Explicit Integration of Subloading tij Constitutive Model in FEM Analysis
Hossain M. Shahin, Teruo Nakai, Dorival Pedroso
finite element method, constitutive equation of soil, explicit integration, plasticity, bearing capacity, tunnel excavation
In this paper, three explicit integration schemes of subloading tij model, an elastoplastic constitutive model for soils, are described. The constitutive model can properly describes- influence of intermediate principal stress on the deformation and strength of soils, dependence of the direction of plastic flow on the stress paths, influence of density and/or confining pressure on the deformation and strength of soils. Three explicit integration schemes are adopted, namely- Forward Euler (FE), Modified Euler (ME) and Runge-Kutta-Dormand-Prince (RKDP) integration schemes The performance of the schemes has been investigated considering two different problems- bearing capacity of flat foundation and shallow tunnel excavation. For each integration scheme a series of analyses have been carried out varying the loading steps (the size of load increment). It is found that t he result of the FE scheme is the most inaccurate among the three different schemes for the same loading steps. The FE scheme requires higher computation time for achieving smaller error. In RKDP scheme the derivatives are evaluated in six different positions, hence it requires higher computation time than that for ME scheme. The ME scheme is found the most efficient for the two different geotechnical problems.