With improvements to the 40km Abergavenny to Hirwaun section of the A465 ongoing since the early 2000s, Socotec is currently carrying out ground investigation works on behalf of the Welsh government for the final two sections. Starting in July 2019 and programmed to last into early 2020, these works extend along the 17km length of the route from Hirwaun to Dowlais Top, incorporating a major interchange with the A470 trunk road.
Supervised by Jacobs UK Ltd, the proposed upgrade works will widen the existing three-lane carriageway road into a dual carriageway, with the majority of activity being carried out overnight in order to meet traffic management requirements.
New sections of highways and junctions are being realigned and/or constructed, together with associated structures and earthworks such as retaining walls, embankments and cuttings. In order to do this, Socotec's team of highly experienced and qualified drillers and field engineers are carrying out investigatory works across potential bat roosting sites, sites of special scientific interest, local nature reserves and areas of conservation.
The information obtained from these works will enhance the existing understanding of the geology, ground and groundwater conditions across the route. It will also clarify the risks from potential geo-hazards created as a result of previous industrial activity, as well as former landfill sites containing deposits of spoil and potentially contaminated by-product materials.
Socotec's ground investigation team is using a range of techniques to suit the variable ground conditions and site terrain, with geology across the route predicted to comprise a mixture of made ground, peat, glacial till and head deposits, overlying carboniferous bedrocks.
The scope includes 204 boreholes to 40m, using a combination of sonic coring, for sampling superficial materials, and rotary coring of bedrock. A total of 94 machine dug trial pits are being excavated for inspection and sampling of shallow materials to a depth of 4m. The presence of near-surface contaminants in some areas requires the use of aquifer protection measures to prevent groundwater exposure to harmful pollutants. Each of these methods will be operated using a quality management system that adheres to BS EN ISO 9001, 14001 and 45001 standards.
Various field-testing methods are being used, including borehole permeability tests and magnetometer and electrical resistivity imaging to investigate former landfill areas, together with the installation of gas and groundwater monitoring instruments in boreholes to record water levels and gas properties.
Where contaminated made ground is suspected, photoionisation detection equipment is used to carry out headspace testing, and interface probe monitoring is employed to detect non-aqueous phase liquids in installations.
More unusually, a borehole camera survey has been used to check for the presence of bats within ground voids.
The ground investigation fieldwork is complemented by geotechnical and geoenvironmental testing carried out at Socotec's in-house, UKAS-accredited laboratories to determine the engineering properties of the soil and rock materials encountered, and the chemical composition in terms of contaminants and waste characterisation. The use of AGS4 format digital data underlies the management of data collection in the field and laboratory, plus onward reporting to the client.
Clare Chapman, operations director, Ground Investigation, Socotec UK, commented: "We are delighted to have been awarded the position of principal contractor for the final phase of the A465 Heads of the Valleys project, which further strengthens the position of Socotec's ground investigation division as a market leader.
"Using our wealth of expertise in geotechnical and geoenvironmental testing and sampling, these ongoing investigatory works will enable the designers to progress a road scheme that will not only enhance transportation links across this major Welsh route but also benefit the surrounding environment for road users and local communities alike."
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