Stress-Dilatancy Relation of Sea Deposits of Mumbai Coast

It is not unusual for the offshore deposits to carry loads in excess to their ultimate capacity, when these soils bear the loads of heavy oil platforms. These soils contain high calcium carbonate content, which make them prone to particle crushing at these high loads. This paper investigates the effect of particle breakage on the load response of offshore marine deposits. Two sea deposits off Mumbai coast were chosen for the tests. Both the soils had similar mineralogical composition. In this study, dilatancy was studied as a function of particle crushing at crushing stresses up to 4.5 MPa. A series of direct shear tests were performed on samples which were crushed to various loads. The experimental results showed that with increase in extent of crushing, dilatancy decreased up to a point and then increased. It also indicates that crushing takes place to a considerable extent even after settlements have reached a near-constant value. The decrease in dilatancy with increase in particle crushing was more pronounced in angular particles than sub-rounded and rounded particles. This was also confirmed from the SEM images. Stress-dilatancy equations of both the soils were developed using drained shear tests. Particle breakage seems to significantly affect the measured coefficient of friction and hence the dilatancy component.