SOCOTEC UK’s Ground Investigation team completed a project on the River Tawe in Swansea, South Wales, on behalf of Swansea City Council and designer Amey. The project involved drilling five overwater boreholes and two land boreholes, with cable percussive drilling used for all but one land borehole which required rotary follow on. The overwater boreholes were drilled on a floating pontoon that had to be lifted by crane and fixed to the river bed using four spud legs. The project also had geotechnical laboratory testing, geo-environmental laboratory testing, a factual report, and AGS data.

The project was carried out under Natural Resource Wales’s marine licence permit, which restricted SOCOTEC UK’s team from carrying out intrusive works two hours before and after high tide. The team also had to complete the works by Tuesday 28 February and could not use artificial lighting on the pontoon. Working hours were from sunrise to sunset, and personnel on the pontoon had to wear life jackets.

SOCOTEC UK’s team faced several challenges, including the presence of aeration pipes along the length of their working area, which were not visible as they lay on the river bed, but they could see “bubbles” at the surface where they were present. The team had to stay away from these pipes, and the engineer positioning the pontoon had to make sure the borehole position was clear of them. The team also encountered sandy clays with large rounded gravels, resulting in some boreholes terminating early.

One land borehole was terminated due to the cable percussive rig’s inability to smash through the made ground encountered, while another borehole was cancelled due to reaching a contaminated material. The team switched drilling methods for this borehole and used a Comacchio 405, which used a drilling method called Symmetrix to get through large concrete bits and other materials in the ground.

SOCOTEC UK successfully completed the ground investigation project on the River Tawe, providing accurate data to help inform the design of a new footbridge.

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