LABORATORY INVESTIGATION OF DRAINAGE CELL AS TRANSPORT LAYER IN RESIDUAL SOILS
DOI:
https://doi.org/10.11113/jt.v78.9228Keywords:
Drainage cell, transport layer, capillary barrier, residual soilAbstract
Transport layer or unsaturated drainage layer is an alternative measure often employed to improve the performance of a capillary barrier system. A capillary barrier is an earthen cover used to prevent rainfall-induced slope failure. In this study, potential of using drainage cell system as transport layer is exploited using laboratory experimental methods. The drainage cell was sandwiched between grade V and grade VI soils in a two-dimensional laboratory slope model to act as transport layer. Coarse particles of gravel were compacted within the drainage cell to facilitate capillary break development at the interface. Each of grade V and grade VI soil was mixed with water content identical to residual water content determined from the soil water characteristic curves (SWCC) of each soil to enable simulation of their initial condition. Both soils are then compacted in the slope model to their dry densities. The whole set up was subjected to three rainfall intensities 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 determined from Intensity-Duration-Frequency (IDF) curve and were applied through a rainfall simulator which is part of the laboratory set up. The results shows that the transport layer formed with drainage cell was capable of producing capillary break and impedes percolation of the infiltrating water into the lower grade V soil layer. The accumulated water was later drained laterally above the interface of grade VI soil and drainage cell transport layer towards the toe of the slope model. In an event that the infiltrating water percolates the drainage cell transport layer due to longer rainfall duration, the drainage cell provides a definite direction through which the infiltrating water flow and diverted laterally. It was found that the modified capillary barrier with drainage cell transport layer performed much better than the conventional capillary barrier system.
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