Performance evaluation of weak subgrade soil under increased surcharge weight

This research investigated the effect of surcharge weights on California bearing ratio (CBR), resilient modulus (MR), and swell potential of subgrade soils (A-4 and A-2-4), commonly used by the road construction industry. Nine different surcharge weights ranging from 2.27 kg to 20.75 kg were applied on both soil samples. The swelling was determined after soaking for 96 h, and the ultrasonic pulse velocity technique was used to determine the MR. CBR values for A-4 and A-2-4 soil increased from 3.5-23% to 18.5%-43.6%, respectively with increasing surcharge weight from 2.27 to 20.75 kg. A-4 soil showed decrease in swelling from 1.30% to 0.14% by increasing surcharge weight from 2.27 to 20.75 kg. The MR values of for A-4 and A-2-4 soil also increased from 35 to 135 MPa and 299–525 MPa, respectively with increasing surcharge weight from 2.27 to 20.75 kg. The MR values obtained through the ultrasonic pulse velocity technique, when compared with the CBR values, showed that the general equation of CBR-MR relationship developed by Garber and Hoel in 2015 overestimates the MR values of A-4 soil and underestimates the MR values of A-2-4 soil; Moreover, same CBR -MR equation cannot be used for all types of subgrade soils.