A co-worker and I got into a debate yesterday about one of the foundations he designed. The foundation acts as a sleeper type pipe rack. It consists of an 8" thick by 2'-0" deep grade beam with a length of 7’-6”. At its worst case, the concrete sticks 1'-0" out of ground, which leaves only 1'-0" into the ground. Frost depth in the local area is 3'-0".
First off, I am concerned with stability issues. The foundation is only buried 1'-0", which leaves very little depth for passive pressure to develop. During its lifetime, it will have to withstand dynamic loads from wind, seismic, and thermal expansion. There is some compressor piping on the rack, so there may be some vibratory pressure loads as well. In reality, the pipe will likely keep the sleeper from overturning, but I don't like relying on pipe to brace a structure. The pipe is not a structural element, and we should not add any additional stress to it.
Second, the foundations come nowhere near frost depth, leaving them susceptible to frost heave. I'm concerned the foundation will heave and put additional stress on some of the flanges and valves. If they ever need to remove a valve, they may take it out without realizing the pipe has heaved. When they go to replace it, they will have a hard time getting it back in because the pipe ends are no longer aligned. There is also the issue of pipes moving and damaging equipment or causing leaks in a natural gas facility. I approached my co-worker with my concerns, and he said he is aware the foundations may heave. He thinks with the sleepers at a 15'-0" or 20'-0" spacing, heave will not cause any issues with the pipe. What he is failing to see is that the rack does not consist of just long, straight runs of pipe. Pipes are jumping on and off of the rack at various locations to attach to equipment. There are very rigid areas of pipe that will not have the flexibility of long, straight runs of pipe. My co-worker also made the argument that transformer foundations are typically not given frost protection, to which I responded that they are able to float because they are connected with flexible wire and not rigid pipe. He also made the argument that sidewalks are not extended down below frost level. I did not even respond to this one.
Am I out of line thinking that this foundation design is incorrect? Has anyone else every designed sleepers for pipe without giving them frost protection?
First off, I am concerned with stability issues. The foundation is only buried 1'-0", which leaves very little depth for passive pressure to develop. During its lifetime, it will have to withstand dynamic loads from wind, seismic, and thermal expansion. There is some compressor piping on the rack, so there may be some vibratory pressure loads as well. In reality, the pipe will likely keep the sleeper from overturning, but I don't like relying on pipe to brace a structure. The pipe is not a structural element, and we should not add any additional stress to it.
Second, the foundations come nowhere near frost depth, leaving them susceptible to frost heave. I'm concerned the foundation will heave and put additional stress on some of the flanges and valves. If they ever need to remove a valve, they may take it out without realizing the pipe has heaved. When they go to replace it, they will have a hard time getting it back in because the pipe ends are no longer aligned. There is also the issue of pipes moving and damaging equipment or causing leaks in a natural gas facility. I approached my co-worker with my concerns, and he said he is aware the foundations may heave. He thinks with the sleepers at a 15'-0" or 20'-0" spacing, heave will not cause any issues with the pipe. What he is failing to see is that the rack does not consist of just long, straight runs of pipe. Pipes are jumping on and off of the rack at various locations to attach to equipment. There are very rigid areas of pipe that will not have the flexibility of long, straight runs of pipe. My co-worker also made the argument that transformer foundations are typically not given frost protection, to which I responded that they are able to float because they are connected with flexible wire and not rigid pipe. He also made the argument that sidewalks are not extended down below frost level. I did not even respond to this one.
Am I out of line thinking that this foundation design is incorrect? Has anyone else every designed sleepers for pipe without giving them frost protection?
