Capillary barrier effect on the response of residual slope to rainfall infiltration

Capillary barrier effect on the response of residual slope to rainfall infiltration

Rainfall-induced slope failure is a common problem in areas covered by residual soil in tropical countries. The soil exists in unsaturated condition as ground water table is located well below the ground surface. Rainfall infiltration results in a reduction of matric suction of soil which in turn re...

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Main Author: Chai, Erwin Pak Shin
Format: Thesis
Language:English
Published: 2008
Subjects:
TA Engineering (General)
Civil engineering (General)
Online Access:http://eprints.utm.my/id/eprint/9557/1/ErwinChaiPakMFKA2008.pdf
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id my-utm-ep.9557
record_format uketd_dc
institution Universiti Teknologi Malaysia
collection UTM Institutional Repository
language English
topic TA Engineering (General)
Civil engineering (General)
spellingShingle TA Engineering (General)
Civil engineering (General)
Chai, Erwin Pak Shin
Capillary barrier effect on the response of residual slope to rainfall infiltration
description Rainfall-induced slope failure is a common problem in areas covered by residual soil in tropical countries. The soil exists in unsaturated condition as ground water table is located well below the ground surface. Rainfall infiltration results in a reduction of matric suction of soil which in turn reduces the soil shear strength, and subsequently triggers the slope failure. Natural formation of the residual soil has lead to the variation of hydraulic conductivity in which soil closer to the ground surface usually has lower permeability as compared to the deeper layer. This condition causes the development of capillary barrier effect at the interface. The water accumulates at the interface and flow for some distance down-slope before it manages to infiltrate into the deeper layer. The distance that the water has to travel before breakthrough is referred as the water diversion length. Numerical simulation using SEEP/W was performed in this study to determine the water diversion length for two cases representing natural slopes i.e. Silty SAND over SAND and Silty SAND over Highly Weathered Granite. Parametric study was performed to study the effect of several variables including hydraulic conductivity of soil, thickness of layers, slope dip angle and the rate of infiltration. Results show that the diversion length is linearly correlated with the difference in the permeability of two soil layers and slope dip angle. The effect of rainfall infiltration depends on the saturated permeability of the upper layer (MRL). The optimum thickness of MRL obtained in this study is 1.5m. Results of numerical analysis are compared with analytical method by Ross model, however good agreement between the two methods was not reached because the difference in saturated hydraulic conductivity of the soils used is not very big. Moreover, under an infiltration rate, the maximum suction existing in the CBL should be as low as possible while the maximum suction attained in the MRL should be as high as possible, which was not the case especially for Silty SAND over Highly Weathered Granite.
format Thesis
qualification_level Master's degree
author Chai, Erwin Pak Shin
author_facet Chai, Erwin Pak Shin
author_sort Chai, Erwin Pak Shin
title Capillary barrier effect on the response of residual slope to rainfall infiltration
title_short Capillary barrier effect on the response of residual slope to rainfall infiltration
title_full Capillary barrier effect on the response of residual slope to rainfall infiltration
title_fullStr Capillary barrier effect on the response of residual slope to rainfall infiltration
title_full_unstemmed Capillary barrier effect on the response of residual slope to rainfall infiltration
title_sort capillary barrier effect on the response of residual slope to rainfall infiltration
granting_institution Universiti Teknologi Malaysia, Faculty of Civil Engineering
granting_department Faculty of Civil Engineering
publishDate 2008
url http://eprints.utm.my/id/eprint/9557/1/ErwinChaiPakMFKA2008.pdf
_version_ 1747814754343190528
spelling my-utm-ep.95572018-06-29T21:50:55Z Capillary barrier effect on the response of residual slope to rainfall infiltration 2008-11 Chai, Erwin Pak Shin TA Engineering (General). Civil engineering (General) Rainfall-induced slope failure is a common problem in areas covered by residual soil in tropical countries. The soil exists in unsaturated condition as ground water table is located well below the ground surface. Rainfall infiltration results in a reduction of matric suction of soil which in turn reduces the soil shear strength, and subsequently triggers the slope failure. Natural formation of the residual soil has lead to the variation of hydraulic conductivity in which soil closer to the ground surface usually has lower permeability as compared to the deeper layer. This condition causes the development of capillary barrier effect at the interface. The water accumulates at the interface and flow for some distance down-slope before it manages to infiltrate into the deeper layer. The distance that the water has to travel before breakthrough is referred as the water diversion length. Numerical simulation using SEEP/W was performed in this study to determine the water diversion length for two cases representing natural slopes i.e. Silty SAND over SAND and Silty SAND over Highly Weathered Granite. Parametric study was performed to study the effect of several variables including hydraulic conductivity of soil, thickness of layers, slope dip angle and the rate of infiltration. Results show that the diversion length is linearly correlated with the difference in the permeability of two soil layers and slope dip angle. The effect of rainfall infiltration depends on the saturated permeability of the upper layer (MRL). The optimum thickness of MRL obtained in this study is 1.5m. Results of numerical analysis are compared with analytical method by Ross model, however good agreement between the two methods was not reached because the difference in saturated hydraulic conductivity of the soils used is not very big. Moreover, under an infiltration rate, the maximum suction existing in the CBL should be as low as possible while the maximum suction attained in the MRL should be as high as possible, which was not the case especially for Silty SAND over Highly Weathered Granite. 2008-11 Thesis http://eprints.utm.my/id/eprint/9557/ http://eprints.utm.my/id/eprint/9557/1/ErwinChaiPakMFKA2008.pdf application/pdf en public http://dms.library.utm.my:8080/vital/access/manager/Repository/vital:69276?site_name=Restricted Repository masters Universiti Teknologi Malaysia, Faculty of Civil Engineering Faculty of Civil Engineering Agus, S.S., E.C. Leong and H. Rahardjo (2005). “Estimating Permeability Functions of Singapore Residual Soils“. Journal of Engineering Geology, April, Vol. 78, No. 1-2, pp. 119-133. American Society For Testing and Materials (1980). Natural Building Stones; Soil and Rock. Annual Books of ASTM Standards, Part 19. GEO-SLOPE International Ltd. Seep/W User’s Guide for Finite Element Seepage Analysis. 2004 Calgary. Alta Canada. 2004. Gofar, N., Lee, M.L. and Kassim, A. (2007) Stability of Unsaturated Slopes Subjected to Rainfall Infiltration. Proceedings of the Fourth International Conference on Disaster Prevention and Rehabilitation, Semarang, Indonesia. 10-11 September 2007: 158-167. Lu, N., and Likos, W. J. (2004). Unsaturated Soil Mechanics. John Wiley & Sons, Inc. Milind, V. K., Craig H. B., and Peter J. B. (2000). Capillary Barriers: Design Variables and Water Balance. Journal of Geotechnical and Geological Engineering, ASCE, Vol 126, No. 8. Parent,S-E and Cabral, A. (2005). Design of inclined covers with capillary barrier effect. Journal of Geotechnical and Geological Engineering, 24,689-710. Pradel, D. and Raad, G. (1993). Effect of Permeability on Surficial Stability of Homogeneous Slopes. Journal of Geotechnical Engineering, ASCE. 119(2): 315-332. Rahardjo,H., and Fredlund, D. G (1993). Soil Mechanics for Unsaturated Soil. John Wiley & Sons, Inc. Stormont, John, C., and Clifford, E. A.(1999). Capillary Barrier Effect from Underlying Coarser Soil Layer. Journal of Geotechnical and Geological Engineering, ASCE, Vol 125, No. 8. Tami, D., Rahardjo,H., Leong, E. C., and Fredlund, D. G. (2004). A Physical Model for Sloping Capillary Barriers. Geotechnical Testing Journal, Vol 2, pp. 173-183.

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