Uncovering Newcastle's coal mining past
Contractors preparing a city-centre site for a mixed-use development are having to deal with the remnants of an old coal mine. Elaine Knutt reports.
If you go down to the centre of Newcastle today, you’re in for a bit of a cliche. The former Scottish & Newcastle brewery site is being prepared for an ambitious new Science Central development, with the ongoing enabling works demonstrating just why the city’s abundance of coal gave the world the concept of “coals to Newcastle”. As well as conventional muck-shifting and contour levelling, contractor Hall Construction Services is currently mining coal from shallow seams within sight of St James’ Park football stadium.
Mott MacDonald’s Simon Longshaw, project manager for the enabling works, is grappling with the strangeness of Newcastle’s history re-emerging to play a part in its future. “We’re dealing with the legacy of an old coal mine, so we’ve got coal seams, ground contamination, buried obstructions and mine shafts. And now we’ve got opencast coal mining and 12m deep excavations in an urban site in central Newcastle. It’s surrounded by high hoardings but it’s also bordered by homes, businesses and student accommodation.”
The mixed-use Newcastle Science Central development will be a 9ha complex combining university buildings, commercial space and 350 new homes set around public spaces. Developed over 15 to 20 years by Newcastle City Council and Newcastle University as part of the Newcastle Science City Initiative, the aim is to attract investment and employment around the university’s strengths in sustainability, stem cell research and life sciences. Mott MacDonald has a wide role as civil, structural, environmental and services engineering consultant.
The clients’ strategy is to fully prepare the site in advance of any development deals, so that a developer can take on a de-risked, landscaped and serviced site. But with the brewery built on the site of the former North Elswick Colliery — which operated throughout the 19th century and into the beginning of the 20th — the key decision was whether to extract the coal commercially for power generation, or leave it in situ. The first option clearly racks up a heavy bill in carbon emissions, but then so does the alternative: the voids above the coal seams would have to be filled with cementitious grout to avoid the risk of future settlement or collapse.
Science Central will be marketed as a centre for science and sustainability
When Newcastle University did a qualitative assessment of the options, factoring in the transport emissions associated with importing the coal that would otherwise have been used, and the embodied carbon in the cement, the scales were tipped in favour of extraction.
Mott MacDonald consulted old mine plans for the site, although at more than 100 years old their accuracy fell short of today’s needs. As well as recorded shafts, the site also had numerous “bell pits” — rudimentary mines formed by digging down from the surface to dig out as much coal as possible. Later backfilled, the poorly compacted soils also created a hazard on site.
However, when ground-probing radar was also used to look for shafts and hidden hazards, it didn’t provide all the answers. “Because the natural ground material was glacial till – a cohesive clay-type soil – and all the arisings were also glacial till, there wasn’t a clear delineation between the undisturbed ground and back-filled areas. The radar found anomalies, but they didn’t always tie up with what we knew about the location of the shafts, so we tended to rely on old-fashioned drilling.”
Bore holes were drilled to test the thickness of the coal seams, and assess where there had been back-filling. “Then we fed all this investigative data into a BIM model to do a 3D mapping exercise that would allow us to estimate the quantity of coal in the ground. By working out the average thicknesses of the coal seams, we could assess the tonnage and whether it would be attractive to a coal extraction company,” explains Longshaw.
Enabling works at Newcastle’s Science Central site involve mining two shallow coal seams
The contract was tendered and let to Hall Construction of County Durham, which operates three opencast coal mining sites in Fife. The contract value is £3m, but Hall also receives the benefit of the extracted coal. Essentially, it took on the project at risk with no guarantee of the tonnage to be found under the ground.
As part of the site’s planning conditions, the council imposed a rigorous monitoring and reporting regime, with microphones, dust gauges and water dousers positioned around the site. The council’s environmental health officer also receives live monitoring updates via text message.
Mott MacDonald is also advising on the site-wide sustainability strategy, and is working with Newcastle University researchers to test the site’s capacity to deliver geothermal energy to the finished development. A research team has sunk a 1.8km bore hole to test the temperature of the water and whether it can maintain a useful working temperature after being pumped to the surface.
The groundworks phase is due to finish by end of September, while a “gateway” building being built by Sir Robert McAlpine should be completed by autumn 2014. It is hoped that the seven-storey office building for new and growing science companies will be a catalyst for developer and occupier interest. The overall site is being marketed as a centre for science and sustainability, and the intriguing story of how the site was prepared will help to create a new legacy to build on.