Power distribution in a liquefaction zone

[EEJaime]

Good afternoon,
This may seem an odd question but it is something I have been asked to deal with. I am located in southern California. We are involved in the design of a hospital replacement building. This occurs in a seismic Zone 4 location, (for those unfamilair with that designation it is for a highly active earthquake zone). On top of that soils studies and borings have identified that this is also in a liquefaction zone. It is an existing campus with code compliant as well as old non-compliant buildings. OSHPD is the state governing agency that oversees all healthcare construction, (Office of Statewide Health Planning and Development). They have deemed that to construct our building, the soil condition must be mitigated, (drilled out, mixed and re-compacted), to a depth of 75 feet under any building or support facility, (chillers, transformers, feeders, etc....). The problem is at the transitions. Wherever we go from our building to an existing building, (like the Central Utility Plant), we have to allow for up to 20" of "differential settlement". That means that one side of a 5kV feeder exiting the CUP through a manhole will drop 20" more than the other side. Does anyone know of a vault system that will allow this kind of damage without failure?

I know that if a Central Utility Plant drops straight down 20" in an earthquake, the (3)-1.5MW generators are not going to be starting and purring along as if nothing had happened, but that is what the state wants us to plan for. Ludicrous as it is-I need to present a design that will accomplish this.

I am just looking for a component of this that has some kind of flexible connection/slotted connection, something that will allow that degree of movement.

Now I know why people make fun of California, wow!
Thank you and regards,
EEJaime

 

[7anoter4]

This is a very unpleasant issue indeed. I know a similar case in an area with very deep holes-sometime 300 ft. deep.
The 2*150 MW Combine Cycle Gas Turbine connected with the auxiliary equipment was mounted on 7 ft. high huge concrete plate
and all this was standing , I think ,on 100 pcs.of 100 ft. depth columns.
A good civil engineer could find a solution even in your case, I'm sure.

 

[dpc]

We encountered differential settlement problems at wastewater treatment plants in the past. We used a variety of approaches to allow for GRADUAL diff settlement. But we did sometimes pile-support the ductbanks as well as manholes. In some cases, the vaults were tied into the building structure to eliminate the differential. In all cases, we found ways to provide sufficient slack cable to allow for the max expected movement - at least we tried to.

Armored cable (CLX) can be run without any raceway, so could be another option to consider.

A SUDDEN 20" drop is another matter, although similar concepts could be considered.