How Deep Is Too Deep For A Shallow Footing?
How Deep Is Too Deep For A Shallow Footing?
(OP)
I have a project with columns of a drive-thru canopy designed to be set on shallow, isolated footings. However, there is a 10'-0" high utility tunnel that runs directly beneath the canopy. The top of the tunnel is 15'-0" below grade. Even though the canopy columns are fairly lightly loaded (max. 45k on 5ksf soil) I have no data on the tunnel design so I cannot assume it can take the surcharge load from the soil. Since there are no deep foundations on the project, I'd like to avoid that route. However, if I drop the shallow foundations down to minimize influence on the utility tunnel, it looks like I need about a 20'-0"+ pier on top of the footing. I'm a bit uneasy with this. It seems this is beyond the realm of a "shallow" footing. Any thoughts?





RE: How Deep Is Too Deep For A Shallow Footing?
RE: How Deep Is Too Deep For A Shallow Footing?
RE: How Deep Is Too Deep For A Shallow Footing?
herewegothen makes a valid point. It is a stand alone canopy. I'll have the contractor run some numbers. Even with mobilization of equipment, it may be more economical to go to piles. They may be willing to go this route for a small portion of the project
RE: How Deep Is Too Deep For A Shallow Footing?
RE: How Deep Is Too Deep For A Shallow Footing?
One caution on the Elastizell...it has a high enough compressive strength that is can act like a footing block, so while it reduces the total stress, it does "throw" it lower in the ground. You can balance the effect, though.
RE: How Deep Is Too Deep For A Shallow Footing?
For this alternative, I'd use a grout type pile on either side of the tunnel and strap the tops together with a concrete beam upon which you set your column.
By the way do you know exactly where that tunnel is? No point in drilling into it.
RE: How Deep Is Too Deep For A Shallow Footing?
I like the idea of adding straps to provide some additional stability
RE: How Deep Is Too Deep For A Shallow Footing?