Model Plate-Load Tests on Collapsible Soil

Several factors influencing the wetting-induced collapse (hydrocompression) of alluvium soils are investigated by oedometer and plate load tests. Factors include wetting period, staged loading duration, plate size, overburden pressure, and soil thickness. Circular plates of 5 cm and 7 cm diameters were employed. Soil samples collected from Al Helwah region in Central Province of Saudi Arabia were statically compacted in 45 cm diameter and 35 cm height steel container. Surcharge pressures of 5,7, and 9 kPa were considered. The load-settlement were modeled under dry and soaked conditions of soil at natural water content of 2% and dry density of 1.4 g/cc. Oedometer and plate load test results are presented and their capability in collapse characterization and evaluation are compared.Results of this research program indicate that Al Helwah soil is highly collapsible and has a collapse potential of 12% under 200 kPa pressure. The plate settlement continues for 3-5 min under dry load increment and 120 min under soaked load increment. Soil stiffness and bearing capacity degraded due to wetting. The reductions are a function of the overburden pressure and plate size. A collapsive strain extending 4 times the plate diameter is observed upon wetting. Also the load step duration and the extent of effective wetting front have significant effects on the test results and interpretation; therefore, they should be considered in the planning, design, and analysis of plate load and full scale footing tests