Cut and Cover - Mixed Face Tunnels
Class 6 - Session 3 continued

I've mentioned waterproofing from time to time, because it is critically important in an underground structure, but it's a very large and complex subject. It goes way beyond this class. Nevertheless, the need to do it correctly is worth reinforcing during this class. The process being used here on this project, and on the earlier project, showed concrete being placed up against a waterproofing membrane.

That membrane has to be perfect, because any penetration of that membrane will create a path for the water in your permanent structure. Earlier in my career, it was done a little differently. The waterproofing was applied to the mud slab and the sand walls, but then it was protected by a 4-inch protection course of concrete. In earlier construction, that protection course might have been brick. It was understood that you needed to do a perfect job on the waterproofing membrane and then it was prudent to cover that membrane, so that it could not be damaged or abused in any way during the subsequent construction.

That very careful belt-and-suspenders approach, which in the case of waterproofing pays off. I wanted to point out to you again, this is a complex subject, something for everybody to focus on during the design and especially in the execution and inspection during the construction.

Historic waterproofing. Hard to improve on this.. No, that is not me on the right hand side of the photo. I do like the outfit he's wearing. Looks like he's in a suit and a tie and that's not a hard hat. Looks like pretty handsome fedora. He looks pretty good on this photo and he is not doing the waterproofing. He looks like the guy who comes down and checks it out. The waterproofing is many, many layers of rolled out material overlapping. That will then be covered with a protection course of either brick or concrete - or some combination of the two.

In the background, it looks like they are covering it with a concrete slab, but going up the walls, traditionally, they would cover it with brick. This photo is about 100 years old. My guess is this tunnel still has no leaks.

Here some membrane waterproofing has been applied to the floor, and it is being protected by layers of brick. The brick here is set in mastic, which is kind of an asphalt material. You have a mud slab, some kind of membrane, and then multiple layers of brick and mastic, which protects the membrane and, at the same time, provides a waterproofing in itself. A similar treatment will be carried up the side walls.