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Foundation Excavation for Irrigation supplies
- This Specification Section covers excavation required for the construction and rehabilitation of irrigation canals, associated structures such as abutments, flumes, piers, and retaining walls and ancillary work such as drainage pipes.
- Excavation shall consist of excavation, removal and satisfactory disposal of all materials necessary for the construction of permanent works in accordance with the requirements of the Specification to the lines, grades and cross-sections shown on the Drawings or as otherwise directed by the Employer’s Representative.
- This work shall include the hauling and stacking, or hauling to sites of embankment also the disposal of unsuitable materials in specified manner, de-watering and pumping, and the trimming and finishing of excavation lines to such widths, depths, levels and profiles as shown on drawings or to such other dimensions and levels as may be ordered by the Employer’s Representative.
Classification of Materials
For payment purposes, materials excavated shall be classified by the types of facilities or structures shown in the Bill of Quantities. The nature of materials such as clay, sand, rock, etc, will not be considered for payment purposes.
- Prior to any
excavationthe work shall be set out as directed by the Employer’s Representative.
- Before commencement of excavation, a survey of the existing ground levels shall be made by the groundwork specialists. The survey records shall serve as an initial measurement for the determination of the final quantities of excavation performed under the Contract, and for related purposes.
- Clearing and grubbing shall be performed in all excavation areas.
- Stripping and storing of topsoil shall be performed as specified:-
- All excavation shall be made in accordance with the provision stated herein or as directed by the Employer’s Representative and to the grades shown on the Drawings or established by the Employer’s Representative.
- Change of Slopes: During
progressof the work it may be found necessary or desirable by the Employer’s Representative to vary the slopes of excavation or the slopes of embankments and the dimensions dependent thereon, and the Contractor shall execute the work in accordance with these specifications. Any increase or decrease of quantities excavated as a result of such variations shall be subject to the provisions stipulated for variations set forth in the Conditions of Contract.
- Sliding Material: Materials which will not stand on the slopes shown on the Drawings or established by Employer’s Representative, and materials which are a part of slides extending beyond the established lines of excavation which move into excavated areas, shall be removed by the Contractor in an approved manner, and the slopes shall be refinished to lines and grades established by the Employer’s Representative. The Contractor shall be required to excavate potential slide areas beyond the limits of the originally staked excavation where, in the judgment of the Employer’s Representative, such excavation is necessary to prevent damage to the work.
- Excavation Lines: Where excavations are not to be covered by structures or other required construction, they shall be made to the full dimensions required and shall be finished to the neat lines and grades shown on the Drawings or to such other lines and levels determined by the Employer’s Representative. All necessary precautions shall be taken to preserve the material below the lines of all excavation in the soundest possible condition. Any over excavation made for the convenience of the Contractor or for any purpose or reason, except as otherwise provided herein, shall be refilled and compacted by the Contractor at his expense as directed by the Employer’s Representative.
- Use of Material: It is anticipated that most of the materials from required excavation will be suitable for use in the construction required under the Contract. As far as practicable, all suitable materials shall be placed in the designated final locations directly from the excavation, except the backfill materials, which shall be placed in temporary stockpiles and later placed in the designated location. As determined by the Employer’s Representative, all materials designated for use in compacted embankments shall be brought to the proper water content before and during excavation.
- Subsurface Water: Part of the required excavation will be below the subsurface water level. Any lines of water levels shown on the Drawings can be considered as tentative information only. The Contractor shall not be entitled to derive any claim therefrom and he shall select his equipment and programme his constructional operations and the timing of these operations so as to complete the works to the satisfaction of the Employer’s Representative.
- Surface Water: The Contractor shall take all necessary precautions to protect the work from surface water by constructing provisional bunds, drains or similar means, or by pumping, as may be approved or directed by the Employer’s Representative.
- Whenever it becomes necessary during the course of the work to determine the volume of excavation in channels which are filled or partially filled with water, the Contractor shall furnish and maintain the required equipment for measuring and shall assist the Employer’s Representative in making such measurements.
- Gravel: Where gravel is encountered during excavation and such gravel is suitable for surfacing operations and maintenance or service roads or paths, or for further gravel lining, as may be determined by the Employer’s Representative, the materials shall in so far as practicable be stockpiled along the right-of-way where designated by the Employer’s Representative.
- Spoil Banks: Excavated materials containing stumps, roots, vegetable matter and other objectionable materials and excavated materials that are not required for backfill, embankments and other permanent construction shall be placed in designated spoil banks in waste areas designated by the Employer’s Representative. Spoil banks adjacent to the canal embankments shall be continuous except for gaps at suitable intervals for transverse drainage as shown on the Drawings or as directed by the Employer’s Representative. All spoil banks and waste areas shall be levelled and sloped to drain and trimmed to reasonably regular lines as shown on the Drawings or as directed by the Employer’s Representative.
when encountered in the excavationshall be removed down to the foundation level or as otherwise indicated on the Drawings. Where, however, unstable shale or other similar materials are interfaced at the foundation level, these shall be excavated to the extent of 500 mm below the foundation level or as otherwise directed. In all cases, the excavation operations shall be so carried out that at no point on cut formation shall the rock protrude above the specified levels; provided, however, that a negative tolerance of 300 mm shall be permissible.
- Slopes in rock cuts shall be finished to uniform lines corresponding to slope line shown on the Drawings or as directed by the Employer’s Representative. Notwithstanding the foregoing, all loose pieces of rock on excavated slope surface which move when raised by a crowbar shall be removed.
- Where blasting is to be used, the same shall be carried out as per instruction of
Slushy Soil Excavation:
- The excavation of marshes and swamps shall be carried out as per the programme approved by the Employer’s Representative.
- Excavation of marshes shall begin at one end and proceed in one direction across the entire marsh immediately ahead of back filling. The method and sequence of excavation and back filling shall be such as to assure, to the maximum extent practicable, complete removal or displacement of all muck from within the internal limits called for on the Drawings or as stated by the Employer’s Representative, and to the bottom of the marsh, firm support, or levels indicated.
Excavation for Surface Drains:
Where the Contract provides for the construction of surface drains excavation for these shall be carried out in proper sequence with other works as approved by the Employer’s Representative.
Preparation of Foundation:
- Upon completion of the excavation of the lines and levels shown on the Drawings or directed by the Employer’s Representative, the foundation for sites shall be inspected by the Employer’s Representative and the cut formation shall be prepared to receive the base course as directed by the Employer’s Representative.
- Where material in a poor state of compaction is encountered at the foundation level, the same shall be loosened to a depth of 500 mm and compacted in 250 mm thick loose layers in accordance with the requirements . Any unsuitable materials encountered shall be removed at the discretion of the Employer’s Representative.
- The bottom of the foundation shall be leveled both longitudinally and transversely or stepped as directed by the Employer’s Representative. Before placing the concrete, the surface shall be watered and rammed if necessary, but no standing water shall be permitted on the foundation. In the event of the foundation having been made deeper than that shown on the drawings or as otherwise ordered by the Employer’s Representative, the extra depth shall be made up with concrete or masonry to the foundation grade at the Contractor’s cost. Ordinary backfill shall not be used for the purpose of bringing the foundation to level.
- When rock or other hard stratum is encountered, it shall be left free of all soft and loose material, cleaned out to a firm surface either level, stepped or serrated as directed by the Employer’s Representative. All seams shall be cleaned out and filled with cement mortar or grout to the satisfaction of the Employer’s Representative.
- Finishing operations shall include the work of properly shaping and dressing all excavated surfaces.
- When completed, no point from the slopes shall vary from the designated slopes by more than 150 mm measured at right angles to the slope, except where excavation is in rock (hard or soft) where no point shall vary more than 600 mm from the designated slope. In no case shall any portion of the slope encroach on the finished lines of structures.
- The finished cut formation shall satisfy the surface tolerance described elsewhere.
- Where directed, the top soil removed earlier and stored shall be spread over cut slopes, embankments and other disturbed areas. Slopes may be roughened and moistened slightly prior to the application of topsoil in order to provide the satisfactory bond. The depth of topsoil shall be sufficient to sustain plant growth, the usual thickness is 75 mm to 150 mm.
Excavation for Structures
- General: The bottom and the side slope of excavation upon or against which structures or other required constructions are to be placed shall be finished accurately to the Drawings and, if required by the Employer’s Representative, shall be moistened with water and tamped or rolled with suitable tools or equipment for the purpose of forming a firm foundation.
- Over Excavation: If at any point in the excavation, the material is excavated beyond the established lines and grades, it shall be over compacted by tamping or rolling in layers not more than 15 cm thick at the Contractor’s expense. Whenever the natural foundation material is disturbed or loosened because of the Contractor’s excavation operation, it shall be consolidated by tamping or rolling, if required by the Employer’s Representative, or shall be removed and replaced at the Contractor’s expense with selected material which shall be thoroughly compacted.
- After the excavation is completed, the Contractor shall inform the Employer’s Representative to that effect and no footing, bedding material or structure shall be placed until the Employer’s Representative has approved the depth and the suitability of foundation material. Rock and other hard foundation material shall be cleaned of all loose materials.
- Unsuitable Material: If, at any point in any structure excavation or excavation for other required construction, material unsuitable for foundations is encountered, as determined by the Employer’s Representative, the Contractor shall, if so ordered by the Employer’s Representative, in writing, remove all such unsuitable material and refill with selected and approved materials thoroughly compacted by tamping or rolling in layers not more than 15 cm thick.
- Stability of Excavation: Excavation for structures shall be carried out to the lines necessary to permit the proper construction of the structure and the Contractor will be responsible for ensuring the stability of side slopes and for the provision of such timbering, shuttering or other support as he may deem to be necessary. The approval of the Employer’s Representative shall not relieve the Contractor of his obligation to carry out all excavation in a safe manner.
- Variation of Slopes: During the progress of the work, it may be found necessary to vary the slopes of the dimensions of the Excavation from those shown on the Drawings or established by the Employer’s Representative. Subject to the provisions set forth in the Condition of Contract, the Contractor shall not be entitled to additional allowance above the unit rates quoted for structure excavation in the Bill of Quantities or to any other variation of the applicable unit rate for excavation.
Excavation for Canals and Drains
- Variation of Dimensions: Canals, farm ditches, and drains shall be excavated (or rehabilitated) to the lines and grades shown on the Drawings, unless the Employer’s Representative determines that the stability of the earth material (in which the canals, ditches, and drain will be constructed and which will form the banks) or other factors make it necessary or desirable during the progress of work to vary the slopes of embankment and the dimensions dependent thereon and so informs the Contractor in writing. Subject to the provisions set forth in the Conditions of Contract the Contractor shall not be entitled to the variation of the unit rates quoted for excavation of drains and canals in the Bill of Quantities in payment for such additional work.
- Over Excavation: Excavation in such a manner as to cause over excavation which in the opinion of the Employer’s Representative is excessive will not be permitted. Canals, ditches, and drains shall be excavated to the full depth and width required and shall be finished uniformly to the prescribed lines and grades; provided that if the Contractor prefers to excavate under water that portion of the canal section may be
over excavatedto not more than 30 centimetresmeasured normal from the prescribed lines and grades; provided further that where the existing cross sectionof a canal or drain is exceeding the design section, refilling will not be required.
- De-watering: De-watering a canal, ditch, or drain for dry excavation will be permitted provided the measures taken by the Contractor have been approved by the Employer’s Representative, and provided further that regardless of whether the canal, ditch, or drain is excavation dry or wet the Contractor shall not be entitled to a variation of the unit rates quoted for excavation of canals, ditches, and drains in the Bill of Quantities in payment for such work.
- Interruption of Local Facilities: Local facilities like irrigation channels, roads etc. are to be properly maintained in the case of their interference with works. The Contractor shall be responsible for maintaining the local facilities so that the services of such facilities are availed. The costs, if any, are to be borne by the Contractor.
Measurement for Foundation Excavation:
- Excavation shall be measured by taking cross sections at suitable intervals in the original position before the work starts and after its completion and computing the volume in cubic meters by the method of average and areas. Where it is not feasible to compute volumes by this method because of erratic location or isolated deposits, the volume shall be computed by other accepted method.
- Where the Bills of Quantities includes an item for stripping in the schedule, measurement for payment for excavation will be computed from elevation 0.2 m below original ground level.
- At the option of the Employer’s Representative, the Contractor shall leave depth indications during the excavation of such shape and size and in such positions as directed so as to indicate the original ground level as accurately as possible. The Contractor shall see that these remain intact until the final measurements are taken.
- Excavation for canals, farm ditches, drains,
andstructures shall be measured in cubic meters for the respective features, limited to the dimension shown on the Drawings or as otherwise directed by the Employer’s Representative.
Payment for foundation excavation:
Payment for the various types of excavation shall be made at the Contract unit rates tendered therefore in the Bill of Quantities. The Contract unit rates for the items of excavation shall include full compensation for the following operations:
- Site clearance where the Bill of Quantities contains no item for clearing and grubbing in the Schedule.
- Assistance in setting out profiles.
- Removal of boulders including loosening to required depth for the removal of surface boulders and other unsuitable materials if any back filling and compacting, if required.
- Excavation in all types of materials.
- Transporting the excavated material and depositing on the sides of embankments spoil banks or stacking as directed.
- Trimming bottoms and slopes of excavation.
- All labour, equipment, tools sheeting, bracing, drills, explosives and other incidental used to complete the work.
A. Payment will be made under the applicable item of the Bill of Quantities for the excavation of the unsuitable foundation material, excavation of slide materials from slides which are beyond the control of the Contractor, and for refilling and compacting of such excavation as directed and approved by the Employer’s Representative. Measurement and payment will be made under the applicable item of the Bill of Quantities for placing of backfill in such excavations. Cost of re-handling and transporting backfill material from stockpiles, if so required, shall be included in the unit rate tendered in the Bill of Quantities for backfill around structures.
B. No Payment will be made for excavation made for the convenience of the Contractor for any purpose or reason, for over-excavation or fill beyond the established lines and grades, and for removal of materials disturbed or loosened because of the Contractor’s Operations.
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