NSF (Nylon Synthetic Fiber) Effectiveness in Stabilizing Weak Subgrade Soil: An Experimental Investigation

Abstract

Improvement in subgrade soil has always been an area of concern for highway and geotechnical engineers. Weak subgrade soil results in a greater thickness of the pavement layer, which increases the cost of pavement construction. It further leads to large deformations, which in turn cause continuous deterioration of the paved surface. To solve this problem, various engineering solutions and soil improvement mechanisms were previously proposed. Tis study was designed to investigate the stabilization of weak subgrade soil with nylon synthetic fber (NSF) in a compromising combination. Previously, some investigations used a lower fber content with a higher fber length, whereas others used a lower fber length with a higher fber content. However, this investigation was uniquely designed to stabilize weak subgrade soil with the consideration of appropriate fber length (10 mm and 20 mm) and content (0.5%, 1%, 1.5%, and 2.5%). Te engineering properties of the soil, the efect of NSF on weak subgrade soil, various fber content and aspect ratios, and the optimum content and critical fber aspect ratio were investigated in a laboratory. Te efect of fbers on compaction, CBR values, and CBR swell values has also been studied. Laboratory results on the modifed compaction tests showed that maximum dry density (MDD) was increased with the increment of fber content, whereas optimum moisture content (OMC) remained constant. Te soaked CBR and CBR swell values of natural soil were 1.80% and 8.95%, respectively. Due to reinforcement, the percentage increase in soaked CBR value at the optimum NSF content is 265.3, 310.0, 282.8, and 342.2 for aspect ratios of 33.33, 66.67, 25, and 50, respectively, with reference to natural soil. Also, the percentage decrease in swelling is 34.7, 52.75, 43.55, and 36.9, respectively. Moreover, the CBR value increases with the increase in aspect ratio by keeping the diameter constant and decreases with the increase in aspect ratio by keeping the length constant. It was also observed that increasing the length and diameter of NSF further increased the CBR value of reinforced soil. Tis increment was substantial at a fber content of 1.5% for an aspect ratio of 50 (length � 20 mm, diameter � 0.4 mm). Tere was also a decrease in the CBR swelling value with an increase in fber content. Finally, this investigation concluded that the use of NSF is a solution to weak soils with regard to moisture and performance problems