Effect of suction on the strength of unsaturated soil

Unsaturated soil condition which give rise to negative pore pressure is important in evaluating the stability of geotechnical structures such as slopes, retaining walls, excavations and footings, Its importance is more so in tropical countries, where rainfall and intense chemical weathering have resulted in the formation of such soils. In this study, the shear strength characteristics of granite residual soil were investigated using consolidated drained triaxial tests with special emphasis on the effects of the negative pore pressure, i.e. the matric suction. These tests involved sheafing under either a constant net confining pressure and varying matric suctions or under a constant matric suction and varying net confining pressure. The influence of confining pressure and matric suction on shear strength was analyzed and a linear relationship was found to relate matric suction and shear strength.