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Excavation

​General requirements 6.6.1

The contractor must:

  1. Carry out all excavation works in accordance with the requirements of the Mines Act 1958 Regulations and Statutory Rules, Occupational Health and Safety Act and all relevant Codes of Practice.

  2. Notify the Occupational Health and Safety Authority.

  3. Nominate the Mine Manager or statutory equivalent for the project.

  4. Comply with the general provisions of Section 21 of the Occupational Health and Safety Act.

  5. Comply with the Occupational Health and Safety Authority Codes of Practice.

Tolerances 6.6.2

Reinforced concrete pipes

Width:

  • the width of a trench mustn't exceed the minimum width by more than 100 millimetres unless approved by the Superintendent. The minimum width of the trench up to the top of the pipe must be in accordance with AS 3725-2007

Depth:

  • the depth of a trench shall be in accordance with the requirement of Drawing 7251/8/301 and, with the exception of where a special base is required, the depth of a trench must be within 100 to 150 millimetres below the proposed level of the bottom of the pipe. The excavation floor must be tried to reduce variations in the floor level to not more than 25 millimetres in the length of any one pipe

  • where required, additional excavation below sockets must be carried out to maintain a clearance of 100 to 150 millimetres below the bottom of the socket

Methods of excavation 6.6.3

For the purpose of this Specification, the methods of excavation are defined as follows:

  1. Trench excavation is the removal of ground from the surface to a depth necessary to execute the Works. A trench excavation is generally longer than six metres. The use of battered or benched excavations must be approved by the Superintendent.

  2. Shaft excavation is the removal of ground from the surface to a depth necessary to construct a drive or tunnel from the shaft. A shaft excavation is generally less than six metres.

  3. Drive excavation is the excavation of a tunnel between shafts or trenches. The drive is generally shorter than six metres.

  4. Tunnel excavation is the excavation of a tunnel between shafts, normally at manholes, inspection shafts or property connections. The tunnel is generally longer than six metres.

  5. Boring is the excavation of a hole between shafts or trenches using a boring machine, creating a hole slightly larger than the pipe outside diameter.

  6. Alternative excavation methods must be approved by the Superintendent.

Securing the excavation 6.6.4

  1. The Contractor must adequately secure the ground surrounding the excavation against movement, in accordance with General requirements of this Specification.

  2. Ground support in tunnels, drives and deep shafts must be left in place, unless otherwise approved by the Superintendent.

  3. For trenches and shafts, all ground support must be withdrawn as the refilling of the excavation proceeds, except where its withdrawal would endanger the safety of the Works, buildings, structures, streets and other surfaces over and adjacent to the line of the Works.

  4. If the ground support is left in position in open excavations, the ground support must be cut off at a depth at least 600 millimetres below the original ground surface.

Nature of ground 6.6.5

  1. If ground conditions endanger adjoining property, major services or require a change in construction method, the Contractor must notify the Superintendent.

  2. Any slippage which may occur during the course of the Works must be removed at the Contractor's expense. The excessive excavation and refill resulting from slippage must be dealt with in accordance with Excessive excavation.

Excessive excavation 6.6.6

Where the excavation depth and width exceed those specified in Tolerances, the Superintendent must assess the structural requirements of the pipe and direct the Contractor to refill the excessive excavation with one of the following, at the contractors expense:

Foundation and embedment zones

In wet sandy conditions, 20 millimetre single size coarse aggregate  compacted to a density index of 70%, elsewhere:

  • 20 millimetre Class '2' crushed rock, compacted to a minimum dry density ratio of 95%

  • 3% cement stabilised 20 millimetre Class '2' crushed rock compacted to a minimum dry density 95%

  • N20 Grade concrete, formed or screened to an even and uniform finish 

Backfill zone

Under road pavements:

  • 20 millimetre Class '2' crushed rock, compacted to minimum dry density of 98% 

Elsewhere:

  • A-grade sand as shown in:

  • Or selected excavated material as shown in the Backfilling Materials section compacted to minimum dry density of 95%

Excavated material 6.6.7

In privately owned property, the Contractor must progressively remove and dispose of all excavated materials from the site not required in the Works.

Excavated materials must be stored in accordance with 'Storage of Materials and Equipment' in the Protection of the Site management requirements section.

Drainage and dewatering 6.6.8

The contractor must:

  1. Keep the excavation free from water.

  2. Not discharge any drainage, dewatering, flushing or other waters into a sewer unless approved by the relevant sewerage authority.

  3. Obtain written permission from the owners, municipal council or authority controlling any constructed or partly constructed drain before using the drain for the discharge of any drainage, flushing or other waters from the trench.

  4. Control discharges to water-courses or drains so they comply with EPA requirements, and they don't adversely affect the beneficial uses of the area, as specified in SEPP - Waters of Victoria.

  5. Construct works and take all reasonable care to prevent silt entering the drainage network using appropriate techniques in relevant EPA publications. At the completion of the Works, the Contractor must leave the Works free of silt and reinstate all areas used for any temporary silt prevention works.

  6. Provide temporary waterways for all waterways, drains, channels and the like, intercepted during the progress of the work. At the completion of the Works, the Contractor must:

    • restore temporary waterways leaving them in their original condition before the commencement of the Works.

    • permanently divert temporary waterways in accordance with the Design Drawings or as directed by the Superintendent.

  7. Allowances must be made to cater for large flows which could cause erosion or damage.

  8. Take care when dewatering excavations or lowering the water table to ensure:

    • the safety of the foundations of the Works.

    • the safety of adjacent buildings, structures and services.

    • the integrity of any excavations, bores, including any private water bore or other subterranean works on the land adjacent to the excavation.

Blasting 6.6.9

No blasting is to be performed without prior approval from the Superintendent.

Unless specified on the drawings or in this specification no additional payment will be made for blasting.

The Contractor is liable for any accident, damage or injury to any person or thing resulting from the use of explosives.

To avoid injury from blasting to any person or livestock, or damage to any works, services, buildings or property on or near the Works, the Contractor must comply with the conditions of the blasting permit, the blasting restrictions specified on the Design Drawings and the following:

  1. Dangerous Goods Act 1985

  2. Dangerous Goods (Explosives) Regulations 2000

  3. Mines Act 1958  and Statutory Rules

  4. AS 2187.1-1998 Explosives - storage, transport and use - storage

  5. AS 2187.2-2006 Explosives - storage, transport and use - use of explosives

  6. all applicable regulations of the municipality in which the blasting operations are being carried out, regarding the use of explosives

  7. other statutory regulations that may apply

 

Last updated:
27 September 2017