Mineshaft -  ASDA Tonypandy

Benefil was used to allow a new ASDA store in Tonypandy to open on time after three mineshafts were discovered when constructing the store’s carpark. Engineers Clarke Bond called in Benefil to join on-site specialist contractors Quantum (Great Britain) Ltd, after brick linings on the 3, 4 and 5m diameter shafts were found to be failing, with any further deterioration likely to result in surface collapse.

The presence of an underground stream and the wet conditions of the shafts made conventional solutions difficult. Quantum treated one shaft with a reinforced spray-applied shotcrete lining, and in a 3-week project, the Benefil team filled all three shafts with a lightweight foamed grout, produced on-site.

The material was tailored to be unaffected by running water, and the density was varied to suit the varying conditions occurring in each shaft. One shaft was flooded, and for this, buoyant and specially waterproofed Benefil 3000 was injected around a steel mesh cube fixed to the walls at water level. 200mm of concrete was then poured on top of the Benefil, effectively sealing the bottom of the shaft. Benefil 5000 was then added up to the surface.Says Peter Lindsell of Quantum: Quantum and Benefil worked closely as a site-based team to adapt the process of filling the shafts as new problems were being encountered on a daily basis. Working under stringent targets for completion, all three shafts were treated to satisfactory condition to enable the client to open the store on programme.

ASDAs James Brown adds: Benefil allowed for a quick, safe and sensitive solution to the problems posed traditional methods would have required contractors to work inside the shafts for sustained periods.