Location: Greatworth, Northamptonshire
Duration: June – October 2020
Stuart Wells Ltd. were employed as a subcontractor to undertake a series of in-situ borehole permeability tests in accordance with BS EN ISO 22282-2:2012 as part of ground investigation works for HS2.
Initially the drilling contractor drilled and installed the groundwater monitoring and pumping wells and Stuart Wells then undertook substantial well development prior to any testing. As part of our scope of works we undertook 4 x no. constant, rising and falling head tests.
50mm and 75mm surface water pumps and associated hoses were used on site and a short equipment test undertaken to establish outline flow and response conditions. Constant head testing was undertaken whereby water was pumped into the borehole.
This comprised of 3no x 90-minute step tests where a steady water level was maintained in the borehole. Upon completion of each step the pumping flow rate was increased to maintain a higher steady water level. Upon completion of the final step test, pumping was stopped and the falling head ‘recovery’ response was observed. Falling head testing was undertaken whereby water was pumped into the borehole until it reached the top of casing level. Pumping was then stopped and the head ‘recovery’ response was observed.
Rising head testing was undertaken whereby groundwater was abstracted from the borehole using a suitable submersible borehole pump. Upon secession of pumping groundwater ‘recovery’ response was observed. In all tests, total injected and abstracted water volume and inflow rate were measured using 2no x propeller flowmeters.
Water level within the borehole was measured manually using a dipmeter and Solinst datalogger. In undertaking these tests in accordance with BS EN ISO 22282-2: 2012 Stuart Wells were able to provide the client with accurate permeability values for each well to aid design. A full factual report was produced and submitted to the client.