This civil work method statement outlines the construction of earthwork excavation and embankment and the logistic requirements such as access road for movement of dump truck to and at the excavated area.
The scopes of this method statement are listed below.
- Setting Out
- Site Preparation
- Excavation & Backfilling
- Compaction
- Sampling & testing
- Temporary Drain & Silt Trap
- Preparing Sub Grade
REFERENCES
The relevant Codes of Practice are as follows:
Approved Construction Drawing
Contract specifications
Applicable codes and standard
Manufacturer technical data
Roles and Responsibilities
Project Manager will be overall responsible for the whole project.
Construction Manager leading the site team will assist the Project Manager in Executing tall the works.
Supervisors shall be full time on site in monitoring the construction work.
A survey team shall be stationed on site to monitor and control each stage off work. All the major setting out will be carried out jointly with the engineer’s Surveyor.
Safety Officer will be on stand-by all the time to ensure that all health, safety, security and environment matters are handling promptly.
Necessary Plant, Equipment and Manpower
The equipment involved in the flexible pavement construction works (but no limited to), according to type and suitability.
Excavator For sample trimming, bulk excavation and loading to dump truck
Dump Truck: To transport the filling material from the cut area or borrows pits to from the embankment
Bulldozer for: Leveling the formation
Back pusher for: Excavation below existing ground in firm or hand material as in digging pipe trenches
Backhoe for: Excavation below existing ground in firm or hard material as in digging pipe trenches.
Compactor 25 ton Vibrating Roller
Grader for: Compacting soil and sub grade
Water Bowser for dust control on working area
Manpower
– Site Engineer
– Safety Officer/Supervisor
– Site supervisor
– Surveyor
– Machineries operator
– General Workers
Earthwork Methodology
Setting Out
Before the commencement of the works, the contractor will be supplied with information necessary to establish the alignment and levels of the works and need to re-establishment of any markers found to be missing.
All survey markers and reference pegs must be preserved except where construction requires their removal and to be replaced with new reference marker.
Prior to commencement of any physical work, a licenses surveyor shall be appointed to carry out demarcation works and establish bench marks on site.
Site Preparation
A temporary system for rapid dispersal of water flowed on to the earthwork or completed formation during construction, or which enters the earthworks from any source shall be devised to prevent water ponding. Where practicable (free from silt or other pollutant), the water shall be discharged into an adjacent drainage system.
Earth drains around the site are provided for siltation control if required. The runoff finally flowed into the silt trap. The silt trap would trap the silt before discharging into existing drainage systems. This arrangement shall be made in respect of all earthworks including excavation, whether for pipe trenches, foundation or cuttings which will be complying with Environmental Management Plan (EMP).
Regular inspection of earth drains should be carried out to ensure uninterrupted flow of runoff, especially during periods of heavy rains. Existing silt trap shall be utilized and maintain.
When necessary silt fence shall be used in combination with silt trap to protect water quality in nearby streams, rivers, lake and bays from sediment (loose soil) in storm water runoff.
Water browsers truck will be used to control dust. Access roads, open areas, haulage roads and stockpiles area will be wet when necessary.
Wash trough will be provided at access road at necessary main access site location.
When any material is disposed outside from the side, the disposed material shall be graded to a neat appearance and shall not obstruct natural drainage or cause damage to highways or property. All precautions shall be taken to prevent any erosion of the soil on the affected areas.
All unsuitable material and surplus suitable material shall be carried out according to the drawings or as per instructions given by the Employer Representative.
Removal of Unsuitable Material
All areas within any construction boundaries will be cleared of material unsuitable to form part of a construction. Unsuitable material will be excavated to expose a good foundation to the minimum required depth and will be spoiled to a designated dump site for general fill as directed.
Unsuitable materials shall be excavated to such depth and over such area as directed by the consultants and be transported and disposed of an approved manner. After the excavation works, survey shall be carried out to verify the as built levels and extent to excavated area before the soil replacement works.
Unsuitable material will be excavated by using excavator and transport by special design for unsuitable material to an approved dumping site.
Any suspected unsuitable material (USM) found at site shall be verified by consultants prior to replacement works. Survey shall be carried out to verify the as-built levels and extent of the USM area before the excavation works.
The engineer has to determine the extension and the depth of soft material to be replaced before the commencement of the works.
Mackintosh probe test to be used for checking the resistance of the soft ground at certain interval as directed by the Resident Engineer who shall determine the depth of soft material to be replaced by the results.
The contractor shall comply with statutory requirements such as payment of royalties, environmental protection, etc.
Voids created due to removal of unsuitable material shall be backfilled with approved suitable material as recommended by consultant (i.e. Backfill with suitable material layer by layer with proper compaction as per specification).
Low pressure tack bulldozer will be deployed to push the top granular material in the required layer to compaction (Maximum thickness 300mm)
The compaction of all embankment material shall be accordance with the requirements. All fill material within 900mm below formation level shall be compacted in layers to 95% of the maximum dry density as B.S 1377 Test 13 at 1000m2/point.
Before start dumping the excavated unsuitable material at proposed dumping area (Outside R.O.W), an approval must be obtained from Employer Representative.
Construction In All Cut Area
The excavation of cutting shall be carried out in accordance with the drawings and to the slopes, levels, depths, widths and heights shown on the drawings.
Prior to commencement of the works, our surveyor will use the co-ordinate point of road alignment and TBM provided by the licensed surveyor for setting out the extension of cutting in accordance with the cross sections.
Peg is set ±20mm – 30m apart indicate of the cut level.
A survey team shall be stationed on site to monitor and control each stage of work. All the major setting out works will be carried out jointly the Engineer’s Surveyor.
Before commencement of massive cut/fill, the haul roads shall be constructed based on site requirement and to ensure smooth flow of the plant and to comply as the requirement as follows.
Typical construction details of access / haul road
Schedule of total lengths of access / haul road
Proposed maintenance of access / haul road
After completion of haul roads, the mass excavation shall be started from the top of the hills or high ground down to formation levels.
Slopes in cutting shall be trimmed mechanically to neat and even surfaces in accordance with the designated gradients. The tolerance for widths of excavations shall not exceed the dimensions shown on the drawings by more than 300mm. Erosion protection measures shall be carried out upon completion of each slope.
All bare/ slope shall be turf/protected.
Construction of berm drain shall follow closely to the slope trimming and surface water shall be regulated to the temporary earth drains and eventually discharge to the silt traps.
The slope of cutting shall be cleared of all rock boulder or rock fragments which move when praised by a crow-bar. Any resultant voids in the slope shall be filled up with class 10/20 concrete or stone pitching.
Water browser will be used to control the dust to the minimum level on the working areas and the haul roads.
Bulk samples of sub grade material shall be obtained in advance of exposure of the sub grade. The in situ dry density at sub grade level shall be obtained together with in situ moisture content. The sampling rate shall be 1000m2/point.
A CBR versus moisture content curve shall be plotted for each sample based on the soaked of CBR of the top face of specimen and compacted with BS 4.5kg hammer in accordance with the BS 1377: 1975 Test No. 16. Dynamic compactor method 1 to achieve the in situ moisture content.
Treatment for Cutting Area
For a length of cutting, the minimum CBR is obtained from samples taken and derived as follows:
- Where the CBR is equal or greater than 5%, 300mm thick of layer shall be scarified and re compact to 95% maximum dry density.
- Where the CBR is less than 5% but greater than or equal to 3% the top 450mm of the sub grade need to remove and replace with approved sub grade fill material.
- Where the CBR is less than 3% but greater than or equal to 2%, the top 450mm of the sub grade need to remove and replace with approved sub grade fill material.
- Where the CBR is less than 2% the top 600mm of the sub grade need to remove and replace with selected fill of approved sub grade fill material or as directed by the Engineer’s Representative.
Construction in All Fill Area
Construction in an all fill area will commence at the base or lowest part of the embankment. Unsuitable material will be removed to expose a good foundation to the minimum required depth, at which time the key will be constructed as directed, with specified material being place on 0.25m compacted layers.
Peg being established at ±30mm – 50m with the indication of fill level. A typical filling sequence as detailed would be the adopted procedure, with the inclusion of some under drainage if and when required to stabilize the fill. Filling would continue up to FL of the platform, establishing the standard berm drain and bond as specified at the top of the platform batter.
Fill materials for use in forming embankments shall be suitable material obtained from designated excavation area in cutting or borrow pits.
Prior to commencement of the works, the selected sample from the source of cutting or borrow pits shall be sent for laboratory test for Proctor Test (B.S 1377.713) moisture contain, liquid, limit, plastic limit, Atterberg limits and grading analysis to determine its suitability for forming embankments.
Trial compaction shall be carried out at the designated area of the site to determine the pattern of compaction for each main type of material to be used. This shall include of compaction plant for each type of material to achieve required compaction.
After the required passes for compaction has been accepted, the filling shall be carried out in layer of the loose depth and shall be compacted by the compaction plant as used and achieved in the trial areas.
Back pusher shall be used to level the sub base material to the compacted thickness of 300mm. Back pusher used to final trimming to achieve the smooth and uniform surface.
A CBR versus moisture content curve shall be plotted for each sample based on the soaked of CBR of the top face of specimen and compacted with BS 4.5kg hammer in accordance with the BS 1377 : 1975 Test No. 16. Dynamic compaction method 1. The sampling rate shall be 1000m2/point with minimum of 3 per length of embankment. The moisture content shall be from ±3% to ±5% of the optimum determined in above increments of 2%.
The CBR value of the sample shall be taken as the minimum derived from its CBR versus moisture content curve over a range ±3% of the optimum moisture content.
The degree of compaction will be at least 95% of maximum dry density for the sub grade final layer (300mm thickness) and 90% of maximum dry density for filling works below sub grade final layer and it will be determined by using BS 1377.
Density test shall be carried out in every compacted layer of approx. 300mm depth and the nos. of test shall be done in accordance with the test plan of the specification.
The requirement for compaction of embankment fill are as follows and shall apply equally to all clayey, silty, sandy or gravelly materials placed in the embankment.
Engineer’s representative will be notified to witness the test and the result sent to the Resident Engineer for further filling works.
As for the slope filling works, the filling shall be in layer and with extended one meter extra for cut back in order to form a compacted slope.
Prior to commencement of massive cut/fill, the haul roads shall be constructed with two lanes width traffic and to ensure smooth flow of the plant and machinery in all cut area.
Excavators shall be deployed to use for excavation and load the cut material to the dump trucks for filling. On the filling area, the dump trucks transport the material to the area and trip from one end. One bulldozer shall be used for spreading the material in layer and shall not exceed 300mm loose depth as adopted. The vibrating roller shall be used compaction.
On reaching to each berm level, the slope trimming shall be completed prior to carry out the subsequent filling for the next berm.
Permanent berm drain needs to be constructed before the access road cut off by the filling works.
Erosion protection measure shall be carried out after completion of trimming work and complying with Environment Management Plan.
Construction in Cut Fill Area
The method for construction in cut to fill area, would be achieved by a combination of the proceeding adopted procedures used in sequence, by removing the fill, or making the cut as per method statement details for all cut construction and by filling or placing of the fill would be achieved as per the method statement details for all construction.
Any variations to construction such as under drainage, Geo-fabric, sand blankets as previously mentioned would also be adopted, where and when these variations were applicable would be directed to ensure totally stable embankment.
Construction of Sub Grade
Preparation of sub grade shall be carried out only after completion of any specified sub grade drainage such as sub-soil drain and table drain.
Construction of sub grade should use an approved sub grade material with soaked CBR value of 5% and to be compacted to 95% maximum dry density.
Road alignment and level pegs at 10 meter interval to be set out to monitor the trimming works to the sub grade levels.
The surface shall be trimmed to the right levels and to the requirement of the contract.
Final level shall be graded by using grader to form the super elevation, fall and cambering.
The trimmed surface shall be rolled by a few passes of smooth-wheeled roller by a 25 tons vibratory roller.
Trial compaction shall be carried out at the designated area of the site to determine the pattern of compaction for each main type of material to be used. This shall include of compaction plant for each type of material to achieve required compaction.
All areas of prepare formation shall be approved by the Resident Engineers prior to the placing of sub-base material. Placing of sub-base shall commence immediately following such approval.
Joint dipping shall be carried out of prior lying of sub base material.
The sub grad level for road shall be finished in a neat and workman-like manner and the widths of embankments and cuts shall be these specified on the drawings.
The top surface of the sub grade shall have the required shape, super-elevation, levels and grades and within plus 10mm and 25mm of the required level.
The degree of compaction will be at least 95% of maximum dry density for the sub grade final layer (300mm thickness) and 90% of maximum dry density for filling works below sub grade final layer and it will be determined by using BS 1377.
Back pusher shall be used to level the sub base material to the compacted thickness of 300mm, back pusher used to final trimming to achieve the smooth and uniform surface.
Compaction shall be carried out in longitudinal direction along the carriageway, and shall generally begin at the outer edge and progress elevated curves when rolling shall begin at the lower edge and progress uniformly toward the higher edge. Water shall Be used when necessary during compaction.
Inspection & Testing
The test laboratory shall undertake a comprehensive test to establish the compaction characteristics of each main geological material type. These tests shall include but not limited to the following:
i) Determination of liquid limit, plastic limit and plasticity index for soils of predominantly sily or clavely nature in accordance with BS 1377 (1975) Tests 2(A), 2(B), 3 and 4.
ii) Determination of particle size distribution, in accordance with BS 1377 (1975) Test 7(A), oven drying or air drying shall not be permitted for specimen preparation.
iii) Determination of drying density moisture content relationship in accordance with BS 1377 (1975) Test 13, oven drying of samples shall not be permitted for specimen preparation.
iv) Determination of CBR value carried out in accordance with BS 1377 (1975) Test 16 using dynamic compaction Method 3 with a 4.5kg rammer and soaking procedure. Material shall not be oven dried and material shall not be reused for additional testing.
v) In situ CBR shall be carried out on site for sub grade layer.
HSSE REQUIREMENTS
i. Contractor is responsible for implementation of all HSSE rules and regulations.
ii. The work will be carried out in accordance with the Project Safety Plan.
iii. The work will be carried out in accordance with the Environmental Management Compliance Plan.
iv. Proper and safe access shall be provided above the ground
v. Regular housekeeping shall be provided out to ensure that the working areas kept clean at all time.
vi. Sufficient safety signboard shall be installed at strategic location around the project site and the working area
vii. All requirements on PPE shall be observed strictly.
viii. Lifting equipment should be inspected and checked at regular intervals and be well maintained before lifting operation. During operation of lifting, no work is done under
loads travelling overhead.
ix. Proper and adequate lighting to be provided when working at night
Relevant Records
All records shall be kept and filed in accordance to the document control set procedures. Record includes those listed below.
- Inspection checklist
- Request for inspection
- As-built drawings