Study on the variation of subgrade strength with the number of days soaked

Abstract

This study presents how the subgrade strength losing with increasing of number of days soaked. The objective of this study to understand the nature of variation of subgrade strength with moisture content and propose a behaviour model for subgrade 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. Variation in moisture content roots variation in subgrade strength. It becomes quite crucial for an engineer to realize the exact nature of dependence of subgrade strength on moisture content. In this study variation of subgrade strength with the number of days soaked was studied by considering, the variation of subgrade strength with days soaking and to analyse the relationship between subgrade strength and days soaking by used regression analysis and statistical Mnitab16 software. 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 there is a significant correlation between moisture content of subgrade soil and number of days soaked. On increasing the number of days of soaking, the subgrade strength decreases due to rises of moisture content, further increasing the number of days of soaking, gradual but not dramatic loss of strength is observed. The rate of increase of moisture content decreases with days of soaking due to subgrade about to saturation. More amount of water absorption on the first day of soaked was the reason for the highest drop in subgrade strength (CBR) of the subgrade soil sample. The conclusions of this study based on the laboratory results and analysis which are applicable to the materials used and the test conditions adopted. So it will help design a good road pavement because subgrade is the foundation of road pavement.