Enhancing subgrade strength of rural roads constructed on soft soils using varied grades of Coir fiber

Abstract

With the urbanization in Sri Lanka, shortage of land for pavement construction has become a major issue as Engineers are supposed to resort to constructing pavements in areas with problematic soils. These problematic soils are commonly clays and silts due to their characteristics of high swell-shrinkage and poor load-bearing ability. "Excavation and Replacement" is conventional for subgrade alteration, but is expensive and time-consuming. Currently, subgrade modification includes the application of natural and synthetic reinforcement. Glass fibers, nylon fibers, polyester fibers (PET), polypropylene fibers (PP), and polyethylene fibers (PE) are geosynthetics. Natural fibers like coir, sisal, palm and kenaf are increasingly popular as they are affordable and environmentally beneficial. Two types of coir fiber (Mattress fiber and Bristle fiber) of 0.25% to 0.75% percentages with 0.25% increments and lengths between 1cm and 3 cm was considered in this study. Potential for increasing the soil's load- bearing ability has been evaluated through laboratory analysis, such as Hydrometer analysis, Standard Proctor Compaction (SPC) test, and California Bearing Ratio (CBR) test. The findings demonstrate that weak soils can be stabilized by adding bristle fiber (0.75% of the soil's dry weight) to reach a CBR value of 2.61%, or 2.15 times that of the control sample.