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→Design
==Design==
==Design==
*Where flow comes off an impervious surface, a drop of 75 mm or more to the surface level of the diaphragm is recommended,
*Where flow comes off an impervious surface, an elevation drop of 75 to 150 mm to the surface of the diaphragm is recommended,
*Typical dimensions for the trench excavation are 300 mm deep and 600 mm wide. The trench may be any length,
*Typical dimensions for the trench excavation are 300 mm deep and 600 mm wide. The trench may be any length,
*The trench should be lined with geotextile before filling with gravel,
*The trench should be lined with geotextile before filling with gravel,