Mass Transit - Cut and Cover Tunnels
Class 5 - Session 4

Here are some of the activities taking place below the decking. These are early activities, demolition of existing structures and excavation. There seems to be a substantial structure which is being demolished here. It might have been an entrance to the subway station. On the left side, you can see the steel beams, which were installed in the secondary holes. They've been exposed so that the bracing can be attached directly to them. At the top of the screen, you can see the deck beams which are running across the excavation and supporting the deck panels. You can also see the top level of bracing.

These are the utilities which are being supported from the deck beam will from the bracing. On the right hand side, you can see the existing the subway structure. This is a good view of the support beam, which has been inserted through the invert of the existing subway and it is supported here on a drilled in pile.

Of course, this is a good reminder that this is a live facility. The trains are running here on two levels, and they run 24/7. There's a tool being used to demolish the existing structure. You can see it's a very low headroom tool. It's especially designed for mining, working in these confined areas. Where is the cab for the operator? There's no cab for the operator. This fellow here is the operator and he is using a joystick to operate between. Water is being applied to control dust.

Now, all of the broken concrete and the excavated material has to be removed from the hole. There's a loader here, a low headroom loader. There is a different kind of machine operating from the street. It's an excavator which has a bucket which can be lowered vertically and used to excavate or to remove material. You can see this is very slow tedious operation. There's not much of a payload in his bucket.

Now, both the excavator and the truck are standing on decking which is extremely effective. It accommodates local traffic, as well as in construction traffic. Here is another device for removing debris from the hole. This is a little more effective, a little more productive. This crane is also standing on the decked over area.

During the day, on off-peak hours, you can close some lanes of traffic and create a workspace. That's what's being done here. Of course, as you approach the rush hour traffic, you close up the openings by replacing the concrete panels, and then you restore the street to its full width to accommodate the traffic.

A special feature on this bucket is that you can lift it up horizontally, bring it over the truck, and then you can tip it to empty the contents into the truck. Again, very slow time-consuming process. This contract to construct this passageway under the existing subway is certainly a complicated and challenging project. It will take four years to complete. I remind you of the opening series of slides, which showed the entire subway system being built 100 years ago in four years. It's hard to reconcile these numbers.