HBPW Innovation For Cornwall Tin Mines

HBPW’s expertise in geotechnical engineering has been playing a major part in a £27m road scheme, which will see the construction of two huge arches across the Red River Valley in Cornwall.

The Camborne to Pool to Redruth project, which has already been under development for more than eight years, is being built by Carillion Civil Engineering on behalf of Cornwall Council.

And, as part of the project, two 12 metre span pre-cast concrete arches will be built across the Red River close to South Crofty Mine.

Geoenvironmental Engineer, Jay Fox, said: “The geological setting of the bridge is complicated in that it is located, partially, on the Great Crossing, a heavily mineralised fault zone. Consequently the area has been extensively mined over the decades, leaving scheme developers with the added headache of a complicated tin mining legacy.”

The primary complications involved constructing foundations over fractured rock and around underground adits and shafts which governed where, and how, the bridge could be constructed. Jay’s job was to look at everything below ground level.

“The original bridge design planned to excavate down to rock below the river. However, there was much uncertainty on the ground conditions and this would have resulted in expensive and logistical problems with ground water control and disposal of contaminated soils. Mining waste in the area includes toxic metals such as arsenic and acidic ground water which can burn skin and erode metal.

“However, following extensive research and discussions, HBPW eventually advised on an alternative micropile foundations solution, which avoids the underground adits and shafts, and has been key in enabling a quicker, safer foundation solution.”

Work on the bridge foundations are scheduled to start later this month and continue into the autumn.