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This paper describes the results of a study into the undrained response of clay specimens reinforced with sand-coir fiber cores in triaxial tests. Coir, used to reinforce sand, is the processed fiber from the husk of coconuts. Coir combines the properties of biodegradability and fiber strength, and remains an under-utilized material of great potential value for ground improvement in parts of the world where such materials are available in abundance. A thin PVC pipe kept centrally inside a split mold is used to form the core in the triaxial tests. The clay is placed inside the mold around the PVC pipe at maximum dry unit weight—optimum moisture content condition while the sand-coir mixture is placed inside the pipe at the same bulk unit weight as that of clay. Influence of variables such as replacement area ratio (ratio of cross-sectional area of sand-coir fiber core to that of the triaxial test specimen), confining pressure, fiber content, and fiber aspect ratio on the behavior of the composite soil specimen is identified and isolated. It is found that stress-strain strength properties of clay specimens reinforced with sand-coir fiber core is appreciably better not only when compared with untreated clay specimens but with sand core reinforced clay specimens as well. Such an improvement is of importance to allow reduced requirement of sand and increased use of natural fiber. An optimum fiber content of 1 % (by weight) was identified for strengthening of the sand core. The reinforcement effect is found to increase appreciably with increase in replacement area ratio and to a smaller extent with increase in fiber aspect ratio. The larger reinforcement effect observed at higher confining pressures suggests that the proposed method is more effective at greater depths.

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This note pertains to an experimental study made on model square footings underlain by woven coir geotextile-reinforced sand. About three-fold improvement in strength was obtained with the use of even a single layer of reinforcement, which suggests that woven coir geotextile is an appropriate material for subsoil improvement. A comparison of the results with those reported in the literature indicates that reinforced soil behaviour and the resulting strength improvement are unique for each reinforcement type and configuration. An equation that would help in obtaining strength improvement of footings on woven coir geotextile-reinforced sand is also presented. If the durability of the coir is increased, woven coir geotextiles would become a preferred material for soil reinforcement in a few countries where coir is abundantly available at practically no cost.

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