BEARING CAPACITY OF SQUARE FOOTINGS UNDER DIFFERENT PRE-QUICKS AND CONDITIONS

Abstract

An upward flow of water through a cohesionless soil mass results in a loss in soil strength. The loss of strength is proportional to the hydraulic gradient under which the water flows. Soil with an upward flow and hydraulic gradient less than its critical value is said to be in pre-quicksand condition. The theory and reasons for the occurrence of pre-quicksand conditions have been enumerated. The details of a bearing capacity tank with an arrangement of controlled upward flow of water, designed and fabricated as a part of this study, have been described. The bearing capacity of footings on the surface of fully submerged sand subjected to various rates of upward flow has been determined analytically. Model tests were conducted on various square footings under ciifferent pre-quicksand condi-tions in the designed tank. The ultimate loads from model tests have been compared with those computed theoretically. At lower hydraulic gradients, experimental values of bearing capacity have been found higher than the theoretical values and vice versa at higher hydraulic gradients. Correlations have been established to estimate, approximately, the settlement and bearing capacity of square footings subjected to different pre-quicksand condit ions.