Permeability: The First Step
The first step in any arena design is to calculate the permeability of the ground upon which the arena will be built. We show you how with this simple test.
Conduct the test as follows:
- Dig several trial pits (normally six)
- Obtain a pipe for each trial pit. The pipes must be open at both ends, at least 450mm long, and at least 200mm wide (underground sewer pipe would be ideal). A large plastic drum with the top and bottom removed could also be suitable if a larger test area was required and if readily available.
- Set a pipe into the middle of each pit, and surround each pipe with a minimum of 300mm of impervious clay, mortar or concrete
- Fill each pipe with water and record the drop in water level with time
A minimum drop of 10mm per hour is required when the water level is no more than 100mm deep. A drop of 100mm per hour or more is preferable. A greater permeability is required if the strata also transmits groundwater from outside the arena (unless cut-off drains are being constructed). Trial pits are best observed in the Winter months, when the water table is high.
Diagram of the Trial Pit
Record your results in a table like this one:
Average the results to get a good estimate of permeability across the site. If you are fortunate enough to have highly permeable (free draining) site, then arena construction will be very straightforward. In many cases, however, the site's natural drainage will not be sufficient, and one or more drainage layers will have to be included beneath the arena surface.
Disclaimer: The foregoing is a design guide only, material properties can vary. Site conditions can impact substantially on a design.