Abstract: It’s important to study the relationship between water content and shear strength of unsaturated soils for engineering practice. On the basis of concluding the previous tests results, direct shear tests of undisturbed soil and remolded soils of which the water contents are controlled by two different ways are conducted, choosing the unconsolidated silt of Tertiary as a study object. The results show that the shear strengths of soils decrease with increasing the water content. The main influence of increasing water content on shear strength is decreasing the cohesion; and the influence on the internal friction angle of soils is little. The relationship between cohesion and water content of unsaturated soils can be described by two lines and the slope of the second line is greater than the first line which imply that when water content reaches some value, the cohesion of soils decline fast. The way to change the water content of remodeled soils by controlling the dry density of soils and adding different mass of water, has not only changed the water content of soils, but also the compaction and structure of soils. So the change of shear strength is influenced by both water content and compaction of soils; and it should be paid close attention when analyzing the test results.

Key words: direct shear test, shear strength, water content, unsaturated soils