Pullout Capacity of Ground Anchors in Non-homogeneous Cohesive–Frictional Soil

Anchors are widely applied as the foundation of structures where significant pullout load is expected. Among various kinds of anchors, plate anchors are frequently employed in practice. The vast majority of the previous works have focused on the pullout capacity of the plate anchors either in undrained homogeneous and non-homogeneous clay or in drained homogeneous sand. The present work has studied the holding capacity of a horizontal anchor plate, subjected to pure vertical pull in homogeneous as well as non-homogeneous cohesive–frictional soil for different combinations of (i) normalized cohesion (c₀/γB), (ii) soil frictional angle (ϕ), and (iii) normalized increment factor of cohesion below ground level (r_c), where c₀ represents the cohesion of soil at the ground level, γ represents the soil unit weight, and B represents the width of the plate. The vertical pullout load (Q_u) of the horizontal strip anchor plate is computed using lower bound limit analysis, in conjunction with finite element discretization. The results have been exhibited in a non-dimensional form as Q_u/c₀B. It has been observed that the non-dimensional pullout capacity (Q_u/c₀B) increases almost linearly with H/B as long as the measure of ϕ is low; whereas, in case of larger values of ϕ, the increment is non-linear. In addition, the non-dimensional pullout capacity Q_u/c₀B has been observed to increase considerably with an increment in r_c. Although lower bound limit analysis is appropriate for associated flow rule materials, the present analysis has been extended considering non-associated flow rule materials for a few cases by utilizing reduced shear strength parameters. The non-dimensional pullout capacity has been observed to reduce slightly in the case of non-associated flow rule materials, especially for higher values of ϕ. Since the lower bound limit analysis gives the conservative estimation of the ultimate load; therefore, the results computed in this analysis can be used safely for the designing purpose.