pja design presentation

8/3/2019 PJA Design Presentation

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Pipe Jacking Design and Best Installation PracticePrepared by the

Pipe Jacking Association


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Key Considerations

Pipe Jacking is an integrated system linking:

soils

jacking shafts

pipes

shields

jacking loads

engineering


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Soils Investigation

Soils investigation is key:

This influences

excavation method

temporary works

length

pipes

ground stabilisation


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Differing ground needs to be assesed as appropriate:

Non-cohesive soils

Cohesive soils

Mixed soils

Fill

Rock

Water presence is a key factor

Soils Data Requirements


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Unstable Ground Conditions

Tunnelling methods depend on

the stability of the ground

Solutions to instability are

either geotechnical processesor physical constraint

Geotechnical options are extensive


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Excavation: Open Face

Hand shields


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Hand shields

Backacter


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Hand shields

Backacter

Cutter boom


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Excavation: Closed Face

Pressurised slurry

Compressed air

Earth pressure balance


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Temporary Works: Shafts and Shield Entry

Segmental

Precast or insitu

Piled

Sheeted or timbered

Battered

Anchorages

Shield entry and exit


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Temporary Works: Thrust Walls

The thrust wall takes the full jacking load

Spreaders distribute the load

Thrust wall failure key risk


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Temporary Works: Manholes

Manhole requirements vary

Shafts bases can be enlarged

Caissons can fulfil mutiple roles

Manhole utilisation impacts on

project costs


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Jacking Lengths and Friction Loads

Design variables include:

thrust walls

pipe design

interjacks

friction lubricants

spoil removal

engineering


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Jacking Loads

Jacking loads comprise:

face loads

pipe string weight

friction

misalignment

time delays

Frictional forces 0.5 to 2.5 tonnes per square metre


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Lubrication

Bentonite

Soil type dependent

Foams


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Pipe Jacking Pipes

Concrete jacking pipes: EN 14457

Installation forces are key

Follow manufacturers recommendations


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Best Installation Practice: Loading

Thrust load and anchorage

Load transfer

Control/failsafe

Interjacks


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Best Installation Practice: Steering

Tolerances: 75mm for line, 50mm for level

Setup and shield entry

Regular checks

Cautious realingment


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Best Installation Practice: Records

Monitoring

Main survey checks

Line and level

Shield position

Pipe rolling Main jacking load

Interjack load

Shield load

Total load

Surface checks


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Summary

Design: Ground

Excavation method

Temporary works

Jacking loads

Lubricants

Pipes and joints

Installation: Steering

Loading Records


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Pipe Jacking Association10 Greycoat Place, London SW1P 1SB

Tel: 0845 070 5201 Fax: 0845 070 5202

Email: [email protected]

Website: www.pipejacking.org

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