Bearing capacity and settlement behavior of square footing on coir geocell–reinforced sand under concentric and eccentric loading

Shallow foundations on weak or marginal soils require reinforcement systems that increase the bearing capacity while limiting settlement and rotation under realistic loading states. Natural fiber geocells have gained importance in sustainable geotechnics because cellular confinement can be combined with biodegradable reinforcement. The response of square footings on coir geocell-reinforced sand under eccentric loading remains insufficiently established after geometric optimization of the reinforcement layer. This study aims to quantify the bearing capacity, settlement, heave, stiffness, and tilt responses of square footings on coir geocell-reinforced sand under concentric and eccentric loading. The laboratory model plate load tests were conducted in two phases. The embedment depth, width, and height of the coir geocells were varied under concentric loading to identify the optimum configuration, after which the optimized system was tested at [Formula: see text], 0.10, [Formula: see text], and 0.25, using the bearing capacity ratio and reduction factor. The results indicate that the optimized coir geocell increased the bearing capacity ratio to 2.65 at 10% settlement and reduced surface heave by 64%, demonstrating efficient confinement and load spreading in sand. The reduction factor increased by 11.5% within the kern and decreased by 11% beyond the kern relative to the unreinforced bed, indicating that the kern boundary is a critical threshold for the reinforcement efficiency. The footing tilt rate decreased by 30.73%, 22.39%, and 21.59% at [Formula: see text], [Formula: see text], and 0.25, respectively, confirming the sustained serviceability benefits under asymmetric loading. These results support the use of coir geocells as sustainable reinforcements for shallow foundations in temporary and medium-service applications. Future work will examine the durability, cyclic loading, and field-scale responses across various pocket sizes and soil states.