Pump House Foundation on Rock 2

[CrazyHorse81]

We are designing a new booster transfer station and a new precast concrete pump house. How do you build a concrete foundation on top of rock? Do you drill and set rebar into the rock, then make your concrete forms and pour the concrete? Or can you simply make the forms. The weight of the pump house and pump station is approximately 45,000 lbs. over a 11'x14' footprint.

 

[cvg]

if the rock isn't "flat" then you might want to anchor it or chip away the rock until it is flat, otherwise no need for anchors. you should clean the foundation rock prior to placing concrete. This might include chipping, scaling, crack cleaning and sealing, sand or water blasting, sweeping, etc. - all depending on the type and quality of the rock.

 

[msquared48]

I've used #4 dowels epoxied 12" into bedrock for higher end house foundations on downslopes or near cliffs regularly in the San Juan Island area of Washington State. It is considered good practice there - 4 ft. spacing is common.

However, if your site is relatively flat, I guess you would have to ask yourself where the structure could migrate to in a seismic event. That being said, being a pumphouse, how much "walking" could your piping system tolerate without rupturing and system failure?

Mike McCann
MMC Engineering

 

[CrazyHorse81]

cvg: I can envision the work you describe to make the site flat. You are suggesting that the site can remain "as-is" but anchors are needed, otherwise flatten the rock and anchors are not needed.

msquared48: I think that the tolerance could have a large range dependent upon how I design the suction/discharge pipe connections to the pump house. It could be designed rigid or flexible, I would suppose; I vote flexible - to maximize pipe "walking" and minimize failure.