Predictive Equation for Soaked CBR of a Clayey Gypsiferous Soil

Sabah Razouki

Presented in this paper is an empirical equation modelling the effect of long-term soaking on strength characteristics of a clayey gypsiferous subgrade soil.

The soil tested is a fat clay of CH group according to the Unified Soil Classification System and A-7-6 (42) group according to AASHTO soil classification system. The soil contains about 34.5% total soluble salts (T.S.S) and about 33% gypsum content.

For this purpose, forty two CBR samples were prepared at 95% relative modified AASHTO compaction. For each soaking period, six samples were prepared, two for each case of the three selected surcharge loads namely 10, 40 & 70 lb (44.5, 178 & 311.5 N). The soaking periods adopted in this study were 4,7,15,30,60,120, & 180 days.

The empirical equation developed in this work enables the engineer to determine the soaked CBR from the unsoaked  one at any desired soaking period and under the effect of any surcharge load. Regression equations were developed to enable the determination of CBR under any surcharge load from the CBR under 10 lb (44.5 N) surcharge load for different soaking periods.

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