Foundation subgrade problem
Foundation subgrade problem
(OP)
There is project were the design foundation depth was 2 m (6.5 ft). During excavation we found 7 m (23 ft) of non-controlled fill and we suppose it has at least 15 m (50 ft). One of the options was to pour concrete with crushed rock in the first 3 ft followed by an engineered fill till we get to the original foundation depth. I suggested increasing the footing dimensions (initially 26x19 ft) to distribute the load and minimize settlements. I believe the first option can cause settlements due to the excessive depth of fill. What do you guys suggest? We can't use piles because of time delays.





RE: Foundation subgrade problem
Essentially, we don't have enough information.
Some options:
So what if it's existing fill, if it has suitable strength (and low organic content) it can support something. Just figure out the strength of the fill and design a foundation to satisfy strength and settlement.
Design an engineered subbase to support the "seat of settlement." You see, if you have a 3-ft wide strip footing, the majority of the settlement response will occur within some distance below the bottom of the footing. Now if you know how much settlement is forecast for the existing fill (i.e., some measure of soil modulus) and you have an aggregate that's much stiffer, you can calculate how thick the engineered subbase must be to limit settlement to some design criteria. It's not likely that you'll need to go all the way to 4B, however.
Grouting can work (but it's expensive).
Surcharging/preloading with a settlement monitoring program can work (it can also give you some idea of soil modulus).
Others. . .
Good luck. Maybe you can provide some more details?
f-d
¡papá gordo ain’t no madre flaca!
RE: Foundation subgrade problem
www.PeirceEngineering.com
RE: Foundation subgrade problem
Your original footing sizes of 26' x 19' would suggest that the structure is either heavy or there are large overturning moments. A piled solution, from the information given, would appear to be in order.
How did you get to this point before the founding condition is known? Was there no geotechnical engineering involvement?
RE: Foundation subgrade problem
I hope the structural engineer learns from his mistake and value the inputs from geotechnical reports.
RE: Foundation subgrade problem
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Foundation subgrade problem
Look at ground remediation techniques (dynamic deep compaction, terra-probe, etc.).
RE: Foundation subgrade problem
Rey Villa, MS, PE
http://geotech-apps.com
http://engineerofrecord.com
RE: Foundation subgrade problem
Having said that, I'd agree with comments recommending you look into ground modification measures (such as deep dynamic compaction) and possibly intermediate foundation types such as aggregate piers. Frequently the firms that do this work take care of both the engineering and the construction/implementation (which speeds up the process). Often it doesn't require any structural re-design (i.e. you keep the same footings and bearing pressure and simply improve the soil so that it meets that criteria).