Abstract
An equation for estimating in-situ undrained shear strength (qu(I)) of natural deposits is derived as qu(I)/2cu(I)=1.0-0.285 ln pm/S0 through the unconfined compression test (UCT) and K0 consolidated-undrained triaxial compression test (CK0UC). The qu(I) of natural clay deposits can be estimated from the qu value multiplied by the reciprocal number of qu(I)/2cu(I) of the equation using the suction (S0) and qu obtained from UCT for a specimen, where cu(I) is in-situ shear strength measured from CK0UC and pm is two times the effective overburden pressure divided by three. The qu(I)/2cu(I) values were unrelated to Ip, qu and pm/S0 and the mean value of these ratios was 0.98 in the range of Ip=26~110 and qu=12~178 kPa. The mean values of the ratios for qu, q*u(I) and qu(I) to 2cu(I) were 0.629, 0.998 and 0.977 and the standard deviation of those ratios were 0.14, 0.10 and 0.16, respectively. Therefore, it can be seen that the improved method is appropriate as well as Shogaki's basic method (q*u(I)). The mean values of qu(I)/2cu(I) were 0.94, 0.99 and 0.91 for Iwai organic and soft clay plus Kahokugata clay, respectively. The coefficient of variations of the qu and qu(I) values were (13~14)% and unrelated to soils, qu or qu(I) values. Therefore, the applicability of the improved method newly developed in this study can be confirmed for Kahokugata and Iwai clays as well as Iwai organic soils. The proposed method is a simple and easy one for practical engineering usage.
