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.
