Abstract: Laterite is a typical problematic soil. Its strength characteristics are more complex than ordinary clay. A series of consolidated quick direct shear tests on compacted Guilin laterite with the same initial dry density and different moisture contents were performed to investigate the factors affecting the strength of the laterite. Changes in cohesion and internal friction angle with moisture content were obtained. Test results show that the cohesions decrease as the initial moisture content increases. The friction angles at peak and residual increase firstly and then decrease as the initial moisture content increases. Besides, the dilatancy of Guilin laterite during shearing is discussed. Comparison of the test data and the calculated values by using Bishop’s and Fredlund’s equations for unsaturated soils show that the two equations cannot properly predict strength of unsaturated Guilin laterite.

Key words: dilatancy, laterite, moisture content, shear strength, unsaturated soil