Performance of Gunite Brow Ditches

Abstract

The main advantages of gunite brow ditches are cost, ease of construction, durability, and simple flow‐capacity equations. The main disadvantages are weakness due to shrinkage cracks; rigidity, which makes them vulnerable to soils movement; susceptibility to chemical attack; aesthetics; and maintenance, which is required to keep them clear of obstruction that can clog pathways. The standard specifications require a setback from the top‐of‐slope of 0.3 m (12 in.). This setback should be adequate for slopes in rock and for compacted sands and gravels. But slopes composed of compacted clay will creep if the slope face is wet to saturated. The three parameters that determine the primary zone of creep for this condition are shear strength, slope height, and slope inclination. An empirical equation [(1)] can be used to estimate the gunite brow ditch top‐of‐slope setback distance for compacted‐clay slopes.