Contribution of hand-knotted coir netting to the bearing capacity of loose sand

ABSTRACT: This paper reports the effect of the inclusion of a new variety of coir product (hand-knotted coir netting) on the bearing capacity of a model footing on loose sand. A series of conditions were considered by varying parameters such as coir netting type, length of coir netting, depth of embedment, number of layers, and vertical spacing between layers of the netting. The preliminary test results indicate that hand-knotted coir netting can be expected to be as effective as many of the synthetic reinforcing materials used previously. Of the two varieties of coir netting used, type NA2 with 20–22 knots per running metre is the better choice for reinforcement. The provision of a single layer of coir netting at an embedment depth between 0.25 and 0.4 times the footing width is found to result in about a threefold improvement in strength. Multi-layer coir netting reinforcement is most effective when placed in three layers within a depth of 0.4 to 0.6 times the footing width beneath the base of the footing. The optimum beneficial effect is realised for a reinforcement length to footing width ratio of 3. Equations are also presented for obtaining a qualitative estimate of the strength improvement of footings on sand reinforced with single and multiple layers of coir netting for different reinforcement configurations. The work reported opens up scope for future research on durability enhancement and prototype testing of hand-knotted coir netting, and for possible large-scale production of the netting on a commercial basis.