THE ISRAELI GUIDE FOR CALCULATING THE SURCHARGE PRESSURE REQUIRED FOR PAVEMENT STRUCTURES LAID ON SWELLING CLAY SOILS

摘要

In the Israeli guide for calculating the surcharge pressure required for pavement structures laid on swelling clay soils, predicting the heave of the pavement surface as a result of subgrade swelling constitutes a basic feature. The prediction necessitates knowledge of the swelling-pressure characteristic (curves) of the clay strata under consideration, usually obtained from laboratory tests on undisturbed clay samples. It is shown that a basic regression equation should be employed that correlates the percentage of swell under a given vertical pressure exerted on the clay with the following parameters: (a) the liquid limit, (b) the ratio between the in-situ moisture content and the plasticity limit, and (c) the in-situ dry density. The derivation of this basic equation is described, together with its adjustment--from the results of any local laboratory testing--to the specific given conditions. In addition, the pavement heave must be limited to a maximum value of 30 mm, on the assumption that half of this value will be differential heaves. To obtain this limit, adequate surcharge pressure is best calculated according to the procedure described in the paper.