Laboratory investigation of drainage cell as transport layer in residual soils

Abstract

The results of laboratory investigation of transport layer using drainage cell system are presented in this paper. The drainage cell was sandwiched between grade V and grade VI residual soil in a two-dimensional laboratory slope model. Coarse particles of gravel were compacted inside the holes of the drainage cell to facilitate capillary break development and modify hydraulic properties between the soil layers. The grades V and VI residual soils were compacted in the slope model to their dry densities. The whole set up was subjected to three rainfall patterns of 1.0586 x 10-5 m/s, 1.2014 x 10-6 m/s and 3.7337 x 10-7 m/s for 2 hour, 24 hour and 7 day, respectively. These rainfall intensities were applied through a rainfall simulator which is part of the laboratory set up. The results show that inclusion of drainage cell in between the two soil layers impedes percolation of the infiltrating water into the lower grade V residual soil layer and facilitates lateral movement of the infiltrating water along the grade VI and transport layer interface towards the toe of the slope model. Similarly, it provides a definite direction through which the infiltrating water can further flow and diverted laterally in case it percolates the drainage cell due to prolonged rainfall pattern.