Perforated pipe and drain trench calculator
A subsurface drain: the pipe, the gravel around it and the geotextile wrapped round the trench.
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How the calculation works
Pipe is the drain length plus joints and wastage. Gravel is trench width × gravel depth × length, less the pipe. The filter geotextile, RNW 150 GSM, wraps right round the gravel with a top lap equal to the trench width (at least 300 mm), plus 5%. Example: 300 m of 110 mm pipe in a 0.45 × 0.6 m trench needs 309 m of pipe, about 78 m³ (125 t) of gravel and about 803 m² of wrap, 2 rolls.
Planning quantities for budgeting and enquiry. A Retech engineer confirms the grade and quantity against your drawings before order.