Numerical Coupling of Stress and Seepage in the Design of Pressure Tunnel under to High Internal Water Pressure

Abstract

This paper is based on the mechanism design of coupling stress and seepage in pressure tunnel, a suggested design criterion for pressure tunnel design procedure in stable rock conditions. Plain concrete lining of pressure tunnels are not absolutely tight and water seeps out of the tunnel resulting to loss of energy and often cause instability in the surrounding rock mass. Nevertheless, prestressing the surrounding rock mass by grouting keeps the seeped water within the vicinity of the tunnel and increase the external water pressure, thereby increasing the tunnel bearing capacity and reduce the seepage/water losses. The crack propagation and the influence of prestressing on the plain concrete lining have been studied and modeling of the phenomenon was performed by hydro-mechanical coupling of stress and seepage calculation performed using Finite Element program. The numerical coupling can be described as follows: the change of stress field changes of permeability coefficient and the change of the seepage field; the new seepage field tend to produce new seepage force and lead to the redistribution of stress field. The numerical model was used to replicate similar research work done and good agreement was recorded. Model was extended to practical example and finally matched with analytical solutions resulting in a rational methodology for the design of plain concrete lining under high internal water pressure of up to 35 bars. The results illustrate the applicability of the present method.