Monkton Heathfield Western Bypass, Somerset

Steve Morgan

Steve Morgan


Tel: 01392 439905


Somerset County Council


  • Preliminary Sources Study Report
  • Site Investigation
  • Ground Investigation Report
  • Geotechnical Report to HD22/08

Preliminary sources study report

CGL was commissioned by Somerset County Council to undertake a Preliminary Sources Study Report (PSSR), Site Investigation and Ground Investigation Report (GIR) written in accordance with HD22/08 for a proposed highway scheme. The proposed new highway is to be known as the Western Bypass and it is to be developed close to Monkton Heathfield, Somerset. The Western Bypass will join the A3259 at Dyer’s Lane in the east.

The route of the highway is to be 558m in length with an additional existing 82m long link road spur to the north, traversing across a construction compound in the east and an agricultural field in the west. A new road bridge is proposed as part of the scheme which will cross a water course, known as Allen’s Brook, which is aligned north to south through the centre of the site.

The site investigation works were undertaken by CGL. The investigation comprised of cable percussion boreholes either side of the water crossing and a series of trial pits and windowless sampling boreholes to profile the shallow ground conditions to enable highway design and earthworks profiling.

The ground conditions encountered during the intrusive investigation were generally consistent with those contained within the published and unpublished BGS information for the area. To the west of Allen’s Brook, the ground conditions comprise Topsoil overlying cohesive and granular superficial River Terrace Deposits, beneath which are solid geology deposits from the Mercia Mudstone Group. To the east of Allen’s Brook, Made Ground was recorded overlying the superficial and solid geology.

On completion a geotechnical risk register was produced to detail the findings of the PSSR and GIR, a number of ‘medium’ hazards identified from the PSSR have remained at a ‘medium’ risk rating based on the findings of the Site Investigation pending either detailed consideration during the Geotechnical Design Report or a site specific risk assessment on review of this document.

CGL was able to add value to the scheme by assessing the suitability of the Mercia Mudstone for reuse as an earthworks medium and formation stratum. Targeted investigation enabled assessment of the geotechnical risks within the highway alignment which further added value for the client.


Improvements to M271 J1

Site Investigation