Drainage masks provide control of emerging water (e. g. a spring line) on a slope’s face with a geotextile covered by hand-placed rock (Fig. 13.21). The material used for a drainage mask should be angular and should comprise 100-500 mm sized stone. The rock provides improved slope stability both by allowing the reduction of pore water pressures without erosion and by adding mass to the slope.
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Fig. 13.20 ‘ ‘Christmas tree” drain |
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Fig. 13.21 Drainage masks |
Drainage spurs have the double function of draining and reinforcing the excavated slopes. Spurs are constructed as stone-filled trenches excavated perpendicular to the slope face (Fig. 13.22) to provide both drainage and buttress support. The material to be used in drainage spurs should be coarse and angular (e. g. broken rock in the size range 100-200 mm) and should be contained within some geosynthetic wrap to ensure soil does not migrate into the large void space. A heavy-gauge geosynthetic is indicated given the abrasive nature of the fill.
Wells are vertical shafts of sufficient diameter in order to lower the water level. They are usually associated with a pumping system and, hence, require constant maintenance.
