W1). Within the style of pipe jacking, what explicit areas on pipe joints ought to engineer’s lookout of?
Since in pipe jacking, the jacked pipes may hardly be jacked within the designed level and alignment and a few deviation from the initial one is often acceptable providing the deviation are inside the tolerance of the Contract. However, so as to avoid harm created to the pipe joints because of overstressing, it’s necessary to estimate the strain concentrations ensuing from these angular deflections.
W2). What are the variations in style between traditional formed concrete pipes and pipes used for pipe jacking?
For pipes used for pipe jacking, they ought to possess the subsequent characteristics:
- a) Pipes ought to have high concrete strength to face up to the strain induced throughout the jacking method.
- b) There’s tight tolerance in pipe dimension and also the pipe joints are specially designed to give untroubled joint details. 2 unremarkably offered joints are rebated joint and butt joint.
- c) Pipes ideally ought to have sleek external concrete finishes to cut back the friction between the pipes and close soil.
W3). Why are intermediate jacks designed in some pipe jacking projects?
When the method of pipe jacking stops, increase of resistance is incredibly quick in some soil. as an example, increase in jacking force of 20%-40% is needed for an interruption of pipe jacking for simply many hours.
For a protracted pipeline, the resistance forces established between the jacking pipes and soil is high. Sometimes, such resisting forces is also thus high that they’ll hardly be overcome by the jacks in jacking pits. Moreover, though the jacks will overcome the high resistance forces induced throughout jacking, high hundreds are intimate with in jacking pipes throughout driving. Jacking pipe’s material e.g.
W4). What’s the operate of packing materials within the joint of concrete pipes in pipe jacking?
Packing materials are regarding 10mm to 20mm thick and are unremarkably fabricated from laminate, particle board or alternative materials. Just in case packing materials are absent in pipe joints for pipe jacking, then any deflection within the joints reduces the contact space of the concrete and it results in spelling of joints because of high stresses induced. With the insertion of wadding within the pipe joints, the allowable deflection while not damaging the joint throughout the pipe jacking method will be augmented.
W5). In pipe jacking/microtunneling, it’s unremarkably accepted that cowl depths of jacking pipes cannot be too shallow (i.e. but 2nd wherever D is that the diameter of jacking pipes). Why?
For pipe jacking/microtunneling, the causes of enormous settlement are loss of face stability, failure to stabilize ground around shafts, presence of criminate house around pipes and defend, drag on pipe joints, etc. The settlement mechanism of shallow depths of pipe jacking/microtunneling is that the formation of a settlement trough on prime of the jacking pipes. The breadth of the trough depends on soil properties; the larger is that the cowl depth of jacking pipes, the larger is that the breadth of settlement trough.
W6). In formed concrete jacking pipes, typically grout holes are designed within these formed pipes. Why?
a). They function the locations for injection of betonies or alternative lubricator. Lubricator is employed for each granular soils and cohesive soils to cut down the resistance resistance. For cohesive soils, the soils cannot compass the pipes by the presence of lubricator and also the cutting off plane lies inside the lubricator as urged by R. N. Craig (1983). On the opposite hand, for granular soils, the lubricator mixes with soils with a considerably reduced friction. With the utilization of lubricator, longer pipe lengths will be jacked while not the utilization of intermediate jacking station.
b). They supply the body of water locations for succeeding grouting works once completion of pipe jacking to fill utterly the void house between the pipes and close soils.
c). They’re used as lifting holes once inserting the formed jacking pipes into rails within the jacking pits.
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