S02 Excavation

S:02 EXCAVATION

Note: The term contractor is used interchangeably to describe both subcontractors & suppliers

1. Scope

1.1. The work of this Section comprises but is not limited to excavation, disposal of surplus

excavated material both on and off the site, cut and balanced fill where achievable, supply of compaction and filling material and the preparation necessary to bring the areas to correct shape and level prior to building construction.

2. Related Work

2.1. Demolition.

3. Reference Standards

Comply with the current relevant Australian Standards.

3.1.1. Comply with particular specifications in Building Regulations and/or Local Council publications.

Definitions

3.2.1.  Rock: Any natural or artificial material encountered in the excavation which cannot be removed until broken up by mechanical means such as rippers, jack-hammers or percussion drills.

3.2.2.  Rippable Rock: Means rock which can be removed by a single tyne, “D9” ripper.

3.2.3.  Non-Rippable Rock: Means all other rock.

3.2.4.  Other than Rock: All other material encountered in excavation.

3.2.5.  Sub-Grade: The natural ground below the excavations.

3.2.6.  Filling: A general term for all material spread and compacted over the sub-grade to make up finished levels or levels to the under-side of the base.

3.2.7.  Sub-Base: Selected filling spread and compacted over the sub-grade to make up levels to the underside of the base.

3.2.8.  Base: A selected filling layer spread and compacted to form an acceptable working surface directly under the building.

3.2.9.  Line of Influence: A line extending downward and outward from the bottom edge of a footing, slab or pavement and defining the extent of foundation material having influence on the stability or support of the footings, slab or pavement.

4. Approval for Variations

4.1. Before starting any excavation work which may involve a variation (whether addition or deduction) because of the nature of the material to be excavated, obtain a determination as to the nature from the Principal. The variation shall be derived from the agreed determination of the Principal and Structural Engineer. If no prior determination has been obtained, the variation, if any, shall be made only at the Principal’s discretion.

5. Use of Explosives

5.1. Explosives shall not be used.

6. Erosion Control

6.1. General: Plan and carry out the work so as to avoid erosion, contamination, and sedimentation of the site, surrounding areas, and drainage systems in accordance with sediment and erosion control diagrams as detailed on the drawings and to Local Council Authority requirements.

7. Dust Control

7.1. General: plan and carry out the works so as to avoid dust contamination and nuisance of the surrounding areas.

8. Survey Marks

8.1.  Definition: The term ‘survey mark’ means a survey peg, bench mark, reference mark, signal, alignment, level mark or any other mark used or intended to be used for the purpose of setting out, checking or measuring the work.

8.2.  Care of survey marks: Preserve and maintain the Owner’s survey marks in their true positions.

Rectification: If the Owner’s survey marks are disturbed or obliterated, immediately give notice and rectify the disturbance or obliteration.

9. Tree Protection

9.1. If applicable, refer to the Arborist Report for Tree Protection Zone requirements Trees to be retained

9.2. Marking: Mark trees which are required to be retained and relocated using suitable non-injurious, easily visible and removable means of identification. Remove the identification on completion Work near trees

9.3. Protection: Protect from damage trees which are required to be retained or transplanted. Work under trees: Do not remove topsoil from or add topsoil to the area within the dripline of the trees.

9.4. Harmful materials: Keep the area within the dripline free of construction material and debris.

9.5. Hand methods: Use hand methods to locate, expose and cleanly remove the roots on the line of excavation.

10. Site Clearing Extent

10.1. General: Clear only the areas to be occupied by structures, paving or landscaping. 10.2.

Clearing and grubbing:

10.2.1.  Clearing: Remove everything on or above the site surface, including rubbish, scrap, grass, vegetable matter and organic debris, scrub, trees noted for removal, timber, stumps, boulders and rubble.

10.2.2.  Turf: Remove turf to a depth just sufficient to include the root zone.

10.2.3.  Grubbing: Grub out or grind stumps and roots over 75mm diameter to a minimum depth of 500mm below subgrade under construction, and 300mm below the finished surface in unpaved areas.

10.2.4.  Take possession of surplus material and remove it from the site.

11. Excess Excavation

11.1 Excess excavation not authorised by the Supervisor or Principal and any consequent additional backfilling, compacting or testing, shall not justify a contract variation or extension of time.

12. Filling

12.1 Bring all filling on to the site unless it can be provided from spoil recovered from the site. Filling shall be sound material, free of perishable material, or any material that will form stable fill, but subject always to Engineer’s approval.

12.2 Filling shall be of the following types:

12.2.1.  Approved Excavated Material: The best of the clean inorganic excavated material, approved by the Engineer.

12.2.2.  Hardcore: Clean hard filling such as broken brick or stone rubble, consolidated in position.

12.2.3.  Porous Filling: Hard core graded from 40mm to 15mm.

12.2.4.  Sand: Salt free, loam free, packing quality

12.2.5. Fine Crushed Rock: 15mm to 5mm clean crushed rock. 12.3. Stockpile site topsoil required for re-use. Protect stockpiles from contamination by other excavated material, weeds and building debris.

13. EXECUTION

13.1. Examine all conditions. Start of work means total acceptance of all conditions.

14. Excavations Generally

14.1.  Suspend any ground works during inclement weather which would result in unsatisfactory work.

14.2.  Excavate accurately to shape and profile and keep free from loose earth and stones.

14.3.  Excavate generally as required or as shown on the Drawings, including but not necessarily limited to the following:

14.3.1.  Removal of all footings and unnatural items to 900mm below grade.

14.3.2.  Preparation of sub-grade as necessary.

14.4.  Trim the sub-grade surface evenly to the profiles shown on the Drawings.

14.5.  Make allowance for settlement and compaction.

14.6.  Allow for falls in slabs on grade to streets, driveways and outlets.

14.7.  Prepare ground and place rubble for rumble-pad access to site.

14.7.1.  Rubble to be 50mm diameter in size

14.7.2.  Excavate behind existing kerb to a depth of 150mm to allow for rubble pad buildup to kerb height

14.8.  Prepare for underground services, referred to in other Sections of the Specification.

14.9.  Prepare for strip footings, footing beams, pad footings, ducts and pits, to depths shown.

14.10.  Carry out additional excavation where necessary to permit full use of suitable mechanical equipment |e.g. rippers) and back-fill with appropriate material as specified in this Section.

14.11.  Crawl space: Provide a clear space under timber or steel bearers.

14.11.1. Minimum clearance: 400mm.

14.11.2. The BCA calls for a general clearance of 400mm under suspended timber floors that can be reduced to 150mm within 2m of an external wall for sloping sites.

14.12.  Provide even plane bearing surfaces for loadbearing elements including footings. Step for level changes. Make the steps to the appropriate courses if supporting masonry.

14.13.  Where excavation exceeds the required depth, fill back to correct depth with material as follows:

14.13.11 below slabs on ground: Hardcore;

14.13.12 below footings, beams and other structural elements: Concrete of strength equal to the structural element, minimum 15Mpa. – In service trenches: 1:2:4 concrete/approved compacted pipe bedding material.

14.13.3 Existing Footings: If excavation is required below the line of influence of an existing footing, use methods which maintain the support of the footing and ensure that the structure and finishes supported by the footing are not damaged.

14.13.4 Grading: Grade the ground surface externally and under suspended floors to drain ground or surface water away from buildings without ponding.

15. Bad Ground

15.1.1. Should unsuitable material be encountered at the prescribed depths of excavation, or soft, wet and unstable areas develop during excavation, obtain instructions from the Engineer before carrying out additional excavations. Back-fill and compact to the correct levels as directed.

16. De-Watering
16.1. Maintain excavations, leveled and filled areas free of water by temporary catch drains, sumps, pumping, bailing or whatever means are suitable and effective.Immediately before placing concrete or masonry on ground remove all free water and foreign matter.

17. Bearing Surfaces in Rock

17.1. Should rock be encountered during excavation the Principal & Engineer is to be notified and their instructions obtained prior to proceeding with the work in that area except where rock has been allowed for in the design.

17.2.  Where structural loads bear on rock, unless otherwise specified, scabble the rock face to give even plane bearing surfaces, level unless required to be sloping or stepped.

17.3.  Bored pier holes shall be taken a minimum of 300mm below the rock surface and the bottoms cleaned of all loose matter.

18. Compaction

18.1.  Place filling in layers not exceeding 150mm deep when measured loose.

18.2.  Bring filling to optimum water content by watering, and compact each layer thoroughly and uniformly with a vibrating roller where practicable.

18.3.  Hand tamp against ground or perimeter beams or walls.

18.4.  Compact each layer of filling to obtain a uniform density of not less than 95% of the maximum density at optimum moisture content as determined by the Dry Density/Moisture Content tests set out in current relevant Australian Standard.

18.5.  Finish the base to the following tolerances:

18.5.1. Variation from designed level: 5mm Variation from 3000mm straight edge: 5mm

19. Clean Up

19.1. On completion of all work specified above, remove all surplus materials imported to the site, level off surplus excavated material, or pile such material on the site as directed by the Contractor.

20. Completion

20.1. Complete all contracted work in accordance with contract documents and written variation orders issued by the Principal Contractor or its authorised representatives, supervisors.

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