1. PURPOSE
This fabrication and erection specification defines the grading, excavation, and backfilling for civil engineering works.
- SCOPE
This specification applies to civil engineering works on all Air Products (AP) sites.
- RELATED DOCUMENTS
3.1 Air Products Engineering Documents
4ECE–M17 Site Preparation and Reinstatement
3.2 In addition, the contractor shall conform to all national and local laws of the country in which construction takes place.
- DESIGN
4.1 The engineer will supply the contractor with drawings showing the extent of works, grading levels, bench mark details, and all relevant dimensions for the excavations.
4.2 The contractor shall furnish the engineer with drawings and/or details of the proposed methods of temporary construction necessary to carry out the works. Such proposed methods shall be subject to approval by the engineer.
- SOIL INVESTIGATION
If a soil investigation has been carried out, a copy of the soils report will be carried to the Contractor, but this will not relieve him of his obligations under the Conditions of Contract.
- EXCAVATION
6.1 Before commencing any excavation work, the contractor shall request from the AP Design Department drawings of all known existing underground hazards (such as high voltage cables and pipes containing hazardous fluids) within the vicinity of the works. Such information shall not negate the contractor’s responsibilities as defined in the Conditions of Contract.
6.2 All excavations shall be carried out to the lengths, breadths, depths, slopes and curves required for the construction of the works as specified on the drawings, with adequate allowance for working space.
6.3 The contractor shall be responsible for all excavation work and shall take all precautions necessary to ensure safe working conditions and to prevent deterioration of the excavation.
6.4 Excavated materials shall not be deposited near the sides of the excavations where the stability of the sides would be endangered.
6.5 When soft spots occur in the excavation, the contractor shall remove the soft material and fill the cavity with a lean concrete or approved compacted fill as directed by the engineer.
6.6 Where the excavation is for a structural slab, beam, or foundation, the last 75 mm of excavation shall be left in until immediately prior to blinding.
6.7 The contractor shall make good with suitable approved material or concrete as directed by the engineer:
Any excavation in excess of the net volume required for the Works as described in the contract.
Any additional excavation at or below the bottom of foundations to remove material which the contractor has allowed to become unsuitable.
The extra cost involved except for removing soft spots shall be to the contractor’s account.
6.8 When underground obstructions other than working services are encountered, they shall be broken out and any resulting voids shall be filled with lean concrete, or approved compacted fill as directed by the engineer.
6.9 All pipes, ducts, cables, mains, and other services exposed by the excavations shall be effectively supported by timber, slings and chains, or other approved means. The size and position of every service shall be carefully measured and recorded on the ‘as-built’ drawings. Any damages to existing services must be immediately reported to the engineer.
6.10 When excavation borders on a highway, public, or factory area, adequate barriers and warning lights shall be provided and the contractor shall comply with the local authority’s requirements.
6.11 Before placing concrete, blinding, or underground service materials on excavated works, the approval of the engineer shall be obtained as to the suitability of the exposed subsoil surface.
6.12 All excavated material suitable for re-use shall be stored safely on site in a location that will not interfere with other operations, as directed and permitted by the engineer. Surplus excavated material shall be removed from site as work progresses and shall be deposited on a tip provided by the contractor or otherwise disposed of as directed by the engineer. All charges shall be to the contractor’s account.
6.13 Excavations close to existing structures or piles or within 3 metres of existing services shall be carried out by hand to avoid possible damage.
- BLASTING
7.1 When the contractor proposes blasting, prior written permission of the engineer must be obtained.
7.2 The contractor shall conform to all statutory regulations and the requirements of Air Products engineering specification 4ECE–M17.
- TIMBERING, SHEET-PILING, TRENCH SHEETING AND UNDERPINNING
8.1 The contractor shall supply, fix, and drive all poling boards, sheet piling, whalings, struts and any other necessary temporary work for supporting the sides of open excavations and trenches.
8.2 When excavations pass under or close to roads, services, foundations to buildings, or structures, all necessary beams, bearers and supports shall be provided to underpin these roads, services, or foundations to the satisfaction of the engineer. Before excavations commence, the contractor shall have all materials available to avoid delays.
8.3 If timbering, piling, sheeting or other supporting members are required to be left in position, a written instruction to the effect must be obtained from the engineer.
- DEWATERING
9.1 The contractor shall carry out dewatering as necessary to keep the site and works free from water. The works consist of all earthworks including filling and excavations whether for pipe trenches, foundations, or cuttings. Dewatering equipment shall be placed outside the main work and must be approved by the engineer.
9.2 When practicable, the water shall be discharged into a permanent outfall for the drainage system. Adequate means for trapping silt shall be provided on temporary systems when discharging into permanent drainage systems.
9.3 The contractor shall provide, when necessary, temporary water courses, ditches, drains, pumping, or other means of maintaining the earthworks free from water. Such provision shall include forming of cuttings and embankments in such a manner that their surfaces have at all times a sufficient minimum crossfall and, when practicable, a sufficient longitudinal gradient to enable them to shed water without ponding.
- BACKFILLING
10.1 The spaces between concrete and/or brickwork and the sides of excavation shall be filled with selected excavated material and shall be well compacted as in clause 11.2, all to the satisfaction of the engineer.
10.2 When excavated material is or becomes unsuitable for backfill material as defined in clauses 11.1.3 and 11.1.4, suitable material for backfill shall be imported to the satisfaction of the engineer at the contractor’s expense.
- MASS FILLING
11.1 Material
11.1.1 Filling material shall consist of suitable approved material, either excavated or imported to the site. Unless defined otherwise on the drawing, the material shall be capable of being compacted as described in clause 11.2 to form a stable fill with side slopes as shown on the drawings.
11.1.2 The contractor shall provide facilities for the engineer to inspect the source of all imported material. Delivery shall not commence until approval is obtained.
11.1.3 Materials listed below are not suitable:
Material from swamps, marshes or bogs.
Peat, logs, stumps and perishable material.
Material susceptible to spontaneous combustion.
Material in a frozen condition.
Clay of liquid limit exceeding 80 and/or plasticity index exceeding 55.
Material having a moisture content greater than the maximum permitted for such materials in the contract, unless otherwise permitted by the engineer.
11.1.4 Materials in a frozen condition, if otherwise suitable, shall be classified as suitable when unfrozen.
11.2 Compaction
11.2.1 Unless specified otherwise, compaction methods shall be agreed before work commences and the water content adjusted as necessary to give optimum moisture content to the satisfaction of the engineer. In case of disagreement, the degree of compaction will be determined by independent authority, selected by the engineer and paid for by the contractor. If the state of compaction is thereby shown to be inadequate, the contractor shall at his own expense carry out such further work as the engineer may decide is required to comply with the terms of the contract. A minimum compaction of 95% maximum density shall be required.
11.2.2 The contractor shall use special equipment such as power vibrating plates to ensure full compaction against, but without damage to, existing structures or services.
11.2.3 All material placed shall be deposited and compacted as soon as practicable after excavation. Embankments shall be built up evenly over the full width and shall be maintained at all times with a sufficient camber, and a surface sufficiently even, to enable surface water to drain readily from them. During the construction of embankments the contractor shall control and direct constructional traffic uniformly over their full width. Damage to compacted layers by constructional traffic shall be made good by the contractor.
11.2.4 If the material deposited as fill subsequently reaches a condition such that it cannot be compacted as specified, the contractor shall either:
Make good by removing the material from the site and replacing it with suitable material; or
Make good the material by mechanical or chemical means to improve its stability; or
Cease work on the material until its physical condition is again such that it can be compacted as described in the contract.
11.2.5 Rocks or boulders over 150 mm across in any direction shall be removed or placed at a depth greater than 1m from formation level.
11.2.6 If carrying embankments up to or over structures, culverts, or pipe drains, the contractor shall bring the embankments up equally on both sides.
11.2.7 If the contractor wishes to continue to use the surface area of embankments for constructional traffic before trimming to formation level, he shall bring up and maintain the total area including (if any) hard-shoulders to a level not less than 150 mm above formation level; whereupon constructional traffic will be allowed to use the surface so formed but any damage to the subgrade caused by the use of such surface shall be made good by the contractor at his own expense. When it is necessary to complete to formation level and this has been done, the movement and use of constructional plant thereon shall not be permitted.
11.3 Preparation and Surface Treatment of Formation
11.3.1 Preparation and surface treatment of the formation shall be carried out only after completion of any specified sub-grade drainage or other underground works and, unless otherwise agreed by the engineer, immediately prior to laying the sub-base or the road-base where no sub-base is required. The sequence of operations for formations of materials other than rockfill shall be as follows:
All surfaces below buildings, paved areas, roads and hard-shoulders shall, after reinstatement of any soft spots, be well cleaned and free from mud and slurry.
The surface shall be compacted by four passes of a smooth-wheeled roller having a load per metre width of roll of 4.5 – 6.3 tonne.
The formation shall be trimmed to the requirements of the drawing.
The trimmed formation shall be rolled by one pass of a smooth-wheeled roller having a load per metre width of roll not less than 2 tonne.
11.3.2 When the completed formation is not immediately covered with sub-base or road-base material, it shall be protected by a membrane of 500 gauge impermeable plastic sheeting with 300 mm laps set to prohibit ingress of moisture. If the contractor allows the moisture content of accepted compacted material to reach a value above the maximum permitted for the material, under the contract, the contractor shall allow the material to revert to an acceptable moisture content and, if directed by the engineer, make good at his own expense the surface by recompaction before laying sub-base or road-base. Alternatively, should there be insufficient time within the contract period to allow the material to revert, the contractor shall remove the material from site, replace and compact as specified.
11.4 Benching
11.4.1 When an embankment is to be placed on appreciably sloping ground, the ground shall be benched in steps or trenched, as shown on the drawings, including, if necessary any under-draining of the affected part of the site.
11.4.2 The benching or trenches shall be kept free of water in accordance with clause 9.
- HARDCORE
12.1 Hardcore shall consist of well compacted, graded, and hard broken brick, slag, shale, or stone free from dust and passing a 100 mm ring or such other grading as specified by the engineer.
12.2 Where hardcore blinding is required, stones, etc. shall be graded from 50 mm down.
12.3 Hardcore exceeding 100 mm in depth shall be compacted to the satisfaction of the engineer.
- THRUST BORES
13.1 The contractor shall drive the thrust bore to the line and levels, and within the tolerances indicated on the drawings. The contractor shall be responsible for checking the nature and profile of existing ground, particularly when driving through embankments, to ensure that the gradients shown on the drawings are correct. Before commencement of boring, the contractor shall serve all statutory notices.