Stability of complex rock tunnel face under seepage flow conditions using a novel equivalent analytical model

The longitudinally inclined layered rock masses under seepage flow conditions have an important impact on tunnel face stability. To solve this issue, a novel equivalent analytical model is proposed in this paper. This model settles the puzzle that the traditional model of limit analysis cannot directly determine the hydraulic head by treating the distribution hydraulic head at the anterior aspect of the tunnel face with the equivalent method, that is, without the tedious calculation by the numerical software. The seepage force is directly considered as a body force in this analytical model. Then, combined with the mirror-image method, layered discretization technique, limit analysis method, and Hoek-Brown yield criterion, an analytical expression for stability determination can be derived. The main factors affecting the stability of tunnel face are analyzed, such as the inclination angle of the flow line, the inclination angle of the rock layer, hydraulic conductivity, rock quality, excavation disturbed zone (EDZ), and the groundwater table height. The calculated diagrams have a certain guiding effects for tunnel construction.