319.1. General 1. Pipe jacking is defined as the installation of a tunnel lining by jacking pipes behind a shield, tunnelling machine or auger boring machine. The technique can also be used to install rectangular or other sections.
2. Excavation shall be carried out from within a machine or shield equipped with jacks capable of maintaining and adjusting the alignment and shall comply with Section 301.
3. Where applicable, machines and shields shall comply with BS EN 12336, and appropriate parts of Sections 314 to 317 of this Specification (excepting 314.2.5 and 314.2.10). Operations shall comply with Section 318 as appropriate.
4. The contractor shall be responsible for the equipment and sys-tems to provide the forces necessary for the installation of the full pipe string and for the design, provision and introduction of intermediate jacking stations.
5. Appropriate provision shall be made for supporting an exposed excavation face where necessary.
6. The Contractor shall submit method statements for all operations for the agreement of the Engineer before com-mencement of work. The methods used shall be in accordance with the Guide to best practice for the installation of pipe jacks and microtunnels published by the Pipe Jacking Association.
319.2. Thrust and reception pits
1. Thrust and reception pits and shafts shall be designed and constructed to allow the safe operation of plant, equipment and handling of materials and to withstand all loadings imposed by ground pressure, superimposed loads from surface structures and the maximum anticipated thrust forces. Where Permanent Works accommodate the thrust arrangements, these shall be designed to ensure that the Permanent Work is not damaged.
2. In all cases the Contractor shall submit his proposals including calculations to the Engineer for his agreement as required.
319.3. Operation 1. All key personnel shall be experienced in the pipe jacking process and hold relevant skills accreditation.
2. Before any particular pipe jack length commences, sufficient pipes and, if required, intermediate jacking station assemblies shall be available to ensure continuous operation.
3. The agreement of the Engineer shall be sought for inclusion in the Permanent Works of repaired pipes.
4. The jacking force applied by the thrust pit jacks, or an intermediate jacking station shall not exceed the allowable distributed or deflected design load for any pipe being jacked.
5. Thrust loads shall be transferred to pipes through a thrust ring which shall be sufficiently rigid to ensure even distribution of the load.
6. Changes to line and level shall be gradual. The manufacturer’s stated permitted draw or angular deflection on any individual joint shall not be exceeded.
7. Intermediate jacking stations shall be inserted to a pre-determined plan. Operation shall commence when loading reaches a predetermined level, which shall be less than the allowable distributed and deflected jacking loads as determined by the manufacturer.
8. To avoid excessive loading it may be necessary to undertake continuous jacking until completion of the drive. Where this is necessary the Contractor shall put in place appropriate measures to minimise noise and disturbance.
9. Where necessary means shall be provided to ensure that the pipeline remains stationary when face balance pressure is maintained and when any jacking rams are retracted.
10. Where required under the Contract, or agreed with the Engin-eer as part of the operational method statement, a lubricating and ground support fluid shall be injected into the annulus between the exterior of the pipe and the ground. This fluid shall be maintained under pressure until completion of the drive. The lubrication injection points shall consist of a minimum of three holes equally spaced around the circum-ference of the pipe.
11. Where necessary, the lubricant may contain an approved additive to limit water loss.
12. Where the quantities of lubricant injected significantly exceeds the theoretical volumes, this shall be reported to the Engineer.
13. Where required under the Contract, grouting of the pipe annulus shall be carried out on completion.
319.4. Packing and sealing
Joint packing material shall be included at each pipe joint and at any jacking station in accordance with the pipe manufacturer’s recommendations.
319.5. Monitoring and instrumentation
1. The Contractor shall maintain site records of jacking loads, line and level measurements, the distance moved and the relation-ship between them. Copies of all records shall be available to the Engineer at intervals to be agreed.
2. The jacking force instrumentation shall be calibrated for each drive by the Contractor. The calibration certificate shall be made available to the Engineer.
3. Survey control and guidance shall generally comply with Section 319.3. Line and level monitoring shall be carried out in conjunction with the pipe deviation angle. Further monitor-ing shall comply with Section 329.
319.6. Tolerances 1. Pipe jacking shall be carried out in accordance with the alignment tolerances given in Section 328.
2. Notwithstanding the specified alignment tolerances, the rate of change of direction in any plane, or combination of planes, shall be agreed with the Engineer, taking into account the pipe length, diameter, over-cut, jacking loads, and the manufacturer’s recommendations.
319.7. Microtunnelling 1. The term microtunnelling is generally applied to small-diameter tunnels and pipelines installed by pipe jacking methods behind a remotely controlled tunnel boring machine.
2. The microtunnelling machine shall be selected with regard to the ground conditions, length of drive and other relevant factors.
3. Microtunnelling shall comply generally with the provisions of Section 319.
4. Microtunnelling machines shall comply generally with the provisions of Sections 314, 315 and 316 as appropriate.