HYDRAULIC AND STRUCTURAL STABILITY OF OVERTOPPING PROTECTION OF EMBANKMENT DAMS USING GABION MATTRESSES

Abstract

Embankment overtopping protection is a practical measure to release large and infrequent floods with no or extremely diminished soil erosion failure due to flowing water over the embankment. The overtopping protection using gabion mattresses, an assembly of a wire mesh frame packed with rock particles, and placed over the embankment crest and downstream slope, is proposed, and its protective ability against soil erosion, structural stability during overtopping and construction performance are investigated. Hydraulics of the overtopping flow is calculated by a nonlinear seepage analysis of flow through the gabion combined with a numerical integration of spatially varied flow over the gabion, then hydraulic shear stress is quantitatively determined to evaluate the soil erosion potential, resulting that it can be prevented safely by placing the gabion underlain by a non-woven geotextile. The structural stability of the gabion mattresses against the sliding failure due to the overtopping flow is assessed by sloping water flume tests and stress-deformation analysis. Embankment slope failure which may be caused by loading of the gabion on the embankment surface is also assessed by circular slip surface calculation. Both assessments show no instability of the gabion sliding along the embankment slope and no degradation in the slope stability. Selecting the farm pond embankment constructed in the early 1900s, the trial test is conducted to construct the gabion mattresses about 200 m² in the placement area, and completed successfully in a very short period and cost-effectively.