Property Line Footing Problem

[jasonmm]

I am working on some CMU houses that are going to be constructed with about 1" of separating between their "property line walls". The structures are totally separate except for measures taken to keep water from getting between the two walls. The builder would like to use a continuous footing with about a 2’ high stem wall then have the 4” slab-on-grade poured (slab and stem wall poured together). We would then go up with the rest of the CMU wall from there. My problem is that I have to put the 8” CMU stem wall on the edge of the footing and this results in a soil bearing failure. The load is about 4.2 kips/ft. I suggested that we pour the footing and slab monolithic and design it as a mat but this is not going to be ideal for their construction process. Does anyone have any ideas on how I can make the stem wall with the wall on the edge of the footing work?

 

[jike]

Take out the overturning moment on the footing with a moment-couple. The top force of the moment-couple would go into the slab. Provide a dowel into the slab to resist the tension. Check slab for tension and reinforce as required.

 

[hokie66]

Jike's method depends on the passive pressure of the soil on the side of the footing providing the compressive force in the couple, which may or may not work. Another method may be to make the effective width of the stem wall greater by adding counterforts, thus better distributing the footing load to the soil.

Another method would be to improve the bearing capacity of the soil at the property line by soil stabilisation or some other method.

 

[UcfSE]

Size the footing so that the bearing pressure works.

 

[jike]

The simplest approach for the bottom force of the resisting moment-couple is the shear developed at the bottom of the footing due to the weight of the wall times the coefficient of friction. Usually this is sufficient.