Insight into Employability of Mohr Coulomb and Hardening Soil Model in the Undrained Analysis

Quite often soil at the site is saturated with water. Any addition of the load onto such soil with low permeability results in generation of excess pore water pressure. Real life problems such as construction of footing, construction of embankment on saturated clayey soil and deep excavation falls under this category. The numerical modelling of such problems must be capable of simulating generation of excess pore water pressure accurately. Mohr Coulomb model is the most widely used constitutive model in the numerical analysis of soil problems. However, being elastic-perfectly plastic, application of this model in simulation of short term undrained simulations needs to be investigated. In the present study, efficacy of the Mohr Coulomb model and Hardening Soil model present in the PLAXIS have been investigated for coupled analysis. It is found that Mohr Coulomb model overestimates the undrained shear strength of the soil significantly and fails to produce the realistic stress path. Hardening soil model captured the realistic pore pressure response whereas the Mohr Coulomb model underestimated the pore pressure and resulted in unrealistic pore pressure evolution. It is recommended that advanced constitutive models such as Hardening Soil model should be employed in short term undrained numerical analysis.