IAEG2006 Paper number 34 © The Geological Society of London 2006 1 FEM analysis of the interaction between a broad embankment and its subsoil JIANFENG CHEN 1 , ZHENMING SHI 2 , XIAOYING ZHUANG 3 1 School of Civil Engineering, Tongji University. (e-mail: jf_chen@mail.tongji.edu.cn) 2 School of Civil Engineering, Tongji University. (e-mail: shi_tongji@mail.tongji.edu.cn) 3 School of Civil Engineering, Tongji University. Abstract: Broad embankment and its subsoil belong to an interaction object, where they affect each other mutually and deform co-ordinately. In order to study the influencing factors of subsoil’s settlement, the paper varies the combination of fill’s height, fill’s stiffness and subsoil’s stiffness and then analyzes these cases by FEM program applying modified Cam-clay model coupling Biot to subsoil and Mohr-Coulomb model to fill. The results show that the settlement of subsoil distinctly correlate with fill’s height and fill’s stiffness and subsoil’s stiffness, which can be concluded as follows: (1) In case of soft subsoil with moderate fill’s stiffness, the maximum settlement points occur at the two shoulders of embankment. As the height of loading increases, the location of the maximum settlement points tend to move towards the central part of embankment and its differential settlement to the centre part of the embankment decreases. (2) In case of hard subsoil with moderate fill’s stiffness, the two shoulders no longer own the maximum settlement and the differential settlement of subsoil decreases. (3) In case of hard fill with soft subsoil, settlement and differential settlement become smaller. With the increase of loading, the differential settlement decreases significantly. Résumé: Le large remblai et son sous-sol appartiennent à un objet d'interaction, où ils s'affectent mutuellement et déforment Co-ordinately. Afin d'étudier les facteurs influençants du règlement du sous-sol, le papier change la combinaison de la taille de la suffisance, a rempli rigidité et rigidité du sous-sol et puis analyse ces caisses par le programme de FEM appliquant l'accouplement modifié Biot de modèle d'Came-argile au sous-sol et au modèle de Mohr-Coulomb pour remplir. Les résultats prouvent que le règlement du sous-sol se corrèlent distinctement avec la taille de la suffisance et ont rempli rigidité et rigidité du sous-sol, qui peuvent être conclues comme suit : (1) en cas de sous-sol mou avec la rigidité de la suffisance modérée, les points maximum de règlement se produisent aux deux épaules du remblai. Pendant que la taille des augmentations de chargement, l'endroit des points maximum de règlement tendent à se déplacer vers la partie centrale du remblai et son règlement différentiel à la pièce de centre du remblai diminue. (2) en cas de sous-sol dur avec la rigidité de la suffisance modérée, les deux épaules ne possèdent plus le règlement maximum et le règlement différentiel du sous-sol diminue. (3) en cas de suffisance dure avec le sous-sol mou, le règlement et le règlement de différentiel deviennent plus petits. Avec l'augmentation du chargement, le règlement différentiel diminue de manière significative. Keywords: embankment, finite element, settlement INTRODUCTION Broad embankment and its subsoil belong to an interaction object, where they affect each other mutually and deform co-ordinately. The settlement of subsoil is directly under the influence of the fill’s height, the fill’s stiffness and the subsoil’s stiffness. The Chen, Shi & Shen (2003) have once analysed the settlement of a broad embankment built on soft subsoil by Finite Element Method (FEM) program applying a linear elastic model with Biot coupling. The results showed that settlements at the shoulders of embankment are greater than those at the central part, and as loading increasing, the location of the maximum settlement point tends to move towards the central part of embankment. These results are entirely consistent with the results taken from the Muar experimental embankment in Malaysia and with the 400m-wide embankment built on soft subsoil of Shenzhen airport in China (see Zhang 1999 for further details). With both these substantial engineering embankment projects their observed settlements were measured to be greater at the two sides than at central part of each respective embankment. The Chen et al. (2003) have analysed settlements of an embankment case but by only meshing the subsoil itself and not by considering the embankment and subsoil together as an interacting object. Instead, this paper has assessed several cases with various combinations of fill height, fill stiffness and subsoil stiffness being analysed and in each case the embankment and the subsoil t were meshed together as a whole. This allows a better study on how these factors influence the deformation of subsoil to take place. A FEM analysis of settlements for these cases has been carried out by applying a modified Cam-clay model to subsoil and the Mohr-Coulomb model to fill. CONSTITUTIVE MODEL The widely applied modified Cam-clay model is particularly pertinent to calculate the deformation of soft subsoil (Chen, Qin & Shi 2003). Moreover, this model can be coupled together with Biot theory to develop into the coupling Cam-clay & Biot model, which is capable of simulating the coupling aspects associated with subsoil deformation,