Method statement for replacing soft soil with permeable materials

CONTENT1.0 Purpose of Method Statement2.0 Relevant documents and Standards3.0 Responsibilities for activity Describe within this Method Statement4.0 Detailed method of carrying out&method statement activity5.0 Quality assurance and quality control measurements6. 0 HSE measures APPENDIX 1: SLR-RC Box Section Construction-Wall steel formwork(data)APPENDIX 2:SLR-RC Box Section Construction-Wall steel formwork(member design)APPENDIX 3:relevant Chinese material specificationAPPENDIX 4:Technical Code for Safety of Forms in ConstructionAPPENDIX 5:Technical Code for Safety of Steel Tubular Scaffold with Couplers in ConstructionAPPENDIX 6: Technical Code of Composite Steel-formAPPENDIX 7: Typical details of the Culvert Back filling

Method statement for Culvertupper portion1.0 Purpose of Method StatementThis method statement provides the details of the materials, the equipment, the procedure and relevant documents related to the construction of reinforced concrete box culvertsupper portion, which refers to the structure above foundation bed concrete level. This method statement shall refer along with MS 08A- Method statement for construction of culvert lower portion.

2.0 Relevant documents and Standards2.1 ICTAD publication SCA/5, section 1000 2.2 BS 8666: 2000 Dimensioning, scheduling, cutting and bending steel reinforcement for concrete structures2.3 Working drawings for culverts2.4 Method Statement for construction of culvert lower portion

3.0 Responsibilities for activity Describe within this Method StatementConstruction manager, structural engineer, site engineer and other relevant personnel within whose scope of works shall be responsible for referred construction activities in related to construction of reinforced concrete box culverts shall carry out according to the method stipulated in this statement unless otherwise changed by the Engineer.

4.0 Detailed method of carrying out method statement activity4.1 Initial setting out, preparation, ground bearing capacity check, foundation construction and concreting are described in MS 08A- Method statement for construction of culvert lower portion.

4.2 Material

4.2.1 Steel and wooden formwork4.2.2 Steel reinforcement4.2.3 Water stop material for Movement joint (300mm width)4.2.4 1.5mm thick, Highpolymer modified asphalt water proofing membrane (500mm width) for movement joint4.2.5 1.5mm thick, Polythene waterproof coating (660mm wide) for movement joint4.2.6 Asbestos asphalt plate 30mm thick for movement joint4.2.7 C40 concrete 40mm thick cover layer for movement joint4.2.8 C20 screed concrete4.3.8 C 30 concrete for retaining wall and culvert foundation at inlet and out let4.3.9 C40 concrete for culvert, retaining wall and cap block

4.3 Construction4.3.1 Steel reinforcement workReinforcement will be clean and free from loose rust and mill scale, dirt, oil, grease and paint at the time of fixing in position and subsequent concreting. Reinforcement will be handled and stored in a manner that they will not be deformed.Bars will be cut and bent cold by applying a slow, even pressure with equipment and methods approved by the Engineer to the dimensions given in the Bar Bending Schedules shown in the relevant construction drawings.All reinforcing bars will be placed in positions shown in the Drawings and will be firmly held in position, with the specified spacing, prior to concreting operations using necessary wire ties at bar intersections, spacer bars, steel chairs of approved type or by other approved means. Wire ties(binding) will be black annealed M.S or G.I. wire, not less than 1.0mm in diameter and will be firmly tied and folded so that they do not project into concrete cover region. The adequacy of supports and ties to secure the reinforcement properly will be subject to the approval of the Engineer. Layers of bars will be separated by spacer bars, concrete cover blocks. All horizontal and vertical reinforcement will be supported on mortar blocks, of approved shape conforming to cover requirements, with tie wires embedded in them, made out of 1: 1 or 1:2 cement sand mix. Supports which are in contact with the external face of the concrete will all be concrete cover blocks. The use of small stones or wood blocks will not be allowed. As far as possible, bars of full length will be used. In case this is not possible splicing of bars will be done as specified in the Drawings or as directed by the Engineer. Lap splicing (as per BS 5400 part -4 and design drawings) will be staggered for different bars and will generally not be located at points, of maximum tensile stress.No concreting will commence until the reinforcements have been inspected and approved by the Engineer.Reinforcement after being placed in position will be maintained in a clean condition until completely embedded in concrete. Special care will be exercised to prevent any displacement of reinforcement in concrete already placed.

4.3.2 FormworkThe formwork will be timber, steel approved by the Engineer. Timber forms will be of approved quality, well seasoned and of uniform thickness, sound, free from warps, loose knots, twists, wavy edges, saps and shakes or other defects affecting the strength of the form work and appearance of the finished surface of the retaining wall. Metal sheets use for formwork will be kept free from rust and dents with no surface blemishes that will impair the concrete surface finish.The supports and scaffoldings will be of metal, sawn timber, round timber or of any other material approved by the Engineer.The temporary staging will be provided to enable the constructional operations to be performed in the required sequence and in a safe manner. The false work will be properly constructed to provide the necessary rigidity and to carry out loads, which will be required to support. Where necessary it will include safe walkways to enable Engineer to inspect the form work, reinforcement and concreting. All formwork will be constructed that there will be no loss of materials from the fresh concrete. Forms will be mortar tight, will be made sufficiently rigid by the use of ties and bracing to prevent any displacement or sagging, and will be capable of withstanding all incidentals loading during concreting.Where internal ties, they will be extracted without damage to the concrete to a depth of at least 25mm from the finished concrete surface and the resulting holes filled with.non shrinkage mortar. No permanently embedded nuts will have less than 25mm concrete cover from finished concrete surface.Immediately before concreting, the forms will be thoroughly cleaned either by water jetting or by any other suitable method, temporary openings being provided for the purpose. Inside surfaces will, coated with an approved material such as mould oil to prevent adhesion of the concrete. This material will not be allowed to come in to contact with the reinforcement.No concrete pouring will be carried out unless the Engineer has inspected and approved the formwork, false work and reinforcement.The engineer will be informed in advance, as to when the formwork removed. The minimum period between concreting and formwork removal for culvert wall will be 01 day& for the slab shall exceed to 7 days. This would be confirmed by required compressive strength.

4.3.4 ConcretingWhen a truck mixer or agitator is used for transporting concrete, the concrete will be delivered to the site of the work and discharged within one and half hours after the addition of the cement to the aggregates. A batch ticket bearing complete batching information will accompany each batch of the concrete delivered at the job site. The temperature of fresh concrete will not allow exceeding 32C unless otherwise specified. The addition of water after completion of initial mixing will not be allowed. Concrete that is not within the agreed consistency limits at the time of placement will not be used.Prior to placing of concrete all formwork and reinforcements therein will be cleaned of all extraneous material, dust and made free of any standing water. It will be ensured that all formwork is made leak proof and that there is no loss of mixing water or grout from the concrete. No concreting will be started without the prior approval of the Engineer.All mixed concrete will be placed and compacted in the formwork, using approved vibrators of the internal, external or combinations thereof depending on the type of job. In all cases of continuous concreting, fresh concrete will be placed before the already laid concrete is less than 30 minutes old and where this time gap is exceeded further placing will be subject to testing the already placed concrete surface to be live. In the event that the surface is not live, it will be treated as a construction joint and to be allowed to set. Constructions joints shall be vertical or horizontal. Cold joints shall be avoided.All concrete generally will be placed and compacted in horizontal layers normally not exceeding 300mm in depth except where adequately sized internal vibrators are used when the depth may be increased up to a maximum of about 400mm.No concrete will be dropped from a height greater than about 1.5 meters except with the prior approval of the Engineer. Where chutes are used for placing of concrete they will be kept clean and used in a manner to prevent segregation. When concrete is conveyed by chute, the pouring will be carried out in a way that to ensure practically continuous flow. Slope of the chute will be so adjusted that the concrete flows without the use of excessive quantity of water and without any segregation of its ingredients. The delivery end of the chute will be as close as possible to the point of deposit. The chute will be thoroughly flushed with water before and after each working period and the water used for this purpose will be discharged outside the formwork.When concreting done for walls of height more than 1.5m, Separate pouring points will be arranged by re arranging the stirrup reinforcement under the inspection of Engineer, so that the tremie pipe can lower down to the required level. The pouring points will be arranged at one meter intervals. The concrete will be spread using poker vibrators. When concreting has to be resumed on a surface which has hardened, the surface will be roughened, swept clean thoroughly wetted and covered with a thin layer of cement grout or as approved. Semi-hardened surfaces will be well brushed to remove all laitance, cleaned and covered with a thin layer of cement grout prior to overlaying with fresh concrete. A concrete surface, which has hardened, will be treated as a construction joint for further casting after not less than 24 hours. The surface will be free of laitance and leaned until the surfaces of the larger aggregate are exposed. The aggregate stones will not be loose.

4.3.4Concreting sequence1. The concreting carries out four steps given below;

100mm thick kicker will be casted by pouring additional concrete height above from the chamfer top level after Step 2 to support formwork erection at step 3.The lateral brace supports will be setup on formwork founded on culvert base to avoid swaying of the frame during concreting of step 3. The brace supports will be independent for each wall. The spacing will be same as vertical studs in longitudinal direction of the culvert.

3. Construction sequence along the longitudinal directionThe foundation bed concrete, which named as part one in above will be placed together (sequence A). Then the part 2,3and 4 will be concreted in different segments separated by the movement joints.

Figure 2. Longitudinal sectional view

The concrete pouring will be carried out using pouring buckets handled by a crane or concrete pump. Whenever the concrete falling height will be more than 1.5m, especially in cases of concreting sidewall of the box culvert, concrete will allowed to pour through a chute arranged in a way that the free falling of concrete is less than 1.5m. The internal vibrators used during concreting work sufficiently, so the concrete will spread, compact in even along the entire layer.

4.4 Back fillingAfter completion of the structure, tie holes will be filled with approved non-shrinkage cement mortar.Prior to the backfill, the excavated area will be dewatered until existing bed exposes, and the slope prepared 1: 0.25 gradient from the bottom of the excavation. The debris and other unsuitable materials within the excavation area will be removed using excavators during the time of bed and slope preparation.

+300mm

Typical Section of structure back filling (Please refer Appendix 7)

The back filling of two sides of culvert / behind the wing wall, will be carried out using graded granular material or permeable soil. The permeability requirement of back filling material will be 10-4 m/s. The light compaction equipment will be used to compact the back fill adjacent to structure. The compacted layer thickness will not be more than 150mm. The compaction will be not less than 95% of the maximum dry density. The backfilling work will be carried out both sides simultaneously. The difference of the two sides filling height will not be allowed to exceed 300mm.The backfilling using ABC has to be done up to the top level of the culvert. Boulder filling with ABC blinding to be done up to 300mm above the maximum water table.The outline of the ABC profile has to be corrected as per the actual construction at site.A suitable thickness of soil cover has to be maintained with the replacement of ABC material in the turfing area.

5.0 Quality assurance and quality control measurements.5.1 Bearing capacity testing will be carried out at proposed foundation level after excavation.5.2 Site layout strictly according to the design drawing.5.3 Material for concrete will be from approved sources, compliance with requirements.5.4 Reinforcement fabrication is strictly in accordance with design drawing.5.5 Reinforcements only from approved suppliers, brands, and in a acceptable conditions, free from dirt, corrosion, grease and oil.5.6 Binding wires shall be minimum thickness 0f 1mm, free from corrosion.5.7 Cube samples will be collected 3 per each 10m3and for each new pouring.5.8 Temperature of the fresh concrete will be kept less than 32oC at the pouring time.5.9 Slump of the concrete before pouring shall comply with the mix design requirements5.10 After reinforcement fabrication completed, Engineers inspection will be called upon to check the reinforcement fabrication in accordance with the design drawing.5.11 During the concrete pouring, internal vibrators are used adequately.5.12 The pouring work will be carried out in approved manner, the layer thickness and time duration between two pouring will be strictly controlled.5.13 The structure back billing will be strictly according to the drawings

6.0 HSE measures6.1. Site staffs are allowed to enter the construction site only with the safety helmets on their heads. 6.2. Safety measures must be taken during the excavation close to buildings, facilities foundations, electricity posts and scaffolds.6.3. To control the speed and keep the distance from other vehicles during the tipper is running; Lighter vehicles should give way to heavier vehicles when passing each other; 6.4. It is forbidden to stand within the operating area of a running machine. All the operations of machines shall strictly conform to the regulated process of safety operation.6.5. When the soil structure is unstable, when the collapse happens and when the water level rises suddenly or any other dangers occur, all the site staffs should immediately stop the work and be evacuated to safe places. They can go back and resume the construction only after the site is confirmed to be safe.

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