Static and cyclic properties of clay subgrade stabilised with rice husk ash and Portland slag cement

In the present study, clay soil collected from new Banda, Uttar Pradesh, India has been treated with rice husk ash (RHA) and Portland slag cement (PSC). Based on unconfined compressive strength test results, the optimum mix obtained is of 82.5%Soil+7.5%PSC+10%RHA. The increase in strength of the optimum mix is about 29.8%, 37.2% and 48.55% for a curing period of 7, 14 and 30 days, respectively. The soaked California bearing ratio (CBR) test gives about 91.75% higher values as compared to unsoaked CBR test for a curing period of 30 days. Strain-controlled cyclic triaxial tests were conducted to study the variation of degradation index, shear modulus and damping ratio of the optimum mix with number of cycles for strain amplitudes of 0.4%, 0.6%, 0.8% and 1% and for frequencies of 0.2 and 1Hz at an effective confining pressure of 100kPa. It is observed that the degradation index decreases at a fast rate for the first 25-50 cycles. From the study, it is concluded that the aforementioned mix may be suitable for pavement subgrade material.