Pore Pressures in Concrete Dams

Abstract

Assuming that concrete is a homogeneous porous material in gravity dams, pore pressure intensities at drain wells near the upstream face of dams were studied. In general, the piezometric head of the seepage flow through a gravity dam may be mathematically represented by the well-known Laplace equation. This equation can be solved numerically by the finite-difference equation developed from a block-centered formulation. By using the boundary conditions of the height of the seepage face in drain wells from the concept in hydraulics of wells and the seepage face along the downstream face of dams, piezometric heads, and in turn, pore pressures in the dam body were obtained. This approach of predicting pore pressures has been verified by 40 years of data from the Tennessee Valley Authority’s (TVA’s) Fontana Dam. The pore pressure intensities in dam bodies and at the drain wells are presented. They are expressed in dam heights, size of drains, and locations of drains from the face of the dams for inspection galleries located at the dam base. The results obtained show the location of the inspection galleries for the lowest pore pressures. The inspection galleries are usually used to intercept seeping water from the drain wells in the dam foundation and dam body. The seeping water intercepted by the dam body can be estimated when the values of hydraulic conductivity of concrete are known. The accumulation of calcium carbonate deposited in the drains can then be studied on the basis of the known values of the calcium carbonate concentration of the seeping water. The data presented may be useful for design engineers in the stability and stress analyses of concrete gravity dams. In addition, the effects of the location (i.e., elevation) of the inspection gallery and the tailwater pressures on pore pressures were studied by using the Fontana Dam as a case study.