In order to study the formation mechanism of the high-cold and high-altitude mountain collapse disaster caused by underlying complex goaf group, the lithology, occurrence of structural planes in rock mass and hydrological conditions of overburden in goaf were obtained through field investigation. Combined with the field investigation results, the landslide disaster mechanism was comprehensively analyzed. The stability of the mountain slope in the underlying goaf and the potential slip arc surface of the collapse body are analyzed by the two-dimensional finite element analysis method. The main causes of surface collapse of mountain slope are: the steep structural plane of rock mass, rainfall and fissure water erosion, freeze–thaw cycle, underground ore body mining disturbance, etc. Geological conditions are the internal cause, while underground mining is the inducement. The combined action of the internal and external causes leads to the special formation mechanism of collapse.

Based on the similarity theory, two physical testing models (double-hole tunnel and single-hole tunnel) with a scale of 1:10 were designed and manufactured. A series of shaking table tests followed by numerical simulations was carried out to obtain the dynamic response characteristics of shallow-buried tunnels with asymmetrical pressure distributions. The similarities and differences in the dynamic response laws between double-hole tunnel and single-hole tunnel were studied. The effects of types of seismic wave (Wenchuan wave, Darui artificial wave, and Kobe wave), peaks acceleration excitation (0.1 g, 0.2 g, 0.4 g, and 0.6 g), excitation directions (horizontal and vertical directions), and excitation modes (unidirection and bidirection) on dynamic response laws of the tunnels were studied. The results show that the variation of acceleration multiplying factor (AMF) shows a nonlinear trend. The AMFs are different at different monitoring points. The type of seismic wave has a significant effect on the acceleration response, with Kobe wave being the most serious, followed by the Darui artificial wave and the Wenchuan wave. In bidirectional excitation, the AMFs are relatively larger than those of unidirectional excitation. A comparison between the numerical simulation and the shaking table tests in both acceleration time history and peaks acceleration shows that the results of the shaking table tests and numerical simulations are credible. The acceleration response of monitoring points near the existing slope is generally magnified. The residual strains are generated at the monitoring points. The variation trends of both tensile strain and compressive strain are opposite. The tensile strains are generally larger than the compressive strains. Many factors, such as the type of seismic wave, peaks of acceleration excitation, excitation direction, and excitation mode, have a significant influence on the dynamic strain response and acceleration response of the tunnels. The research results could promote the understanding of dynamic response characteristics of the tunnels.

Water-jet drilling (WJD) is an effective method for stimulating, exploring, and developing oil and gas resources. The self-rotatory water-jet bit (SRWJB) is a type of potentially efficient bit applied in WJD. In this study, the three-dimension drilling model of the SRWJB is established, and the numerical simulation of this model is conducted based on the sliding mesh model combined with RNG turbulence model. The numerical simulation method was validated using experimental results. To improve the drilling performance, the effects of the standoff distance, bit rotation speed, and nozzle layout parameters on the SRWJB drilling capability were investigated. The results show that there exists an optimal standoff distance for the single water jet under the condition of maximum removal volume, that is 15 mm in this experiment. A high rotation speed will make the streamline bend and decrease the jet convergence, which weakens the jet rock-breaking capacity. To achieve a high rock-breaking performance, the design considerations of the SRWJB are as follows: (1) There is an optimal rock-breaking rotation speed for SRWJB by comprehensively considering the jet deflection, moving speed and impact times, such as 200 rpm for the 12 MPa; and the optimal rotation speed increases with the increase of jet pressure. (2) The nozzle arrangement angles should be near 10° to weaken the water cushioning effect. (3) There is an optimal combination of distribution radii for the middle nozzles and lateral nozzles for effectively drilling a large and round borehole. This work will provide a reference for the optimal design of an SRWJB and its application in drilling.