The Drifts
The Gascoigne Wood Drifts were the second stage of the development of the Selby Superpit. The undergound connection with Wistow Mine was of the upmost importance as all production surfaced at Gascoigne Wood. The drivages were started at almost the same time as the actual shaft sinking at Wistow in early 1978. The two drifts were parallel and set at 70.40m centres and were driven at 1 in 4 to 832m where a sealing ring was installed to stop water ingress.
The geology of the Selby area means that water was always going to be a major problem to be overcome, as it was during the shaft sinking in the Doncaster coalfield in the early part of the century and Kellingley Colliery in the late 1950s/early 1960s. It involved major mining engineering work starting from the initial ground works.
Their were three major water problems encountered during the drivage of the drifts. The Bunter Sandstone, a major aquifer in the Selby area and a major supplier of water, accessed by many borehole-wells. It is situated beneath the glacial deposits. The Lower Magnesian Limestone where up to 340 litres of flow per minute were expected and the Basal Sands where ingress from the Magnesian Limestone strata could cause running quicksand, at artesian pressure to be encountered. This problem had caused huge problems at Bentley Colliery during the shaft sinking process.
The Bunter Sandstone outcrops 800m east of the drifts and was one of the factors for the site being chosen.
The initial access to the drifts was by open cut method. The cuttings were initially de-watered by up to 60 pumps to allow the construction of the circular tunnel lining. A 1.5m, 10m depth, ventilation shaft was constructed at 40.25m in each of the drift portals. A system of de-watering wells were installed at the top 148m of the drift. The drifts was driven by modified single boom S.B.600 Dosco roadheader. This modification allowed the construction of circular, graphite-cast iron tubbing rings each sealed to the last and grouted to seal the tunnel. As the tunnel progressed, the heading was pre drilled and grout cones were injected to seal water ingress 30m in front of the face of the headings. This continued for 14 stages in 13m sections until the 178m area was completed. The next problem to be encountered was the Basal Sands, as predicted, 200m from the surface. This problem was overcome by using technology used in shaft sinking. The ground was frozen from the surface, using the existing technology involving 100 drill holes around each heading and the headings were driven 108m through solid ice. The heading had waterproof seals installed as they progressed to allow the sand layer to thaw. At 832m mark in the drivage sealing rings were installed to ensure a dry drift was achieved.
Selby Superpit 