Development of an analytical model for the analysis of pullout capacity of anchors embedded in frictional soils

Abstract

Anchors, made of steel, pre-cast or cast-in-place concrete, timber are generally designed and constructed to resist outwardly directed loads imposed on the foundation of a structure. Depending on the placement, it may be horizontal, vertical or inclined. The aim of the present study is to develop an analytical model for the estimation of pullout capacity of vertical anchors embedded in frictional soils. The analytical model can consider more realistic variations in pullout capacity due to installation at a wider range of embedment depth. The model is based on the principle of limit equilibrium. The predictions from the developed analytical expression were compared to the available experimental and numerical investigations. Results show that the present model can predict the pullout capacity of shallow and intermediate anchors with more accuracy and reliability compared to the available pullout capacity prediction models. In addition, a comprehensive parametric study is also presented. It is found that with the increase of friction angle (φ'), pullout capacity increases significantly, the effect being higher at high friction angles (φ^'>30°). The demarcation aspect ratio (ratio of anchor length to height) between single and continuous anchor is 10 rather than 5, which was proposed by Das (1990). Parametric studies further reveal that the active pressure components although play an insignificant role at an embedment depth ratio of less than 2.5, the effect is substantial thereafter. It appears that omission of contribution from side flanks results in a discrepancy of as much as 37% in highly frictional soils at an embedment depth ratio (H/B) greater than 3. Finally, it is observed that a constant value of δ⁄φ' assumed in most pullout capacity prediction models for all the range of H/B and L/B to analyze the pullout capacity is not actually valid. The present study suggests a cautious selection of δ⁄φ' parameter for square anchors and anchors laid at H/B<4.