The purpose of this investigation was to assess the ground conditions likely to be encountered during the installation of a new sewer and to assess the stability of the slope, as the site lies within an area of known landslip within the Stroud Valley in Gloucestershire. Ground investigation work was undertaken at the crest, mid slope and toe of the site. Staging was built to safely position the drilling rig for the mid slope borehole. Inclinometers were installed in the boreholes.

Brief description of works

  • SlopeGraphFour boreholes were drilled using a multi-purpose Comacchio MC305 drilling rig. Boreholes were advanced using a combination of percussive sampling through clays and gravels and water flush rotary coring in the underlying limestone.
  • The boreholes were installed with 70mmOD inclinometer access tube set in bentonite cement grout.
  • A scaffold platform some 12m long and 3m high was erected by specialist contractors on steeply sloping ground to allow the drilling rig to set up on the mid slope borehole.
  • Sitework was supervised by a qualified engineering geologist from CC Ground Investigations. Detailed logging was under- taken to identify slip planes or zones of movement.
  • Long term monitoring of the inclinometers (over two years) was undertaken by Engineers from this Company.
  • Laboratory testing was undertaken and included soil classification tests, multistage total stress and effective stress triaxial testing. Point load index and unconfined compressive strength tests were completed on rock cores. Environmental samples were tested for a range of chemicals.

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