Mine Infilling

The company has been involved in the stabilisation of old shallow mine workings from surface for over 30 years and for the past 20 years, infilling of redundant stone mines in the West Midlands and other areas of the UK. Many of these schemes have been funded through English Partnerships Land Stabilisation Programme. Forkers is considered a specialist in this field and is in the unique position of being able to resource large mine infilling schemes from its in-house resources.

Previous projects have included:

• Treatment of shallow limestone, ironstone, sandstone and chalk workings generally up to 150m deep
  
• Infilling both dry and flooded mines including dealing with artesian water conditions
  
• Bulk Infilling of open workings with pfa/cement or sand/cement paste, sand, gravel and crushed stone
  
• Infill quantities of up to 500,000 tonnes of pfa
  
• Computer controlled continuous batching plants with outputs of up to 150m3/hr
  
• Pumping mixed infill materials up to 3000m to injection points using high output trailer mounted concrete pumps and use of stage pumping stations
  
• Establishment of substantial temporary infrastructure including surfaced access roads, material storage areas (for large volumes of PFA – up to 5000m3) and mixing areas, container surrounded worksites to provide dust and noise protection, overhead water misting dust control systems, drive through vehicle wash and temporary weighbridge
  
• Creation of infill barriers in mines and roadways up to 15m in height by installation of granular materials from surface through large diameter cased boreholes including gravel, crushed stone, sand, concrete, or in-situ reinforced concrete barriers to mine galleries where access is possible
  
• Design and construct areas of ‘temporary infill’ for possible future removal. For example the recent Step Shaft Mine Gallery project for Dudley MBC required the temporary infilling of the unstable mine gallery with 10,000t of sand to prevent further degredation and collapse. The sand can be removed at a later date when funding is obtained for a full stabilisation and support project which will be part of and an expanded underground tourist network based on the existing canal system. The sand was placed by a combination of pumping and conveyoring to infill hole positions, retained by granular barriers constructed at each end of the temporary infill area.
• Establishment of conveyor systems to transport granular infill materials to injection points in sensitive or inaccessible locations
  
• Use of specialist ‘dual head’ rigs allow clean, simultaneous drilling/casing methods to drill unstable & broken ground and to provide accurate, one pass fully cased holes for injection, monitoring, water abstraction or down hole surveys. These rigs also allow maximum use of angle hole drilling to minimise work impact in inaccessible, sensitive or residential locations
  
• Abstraction and control of mine water levels during infilling using borehole pumps and in-hole monitoring equipment.
  
• Ultrasonic and CCTV surveys of mines to assess condition and monitor infill progress

Example Mine Infill contracts include:

• MonsHill, Dudley – 200,000t PFA,
  
• Bosty Lane, Walsall - 60,000t Sand, 10,000t Stone
  
• Castlefields, Dudley - 500,000t PFA,
  
• James Adams, Walsall - 100,000t PFA
  
• Wrens Nest, Dudley - 220,000t PFA,
  
• Dark Cavern, Dudley - 200,000t PFA, 15,000t stone, 25,000t Sand
  
• Bream, Forest of Dean - included 3,000t PFA, 800m3 foamed concrete, 250m3 concrete & 1000m3 crushed stone
• Step Shaft gallery – 10,000 tonnes Sand

The Mine infill contracts shown above have required working in sensitive or densely populated residential areas, an operational cemetery, ecologically important areas including SSSI’s, SINC’s, nature reserves and sites of geological importance.

Such schemes have required detailed planning, management, proactive customer care and public relations, liaison with environmental specialists and agencies such as English Nature, together with the establishment of specific protection and reinstatement plans. We have achieved notable successes in this area by employing partnering and teamworking philosophies, consultation and involvement of all stakeholders throughout the project.

As an example of this commitment, the Bosty Lane Emergency Infilling Scheme in Walsall required infilling of collapsed and open limestone workings beneath existing residential properties. The works required access to all affected properties to undertake drilling and infilling work and extensive use was made of specialist dual head drilling rigs with clean drilling methods and sophisticated kinematics allowing maximum use of angled drilling with multiple holes drilled from key location thus minimising working area requirements and the impact to the public.

Construction of 130 lin m of stone infill barrier to the 7m high open section of mine used an innovative auger fed placement and distribution system based on a dual head drill rig, which was developed in-house. The system allowed a 65% reduction in the number of drill holes required for barrier construction thus giving a considerable time and cost saving to the client.

The project received commendations from Walsall Council Chief Executive and Residents Committee. Walsall Council have also used the scheme as part of a 2004 Local Authority Awards Submission emphasising the successful partnering achieved. The project was also short listed in the 2005 ICE Midlands Awards.