Evaluation of k₀ of granular soils using DMT indices

A series of CPTs and DMTs are performed in the calibration chamber in order to develop methods that estimate the coefficient of at-rest earth pressure (K₀), which is an indirect measure evaluating the stress history of granular soil. Among DMT indices and the q_c value, K_D is observed to be the most sensitive to the stress history while q_c and E_D show the similar trend of change as the vertical stress and stress history. The relation of Baldi et al. (1986) appears to be applicable for only NC sands as it does not include the term representing the effect of horizontal effective stress. The relations suggested in this study, K_D=K₀ χ(E_D/σ́_m)^δ and K_D/K₀a₀(E_D/p_a)^a1(σ́_m/p_a)^a2, are observed to provide comparable accuracy in K₀ values with those of Jamiolkowski and Robertson (1988) and Mayne (1995, 2001), regardless of the stress history. Suggested relations use only DMT indices while Jamiolkowski and Robertson (1988) require both CPT and DMT results, and Mayne (1995, 2001) needs both the CPT result and the OCR value. Although the adoption of OCR in Mayne (1995, 2001) offers a considerable improvement in the accuracy of the K₀ value, it is not considered practical since the inclusion of both soil property (OCR) and index parameters in an empirical correlation provides excessive redundancy.