Differences between pipe jacking and micro-tunnelling? Pipe jacking is a general scheme of installation of pipes with a tunnelling shield in front and the pipes are jacked from a jacking pit toa receiving pit.
Tunnelling shield for pipe jacking can be mechanical and electrical equipment for conducting the excavation work or itcould be a manual shield for workers going inside the shield to do manual excavation.
For microtunneling, it is a type of pipe jacking of small sized non-man-entry pipes that are remotely controlled. Generally there are two general kinds of micro-tunnelling machines:. Similar to Pressurised slurry TBM, excavated material is transported from excavation face to surface suspended in aslurry.
Excavated material is transported from excavation face to drive pit by a cased screw auger. The existing ground top of cut elevation ft is most nearly: 2. A design engineer c. Absolute is equivalent to gauge pressure plus atmospheric. Explain clearly with a neat sketch how you will verify the coefficient of permeability of a clay sample in the laboratory and derive the expression used to compute the permeability.
We ensure premium quality solution document along with free turntin report! Sign In Sign Up. Already have an account? Get multiple benefits of using own account! Microtunneling — MTBMs work best in soft formations and high water tables but they can be used to bore through all types of soil, sand, clay, and even through hard rock. Installation lengths can exceed meters with varying depths. Pipeline diameters varying from to mm can be installed using this method.
Since it is launched from the surface and arcs down into the ground before it comes out the other end, this method cannot be used for installing gravity pipelines.
HDD is best suited for installing pressure lines, water lines, cables, gas pipelines, pump sewer systems, and conduits. Installation of pipelines using HDD is cheaper than microtunneling. Microtunneling — This method is excellent for installing pipelines requiring precise grades such as gravity sewers.
It is also used for installing other pipelines such as gas, water, and cable lines. Even though microtunneling is a bit more expensive than HDD, the accuracy, reliability, and lower maintenance cost of pipelines post-installation, makes it a better choice in most cases.
The first stage involves drilling a pilot hole using a steerable guided drill along a planned path. The pilot hole is approximately 1 to 5 inches in diameter along the proposed centerline of pipe alignment. When the drill string reaches the exit point, the second stage is initiated. The second stage involves attaching a reamer of approximate size as the product pipe to the end of the drill string after removing the drill bit and pulling it back to the entry point.
Sometimes several passes may be required before the desired bore diameter is achieved. The bore diameter is approx. The product pipe is attached to the reamer and pulled through the borehole. All along the process, electronic monitoring of the drill path is carried out to obtain the maximum degree of accuracy.
A slurry system helps circulate the drilling fluid and helps transport the drill cuttings back to the surface. Microtunneling — A launch shaft is excavated to the depth of pipe installation and the jacking frame is set up.
The rotating cutter head of the MTBM excavates the ground as it progresses. The laser guidance system installed in the MTBM relays grade and position to the operator at all times.
The thrust wall at the back of the launch shaft helps the product pipe to be pushed into the borehole created by the MTBM. On shorter drives, the pipe jack can also be installed using manual excavation. Pipe jacking systems are more often than not supplied with jacking frames, which are designed to provide the level of jacking pressure likely to be required by the TBM being used.
The requirements for the jacking frame on any project are determined by the ground conditions, length of drive and the type of TBM being used. An essential feature of pipe for both microtunnelling and pipe jacking is that the entire joint is contained within the normal pipe wall thickness.
The microtunnelling and pipe jacking techniques offer advantages over traditional open-cut construction as well as over other underground construction methods. Pezzimenti Trenchless Company Director Joe Pezzimenti says that the laser guidance system used in microtunnelling makes this far more accurate than other trenchless construction methods, and that accuracies of between 15 mm and 25 mm have been achieved.
Rod Davies Infrastructure Director Rod Davies agrees that there are many environmental advantages to using microtunnelling and pipe jacking over other underground construction methods.
In addition, there is minimal interface with the local and wider environment. These methods also offer safety benefits. Harker Underground Construction Trenchless Consultant Michael Harker says that in some cases, these methods are the only way construction is possible due to depth, obstructions e.
He also adds that while traffic disruption is a common disadvantage of above-ground construction, another factor that is often overlooked is the financial stress applied to businesses as a result; microtunnelling and pipe jacking can reduce this disruption. This may turn out to be of considerable value as further studies are done and the environmental benefits and drawbacks are highlighted for various construction methods.
Innovations are constantly being developed and incorporated into trenchless technology, with microtunnelling and pipe jacking being no exception. With a focus on increasing efficiency, safety and reduction of preparation time, Rod Davies Infrastructure has developed the Platypus Vacuum Microtunnelling System.
Google Scholar. Clarkson, T. Pipe-jacking; State of the art in U. Vol , No. Herrenknecht, M. The development of microtunnelling machines. Isibashi, N. Jacking concrete pipes n. Pipe Jacking Association Manual. Microtunnelling in Yorkshire. World Tunnelling.
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