Determination of Collapse Potential of Gypseous Soil from Field and Laboratory Tests

Abstract

Collapsible soils are known as problematic soils, which possess considerable strength when dry and lose their strength when inundated experiencing excessive settlements. The soil response to inundation (i.e. landslides or significant soil settlements) could not be predicted beforehand. The irrecoverable volume reduction of collapsible soils takes place fast and sudden and no measurements can be taken to stop the problem once it initiates. The collapse potential increases with time due to soaking and leaching which is attributed to the dissolution and washing out of gypsum. In this paper, a comparison is made between the collapse potential predicted form laboratory standard collapse test with filed collapse (coefficient of resolving slump) estimated from plate loading test. The soil site for investigation was in Rumaila, Basrah Governorate. Results of collapse test carried out on two samples showed that the collapse potential, Ic of the two samples is 5.091% and 3.502%, the soil is considered of moderate degree of collapse. The coefficient of average resolving slump for saline soil was calculated from field plate load test to be 0.94% to 1.2%. The difference in boundary conditions between the two approaches was found clear in the evaluation of collapse potential.