Initial feasibility studies of potential stabilisation options assessed a number of environmental constraints which would impact on the stabilisation of the mines and the method by which this is achieved. The key environmental constraints included the existence of protected bat species within the mines complex, the archaeological significance of the mines themselves and the hydrogeology of the area.
A number of different options were examined ranging from structural support of the mines, through to surface and underground infilling. Investigations indicated that the best possible way to achieve stabilisation of the mines would be through underground infilling. Nevertheless there were certain areas within the mines which were considered extremely hazardous to access from underground and, as a consequence, such areas were stabilised from the surface in combination with underground infrastructure.
An initial environmental assessment of the infilling options - Pulverised Fuel Ash/cement grout, stowing with stone, foamed concrete infill and sand infill - was undertaken to identify the likely impact from each of these options, especially in terms of the impact on the bats, the archaeology and hydrogeology of the area. The option chosen was foamed concrete.Back to Top
Parsons Brinckerhoff concluded that an underground operation was the only safe, economic and technically sound way of delivering the successful stabilisation of the Combe Down Stone Mines. This involved the construction of arterial roadways through the mines to compartmentalise areas into manageable treatment blocks. These roadways provided routes for safe access, good ventilation, drainage, rapid movement of material, mechanised equipment and labour within the mines, as well as construction monitoring.Back to Top
The initial phase of roadway construction revealed a previously unmapped area of the mine, Sector X. The conditions in this part of the mine were identified as being particularly hazardous. Her Majesty's Inspector of Mines served an Improvement Notice in September 2001 which required the Council to commence the stabilisation of 'Sector X' and 'North Road' within 7 days. This meant the Council had to begin stabilisation immediately, prior to full funding and all necessary permissions being in place, requiring emergency procurement.
Finally, physical inspection of the Byfield and Firs Mines was also carried out within the constraints of safety imposed by HMIM and by August 2001, Parsons Brinckerhoff had examined the mines to a sufficient degree to allow for the Main Stabilisation Scheme to be designed in outline.Back to Top