I have a project that is Seismic Design Category D. I'm researching and I thought there were requirements that stemmed from the Northridge Earthquake in 1994 related to the limiting the height/length of the sprinkler service entry.

Is there a 5-foot limit from the underground to the riser for seismic projects?

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What is the best way to cut in to an existing underground line that may have a thrust block at the end?

We are doing a project that has scope to retrofit an 8" backflow into an existing approximately 200' of 8" underground. There is an existing detector check valve in the line which will be removed. Because of the age of the building and underground (about 30 years old) it is assumed the piping has a thrust block at the end. But with cutting into the line and adding a couple 90 degree elbows to get the backflow above ground there is fear that the line may slip back to the water main because the thrust block at the end of the 200' run is no longer holding the entire line in place.

We are planning to add a thrust block to the new 90s, but the issue is that there is only a shut off valve that is in the straight line of the 200' of pipe. If we shut that valve, there will still be pressure on the front side of the valve and when we cut into the pipe, the pipe may slip.

Any suggestions on securing the pipe on the supply side of the new backflow or limiting the pressure prior to the concrete being poured on the elbows for the backflow?

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One of the frustrating non real-world things in consulting is that on the contracting side, 99.9% of the time we start at flange inside the building. Red-line the contract if needed, or work out an informal deal with the underground contractor. 

On the consulting/engineering side we have this whole underground spec section, just for five-feet out, including tracing wire and tape, testing offsite soils, soils disposal, shoring, compaction, size of rock, etc.  I understand the civil engineers will only take it to five feet. 

I’ve asked my people why we can't just match reality and just start inside the building? I am told if we did there is this 5-ft. gap that has to be claimed by someone (despite what is done in reality).

Have you addressed this in your experience in any way? I am wondering how others deal with it. On the contracting side we all just made it happen.  On the consulting/paperwork side, it’s hard to make the paperwork match reality.  Do you even seen thrust block calcs submitted from anyone since it is part of the imaginary five-feet out?

Sorry, ranting a bit, it came to mind again today because I have constructability comments from the architect that recognized that in this particular case, the AHJ permit covers from the flange, their solution is to have my spec cover the entire fire line. I’m not comfortable with that.   

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Do underground gate valves for fire main water supplies have to be monitored and supervised?

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For straight pipe couplings, are thrust blocks required, or is it only at any change of direction in the piping? It seems as though restrained joints seem to be common now, but the question came up when using thrust blocks instead of the restrained joints.

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