Shoring for residential infill construction

[DenverKev]

Here's the problem:

Lots of homes in Denver are being scraped and replaced. One time in roughly every 300 homes, the excavation can cause an "issue" on the adjacent property.

So now, the City requires shoring before excavation. The status quo solution has been drilled & reinforced piers, adding $5k to every job. (I'm not against the shoring, safety is always #1)

There isn't enough room between houses for a stepped excavation.

I'm just wondering if anyone knows of a less expensive way to accomplish this?

They used to allow shotcrete to be sprayed on the excavation walls, but stopped that because the "issue" could happen between the excavation and the curing of the shotcrete.

Just brainstorming, if you think of the 40'wide x 60'long x 10' deep excavation as a trench, there are plenty of ways to temporarily shore a trench with reusable equipment.

 

[MiketheEngineer]

How about something like they use on tilt up buildings?? They are simply tubes (3'' - 4'') that set at about 45 degrees. But how do you pour around these??

 

[DenverKev]

Well, I'm trying to get away without pouring anything except the spread footings. Think PWF.

Which way do the tubes lean? toward the basement or away from the basement?

 

[csd72]

We did a basement shoring with buildings adjacent.

We used precast panels about10' wide and 8 to 12" thick with diagonal shores to a central footing (these will be heavy duty-standard tilt-up shores will not cut it).

We excavated a 10'wide trench to install every 3rd panel, leaving the remaining soil in place. Lean mix concrete was placed in the space behind the panels to endure stiff support of the soil. Eventually you have all your panels installed and you install a conventional slab on formwork between leaving blockouts at the shoring.

 

[PEinc]

In my opinion, that is a eventual recipe for disaster. You were lucky or else you never really needed any shoring to begin with. If you were close enough to the adjacent building, you could have damaged the building just by excavating the trenches. Shoring is not often an acceptable substitute for underpinning.

 

[csd72]

PEINc,

It worked, and the existing adjacent building was 1' away.

It was a rendered 2 story solid brick mansion that was falling apart in places.

No problems were encountered, and believe me if any building would have had problems this would have been it.

I agree it does depend on the soil though, this was in clay with a sandstone bedrock only 15' below.

Anyway, how do you underpin - in stages doing almost exactly the same procedure. If the 10' is the issue then use narrower panels in the critical areas.

 

[PEinc]

Good soils can be very forgiving. However, sometimes you don't know how good, or bad, the soils will be until you make the excavation. If you do this to enough buildings, sooner or later you will have major problems.