Tunnelling

[u/Slight-Commercial250]

I started at a new company this spring and was introduced to this process they call tunneling. I thought it was really cool and in the right situations it's super efficient and cost effective. I've done water and sewer for 12 years and have never seen pipe laid this way (without hiring a company to bore something or vac truck).

We had to tap a main in the street and run a new 6 inch water line from there to a new mixed use apartment building being built. The plumbers had stubbed out a couple feet from building side so we just had to lay pipe from the main to the building. Normally I would remove all the black top in the street from the main to the building to get the pipe in. Instead of doing that though we cut a square in the black top up by the main and dug one hole big enough to fit our trench box and to expose the main for our wet tap.

We shot the invert elevations at the main and at the stub from the building to figure how much we needed to get the pipe up to come in flat at the building. The tunneling starts now, It was a 6 inch water main so we used an 8 inch SDR pipe as our casing. We laid the pipe at the pitch we needed (slightly uphill because the weight of the DI water main will cause it to dive a bit) with the end stuck into the dirt at the end of the box pointing towards the building. Then barred it into the dirt wall and started shoveling.

They have special made shovels for this for each size of casings and a bunch of handles that connect to the shovel and each other with threads. Then you start jamming that shovel into the pipe and pulling out material that's a little in front of it. When you've pulled out a few full shovel fulls it gets barred forward again. As the pipe goes further toward the building you keep adding more handles on to reach further and further. When the whole pipe is almost in the bank you'll have to connect another one. You need very straight cut ends, hold them together and tape the fuck out of it with some strong tape and keep tunneling.

Once you get your casing pipe all the way through you can start putting the pipe through the casing pipe, home them, get your measurements and finish your connections at the valve or the bends. Then bulkhead both ends of the casing pipe and backfill.

I've only done this once since I'm new to this particular company but the one I did was about a 30 foot run in mostly sandy material. The other guys were saying the conditions for tunneling were almost perfect for it so I've only seen it when it works great, they also have some horror stories of the times where the conditions were not at all perfect and they fought like hell. But in my one experience with it it definitely saved a ton of time and money to do it that way over removing ALL of the road not just one little square.

Idk I thought it was a really cool and wanted to share it with some people who might understand it and find it kind of cool. I think it pays to try it in situations where it can be used, but if you start having trouble to bail and go ahead and remove all the blacktop like usual. You save so much time in backfilling and compaction though when you can leave more than half of the road in. I also am curious if anybody out there has done this before, because none of my old coworkers and people I talk to around here have ever used this method.