Construction & Contractors/Vibration Damage Criteria for Underground PCCP Pipelines
I am working on a project that involves driving steel sheet piling ten feet from the centerline of a 72" diameter PCCP force main. I have been doing research on vibration damage criteria for underground concrete pipelines and in order to determine if we need to use vibration monitoring or not. The PPV I have calulated from the FTA Noise and Vibration Manual 2006 is about 4.95 in/sec as an upper limit. I have also found from Siskind, 2000 a tolerance for underground utilities at 5.00 in/sec. My questions are is the 5.0 in/sec a reasonable tolerance for vibration and if so is 4.95 close enough to the tolerance level to warrant monitoring during construction.
Where in the FTA manual are you getting the parameters? If you are using the equation in 12.2.1 and the data in Table 12.2, you would get 4.34 ips as a typical value for pile driving and over 10 ips for the upper limit (the physical distance being 7 ft to the pipeline wall). The Table 12.2 does not give reference vibration terms for sheet piling so I wouldn't expect the reference vibrations to be at the upper limit, but I can't replicate 4.95 ips either.
Criteria for vibration protection of structures, including pipelines, tend to be conservative because of the likelihood that the recommendations will be misconstrued or misapplied, and also because the frequency and damping characteristics, and therefore the induced strains in them, differ for various structures. In my opinion, Siskind's recommendations, which were developed based on years of empirical information on the performance of pipelines, are fairly realistic. Arguing for a higher limit than is recommended in the literature would require showing that somehow the pipeline in your case does not need to be treated as conservatively. In your case, not knowing anything about the age of the RCCP, the internal pressures, or the media within which is constructed, I would err on the side of conservatism.
That means that you probably don't have much flexibility from the perspective of damage occurrence criteria. Then the other matter is what vibrations are you likely to experience. If you believe 4.95 is at all likely to occur (even though you characterized it as an upper limit) then I think monitoring is necessary. If you monitor and don't see anything that is a significant percentage of the threshold, you can always reduce or stop the monitoring.
You might want to check your assessment against the criteria in Dowding's book Construction Vibrations. He has a whole section dedicated to pile driving. His Figure 15-4 shows the relationship between distance and the three components of vibration motion, for the mean and the 95% levels. It might give you some insight into how to consider the data you have.
Keep in mind the displacement of the material around the front of the piling as it advances. If the medium is fairly compressible the displacements 7 ft away will probably be negligible. If the sheet piling has a large cross section and the material is stiff and dense, it is possible that the displacements could induce compressive strains on the wall of the pipeline at that short distance. Something to think about.