Stabilization of Sandy Soil with High Salinity Conditions using Rice Husk Ash and Gypsum to Improve Physical and Mechanical Properties

Sandy soil is a non-cohesive type with no binding force among particles. Non-cohesive soils have loose grains and are not solid. In high-water level conditions, the sandy soil changes its properties to liquid, causing the cohesion value between grains and its shear strength to be lost. This condition can damage civil structures, such as collapse and construction failure. Therefore, soil improvement is carried out by adding rice husk ash and gypsum, which contain SiO2 and CaSO4.2H2O, to bind sand grains. Soil samples were tested by comparing the magnitudes of the cohesion values and the internal shear angles through direct shear tests. The mixing percentages for rice husk ash were 5%, 10%, and 15%, and for adding gypsum was 5%, with curing times of 3 days, 7 days, and 14 days (about 2 weeks). The soil sample used was sandy soil from Congot Beach, Yogyakarta, which has poorly graded sand. The optimal content for improving sandy soil was to use 5% gypsum and add 10% rice husk ash, which was proven to increase the carrying capacity of the soil. This improvement was evidenced by an increase in cohesion from the initial value of 0.029 to 0.061 and a change in shear angle from 19.82° to 29.18° in the sample taken after 14 days (about 2 weeks). The bonding observed due to stabilization was confirmed using the results of X-ray diffraction (XRD) and scanning electron microscopy (SEM).