Experimental simulation of seepage field distribution for small interval tunnel under varying-head infiltration

Abstract

In complex hydrogeological environments, it is difficult to achieve a dynamic equilibrium state for the recharge, seepage, and discharge of tunnel groundwater. Especially in case of reservoir flood discharge, local heavy rainfall, extreme dry climate or other emergency situations, the groundwater level will rapidly change, and the tunnel will be under the action of hydrodynamic head height within a certain period of time. Therefore, as urban tunnels in water-rich areas develop towards large cross-section, small spacing and complex sensitive stratum, studying the spatial distribution characteristics of seepage and stress fields in small interval tunnels under variable water head infiltration conditions is an urgent problem to be solved. In this paper, using the self-developed seepage model testing equipment, tunnel seepage tests under different hydrodynamic head heights and heavy rainfall conditions are carried out on the Kexuecheng Tunnel, which is a typical small interval tunnel in complex hydrogeological environment of Chongqing, China. According to the test results, as the burial depth and water level increase, the water pressure at each monitoring point gradually increases. Benefiting from the superimposed drainage effect of adjacent hole, the average water pressure at the inner side is 8 ∼ 12% lower than that on the outer side. The grouting circle and high groundwater level will further aggravate the asymmetric distribution of hydrodynamic pressure on the lining structure. However, as the hydrodynamic head height increases, the effective stress of the stratum decreases, and the earth pressure on the tunnel decreases by 24 ∼ 40%. Under heavy rainfall conditions, the evolution of lining structure pressure can be divided into initial infiltration stage, rapid growth stage, gradually stable stage and slowly decreasing stage. Suffered by the influence of rainstorm on seepage field and stress field, the overall pressure acting on the vault, left haunch, right haunch and bottom of lining structure increase by 45.4%, 132.3%, 117.4% and 147.4%, respectively.