C7 Erosion control
An important element in roadside slope management is the preservation and encouragement of the natural vegetation. However, the effects of road construction on erosion can often extend well beyond the right of way. In mountainous terrain, road construction itself often facilitates access to areas of forest that then become logged for timber as development takes place within the wider road corridor. The gradual depletion of forest cover can lead to increased runoff, causing slope erosion, gullying and downcutting in stream channels, which eventually increases the incidence of landslides. This process may be exacerbated by the indiscriminate dumping of excavation spoil during construction, creating debris hazards downstream (e.g. Kojan 1978; Hearn 1987; Zurick & Karan 1999; Hart et al. 2002; Campos et al. 2010 with respect to road corridors in Nepal, the Philippines and Brazil).
However, even where these effects are minimized through good land use planning and engineering management practices, there is usually a significant potential for erosion to occur on unprotected cut and fill slopes, in stream channels and at other drainage discharge points (Section C6). Erosion on roadside slopes is sporadic and difficult to predict since it is related to rainfall events, slope drainage patterns and the characteristics of the ground. The largest volumes of erosion are usually generated from short-duration, intense rainfall events. Methods used to combat this erosion are described and discussed below in the context of slopes and streams.
Figures & Tables
This book provides a complete guide to the study, design, construction and management of landslide and slope engineering measures for mountain roads, with an emphasis on low-cost. The geographical focus of the book is on the tropics and sub-tropics, but is also highly relevant to other regions where heavy rain, steep slopes and weak soils and rocks combine to create slope instability. The causes and mechanisms of landslides are described, and the hazards they pose to mountain roads are illustrated. Methods of desk study, field mapping and ground investigation are reviewed and illustrated, with an emphasis on geomorphological and engineering geological techniques. The design and construction of alignments, earthworks, drainage, retaining structures, the stabilization of soil slopes and rock slopes, and the control of erosion on slopes and in rivers and streams are covered. Slope management as part of road maintenance and operation is reviewed, and procedures for risk assessment and works prioritization are described.