Infrastructure Projects - Construction Technology
A Practical Guide to Construction Techniques and Practice
Welcome to class 10. It is a continuation of constructing highways in downtown areas. We are still at the same project, but we're going to explore different areas of the project and different means and methods of maintaining traffic. By the way, the subject of maintenance and protection of traffic is often abbreviated as MPT. The next time you hear about people discussing MPT, it is maintenance and protection of traffic. MPT and utility work are the two most critical features of any downtown project.
The placing of the final roadway is really the least of your concerns. It's the MPT and utility relocations that require the most time and effort and become the most problematic features of any downtown construction. We're now at the North End of the project. The work zone here was a little more generous, a little more breathing space. That certainly has simplified the work. The first activity here, as usual, is the relocation of utilities. These new utilities are being installed to replace existing ones which would conflict with the new construction.
In this case, these are Con Edison ducts, which have been laid, and they will be encased in concrete. On the left hand side, you can see the barrier, the fence and the privacy screen to isolate the work zones. Beyond the barrier and privacy screen, you can just make out the sidewalk bridge and some office trailers situated on top of the sidewalk bridge. There's a high-rise office tower being built immediately alongside of the highway construction.
Even though there is some more working room here, which is very helpful, you find that you are still constrained by the adjoining projects and this is not unusual. You are impacting the adjoining project and the adjoining project is impacting you. There is this constant need for planning and coordination with adjoining projects and all of the adjoining property owners. When the Con Edison ducts were complete in the area on the left of the photo that allowed you to proceed with this duct bank, which is telephone duct bank.
There is more generous space here, but not enough to carry out these activities simultaneously. Therefore, they have to be done sequentially and of course, that adds to your schedule. You can see every phase of the work. You can see the PVC duct, which are then encased in concrete. Then, the backfill is placed in layers and compacted. The compaction of any backfill material is critical on any project and every project. It is especially critical here, because it is followed immediately by placing pavement.
There are many situations where the utilities are done. The work is backfilled and it may stay in that condition for quite some time. It may even be covered with temporary pavement that is subject to the traffic live load for a period of time. Then, finally, as the last element of work, the area is paved over. That, in a way, is an ideal scenario, because it allows plenty of time for any settlement to take place. On this project, there was no time. There was zero time. That really places a lot of focus and attention on the need to backfill with 100% certainty.
This photo shows the installation of a gas main. You can see all of this Geotech fabric. It is somewhat unusual to see it. Generally, that's used to separate materials so that there cannot be any infiltration from one to the other. That might be the concern here. The pipe is surrounded by sand and the sand is surrounded by the geotextile fabric. This would certainly keep the sand in place and prevent it from migrating. You have to wonder, there is so much effort going into this, there's probably some other purpose in mind.
It would certainly identify the gas main. When someone else was excavating in the area, they would find this envelope wrapped around the sand encased gas main. It might provide kind of a warning to assist other people in locating the gas main. Obviously, the gas mains are very sensitive and they cannot be disturbed. This may serve this kind of warning purpose, as well.
The gas main represents the third utility to be installed in this area. Everything is done sequentially. Of course, this impacts the time. Whenever you are performing utility work, it is very important to have the representative from the utility company present. You really need to stay in careful communication with the utility company. They should be witnessing the work as it goes in, they should be available to address conflicts, interferences, troubleshoot problems as they occur in the field. With respect to something like a gas main, they need to witness the pressure test.