Deep Excavation

One of my latest projects is to provide shoring for an enclosure that is about 15’x20’, but is about 60’ deep. I have a 100psf surcharge at the surface. Large section steel soldier piles and larger steel walers. The soil is highly plastic clay. The backfill against the lagging is fine sand and filter fabric to keep it from seeping through. The construction is temporary.

For shallower excavations I’ve simply used the Kp*(the surcharge) as a uniform load full height. I find it difficult to imagine that the effect of the surcharge would have an effect at the full depth. Does anyone have any comments about reducing the effects of the surcharge?

There is no geotekkie on this project, and, I’ve done these before; I’m just wondering if I’m being too conservative.


The surcharge adds to the pressure at any depth below surface. The properties of the soil would influence the magnitude of lateral pressures, particularly if they are temporary. Without some input from a geotech, I do not think you are being overly conservative.

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@BAretired Thanks… that’s the approach I used… didn’t know, but better safe than the other…

Again, thanks.


If your surcharge has a limited area of applicability (e.g. only within 10’ of the excavation, or from a roadway), you could consider ending the effect at some depth. Otherwise I’d agree with BA.

Thanks… I ignored reducing it with depth… and ran with the effects full height… thanks for the confirmation.