Abstract
The mechanics of root reinforcement have been described satisfactorily for a single root or several roots passing a potential slip plane and verified by field experiments. Yet, precious little attempts have been made to apply these models to the hillslope scale pertinent to landsliding at which variations in soil and vegetation become important. On natural slopes positive pore pressures occur often at the weathering depth of the soil profile. At this critical depth root reinforcement is crucial to avert slope instability. This is particularly relevant for the abandoned slopes in the European part of the Mediterranean basin where root development has to balance the increasing infiltration capacity during re-vegetation. Detailed investigations related to root reinforcement were made at two abandoned slopes susceptible to landsliding located in the Alcoy basin (SE Spain). On these slopes semi-natural vegetation, consisting of a patchy herbaceous cover and dispersed Aleppo pine trees, has established itself. Soil and vegetation conditions were mapped in detail and large-scale, in-situ direct shear tests on the topsoil and pull-out tests performed in order to quantify root reinforcement under different vegetation conditions. These tests showed that root reinforcement was present but limited. Under herbaceous cover, the typical reinforcement was in the order of 0.6 kPa while values up to 18 kPa were observed under dense pine cover. The tests indicate that fine root content and vegetation conditions are important factors that explain the root reinforcement of the topsoil. These findings were confirmed by the simulation of the direct shear tests by means of an advanced root reinforcement model developed in FLAC 2D. Inclusion of the root distribution for the observed vegetation cover mimics root failure realistically but returns over-optimistic estimates of the root reinforcement. When the root reinforcement is applied with this information at the hillslope scale under fully saturated and critical hydrological conditions, root pull-out becomes the dominant root failure mechanism and the slip plane is located at the weathering depth of the soil profile where root reinforcement is negligible. The safety factors increase only slightly when roots are present but the changes in the surface velocity at failure are more substantial. Root reinforcement on these natural slopes therefore appears to be limited to a small range of critical hydrological conditions and its mitigating effect occurs mainly after failure.
Access this chapter
Tax calculation will be finalised at checkout
Purchases are for personal use only
Preview
Unable to display preview. Download preview PDF.
References
Abe K and Ziemer R R 1991 Effect of tree roots on shallow-seated landslides USDA Forest Service, Gen. Tech. Rep. PSW-GTR-130, 11–20.
Allison L H 1935 Organic soil carbon reduction of chromic acid. Soil Sci. 40, 311–320.
BS 1990 Methods of test for soils for civil engineering purposes. Shear strength tests (effective stress). BS 1377-8, British Standards Institute.
Cammeraat L H, Van Beek L P H and Kooijman A 2005 Vegetation succession and its consequences for slope stability in SE Spain. Plant Soil 278, 135–147.
Cammeraat L H, Van Beek L P H and Dorren L K 2002 Eco-Slopes Field Protocol. University of Amsterdam, Amsterdam, the Netherlands, 73 pp.
Danjon F, Bert D, Godin C and Trichet P 1999 Structural root architecture of 5-year-old Pinus pinaster measured by 3D digitising and analysed with AMAPmod. Plant Soil 217, 49–63.
Dawson E M, Roth W H and Drescher A 1999 Slope stability analysis by strength reduction. Géotechnique 49, 835–840.
Drexhage M and Gruber F 1999 Above- and below-stump relationships for Picea Abies: Estimating root system biomass from breast-height diameters. Scand. J. Forest. Res. 14, 328–333.
FAO 1990 Guidelines for Soil Profile Description, 2nd edition. Soil Survey and Fertility Branch Land and Water Development Division. FAO, Rome.
Fourcaud T, Danjon F and Dupuy L 2003 Numerical analysis of the anchorage of maritime pine trees in connection with root structure In B Ruck etal. (eds), Wind Effects on Trees. Int. Conf., Karlsruhe, pp. 323–329.
Genet M 2004 Le rôle de la cellulose dans le résistance a la traction des racines DEA Sciences du Bois LRBB. 28 pp.
GEO 2000 Geotechnical Manual for Slopes. 4th reprint. Geotechnical Engineering Office. The Government of the Hong Kong Special Administrative Region, Hong Kong.
Gray D H 1995 Influence of vegetation on the stability of slopes. In DH Barker (ed), Vegetation and Slopes, pp. 2–25. Institution of Civil Engineers, London.
Itasca 2002 FLAC 4.0 User Manual.
La Roca-Cervigón N and Calvo-Cases A 1988 Slope evolution by mass movements and surface wash (Valls d’Alcoi, Alicante, Spain). In A Imeson and M Sala (eds), Geomorphic Processes. Vol. I, pp 95–102. Hillslope Processes. Catena Verlag, Cremlingen.
La Roca-Cervigón N 1991 Untersuchungen zur räumlichen und zeitlichen Variabilität der Massenbewegungen in Einzuchsgebiet des Riu d’Alcoi (Alicante, Ostspanien). Erde 122, 221–236.
Lamas F, Irigaray C and Chacón J 2002 Geotechnical characterisation of carbonate marlsfor the construction of impermeable dam cores. Eng. Geol. 66, 283–294.
LI-COR 1990 LAI-2000 Plant Canopy Analyzer. Instruction Manual. LI-COR, Lincoln, NE.
MacDonald D, Crabtree J R, Wiesinger G, Dax T, Stamou N, Fleury P, Gutierrez-Lazpita J and Gibon A 2000 Agricultural abandonment in mountain areas of Europe: Environmental consequences and policy response. J. Environ. Manage. 59, 47–69.
Mulder H F M 1991 Assesment of landslide hazard. Doct. thesis. Utrecht University, Utrecht, the Netherlands, 150 pp.
O’Loughlin C L 1974 The effect of timber removal on the stability of forest soils. N. Z. J. Hydrol. 12, 121–134.
Riestenberg M M 1994. Anchoring of Thin Colluvium by Roots of Sugar Maple and White Ash on Hillslopes in Cincinnati. U.S Geological Survey, Bulletin 2059-E. United States Government Printing Office, Washington DC, 25 pp.
Schmidt K M, Roering J J, Stock J D, Dietrich W E, Montgomery D R and Schaub T 2001 The variability of root cohesion as an influence on shallow landslide susceptibility in the Oregon Coast Range. Can. Geotech. J. 38, 995–1024.
Sidle R C, Pearce A J and O’Loughlin C O 1985 Hillslope Stability and Land Use. AGU Water Resources Monograph 11.
Skempton A W 1985 Residual strength of clays in landslides, folded strata and the laboratory. Géotechnique 35, 3–18.
Tsakumoto Y and Kusakabe O 1984 Vegetative influences on debris slide occurrences on steep slopes in Japan. In Proc. Symp. Effects Forest Land Use on Erosion and Slope Stability. Environment and Policy Institute, Honolulu.
USACE 1983 Engineering Properties of Soil and Rock. United States Army Corps of Engineers, TM 5-818-1/ AFM 88-3 Ch. 7, Chapter 3, Washington, 27 pp.
Van Beek L P H 2002 Assessment of the Influence of Changes in Land Use and Climate on Landslide Activity in a Mediterranean Environment. Netherlands Geographical Studies 294, KNAG, Utrecht, 364 pp.
Vidal H, 1966. La terre armée. Annales Institut Technique Batim., Paris, No. 223–229: 888–939.
Waldron L J 1977 The shear resistance of root-permeated homogeneous and stratified soil. Soil Sci. Soc. Am. J. 41, 843–848.
Wu T H 1984 Effect of Vegetation on Slope Stability. Transportation Research Record 965. Transportation Research Board, Washington, DC, 3746 pp.
Wu T H, McKinnel III W P and Swanston D N 1979 Strength of tree roots and landslides on Prince of Wales Island, Alaska. Can. Geotech. J. 16, 19–33.
Wu T H, Beal P E and Chinchun L 1988 In-situ shear test of soil–root systems. J. Geotech. Eng.-ASCE 114, 1377–1393.
Wu T H 1995 Slope stabilization. In RPC Morgan. & RJ Rickson (eds), Slope Stabilization and Erosion Control, pp. 221–264. Spon, London.
Wesemael J C 1955 De bepaling van het calciumcarbonaatgehalte van gronden. Chemisch Weekblad 51, 35–36.
Yarbrough L D 2000 Channel bank stability and design-considering the effects of riparian vegetation and root reinforcement. MSc thesis, University of Mississippi, Oxford, 139 pp.
Author information
Authors and Affiliations
Editor information
Rights and permissions
Copyright information
© 2007 Springer
About this paper
Cite this paper
Beek, L.v., Wint, J., Cammeraat, L., Edwards, J. (2007). Observation and simulation of root reinforcement on abandoned Mediterranean slopes. In: STOKES, A., SPANOS, I., NORRIS, J.E., CAMMERAAT, E. (eds) Eco-and Ground Bio-Engineering: The Use of Vegetation to Improve Slope Stability. Developments in Plant and Soil Sciences, vol 103. Springer, Dordrecht. https://doi.org/10.1007/978-1-4020-5593-5_10
Download citation
DOI: https://doi.org/10.1007/978-1-4020-5593-5_10
Publisher Name: Springer, Dordrecht
Print ISBN: 978-1-4020-5592-8
Online ISBN: 978-1-4020-5593-5
eBook Packages: Earth and Environmental ScienceEarth and Environmental Science (R0)