The objective of this method statement is to define the installation sequence of casing pipe by means of Pipe Jacking using Herrenknecht Automatic Tunneling Machine with Slurry Material Removal (AVN machines).
Table of Content
- Soil investigation.
- Identification and location of existing utilities.
- Responsibilities
- Labor, equipment’s and material required to complete the work.
- Handling and disposal of unsuitable materials.
- Dewatering.
- Excavation.
- Pipe jacking method.
- Installation of carrier pipe.
- Backfilling and restoration of surface features.
- Technical Data Sheet of Herrenknecht Automatic Tunneling Machine with Slurry Material Removal (AVN machines).
Soil Investigation
Soil sample shall be taken and submit to approved laboratory for testing to decide whether pipe jacking is feasible. Trial pits are particularly useful in obtaining information on the uniformity, extent, ground water table and composition of soils. The Engineer s interpretation of the Soil Investigation report shall be provided along with any assumptions made.
Identification and Location of Existing Utilities
Location of utilities prior to any works is essential. All existing utilities shall be exposed.
Coordinates and levels of the utilities shall be recorded, Shop drawing shall be prepared to show existing utilities and proposed pipe jacking pipeline. It will then be submitted to required authorities to obtain relevant NOC(s).
Responsibilities
Project Manager
Project Engineer
QA/QC Engineer
Site Engineer
Safety officer
Materials
Material shall be procured as per project specification.
Casing Pipe with smooth walled with minimum yield strength of 36,000 psi (ASTM A1011)
Carrier pipe meet requirements to Dubai Municipality.
Grout.
Dielectric material.
Plant & Equipment
- Pipe jacking set up
- Air compressor and Jack hammer
- Hydraulic pump and jack
- Dewatering Pump
- Spacer block
- Thrust ring
- Jacking Sheild
- Guide rail.
- Excavator
- Generator
- Wheeled bogey attached with air wich
- Tipper truck
Labour Requirements
- Experienced personnel for excavation
- Pipe fitter
- Operator
- Mason
- Carpenter
- General Worker
PPE List
- Gloves
- Overalls with Company emblem
- Reflective Safety vest
- Safety Shoes
- Protective Helmets
- Safety goggles
HSE Requirements
- All Personal Protective Equipment used for the work force will be selected based on the findings from the risk assessment and will be effectively managed.
- Adequate information, instruction and training will be provided to all personnel involved with the work on the wearing and use of Personal Protective Equipment.
- Only experienced person shall be allowed to work inside the jacking pit and excavation area.
- Clean working conditions inside jacking operation area and removal of spoil, debris, and others materials shall be maintained during operation.
- Good ventilation shall be provide d for personal working inside the casing pipe and doing excavation.
- Good house keeping shall be maintained around the works.
- Adequate barricades, warning lights or signs to safeguard traffic in the immediate area of the operation.
- No attempt shall be made in strong wind where control of the element may be lost.
- In the case of accidents on site or any near misses, the incident will be reported immediately to the Safety Officer and further necessary arrangements to be made.
- No soil and material shall be allowed after completion of work.
Pipe Jacking Method Statement
Preparatory work
- Road surface levels shall be taken along the pipe jacking route 10mm each side every 2m jointly with Engineer Surveyor before, during and after the operation of pipe jacking.
- The launch pit and reception pit shall be constructed. The sizes of pits are depending on pipe diameter, pipe length of jacking, site conditions and shall comply with Manufacturer’s recommendations. Please refer to Technical Data Sheet.
- A thrust wall shall be constructed to provide a reaction against which to jack. In poor ground, pilling or other special arrangement shall be undertaken to increase the reaction.
- At the mouth of tunneling, a concrete wall shall be casted to avoid soil collapse and smooth jacking of pipe.
Pipe Jacking
- Hydraulic jacks shall be positioned on a support frame against the thrust wall parallel to line and gradient and driven by a diesel driven hydraulic power pack.
- Hydraulic jack shall be operated by banksman on instruction from the pit bottom.
- A thrust ring shall be placed between the steel pipe and jacks to distribute the jacking force onto the pipe to prevent it from buckling.
- The leading edge of the first pipe shall profiled to suit the soil condition, i .e. in soft ground a hood shall be used.
- The soil shall be excavated at the face by using air compressor and jack hammer.
- During excavation if water is encountered, dewatering system of sufficient capacity shall be maintained to remove water continuously, keeping excavation free of water and while back filling operation is taking place.
- The excavated soil shall be loaded into a muck skip placed on a wheeled bogey, which is pushed into the pipe manually and pulled out to pit by an air winch situated between the jacks.
- The pipe shall be jacked forward as the excavation proceeds in reception pit.
- When the pipe has been pushed to the limit of the jacks stroke, the jack will be retracted and a spacer block placed between the jack and thrust ring. Jacking will then continue.
- This process shall be repeated until the pipe is fully pushed in.
- Then next pipe shall be placed at pit bottom welded in place and whole process repeated until the drive has reached the reception end.
- Surveyor shall check line and levels regularly during the pipe jacking process.
- For all above activities daily activities log shall be maintained on site, that will include:
- Start and finish time of casing pipe advancement.
- Total length of casing pipe installed.
- Maximum jacking force exerted during installation of each casing pipe section including forces required to re-initiate jacking following periods of system shutdown. General descriptions for each dissemble ground condition mined.
- Settlement monitoring readings.
Installation of Carrier Pipe
After casing pipe has been installed, the carrier pipe shall be laid to line and level.
Carrier pipe shall be supported on spiders clamped to the pipe or on flat bars welded across the steel sleeve.
Once all the carrier pipes are securely fixed in position and checked, a breather pipe will be placed at the soffit.
Then concrete/block work head walls shall be built at the end of the steel pipe.
Grouting
Prior to grouting the carrier pipe shall be filled with water and in case of uPVC this will be circulated to avoid damage due to the heat of hydration.
The annulus between the carrier pipe and the sleeve shall be filled with foam concrete (1000kg/ m3)
Foam concreting shall be continuous until sleeve is completely filled.
Grout Mix Design:
SRC: 432 kg
Dune Sand: 1214 kg
Water: 360 kg
Superplasticizer: 3 liter
Slump: Collapse
Backfilling
Backfilling will be carried out after inspections are done by all concern authorities and approved by them.
The thrust and reception pit shall be backfilled layer by layer in accordance to specifications.
After completion of backfilling, the original condition of the ground shall be re – instated.
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