Infrastructure Projects - Construction Technology
A Practical Guide to Construction Techniques and Practice
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We have made many references to drilled in piles, sometimes called mini piles. I don't know if I ever showed you the machine that actually installs the piles. This is a typical setup to install the drilled in pile. The work is being done at night. For this particular project, they are going to drill through the overburden and then drill through the roof of the subway tunnel, and then through the invert of the subway tunnel, and continue down to bedrock. Because they're penetrating the subway tunnel, obviously, the tunnel needs to be taken out of service. That can typically be done during evening hours. That's why this rig is shown here working at night.
The pile will be progressed through the invert and then onward into the bedrock. After the pile is seated in bedrock, it would have to be cut flush with the invert, because you could not leave the pipe in this configuration. It would be too close to the train. You would have to complete a pile before you restored the train traffic - or you could uncouple the pipe and return the next evening and re-couple it and continue. There probably is an option to drill these mini-piles just outside the wall of the tunnel. We don't have enough information to know why it was installed inside the tunnel. By having it inside, you could simplify the procedure for re-supporting the track on top of the mini-piles. That could have been their goal here. With the mini-pile located outside the tunnel, the final operation of re-supporting the track, would have required a different kind of structure. Probably, more labor and larger pieces would have been involved. I'm sure this was taken into consideration and the decision was made to come up with a system that allowed for the efficient installation of the mini-piles through the tunnel. The mini-piles, located near the center of the tunnel, would always have to be done through the tunnel space. I believe they just focused on procedures that would allow them to do that with the good rate of production. They simply apply those procedures to all of the mini-piles. |
Here's another shot of a similar rig working on a different project. I've included this to show you that this rig is very versatile. You can use mini-piles for many applications. In this instance, they are being used to support a new bridge pier. The reason they elected mini-piles is that they are being installed underneath the existing bridge. There would not be enough headroom to drive conventional piles. Because this rig takes up less headroom and is installed in shorter lengths, you can see the operator as handling a piece, which looks like it might be about 10-feet long. This kind of a machine can work in a low headroom condition and still produce piles of any length that you need.
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