A New Entrance Door in Existing Building

[jike]

An Architect wants to place a new door in an existing building that has an earth berm with a foundation just under the existing floor. I pointed out to him that this could get expensive with the cost of underpinning down to frost for the existing footing. Another aspect that makes it interesting is that we are in granular material.

We talked about using insulation but I am not totally convinced that the insulation will cover all paths of frost potentially getting below the footing.

Another thought was to install helical anchors down to below frost level but it still may be possible for frost to push up on the bottom of the footing unless it was underpinned.

Any other ideas?

 

[civilperson]

The expense will be moderate if the existing footing can span across the new excavation, assume 5' wide plus 4' on each side for 13' span. Or a center post can be installed and half the the new foundation built, then post removed and the the other half built.

 

[jike]

Underpinning in granular material where soil can run out from beneath the existing slab can be problematic.

 

[cvg]

if the soil is granular, are you sure it is susceptible to frost heave? (for practical purposes, soil with less than 5% passing the #200 sieve) If not, you could excavate and replace with gravel to reduce the potential for frost action.

 

[jike]

cvg:

It has a good quanity of silt (which is subject to heaving). It is certainly not practical to try to excavate under an existing footing in granular material and then try to replace it.

 

[civilperson]

Pressure grout of any voids created by granular material flow will remedy the existing sub-grade after the new foundation is built. Small holes, (2.5" or so), will be sufficient to insert the pressure pipe and provide a relief vent when full.

 

[PEinc]

This must be a real whopper of a door for all of the concerns and recommendations that have been expressed.

So, just how big is this door? What type of wall is it? What is the current load per LF along the wall. Without this info, I don't see how anyone can make recommendations.