Development of a new three-dimensional anisotropic elastic visco-plastic model for natural soft soils and applications in deformation analysis.

摘要

This study focuses on three interrelated aspects: (a) development of anisotropic Elastic Visco-Plastic (EVP) constitutive models; (b) verification of the EVP models by comparing simulation results with measured results from four types of tests on a Hong Kong Marine Clay (HKMC), and (c) application of the constitutive models in fully coupled consolidation analyses of case histories. The four types of tests are (i) standard oedometer compression/creep tests, (ii) oedometer tests compressed at a single stage of constant strain rate or stepped changed strain rates, (iii) triaxial K0-consolidation tests, and (iv) K 0-consolidated undrained triaxial compression and extension tests at multistage constant strain rates. The case histories include a test embankment at the new Chek Lap Kok International Airport in Hong Kong, Haarajoki test embankment in Finland and a small-scale physical model soft clay foundation improved by Deep Cement Mixed (DCM) soil column.; First, a new general one-dimensional (1-D) EVP constitutive model using a non-linear creep function is developed and presented for the time-dependent stress-strain behaviour of clays under a K0-stress condition including loading, unloading and reloading. This new 1-D EVP model is an extension of the 1-D EVP model proposed by Yin and Graham (1989, 1994) based on the 'equivalent time' concept. The new elements in the newly developed 1-D EVP model are that (a) a non-linear creep function with a limit for the creep volumetric strain is adopted and (b) a 'limit time' line is used. A method for determining all model parameters is presented using data from one conventional standard oedometer compression/creep test on natural HKMC. The 1-D EVP model is verified by comparing modeling results with measured results from (a) conventional standard oedometer compression/creep tests, (b) oedometer tests compressed at a single stage of constant strain rate or stepped changed strain rate and (c) triaxial K0-consolidation/compression tests on the HKMC.; A three dimensional (3-D) anisotropic EVP model for normally consolidated and overconsolidated clays is then developed on the basis of the 1-D EVP constitutive relationship. This 1-D EVP relationship is used to determine the visco-plastic scaling factor and is taken as a strain hardening law similar to that used in the Modified Cam-Clay model. Yin and Graham's 'equivalent time', 'limit time line' concepts and a non-linear creep function with a limit for the creep volumetric strain are also incorporated in the 3-D EVP model. A symmetrical elliptical loading locus along an aK0 -line in the p'-- q plane is incorporated in the 3-D anisotropic EVP model to initiate the field K0-stress condition. (Abstract shortened by UMI.)