Radius of foundation influence 1

[dmev]

When excavating near a building how do you determine the radius of foundation influence so as not to undermine the building?

 

[fattdad]

Boussinesq and Westergaard have equations for horizontal and vertical stress distribution with depth and distance from the point of loading (or the area of loading).

use those equations.

f-d

¡papá gordo ain’t no madre flaca!

 

[msquared48]

You know you're too close when the adjacent property owner starts taking pictures.

Mike McCann
MMC Engineering

 

[BigH]

msquared48 - even if you are not "that" close, a smart owner will take pictures! There are a number of figures in various texts and such that show the angles that should be used . . . my books are now packed for move - but will try to put my hands on one. Comes to mind - 45deg from bottom of existing footing down to yours - or vice versa if yours is higher. I wouldn't put footings any closer than 2B if at same level. Too, a lot depends on the type of foundation material you have. If on rock - then most of this is "mute". If on clays, you may need to be a bit more conservative. If on sands, the influence of the new footing will not be as great on the old as if they were built at the same time.

 

[grabens]

I agree with Big H, 45deg from bottom of existing footing down to yours. However, the soil/rock type will have a significant impact on the answer to this question.

 

[molerat2210]

Do the homework dmev. The equations can be found in NAVFAC DM 7.1. Plenty of equations to determine the stress at a point from a line load, column load or whatever. Make spreadsheets out of it and charge client lots of money.