We started excavating to pour a square spread footing and found some unexpected underground construction in the area that interferes with our spread footing. A 24" drilled pier would fit, but we would need a higher bearing pressure.
The site has bedrock overlain by gravely clay. Right now the geotechnical engineer has given us 4,000 psf for spread footings on bedrock. He says that if we used a deep foundation we could get 50,000 psf out of the soil. How deep is "deep"? We've excavated 2' down and I don't know if we could go much deeper than 4' more without hitting bedrock. 50,000 psf seems like a huge increase in bearing strength. How is the soil stronger than the bedrock at any depth?
The site has bedrock overlain by gravely clay. Right now the geotechnical engineer has given us 4,000 psf for spread footings on bedrock. He says that if we used a deep foundation we could get 50,000 psf out of the soil. How deep is "deep"? We've excavated 2' down and I don't know if we could go much deeper than 4' more without hitting bedrock. 50,000 psf seems like a huge increase in bearing strength. How is the soil stronger than the bedrock at any depth?
