Foundations Flashcards
Unified Soil Classification Types from largest to smallest
Boulders
Cobbles
Gravel (also referred to as coarse-grained soils)
Sand (also referred to as coarse-grained soils)
Silt (also referred to as fine-grained soils)
Clay (also referred to as fine-grained soils)
The hand test
If it takes 2 hands to lift, its a boulder, if it only takes one hand its a cobble. If you can easily lift one particle between 2 fingers, it’s gravel, but if individual particles are large enough to be seen but too small to be picked up singly, it’s sand. If particles are too small to see with the unaided eye, it’s silt or clay. When wet, clay soils are like putts and are hard when it’s dry. Silts is not sticky when wet and has no cohesiveness when dry,
Frictional or cohesion less soil
A soil, such as sand or gravel, that relies primarily on friction rather than attractive or repulsive forces between particles for its strength
Fabric
Clay particles tend to arrange themselves into complex internal structures, called fabric
Cohesive soils
A soil such as clay whose particles are able to adhere to one another by means of cohesive and adhesive forces
Expansive soils
Prone to expand and contract with changes in moisture content
Well-graded soil
Includes a broad, well-distributed range of particle sizes
Gap graded soil
A soil graded so as to contain a broad range of particle sizes, but with certain sizes omitted
Uniformly graded soil
A special instance of a poorly graded soil in which the soil particles are mostly of one size
The maximum practical reach of small excavating machines
16’
Soil mixing
A method of retaining soil during excavation
The sides of an excavation are strengthened by blending Portland cement and water with existing soil, mixing in place
Ground improving
Can also be used to create cutoff walls to prevent water seepage into excavations, to stabilize of strengthen areas of weak soil around or under buildings, or to remediate biologically or chemically contaminated soil by adding chemicals that neutralize the contamination
Slurry wall
Complex and expensive method of constructing a complete, steel-reinforced concrete wall in the ground, even several storming below the surface, before excavation takes place
Economical only when it becomes part of the permanent foundation
Walers
Beams that space across the face of the sheeting
Rakers
A sloping brace for supporting sheeting around an excavation
Tiebacks
A ties, one end of which is anchored in the ground, with the other end used to support sheeting around an excavation
Types of shallow foundations
Slab on grade
Crawl space
Basement
Column footing
Wall/strip footing
Tie beams or grade beams
Reinforced concrete beams that link together column footings
Footings cannot extend past what?
A property line
Combined or cantilever footings
Used when columns must abut a property line; ties the outside edge columns with an interior column to create a balanced footing
Shallow frost-protected foundations
Used to save costs where frost lines are deep
Footings placed closer to the ground surface, but insulated in such a way that the ground underneath them cannot freeze; insulation board placed around the perimeter of the building to allow heat to flow under the footings and stay at a temp above freezing
Mat foundations
Used in situations where the bearing capacity of the soil is low in relation to building loads
Column footings are placed closely together and are merged into a single mat, or raft, that supports the entire building
One story of excavated soil weighs how much?
About the same as 5-8 stories of superstructure
Floating (compensated) foundation
A mat footing placed at a depth such that the weight of the soil removed from the excavation is close to the weight of the building constructed above
Deep foundation types
Caissons
Piles
Caisson or drilled pier
Similar to a column, but extends through unsatisfactory soil beneath the substructure of a building until it reaches a more suitable stratum
Drilled and poured; 18” - 12’ and wider
Reinforcing is seldom used in the concrete except near the top of the caisson where it joins the uilding structure above
Piles
More slender than caissons and usually forcibly driven into the earth rather than drilled and poured
Used where no cohesive soils, subsurface water, or excessive depth of bearing strata make caissons impractical
Usually driven closely together in clusters at contain 2-25 piles each; the piles are later joined at the top by a reinforce pile cap to distribute the load of the column or wall above among the piles
End bearing pile
When a pile is driven until its tip encounters firm resistance from a suitable bearing stratum such as rock, dense sands, or gravels
Friction pile
When no firm bearing layer can be reached, the isle can have a considerable load-carrying capacity through frictional resistance
Pile Materials
Wood/timber (economical; cannot be spliced and are limited to the length of available tree trunks, and can decay)
Steel/H sections (displace little soil and can be welded together; corrosion is an issue and can’t be inspected afterwards to ensure they’re straight)
Steel/pipes (can be open or closed; open piles are easier to drive in and displace less soil; closed require larger hammers; open can be inspected; filled with concrete after driven)
Mini piles and helical piles (driven in, not hammered)
Concrete (square, octagonal, or round and can be open in larger sizes; prestressed when precast and must be handled carefully to avoid cracking; site cast concrete installed by driving a hollow steel shell into the ground and then filling the shell with concrete)
Pressure-injected footing / compaction-grouted footing
Rammed aggregate piers / stone columns
Drainage at foundations
Some combination of porous backfill material, such as well-sorted gravel), drainage mat, and perforated drain piping
Water that approaches the foundation wall falls through the mat to reformatted drain piping at the bottom of the wall and along the perimeter of the building
Water then flows by gravity either to daylight at a lower surface elevation, a municipal storm sewer system, or a sump pump
The slits in the pipe face down
Dampproofing
Moisture-resistant cement plaster or asphalt compound applied to basement walls where groundwater conditions are mild or waterproofing requirements are not critical
Plaster dampproofing, or large coating
Asphalt (bituminous) dampproofing
Waterproofing
Provides more robust protection against water entry
Can protect interior spaces from moisture in very wet soils or even when foundations are submerged below the water table and exposed to continuous hydrostatic pressure
Plastics, asphalt compounds, synthetic rubbers, natural clays
Liquid applied membranes seamless and easy to form around intricate shapes
Sheet membranes consisting in size and quality but can leak because they can’t be molded around intricate shapes
Fully adhered membranes are continuously bonded to the substrate and less likely to leak
Loosely laid
Pre-applied membranes
Integral waterproofing
Passive radon control
A layer of gravel or other gas-permeable material beneath the concrete slab
Over the gravel layer, a gas-impermeable plastic sheet or membrane
After the pouring of the concrete foundation walls and slab on grade, sealing of all joints, penetrations, and cracks in these components
Coating of the outside of basement walls with dampproofing or waterproofing
One or more vent pipes extending vertically from the gas permeable gravel layer through the roof of the building
