Drainage of supported excavations

Summary The paper provides the approximate closed-form expressions for the estimation of the amount of ground water infiltration, the seepage exit gradient and the hydraulic pressure distribution on the cutoff elements in the case of sheeted excavations below the water table. The expressions are obtained by a multiple regression-type fitting of the results of an extensive parametric finite-element analysis for the two-dimensional steady-state flow in the soil around a sheeted excavation. In addition to the problem geometry, the effects of an impermeable base and a thin low permeability layer penetrated by the sheeting are also studied. The predictions of the approximate expressions deviate from the corresponding finite-element results by less than 15%, for a wide range of geometries and soil characteristics. It is shown how shape factors might be used to adapt the semi-empirical formulae for the case of excavations with limited length (circular and rectangular).