Using a Laboratory Model Test to Evaluate Collapsibility of Gypseous Soils Improved by Sludge

Collapsibility of gypseous soils may cause excessive settlement and severe damage to engineering structures. Many improvement methods have been employed to reduce the collapsibility of these soils, such as by using physical methods or chemical additives. The collapsibility of the improved gypseous soils has conventionally been evaluated by using the odometer test, which may not accurately replicate the field conditions because of the small size of the test specimens. In this research, a laboratory model test of 600x600x600 mm with a model footing of 100x100mm was developed to measure the collapse characteristics of sandy soil with a gypsum content of 37%. The test was first conducted on specimens in the model at three different relative densities. The test was then performed after compacting the top layer of the test specimens [thickness from 50 to 100 mm] to the maximum dry density, as obtained from the Standard Compaction Test. Water treatment sludge was also used to further improve the top compacted layer. The results indicated that the collapsibility settlement reduction factor was 75% when the top layer of 50 mm thickness was compacted to the maximum dry density. Additionally, when the sludge was used with the top layer, the collapsibility settlement reduction factor was 86%