Stability Analysis and Control Measures of Tunnel Face in Water-Rich Sandy Dolomite Stratum

Revealing the conditions for the occurrence of sand gushing accidents in tunnels with water-rich sandy dolomite strata can help the tunnels to be constructed safely. In this paper, we found that sandy dolomite and the water environment are the key factors causing sand surges through geophysical prospecting at the tunnel face where 12,000 m 3 sand surge occurred. Through the flow-solid coupling model, the extrusion deformation at the tunnel face is the main deformation form in the tunnel of water-rich sandy dolomite strata. The influence of different factors on the deformation value of the tunnel face is from strong to weak: sandification degree, head height, and tunnel depth. Combined with the study of pressure arch characteristics of the model, the limit equilibrium theory considering seepage effects and pressure arch characteristics is proposed. We get that sand surges will occur in the tunnel in the intensively sandy dolomite strata where the head exceeds 80m. For the intensively sandy dolomite strata with head below 80m, the stability of the tunnel face is controlled by the degree of seepage damage. According to the reason of sand gushing, the comprehensive control measures consisting of risk identification by over-detection, double-layer close-packed pipe shed, grouting sealing technology and dewatering technology, and Milling and blasting combined construction method are proposed, and the effective control of tunnel working face is realized in practical application.