**Title**

**Extended Mohr–Coulomb (EMC)**

**Description**

Despite the routine nature of the task, there is no well accepted or reliable approach for predicting the settlement of shallow foundations in sand. This is attributed to the continued pursuit of solutions that rely on some tenuous link between penetration test data and ‘ground stiffness’, and then use this ‘ground stiffness’ to estimate the footing settlement via some elastic solution that approximates (often very roughly) the actual boundary conditions of the foundation. It also appears that the wide availability of sophisticated soil models in commercial FE software has done little (if anything) to improve the situation. It is supposed that this is due to either a lack of confidence or a lack of guidance in the application of advanced soil models.

This problem was addressed by developing a simple soil model and outlining a procedure to obtain the model parameters using data obtainable from a geotechnical site investigation. The soil model incorporates a simple isotropic linear elastic component (Hooke’s law), a Mohr–Coulomb yield surface, the original Cam Clay flow rule and a simple asymptotic strain-hardening rule. Two elastic stiffness profiles were considered: one was derived using bender element shear wave velocity measurements on reconstituted soil samples and the other using in-situ shear wave velocity data from SCPTs. All other model parameters were obtained using data from anisotropic drained triaxial compression tests on disturbed samples reconstituted to estimated average in situ relative density. It was found that an excellent match

**References**

Doherty, J. P. & Muir Wood, D. (2013). An extended Mohr–Coulomb (EMC) model for predicting the settlement of shallow foundations on sand. Géotechnique 63, No. 8, 661–673

The version of the model implemented in OptumG2 is a slightly modified and extended version of the original Extended MC model of Doherty and Muir Wood.

It allows for direct specification of E50 and Eur (both of which can be made pressure dependent) and there is a choice of flow rule: either constant dilation of Taylor’s flow rule.

Examples of validation and application of the model can be found in the OptumG2 Materials and Examples manuals which come with the program.