This paper investigates the regularity of microstructural evolution of Shenzhen granite residual soil in an attempt to determine its macrostructural deformation characteristics. The pore distribution and microstructure characteristics of granite residual soil are examined experimentally under different consolidation stresses, coupled with mercury injection tests and scanning electron microscopy. It is found that a microstructure exists in the granite residual soil and that the structural characteristics of granite residual soil in Shenzhen. The calculated pre-consolidation stress and structural yield strength of the granite residual soil are similar, indicating a phenomenon that resembles over-consolidation in the granite residual soil. This is fundamentally different from the mechanism of conventional over-consolidation in soil. It is also found that the relationship between the increment of mercury in soil samples and the stress of the mercury under different consolidation stresses is mainly trimodal. The significance of the research presented in this paper lies in the development of a clear understanding of the influence of the microstructure characteristics of granite residual soil on its macrostructural deformation, thereby providing a theoretical basis for engineering applications involving granite residual soil and the analysis of foundation deformation.

Effective high slope risk assessment plays an important role in the safety management and control of the open-pit coal mining process. Traditional slope stability risk assessment methods rarely consider the time factor or evaluate the dynamic change of high slope in an open-pit mine at a certain time in a sensitivity assessment. This paper develops an interval trapezoidal fuzzy soft set method to achieve the high slope dynamic risk evaluation. The proposed dynamic interval trapezoidal fuzzy soft set method for risk assessment of high slope in an open-pit coal mine is developed by integrating the time points and weights of slope risk factors. The extended interval trapezoidal fuzzy soft set was used to calculate the weights of risk factors at different times, and the Fuzzy Analytical Hierarchy Process (FAHP) method was applied to determine the weights of risk factors. The weight change of different risk factors with time can be easily achieved with the proposed method. As a case study, this approach is implemented into a risk assessment model for the north high slope in Shengli #1 open-pit mine located in Xilinhot, Inner Mongolia. The model complies with three time points and contains 4 primary risk factors (S) and 17 secondary risk factors. The results indicated that the hydrological climate conditions and slope geometry conditions were the high risk factors affecting this open-pit coal mine slope. The reasonability and effectiveness of the evaluation results were verified with in-situ observations and measurements. This dynamic risk assessment method is helpful for improving safety management and control for the high slopes of open-pit mines in the coal mining process.

Rainfall infiltration is one of the main triggers of inner dump slope failure in the process of mining coal. Changes in water content throughout the process of rainfall infiltration have rarely been studied. The reductions in soil strength due to water migration have seldomly been considered in the existing analytical solution of the safety factor (F.S) for unsaturated inner dump slopes in an open-pit mine. In this work, a new mechanical model was developed by improving the conventional analytical solutions of F.S for unsaturated inner dump slopes to accommodate water-induced degradation in the mechanical strength of waste material. Parameter analysis was carried out via a case study of the Shengli #1 open-pit coalmine. The results showed that the wetting front depth increased with increasing rainfall time, and the increasing rate was constant during the non-compressive infiltration stage, while it decreased gradually in the compressive infiltration stage. The F.S of the transition layer decreased at first and then increased with increasing infiltration depth. By considering the water migration in the inner dump slope, the calculation result of F.S by the analytical solution in the paper can more precisely represent the in situ conditions. It was larger than that of the saturated strength, but smaller than that of the natural strength. The position of the minimum F.S did not alter in the wetting front, but was close to the position of the wetting front. The depth of the potential slip surface can be calculated by the converse solution of the analytical equation when F.S = 1 for rainfall infiltration, and the most dangerous slope surface can be determined. The depth (h_min) of the potential slip surface increases with increasing wetting front (h_f) by a linear function, and increases with increasing depth ratios of the saturation layer (λ). The depth ratio (i) of the minimum F.S increases with increasing λ by an exponential function. The improved analytical solution can be used to evaluate the potential sliding surface under rainfall conditions, which is helpful for evaluating slope stability and analyzing dangerous surfaces under rainfall conditions and providing guidance for reinforcement schemes.

Based on the compound soft rock movement law, the rock formation structural features for a mining roadway were examined. Furthermore, the presplitting, extension, and coalescence mechanism of rock formation and the engineering needs for reusing an abandoned underground roadway were studied. According to engineering and geological conditions, an analytic expression of the inertial force, the moment of inertia, and the vertical stress acting on the breakage are obtained by constructing a structural mechanical model of the overlying strata. The transfixion law, the tensile shear failure characteristics, the release rate in the fracture expansion process of presplitting fissures, and the evolution law of the plastic zone in reused roadway surrounding rock on conditions of 0 m, 0.5 m, 1 m, 1.5 m, and 2 m fissure intervals are analyzed by creating a three-dimensional numerical model. The stress distribution and deformation laws of the roadway under mining disturbance are obtained. The results show that when the fissure interval is 1 m, the peak value of the horizontal stress reaches 10~12 MPa, and the stress concentration factor is 1.8~2.2, which promotes fracture expansion and transfixion and controls plastic damage development on both sides of a fracture. The elastic strain energy of the reused roadway is reduced to 32.7% of the peak value. The deformation of the roof is coordinated and deformed. It is helpful for the compound soft rock strata to fall and plug the area, forming a stable composite reused roadway surrounding the rock structure. A 1 m presplitting fissure interval is adopted for field testing, and the monitoring results show that 0~3.0 m behind the mining face, presplitting fissures will be connected and begin to fall. Moreover, 3.0~6.0 m behind the mining face, compound soft rock strata will fall and plug the area fully, forming a reused roadway structure. Severe deformation of reused roadway was reduced, and the stability of surrounding rock was improved by implementing the roof presplitting approach.