The mechanism of intermittent water and mud inrush is a difficult problem faced by disaster prevention and safe construction in karst tunnels. Aiming at revealing the mechanism of intermittent water and mud inrush, we developed an integrated testing system for filling medium deposition in karst caves and intermittent water and mud inrush. By conducting a serial of laboratory experiments, we analyzed the sedimentary characteristics of the filling medium in karst caves and the catastrophic process of intermittent water and mud inrush induced by dredging and rainfall under realistic sedimentary conditions. The results show that the filling medium exhibits layered deposition characteristics, which are affected by the water circulation time, the amount of sediments carried by water and the water flow rate. The first inrush incubation time reduces with the water head increases. The critical water head and the disaster incubation time increase with the deposition height increases. Under the same conditions, the first inrush incubation time of gravel type, silt type, and clay type filling medium decrease sequentially. The results can provide a theoretical basis for preventing intermittent water and mud inrush disasters in karst tunnels.

In order to study the influence of water content on the mechanical properties of sandstone and evolution of crack propagation, laboratory compression tests and Engineering Discrete Element Method (EDEM) numerical simulation of sandstone under different conditions were carried out by the RMT-150B rock mechanics test system. The sandstone samples were from Nanyang, Henan Province, containing a total of 12 rock samples. Under the confining pressure of 0, 5, 10, and 20 MPa, the rock samples with 0%, 1.81%, and 3.24% water content were tested. The findings demonstrated that as the sample’s water content grew, the peak strain increased but the peak strength, elastic modulus, maximum energy rate of individual acoustic emission events, and cumulative acoustic emission energy rate all reduced. While the ratio of tensile cracks to shear cracks inside the rock samples rose with increasing water content, the failure mode of sandstone changes from shear failure to tensile failure with the increase of water content, but the sandstone specimens in the three conditions exhibited shear macroscopic fracture surfaces. Research results will provide reference for the safe construction of underground projects in water rich areas.

So as to efficiently address the distortion of surrounding rock in tunnels constructed utilizing ADECO-RS, it is crucial to define suitable parameters for advanced support systems. This study took the 8 # tunnel in the F3 portion of the E60 Expressway in Georgia as an engineering case. Initially, the original support scheme underwent systematic monitoring and analysis in the field. Subsequently, the FLAC3D 6.0 software was employed to examine the influence of the advanced pipe roof and tunnel face fiberglass bolts on the steady state of the surrounding rock. Optimization of the support parameters was also proposed. Further, the sensitivity of different parameters to the distortion of the rock surrounding the tunnel was analyzed and ranked via an orthogonal experiment. Ultimately, the effectiveness of the optimization scheme was evaluated by numerical methods and field observations. The findings of the research indicate the following: (1) The monitoring results of the original support parameters show that the irrational design of the support parameters can bring about deformation non-convergence in the tunnel’s surrounding rock. Support parameters must be optimized. (2) The spacing of the pipe roof is positively correlated with the distortion of the surrounding rock. In contrast, the length and the grouting strength are negatively correlated with the distortion of the surrounding rock. The reinforcement density, length, and lap length of glass fiber bolts exhibit an inverse relationship with the distortion of the surrounding rock. (3) The efficacy of pipe shed grouting in mitigating subsidence and deformation of the vault is superior, followed by the spacing of the supports. In contrast, the length of the supports demonstrates comparatively lesser effectiveness. Under optimal parameters, the vault subsidence was reduced by 23.2%, 10.2%, and 2.0%, respectively. The most significant factor controlling the extrusion deformation of the tunnel face is bolt lap length, followed by reinforcement density and then reinforcement length. Extrusion displacement was reduced by 52.5%, 40.3%, and 9.3%, respectively, under the optimal parameters. (4) In comparison to the primordial support system, the optimized support scheme reduces the subsidence of the vault by about one time and the convergence deformation around the cave by about two times. The research findings offer guidance for analogous engineering support design and parameter optimization.