Study Of Subgrade Strength Related To Moisture

The design of the pavement layers to be laid over subgrade soil starts off with the estimation of subgrade strength and the volume of traffic to be carried. Design of the various pavement layers are very much dependent on the strength of the subgrade soil over which they are going to be laid. Weaker subgrade demands thicker layers whereas stronger subgrade goes well along with thinner pavement layers. The Indian Road Congress encodes the exact design strategies of the pavement layers based upon the subgrade strength. Subgrade strength is mostly expressed in terms of CBR, the California Bearing Ratio. Hence, in all, the pavement and the subgrade together must sustain the traffic volume.The subgrade strength owing to its inconsistency or variable nature poses a challenge for the engineer to come up with a perfect design of pavement. For example, the subgrade is always subjected to change in its moisture content due to precipitation, capillary action, flood or abrupt rise or subsidal of water table. Change in moisture content causes change in the subgrade strength. And it becomes quite essential for an engineer to understand the exact nature of dependence of subgrade strength on moisture content. The project attempts in understanding the nature of variation of subgrade strength with water content. Thus, various soil samples are put to test for their strengths at different moisture contents by soaking them in waterbath for different days. Required inference can be drawn through the test results.