Study on the impact of moisture content on subgrade strength

Abstract

This study presents the relationship between subgrade strength and moisture content. Major function of subgrade is to provide support to pavement. Subgrade soil type, compacted density and moisture significantly affect pavement design. Surface and subsurface drainage of pavement and from adjoining land also affect subgrade strength significantly. Subgrade strength is mostly expressed in terms of California Bearing Ratio. The subgrade strength owing to its inconsistency or variable nature poses a challenge for the engineer to come up with a perfect design pavement. For example, the subgrade is always subjected to change in its moisture content due to precipitation, capillary action, and flood or subside of water table. Change in moisture content causes change in subgrade strength. It becomes quite essential for an engineer to understand the exact nature of dependence of subgrade strength on moisture content. In this study variation of subgrade strength with moisture content was studied considering, the variation of subgrade strength with days soaking and to analyse the relationship between subgrade strength, moisture and days soaking by used statistical software Mnitab16. Thus the different soil samples were tested for their proctor density, optimum moisture content, California Bearing Ratio after being soaked in water for 1 day, 2 days, 3 days and 4 days and Un-soaked for each sample. Study shows that a strong curvilinear correlation between subgrade strength and moisture content. On increasing number of days of soaking, subgrade strength decreases due to increases of moisture content. The rate of change in subgrade strength per percentage change in moisture content during un-soaked from the optimum moisture content was one to seven times larger than during soaking for four days from optimum moisture content with the average of about five times. So it will help design a good road pavement because subgrade is the foundation of road pavement.