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Soakaways Expanded Info



Article 969 [ added on 02-02-2011, updated on -- ]

 

Generally

As the name suggests a soakaway allows rain and uncontaminated surface water to soakaway into the ground. Currently it is a preferred option and can, subject to site conditions, be applied to most new builds. Historically rain and surface water was connected onto storm sewers and then into rivers and water ways resulting in huge rises in water levels and contributing to the flooding of recent years. The merit of a soakaway system is the slow release of water into the water table.

Construction

In its simplest form a soakaway is a rubble filled excavation based on empirical standards. In most small domestic situations this is a satisfactory solution. Larger schemes require a scientific approach to determine the size and location of soakaway systems. The Approved Document to Building Regulation H contains guidance and a formula for determining the porosity of soil – “a percolation test”. More complex schemes require the input of a geo technical engineer for a comprehensive assessment of flow, capacity and ground capability. There are numerous other guidance documents and codes of practise.

Location

Any soakaway system should be located sufficiently distant from all structures so as not to pose a risk to substructures or create nuisance. In small domestic situations a dimension of 5 metres away from any structure can be acceptable but consideration needs to be given to soil type. Less porous soils would require a greater dimension. Very large schemes require a geo technical input regarding location.

It should be quite obvious that soakaways will not be suitable in areas with a high water table i.e. water logged. These areas require a different solution such as a pumped system to an acceptable outlet or a water reclamation scheme.

Soakaway Yype

As previously mentioned the simplest is no more than a rubble filled excavation. A more engineered solution consists of a brick built chamber or concrete manhole rings either left void or filled with clean inert material – gravel, crushed brick, etc. the brick built  chamber should have a number of open joints and the concrete rings bedded dry to enable the water to escape.

Alternative solutions include gravel filled trenches cut to an appropriate layout with the water connected to the trenches by porous drain ware. Some systems can incorporate boreholes to conduct water to a deeper more porous strata. There are numerous other proprietary soakaway systems.

Soil Type

Soakaways will be more appropriate in non – cohesive soils i.e. sandy soils. Clay / marl soils present difficulties by their very nature and although not impossible soakaways in these areas require careful consideration and design.

Maintenance – Longevity

Soakaways are almost maintenance free but it must be accepted that, in time, silting up will occur. The situation could be factored into the design and features incorporated to allow replacement or replenishment of the fill material.

Soakaways consisting of brick or concrete chambers can incorporate an access hatch to allow excavation of the fill material and its replacement.

Other systems will require a dig out and reconstruction.

 

 

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