuses on uniform freeze-thaw tests. However, the situation of unidirectional freeze-thaw action is widely present in cold region engineering, and there is a lack of sufficient understanding of the evolution of mechanical properties and damage models under unidirectional freeze-thaw conditions. Therefore, this study selected sandstone as the research object and conducted unidirectional freeze-thaw cycle tests and uniaxial compression tests. The elastic modulus, uniaxial compressive strength, stress-strain curves, and failure modes under uniaxial compression were analyzed for sandstone samples parallel and perpendicular to the freeze-thaw direction after undergoing freeze-thaw cycles. The results indicate that, following unidirectional freeze-thaw action, the compressive strength of sandstone parallel to the freeze-thaw direction is greater than that perpendicular to it, while the elastic modulus parallel to the freeze-thaw direction is smaller than that in the perpendicular direction. Both the peak stress and strain in the parallel direction are higher than those in the perpendicular direction. In uniaxial compression tests, the failure mode of sandstone parallel to the freeze-thaw direction remains consistent with that of samples that have not undergone freeze-thaw action, exhibiting X-shaped shear failure, whereas the failure mode perpendicular to the freeze-thaw direction manifests as splitting along the loading direction. Under unidirectional freeze-thaw action, the mechanical properties of sandstone transition from isotropy to anisotropy. Based on the aforementioned experimental observations, an anisotropic coefficient for unidirectional freeze-thaw was introduced, and a damage model for sandstone under unidirectional freeze-thaw conditions was established. The model was subsequently validated using experimental data.

In rock-lined caverns with compressed air energy storage (CAES), the hoop tensile strength of rock is an important parameter for calculating the ultimate bearing capacity and long-term stability of the cavern. The existing methods for measuring the tensile strength of rock are direct tensile tests or indirect tensile tests, such as Brazilian splitting and point load bending tests, which cannot truly reflect the circumferential stress of rock under high internal air pressure. Based on this, a new measurement method is proposed. By injecting high-pressure air into the drilled rock sample, the rock burst pressure is obtained. Then a calculation formula for the rock tensile strength is proposed considering the rock pore stress. In the experiments, the inflation rate and the temperature are changed, and it is found that the rock burst pressure is negatively correlated with the inflation rate and positively correlated with the temperature. It is found that when the number of cycles is relatively small (n≤100), the rock burst pressure is positively correlated with the number of cycles. The results can guide the design and calculation of rock-lined caverns for CAES, which is conducive to the promotion and application of CAES technology and has important engineering application value.

The accumulation of excess pore water pressure (EPWP) under cyclic loading may induce partial or complete liquefaction of saturated coral sands, posing significant threats to the safety of structures and foundations. In numerical simulations and analyses, accurate prediction of EPWP development is essential, with the determination of threshold strain serving as a critical step. A novel method has been developed to determine the threshold strains (pore pressure threshold strain γ_tp, stiffness degradation threshold strain γ_td, and flow threshold strain γ_tf) for the EPWP generation and stiffness degradation in saturated coral sands under complex stress paths. This was achieved isotopically consolidated, undrained single-stage and multistage cyclic shear tests, including 90° jumps and continuous rotations of principal stress. The findings indicate that while γ_tp, γ_td, and γ_tf are relatively insensitive to the cyclic stress, they are significantly influenced by the initial relative density (Dr). Additionally, the gap between γ_tp and γ_td widens as D_r increases. Under varying cyclic loading conditions and initial physical states, γ_tf corresponds to the EPWP ratio of approximately 0.9, with a corresponding stiffness index of around 0.10. The proposed method for determining γ_tp, γ_td, and γ_tf can effectively reduce the number of required cyclic tests, making it suitable for use as input values in numerical calculations or analytical methods, and for characterizing soil behavior under stress and strain conditions.

To study the wetting deformation characteristics of undisturbed loess under true triaxial force-water path, the true triaxial apparatus with rigid-flexible-flexible loading boundary was used to carry out the true triaxial single-line humidification test of undisturbed loess in Xi’an under different spherical stresses, intermediate principal stress parameters and stress ratios. The influence of true triaxial force-water path on the humidification deformation characteristics of undisturbed loess was comprehensively analyzed. The test results show that the relationship curve between the wetting volumetric (deviatoric) strain and the spherical stress presents a three-stage of slow-steep-slow. When the spherical stress is in the second stage, the wetting collapsibility of the soil is the largest, and a large wetting deformation can occur. At a certain stress ratio, the wetting volumetric strain gradually increases with the spherical stress, and the increase of the wetting volumetric strain decreases when the spherical stress exceeds 200 kPa. Finally, the variation law between the intermediate principal stress and each humidification strain is analyzed, and the calculation expression of loess collapsible deformation considering the intermediate principal stress is given according to the test results.

The strength and deformation characteristics of rockfill materials are known to be closely related to their gradations. In order to predict the mechanical behavior of rockfill materials with different initial gradations, the influence of gradation on the mechanical properties of rockfill materials is first discussed within the framework of critical state constitutive theory. Subsequently, a method is proposed for rapidly predicting the initial and critical state void ratios for given gradations. Finally, by incorporating a state-dependent elastoplastic constitutive model, a prediction method for the gradation-related mechanical characteristics of rockfill materials is established. The results indicate that a good linear relationship exists between the minimum void ratio e_min and the critical state void ratio e_cs under low-stress conditions. Utilizing a particle packing algorithm, the critical state position of rockfill materials with specific gradations in the void ratio-pressure (e-p, e is the void ratio of the rockfill material in its current state, and p is the mean stress) space can be reliably predicted. Ultimately, this proposed prediction method facilitates the calibration of constitutive model parameters based on the test results of rockfill materials with known gradations, which subsequently allows for effective prediction of the mechanical behavior of other rockfill materials with different specified gradation profiles.

The cohesion effect induced by liquid bridges between particles, which promotes particle aggregation, is widespread in both natural environments and engineering applications. Understanding the migration and clogging processes of particles in fractured media under the influence of capillary-cohesion is crucial for advancing particle transport knowledge. Through visualization experiments and seepage calculations, the processes of capillary-cohesive particle migration and clogging are studied. A phase diagram of clogging patterns in the space of capillary-cohesion and flowrate is proposed. Experimental results show that capillary- cohesion induces particle agglomeration, increasing effective particle diameter and significantly enhancing fracture clogging. Stripe-like clogging patterns occur at high flow rates, while complete clogging patterns or entrance sealing patterns occur at low flow rates. Hydrodynamic analysis reveals that fluid velocity distributions control the growth of clogging stripes and the change in residual flow channels in the complete clogging patterns. Furthermore, Smoluchowski theory effectively describes the linear growth behavior of clogging stripes over time. These findings elucidate the mechanism of capillary-cohesive particle migration and clogging in rock fractures, providing theoretical and technical guidance for evaluating and controlling particle transport in fractured media.

Mining disturbance can easily aggravate the creep instability of roadway surrounding rock, and its propagation mode in surrounding rock is damped oscillation disturbance. In order to explore the creep characteristics of rock under the damped oscillation disturbance, X-ray diffraction, nuclear magnetic resonance and pseudo-triaxial creep tests were carried out. Based on the test results, a discrete element numerical model of sandstone was established. The parameter calibration results show that the combination of linear parallel bond model and Burgers model can simulate the creep behavior of rock. Combining the sinusoidal disturbance function with the exponential function, a function expression for simulating the attenuation oscillation disturbance is proposed. The application of attenuation oscillation disturbance in numerical simulation is realized by Fish language, and the creep process of sandstone under attenuation oscillation disturbance is simulated. The simulation results show that compared with the undisturbed rock sample, the accelerated creep time of the rock sample under the action of attenuation oscillation disturbance is earlier and the creep deformation is larger. Before and after the disturbance is applied, the distribution of crack dip angle changes from concentration to dispersion, and the failure mode is tensile-shear composite failure mode. When the attenuation oscillation disturbance is applied, the creep deformation of rock shows a similar attenuation oscillation trend. The greater the deviatoric stress, the greater the influence of attenuation oscillation disturbance on rock deformation. The application of attenuation oscillation disturbance is more likely to lead to the fracture of contact bond between particles and accelerate energy dissipation. The attenuation oscillation disturbance element and the nonlinear viscoplastic body are introduced into the Burgers model, and an improved Burgers model is established. The theoretical curve is in good agreement with the experimental data. The model can better characterize the creep process of sandstone under attenuation oscillation disturbance.

In the constructural backfill mining, the composite bearing structure of 'backfill body-immediate roof' structure will be subjected to different loading rates depending on the mining speed and other conditions. According to the loading rate of 0.15− 2.40 mm/min, the uniaxial compression test of five groups of rock-backfill composite were carried out, and digital image correlation technology and acoustic emission monitoring were carried out to analyze the evolutionary characteristics of its energy loss. It can be seen from the experiment that the strength of siltstone is significantly greater than the strength of the rock-backfill composite and the backfill body, and the strength of the combination is closer to the strength of the filling body than the siltstone. It can be seen that 0.60 mm/min is the critical load for this group of experiments. When the loading rate of the rock-backfill composite is 0.15− 0.60 mm/min, the rock-backfill composite ultimately realizes the synergistic deformation of the siltstone and the backfill body in the rock-backfill composite and destruction of the rock-backfill composite in the process of loading, and when the loading rates are 1.20−2.40 mm/min, rock-backfill composite failed to achieve the collaborative deformation damage of the siltstone and the backfill body parts. When the loading rate is lower than 0.60 mm / min, due to the strength difference between the siltstone and the filling body and the non-uniform deformation of the contact interface between the two, a large crack penetrates the whole specimen. It can be seen that the final failure mode of each group of specimens is a tensile and shear mixed failure mode. By analyzing the dissipation energy changes of the rock-backfill composite and the backfill body, it can be seen that when the loading rate is greater than the critical loading rate, the pre-peak dissipation ratio of the rock-backfill composite is greater than that of the backfill body, and the composite can be destroyed in a coordinated manner. By calculating the energy storage coefficient and energy storage limit of the rock-backfill composite under different loading rates, it is found that when the loading rate is less than 0.60 mm/min, the higher the loading rate, the higher the energy storage limit of the combination specimen, and the speed of absorbing elastic energy is also rising synchronously. Finally, the backfill body part is destroyed first, and the energy released by the instantaneous damage is transmitted to the siltstone part of the rock-backfill composite, so that the elastic energy absorbed by the siltstone part can reach the energy storage limit. The crack in the backfill body part extends into the sandstone to achieve synergistic damage. The results of this study are intended to provide suggestions for ensuring the stability of the composite bearing structure of ' backfill body-immediate roof ' structure under different mining and filling rates.

Tectonic fault cores are formed substantially of clay minerals. Even a slight change in mineral composition or in water saturation can result in a significant alteration of the sliding regime on the fault. We present results of laboratory experiments on a slider model set-up that was used to study the regularities of slip behavior in a model fault filled with gouge. The gouge consisted of quartz sand and clays of different types (bentonite, illite and kaolinite). The slip behavior essentially depended on gouge mineralogy. The accumulated stress could release via both fast and slow slips. The scaled kinetic energy for fast slips was 10⁻⁵–10⁻³, while that for the slowest slips was 10⁻⁹–10⁻⁷. Fast stick-slip is characteristic of model faults filled with quartz sand in dry and moistened conditions. A gradual transformation from stick-slip to stable sliding was observed for quartz sand/clay gouge as the clay content approached 20%. Under moistening clay, mineralogy played a key role. If the illite clay content was 5%, the moistening led to an increase in peak velocity by more than an order of magnitude; if the bentonite clay was 5%, it led to stabilization of sliding. While alteration in friction coefficient after moistening remained relatively small, the scaled kinetic energy could vary by several orders of magnitude.

Vacuum preloading, as a widely adopted ground improvement method for saturated soft soils with high water content, is extensively applied in large-scale coastal reclamation projects. However, post-reinforcement bearing capacity remains insufficient in many engineering cases, particularly with limited strength improvement in deep soil layers. Numerous studies have demonstrated that the consolidation efficiency of vacuum preloading is constrained by two critical factors: depth-dependent attenuation of vacuum pressure and fine particle enrichment-induced clogging of drainage paths near prefabricated vertical drains. To address these challenges, this study integrates electro-osmosis with vacuum preloading (EVP) during the later stage of vacuum preloading in the dredger fill project of Yueqing Bay North Port Area. A large-scale model test pool was employed, where conventional vacuum preloading was conducted for 108 days until settlement stabilization, followed by a two-phase EVP intervention. The first phase lasted 11 days, after which electrode polarity was reversed for the second phase (6.5 days), totaling 17.5 days of EVP reinforcement. Post-EVP results revealed significant improvements: at depths of 20 cm, 60 cm, and 100 cm, soil water content decreased by 4.2%, 4.84%, and 2.34%, respectively, while vane shear strength increased by 32%, 75%, and 61.1%. The test results indicate that superimposing the electro-osmosis method during the later stage of vacuum preloading can achieve a significant improvement in vane shear strength (with a water content reduction of less than 5%). Particularly for deep soil layers with low initial strength that are difficult to reinforce solely by vacuum preloading, the strength increased by 61%−75%, demonstrating effective reinforcement performance.

This study investigated the dynamic response of a high steep rock slope with a double-layer ductile shear zone using the right bank slope of the Banda Hydropower Station dam site area in the upper reaches of the Lancang River as the research subject. Shaking table model tests were conducted to simulate seismic behavior by incorporating the dimensionless peak acceleration amplification factor for the slope and applying seismic waves of varying types, excitation directions, frequencies, and amplitudes. Experimental results showed that: (1) Increased frequency and amplitude enhanced the dynamic response, with frequency exerting greater influence than amplitude. (2) The slope model exhibited evident elevation amplification within the slope and nonlinear near-surface amplification on the slope surface. (3) Under horizontal seismic loading, thicker ductile shear zones demonstrated pronounced energy absorption and dissipation effects. (4) Under vertical seismic loading, thicker zones continued to absorb energy, while thinner near-surface zones amplified seismic wave amplitudes.

Quantitative characterization of the anisotropy of rock joint roughness is crucial for evaluating joint mechanical properties. However, the complex structure of joint surfaces and the limitations of current analytical methods pose significant challenges to roughness calculation and anisotropy evaluation. This study focuses on shale from the Pengshui area in Chongqing, China, combining fractal topography theory and the joint roughness coefficient (JRC) to characterize the anisotropy of joint surfaces. Using a 3D laser scanner, the morphology of joint surfaces from shale samples fractured in different directions was captured. JRC and Fractal Dimension (D) of joint profiles were then calculated in various directions to compare joint surface anisotropy. The results indicate that: (1) JRC, which considers both fractal properties and amplitude characteristics of joint profiles, shows a stronger correlation with fracture orientation than D. Using the bedding plane of shale as a reference, a larger angle between the reference plane and the fracturing direction results in a higher JRC value for the joint surface. (2) The JRC values for a single joint surface can be approximated by an elliptical fit, with the area of the ellipse increasing as the angle between the rock bedding and the fracturing direction increases. This implies that when the fracturing direction is perpendicular to the bedding plane, the fracture surface is rougher. This research provides a reference for characterizing joint surface anisotropy and offers guidance for understanding the relationship between fracturing direction and joint surface roughness.

The stress analysis of sliding surface is the key link to evaluate the stability of slope and predict the risk of landslide. There are many methods to solve the sliding surface stress, but there is no reasonable method to evaluate these methods. In order to solve this problem, a sliding surface stress test device used in landslide model test was proposed. The structural characteristics and design principle of the device were introduced in detail. Three cases were designed to test the sliding surface stress by model test. Based on the correlation analysis and probability P value in the statistical analysis results of paired sample t-test, the applicability of Morgenstern-Price (M-P) method, elastic theoretical solution of sliding surface stress based on slope unloading and numerical analysis method in solving sliding surface stress was evaluated. The main conclusions are as follows: (1) The absolute error between the test results and the theoretical values of the 9 sliding surface test units is within 2.5%. The statistical analysis results show that the difference between the test results and the theoretical values is not significant, and the stability of the test results is good. (2) The elastic theoretical solution and numerical analysis method can accurately calculate the stress state of the sliding surface, but the calculation result of the M-P method has a large deviation from the actual one, which is not suitable for the calculation of slip surface stress in non-limit state. (3) The application of sliding surface stress elastic theory solution based on slope unloading in embankment slope is expanded, but this method still has great limitations. The sliding surface stress test device proposed in this paper expands the new method of sliding surface stress test, and provides a guarantee for the accuracy verification of sliding surface stress calculation and stability analysis theory.

The mechanism of shield-soil interaction has always been a significant issue in academia and industry. For the active articulated shield, the presence of the active articulation system has an inevitable impact on shield-soil interaction. Therefore, a shield-soil interaction model considering active articulation was proposed and numerically solved using the time-incremental method. The model was validated through a case study of the Binzhong interval in Fuzhou Metro Binhai Express. The influence of active articulation on shield heading, resultant moment of earth pressure on shield shell, and resultant propulsion moment was carefully studied. Key conclusions include: (1) The shield-soil interaction during continuous excavation is more accurately reflected by the model and its numerical solution method. (2) Increasing the pitch articulation angle significantly reduces shield heading. (3) With a smaller coefficient of subgrade reaction, the articulation angle is approximately linearly correlated with the resultant moment of earth pressure; this relationship transitions to nonlinearity as the coefficient increases. In upper-soft lower-hard strata, the resultant moment varies with pitch articulation direction and becomes more pronounced with larger articulation angles. (4) Within the small-angle attitude correction range, a certain articulation angle reduces the resultant propulsion moment, enabling efficient attitude control. These findings provide theoretical support for shield axis deviation calculation and shield attitude control strategy.

Stratified rock slopes are prone to damage under strong earthquake, leading to geological disasters such as crumbling, landslides and debris flow, and their stability evaluation and support structure optimization are key issues for engineering construction and academic research. Based on field investigations, theoretical analyses, numerical simulations and physical model tests in strong earthquake regions, scholars at home and abroad have carried out a lot of fruitful researches on the damage mechanism and reinforcement measures of rock slopes in strong earthquake regions. Starting from four aspects, including destabilization and damage characteristics of laminated rock slopes, types of support structures, reinforcement mechanisms of support structures and new seismic support structures, the research status of rock slope support structures under strong earthquakes is systematically reviewed, the shortcomings in the current basic research and technical methods of support structures are indicated, and the future research and development directions of seismic support structures for slopes are prospected. This study provides theoretical support for revealing the instability mechanisms and reinforcement strategies of stratified rock slopes in strong earthquake regions, while establishing a scientific foundation for developing more reliable support structures.

Current machine learning models for recognizing geological conditions during shield tunneling heavily rely on precise geological data labelling, limiting their applicability in complex geological environments. To address this, we propose a continuous dynamic time warping (CDTW)-based agglomerative hierarchical clustering model (CDTW-Agglomerative), which integrates a linear interpolation framework to overcome DTW’s discretization issues. An online learning mechanism is implemented for dynamic strata recognition. The model’s accuracy and reliability are validated using Xiamen Metro Line 3 data, with generalization tested on Line 6 data. Results show recognition accuracies of 85% and 73% on the two datasets, demonstrating robust generalization. CDTW-Agglomerative outperforms DTW-Agglomerative, SoftDTW-Agglomerative, and CDTW-based models (K-means, K-medoids, Spectral clustering). Notably, it identifies cutterhead stratigraphy without requiring pre-labelled geological data, supporting intelligent decision-making for tunnelling parameters.

The problem of soil cutting widely exists in engineering fields such as tunnelling, port and waterway dredging, geological drilling, and civil construction. Accurately characterizing the three-dimensional soil failure surface in front of the cutting tool during the soil cutting process is of great significance for analyzing soil disturbance states, evaluating tool cutting performance, and understanding soil-tool interaction mechanisms. A nonlinear elastoplastic damage-based constitutive model is employed to describe the deformation and failure process of soil. Based on the characteristics of damage energy dissipation per unit area of the soil medium, a new numerical method is proposed to directly characterize the three-dimensional soil failure surface. Numerical simulations of flat-tool cutting processes under various operating conditions verify the effectiveness and robustness of the proposed characterization method. The influence of cutting angle and depth on the width, rupture distance, soil disturbance area, and shear failure angle of the three-dimensional soil failure surface is discussed in combination with theoretical calculations. Furthermore, the shape of the three-dimensional soil failure surface for complex-shaped tools obtained through this numerical method is consistent with experimental results, further validating the applicability of the proposed method for complex tool scenarios.

To investigate the stability of the excavation face during tunnel traversal through an upper-sand-lower-clay composite stratum, centrifugal model tests and numerical simulations were combined to analyze the displacement variation in instability zones, profile characteristics of final instability zones, earth pressure evolution patterns, and ultimate support pressure under different stratigraphic boundary positions and burial depth ratios. Test results indicate: Significant instability occurs when the stratigraphic boundary is at the tunnel face center, while stability is maintained when the boundary is at the tunnel crown. Displacements concentrate in the upper sandy layer with negligible changes in the clay layer, demonstrating that initial instability disturbance influences subsequent instability zone development. Analysis of normalized vertical earth pressure and excavation face retreat displacement curves reveals that increased burial depth ratios and clay layer thickness enhance formation resistance to disturbances. Support pressure ratio-displacement curves for two instability cases exhibit three distinct stages, with the upper side central point of the excavation face reaching ultimate support pressure first. When the burial depth ratio increases from 1.0 to 1.5, the ultimate support pressure shows minimal change. 3D finite element simulations of the excavation process validate the ultimate support pressure, failure patterns in instability zones, and earth pressure evolution, with numerical results showing good agreement with experimental data.

Combining bridge row piles with energy piles to create energy row piles can harness shallow geothermal energy for bridge deck deicing in winter and cooling in summer, respectively, while also supporting the mechanical loads of the bridge deck. This study investigates the thermo-mechanical response of energy row piles under heating-cooling cycles through field tests, and analyzes the interactions among energy row piles, slab, and unheated piles. An interface model considering the cyclic shear characteristics of the pile-soil interface is developed in a finite element software, and thermo-mechanical coupling numerical models of energy row piles are established to further explore the changes and mechanisms of long-term settlement of energy row pile under the combined effect of mechanical loads and heating-cooling cycles. The findings reveal that interactions among the energy row pile, slab, and unheated piles can result in load redistribution, leading to high thermally induced stresses of approximately 80% of the maximum thermally induced stress of the energy row pile (i.e. 1.1 MPa) at the top of the energy row piles due to strong restraining effects. Meanwhile, the slab experiences tensile stress exceeding the tensile strength of C30 concrete, reaching 3.75 MPa. Moreover, when the mechanical load is large, energy row piles progressively develop long-term settlement with an increasing number of thermal cycles, exhibiting a negative exponential growth pattern. This phenomenon is attributed to the mechanical load driving the pile-soil interface toward its limiting state, where cyclic shear at the interface readily induces plastic shear displacements, ultimately resulting in the long-term settlement of the energy row piles.

The variation in characteristic values of stress waves before and after passing through a material serves as a critical basis for evaluating its wave attenuation capacity. This can be characterized by the ratio of transmitted wave amplitude to the initial incident wave amplitude (i.e., transmission coefficient) in SHPB tests. However, due to the close correlation between the transmission coefficient and waveform parameters, it remains challenging to establish a quantitative characterization method for the transmission coefficient. Therefore, this study focuses on porous, irregular, and fragile calcareous sand as the research object. By combining physical experiments with numerical simulations, we investigate the influence of pulse width, platform duration, rising edge rate, falling edge rate, peak stress, and the central axis of symmetry on the transmission coefficient of calcareous sand. It is found that the transmission coefficient responds significantly to the coupling effects of the pulse width and the central axis of symmetry of the stress wave, the coupling effects of the platform section duration and the rising and falling edge rates, the coupling effects of the pulse width and the peak stress, as well as the coupling effects of the falling edge rate and the pulse width. Conversely, the response to the coupled effects of peak stress, rising edge rate, and falling edge rate is not pronounced. Owing to the difficulty in completely decoupling these waveform parameters, a prediction method is proposed for the transmission coefficient based on the gradient boosting algorithm, which effectively addresses multi-factor coupling issues. When the number of training samples reaches 91, the prediction accuracy exceeds 96%, which can effectively establish the mapping relationship between waveform parameters and transmission coefficients, providing a reference basis for the load design and calculation of protective engineering structures.