Work Method Statement for Substructure Works - Excavation work, Formwork, Reinforcement, concrete, PCC, Waterproofing works
Work Method Statement for Substructure Work
The sub-structure work includes various works like Earthwork excavation, Formwork, Reinforcement works, Reinforced cement concrete works, Back-filling works, PCC works, Waterproofing works.
here the detail work methodology to be followed for each work and Plant & machinery used for each work is explained in detail.
1. Earthwork Excavation
- The work methodology for Excavation work includes all Site Grading, General Excavation, Stacking, Dewatering and Disposal works.
- The Construction drawings are taken from the consultants and studied initially before starting the work..Raise Request For Inspection and get the Clarification if any doubts.
- The area is cleaned from any Vegetation, Shrubs, and debris.Before Starting the Excavation Work.
- Prior to Starting Excavation, Existing natural Ground level shall be noted by carrying out Block levels . Joint Records shall be maintained about Existing NGL. The Building Layout shall be Marked as per the Co-ordinates given and approval shall be taken from the Concerned before commencing the activity.Layout pillars and Bench marks shall be established near the buildings and approval shall be taken from the Concerned. Adequate Protection shall be Provided around the Pillar.
- Excavation shall be Carried out as per the approved Excavation Plan.Excavation will be done with excavator up to the required depth and plan Dimensions with Working Space.
- The depth of excavation shall be periodically checked by a surveyor to avoid over excavation. the bank of excavated area shall be sloped 30 degrees and shall be maintained to avoid a collapse of the bank into excavated area
- All excavated material shall be kept a minimum of 1.0 meter from the edge of excavation or shall be stockpiled to the area designated by the Engineer.
- For all excavation activities, adequate safety barriers, sign boards, advance warning signs would be used
- Suitable Dewatering system shall be maintained during excavation process to avoid water logging of the area. Natural Drainage plan of the area shall be maintained during the Excavation Process.
- Adequate suitable Excavated Earth required for Back-filling shall be Stacked at Designated area away from the excavated Pit.
- Surplus Earth Shall be Carted away from the area using Dumpers to place specified by the Local Authorities.
- Typical sheet pile shoring with MS channel framing.
- MS sheet of suitable thickness will be used at the exposed face of earth with support of ISMC channels at uniform spacing.
- ISMC channel will be anchored at the pit bottom with rebar of 32 dia.
- Similarly, ISMC channel top will be tied back with help of 10mm dia road anchored at sufficient distance on the road
- EARTH PROTECTION:
- SHORING SYSTEM - In cases where the depth of excavation is at more than 4mts and at the boundary line, to avoid collapse of earth.
Plant & Machinery
- Total Station
- Dewatering submergible pumps
- Excavation workers who are skilled in the excavation work.
2. Form work
- The formwork Include all fabrication and erection of Formwork.
- Formwork is designed for load and lateral pressures due to dead weight of concrete, superimposed live load of workmen, materials, Plant & Machinery. Formwork isdesigned to have sufficient strength and rigidity to carry head of concrete without deflection exceeding the acceptable tolerance limits.
- Formwork design is done based on height of pour, rate of pour, thickness of member, density of concrete, workability of concrete, placing of concrete, wind load and construction joints.
- Care is taken while designing the formwork to allow de mould without vibration, disturbance/damage to the concrete.
- Suitable camber is provided to compensate for anticipated deflections.
- Formwork is fabricated to confirm shape, line, level and dimensions of the concrete member as shown in the drawings.
- Components of formwork is cleaned thoroughly. Approved Mould releasing agent shall be applied to skin of the formwork before erection in case of vertical concrete members and before tying the reinforcement in case of Horizontal concrete members.
- Adequate lateral ties, braces and props shall be provided to ensure stability and rigidity of the formwork.
- All supports are rest on natural/firm and leveled surface.
- Forms shall be tight enough to prevent loss of cement slurry/grout to produce dense homogenous and uniform concrete surface with uniform color and free from any surface defects.
- Formwork are removed only after specified time.
- After Removal of Formwork, the assembly is cleaned thoroughly and repaired and stacked properly and Reused for Further Works.
Plant & Machinery
- Total Station
- Auto Level
- Measurement tape (metallic of 3m & 5m length)
- Handling and Erection equipment like Crane.
- Skilled carpenters and Helpers.
3. Reinforcement Work
- Reinforcement steel will be procured from approved primary manufacturers.The same shall be inspected and tested prior to the incorporation into the works. Test Certificates shall be collected from the manufacturers.
- Reinforcement steel will be straightened in the re -bar yard using hand levers.
- Cutting length as per BBS will be marked on each bar with the help of chalk piece. The bars will be cut in required lengths with the bar shearing machine.
- These cut reinforcement bars will be bent as per the shapes shown in the BBS and the construction drawings. Laps will be staggered provided as per the construction drawings. Any additional laps will be provided only after getting the approval of consultants.
- The cut and bent bars will be transported (manually or with tower crane as suitable) to the site of works and the same will be tied with 16 gauge annealed MS binding wire. The bars will be tied in accordance with the construction drawings.
- The reinforcement bars will be fixed ensuring adequate covers all rounds. PVC or other approved Cover blocks will be provided for the purpose. The reinforcement for the foundations will be erected with respect to center line and pedestal marking already marked over PCC.
- Cover for Reinforcement will be provided as per the drawing.
- Column bars verticality will be ensured with the help of MS pipe tied on both sides.
- The works area will be cleared off all scrap bars. The same will be stacked separately.
Plant & Machinery
- Bar Shearing Machine
- Bar Bending Machine
- Hand Levers
- Pin Plate & Hammer
- Skilled Bar Benders, Fitters and helpers.
4. Reinforced cement concrete works
- This includes concreting for RCC works
- The ingredients viz., Coarse Aggregates, Fine Aggregates, Cement, Admixture and Water will be approved by the consultants. The ingredients will be inspected and tested prior to their incorporation into the works.
- The ingredients will be stored at the bulk storage area near the concrete batching plant.
- A detailed Mix Design will be submitted by Contractor for the approval of the consultants and the same will be followed for all the works on the project. Mix Design will be as per the technical specifications and will include water-cement ratio, workability, minimum cement content, gradation of aggregates,
- Prior to the commencement of the works, the readiness of the site will be confirmed from the site engineer. Formwork and reinforcement will be inspected and approval taken. Provision of plumbing lines, conduits, anchor bolts, inserts, etc., will be checked and ensured as per the construction drawings. The mix design will be validated at project for each grade of Concrete.
- Construction Aids for Concreting such as vibrators, concrete mixer machine, mini dumper, chute etc. will be checked and verified for their working condition.
- The concrete ingredients will be mixed at the site as per the approved mix design.
- Mini dumper will be used for transportation of concrete.
- Placement of concrete will be done by chutes/boom placer/buckets/Concrete Line pumps
- Slump Test will be carried out as specified. Test cubes for determining the compressive strength of concrete will be taken as per the technical specifications.
- Sampling frequency as per IS 456.
- Each set will be tested for 7 days and 28 days. The lab results will be made available to the consultants/client.
- The concrete will be poured directly into the forms. The same will be poured within the initial setting time of concrete. The concrete will be placed in successive horizontal layers of uniform thickness and will be placed as rapidly as possible to prevent formation of cold joints.
- The poured concrete will be compacted with approved vibrators to the required density. Care will be taken to ensure that sufficient number of vibrators with correct size needles is available in good working condition during concreting and operated by experienced operators. Needle vibrators will be inserted rapidly and vertically at points less than 450mm apart and drawn out slowly when slurry begins to appear on the surface.
- Surface of RCC will be finished properly by trowel by skilled masons. Level of finished surface will be checked according to the relevant drawings.
- Adequate curing of the RCC will be done manually by pouring water or by ponding or by continuous cover of saturated sacks, etc. Curing will be continued till 7 days for RCC. Alternatively curing also will be carried out with use of curing compound one time application.
- Corrective action if required will be taken up to rectify surface defects as detailed in the specification or as per Technical data sheet of the repair mortar.
- CONSTRUCTION JOINTS:
- All pre-determined Construction Joints shall be as per pour sequence
- In case of Water Retaining Structures, the Construction Joints shall be provided as per pour sequence Water Stopper of approved make shall be used as per the manufacturer’s instructions
- At Retaining Walls/Slab on Grade :At the Construction Joint, the dowels for the next pour will be provided as per rebar detailing ,the Skin of the Hardened Concrete will be removed. The Surface then shall be made rough by hacking. The Shear Key will be provided at joints with help of chicken mesh .The joint shall be cleaned thoroughly with water jet/air jet and all loose materials will be removed. Old joint during the pour shall be treated with 1:1 fresh Cement Slurry and immediately Fresh Concrete Shall be Placed and vibrated.
Plant & Machinery
- Concrete mixer machine with weigh batcher
- Mini dumper
- Shovels, etc.
- Skilled Concreting workmen and Masons.
5. Back-filling works
- All source soils will be tested. the backfilling will be carried in compacted layers of not more than 300 mm thickness using dozers , rollers and earth rammer. Watering will be carried out using water tankers. After achieving 95% (Sub base Course) proctor density next layer of soil spreading will be carried out. Frequency one sample for every 250 sqm.In Case of Isolated footings filling will be carried in layers around the periphery and compacted with Earth rammer if the working space is around 600mm incase of inaccessible area compaction will be carried out with hand tamping with use of mechanical tool.Clods of earth are removed from the piled up earth. All pebbles, organic substances are removed from the earth.
- After the foundation concreting is over backfilling is carried out manually and with help of mechanical equipment’s till the bottom of PCC for SOG and layer filling and compaction wise will be carried out for retaining walls .
- Filling will be done for loosely laid 300mm backfill material &compacted to200mm thick watered (OMC±3%) and compacted with mechanical compaction machine or hand operated compactor as per specifications to achieve specified Proctor density. Density test will be carried out in accordance with the relevant IS code. Dust will be controlled by sprinkling water over the earth.
Plant & Machinery
- Backhoe Loader
- Dumpers for disposal
- Tamping rods or mechanical earth compactors
- density testing apparatus
- water tankers etc.
- Workmen for backfilling, tamping & competent operators for Backhoe Loader, drivers.
6. PCC Works
- Ingredients for PCC viz., Coarse & Fine Aggregates, Cement and Water will be inspected and tested prior to incorporation into the works.
- Inspected and tested coarse and fine aggregates will be stacked near the mixing plant separately in bins. The quality of the materials will be judged frequently on a periodic basis to see their fitness for use.
- Check the center of the excavated pit; check the dimensions and orientation of PCC. Approval for the founding strata will be obtained .
- Clean the excavated surface by removing all the loose materials. All handling equipment will be maintained regularly at the site to ensure fitness for use.
- Prepare the formwork for PCC to correct dimensions and levels.
- Ingredients for PCC are mixed mechanically in the batching plant according to the mix mentioned in the specifications &dwg.
- PCC will be transported from the mixer to the site by means of transit mixers
- Placing of the concrete will be done manually. Chutes will be provided to avoid segregation. The poured PCC will be compacted manually with steel rammers.
- Surface of PCC will be finished properly with the help of masons. Level of finished surface will be checked as per the relevant drawing.
- All loose materials will be collected and carted away.
- Adequate curing of PCC will be ensured by pouring water manually for one day prior to applying waterproofing primer.
Plant & Machinery
- Batching Plant,transit mixer
- Iron Pans
- Masons and experienced concrete workmen.
7. Waterproofing works
- tie rod holes or form tie holes shall be repaired with patching mortar or cone plugs secured in place with Dr Fixit Pidigrout 10M.
- The concrete surface shall be cleaned or prepared using wire brush or by splashing water on the surface ensuring there is no loose concrete or laitance or any other foreign material
- Ground Water Table to be kept under the raft level
- All corners shall be chamfered with CM 1:4 to avoid right angles for laying membrane for (Retaining walls & core walls).
- Prior to application of membrane entire area to be primed with bituminous primer polyplus WB as per the rate of application mentioned in TDS.
- After drying of the membrane PS 3500 ,3.5mm thick modified membrane to be fixed to the concrete surface and rolled with roller uniformely.The 50mm side laps and butt joints with bitustick TS to be provided for further continuity of the membrane
- Membrane laid to be protected with adequate protection measures to prevent damages from traffic .If found damaged to be repaired as per the manufacturer instructions.
Plant & Machinery
- Wire brush
- Paint brush
- Machine Grinder
- Straight Edge
- Air blowers
- Skilled Applicator & Masons.