Slope Stabilization Using Vegetation

The use of vegetation for slope stabilization started in ancient times. A fine historical review may be found in Greenway (1987 ). Krabel (1936 ) was among the first to use soil-biotechnical construction in the United States. In more recent times, the roles played by vegetation in some specific geotechnical processes have been recognised. Vegetation may affect slope stability in many ways. Comprehensive reviews may be found in Gray (1970 ), Gray and Leiser (1982 ), Greenway (1987 ), and Coppin and Richards (1990 ). The stability of slopes is governed by the load, which is the driving force that causes failure, and the resistance, which is the strength of the soil-root system. The weight of trees growing on a slope adds to the load but the roots of trees may serve as a soil reinforcement and increase the resistance. Vegetation may influence slope stability indirectly through its effect on the soil moisture regime. Vegetation intercepts rainfall and draws water from the soil via evapotranspiration. This reduces soil moisture and pore pressure, increases the shear strength of the soil, and increases the resistance. Vegetation roots tend to increase soil permeability and increase infiltration and soil moisture, while the organic layer associated with vegetative cover tends to retard infiltration. The objective of this paper is to outline the methods that may be used to evaluate the influence of these factors on slope stability. Emphasis is placed on the mechanics of slope stability.