Modelling of pullout resistance of concrete anchor block embedded in cohesionless soil

Abstract

Anchor block is a specially designed concrete member intended to withstand pullout or thrust forces from backfill material of an anchored earth retaining wall by passive resistance of soil in front of the block. Present study describes the theoretical and numerical investigations into the behaviour of an anchor block in cohesionless soil. While analysing theoretically, a passive wedge of soil was assumed to develop in front of the anchor block due to the pullout force exerted from retaining wall via rebar. The equilibrium condition of the wedge was employed to propose a new analytical method to estimate the pullout capacity of an anchor block embedded in shallow depth. The comparison of the proposed theoretical predictions with the existing theoretical and experimental studies shows that, the proposed method provides a better estimate of the pullout capacity. Furthermore, the theoretical results are facilitated with charts which may be used in hand calculations to obtain an estimate of anchor capacity for most frequently used shapes, cube and square with half of height/length of block as thickness. The use of these charts is illustrated by worked examples. Finite Element (FE) analysis was also conducted using PLAXIS to investigate the effect of anchor shape, embedment depth and ground water table on pullout resistance of anchor block. The effect of anchor shape was found to be considerable for small aspect ratio of anchor block, whereas the influence of ground water table was substantial only when the ground water table was located anywhere between the ground surface and the base of the anchor block. Based on numerical analysis, an empirical correlation was developed to determine the correction factor that accounts the effect of ground water table. The proposed analytical method showed very close agreement with FE analysis for shallow embedment depth of anchor block. In addition, the failure modes of the soil body were also observed. These findings may be useful to all those dealing with civil engineering projects and research works on anchored retaining earth wall.