Horizontal capacity of single piles: an extension of Broms’ theory for c-ϕ soils

Several methods are available for the evaluation of the horizontal capacity of piles in cohesionless (c′ = 0) or in purely cohesive (su > 0 and ϕu = 0) soils. In this paper, the well-known theory by Broms (1964a, 1964b) is extended to soils possessing both cohesion and friction (c-ϕ soils). A simple profile of the ultimate soil pressure (plim) with depth is assumed, accounting for soil cohesion and pile embedment and encompassing Broms’ profile for drained loading. By considering translational and rotational equilibrium, equations for the different mechanisms of failure – short, intermediate and long piles - are given. The results are also presented in the form of non-dimensional graphs, allowing for an expeditious evaluation of the horizontal capacity of piles and the maximum bending moment. For most cases, it is found that giving consideration to the soil’s effective cohesion (c′) can lead to significant advantages in terms of increased pile capacity and the consequent reduction in pile dimensions and costs. A comparison of the proposed solution with some documented field cases allows for the first validation of the study.