Seepage and antiseepage measures in foundations of hydraulic structures

Abstract

1. Rock foundations of dams are inhomogeneous water-bearing systems, seepage in them has a complex and nonuniform character; for substantiating antiseepage measures the seepage model of foundations maximally corresponding to real conditions can be represented in the form of a three-dimensional piecewise-homogeneous model consisting of a number of structurally homogeneous fragments cut by systems of water-conducting fractures (zones) and confining interlayers. 2. The effective thickness of grout curtains on average is equal to 10–12 m, in zones of large-scale fracturing of the rocks — up to 20 m and more; the head gradients in the grout curtains do not exceed 10–18; the effectiveness of grout curtains depends substantially on the permeability of the surrounding rocks, and therefore the role which the grout curtain and drainage play under particular conditions is different. 3. The actual diagrams of uplift pressure in the foundations of many operating structures are below the design and standard ones. Under favorable hydrogeologic conditions a reduction of the heads by the watertight grout curtain and drainage in rock foundations of structures is not difficult and can be provided to values considerably less than the standard ones according to SNiP. A generalized diagram of the seepage heads is recommended for calculating the stability of dams on rock foundations in the presence of a grout curtain and drainage. 4. Watertight curtains made by the diaphragm wall method have a high effectiveness and economy. Their filler should be selected with consideration of the properties of the surrouding soils, SSS, and seepage strength of the foundation and diaphragm wall.