Effect of soil drainage on california bearing ratio of soaked clay

Abstract

The quality of pavement is affected mostly by the type of subgrade soil, and in many countries, the subgrade soil is clay. The California Bearing Ratio CBR of clay is generally very low which leads to a thicker layer of pavement and sub base materials. This increase in quantities leads to a significant increase in cost. Since the use of the clay as subgrade is inevitable, many private and public institutions searched on a way to increase its CBR, but most of the conducted studies focused on increasing clay CBR by reinforcing the clay either by geogrids or by fibers which are very expensive. One common finding in all the studies was that the CBR of unsoaked clay is higher than CBR of soaked one which means that CBR of clay is affected by its moisture content. In our work, the objective is to increase the CBR of clay by draining it instead of reinforcing it. Drainage can be obtained by adding a layer of granular soil between clay layers. Sand was used as granular soil for the sake of its workability in the CBR mold and for its relatively small particles size. Our aim is to verify if sandy layer can play a drainage role for the clayey soil and to also find the most efficient position of the sandy layer. We collected six soils from different regions to cover as much as possible the different clay types in Lebanon. For each soil, we found CBR values for clay alone and clay with layer of sand and compared them. Identification tests were necessary in order to build our analysis. At the end, from the results and analysis, we found the position of the sandy layer which increases most the clay CBR and we proved that the existence of sandy layer is beneficial for CBR of clay.