EFFECT OF FINE-GRAINED SOIL LAYER THICKNESS ON THE PERFORMANCE OF MODIFIED CAPILLARY BARRIER SYSTEM
DOI:
https://doi.org/10.11113/mjce.v27.15942Keywords:
Capillary barrier, unsaturated drainage layer, fine-grained layer, breakthroughAbstract
Slope instability due to rainfall infiltration constitutes major natural disasters in many tropical countries covered by residual soil. In these types of soils, groundwater table usually exist at considerable depth with significance thickness of unsaturated soil above water table. Negative pore water pressure or matric suction exist in the unsaturated soils and contributes additional shear strength to the soil. However, the matric suction reduces due to rainfall infiltration and invariably reduces the additional shear strength provided by the matric suction. The principle of capillary barrier is amongst the methods employed to reduce infiltration of rainfall into unsaturated soil and the infiltrating water into the system is stored in the upper (fine-grained) soil layer. Therefore, this paper highlights the effect of different thickness of fine-grained soil layer on performance of a modified capillary barrier system using numerical modelling approach. The capillary barrier was constructed from residual soils and subjected to three different rainfall intensities of 1 hour, 24 hour and 7 day. The thickness of fine-grained soil layer was varied from 0.1 m to 0.3 m while the coarse-grained soil layer and the unsaturated drainage layer were maintained as 0.3 m and 0.1 m respectively. The results shows that 0.3 m thick fine-grained soil layer is more effective in preventing breakthrough occurrence in case of capillary barrier without unsaturated drainage layer. However, when the capillary barrier was modified with gravel as unsaturated drainage layer, 0.1 m thick fine-grained soil layer was sufficient to prevent breakthrough occurrence for 1 hour and 24 hour rainfall intensities. In the case of 7 day rainfall intensity, breakthrough occurred after 4th day of rainfall infiltration in all the varied thicknesses of the fine-grained soil layer. Therefore modified capillary barrier with unsaturated drainage layer enhance the performance of capillary barrier system by transporting the infiltrating water before breakthrough occurrence. Similarly, it helps in reducing the thickness of fine-grained soil layer.References
Ahn, T. B., Cho, S. D. and Yang, S. C. (2002). Stabilization of soil slope using geosynthetic
mulching mat. Geotextiles and Geomembranes. 20(2), 135-146.
ASTM (2008). Standard Test Methods for Determination of the Soil Water Characteristic Curve
for Desorption Using Hanging Column, Pressure Extractor, Chilled Mirror Hygrometer,
or Centrifuge, Designation D6836, American Society for Testing and Materials,. West
Conshohocken, United States:
BSI (1990). Methods of Test for Soils for Civil Engineering Purposes (BS 1377:Part 1-9).
British Standards Institution, London.
Fredlund, D. G. and Rahardjo, H. (1993). Soil Mechanics for Unsaturated Soils. John Wiley &
Sons, Inc.
Gumbel, E. J. (1958). Statistics of Extremes. New York: Columbia University Press.
Khire, M., Benson, C. and Bosscher, P. (2000). Capillary Barriers: Design Variables and Water
Balance. Journal of Geotechnical and Geoenvironmental Engineering. 126(8), 695-708.
Krisdani, H., Rahardjo, H. and Leong, E. (2005). Behaviour of Capillary Barrier System
Constructed using Residual Soil Waste Containment and Remediation (26pp. 1-15).
Leong, E. C. and Rahardjo, H. (1997). Permeability Functions for Unsaturated Soils. Journal of
Geotechnical and Geoenvironmental Engineering. 123(12), 1118-1126.
Li, J. H., Du, L., Chen, R. and Zhang, L. M. (2013). Numerical investigation of the performance
of covers with capillary barrier effects in South China. Computers and Geotechnics.
(0), 304-315.
Md.Noor, M. J. (2011). Understanding Rainfall-Induced Landslide. UiTM Press: Universiti
Teknologi Mara, Shah Alam, Malaysia.
Morris, C. E. and Stormont, J. C. (1997). Capillary Barriers and Subtitle D Covers: Estimating
Equivalency. Journal of Environmental Engineering. 123(1), 7.
Rahardjo, H., Hritzuk, K. J., Leong, E. C. and Rezaur, R. B. (2003). Effectiveness of horizontal
drains for slope stability. Engineering Geology. 69(3–4), 295-308.
Rahardjo, H. and Leong, E. C. (2002). Horizontal Drains in Unsaturated Soil Slopes.
Proceedings of the 2002 3rd International Conference on Unsaturated Soils 10-13
March. Recife, Brazil, 773-777.
Rahardjo, H., Santoso, V. A., Leong, E. C., Ng, Y. S., Tam, C. P. H. and Satyanaga, A. (2013).
Use of recycled crushed concrete and Secudrain in capillary barriers for slope
stabilization. Canadian Geotechnical Journal. 50(6), 662-673.
Rahardjo, H., Leong, E. C., Satyanaga, A., Song, N. Y., Tuan, T. H. and Juay, H. C. (2014).
Rainfall-Induced Slope Failures and Preventive Measures in Singapore Geotechnical
Engineering Monograph, NTU-HDB Research Collaboration, NTU, Singapore.
Rahardjo, H., Leong, E. C., Michael, S. D., Jason, M. G. and Tang, S. K. (2000). Rainfall
Induced Slope Failures Geotechnical Engineering Monograph 3, NTU-PWD
Geotechnical Research Centre, NTU, Singapore.
Rahardjo, H., Santoso, V. A., Leong, E. C., Ng, Y. S. and Hua, C. J. (2012). Performance of an
Instrumented Slope Covered by a Capillary Barrier System. Journal of Geotechnical
and Geoenvironmental Engineering. 138(4), 481-490.
Ross, B. (1990). The diversion capacity of capillary barriers. Water Resources Research. 26(10),
-2629.
Simms, P. H. and Yanful, T. K., 2004. Estimation of Soil-Water Characteristic Curve of Clayey
Till Using Measured Pore-Size Distributions. Journal of Environmental Engineering,
ASCE. Vol. 130, No. 8, pp. 847-854.
Stormont, J. C. (1996). The effectiveness of two capillary barriers on a 10% slope. Geotechnical
& Geological Engineering. 14(4), 243-267.
Stormont, J. C. and Anderson, C. E. (1999). Capillary Barrier Effect from Underlying Coarser
Soil Layer. Journal of Geotechnical and Geoenvironmental Engineering. 125(8), 641-
Stormont, J. C. and Morris, C. E. (1997). Unsaturated Drainage Layers for Diversion of
Infiltrating Water. Journal of Irrigation and Drainage Engineering. 123(5), 364-366.
van Genuchten, M. T. (1980). A closed-form Equation for Predicting the Hydraulic Conductivity
of Unsaturated Soils. Soil Science Society of America Journal. 44(5), 892-898.
