Foundaiton optioins for this building
Foundaiton optioins for this building
(OP)
Hello,
Doing a small one-storey building to be used as office and vehicles/equipment storage. Total floor area is about 8000sf.
The site is near a lake and the soil is soft. The soil report suggests to replace the top 10ft. under the footprint plus 10ft beyond the footprint with engineered fill and place the building on conventional strip/spread footings. see sketch. The soil engineer mentioned that this is the best option for the footings.
My concerns are: excavating 10 ft. near the lake where the groundwater is about 5 ft. below the surface would be challenging, and the cost of the excavation, dewatering, and the engineering fill.
Is this really the best option for this small building? I am thinking of 30in diameter piles spaced at about 24 ft connected with 4 ft. deep perimeter grade beam and 8in thick structural slab ( 2-way slab) on the grade level.
Doing a small one-storey building to be used as office and vehicles/equipment storage. Total floor area is about 8000sf.
The site is near a lake and the soil is soft. The soil report suggests to replace the top 10ft. under the footprint plus 10ft beyond the footprint with engineered fill and place the building on conventional strip/spread footings. see sketch. The soil engineer mentioned that this is the best option for the footings.
My concerns are: excavating 10 ft. near the lake where the groundwater is about 5 ft. below the surface would be challenging, and the cost of the excavation, dewatering, and the engineering fill.
Is this really the best option for this small building? I am thinking of 30in diameter piles spaced at about 24 ft connected with 4 ft. deep perimeter grade beam and 8in thick structural slab ( 2-way slab) on the grade level.






RE: Foundaiton optioins for this building
DaveAtkins
RE: Foundaiton optioins for this building
The top 10 ft of soil can't be founded on. A mat means we still need to excavate 10 ft. and then back fill on top of it. There is no basement.
RE: Foundaiton optioins for this building
RE: Foundaiton optioins for this building
1. No redundancy, if there is a "problem" with just one pile... the building is in trouble.
2. Mobilization of pile driving equipment is a major cost. The equipment to install 30" diameter piling will be large (expensive).
The loads must be very light (for piling), perhaps you consider treated timber piling, with a reasonable spacing (say, 5', or so). The pile would provide 100% of support for a mat foundation that is also the floor for the building.
www.SlideRuleEra.net
www.VacuumTubeEra.net
RE: Foundaiton optioins for this building
SlideRuleEra,
I am afraid you mis-read my post. My proposal will have 20 to 25 piers not 4. Any comments on the cost difference between the proposal of my soil engineer of replacing the top 10ft of soil with compacted engineered fill and the 30" pile proposal? Keep in mind that the soil is soft and the depth of these piles will not be more that 25ft. So, they can be drilled in a couple of days.
RE: Foundaiton optioins for this building
RE: Foundaiton optioins for this building
RE: Foundaiton optioins for this building
Soft soil and 25' depth are ideal for treated timber piling. Construction of a pile supported mat should be much simpler and faster than grade beam / structural slab. I still suggest making an estimate of 320 -350 treated timber piling with mat to compare with 20 - 25 drilled piers, 30" dia., with grade beams including necessary excavation / backfill, plus structural slab.
www.SlideRuleEra.net
www.VacuumTubeEra.net
RE: Foundaiton optioins for this building
That said, I still think your pile supported option should be investigated further. I suspect even with soil improvement the geotech has indicated a potential for movement. The pile supported option is much better in that regard, plus it will alleviate some of the unknowns with the soil stabilization option. Even if the pile supported option were 25% more expensive than soil stabilization I would likely still recommend that to my client. At the end of the day it is up to the owner to decide.
What size of vehicles do they want to store? In my area they are always very large, so pile supported slabs are rarely feasible.
RE: Foundaiton optioins for this building
I wonder though -> if you have the space to excavate could you just pull out the material even if it turns into a pool. Then just fill 'the pool' with large 3" stone or crushed concrete then choke out the top portion with something that has fines? Doesn't seem right, but I'd be curious to know why/why not?
EIT
www.HowToEngineer.com
RE: Foundaiton optioins for this building
RE: Foundaiton optioins for this building
I have not worked with timber piles in my 20+ years of experience so find it uncomfortable to use them for that reason.
contacted a helical pile contractor to get their input and Will meet the geotechnical to discuss and will see what happens.