Limit Equilibrium Method Back Analyses of Geotextile-Reinforced Embankments on Soft Bangkok Clay – A Case Study

The limit equilibrium method (LEM) was used to back analyze the performance of three full-scale test embankments constructed over soft Bangkok clay. The control embankment was unreinforced while the other two embankments were reinforced with multiple layers of low-strength geotextile and with a single layer of high-strength geotextile, respectively. The analyses results confirmed the embankment performance indicating a two-stage failure mode of the reinforced embankments, namely: (i) the critical stage followed by (ii) the collapse stage. The critical stage occurred at the onset of plastic deformation of the soft clay foundation. The collapse stage occurred at the onset of embankment collapse when the reinforcement was on the verge of experiencing tensile failure or rupture. The critical reinforcement strain at the critical stage was independent of geotextile stiffness and on subsoil conditions and was 2.5 to 3%. The localized strain corresponds to the mobilized strain at the collapse stage in excess of the critical strain and can be estimated using a new method requiring two parameters: the in-soil stiffness and the reinforcement inclination factor. Back-analyses confirmed the horizontal and bisectional directions of reinforcement tensile force corresponding to the critical and collapse heights, respectively.