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.
