Cyclic Triaxial Test of Dynamic Soil Properties for Wide Strain Range

Abstract

Dynamic material properties of soil needed for the nonlinear analysis of earthquake response of the ground have usually been measured in the laboratory using the torsional column shear device. The cyclic triaxial test, despite its easier accessibility and handling for practicing engineers, has seldom been looked upon as a rational way to make a reliable measurement of dynamic properties. In this experimental study a highly sensitive gap sensor and a sealed load transducer are introduced inside the triaxial cell to eliminate the frictions of the conventional displacement sensor and the loading piston. A series of cyclic triaxial tests featuring these improvements have been carried out for saturated Toyoura sand with various void ratios and confining pressures, disclosing the following facts. (i) Reliable measurements of the shear modulus and its strain dependent variation within a wide strain range of the order of 10 -6 to 10 -3 are possible with the improved cyclic loading test, permitting a direct connection with the insitu shear wave velocity. (ii) An essentially good agreement of the modulus is quantitatively recognizable between the triaxial test and the torsional shear test, implying that the different stress and confining conditions inherent to the individual testing devices give no significant effect on the evaluation of the modulus. (iii) This test gives a reasonable hysteretic damping ratio as well as its strain dependency although the damping ratios measured by other researchers with different testing devices widely differ from each other indicating the difficulties for evaluating accurate damping ratio.