Effects of Capillary rise on Properties of Subgrade Soils: Case study on Jimma to Bedele Road

Abstract

Design of the pavement layer to be laid over the subgrade soil can start with the estimation of subgrade strength or capacity and the volume of traffic to be carried. Various pavement layers are very much dependent on the strength of subgrade soil over which they are going to be laid. The subgrade soil can be subjected to change in moisture or saturation level due to capillary rise/saturation (hc). Change in moisture level in subgrade soil causes change in mechanical properties of subgrade material leading to pavement weakness and it can be quite essential for engineers to understand the effects of capillary rise on the variation of moisture in subgrade soil and effects on the strength properties. The hydraulic conductivity of subgrade soil can be strongly dependent on the texture (contents), grain size, densities and voids of the soil. Keeping this in mind this study has been carried out to evaluate the effects capillary rise/saturation on properties of subgrade soil. This research has also shown that measuring the height of capillary rise/saturation through, rate capillary rise through and effects of capillary saturation on the strength properties of subgrade soil. The strength properties of subgrade soil is mostly expressed in terms of CBR and understanding the dependence of CBR strength of subgrade soil on water content (moisture variation) contribute better towards the design and maintenance practices. The strength of subgrade soil may vary largely on the amount of saturation in it. Hence in this research experimental investigation has been made are to determine hydraulic conductivity (rate of capillary rise) of the subgrade soil at different level of densities and height of capillary rise through subgrade soil and important geo-technical properties specific gravity, liquid limit, plastic limit, plasticity index, free swell index, Dry density and California Bearing Ratio at different level saturation from day (0) to day (4) through the purposive sampling for each station. It observed that for each stations (type) subgrade soils, Hydraulic conductivity or rate capillary rise of subgrade soil within any densities and the strength properties reduced. For type one soil at station 25+200 subgrade soils, the CBR values reduced by 82% to the un soaked condition or no change in moisture and for second type at station 35+00 soils, the CBR values reduced by 77.3% to Unsoaked condition. This review Provide a subgrade soil with non-susceptible to hydraulic conductivity which can reduces flow of water through them which is providing the subgrade soil with a minimum diameter of grain size with corresponding to 10% finer in the distribution and further study should be carried out on the other factor that cause variation of moisture in a subgrade soil.