Volume change behavior of a fissured expansive clay containing anhydrous calcium sulfate

摘要

Expansive clays in eastern Saudi Arabia are generally fissured and contain high quantities of anhydrous calcium sulfate. Similar to clay minerals, this secondary mineral causes swelling when hydrated and forms gypsum that, in turn, dehydrates and transfers back to anhydrite during compression. The main objective of this paper was to understand the volume change behavior of a local expansive clay containing 50% anhydrous calcium sulfate. Swelling and consolidation tests were conducted on undisturbed field samples according to the constant volume method. A conventional oedometer sample was used to determine the maximum possible volume change. Likewise, a large-scale oedometer sample was used to capture the influence of fissuring on volume change. The large-scale sample was thoroughly instrumented to determine both the vertical and the lateral swelling pressure. Results indicated a twofold increase in swelling pressure of the desiccated clay when corrections were applied to account for sample disturbance. The corrected vertical swelling pressure of the clay was 320 kPa for the conventional sample and 245 kPa for the large-scale sample. The lateral swelling pressure was 40% of the vertical swelling pressure and the swelling index was one-third of the compression index for the investigated soil.