Optimization of unconfined compressive strength of fine-grained soils modified with polypropylene fibers and additive materials

A number of studies have been conducted recently to investigate the influence of randomly oriented fibers on some engineering properties of cohesive and cohesionless soils. However, few studies have been carried out on fine-grained soils modified with discrete fiber inclusions and additive materials. This experimental study was performed to investigate the effect of randomly distributed Polypropylene fibers (PP) and some additive materials [e.g., Borogypsum (BG), Fly Ash (FA) and Cement (C)] on unconfined compressive strength of a fine-grained soil cured for 7,14 and 28 days. The Taguchi method was applied to the experiments and a standard L9 Orthogonal Array (OA) with four factors and three levels were chosen. A series of unconfined compression tests (7, 14 and 28 days) were conducted on each specimen. 0-20% BG, 0-20% FA, 0-0.25% PP and 0-3% of C by total dry weight of mixture were used in the preparation of specimens. Experimental results showed that the most effective material for increasing the unconfined compressive strength of the samples was poly propylene fiber. The values of unconfined compressive strength for curing times of 7, 14 and 28 days in optimum conditions were 0.94 MPa, 1.25 MPa and 1.95 MPa, respectively.