Effect of interbedded sandy layer on CBR of clayey soil

Abstract

The quality of pavement is affected mostly by the type of sub-grade soil, and in many countries, the sub-grade 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 sub-grade 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 geo-grids 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 and reduce the moisture content and thus increase the CBR of this clay subgrade. 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 imbedded with sand and compares 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 the clay CBR and we proved that the existence of sandy layer is beneficial of CBR value of clay.