Mining Subsidence Remediation Great Heck
Case study
Mining Subsidence Remediation Great Heck
Mining subsidence remediation and land drainage works at Great Heck for The Coal Authority, including drains, carrier drains, ditches, lagoons, headwalls and outfalls.
Scope
Lying alongside the Aire and Calder Navigation Canal mining subsidence has proved problematic for the Coal Authority. Sweeting Bros Ltd were contracted to undertake comprehensive land drainage remediation measures over a number of years.
Plans were drawn up between the Coal Authority taking the Client role and ourselves taking the Principal Contractor role. The scheme was to cross multiple landowners property and was designed as a pumped land drainage system comprising access haul roads, perforated land drains both new and connecting to existing systems, carrier drains in various sizes up to 450mm, culverts, ditches, lagoons, headwalls and outfalls.
Statistics:
- 121,000 metres perforated land drain installed to
depths up to 2.5m depth - 3200 metres of carrier drains
- 85 Ditch Outfalls
- 11 Buried Chambers incorporating silt traps or
inspection units - 18,300 tonnes of aggregate
- 30 GRP headwall outfalls
- Depths of works: up to 5.5m
- Maximum pipe diameters: 1200mm
- Trench boxes used due to poor ground conditions
- Localised de-watering
Key Aspects
Land Drainage
Following GPS surveys in the field and desk top studies to ascertain utilities and unexploded ordnance risks, Sweeting Bros Ltd are able to design land drainage plans using computer software. Transferring this information to the onboard computer of 5 Mastenbroek trenching machines, the design is able to be installed with pinpoint accuracy.
Ditches
It was necessary to link up the land drainage scheme with existing watercourse systems and in places create additional cuts and lagoons to enable water storage and discharge in a controlled manner. Client specific profiled bucket attachments were used to form the angled banks.
Culverts & Lagoons
Access roads through landowners property were to be maintained or re-routed. Culverts and stabilisation works were also a feature using gabion baskets and anti-scour protection measures for longevity of the installation.
Land Drainage Outfalls and Trenching
Land drainage outfalls into erosion protected ditch with culvert
Trenching machine excavating, installing pipework & backfilling in a single operation using GPS alignment
Challenges
Landowner Access & Liaison
Crossing numerous landowners property, it is necessary to form good working relationships to facilitate access, and understand their particular use of the land. Cropping and harvesting times all play key parts in the delivery of the contract and works need to be programmed to accommodate this.
Road/Footpath Closure
Works often entailed footpath restrictions and/or road closures and diversions to protect or segregate the public. It was necessary to obtain all licensing and permissions from the relevant authorities, whilst maintaining good relationships with residents. Communication of any anticipated inconvenience was undertaken at the earliest opportunity as part of the project programming.
Health & Safety
All workings were carried out compliantly under CDM 2015 protocols requiring Construction Phase Plans together with comprehensive assessment of all risks and method statements to minimise risks for all work elements.
Sweeting Bros Ltd are unique in that we have invested in mountain rescue sleds and equipment to facilitate patient evacuation in the event of an accident. Our work is often in secluded, inaccessible areas with very poor ground conditions such that ambulances or a helicopter may sink.
Biosecurity
Moving machinery from one property to another often requires biosecurity and environmental protocols to minimise transfer of contaminants or invasive species such as black grass. This is particularly important when working in protected sites such as SSSI.
Working with Water
Working in or around water poses hazards for employees arising from the natural environment. The presence of vermin and exposure to leptospirosis twinned with the possibility of drowning, all add to the normal risks involving accidents concerning machinery and moving parts.
Pumping out of accumulating / rising ground water is often necessary to ensure safe working conditions.
Planning a land drainage project?
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