Practical Calculation Of Water Pressure Load On Tunnel Lining

With the expansion of road net to mountainous regions and the improvement of route standard, especially with the large-scaled construction of high-speed railways and express ways, large amounts of problems of high water head tunnel will be met. The groundwater treatment which"mainly use drainage"does not meet the current environmental protection policy, and the corresponding guidelines for calculating external water pressure on tunnel lining does not meet the requirements of engineering design as well. According to new concept of water control in tunnel, the amount of water inflow should be limited. In this case, water pressure becomes one of the major loads of lining structure. This paper focuses on the problem of tunnel lining water pressure load of high water head tunnel, uses theoretical derivation, numerical simulation, laboratory test, and analysis of engineering example to intensively and systematically study the practical calculation of water pressure load on tunnel lining.(1) Aim at determination of the water pressure upon the tunnel lining in jointed rock mass, and a conclusion is presented: the value of water pressure of lining, which transferred through rock block, equal to the value of pore water pressure, and the direction is perpendicular to the free face, regardless of the shape and size of the rock block.(2) According to seepage theory, the equations for calculating seepage force in rock mass/lining are obtained, and the formulas of water inflow of tunnel are deducted as well. Use of conformal transformation and aim at the boundary conditions of two different lining water pressure (a.φ= y, b.φ= ha), the equations for calculating the water inflow of underwater tunnel and the seepage force are also deducted.(3) Based on axisymmetric solution, through integrating seepage force of lining, a conclusion is obtained, that is external water pressure acting on lining is equal to pore water pressure in the interface between rock mass and lining. By analysis of sensitivity of the reduction factor of lining water pressure, the main factor determining the reduction factor of lining water pressure is the relatively permeability of lining to rock mass is obtained.(4) Through numerical simulation, the effect of excavation and supporting on the ground water potential and the distribution of water pressure of composite lining with waterproofing sheet and drainage system is studied, and a method for determining"equivalent permeability coefficient"of the composite lining (kl*) with waterproofing sheet and drainage system is presented for the practical calculation of lining water pressure.(5) The distribution of lining water pressure for different drainage style is discussed to provide the base for choosing suitable drainage system.(6) A laboratory test proved that maintain the drainage system behind the lining unimpeded is an efficient method to decrease the lining water pressure. When full sealing waterproofing system used, water pressure finally acting on lining can not be deducted, no matter use of grouting.(7) Based on use of axisymmetric solution, two feasible simple methods are presented for estimating water pressure upon lining, and applicability of axisymmetric solution for non-circular cross section tunnels and shallow tunnels are also presented in this paper.(8) Integration of study results in this paper, several projects are choosen for analyzing the characteristics of water pressure upon tunnel lining, which can be used as references for similar engineering activities.