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 and the development laws of dynamic shear modulus G and damping ratio λ were comparatively analyzed. The test results reveal that: at small strains, the dynamic shear modulus G increases significantly with both N_b and . The maximum dynamic shear modulus G_max exhibits a linear correlation with N_b and a power-law correlation with . 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 λ-γ_d curve moving upward and characterized by greater energy dissipation. In contrast, increasing produces opposite trends in both G/G_max-γ_d and λ-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.

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.

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.

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.

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.

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.

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.

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.

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.

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.