Abstract

The effect of long-term soaking on the California Bearing Ratio (CBR) of compacted gypsiferous soil containing about 64 0ypsum was studied. Sixteen CBR samples compacted at optimum moisture content and 950f the modified AASHTO dry density were prepared in accordance with ASTM (D 1883-87). Two samples each were soaked for periods of 0, 4, 7, 15, 30, 60, 120, and 180 days with a 20 lb (89 N) surcharge load. The water in the soaking tank was changed continuously to avoid full saturation with gypsum. The tests revealed a sharp drop in CBR with soaking period, especially within the first week. Thereafter, the loss in CBR took place at a smaller rate so that the soil strength became constant after about six months. The decrease of total soluble salt and gypsum content in soil with increasing soaking period is in full agreement with the loss in CBR with soaking period. The paper reveals that a soaking period of four days can lead to serious overestimation of soil strength for these soils.

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