Use of coir geotextiles in unpaved road construction

ABSTRACT: This paper reports the beneficial effect of five varieties of coir product inclusion (three types of woven coir geotextile and two types of hand-knotted coir netting) on the California bearing ratio (CBR) behaviour of four soils: a natural soft clay; a commercially available soft clay; lateritic soil; and sand over soft clay subgrade. The study indicates that CBR improvement sufficient to eliminate the need for a strong base course in unpaved roads is achievable through the use of these coir products. Woven coir geotextiles are found to perform much better (about a twofold improvement) than hand-knotted coir nettings (about a 1.5-fold improvement). Lateral confinement of the soil within the cells of the geotextile/netting is identified as the principal reinforcement mechanism. The general strength mobilisation theory applicable to geosynthetic reinforcements, according to which the lower the CBR value of the subgrade is, the higher is the degree of improvement due to reinforcement inclusion, is not valid for coir geotextiles and nettings. The paper also highlights the importance of testing under soaked conditions, even for non-swelling soils.