Footings
Piles are best for low bearing capacity (a boat) transmit load to deeper more firm soil. Structure with heavy loads on dense earth: Structural steel pile
-Jetted pile= rarely used
-Wood pile= light for moderate loads
-Boat footing, mat foundation= low bearing capacity
Pile with “driven to refusal”:
Pile driven to a point where additional blows will result in no significant penetration. Pile does not need for bedrock
Wood piles: Where untreated wood piles permitted:
If they are below the longest ground water level.
If untreated wood is constantly wet.
They are in no danger of deterioration.
Wet and dry causes mold and decay.
They are not subject the allowable unit stresses.
Piles: When upper soils have insufficient bearing capacity, then piles transfer loads to firmer soil.
Load on footings= Reduction of soil’s void volume, “not” shrinkage, differential settlement, reduce bearing capacity
Ratio of load to bearing capacities are high: best to use mat foundation
area is very high p/a= low match bad bearing capacity (bath tub)
6 story building with 25 ft of loose fill: Great beams and piles extending the loose fill.
Spread footings: Good soil at shallow depth. On re-compacted soil is not economical. Loose leaf with 5 ft depth will not satisfy
Mat foundation: Large whole building mat is only for fair to poor soil. Loose fill is not known to be used with mat foundation.
Foundations: Conventional: Concrete and cost less
Piles: Costly, wider range of materials. Timber, steel, concrete, very slow construction process
Frost:
Frost line level: Foundation design in northern climate is 5ft down dye to frost line level.
“Not” earthquake, against snow drift, rest on undisturbed soil
Frost action: Freezing then thawing—> heave of ground stress to building –> serious damage
Soil frost depth varies frost line= Soil does not freeze below frost line
Frozen footings: Place concrete footings below freeze line. Three to five feet below grade. Below frost penetration
If soil in parking lot rise in winter: Frost and heaving of sub soil – Ice expands
Footing excavation is frozen:
Excavate frozen ground
Never place concrete on frozen ground, when thaw, it shrink and cracks
Hating and thawing: Not practical, not reliable
Frost line in North Dakota: 6 ft
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