Soakage Test

With the modern emphasis on Sustainable Urban Drainage schemes (SUDs), there has been an increase in the use of soakaways and permeable pavements for the disposal of surface water.   To design such infiltration systems, it is necessary to determine how fast water will pass through the ground.

If you are planning to use a soakaway, then contact BRD for initial advice as the likelihood of their successful use can often be determined by interpretation of the geology alone.  If the ground is likely to be suitable, then BRD can undertake soakage tests either as a standalone project, such as supporting information to a flood risk assessment, or integrated into a more general ground investigation.

For soakaway design, the most common test is the BRE Digest 365 ‘Soakaway design’ test that essentially involves excavating a pit of known dimensions, filling it with water and recording how quickly the water seeps into the ground.  The data collected is analysed to calculate a soil infiltration rate employed in the design methodology. 

Other types of test are available to determine permeability including variable head tests in boreholes, shallow depth percolation test, and correlations from laboratory particle size determinations.  Again BRD's experience can guide Clients on the best approach for any particular situation.

In some areas of the country, the near surface soils are effectively impermeable (i.e negligible permeability) such as clays, but at depth there may be permeable soils which could accept surface water. In such circumstances a deep borehole soakaway design may be appropriate.  BRD have extensive experience of undertaking suitable tests within boreholes to confirm such a design is viable.

Increasingly tests are being undertaken to provide definitive proof that soakaways or other infiltration devices will not work so that permission to discharge surface water from the site is granted.