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Plunge Column Construction Method Statement

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PURPOSE

This Method Statement describes the construction process of 1500 mm diameter Plunge columns construction in the project.

SCOPE OF WORK

The scope of work and the construction sequence for installation of permanent plunge column shall be as mentioned below:

  1. Traffic Management and Barricading
  2. SHE Measures.
  3. Design and Drawings
  4. Site Establishment
  5. Surveying
  6. Pre-excavation
  7. Boring into soil to the design depth
  8. Muck Removal
  9. Fabrication of structural steel flange column
  10. Cage preparation and cage lowering
  11. Tremie Lowering
  12. Concreting for Plunge Column
  13. Back filling

SITE ESTABLISHMENT & SETTING OUT

Good firm access shall be provided to allow safe passage of plant and equipment throughout the Plunge Column construction area.

Adequate, hard, all weather platforms shall be provided and maintained for the execution of the plunge column operations. Platforms shall provide sufficient bearing capacity for the pilling rig and cranes.

Safety barriers shall be provided at all times to prevent unauthorized access to the operation area.

The position of the Plunge Column shall be determined by the setting out as per approved drawing.

Equipment to be Deployed

  1. 70 Ton capacity crawler crane
  2. Supporting crane(70Ton)
  3. Hydraulic self-propelled Kelly Rig
  4. Polymer setup\
  5. Tremie pipe (200 mm Dia; with hopper)
  6. Welding sets
  7. Cutting and bending machine
  8. Transit Mixer
  9. Batching Plant (60 cum/hr)

Requirement of Materials

CONSTRUCTION PROCEDURE

 Traffic Management and Barricading

Traffic management shall be carried out as per the approved Traffic Diversion Plan. For heavy equipment mobilization, necessary precautions shall be taken to bring the required items within the work area boundary by carefully managing the traffic.

The work location shall be barricaded as per the site requirement and all the equipment shall be installed inside barricaded area.

HSE Requirements

All the workers shall be provided with required PPE (safety jacket, shoes, helmet, hand gloves etc.) before they are engaged in the work.

Safety induction shall be provided to the supervisors, engineers and workers.

Tool box meetings shall be organized every day by site supervisor before start of work in order to keep workers aware of associated risks and safe working in order to avoid accidents/injuries.

Unauthorized/outsiders shall not be allowed to enter inside/stay near the area barricaded during work in progress.

First aid facilities shall be made available at site and male nurse shall be available at principal work spot to render the first aid services, if so required.

Proper Lighting arrangement shall be maintained during night work (or in day time in case of low visibility).

Housekeeping shall be maintained at work spot to avoid any undesirable incident.

Emergency contact number shall be available and displayed at the designated locations near the work spot to tackle any emergency situation occurring at site.

All the machines shall be inspected before deploying to the work and proper guarding for moving parts shall be in place prior to commencement of work. Operators with valid licence (where applicable) shall be allowed to operate the machines.

Silent type DG sets shall be deployed at work location.

Drip tray shall be provided underneath the machinery to avoid land contamination.

Dust bins shall be available at prominent locations of work site to collect generated waste out of site activities.

Risk assessment shall be discussed among all concerned prior to start of the activity.

After completion of work at a particular stretch required back filling shall be taken up depending upon site requirement.

After completion of work post inspection shall be carried out to ensure that the tidiness has been maintained and the work location has been restored to original condition.

Design & Drawings

The work shall be carried out as per the approved design and drawing.

Controlled copies of relevant drawings shall be made available at site and shall remain available with site engineer throughout the work.

Site Establishment

Before starting any activities, a site utilization plan is drawn showing the various establishments at site such as location of Panel formation, Putting DG’s, Polymer tanks, Muck bin, office etc. through a detailed survey. The site area shall be then cleaned properly and made free from any on and over ground obstruction and necessary barricading shall be installed. All plant and equipment shall be placed as per this plan.

Surveying

Upon clearing the site area, the setting outpoints shall be marked for the subjected Plunge Column panel and with reference to that guide wall, points shall be marked through requisite survey.

Reference pillars shall be always preserved for checking of constructed guide wall at later stage. All the survey points/coordinates shall be maintained in survey sheet and checked/approved by Engineer prior to construction work.

Pre Trench

During this pre excavation process, investigation and verification of underground utilities shall be done at the subjected location. Manual excavation shall be done for finding the underground utilities.

In case of any utilities found, the mapping shall be done through requisite survey and a drawing shall be drawn. In order to construct the Plunge Column such utilities if required to be shifted marginally, the same shall be done either through local shifting or providing the local diversion as agreed upon by the utility owner.

The diversion process if necessary shall be done in consultation with utility owner. Utility diversion shall be done as per approved method statement. The utility diversion method statement shall provide detailed information about the underlying utilities and the process to be followed for the diversion process.

Plunge Column Boring

(a) Boring of Soil

1.5 meter dia; Boring of soil shall be carried out using a rotary Hydraulic pilling rig in normal soil strata to the required depth as per approved drawings.Soil stabilization will be ensure by polymer final depth of concrete shall be confirmed by sounding method.

The verticality of the Bore shall be monitored during installation and later checked before lowering of cage. The eccentricity shall be jointly done with verticality.

(b) Setting out of guide frame

Minimum 200mm trench shall be excavated, a leveling PCC (M15/M20) will laid for placing the guide frame as per the Drawing attached.

(c) Placing of Guide frame

After placing of PCC guide frame shall be placed carefully in line and level layout as per the surveyor.

(d) Instillation of temporary casing

To stabilize the upper bore, temporary steel casing of length 2.5 m shall be installed at the bored pile locations as follows:

A 1500mm Dia bore shall be drilled using a Hydraulic Boring machine to a required depth.

A 2.5m long steel casing shall be installed in the 3-4m deep bore holed by lowering the casing with crane. Verticality shall be checked and ensured during installation.

The casing shall then be driven into the ground with rotary machine until about 300 mm is left protruding above the ground.

Drilling rig is then used to progress the excavation to the bottom of the casing pipe and then polymer shall be added before any further excavation is made.

During excavation polymer shall be added continually from the storage tank such that level is maintained within 1000mm below top of casing pipe. Excavation depth shall be found by sounding tape.

(e) Polymer Slurry Preparation, Storage and circulation

Dry polymer powder shall be tested and approved prior to the use. The batching plant shall be erected on adequate impermeable slab. Dry polymer powder shall be mixed in the mixing tank with the water.

The mixing shall be achieved by dedicating a pump and compressed air system. The mixing tank capacity may be 1.5 times the excavation’s volume. The mixing tank shall be connected to the slurry storage tank with appropriate routing valves. Thus polymer slurry is made ready for use with required properties.

In the second phase the polymer slurry shall be pumped to the trench and circulated continuously till excavation is over. While the panel excavation is going on the polymer slurry continuously flows to the trench and thus stabilizes the trench throughout its depth. While excavation, the polymer slurry get mixed with soil and loses its properties.

Continuous circulation of fresh polymer shall help to keep the properties of the polymer slurry even then it is mixed with the soil. The return slurry shall be pumped into the sedimentation tank.

The sedimentation tank shall be kept open to the top to allow an easy cleaning and removal of sediments. As sedimentation tank is included with three deflector vertical plates, continuous flow of slurry shall occur in “cascade” like mode and increase the speed of the sedimentation occurring between different compartments.

The final de-sanded slurry shall be connected to the storage tank with after being treated properly to achieved required property and sent to storage tank with proper pumping arrangement.

The polymer characteristics shall be checked with respect to the following prescribed values:

Sr. No. Test Permissible Value
Fresh mix Reused Slurry Prior to concrete pour
1 Density (kg/m3) 1.00 to 1.04 ≤ 1.06 ≤1.05
2 pH Value 11 to 12 11 to 12 9-12
3 Marsh Cone Viscosity API (s) 55-140 55-140 50-140
4 Sand Content (%) – <2% ≤2%

Muck Disposal

The Bore Muck generated from excavation process shall be shifted to space available near by the work area using JCB. The shifting shall be continued till the completion of grabbing operation. After Completion of grabbing the working area shall be cleaned for stacking of Stop End and Reinforcement Cage.

The Bore muck initially dumped at available space near working area then shifted to designated dumping yard by covered and leak proof tipper/truck having the fitness certificate checked by Engineer.

The tyres of the truck shall be cleaned thoroughly and be made free from muck before the truck exits the site. After removing all the muck the area shall be cleaned using water through the water pipe line arrangement at site.

Preparation of Reinforcement Steel Cage Cutting, Bending

The reinforcement cage shall be in single piece or two pieces depending upon the site condition and equipment availability, the cage may be fabricated and lowered into Bore Pile. The reinforcement should be cut and bend at the steel yard or at site as per bar bending schedule and the cages shall be prepared at site over a level ground. Necessary spacer bars, fixtures, inserts and cover blocks shall be provided along with the reinforcement cage.

Care shall be taken to fabricate the cage in true line and level with cover blocks fixed with proper supports and brought to the panel by crane. Cover blocks shall be provided at close spacing of 1.5m to 2.0m. While cage fabrication, roller cover block shall be introduced to the outer rebar’s before fixing.

Fabrication of Rebar Cage

Based on the approved reinforcement drawing, the Bar Bending schedule shall be prepared and shall be submitted for approval.

The reinforcement shall be cut and bent as per approved Bar Bending Schedule in reinforcement yard situated at the casting yard. The cut and bent steel shall be shifted to the site with the help of Trailer for making the cage.

The reinforcement cage shall be fabricated at the site. If there is insufficient space on site, the same shall be fabricated at the casting yard or other offsite location and the prefab cage shall be shifted to site through trailer.

The reinforcement cage shall be fabricated using the Binding wire and wherever required welding shall be done. The cage shall be fabricated over the fabrication bed consisting either of steel chairs, channels or wooden sleepers.

The clear cover shall be maintained as per design which is 75 mm. Concrete spacers (same grade as Plunge  Column concrete , circular or trapezoidal skid shape) shall be fixed to the cage typically at intervals of 1500mm horizontally and 4000mm vertically.

Cutting / Shearing of Rebars 

The bars with improper ends like bent, too much heated, improper manufactured ends etc., are cut with Handsaw machine or sheared with shearing machine. This is done in order to achieve a flat surface for further forging of the rebar. Also the face of the rebar becomes perpendicular to the axis of the bar. This flat face also helps in abutment of two rebar when in contact with each other.

Cage Lowering and fabricated plunge Column

After cage preparation, lifting and placing of the cage shall be done with the help of service crane and the cage lifter. The cage lifter shall be fixed directly to the lifting hooks of the cage with shackles and slings of the crane.

The cage shall be lowered up to the desired level and shall be rested with the help of resting hooks and supports from guide frames. Front and rear sides of cages shall be marked on site to identify the soil face and excavated face during placement.

Lifting points and lifting lugs are designed (to be approved by designer) in such a manner which shall not cause distortion of the cage.

the plunge column shall be lifted with service crane and inserted in eccentric part of cage to the required depth as per the drawing, holding and jointing of both reinforcement cage with fabricated plunge column shall be done.

After removal of all the hanging supports, both reinforcement and plunge column shall be lowered with service crane, maintain the eccentricity and verticality of plunge column by fixing the survey coordinates on guide frame. The lowering of cage and plunge column shall be done to the required depth of pile as per the approved drawing.

Tremie and Lowering

After lowering of reinforcement cage, tremie of minimum 200mm dia and length of 1.2 to 2m shall be lowered in pieces and connected while lowering for full depth of trench with the help of service crane and hopper of approximately 1.5 cum capacity shall be attached to the top of tremie pipes.

Concreting

Concrete of required grade M35 shall be batched in the batching plant and same shall be transported through the transit mixer and poured to the hopper/tremie pipe. Initial setting and final setting time of concrete shall be 5-6 hrs and 13-14hr respectively.

The concrete shall be directly discharged into the hopper/tremie. Before initial discharge there shall be at least 2 nos. delivery trucks on site. Uniform rising shall be ensured by periodically measuring the rise of concrete adjacent to the tremie location not less than once per concrete truck per tremie.

There must be a minimum 1.0m immersion of the tremie pipes in the concrete. This is necessary to avoid polymer inclusions in the concrete. Tremie pipes shall be shortening depending on the rise of level of concrete. The tremie lengths and concrete rise shall also be monitored / recorded.

Concrete shall continue to a minimum cut-off level at bottom of base slab as per the drawings as required to ensure sound homogeneous concrete at cut-off level. Any significant remaining portion of Plunge Column from bottom of base slab to top of concourse slab shall be filled with M5 /M10 Grade slurry Mortar Design Mentioned Below:-

Cement Fly ash Sand Water Admixture
90 KG 100 KG 1625 KG 310 KG 1 KG

The next remain level of plunge column from concourse slab to the top slab shall be filled with backfill soil and sand as required.

Quality Control / Assurance

Quality Control and Quality Assurance of Plunge Column operations at different stages shall be done using the approved ITP & Formats.

Particular care must be shown with respect to control of polymer slurry. Drip trays to be used underneath compressors and generators. Site is to be kept free of dust. Noise levels shall be kept well within the allowable limits.

Environmental Management

Health Safety and Environment HSE plan shall be followed throughout the construction program. The Construction of Plunge Column involves the use of heavy machines such as crane, excavators and trucks etc. and these machines inevitably create noise.

However, in order to minimize the noise and discomfort to the people living in the neighborhood or the shopkeepers and people coming to the nearby markets, all the machines shall be provided with suitable silencers and with acoustic enclosures, Noise barriers shall be erected to minimize the noise pollution.

The construction shall also involve the removal of earth from site to dumping areas by dumpers that shall use the public roads. During transportation the dumpers shall be covered by tarpaulins.

The muck shall be disposed during the night hours only and one supervisory level staff shall be engaged permanently at dumping yard with JCB for leveling the upcoming soil leveling, while dumping the soil.

Simultaneously the area leveling and shall create a proper way for soil dumping. The used polymer slurry shall be transported in dumpers.

The washing bay shall be installed near each exit gate. These washing bays are of improved design using a heavy-duty pump having high head and large discharge. The tires and the undercarriage of the vehicles shall be washed before the vehicle leaves the working area for dumping site.

In case water is not available due to water scarcity, tire shall be cleaned manually with wire brush. Required persons shall be engaged to clean the sides of the vehicles manually. The working area shall be kept clean and tidy.

Safety and Emergency Procedures

During excavation all necessary precautions to ensure stability to the excavations and guide walls shall be taken. If excavation be suspended for any reason, polymer in the trench shall be agitated, periodically with the grab or by circulation for a maximum period of 24 hrs. This shall be followed by back filling of trench with excavated materials.

In the event of a sudden loss of polymer slurry or trench collapse, the excavation shall be immediately stopped and the trench back filled with excavated materials.

Necessary Attachments

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