The paper presents the effect of using cashew nut shell liquid (CNSL), a low-priced agro by-product and renewable resource, to treat coir geotextiles. Large-scale direct shear tests were performed on sands reinforced with untreated treated geotextiles at different normal stresses (50 kPa, 100 150 kPa). Sands three particle sizes (coarse, medium, fine) used for study. strength parameters soil sa...