Daylight basemetn Foundation wall sliding
Daylight basemetn Foundation wall sliding
(OP)
Wondering what other people do for foundation wall sliding when you have a daylight basement (supported at top and bottom of wall and able to transfer top reaction to the shearwalls). In our company, we look at the base reaction from the wall caused by at rest pressures, and subtract out any resistance from friction of the wall/fdn/soil weight, friction from the wall dead lodings (ie floors and roofs), possibley the floor slab friction, and passive resistance. If we can not get a FS of 1.0 for a fdn wall (dont believe the retaining wall FS of 1.5 from chapter 1610.2 applies)we increase foundation size to achieve 1.0.
To me that seems logicial, and if anything Im not really sure I believe we are liberial by not keeping with the 1.5FS, but lately we have been competing aginst a full service firm that has a 2'-0" wide footing under the foundation wall for a commercial building with a daylight basement with 12'-0" of backfill on one side, when I would have needed an 8'-0" wide footing. The building is way to long to say that the wall is capable of spanning side to side.
Because of the daylight basement issue, I dont think you can simply blow off sliding or say that you have a slab present which resists the sliding, but maybe I am missing something.
Does anyone have any ideas as to why my foundation is so large in comparison, or is the competing engineer probably just undersizing their footings. Also, what do you do when you compition is obviously missing something in their design. Thanks
To me that seems logicial, and if anything Im not really sure I believe we are liberial by not keeping with the 1.5FS, but lately we have been competing aginst a full service firm that has a 2'-0" wide footing under the foundation wall for a commercial building with a daylight basement with 12'-0" of backfill on one side, when I would have needed an 8'-0" wide footing. The building is way to long to say that the wall is capable of spanning side to side.
Because of the daylight basement issue, I dont think you can simply blow off sliding or say that you have a slab present which resists the sliding, but maybe I am missing something.
Does anyone have any ideas as to why my foundation is so large in comparison, or is the competing engineer probably just undersizing their footings. Also, what do you do when you compition is obviously missing something in their design. Thanks





RE: Daylight basemetn Foundation wall sliding
If there is a 12 foot horizontal force there is also a component vertical on the footing that is resisting movement equal to the frictional force on the wall times the horizontal force.
Are you using a friction resistance at the foundation level that is consistent with that used to calculate the horizontal force or are you just using some concervative structural friction factor.
You should discuss your approach with an experienced geotechnical engineer. In my experience, structural engineers underutilize the capacity of the soil. Your competition, sorry to say, probably has already developed an approach based on geotechnical principals.
RE: Daylight basemetn Foundation wall sliding
Takde a look at the total dead load of the structure, apply the slidingcoefficient, and compare it to the base force. The result might give you the FS you need.
Mike McCann
McCann Engineering
RE: Daylight basemetn Foundation wall sliding
personally, I see this scenario failing at the foundation in one of at least three modes...
1. Shear through the stemwall (assuming it is short), or
2. Shearing of the soil at the base of the stemwall from the back to the front of the structure, or
3. A vertically diagonal slippage of the underlying soil, actually lifting the slab, possibly buckling it. This would imply that the failure was inside of the endwalls - kind of like crushing a pop can from the side. It implies that the structure would have to be lifted, at least in part, in order to fail.
#1 is easily calculable as is #2. #3 is a much harder to model.
Mike McCann
McCann Engineering
RE: Daylight basemetn Foundation wall sliding
RE: Daylight basemetn Foundation wall sliding
Never, but never question engineer's judgement