The 12 th International Conference of International Association for Computer Methods and Advances in Geomechanics (IACMAG) 1-6 October, 2008 Goa, India Pullout Behaviour of Square Anchors in Reinforced Clay P. Bhattacharya, Debjit Bhowmik, S. P. Mukherjee Dept. of Civil Engineering, Jadavpur University, Kolkata, India B. C. Chattopadhyay Dept. of Civil Engineering, Bengal Engineering and Science University, Shibpur, Howrah, India Keywords: Anchor, Pullout, Reinforced Clay, Non-linearity ABSTRACT: Behaviour of square plate anchors under uplift load in reinforced clay has been studied using a three dimensional finite element displacement model with ANSYS software. Soil anchor System has been discretized with eight noded isoparametric brick elements for the soil and four noded isoparametric shell elements for the plate. Geotextile used as Reinforcing material has been modelled with two noded spar element activating tension only. Nonlinear soil behaviour has been considered with Drucker Prager model and the geometrical nonlinearity of geotextile has also been addressed in the analysis. Analysis has been carried out with embedment ratio up to four representing shallow anchor and the placement of geotextile has been varied from the top of the anchor plates. To validate the analysis model tests have also been carried out with 75mmX75mm and 50mmX50mm square plates. The results are presented with parametric variation and with normalized plots to obtain an estimate of pullout capacity. 1. Introduction Different types of anchors are used for offshore and onshore civil engineering structures to resist the uplift load or inclined pulls. For the last four decades a number of research papers have proposed approximate techniques to predict the uplift capacity of anchors based on analytical and model test results. But most of the studies are limited to cohesionless soil. On the other hand the study on the behaviour of anchors in cohesive soil are only a few and such results can only be found from the works of Meyerhof(1973), Das(1978, 1980), Rowe and Davis (1982), Davie and Sutherland(1977), Merrifield, Sloan et al(2003, 2005), Yu and Sloan (1997). However in reinforced clay, the behaviour of plate anchors is not well addressed and so far very few works like Nene and Garg (1991) have been reported. The present paper aims at the stability of square horizontal plate anchors in reinforced clay by numerical procedures based on finite element formulations and laboratory model test results. The soil-anchor system was modeled with 8-noded Isoparametric brick elements and the geotextile which is used as a reinforced material has been modeled as two noded spar elements. Both, material non-linearity of soil and the geometric non-linearity of geotextile have been considered in the analysis. The solution has been obtained by incremental-iterative procedures following modified Newton–Raphson method with the help of ANSYS General Purpose Software. In addition to that laboratory model tests were conducted on square plate anchors embedded in reinforced clay. The uplift capacity of anchors has been typically expressed in terms of breakout factors, embedment depth and position of reinforcement. 2. Pullout Capacity of Anchors in Clay According to Rowe and Davis (1982), the analysis of anchor behaviour is generalized into two distinct categories viz ‘Immediate Breakway’ and ‘No Breakway’. In the present analysis, the Immediate Breakway case has been utilized wherein, upon loading, the vertical stress immediately below the anchor becomes zero and there is no contact of the anchor with the soil. The ultimate pullout capacity in undrained homogeneous clay is generally expressed in terms of breakout factor Nc which is a function of embedment ratio H/B and the overburden pressure which is expressed as a nondimensional quantity of γH/Cu Where γ = unit weight of soil, H = embedment depth and Cu = undrained shear strength of soil. In case of reinforced clay, the effect of reinforcement is to mobilize additional shear stress in soils due to appearance of tensile force in the reinforcing material geotextile used in the present investigation. In the deformation analysis by the Finite Element method adopted, the frictional property between the geotextile and the soil has been incorporated in the interaction model. The breakout factor for reinforced clay has been derived from the ultimate pullout capacity determined from the finite element model and validation of the theory has been carried out by experimental findings for 3441