Soft zones in otherwise firm and stiff clays

[irvy]

I have recently worked on recommending foundations for sites in Mercia Mudstone, which generally is a competent stratum for shallow strip footings, and would like to know the following:

If soft zones are encountered at depths of 1.00 - 2.00 m, is it more appropriate to excavate deeper trench footings in the hope of finding a more competent stratum, or to consider piled foundations, thinking of the fact that trench footings become uneconomical below 2.50 m??

 

[Ginger]

This rather depends on the physical size of the softer zone in relation to the dimensions of the structure you wish to place on it. It is really a matter of engineering judgement as to how you get around the problem. You don't seem to be aware of how thick these soft zones are. i think you need to accumulate more SI data and this will probably determine the appropriate solution.

I realise that this is a wooly answer but without the data you can't make an informed decision. Andy Machon

 

[Focht3]

Andy's right. More data needed.

Are you concerned about settlement? Extrusion of the soft zones? Or just anxious because the zones are soft? Have you checked your settlement analyses to see if you really have a problem?