A new pile-soil interface and its application in battered mini piles under monotonic lateral load in cohesive soil

Numerical modelling of laterally loaded piles requires a robust pile-soil interface model. The conventional Coulomb friction model has limitations when predicting the soil-structure interaction at shallow depths for battered mini piles (BMPs) in cohesive (fine-grained) soils. This paper proposes an efficient pile-soil interface model to simulate laterally loaded BMPs in cohesive soils using three-dimensional finite element models (FEM). BMP systems have been commonly used to support lateral load-dominated lightweight superstructures. They are hybrid foundations with BMPs oriented at different inclinations and directions, mimicking tree root systems. FEM results indicate that the Coulomb model is unsuitable for simulating the pile-soil interface at shallow depth due to underprediction of shear resistance. The proposed interface model comprising a surface-to-surface cohesive damage interface with friction captures the lateral performance of BMPs accurately. The proposed model was implemented for a range of pile and soil properties to verify its suitability in understanding the behaviour of BMPs. The ultimate lateral capacity of BMPs increases with penetration length up to 1.5 m. While an increase in diameter and undrained shear strength increases the capacity, the lateral load eccentricity negatively impacts it. Interaction diagrams are developed to serve engineers estimate the ultimate lateral capacity of BMPs.