Triaxial tests on mechanical properties of undrained and unvented unsaturated clayey sandy soil

In order to study the characteristics of strength, deformation and resilience modulus of unsaturated clayey sands soil under the undrained and unvented condition at different water contents and compaction degrees, an improved unsaturated soil triaxial instrument is used. Two types of tests on the clayey sandy soil of the subgrade of Guangfo Expressway are carried out: (1) twevel undrained and unvented triaxial shear tests with the dry density of 1.85 g/cm³, the water contents of 10.47%, 13.63%, 14.5% and 16.02%, and the confining pressures of 50, 100 and 200 kPa; (2) nine resilience modulus tests under cyclic loading and unloading conditions with the dry densities of 1.70, 1.80, 1.85 g/cm³, the water contents of 10.47%, 13.63% and 16.02 %, the confining pressures and the deviatoric stresses of 100 and 200 kPa. The 6-level stress loading and unloading method is adopted, and each sample is subjected to 2 loading and unloading cycles under undrained and unvented shearing. The results show that the optimum water content is the critical value at the turning point of internal friction angle, cohesion and strength of soil. The strength of the dilatancy greatly relates with the confining pressure and the water content. With the increase of the confining pressure and the water content, the dilatancy gradually decreases. With the progress of shearing, the pore water pressure and pore gas pressure both increase first and then decrease, and with the occurrence of shear dilatation. The curves of the pore gas pressure and the pore water pressure are gradually separated, and the matrix suction increases. Under the same water content, the greater the net confining pressure, the greater the pore gas pressure and the pore water pressure. Through the data analysis, the multivariate nonlinear function expression for the water content, the compaction degree and the resilience modulus is established. The significance of the influences of the water content and the compaction degree on the resilience modulus is analyzed. The influences of the water content on the resilience modulus much greater than those of the compaction degree. The research results may provide a useful reference for the design and construction of the related highways.