An EVP Approach for Embankment Surcharge Design

Greg G. Qu, Sean Hinchberger, Keli Shi, Paul Dittrich

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Transportation Geotechnics

ABSTRACT: This paper presents an alternative embankment surcharge design method to the conventional Terzaghi approach. The objective of surcharge is to reduce the long-term settlement to an acceptable level in the design life. Terzaghi's primary consolidation and secondary compression concept is widely adopted in practice to guide the embankment design. However, the Terzaghi method has limitations due to its phenomenological nature. Recently, researchers have made significant progress in the study of soil viscoplasticity. Numerical analyses and case studies have shown that the elasto-viscoplasticity (EVP) theory has accurately predicted consolidation and creep/viscoplastic deformation. Due to the complexity of EVP constitutive models, they have not been widely applied in common engineering practice. This paper presents a practical design approach based on solutions derived from EVP theory. A step-by-step design approach is introduced and then illustrated through a simple example. Recommendations are also provided for parameter selection. RÉSUMÉ Les auteurs présentent une méthode alternative à la méthode traditionnelle de Terzaghi pour la conception de préchargement des remblais. L'objectif de préchargement des remblais est pour réduire l'affaissement de terrain de longue durée à un niveau acceptable qui est conformément à la durée de vie de projet. Selon les auteurs, la théorie de Terzaghi est présente plusieurs limites pour les calculs des tassements du sol fins au cours du temps. Plus récemment, des progrès importants ont été accomplis dans le domaine de la visco-plasticité de. Les analyses numériques et les études de cas ont montré que la déformation de fluage peut être prévu avec précision par la modele de élasto-visco-plasticité (EVP). À cause de la complexité de la modele de EVP, elle ne soit pas totalement appliquée dans la pratique. Le présent article décrit une solution analytique s'appuyant sur la théorie de EVP et aussi un exemple pas à pas pour sa application. Un débat et recommendation à propos de la sélection des paramètre de conception sont fournies aussi. 1 INTRODUCTION This paper presents an alternative surcharge design method to the conventional Terzaghi approach. Long-term settlement often governs the embankment design, especially for embankments on soft compressible clay deposit. Terzaghi's secondary compression concept (Terzaghi and Peck 1987) has been widely used in practice to guide the design (FHWA 1986, NAVFAC 1986). The corresponding method is basically a phenomenal/observational approach in describing creep. This approach assumes (1) no creep during consolidation, (2) that creep takes place right after consolidation completion, (3) creep lasts forever. These assumptions brought several limitations such as, (1) neglecting creep during primary compression, (2) assuming infinite secondary compression with time, (3) not being able to quantify the creep settlement with time after surcharge removal. In practice, engineering experience and judgement is often required to overcome the inherent limitations of the Terzaghi approach. Alternatively, Suklje (1957) proposed the isotache concept to describe the time-dependent behaviour of clay in one-dimensional compression. The isotaches were defined as a series of compression curves constructed from tests performed at different constant strain rates. Since then, the concept of isotaches has been extended to yielding in general stress space (Tavenas et al. 1978, Adachi and Oka, 1982, Graham et al. 1983, Leroueil et al. 1985, Hinchberger and Rowe 2005, Qu et al. 2010). The term 'overstress' has been used as an equivalent to isotache by some researchers in a generalized stress space. In contrast to Terzaghi approach, the isotache concept incorporates the creep during consolidation and defines a static state, representing the end of creep. Recently, researchers have made significant progresses in the overstress viscoplasticity modeling (e.g., Leroueil et al. 1988, Yin and Graham 2002, Rocchi et al. 2003, Hinchberger and Qu 2009). Numerical analyses and studies have shown that the overstress elasto-viscoplasticity theory accurately predicted the creep/viscoplastic deformation and consolidation in both loading and unloading processes (Zhu and Yin 2000, Nash and Ryde 2001, Kelln et al. 2008, Leoni et al. 2008, and Hinchberger and Qu 2009). However, due to the complexity of the viscoplastic constitutive models, they have not been widely applied in day-to-day geotechnical engineering practice. The objective of this paper is to provide a straightforward design approach in the overstress

RÉSUMÉ: P APPROACH FOR EMBANKMENT SURCHARGE DESIGN

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Cite this article:
Greg G. Qu; Sean Hinchberger; Keli Shi; Paul Dittrich (2014) An EVP Approach for Embankment Surcharge Design in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper232,author = Greg G. Qu; Sean Hinchberger; Keli Shi; Paul Dittrich,title = An EVP Approach for Embankment Surcharge Design,year = 2014}