A NEW METHOD OF CORRECTING UNCONFINED COMPRESSIVE STRENGTH OF NATURAL CLAYS FOR SAMPLE DISTURBANCE

抄録

In Japan, the unconfined compression test is used widely to determine undrained strength for natural clays. The scatter of test data caused by sample disturbance, however, prevents this test from being used effectively and economically in geotechnical engineering practice. This paper is aimed at proposing a simple rational approach to correct the unconfined compressive strength, q_u, of natural clays for sample disturbance. The effect of sample disturbance on q_u is analyzed both qualitatively and quantitatively based on the experimental data for five types of natural clay. The results indicate that q_u normalized by the corrected yield stress, p_yf, decreases linearly with the increase of the defined degree of sample disturbance. The straight line representing the relationship between the reduction value of q_u/p_yf and the disturbance degree is determined by regression analysis. The slope of the linear regression line is defined as a strength correction coefficient. Based on such correction coefficient, a simple method is proposed in this paper for correcting q_u for sample disturbance. The problem of scattered test data on q_u can be eliminated with the proposed method. Analyses and comparisons are also made of the experimental data on unconfined compression tests and triaxial consolidated undrained shear tests for some natural clays as well as the data published in the literature. The results indicate that the proposed method is valid for natural clays.