Excavating near an existing pad foundation

[nivoo_boss]

Hey everyone!

So I designed a new foundation next to an existing one. The new one is to be settled about 1,6 m below the existing 1,4x1,4 m pad. It is close to the existing one. The load from the existing foundation is around 70 kN.

Do you have any rules of thumb when slope stability becomes an issue here? The existing one has settled for about 12 years. The soil is dry. A picture is below. The red arrow points to the existing one, the green one to the new one.

 

[EireChch]

Its not a slope stability issue. You will undermine the old foundation if you don't approach this correctly. You need to underpin and extend the old foundation down to the same level is your new foundation. You need to do a hit and miss approach so as to not destabilize the existing foundation.

If you dont want to underpin, you could consider sheet piling adjacent to the old foundation, however it would need to be press in vibration less sheet piling, and you probably need maybe 600mm of space between edge to edge of foundations. Even that might be too tight.