Choosing a Coastal Residential Foundation Type?
Choosing a Coastal Residential Foundation Type?
(OP)
What are the general design considerations when deciding between a shallow foundation vs. piles for a coastal residential foundation design. A colleague is saying you have to go with piles because beach sand does not compact well? do all agree with this? can someone ellaborate?
In general I though sand typically has high bearing capacity and is ideal for shallow foundations and that you would only go to pile foundations when the allowable bearing capacity could not be met with a reasonable shallow foundation footprint? I know that piles might be better if flooding/erosion is of concern.
In general I though sand typically has high bearing capacity and is ideal for shallow foundations and that you would only go to pile foundations when the allowable bearing capacity could not be met with a reasonable shallow foundation footprint? I know that piles might be better if flooding/erosion is of concern.





RE: Choosing a Coastal Residential Foundation Type?
Depending on the location on the beach, you also might want to consider elevating the structure 10 to 12 feet or so to avoid the smaller storms and tsunamis. You'll have to kiss the structure goodbye with the larger ones.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Choosing a Coastal Residential Foundation Type?
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RE: Choosing a Coastal Residential Foundation Type?
assuming the house is on the beach but the grade is elevated high enough above storm surge and flood levels is there any reason to not go with shallow foundations?
thank you!
RE: Choosing a Coastal Residential Foundation Type?
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Choosing a Coastal Residential Foundation Type?
you have to go to piles (which I assume is typically more expensive) over shallow foundations? thanks again!
RE: Choosing a Coastal Residential Foundation Type?
Piling are most useful with "poor" soil. They either transfer the load "down" to a "stronger" soil layer (point bearing piling), or
Distribute the loading (vertically, along a portion of their length) - friction piling. Then the loading distribution is low enough for the "poor" soil to support to support the load.
A second use for piling is to support very heavy loads that cover a small area - such as massive industrial equipment.
A third piling use is to resist uplift. A shallow foundation typically resists uplift with its weight alone. A properly selected pile type can mobilize the strength and weight of the soil along its length to resist uplift.
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RE: Choosing a Coastal Residential Foundation Type?
Now, this get into how much you want to compact the sand. If you are looking to base it on a Proctor, you may not even be able to get a good curve to go off of. If you go to a relative density, then you will likely be shooting for a lower percentage. Where these values are set, how the contractor works with the material, whether or not there are moisture constraints, and how good the techs are with testing it (surface tests or down in the material) will all impact the perceived difficulty of working with the material.
So, I agree and disagree.
RE: Choosing a Coastal Residential Foundation Type?
There are many structures along the coast sitting on shallow foundations. The reasons not to do this have been well covered by others in this thread.