Sains Malaysiana 40(10)(2011): 1065–1073

Soil-root Shear Strength Properties of Some Slope Plants

(Sifat Kekuatan Ricih Tanah-Berakar Beberapa Tumbuhan Cerun)

Normaniza Osman* & Mohamad Nordin Abdullah

Institute of Biological Sciences, Faculty of Science, University of Malaya

50603 Kuala Lumpur, Malaysia

Faisal Haji Ali

Department of Civil Engineering, Faculty of Engineering, University of Malaya

50603 Kuala Lumpur, Malaysia

Diserahkan: 21 Mei 2010 / Diterima: 10 Februari 2011

ABSTRACT

Rapid development in hilly areas in Malaysia has become a trend that put a stress to the sloping area. It reduces the factor of safety by reducing the resistant force and therefore leads to slope failure. Vegetation plays a big role in reinforcement functions via anchoring the soils and forms a binding network within the soil layer that tied the soil masses together.  In this research, three plant species namely Acacia mangium, Dillenia suffruticosa and Leucaena leucocephala were assessed in term of their soil-root shear strength properties. Our results showed that Acacia mangium had the highest shear strength values, 30.4 kPa and 50.2 kPa at loads 13.3 kPa and 24.3 kPa, respectively. Leucaena leucocephala showed the highest in cohesion factor, which was almost double the value in those of Dillenia suffruticosa and Acacia mangium. The root profile analysis indicated Dillenia suffruticosa exhibited the highest values in both root length density and root volume, whilst Leucaena leucocephala had the highest average of root diameter.

Keywords: Angle of friction; cohesion factor; factor of safety; root length; shear strength

ABSTRAK

Pembangunan pesat di kawasan berbukit di Malaysia menjadi satu trend dan ini memberi tekanan kepada kawasan cerun. Ianya mengurangkan faktor keselamatan dengan pengurangan daya tahan yang boleh menyebabkan ketidakstabilan cerun. Vegetasi memainkan peranan penting dalam fungsi penguatan dengan membentuk rangkaian ikatan pada lapisan tanah. Berlandaskan kepada kepentingan terhadap penguatan tanah-akar ini, kajian telah dijalankan ke atas tiga spesies tumbuhan iaitu Acacia mangium, Dillenia suffruticosa dan Leuceana leucocephala dan pokok-pokok ini diuji daripada segi ciri-ciri kekuatan ricih tanah-akarnya. Keputusan menunjukkan Acacia mangium mempunyai kekuatan ricih yang tinggi iaitu 30.4 kPa dan 50.2 kPa pada beban 13.3 kPa dan 24.3 kPa, secara berturutan.  Leucaena leucocephala menunjukkan nilai faktor kohesi yang paling tinggi iaitu hampir dua kali ganda berbanding Dillenia suffruticosa dan Acacia mangium. Daripada segi analisis profil akar, Dillenia suffruticosa menunjukkan nilai yang tinggi bagi kedua-dua ketumpatan akar dan juga isipadu akar manakala Leucaena leucocephala mempunyai nilai purata diameter akar yang paling tinggi.

Kata kunci: Faktor kohesi; faktor keselamatan; kekuatan ricih; panjang akar; sudut geseran

RUJUKAN

Abe, K. & Iwamoto, M. 1986. Preliminary Experiment on Shear in Soil Layers with a Large Direct-Shear Apparatus. Journal of the Japanese Forestry Society 68(2): 61-65.

Abe, K. & Ziemer, R.R. 1990. Effect of Tree Roots on Shallow-Seated Landslides. Presented at the Subject Group S1.04 Technical Session on Geomorphic Hazards in Managed Forests, XIX World Congress, International Union of Forestry Research Organizations, August 5-11, Montreal, Canada.

Abe, K. & Ziemer, R.R. 1991. Effect of tree roots on a shear zone: modelling reinforced shear stress. Canadian Journal of Forest Research 21: 1012-1019.

Alday, J.G., Marrs, R.H. & Ruiz, C.M. 2010. The importance of topography and climate on short-term revegetation of coal wastes in Spain. Ecological Engineering 36: 579-585.

Anisuzzaman, G.M., Nakano, T. & Masuzawa, T. 2002. Relationships between soil moisture content and root morphology of three herbs on alpine scoria desert of Mt. Fuji. Polar Bioscience 15: 108-113.

Baets, S., De, Poesen, J., Torri, D. & Salvador, M.P. 2009. Modelling increased soil cohesion by plant roots with EUROSEM. EGU General Assembly 2009.11

Bankhead, N.P. & Simon, A. 2010. Hydrological and hydraulic effects of riparian root networks on streambank stability: Is mechanical root-reinforcement is the whole story? Geomorphology 116: 353-362.

Burylo, M., Rey, F. & Delcros, P. 2007.Abiotic and biotic factors influencing the early stages of vegetation colonization in restored marly gullies (Southern Alps, France) Ecological Engineering 30: 231-239.

Collison, A.J.C., Anderson, M.G. & Llyod, D.M. 1995.Impact of vegetation on slope stability in a humid tropical environment: a modelling approach. Proc. Instn .Civ. Engrs Wat., Marit. & Energy 112: 168-175.

Danjon, F., Barker, D.H., Drexhage, M. & Stokes, A. 2007. Using Three-dimensional Plant Root Architecture in Models of Shallow-slope Stability. Annals of Botany 101(8): 1281-1293.

Danjon, F. & Reubens, B. 2008. Assessing and analyzing 3D architecture of woody root systems, a review of methods and applications in tree and soil stability, resource acquisition and allocation. Plant and Soil 303: 1-34.

Devkota, B.D., Paudel, P., Omura, H., Kubota, T. & Morita, K. 2006. Uses of Vegetative Measures for Erosion Mitigation in Mid Hill Areas of Nepal. Kyushu Journal of Forest Research 59(3): 265-268.

Docker, B.B. & Hubble, T.C.T. 2008. Quantifying root-reinforcement of river bank soils by four Australian tree species. Geomorphology 100: 401-408.

Dowell, G.R. & Bolton, M.D. 1998. On the micromechanics of crushable aggregates. Geotechnique 48(5): 667-79.

Fan, C.C. & Su, C.F. 2008. Role of roots in the shear strength of root-reinforced soils with high moisture content. Ecological Engineering 33 (2): 157-166.

Florineth, F., Rauch, H.P. & Staffler, H. 2002. Stabilization of landslides with bio-engineering measures in South Tyrol/Italy and Thankot/Nepal. International Congress INTERPRAEVENT 2002 in the Pacific Rim- Matsumoto/Japan Congress Publication 2: 827-837.

Genet, M., Stokes, A., Fourcoud, T. & Norris, J.E. 2010. The influence of plant diversity on slope stability in a moist evergreen deciduous forest. Ecological Engineering 36: 265-275.

Gray, D.H. & Ohashi, H. 1983. Mechanics of fiber reinforcement in sand. Journal of Geotechnical Engineering 109(3): 335-3563.

Huat, B.B.K., Faisal, H.A. & Maail, S. 2005. The effect of natural fiber on the shear strength of soil. American Journal of Applied Sciences (Special Issue) 9-13.

Loades, K.W., Bengough, A.G., Bransby, M.F. & Hallet, P.D. 2010. Planting density influence on fibrous root reinforcement of soils. Ecological Engineering 36: 276-284.

Normaniza, O. & Barakbah, S.S. 2006. Parameters to predict slope stability-Soil water and root profiles. Ecological Engineering 28: 90-95.

Normaniza, O, Faizal, H.A. & Barakbah, S.S. 2008. Enginering properties of Leucaena leucocephala for prevention of slope failure. Ecological Engineering 32: 215-221.

O’Loughlin, C. 1974. The effect of timber removal on the stability of forest soils. Journal of Hydrology 13(2): 121-134.

Petrone, A. & Preti, F. 2010. Soil bioengineering for risk mitigation and environmental restoration in a humid tropical area Hydrology and Earth System Sciences 14: 239-250.

Schroeder, W.L. 1985. The engineering approach to land slide risk analysis. In: swantson, E.d (E.D,) Workshop Slope Stability: Problems and Solutions in Forest Management. February 6-8, 1984, pp 43-55.

Schwarz, M., Preti, F., Giadrossich, F., Lehmann, P. & Or, D. 2010. Quantifying the role of vegetation in slope stability: A case study in Tuscany (Italy). Ecological Engineering 36: 285-291.

Stokes, A. & Mattheck, C. 1996. Variation of wood strength in tree roots. Journal of Experimental Botany 47(298): 693-699.

Tosi, M. 2007. Root tensile strength in relationship and their slope stability implications of three shrub species in Northern Apennines(Italy). Geomorphology 87: 268-283.

van Beek, L.P.H., Wint, J., Cammeraat, L.H. & Edwards, J.P. 2005. Observation and simulation of root reinforcement on abandoned.Mediterranean slopes. Plant and Soil 278: 55-74.

Wu, T.H., Beal, P.E. & Lan, C. 1988. In-situ shear test of soil-root systems. Journal of Geotechnical Engineering, ASCE 114(12): 1379-1394.

Zhang, C.B., Chen, L.H., Liu, Y.P., Ji, X.D. & Liu, X.P. 2010. Triaxial compression test of soil–root composites to evaluate influence of roots on soil shear strength. Ecological Engineering 36: 19-26.

Zhong, Q.W., Liang, H.W. & Ting, T.L. 2009. Revegetation of steep rocky slopes: Planting climbing vegetation species in artificially drilled holes. Ecological Engineering 35: 1079-1084.

Zhou, Y., Watss, D., Li, Y. & Cheng, X. 1998. A case study of effect of lateral root Pinus yunnanensis on shallow soil reinforcement. Forest Ecology and Management 103: 107-120.

*Pengarang untuk surat-menyurat; email: normaniza@um.edu.my