Abstract: through the triaxial CU tests of compacted silts under different water content by using an unsaturated GDS triaxial apparatus , the strength and yielding characteristics of the silts taken from Beijing-Kowloon-Railway subgrade are analyzed ,which provide an experimental basis for the establishment of soil mechanics model. Some conclusions can be made from the research as follows: (1) Higher strength and a tendency to work softening of stress and strain curves are shown of the samples compacted dry side of the optimum water content ,which also exhibit shearing dilatation initially and then shearing shrinkage; but for samples compacted wet side of the optimum water contents, lower strength and work harding trend are observed and the samples always exhibit shearing shrinkage characteristics. (2) The strength and yielding stress decrease with the water content increasing,which shows the softening effect of water on the soils behavior. (3) The yield loci at failure on q-p plane of different water contents exhibit linear relationship. The slopes of the critical state lines are independent of the water contents. (4) Cohesive increasing reflects the contribution of the water content to shear strength, and a power relation is shown between the cohesive and water content. (5) A formula taken water content as variable is deduced for calculating the shear strength, which shows good agreement with the testing data and can be used in practice.

Key words: compacted silt, water content, strength, yielding characteristics