So-called “Californian Drains” are sometimes used. These consist of parallel and closely-spaced tubes, arranged vertically or sub-horizontally. The tubes can be perforated or grooved and are installed into natural ground or fill. The main objective of such drains is the reduction of pore water pressure in a certain area, in order to lower the water level or treat a retained water pocket. A typical application, to stabilise a slope with high pore water pressures, is illustrated inFig. 13.17.
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Fig. 13.17 “Californian drain” |
13.4.2 Drainage Layers for Rigid Pavements
In a rigid, concrete, pavement structure, water filters mainly through
• open joints between the concrete slabs;
• open pavement-shoulder joints; and
• and the areas between the verges and the pavement.
Unless transverse drains are used (see Section 13.4.5), this filter water is collected by the drainage layers and is directed to longitudinal drainage pipes. The drainage layer should be constructed of a non-sedimentary granular material, placed between the pavement’s aggregate base and the subsoil. It is also advisable to place a geotextile to separate the different layers. The minimum thickness of the drainable base should be approximately 0.15-0.20 m.
