Using Equipment next to an existing retaining wall

[fp23]

I'm working on a TI project on an existing precast concrete building. Our work is on the main floor (mostly just a new door opening in a non-structural wall) but below this is a 28' tall retaining wall (2 stories of basement with no floor bracing it except at top and bottom). They are demo'ing an existing slab on grade outside the building and I got a question from the contractor about using a bobcat with a Jackhammer to break up the slab next to the retaining wall. The existing drawings have a retaining wall loading profile which doesn't show any surcharge load (not even snow or live). The ground snow is around 100psf here. I'm thinking of telling the contractor they can use equipment as long as it doesn't exceed 75 psf (roof snow load for the existing building) since this wall has been supporting a surcharge of snow and live load for 20 years. Without getting into an in-depth analysis, it seems like my other option is to tell the contractor that they need to keep all equipment 28' away from the retaining wall, but this feels a little too conservative to me. Just curious to get some other opinions on this. I don't have any soils info but are there any other resources/guidelines for distance away from a retaining wall where a surcharge load will be negligible (other than the 45 degree rule?)

 

[JAE]

When you say "retaining wall" I'm presuming this is simply a 28 ft. tall basement wall correct?

If so I'm wondering what is the comparative magnitude difference between the 28 ft. of lateral earth at-rest pressure and a small bobcat working on the surface above.

You could assume an earth load between 35 psf/ft (highly drained granular) to 65 psf/ft (clay) and get a feel for the magnitude of the original design bending moment on the wall. Then, compare that to the effect of a concentrated load on the surface creating bending in the wall. There are methods published that show this effect of a concentrated load on lateral earth pressures in most any foundation textbook. The attached image comes from my Peck-Hanson foundations book.

 

[MTSOE]

When you say the slab has been supporting a live load for 20 years, do you mean a vehicular live load? What is the purpose of this slab? I would definitely be at ease about putting a skid steer on this slab if I knew the area was used for ploughs to stockpile snow or garbage trucks to pick up bins. I personally like this logic statement style of engineering but others may feel otherwise.

 

[fp23]

Thanks JAE and MTSOE. Yes it's essentially a 28'x30' 12" prestress concrete plate that is pinned on 4 sides with soil loading for the full height. There isn't a drivelane or any kind of vehicle access next to the wall (at the top) but i think it's likely that small snowplows have been driven all around it and that it's seen several feet of snow and other temporary structures.

JAE, thank you for the reference, that's exactly what I needed. I like your approach to comparing this to the existing loads (maybe it's under 5% increase) I need to buy a soils book (don't worry i've read one , started my own firm and haven't bought one yet)