Type of Foundation
Type of Foundation
(OP)
Hello everyone, A two storied house having ground floor area 2900 square feet is being built on a weak soil strata. From the soil testing data, it was observed that up to a depth of 2m, the soil is fine sand with standard penetration test, N value=4. 2m-2.7m fine sand with N = 2. 2.7m-4.5m: Sandy clay; N=10. 4.5m-6m: Clayey sand; N = 15. 6m-7.5m stiff lateritic clay with pebbles; N = 20. 7.5m-9m stiff lateritic clay with pebbles; N = 11. 9m-10m stiff lateritic clay with pebbles; N = 12.
Water table is just below the soil surface at a depth 20cm.
What type of foundation shall be adopted?
The soil testing data has been attached
Water table is just below the soil surface at a depth 20cm.
What type of foundation shall be adopted?
The soil testing data has been attached





RE: Type of Foundation
RE: Type of Foundation
lateritic clay at 6m."
There you are, what else do you need?
RE: Type of Foundation
Could the house actually be a "ground plus two" structure with parking underneath or protection from flood surges? In that case, they would be involved.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Type of Foundation
RE: Type of Foundation
RE: Type of Foundation
RE: Type of Foundation
RE: Type of Foundation
My suggestion is to do the following - place about 2.5 m to 3 m of fill across the building footprint and say 3 m beyond. Put in a crude settlement plate for monitoring the settlement. As the material is fine sand, it should be almost instantaneous. Let the fill sit for a minimum of a week. Remove the fill. Raise grade, if needed, with river sand - again, place it up to 3 m beyond the building footprint. Construct your building. The preload will have taken out the settlement that would be induced by the structure on the upper loose zones. You can then follow strip footings with a slab on top as per Oldestguy suggestion.
For sites such as these, the use of preloading is a very useful tool in your foundation arsenal.
RE: Type of Foundation
However, to save money on pre-loading, consider this. Instead of covering the whole site with one fill layer, do this.
Place a "windrow" of fill, perhaps 4 meters high one meter wide on top, at one end of the site.
With a settlement platform there see how long for settlement to stabilize. With that guide move the windrow gradually across the site, called a rolling surcharge.
My experience with this method is that it works quite well on all sorts of compressible stuff, including loosely dumped fill as thick as 8 meters.
Always keep the top width as it is moved. One dozer working usually is all that is needed, but I have had back-hoes move it with piles as high as 7 meters.
Usually 3 meters high rolling surcharge is used with success.
When reading those settlement platforms, place your instrument on the pile and read the bench mark as a long survey rod left permanently attached to a nearby power pole.