FEATURE 23 in modular form allowing expansion in both the vertical ( Depth ) and lateral ( length ) direction and has allowed for quick “ plug-n-play ” type installations .
In-situ percolation test for soils . ( French Drain ) Fig 1
• SANS 10400 : P , 4.25 calls for such a test described as a test pit . The test hole shall be 300 X 300mm square or 300mm diameter and 350mm deep .
• 4.25.3 The test hole shall be roughened to provide a natural infiltration surface . Any loose material from the bottom of the hole shall be removed and replaced with a 50mm thick layer of gravel to prevent soaking when the hole is filled with water .
• 4.25.4 The prepared hole shall be filled with water to a height of not less than 300mm above its bottom and maintained at such a level for a period of not less than four hours . At the end of this period , the level of water shall be recorded , and the drop in level as the water soaks away over a subsequent period of 30 mins shall be measured .
• 4.25.5 The percolation rate shall be reported as the time taken in minutes for the water level to drop 25mm . where a number of holes are tested , the average shall be reported .
The purpose of the test measures the rate at which clean water , under constant or near constants hydraulic head , percolates into the surrounding soil in both vertical and horizontal direction .
Design Considerations The design and investigation of subsoil drainage systems is an uncertain process . Only in an extremely limited number of situations can the need for sub soil drainage be identified without detailed subsurface investigations , filed observations and soil tests . Apart from 10400 : P detailing the requirements any aspect beyond what the standard expresses , specialist advice should be sought .
One type of geotextile .
Fundamental design considerations include depth and extent of the system to ensure adequate coverage of any area to be drained , drainage capacity to remove all subsoil liquid as quickly as possible , long-term durability / survivability , any dynamic flow of water should be determined and the drain network located so as to intersect as best as possible , and lastly , the obvious , quintessential considerations of quality versus cost and installation time , disruption .
References
1 . Sub Soil drainage extracted from the Urban Stormwater Management Manual , authored by Ir . Azmi Bin Amat of Malaysia . General Introduction .
2 . Direction from Darryn Meisel of TeMa South Africa for types of drains and for product photographs . 3 . SANS 10400 : P available from www . sabs . co . za PA
“ The design and investigation of subsoil drainage systems is an uncertain process .”
Materials required for a successful installation .
August 2022 Volume 28 I Number 6 www . plumbingafrica . co . za