Chapter 2: Foundations and Sitework Flashcards
What are the different loads on a foundation?
Live load: people, furniture (changes over time)
Dead load: the building itself (permanent/fixed)
Wind load: wind pressure
Foundations must be economically and technically _____; it must not have adverse effects on the _____ structures.
Feasible; surrounding
How do you classify earth materials?
- Particle size
- Moisture content
- Presence of organic content
May cause damages to finishes, cladding and other components where the building becomes distorted.
Differential settlement
A dense, continuous mass of mineral materials that can be removed only by drilling, fracturing, or blasting. Strongest, most stable, and strength varies with mineral content and physical content.
Consolidated rock or bedrock
Any earth material that is particulate
Soil
Greater than 12 inches in diameter, must be picked up with two hands
Boulders
Smaller than boulders, but greater than 3 inches in diameter, and can be picked up with one hand.
Cobbles
Coarse-grained soils
Gravels and sands
Spherical, less than 0.0029 inches, and is too small to be seen by the naked eye.
Silt
Too small to be seen by the naked eye, smaller than silt, less than 0.0029 inches in diameter.
Clay
Fine-trained soils
Silts and clay
3 inches - 0.187 inches in diameter
Gravel
0.187 inches - 0.003 inches, too small to be lifted individually
Sand
Not suitable for the support of building foundations
Organic soils (peat, topsoil)
Coarse-trained soils consist of relatively large mineral particles with _____ or _____ attractive or repulsive forces acting between them. They are not very affected by moisture content.
Little; no
How are both coarse and fine-grained soils used for building construction?
Coarse-grained soils are stronger, while fine-grained soils fill in the gaps.
Soils, when relying primarily on internal friction for strength.
Frictional/cohesionless
Smaller-grained soils may be subject to a wide array of _____ forces.
Interparticle
Spaces between the particles
Soil pores
When water-saturated sands or silts lose virtually all of their strength and behave as a liquid when subjected to sudden, large changes in load, such as an earthquake.
Soil liquefaction
Draining water away from foundations and substructures or from under slabs on grades and pavements.
Free draining
Buildings will withstand better with highly-_____ soil.
Cohesive
Material which is moldable when moist
Plastic
Ability to sustain a higher moisture content before arriving at a flowable consistency
Liquid limit
Range of particle sizes
Gradation
Broad range of particle sizes
Well-graded
Limited range of particle sizes, more void space and free draining
Poorly graded or “well sorted”
Limited, narrow range of particle sizes
Uniformly graded
Particle size distribution
Sorting
Clay properties vary with moisture content and _____ composition. Some are highly expansive when wetted, some are virtually impervious to water, and some are subject to consolidation or gradual compression _____ _____.
Mineral; over time
Generally, a larger particle size creates a _____ soil.
Stronger
For raising the grade
General purpos fill
Geotechnical reports describe _____ and their properties.
Soils
Complex method to construct a steel-reinforced concrete wall many stories below the surface
Slurry wall
Viscous mixture of water and bentonite clay
Slurry
Beams that span across the face of the sheeting
Walers
When crosslot bracing cannot be used because the excavation is too wide; bearing against temporary footings
Rakers
Removal of water from the excavation or surrounding soil; removal from sumps.
Dewatering
Pit where water accumulates; low points in excavation or surrounding soil
Sumps
Depresses the water table
Well points
Soils directly below the building substructure are _____ and _____.
Weak; unstable
Used for small building design of foundations where soil analysis is unnecessary.
Allowable foundation pressures/allowable soil pressures
When clay with high moisture content is put under continuous pressure, the water is pressed out of it causing a gradual reduction in soil volume.
Consolidation
The water content at which the soil transitions from solid to plastic.
Plastic limit
A _____ _____ may include recommendations for allowing bearing walls for various soil strata, appropriate foundation types, estimated rates of foundation settlement, soil drainage, foundation waterproofing, and other relevant information.
Geotechnical report
Trees and plants, stumps, large roots, and other surface materials are removed with heavy machinery.
Grubbing and cleaning
_____ is necessary for basement construction, to reach undistributed, adequately firm soil for shallow footings, for trenches for buried utilities, and to remove native soils that are contaminated or too weak or unstable to build over.
Excavation
Sloped back; less expensive than sheeted excavation, requires a site without property lines, adjacent structures, or other limits on excavation.
Benched
Angle low enough that the soil will not slide back into the hole; can be steep for cohesive soils such as stiff clays or shallower for frictional soils such as sand and gravel.
Maximum allowable slope/angle of repose
Supports the sides of an excavation and prevent collapse
Shoring
Steel columns driven vertically into the earth at close intervals around an excavation site. Braced by rakers, followed by waterproofing and cast in place concrete wall foundation.
H-piles/soldier beams
Vertical sheets of various materials are aligned tightly against one another and driven (not drilled) into the earth to form a solid wall (most common: steel; but wood, aluminum, PVC plastic, composite polymers, or precast concrete can be used)
Sheet piling/sheeting
Driven into earth
Piles
Building g superstructure temporarily supported on cribbing while new foundation is built.
Underpinning
Allows ground water to flow downward where it is collected by drain piping.
Drainage mat
Draws water away from the substructure
Drain piping
A moisture-resistant cement plaster or asphalt compound applied to basement walls where groundwater conditions are mild or waterproofing requirements are not critical.
Dampproofing
Resists the passage of water even under more demanding conditions of hydrostatic pressure. It is more costly, and is used where groundwater conditions are severe or the need to protect subgrade space from moisture is critical.
Waterproofing
Used instead of bracing; holes are drilled at intervals through the shoring and steel cables or rods are inserted, grouted in place, stretched tight, and fastened to the walers. Leave the excavation unencumbered.
Tiebacks
Temporary steel wide-flame columns, which are driven into the earth at points where braces will cross
Crosslot bracing
