Assessment Of Permeability And Groundwater Drawdown In Peat, Glastonbury

South West Geotechnical were commissioned to investigate the permeability of peat and the likely effects of groundwater drawdown due to peat extraction to assist with an extraction planning application.

Sensitive receptors border the proposed site, and it was necessary to establish the permeability of the peat in order to appraise drawdown effects, and thereby any settlement effects that may occur.

Working in close liaison with the planning authorities experts, SWG designed and implemented a large scale pumping test in order to establish the typical permeability (k-value) of the peat.

A central pumping well was put down near to the centre of the site, as remote as possible from nearby drainage ditches. Two arrays of monitoring wells were extended at increasing spacings away from the well in order to monitor drawdown during pumping.

Testing, including an initial trial, step tests, and full pump test followed by a recovery test was undertaken over a period of 3 weeks, often requiring round the clock manual monitoring.

Although manual data was requiredto be collected to guide the testing stages, detailed analysis was undertaken on automatically collected data using down-the-hole leveloggers and an above ground barologger.

A variety of analyses was used to interpret the data and arrive at a realistic k-value for mass flow within the peat.

Using the parameters established from the pump test, modelling of groundwater flow enabled the zone of influence of groundwater drawdown to be calculated. From this, mitigation measures, including the staging of extraction, the installation of cut-off trenches and sheet piling were able to be designed to allow safe extraction of the peat without adversely affecting adjacent land or property.

Assessment Of Permeability And Groundwater Drawdown In Peat, Glastonbury

Assessment Of Permeability And Groundwater Drawdown In Peat, Glastonbury