The purpose of this method statement is to define the standard work process for Structural Excavation and Backfilling related activities.
Method of statement addresses work operation associated with structural excavation and backfilling. All necessary setting out, tree cutting, clearing and grubbing will be completed prior to performing this operation.
This work consists of excavation for bridges, trenches, pipelines, ducts, culverts, headwalls, cut off walls, catch pits, manholes, inlets and retaining walls and will include drainage, pumping, sheeting and the installation and removal of cofferdams if necessary as well as disposal of material arising from the excavation, and backfilling to the level of the original ground.
It will include removal of any part of the existing structure below ground which is required for construction of the new structure.
Related Abbreviations:
- FCR: Field Change Request
- RFI: Request for information
- DCN: Design Change Notice
- JHA: Job Hazard Analysis
- IFC: Issued For Construction
- ITP: Inspection Test Plan
- BOQ: Bill of Quantities
Roles & Responsibilities
Earthworks manager is responsible for overall implementation of this procedure and ensuring that the work method statement supports the construction efforts of the project.
Earthworks Superintendent:
- Providing technical support consistent with demands of the excavation and backfilling schedule.
- Supervising and coordinating the manpower, material requisitions, technical compliance, and monitoring testing activities associated with excavation activities.
- Implementing inspections through site foreman.
- Reporting major defects for evaluation
- Performing all inspection activities
- Reporting defects for evaluation and records
- Maintain inspection records as part of associated packages
Earthworks Foreman:
- The management and execution in accordance with the scope of works
- Work in accordance with Health, Safety and Environmental plans and procedures
- Supervising labor and operators on site.
- Participating the daily Start Up and work plan sessions.
Surveyors: Stake out levels for each cross section.
Laboratory: Laboratory personnel reporting to Quality Control will be responsible performing tests and laboratory tests and for documenting and reporting the results of these tests.
Quality Control Manager:
- Check the works according to ITP requirements.
- Will be responsible for requesting and coordinating inspections and tests among laboratory personnel, QC personnel and construction personnel.
Quality Control Engineer:
- Checking the works according to ITP requirements.
- Coordinating the disposition and approvals thereof for documented non conformances.
- Preparing the Earthwork Inspection and Test Matrix.
- Identifying the need for and coordinating the preparation of detailed inspection checklists.
- Determining frequencies of ongoing test and inspections of Structural Excavation & Backfilling Activities.
- Ensuring review of applicable laboratory or field test reports for acceptability and recording of applicable results on the appropriate checklist.
- Developing and maintaining a summary sheet of inspection and test results for each activity and of earthwork activity.
Necessary Machinery, Tools & Equipment
The following basic machinery and equipment shall be utilized for the structural excavation and backfilling activities.
- Bulldozers
- Graders
- Excavators
- Loaders
- Dump Trucks
- Water Trucks
- Vibratory Rollers
- Light Towers for Night Shift
Structural Excavation Work Requirements – General
Foundation excavation shall be made in accordance with the area of the foundations shown on the Drawings and shall permit placing of the full width and lengths of concrete show.
Excavation will be taken to the level shown on the Drawings.
No foundation or blinding concrete will be placed prior to approval of the excavation bottom by the Engineer.
The bottom of the excavation, trench will be compacted to 95% of MDD.
Over depth excavation below founding level by the Engineer. Over depth excavation below founding level and over width excavation beyond the lateral limits shown on the Drawings shall be backfilled with the same class concrete as for the foundation and will be poured with the foundation.
Where rock is exposed at founding level the excavation will be prepared by trimming and removal of loose rock fragments before blinding with concrete.
Drilling and blasting required in any foundation excavation will be completed prior to placing foundation concrete.
When unsuitable material is encountered at founding level, over excavation and replacement with Suitable backfill material, concrete will be executed. The necessary depth of over excavation and the suitability of the proposed backfill material will be approved by the Engineer prior to commencement of the work.
Where piled foundations are to be used, excavation for the file cap will be completed before the piles are installed. After piling is completed, loose and displaced material will be removed, leaving a smooth solid bed to receive concrete.
Cofferdams will be used whenever water-bearing ground is encountered above the level of the bottom of excavation. They will be sufficiently large to give easy access to all parts of the excavation and will be of dimensions not less than those for which payment for excavation is made.
Excavation and Backfilling for Culverts, Storm Sewers and Ducts
Precast concrete and steel pipe culverts and pipe ducts will be installed in trenches cut into previously constructed and compacted embankment either from the subgrade or from an embankment height at least twice the nominal diameter of the pipe.
Unless otherwise noted on the Drawings, trenches will be no wider than the external diameter of the pipe plus 300 mm on each side.
If trenches are dug too wide, the pipe culvert will be bedded in a concrete cradle.
Pipe bedding will be either graded aggregate 12 mm nominal size to Table 1 of BS 882, or concrete Class 12 shown on the Drawings. Exposed concrete bedding will be cured for a minimum of 3 days.
Pipes will be laid so that the lower portion of each pipe is supported for its entire length to a depth at least equal to ¼ the external diameter. They will be fitted and matched so that when laid in the trench they form a pipeline with a smooth and uniform fall invert.
Granular material for pipe bedding will be compacted to the minimum bed thickness shown in table below. 50 mm less bedding may be provided under the sockets of spigot and socket pipes.
Table: Sewer Pipe Bedding Thickness
|
Pipe Diameter (mm) |
Minimum Bedding (mm) |
|
<300 300 to 500 >500 |
150 200 250 |
Granular bedding material will be placed and compacted in uniform layers on both sides simultaneously to 50 mm above the top of the pipes. Selected excavated material or approved granular fill will then be placed and compacted above the pipe for the full trench width to not less than 300 mm finished thickness.
Where rock, or similar material is encountered in the excavation bottom, it will be removed for a depth of 150 mm. The extra excavation will be backfilled with a properly compacted granular material.
In situ concrete pipe culverts shall be cast in trenches cut into previously constructed and compacted embankment from the subgrade or from an embankment height at least twice the nominal diameter of pipe.
The trench width will be no greater than the external diameter of the pipe plus 300 mm each side when external forms are elected to be used or plus 80 mm each side when external forms are elected not to be used.
If forms are used and trench wider than specified is excavated, backfill to the height of the external haunch of pipe will consist of bedding concrete class 12.
If specified, the side walls of the pipe will be increased to fill the channel width. Overdepth excavation will be compensated for by increasing the thickness of concrete base or as otherwise instructed by the Engineer.
Scheduling Excavation for Structures
Works will be scheduled so that no excavation is left in an exposed condition for a period greater than 30 days.
If earthworks progress is not integrated with the drainage structural work to the point where the road embankment dams the natural drainage, the Engineer may order the Contractor to open adequate temporary water structure through the roadway at locations where drainage structures are to be installed. Damage to the roadway caused by water passing through these openings will be repaired.
Backfilling For Structures
Only selected granular materials that will produce a stable, dense, backfill will be used for structures.
In addition, backfill for metal pipe culverts will contain less than 1.5 % of combined chlorides and sulphates.
Selected backfill, which will be subject to the prior approval of the Engineer, will consist of well graded natural sands and gravels, crushed gravel and crushed rock (but excluding argillaceous rock types) with the properties shown in Table below:
Table: Selected backfill properties
| Particle size
Material passing 75 mm sieve Uniform coefficient 10 % Fines value |
75 mm maximum
15 % maximum 10 minimum 100 Kn minimum |
No cast in place concrete structures will be subjected to pressures from backfilling until 3 days after expiration of the period designated for removal of forms.
Backfill placed around the culverts, abutments and piers will be deposited on both sides to approximately the same elevation at the same time.
Care will be taken to prevent any wedging action against the structure.
Slopes bounding the excavation will be stepped to prevent such wedge action.
Materials will be placed in layers and compacted by means of rollers, vibrating plates or mechanical rammers.
Each layer will be compacted to 95% of the MDD measured according to AASHTO T160 (method D). In no case will any layer be uniform and within the optimum moisture range.
At box culverts backfill will be completed to the level of the original ground line and to the full width of the excavation area.
If the top of the culvert extends above the original ground line, Backfill operation will continue to the top of the culvert and for a width of 3 m on each side of the culvert to the full width of the roadway embankment.
At pipe culverts and storm sewers (including metal pipe and metal arch culverts) backfill will be completed around the culvert as specified to the level of original ground line and to the full width of the excavation area.
Incase the top of the culvert extends above the original ground line, backfill operation will continue to the top of culvert for a width of 1 ½ times the maximum external width of the culvert on each side of the centerline of the culvert to the full width of the roadway embankment.
At bridges backfill will be completed to piers and abutments to the level of original ground or to the top elevation of any adjacent embankment if appropriate.
Backfill around retaining walls will be compacted to the finished level shown on the Drawings.
Catch pits, manholes, inlets and other structures will be backfilled in accordance with methods specified in the specifications.
Method of Excavation Measurement
Measurement of Structural excavation will be limited to excavation for foundation for bridges, retaining walls, box culverts or cross sectional area exceeding 1 square meter, box culvert wing walls, head walls, toe walls and aprons, manholes, pump houses and substations.
For box culverts 1 sq. meter or less, pipe culverts, storm sewers and ducts, measurement of structural excavation in rock will be made.
The cross sectional area of the box culverts will be that of the net opening of the culvert. For pipe culverts and box culverts of net opening are of 1 meter square or less, no measurement will be made for excavation of abutments, wing walls, headwalls, toe walls and aprons etc. unless the excavation is declared ‘in rock’.
The pay volume of structural excavations will be that within a plane prism bounded by a lower horizontal plane, vertical planes and an upper horizontal plane.
Unless otherwise shown on the Drawings, the limiting planes will be defined as follows:
Bridge Foundations: The lower plane will be the underside of the blinding concrete and the vertical planes are planes 500 mm outside the foundation dimensions in plan.
The upper plane will be the existing mean ground level over the plan area of the foundation at the time when fill possession of the site is given.
Box Culverts: The lower plane will be the underside of the blinding concrete and the vertical planes are planes 500 mm outside the floor slab dimensions in plan, including apron slabs and toe walls.
The upper plane will be the mean of the existing ground level over the plane area of the culvert floor slab, including apron slabs and toe walls.
Where there is a significant change in ground level over the culvert length, the volume of excavation will be calculated by dividing the culvert into several smaller lengths.
In case the culvert is located in an embankment, the upper plane will be as described above irrespective of whether or not the embankment has been constructed in advance of the culvert.
Excavations for toe walls below the general level of the floor slab will be measured as the actual original volume of material excavated.
Miscellaneous Structures: Excavation measurement for retaining walls, wing walls, head walls, toe walls and other miscellaneous minor structures will be according to the methods described for box culverts.
Box Culverts within Existing Road: Where structural excavation is carried out for installing a new box culvert within existing road, excavation below existing bituminous layers will be classified as structural excavation for the length of that section of culvert which lie within existing road / embankment.
The vertical plane will be the minimum excavation limits as shown on the drawings or 30 cm from the outer face of the culvert.
Removal of existing bituminous layers will be paid under relevant pay items appearing in the BOQ.
Where structural excavation is out for replacing an existing box culvert (with net opening area exceeding 1.0 m2) at the same location, only that volume of soil which lie between the outer face of the existing culvert wall and the limiting vertical planes as described under specifications for roads will be measured for payment.
Excavation for Irish Crossing cut off walls will be measured net, without any additional space along both faces of the cutoff wall.
Any excavation below natural ground within Irish crossing walls for road construction as shown on relevant drawings will be classified as roadway excavation and measured under relevant pay items of Clause 203 in General Specifications for Roads.
When ground or tidal water is encountered during structural excavation, only the original volume of material excavated below water level shall be measured by cubic meter for payment under ‘Extra Over for Structural Excavation Under Water’
Excavation, bedding, backfilling for pipe culverts and ducts and box culverts of cross sectional area 1 m2 or less will not be paid directly but will be considered as subsidiary work to other related items in the Bill of Quantities except for excavation in rock.
The amount of completed and accepted work, measured as provided for above will be paid for at the unit rate per cubic meter for Structural Excavation in Soils and Structural Excavation in Rock in the BOQ which rate will be full compensation for execution, clearing, compaction of bottom of trench, side support, removal of any portion of existing structures below ground necessitated by construction of the new structure, trimming, cleaning, backfilling, compaction, disposal of surplus materials and supplying equipment, tools, labor, and other items necessary for proper completion of the works.
The unit rate per cubic meter in the BOQ for ‘Extra Over for Structural Excavation Under Water’ will be full compensation for sheet piling, pumping, dewatering, materials, equipment, labor and other items necessary for the proper execution of the works related only to the presence of water in the excavation.
In a mixed soil and rock strata excavation, when the soil layers are less than 50% of the total excavated thickness, the entire volume excavated will be paid for as ‘Structural Excavation in Rock’.
Where the percentage of the strata classified as ‘Structural Excavation in Soil’ is greater than 50 % of the total thickness below the stripped overburden, the soil and rock layers will be measured separately.
Overburden will be paid for as ‘Structural Excavation in Soil.’
Structural Excavation and Backfill Execution Plan
All necessary clearing and grubbing and topsoil excavation (where necessary) will be completed prior to the beginning of the excavation.
The location will be demarcated to show the limits and depths of the excavation. The disturbing and spoiling material and vegetation outside of the expropriation limits will be avoided to the extent possible.
The excavation will be done to the formation level for the full construction width.
The excavation will start either with bulldozers or excavators together with the construction of the slopes. The material that is excavated by excavator will directly loaded to the dump trucks and transported to the fill or deposit area.
For further 20 cm the existing material will be scarified, watered as necessary, mixed and compacted. The prepared formation will be in such condition that it will be well drained all times.
All slopes, lines and grades will be true, and accurate and according to those on the drawings or otherwise directed and approved by the Engineer.
The material, which is tested and defined, as unsuitable material will directly hauled to the disposal areas that is approved by client and stored properly.
The material which is tested and defined as suitable material however not proper for fill operations due to water content or climate conditions will be loaded, hauled and stored in the deposits area. If the weather condition is not suitable for fill operation, the excavation will continue as mentioned above however the material will be transported to the deposit areas defined by the client.
Construction of fill layer consists of spreading of appropriate non-cohesive fill material by layers and compaction to the required level specified by design.
Fill material shall be deposited to site by dump trucks and spread either by a dozer or a motor grader so that the spread layer will have a thickness according to the type of the material.
Compaction of material shall be handled using single drum smooth-pad rollers and/or single drum padded rollers.
Compaction direction shall be from lower elevations to higher elevations and passes shall be performed so that drum of the roller will overlap its previous pass by %10.
Next set of passes shall not be performed unless a set of passes is completed on all lanes. Rollers shall perform their last passes without vibration so as to attain a smooth finishing surface. If fill material is too dry and having moisture below its optimum content, water trucks shall be utilized so as to attain optimum water content. In the case that fill material has a moisture content above optimum, material shall either be ripped and aerated or be waited until excess water self-drains or evaporates till optimum water content.
Once the required number of passes is performed on the entire strip of the fill, the degree of compaction shall be measured at a number of randomly selected points so that the number of test points represents the strip accurately.
Provided that target degree of compaction is reached, same procedure shall be followed for the next strip of fill.
For the adjacent fill strips, material spreading process shall be performed so that one fill strip overlaps the adjacent one to assure stability and uniform behavior of fill layers.
The excavation will be performed with bulldozers and hydraulic excavators.
Excavators will load directly from the excavation to the articulated dump trucks and the trucks will haul the material to the fill or waste area.
Material excavated by bulldozers will be loaded to trucks by loaders.
The material will be hauled to fill or waste areas.
Health and Safety Requirements
All accidents are preventable and organizations achieve this by adopting a Zero Accident philosophy, by ensuring the health and welfare of workforce, and by insuring that the care for the environment receives the highest priority.
Company will strive to meet and exceed the client’s expectations by providing a proactive, dedicated management structure and leadership in all aspects of HSE Management.
The participation of the total project team, including managers, supervisors, employees, and sub-contractors in the HSE Plan are the critical success factor for the project.
This is accomplished and controlled by deploying our ‘HSE is not an optional extra!’’ concept as the project culture.
A key feature of this is dedication to the philosophy of “zero accident” which will be linked to the company’s “Incident and injury free” philosophy.
This value based approach aligns with Company’s HSE perception and company shall apply the same approach to our sub-contractors so that they adopt and implement similar values.
By this, all employees and sub-contractors shall conduct themselves and execute their work in a safe and healthy manner and establish the same approach for the protection of the client property, as well as the natural environment.
This standard shall be communicated to all those persons involved in this project, irrespective of nationality or language.
Each person on the project is considered as a stakeholder in this HSE commitment.
The work scope will be managed in line with company’s HSE Management system, which can be viewed as a pyramid that has five layers;
The HSE management systems pyramid is built from generic to specific.
The foundation, which is fundamental, is Management Commitment.
Commitment made is that HSE has equal priority with any other aspect of the company business, as detailed in the policy statement. The next level is the HSE Manual (procedures) that specifies safe systems of work.
A project specific construction risk assessment and procedures that are tailored to be directly relevant to the work to be performed comprise the third level.
The fourth level in the HSE management system pyramid consists of Job Hazard Analyses (JHA) where work-package or task based upfront activities is the basis for daily site activities.
Finally, the pinnacle of the pyramid is Innovation.
Safety Program will consist at a minimum of the following:
Management commitment in writing to be available.
Remove barriers that cause incidents and accidents.
Weekly site meetings with supervisors and workers will be the focus on two-way communication and will highlight potential roadblocks to “Zero Accidents” and “Incident and Injury Free” workplace.
Positive, reinforced feedback and recognition for the correct behaviors will be highlighted and recognized.
Resources (money, human and hardware) will be dedicated and provided to the project in support of the HSE management systems. At no time during the life of this project will cost or schedule concerns supersede HSE priorities.
HSE program on the project will be led by Site Manager and supported by Site HSE Manager. Safety in execution will be the number 1 priority on the project. Management firmly requires that line managers accept accountability for safety and this philosophy and extends through the project.
Strive for continual improvement, organization believes that excellent HSE performance should be a core value of any World Class Company. Whilst measuring reactive indicators is an essential element in any HSE Program the main focus proposed by company is on establishing and measuring a range of proactive Key Performance Indicators (KPI’s) that will be implemented by the project team, in order to achieve an Incident and Injury Free environment.
All personnel will successfully complete all required company training requirements and will receive an additional two hours of safety orientation and training prior to starting to work.
Organization has already committed resources for training and has obtained approval to conduct in-house training for specific programs, and will continue to dedicate skilled resources to project enhancement.
Extensive WRP (work responsible person) training will be deployed to enhance the quality of the first line site supervision. Work Permit courses will be held in addition to the client training programs to emphasize and enhance the understanding and the value of the use of work permits as an integral part of the project safety program.
Safety Task Analysis will be prepared and updated as required and used as basis for daily work talks and in the execution of daily job performance. This is in addition to the construction risk assessment and will be a key focus for leadership on the job site. Each foreman and lead hand will keep on his person a copy of the STA for his assigned tasks. It will be used as an adjunct to the daily toolbox talks.
A program of daily observations, weekly and monthly site inspections and regular audits will be implemented with management representatives and action on any noted discrepancies will be acted upon promptly. Results are published and used as a part of the weekly HSE briefing to inform the workforce of good and poor points.
Subcontractors HSE Performance will be reviewed and assessed regularly.
Behavioral Based Safety will be employed and will be extensively covered in all training and safety sessions. The focus of this program is to insure that all personnel understand the consequences of satisfactory and unsatisfactory behavior on this project.
Safe Work Observations Teams will be initiated within the project work force. Data will be collected and reviewed daily. This program is a further expansion of the Behavioral Based Safety Program.
Daily Toolbox Talks and weekly HSE meetings will be a normal part of the project work activity. Weekly HSE inspections results will be used the next morning as the basis for weekly HSE meetings. Each employee will be briefed on the results and the findings will be openly discussed.
Any incidents and near misses will be reported promptly and rapidly investigated to determine root cause and to identify any deficiencies in procedures or execution plans.
Safe tools and safe equipment will be utilized on this project. All equipment and hand-tools shall be inspected, checked, and recorded. This includes daily safety checklists for all trucks and heavy equipment. Items requiring color-coding will be properly documented.
Project QA/QC Requirements
Earthwork inspection and testing criteria has been established in the reference technical specifications. Specific inspections, field tests and laboratory tests with testing criteria shall be identified by listing and describing on the Earthwork Inspection and Testing Matrix.
The matrix checklist shall specify the required inspections/tests, provide reference to the test method, and indicate scheduled tests and inspection test result.
Inspections identified on the matrix are performed by Quality Control Inspectors with direction provided by the QC Engineer.
Laboratory testing shall be performed in accordance with approved laboratory procedures and appropriate standard or code of practice.
Tests and inspections shall be performed as outlined on attached partially completed checklists and as directed and/or expanded by the QC Engineer. Tests shall be performed in accordance with the specifications, when necessary by detailed field or laboratory procedures.
Additional inspection items of detailed routine earthwork activities performed by construction may be added to the checklist at the discretion of the QC Engineer utilizing additional copies.
Additional earthwork or related material inspections/tests may be developed by the QC Engineer based on new or revised specification requirements or as directed by the QC Manager.
These tests and inspections shall be outlined on checklists prepared and processed in accordance with this procedure.
Related laboratory and field tests shall be performed in accordance with existing or specially created, approved laboratory procedures.
Quality Control Inspector shall monitor Earthwork activities to assure that both the material and Earthwork methods are acceptable.
Subsequent testing and inspection frequencies shall be in accordance with requirements of applicable Standard’s and Specifications as directed by the QC Engineer.
Non-conformance shall be resolved in accordance the specifications.
Non-conformance prior to Quality Control acceptance of material and Earthwork activities.
Deficient conditions noted during in-process work (i.e. out-of-spec. density tests or lift thickness inspection results) need not be recorded on a formal Non-conformance Report, but the condition shall be corrected and re-test/inspection results shall be satisfactory before ongoing work is allowed.
The deficient condition and subsequent verification of resolution shall be recorded on the applicable Inspection and Testing Matrix form.
Tests or inspection reports for resolution shall be referenced to the failed reports.
Inspection shall be recorded and reported using a standard inspection report and inspection checklist (when applicable) to the Site QC Manager.
Tests data and results shall be recorded and reported on appropriate test reports to the Site QC Manager. Acceptance or rejection shall be noted on the applicable checklist.
The result of the Earthworks Tests shall be available for use by the Client.
All Test Records for construction quality control shall include the location of the test, elevation and source of material.
The summary sheets shall be supplied to the client on a monthly basis and shall be accompanied by a summary of the actual results so that statistical analysis may be carried out.