Studies are lacking in establishing the quantitative relationship between the mechanical response and the rock and soil mechanical parameters by digital rotary penetration. In this study, based on the custom-built rock and soil strength parameter test device and the three-dimensional flexible boundary loading device, we conducted an experimental study of the manufactured sand-soil model with moisture contents of 5%, 10%, and 15% under different confining pressures (0, 0.12, 0.18, 0.24, and 0.42 MPa). Analysis was conducted on the influencing factors and laws of water content on the experimental results, and a quantitative relationship model (W-T-BC model) between the drilling torque and the bearing capacity of manufactured sand-soil under the condition of different water contents was established. Through failure detection verification on the manufactured sand-soil-filled subgrade of the Taihang Mountains Expressway in Beijing, the average conformity between the calculated value of the bearing capacity of the W-T-BC model and the standard experimental bearing capacity was 93.23%, which proved the validity and accuracy of the model. Finally, the rigid-soft interface grid body of sand-soil particles was analyzed. The reason why the manufactured sand-soil exhibited better stability than homogeneous soil under the action of external force in microcosmic aspect was expounded. The establishment of the W-T-BC model provided a scientific basis and important reference for further study of the relationship between mechanical response and force parameters under different conditions of different materials.

Overburden deformation has a considerable influence on slope stability during underground mining works. A simulation experiment for underground mining is performed in this study. The movement of the overlying strata caused by mining during the mining process observed using a three-dimensional (3D) optical displacement monitoring system. Based on the simulation experiment results, a particle contact-based meshfree method (PCMM) is proposed; The elastoplastic analysis and sliding process simulation of slope are realized By intruducing the softening Mohr-Coulomb model and maximal tensile stress model into continuous media elements. The deformation process and the slope failure are analyzed by using the PCMM numerical simulation method. The results showed that the overburden gradually degraded as the work face continuously pushed forward. Furthermore, the basic roof bore the force generated by the upper rock mass. Hence, a "rock beam" force distribution developed. The farther the distance from the coal seam, the smaller the subsidence. The rock strata subsided and induced the "beam" structure effect when the work face continued to advance past the design stop line, causing a rock mass partial settlement on the slope and a serious horizontal movement on the free face. This behavior significantly affected the slope stability, even inducing cracks and potential slip and sliding surfaces. The numerical simulation results indicated that the deformation process of the overlying strata is "immediate roof starts to collapse -- rock mass of the main roof collapses-- overlying strata generate an abscission layer --fracture of the free surface develops --the overlying strata begins to sink". Meanwhile, the slope deformation and failure process is "overlying rock mass exhibits shear failure-- the overburden is completely sheared-- the overburden collapses slope surface exhibits a tensile crack-- stepped crack is connected-- the slope begins to slide to the outside." The research results provide guidance for underground mining.

The present paper is devoted to investigate the effects of waste polyester fiber fabric blocks on the strength and mechanical behavior of cemented sand. In the investigation, samples were prepared at four different percentages of waste polyester fiber fabric block content (0.0%, 0.5%, 1.0%, and 1.5% by weight of soil) and two different aspect ratios (2 : 1 and 3 : 1), and conventional triaxial compression tests were carried out after the curing period. The test results indicated that the addition of fibers increased peak and residual shear strengths of cemented sand and changed its brittle behavior to a more ductile one. As the fabric block content increased, the brittleness index and initial stiffness decreased, and the peak strain and internal friction angle increased. The optimal combination of the content and aspect ratio was determined to be 0.5% and 3 : 1. The integration of the fabric blocks with the cemented sand matrix was analyzed by using the scanning electron microscopy (SEM). It is found that the reinforcement effect is related to the bond strength and friction at the interface. The micromechanical properties of the fiber/matrix interface were influenced by the undulations between the fabric block components. In summary, this study presented a low-cost and environment-friendly method for reinforcing cement-stabilized sand.