Impact of constitutive models on the numerical analysis of underground constructions

Abstract

The constitutive model frequently used in numerical calculations of tunnel excavation is linear-elastic perfectly plastic with a Mohr-Coulomb (MC) failure criterion. Generally, this leads to shallower and wider surface settlement troughs than those observed experimentally. It is therefore necessary to use adapted constitutive models for the design of underground works. In this paper, three constitutive models are implemented in a two-dimensional simulation of an underground excavation in plane strain: a linear-elastic perfectly plastic model (the MC model), an elastoplastic model with isotropic hardening [the hardening soil (HS) model, Schanz et al., Beyond 2000 in computational geotechnics, Balkema, Rotterdam, pp. 281-290, 1999 and an extension of this model which implies an evolution of the stiffness modulus in the small-strain range according to the strain level (the HS model with smallstrain stiffness ''HS-Small'', Benz, Small-strain stiffness of soils and its numerical consequences. Ph.D. thesis, Universitat Stuttgart, 189 pp., 2007). The study is based on the results of drained triaxial compression tests representing an overconsolidated clay (Gasparre, Advanced laboratory characterisation of London clay. Ph.D. thesis, Imperial College London, 598 pp., 2005); and is then applied to a shallow tunnel. The impact of the constitutive model is highlighted as well as the limits of the simplest constitutive model.

Three-dimensional numerical simulation of mechanized twin stacked tunnels in soft ground

“…In addition, as for a single tunnel, the smaller the tunnel depth is, the greater and narrower the surface settlement trough is. This result is in good agreement with the 2D numerical results obtained by Hejazi et al (2008). As expected, the settlement profiles in the transverse section in all three cases are always symmetric over the tunnel center.…”

3d Modelling for Mechanized Tunnelling in Soft Ground-Influence of the Constitutive Model

“…The minimum difference is obtained for the normal forces. Considering the disadvantages of the MC model introduced in previous studies (Bolton et al, 1994;Addenbrooke et al, 1997;Masin and Herle, 2005;Hejazi et al, 2008), the above results show the importance of the complexity of aconstitutive model in tunnelling engineering.…”

“…However, less works have been devoted to its effect on the tunnel lining behaviour. Generally, simple constitutive models lead to a shallower and wider settlement trough than the one observed experimentally (Bolton et al, 1994;Addenbrooke et al, 1997;Masin and Herle, 2005;Hejazi et al, 2008;Rodriguez, 2008;Lambrughi et al, 2012). Their studies indicate that in order to take into account some of the fundamental aspects of soil behavior, such as the variation inthe stiffness modulus, according to the stress state and the difference in the modulus during the unloading and loading phases, it is at least necessary to use an elasto-plastic model with strain hardening.…”

Numerical investigation of the effectiveness of a bored pile wall for the minimisation of settlement resulting from tunnel driving

“…It is known that numerical calculations with Mohr-Coulomb normally predict the settlement trough too wide and flat [1] [5]. The simple elastoplastic model was nonetheless included in the comparison, because it is still the most common material model in geotechnical practice.…”

“…dilatancy, different stiffnesses on loading and unloading, dependence of stiffness on stress level, is essential [5] [12]. The requirements stated are fulfilled by the hypoplastic model.…”