Below is a brief method statement that details general procedures to be followed for excavation & backfilling of foundations, Sub-structures & Trenches for any type of the construction and road project.
The method covers survey works, excavation, backfilling, compaction and area cleaning after the completion of works.
Separate work method statement, will be generated by the sub-contractor for anti-termite treatment and control that is related to the excavation works.
Below is sequence of work:
- Excavation.
- Compaction/Consolidation of formation of excavation.
- Anti-Termite Treatment.
- Blinding Concrete/ RCC Footings/ Tie beams.
- Backfilling
Equipment Tools & Manpower
- Bulldozers
- Excavators
- Shovels
- JCBs
- Water Tanker
- Total Stations
- Auto Levels
- Dump Trucks used for disposal of debris
- Plate Compactor
- Bobcat
- Telehandler
- Manual Shovel
- Dump Truck used for disposal of debris
Health & Safety Requirements
Water shall be sprayed as required on heaped excavated materials to control the dust.
Importance shall be given to all safety procedures so that the excavation activities can be carried out in safe conditions.
For all excavations in traffic areas, adequate barriers, signboard, warning signs, traffic control and flashing lights shall be provided.
Warning tape shall be installed around the excavated area 1m away from the top of excavation.
Steel bars shall be used as posts with warning tape on the excavation’s perimeter.
If an existing service is exposed during the excavation, the service should be properly protected and supported during all the activities.
For deep excavations the sides of the excavation shall be sloped, stepped or shored for stability.
Proper and safe access to the bottom of the excavation shall be given by ladder staircases with top and mid rails and toe boards.
Utmost importance shall be given to safety of personnel and protection of existing above /underground services.
It will be ensured that the personnel involved are thoroughly aware of the Contractors / Engineer Safety regulations.
To achieve the above the following shall also be ensured:
Tool Box Meetings will be conducted before starting the works.
HSE audits on site shall be carried out every fortnightly and report submitted in approved format.
All personnel will be provided with suitable Personal Protective Equipment.
Required permits will be obtained from the concerned authorities before starting the works.
Plant & Equipment’s shall be fully tested for safety compliance.
Third party load test certificate shall be submitted for tower crane before use.
Excavations shall be adequately barricaded and warning signs and lights shall be posted in line with the safety requirements.
Safe means of getting in to and out of excavation pits shall be provided.
Underground and above the ground services will be identified, rerouted or isolated (as appropriate) prior to the commencement of the excavation works.
Roles & Responsibilities
Project Manager
He shall be responsible for the following:
Ensuring that the project works in his supervision are carried out in accordance with company policies and in accordance with the requirements of the quality plan.
Ensuring the full compliance of subcontractors with company quality policies and with the requirements of the project quality plan.
To ensure that all the equipment required to execute the works according to the construction program are available, in good condition, and provide any additional equipment that might be required.
Coordinate with the Construction Manager, Project Engineer, Safety Engineer, Foreman and Surveyor for a safe and proper execution of the works.
To guide specific attention to all safety measures in co-ordination with the safety officer/engineer.
Construction Manager
Ensure area is ready and safe to start the works.
Set up required equipment and plant through discussion with the Project Manager and Project Engineer/Works Supervisor.
Ensure the works are carried out according to the specification, quality and approved shop drawings.
Liaise and co-ordinate with the Project Manager for the agreed sequence of works with respect to the construction program.
Allocation of required manpower through co-ordination with the project manager.
Provide the risk assessments for the works in hand.
Provide sufficient and safe access for operatives, trucks and pumps.
Take precautionary measures with regards to protecting works from hot weather, wind, rain and sun.
Project Engineer
The engineer shall carry out his duties in a manner that shall be coordinated by the project manager on a daily basis, and shall ensure proper distribution of the workforce and equipment at required locations.
He shall be aware of test frequencies related to the formation level.
To control disposal of waste excavated material according to the instructions received from the project manager.
Coordinate with the safety officer to maintain safe working and proper housekeeping of the site.
To comply with the safety measures and ensure that all Safety Officer Teams are aware of the same to prevent accident and loss.
Monitor and check all activities and ensure that works shall be carried out according to specifications, quality and approved drawings.
To inform the QC Inspector of the working areas ready for inspection.
QA/QC Engineer / Inspector
Ensuring that Consultant/Client inspection requests are implemented.
Compilation of all necessary quality control checklists
Assisting Consultants during the Inspections.
Coordinating with the third party lab regarding tests and results.
The control work performance by means of checking the work before consultants’ inspection and issuing RFIs & punch lists as necessary.
Completion of documentation to verify the work performed.
Controlling all inspection activities on site in line with ITPs.
Ensuring that all test equipment including surveying equipment is calibrated and is suitable for use on-site.
Surveyor
To establish benchmarks from agreed reference points, provide required setting out and level markings and follow up with regular checks.
Co-ordinate with the Project Engineer / Foreman and ensure the approved shop drawings/construction drawings shall be implemented properly.
Maintain survey details and reports, periodically check the progressing works and advise the project manager of any deviation from the drawings.
HSE Engineer/Officer
To ensure implementation of all safety measures related to the nature of works being carried out, and in accordance with the Project Safety Plan.
Ensure that all the persons involved in the works are aware of their responsibilities, and that they have enough understanding of the safety procedures.
The safety officer in co-ordination with the Project Manager shall ensure that all the implemented safety measures are effective enough to maintain safe working on the site.
To maintain continuous inspections of the site activities, advise and train persons on a daily basis to prevent accidents and personnel injury.
Give special concern to housekeeping, and ensure that the site is maintained clean and tidy.
To ensure all the relevant safety sign boards for different works are in place.
Foremen/ Works Supervisor
Ensure the works are progressed in the sequence as agreed with the Project Manager.
Liaise with the Project / Construction Manager for the allocation of the work force, ensuring adequate manpower is available.
Liaise with the site manager to ensure all the required plant / materials are available to construct the works.
Full time supervision shall be required to ensure the works are carried out in accordance to specifications, quality and approved drawings.
Excavation Works Method
Before commencement of the work, ascertain the nature and location of all existing above and underground services on site by visual survey and making trial pits or by reviewing the service layout drawing (if available).
Excavation shall be executed to the lines and grades indicated on the drawings. The surveyor shall monitor the excavation depths to prevent any over excavation. The excavation levels shall be maintained within the specified tolerance limits i.e. plus or minus 25mm.
Mechanical excavation around the footing locations shall be stopped at 150mm above the footing top level. Deeper excavation shall be done by hand to the footing’s top level.
The surveyor shall mark layout of the footings using pegs. The Layout shall be offered for inspection to the consultant for approval.
Once the footing layout is approved excavation of the footing shall begin.
In case of an area is excavated beyond the required formation level, the extra depth shall be filled by blinding concrete under the footing.
Clashes with Existing Services
Where permanent works are clashing with existing services, the following steps shall be taken:
The Client shall be notified in advance of any proposed service interruption.
No interruption to any existing services shall be done until permitted in writing by the concerned authority.
Where acceptable, excavation shall be done by using suitably sized mechanical machines or by hand.
An experienced Flagman shall accompany the mechanical operation, to observe the excavation in case an unmarked service is observed.
If an uncharted or incorrectly charted service is encountered during the excavation, the client shall be informed and such services shall be removed /sealed/rerouted as per the directions of the concerned Authorities.
Structures Adjacent to the Project Plot
Care shall be taken not to under excavate the footings of adjacent buildings and structures.
If the top of an adjacent footing or foundation is encountered, the Consultant shall be notified and an appropriate shoring to the soil adjacent and below structure shall be proposed for the Consultant’s approval before proceeding with any work in the affected area.
The sides of any excavation, that are likely to collapse, shall be sloped, stepped or shored to an extent depending on the materials being excavated.
During the trench Excavation extra care shall be taken to ensure the sides are stable, sufficiently wide for ample working room.
A sloped ramp, adequate for movement of loaded dump trucks shall be built using the excavated fill material.
If any protection, rerouting, termination or removal of services is required for the smooth progress of work, it shall be discussed and written approval shall be obtained from consulting engineer as appropriate.
Shoring & Bracing, where required, shall be carried out as per shop drawings approved by engineer.
A warning tape shall be tied along the perimeter of excavation at a distance of 1 meter from the edge of excavation as a warning sign to restrict the movement of equipment.
Flash lights will be provided when working at night as required.
All testing shall be done as required in the project specification and contract documents by the approved accredited testing lab.
Survey
Establish and protect sufficient number of stations (TBM) to re-establish the stations if they are disturbed during earthwork.
Preparation of Sub-grade for Foundations
Excavate to the required elevation and dimension as shown on the drawings within a tolerance of +/- 25mm and sufficient distance from foundations to permit placing and removal of concrete formwork, installation of services and for other construction required and for inspection and remove the soil to the approved dumping area.
Excavate by hand to the final grade and level wherever is required.
Excavated soil shall be tested for suitability as backfilling material.
Over excavation, if any, shall be backfilled with satisfactory soil material only when acceptable to Engineer.
Moisture of backfill material shall be controlled within +/-2% of optimum moisture content as per the requirement of specification clause and shall than be compacted to not less than 97% of MDD or 77% relative density as applicable.
Inspection shall be carried out by the Engineer, when excavation has reached the required sub grade elevations.
3 in-situ density tests shall be carried out for each building.
If unsuitable bearing materials are encountered at required grade elevations excavations shall be carried out deeper and replacement of the excavated material to the depth shall be as directed by Engineer.
Under paved areas satisfactory fill materials compacted as specified shall be used.
Under foundations of structures plain concrete filling of 14MPa minimum compressive strength shall be used.
The elevation of any point and the line of any edge or centre of earthworks shall be as per the drawing shown and within acceptable tolerances.
Adequate precautions shall be taken to protect the bottom of excavation till the placement of blinding concrete.
Excavated material approved for back filling shall be stockpiled at a location approved by Engineer.
All excavation shall be kept free of water.
Stability of the excavated area shall be maintained with required slope at the sides of the excavation.
Do the necessary bracing where sloping is not possible.
Excavation in restricted areas shall be carried out by hands.
RFIA for correct elevation and test request to be raised and approved by the engineer.
Dewatering
If the existing ground water table is above the formation level, dewatering shall be required and in this case a detailed proposal for a dewatering system shall be submitted for approval.
Anti-Termite Treatment
Anti-termite treatment of soil along the perimeter of the building and soil faces in contact with the building including treating backfill with approved anti termite materials as required shall be carried out as specified in the drawings/Contract specifications by approved subcontractor.
The rate and safety precautions for application shall be in accordance with the manufacturer recommendation of approved anti termite treatment procedure.
Backfill and Compaction
Preparation of surface like removal of vegetation, debris, unsatisfactory soil materials and deleterious materials shall be done prior to the placement of backfill material.
Selected excavated materials approved by the Engineer shall be used for Fill/Backfill purposes.
Prior to using the backfilling materials necessary tests shall be carried out to establish its suitability. For Test requirements refer contract specifications.
Before carrying out the backfilling of foundations it will be ensured that the foundations are cured to the specified period, formworks removed and protected with required coatings.
The backfilling shall be done in layers not exceeding 200 mm compacted thicknesses.
Moisture in compacted fill or backfill material shall be maintained within 2% above or below OMC.
Compaction requirements shall be as defined below:
|
Area Classification |
COHESIONLESS SOIL
BS 1377 Relative Density |
COHESIVE SOIL
BS 1377 Degree of compaction |
|
Under foundations and slabs on grade of buildings |
77% |
97% |
|
Trenches and walkways a-Top 400mm of subgrade b-Each layer more than 400mm below subgrade |
75% 70% |
95% 90% |
Trenches shall not be backfilled until all required inspections and tests are performed and until the Engineer has verified that the utility systems have been installed and tested in accordance with the specifications and drawings.
All inspection and testing shall be carried out and approved as required by the contract.
Request for inspection for correct elevation and test request to be raised and approved by the engineer.
Field Tests
For trenches
One field density test of subgrade for every 200 square meter area, but in no case less than 3 tests per days operation.
In each compacted fill or backfill layer 1 field density test for every 200 square meter areas, but in no case less than 3 tests per day’s operation.
For walkways
One field density test of subgrade or finish grade for every 500 square meter but in no case less than 3 tests per days operation.
In each compacted fill layer make at least 1 field density test for every 500 square meter but in no case less than 3 tests per day’s operation.
For aggregate road base
One in-situ density test for every 300sq.mtr of aggregate road base lay.
One sample for every 1000 cum. shall be tested for Grading, Atterberg limits, Plasticity index, Sand equivalent, MDD. C.B.R and Loss of Abrasion.
Back filling within building
In each competed fill layer make at least one field density test for every 500 Sq.mtr. but in no case less than 3 tests per day’s operation.
Routine test for each type of borrow pit materials shall be done as required in Contract specifications.
Debris and spoils emanating out of excavation operations will be removed at regular intervals to a designated Tip at the site.
Location of the dumping area shall be finalized before the commencement of works.
Construction debris shall be dumped in the approved municipality dumping area.