Influence of Tie Beams on the Settlement Behavior of Isolated Footings on Heterogeneous Ground

Isolated pad foundations are commonly used in low-rise structures and are often connected with tie beams, although their contribution to settlement control is typically underestimated. This study investigates the influence of tie beams on the performance of footings resting on heterogeneous ground comprising sand and peat. Two small-scale physical model tests conducted with and without tie beams were used to calibrate a three-dimensional finite-element model, which was then extended for parametric analyses. The results show that tie beams significantly increase system stiffness, reduce total settlement on weak peat by 73%–79%, and decrease differential settlement by about 78%, lowering angular distortion from 106/300 to 23/300. Without tie beams, settlement propagated to a depth of roughly 5B (where B is the footing width), whereas tie beams confined deformation to about 3.5B, demonstrating their ability to restrict deep-seated movement. Parametric studies revealed that with partial soil improvement, tie-connected systems achieved near-zero differential settlement at an improved thickness of 1.5B, while unconnected systems required full improvement of the peat layer (approximately 3B). Lateral improvement up to 1.5B was also sufficient when combined with tie beams. The findings highlight how tie beams, with limited ground improvement, provide a cost-effective and sustainable approach for managing settlement on variable ground.