International Journal of Geomechanics

In this research, the finite-element numerical software COMSOL Multiphysics is used to simulate the electric pulse rock-breaking process, and the novel numerical model takes into account the multiple fields of electrical, thermal, and mechanical physics. The electric field strength inside the rock under the action of the electric pulse is updated by the full coupling function of COMSOL (version 6.1) software, and the electric damage variable χ is used to describe the process of electric breakdown inside the rock, to simulate the formation of plasma channel in the process of electric pulse rock-breaking. The voltage change curves and plasma channel trajectories in the electric breakdown process of the model in this paper are compared with the literature to verify the accuracy of the model. The formation process of plasma channels captures the temperature and stress changes during the whole process of electric pulse rock-breaking, to reveal the mechanism of the electric pulse rock-breaking process. With the presence of conductive particles inside the rock, the particles can effectively promote the formation of plasma channels, increase the area of electrical damage, and improve rock-breaking efficiency. Before the formation of the plasma channel, the internal temperature of the rock is about 600 K, and the stress is about 10⁻² MPa; when the channel is formed, the energy of the electric pulse is mainly concentrated in the plasma channel, and the temperature of the plasma channel rises to 10⁴ K. When the maximum stress exceeds the critical stress of the rock, the rock undergoes fracture. Furthermore, an appropriate increase in the rise time of the electric pulse increases the speed and area of rock-breaking, subsequently improving the efficiency of rock fracture. The results of the numerical modeling in this paper help to better understand the mechanism of the electric pulse rock-breaking process, which is of great engineering significance for the development of new electric pulse rock-breaking technology in the realm of geotechnical engineering.

Addressing the challenges of wet and soft loess foundations is crucial in geotechnical engineering due to their inherent low strength and high compressibility. High-temperature sintering technology is a leading method for enhancing loess foundations, known for its fast processing and effective reinforcement. This paper focuses on the effects of saturation on the compressibility of sintered loess, using results from saturation and compression tests. It highlights how saturation influences loess differently under various sintering conditions. Particularly, loess sintered at 200°C breaks down after saturation, losing its resistance to deformation. By contrast, loess sintered at other conditions retains some deformative resistance, but its compressibility still increases. The study finds an inverse relation between sintering temperature and the increase in compressibility after saturation. Additionally, it examines changes in compressibility indices, which include the compression coefficient, compression index, and modulus of compressibility. These are analyzed based on different saturation times, establishing a law that links saturation time to the compressibility of sintered loess.

This study focuses on the issue of gas overflow encountered during the mining of coal seams at the Anshun coal mine. Initially, a mechanical model is constructed to analyze the displacement and vertical stress distribution in the upper neighboring coal seam following the mining of the protective seam in the field. Subsequently, similar indoor simulation experiments, utilizing the digital image correlation method, are conducted to examine the evolution characteristics of the overlying rock strain during the back mining process of the lower protective seam. Numerical simulation is then employed to analyze the plastic zone, stress distribution, and evolution characteristics of the overlying coal seam during the recovery of the lower protective layer. The study finally investigates the unloading effect of the top plate and the permeability characteristics of the protected layer. The results demonstrate that the maximum main strain concentration area in the overlying rock increases as the working face progresses, transferring asymmetrically from the middle of the mining area to the cuthole side and the working face side, with the concentration on the cuthole side being notably larger. As the lower protective layer advances, the unloading range, unloading height, stress concentration area, peak value, and unloading coefficient are observed to increase gradually before stabilizing. The numerical simulation reveals a predominance of shear damage around the mining area, where high permeability facilitates gas flow. Additionally, the collapsed gangue in the mining area's center is recompacted, leading to reduced porosity and permeability. Stress concentration is noted on both sides of the coal seam, resulting in high stress at both ends and low stress in the middle of the unloading area. Furthermore, the permeability coefficient growth rate diminishes with the advancement of the lower protection layer, exhibiting negative growth in some areas, while the permeability coefficient in the unloading area remains high at the late stage of workface recovery, thereby constituting an efficient gas extraction zone. This study provides a theoretical foundation for the safe and efficient mining of protruding coal seams in southwest China.

A novel finite-element (FE) procedure for analyzing slope stability was recently developed and encoded into a Fortran computer code S⁴DINA 2.0. This innovative approach involves a gradual increment in the principal stress deviator in a specific way until an unstable condition is reached. In the original version of S⁴DINA 2.0, the initial stress field was assessed using the gravity loading procedure (GLP), which has various limitations. This paper introduces the fictitious excavation method (FEP) as an alternative procedure for estimating initial stresses. After incorporating the FEP into S⁴DINA 2.0, a parametric investigation was conducted to explore the effect of the coefficient of soil pressure at rest (K₀) and Poisson’s ratio (ν) on the GLP and FEP, which used three selected slope examples. The evolution of the factor of safety (FOS), as determined by the stress deviator increasing model (SDIM), was examined for ν for a variety of soil friction angles (ϕ′). The findings of this paper were documented in detail. The inclusion of K₀ as an inherent soil property in the GLP was unfeasible due to the formulation nature of the GLP. In addition, when this method is used, the resulting FOS might significantly deviate from the accurate result in numerous instances. However, in scenarios where K₀ exceeds one, the FEP remains the exclusive solution, and when K₀ is less than one, selecting the FEP with an appropriate ϕ′ value is the best choice for achieving a rigorous FOS.

Accurate prediction of excavation deformation and stress affects the safety of excavation engineering and the surrounding environment. However, the traditional calculation method ignores the influence of soil shear action and its nonlinear deformation characteristics. Therefore, this paper proposed a coupled analytical method for braced excavation considering the continuity of soil deformation and nonlinear pile–soil interaction. A nonlinear Pasternak two-parameter foundation model was developed based on the Pasternak foundation model and nonlinear p–y curves. The control differential equations for the excavation in the critical and embedded sections were derived. Also, the numerical solutions of excavation deformation and force under different boundary conditions were obtained by the finite difference method and Newton's iteration method. Further, the excavation calculation procedure considering the construction process and nonhomogeneity of soil was suggested. Through finite-element (FE) and engineering case analyses, the traditional calculation method overestimated the excavation deformation and internal force, while the proposed methods were consistent with the measured results. Finally, the effects of soil shear stiffness and initial foundation reaction modulus on the excavation were discussed, and we found that the two parameters had more significant impact on the wall bending moment than displacement. The results provide some reference for the design calculation of braced excavation.

In response to the problem of deformation caused by surrounding construction disturbances in existing shield tunnels in soft soil areas, lateral horizontal grouting is often used. Based on an independently designed and developed lateral grouting experimental device, the mechanism of horizontal lateral grouting on the convergence deformation of the tunnel was determined. A three-dimensional finite-element analysis model was established to study the force and deformation characteristics of the tunnel tube sheet, and to verify the correctness of the model test results. The grouting remediation efficiency, η, was introduced to establish the relationship between the grouting volume and the convergent deformation. The results show that the tunnel tube sheet was subjected to asymmetric additional soil pressure along the ring direction, and asymmetric displacement occurred, which was most obvious on the grouting side. The additional moment distribution was symmetrical and spindle-shaped, and the peak bending moments mostly appeared in the arch roof, the arch bottom, and the arch whist. With a continuous increase in grouting volume, the efficiency of the grouting remediation decreased, and the two were negatively correlated.

The matric suction must be measured when calculating the shear strength of unsaturated silt, but the measurement method is cumbersome and time-consuming. The saturation degree of silt is easily measured; therefore, a simplified calculation method for the shear strength of unsaturated silt using the saturation degree instead of matric suction is valuable in practical engineering. A new calculation method based on the saturation degree of silt is proposed to determine the smooth transition from a saturated to an unsaturated state. Suitable parameters for unsaturated Zhengzhou silt are determined, and the results of an unsaturated triaxial test and the soil–water characteristic curve are used to establish the proposed calculation method. A comparison of the results of Vanapalli's method and the simplified calculation method indicates high consistency and a low error. Therefore, the simplified method is more suitable for practical applications than Vanapalli's method.

Collapsibility significantly impacts the bearing capacity of pile foundations in loess areas. To improve the load-bearing capacity of piles, the pile-base postgrouting technique is widely used worldwide. However, there are still several related issues to be solved: the impact of loess collapsibility on the bearing capacity; the effectiveness of the pile-base postgrouting technique in enhancing the bearing capacity; and the diffusion pattern of the grout during the grouting process. To investigate these issues, this experiment utilizes a visual static pressure device combined with numerical simulation. According to the experiment, the maximum axial force and neutral point appeared to shift downward after grouting, resulting in a 17.5% increase in the bearing capacity of the pile foundation. Additionally, an increase in grouting pressure leads to a rise in both the number of shear cracks and the diffusion radius. As the permeability of the grout improves, the number of shear cracks and diffusion radii tend to stabilize after an initial increase. These discoveries enable a thorough analysis of the changes in side friction and base resistance of postgrouted piles in collapsible loess. Furthermore, they provide valuable references and guidance for the implementation of the pile-base postgrouting technique in loess areas.

The prevailing design methodology for foundation pit support structures conventionally treats the pit cross section as a two-dimensional plane, facilitating the computation of soil and water pressures acting upon the retaining structure. Regrettably, this conventional approach tends to overlook the critical corner effect, particularly when the foundation pit is in proximity to a subway tunnel, where the nuanced nature of this corner effect remains indeterminate. Consequently, this research is directed toward an in-depth investigation of a deep foundation pit contiguous to a subway tunnel. A systematic evaluation and optimization of the corner effect pertaining to the deep foundation pit are undertaken through a combination of comprehensive field monitoring and simulation methodologies. The results show that a substantial mitigation in the deformation of the supporting structure, settlements of the ground surface and adjacent buildings, as well as the displacement of the subway tunnel, were achieved through a consideration of the corner effect. Notably, the ameliorative impact of adjacent buildings on the corner effect is observed. Further scrutiny reveals that the supporting structure within a distance of 12 m from the pit corner is most susceptible to the corner effect, as evidenced by a plane strain ratio (PSR) falling below 0.8. Beyond a spatial threshold of 20 m, the PSR attains a value of 1.0, indicative of a negligible corner effect and the foundation pit section existing in a plane strain state. The adjustment of pile length or diameter based on the PSR emerges as a viable strategy that can realize the construction cost optimization on the premise of ensuring the stability of the foundation pit. The impact of pile diameter variation is paramount, corresponding to a reduction in the range of PSR values below 0.8 from 12 m to 9.8 m. The corner effect is significantly diminished.

The present study focuses on the estimation of uniaxial compressive strength (UCS) in geotechnical projects. UCS is a crucial parameter in designing such projects, and traditional methods of measurement outlined by standards are often time-consuming and cumbersome. Additionally, obtaining standard core samples is always a challenging task in fractured or discontinuous rock masses. To overcome these limitations, alternative techniques such as simple regression (SR), multivariable regression (MVR), and artificial intelligence (AI) have been utilized to estimate UCS based on easily derived geotechnical parameters. While SR and MVR provide simple equations that can be used without the need for complex calculations, AI techniques offer the potential for higher prediction accuracy. However, AI models often require more complex solutions due to their intricate algorithms and computational processes. This makes AI less practical for ongoing geotechnical projects in which simple and quick estimations are often preferred. In this study, both the SR and the MVR models were employed to estimate the UCS using the Schmidt hammer rebound number (R_N), density (ρ), porosity ($\text{ϕ}$), and point load index (Is₅₀) as input parameters. Various SR and MVR models were tested, and the best-performing models were selected based on performance indices such as the normalized root mean square error (NRMSE), relative root mean square error (RRMSE), variance accounted for (VAF), efficiency (E), and correlation coefficient (R²). Furthermore, this study proposes a new performance index (PI_mod) to evaluate the predictive capabilities of the models. This index likely incorporates additional criteria or metrics beyond the aforementioned traditional performance indices. Overall, the equations derived from the regression models in this study offer a simpler and more practical approach for geotechnical practitioners to quickly assess UCS in any given area, providing a useful tool for their work.