Groundwater under building foundation
Groundwater under building foundation
(OP)
The building in question is a manufacturing facility approx. 400'L x 200'W. The building was constructed on select fill over expansive clay; the select fill ranges from 7' to 14' thick. Even with the select fill thickness, the building has suffered substantial foundation damage due to swelling of the expansive clays. Poor landscaping irrigation and sewer line breaks below the slab were originally to blame for the excess water reaching the clays. However, these water sources have been removed (sewer line repairs completed in late 2007 and irrigation improvements completed in 2005). Unfortunately, the groundwater levels are not subsiding and the foundation is continuing to move. We are considering installing horizontal drain pipes below the foundation in hopes of removing/lowering the remaining groundwater above the clay layer. My question is this - what type technology exists to bore a drainage pipe 450'-500' under the building foundation? Whtt type pipe, sleeve, size, etc?





RE: Groundwater under building foundation
RE: Groundwater under building foundation
RE: Groundwater under building foundation
RE: Groundwater under building foundation
RE: Groundwater under building foundation
The technology to install horizontal drains at the clay surface via directional drilling
is readily available.
Consider that drainage may trigger additional settlement of the fill...
BTW, I find the swelling clay theory rather unlikely,
though not impossible:
How much heave has occurred?
What is the strength of the clay soil?
What is the LL / PL of the clay soil?
For heave to occur, swell must be greater than consolidation (which may happen simultaneously),
and swell pressures must exceed the fill and structure weight.
For damage, there would generally have to occur
at least 1 inch of differential settlement,
depending on the structure type.
RE: Groundwater under building foundation
Regarding the expansivness of the site clays, can you provide natural moisture content and Atterberg limits?
f-d
¡papá gordo ain't no madre flaca!
RE: Groundwater under building foundation
RE: Groundwater under building foundation
The building is most definitely heaving; we have seen movements of 4-6 inches in some parts of the building. Other areas have experienced some settlement but nowhere near the magnitude of the heaving seen in other areas.
The expansive clay has average values as follows:
LL=63, PL=18, PI=45
No flyash, bottom ash, etc. was included in the select fill.
Drainage was not installed in the first place because there was no need for it at the time. I have seldom seen buildings in this area constructed with subsurface drainage.
We have been working with our preferred geotechnical consultant for several years now, and I have a lot of faith in his position that this movement is due to heaving/swelling in the expansive clays. We have completed 4 floor surveys, installed piezometers, completed borings, etc.
I am simply trying to get some input on how to remove the water from below the building.
RE: Groundwater under building foundation
RE: Groundwater under building foundation
RE: Groundwater under building foundation
RE: Groundwater under building foundation
RE: Groundwater under building foundation
nwitt, yes, a dessicated PI 45 clay, expansion index about 130+,
even with a 1000psf surcharge might still swell 5 percent.
Have you considered a perimeter well-point system?
You would essentially surround the building footprint with a PVC manifold pipe
connected to numerous small diameter vertical screened pipes.
You would then pump the system until dewatering is complete. And likely watch the building settle...
This approach is typically for temporary dewatering,
but makes sense if the site drainage problems have been fixed.
ht
RE: Groundwater under building foundation
RE: Groundwater under building foundation
RE: Groundwater under building foundation
In your case, this would have to be done from trenches outside the building, probably way too expensive to consider.
Grouting contractors have installed grout pipes radially from large diameter man-holes. Could you do the same procedure by jacking well points radially from man-holes, then use sump pumps in the manholes?
I suspect drainage will not cure the problem however, due to the affinity that the clay has for water.
Has anyone looked at lime injection to reduce the clay affinity for water?