Vertical drain (for ground improvement)
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The vertical drain is made of a flexible polypropylene core wrapped with a synthetic geotextile filter chosen for its filtration properties and its resistance to abrasions upon installation.
The polymer core, depending on its manufacturer, is found in various shapes of undulations or surmounted with small dowels or vertical strips to maintain the air space between it self and the filter to ensure percolation of the water toward the surface. The vertical drain measures approximately 100 mm (4%u201D) wide by 6 mm (¼%u201D) thick and generally coiled in lengths of 305 metres (1000%u2019).
The drain is inserted in the soil mass with a hollow mandrel mounted on a vertical lead which is, in turn, most often attached and powered by a hydraulic backhoe. Occasionally, the lead is hung from a crawler crane and the mandrel activated by an independent hydraulic power pack. A static force is thus used to insert and anchor the drain at the desired depth. When hard layers of materials are encountered, a vibrator can be attached to some mandrels, or the holes must be pre-drilled with augers or, exceptionally, with drill rigs to overcome the resistance.
