Effect of vetiver root on triaxial shear strength of a cohesionless soil

Abstract

ABSTRACT This paper describes an investigation of sandy soil reinforced with vetiver (Vetiver zizanoides) root. Vetiver roots were chosen because of root morphology and root system. Consolidated drained (CD) triaxial compression tests were done on thirty reconstituted samples, mostly of sand-root matrix, where the emphasis was given to prepare the samples more-or-less for a fixed moisture content and density. Among these, three samples were prepared using clean sand for comparison and others were prepared reinforced with vetiver roots. In case of sand-root matrix, root length (RL) and root content (RC), defined as the percent weight of root on total sample weight, were varied in the range 2.54 ~ 6.4 cm and 1.0 ~ 3.5%, respectively. Shear strength parameters were determined from CD triaxial shear tests in the form of apparent cohesion c and angle of internal friction ϕ. The test result shows that the inclusion of root increases the overall strength of soil while decreasing ϕ (compared to the value bared sand) and increasing c, which was zero for bared soil. The increase of c was substantial and in the range of 18–64 kPa. It appeared that for each RC, there exists an optimum RL for which apparent cohesion, and hence overall strength was maximum.