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.

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.

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.

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 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 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.

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.

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.

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.