Geometrical effect on the behaviour of embankment on soft ground

Abstract

Many embankments constructed on soft ground are susceptible to failure and large settlements due to its low strength soil condition. Geosynthetics are used effectively as a reinforced material to increase the shear strength, and stiffness of the reinforced embankment and consequently, to reduce the total and differential settlements. In the first part of the study, four different cases of embankments with and without reinforcement, constructed on soft and stiff grounds were studied through small-scale physical modeling using centrifuge test and numerical modeling using finite element simulation. Comparison between the results using both finite element models and centrifuge tests was carried out to validate and identifies the reliability of the finite element method. In centrifuge test, a model scale with various sizes was simulated to a constant full-scale dimension using different acceleration fields. The results show the different deformation behavior for these different embankment cases and indicate the significant effect of the geosynthetics reinforcement on increasing the stability of embankment. The comparison analysis presents a good agreement between results of these two methods. It validated the finite element technique in analysis of different embankment cases. The second part of the study focus on the geometrical effects on the behavior and failure mechanism of embankments. Two full-scale case history embankments in Malaysia and Canada, the Muar trial embankment and Vernon highway embankment were verified. Three dimensional effects on Muar trial embankment were evaluated by comparing the results of two and three-dimensional analysis, in terms of predicted displacements, lateral movements, excess pore pressure, factor of safety, and failure height of the embankment fill. Moreover, this study attempt to evaluate the boundary limits for the applicability of two and three-dimensional analyses by determining the suitable geometry configuration of embankment in utilizing the geotechnical analysis. The ratio of the calculated failure height of three to two dimensional Finite Element analyses (Hf,3D/Hf,2D) has been determine for embankment cases with different base aspect ratio of the length to width (L/B). Two shape-factor equations related to the bearing capacity of spread footings and safety factor of embankments also utilized to account for the geometrical behavior of the embankment regards to its geometrical configuration. Results of three-dimensional analyses have better agreement with the actual field measurements. It is concluded that neglecting the three dimensional effects could mislead the design of the embankment in some condition. In conclusion, it is recommended that for “long embankment” with the length to width ratio more than two (L/B > 2), it may appropriate to use two-dimensional analysis as the three-dimensional safety factor converges to two dimensional safety factor. For “short embankment” with the length to width ratio less than two (L/B < 2), three dimensional effects on the embankment behavior becomes considerably great and should be considered as important factor in design and analysis of embankments.