MINE SUBSIDENCE RISK MITIGATION WORKS: LEE 5 AND LOT 22 SITES AT COTTAGE CREEK PRECINCT - HDC287

The scope of works for the mitigation process to be considered by the Contractor includes, but is not limited to the items below. 

 

• Perform a grout trial program to assess appropriate grout mixes;

• Mobilisation and demobilisation, including site facilities (potentially including lighting) as necessary;

• Drill grout holes as required to below the base of the mine workings. All grout holes are to be drilled from within the Contractor’s work area.

• Install steel or plastic casing of sufficient strength to prevent “squeezing” of the casing and of sufficient diameter to allow tremie placement in the soil zone/ weathered rock zone. The steel casing is to be removed at the completion of the work, while the plastic casing below a depth of10m may remain if it is grouted in place;

• Install plastic casing, if needed, to mine level to keep the grout hole open;

• Supply, mix and pump grout into grout holes using a tremie pipe to mine level. The volume of grout injected maybe calculated using weight of dryash after validation of unit weight).To reduce the time frame of the project, provide a batch plant (including support vehicles i.e. trucks bringing in ash) capable of pumping a minimum of 200m3/day In a 10hr workday

• Provide a borehole camera and downhole sonar device with operator, onsite full time or available at short notice (to avoid non-chargeable standby time);

• Provide downhole geophysical and borehole deviation surveys available at completion of drilling each grout hole; with an option for verification holes and downhole velocity work.

• Meet environmental requirements, including dust control;

• Provide offsite water / waste material disposal;

• Provide Traffic Management;

• Provide onsite water management (pump, hoses and sandbags) appropriate for pollution management (silt traps);

• Obtain necessary work permits from Newcastle City Council and other pertinent agencies as needed (e.g. Hunter Water Corporation and Environmental Protection Agency);

• Obtain groundwater license from Office of Water Science

• Provide consultations and assistance in developing completion report.

 

In general, the subsurface conditions can be summarised as follows:

 

The soil zone is approximately 30mto35m thick with the groundwater level anticipated to be at a depth of 3m.The depth to groundwater varies with the tide;

 

• Interbedded siltstones and sandstones from the Lambton Subgroup of the Newcastle Coal Measures to a depth of approximately 68m. Previous boreholes encountered subsidence fractures in this material;

• The Borehole Seam is at about a depth of 68m to 74m, with some voids and  caving due to mining;

• The Borehole Seam is underlain by the Waratah Sandstone.

NSW Regions: Hunter

Open Tenders - An invitation to tender by public advertisement with no restriction placed on who may tender. Tenderers will normally be required to demonstrate in their tender that they have the necessary skills, resources, experience, financial capacity, and in some cases licences, accreditations, etc., to fulfil the tender requirements.

• Contract Award Notices:
  • HDC287  BFG Daracon Pty Ltd

Approvals: 4 weeks

Driling & grouting: 10 weeks

Validation Report and Rectification Works: 20 weeks

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