Site Flashcards
Foundations
Transfer buildings structural loads to the ground
- reach bedrock or soil competent enough to bear weight, of building
- Get below frostline
Buoyant upload forces
When underground water pushes upon a building
- makes it want to “float”
Dead loads
Weight of the building, permanent
Live loads
People, furnishings, weather, temporary or moving
Lateral loads
Wind, seismic, soil and hydrostatic pressure (lateral soil loads)
Building settling
We want buildings to settle evenly
- IF a building is on rock, settling is negligible
- People start to feel the difference at I degree slope
Largest to smallest particles
Boulders
Cobbles
Gravel
sand
Silt
Clay
Organic soil
Peat and top soil
Must be cleared from the site and stored because the building can’t bear on it
Changes form with biological activity /(plants, rot, etc. )
Can re-use later for landscaping
Arrange from least to most competent particles for supporting a building
Gravel
Sand
Silt
Clay
Which particle is weird and changes behavior most?
Clay - plate like particles, high liquid amount, can be highly expansive, can consolidate (remove moisture under pressure) , brittle, sticky
Which are frictional?
Gravel, sand- rely on internal friction for strength
Which are cohesive?
Clay and silt (less than clay)
What is the liquid limit of a soil?
The water content at which the soil transitions from semi-solid to fluid.
Sand and silt change a lot with water content - IF there is too much water in the ground or an earthquake happens, the ground can liquify
What is plastic limit?
How much water a soil can absorb before starting to expand
It we keep adding water, once it flows it has reached its liquid limit
What is shear strength (as it applies to earth materials)?
The resistance of particles sliding over each other due to friction or interlocking, and possibly cementation or bonding at particle contact
Densely packed course grain soils exhibit higher shear strength - carry heavier building loads / sq unit of area
Loosely packed coarse grained soils exhibit less shear strength (holds less weights )
Smaller ground soils: sand, silt, clay, have an even lower shear strength and can carry less building (these are more prone to change with water)
Poorly graded soil
= well sorted - best for drainage
Sorted is inverse of graded
Well graded soil
= poorly sorted - good support, wider variety of sizes, packed in better and tight, stronger
Sorted is inverse of graded
Brownfield site
A contaminated or believed to be contaminated site
- disposal (chemicals)
- hazardous materials (underground gas tank)
- Paint factory, dry cleaners
- former mill/ oast house (kiln)
What is the angle of repose?
The steepest angle that the side of the excavated area can be before the soil backslides into the pit
- measured up from horizontal
- steeper for cohesive soils (clay)
- lower for friction soils like gravel and sand
Soldier beams
Wide flange steel beams driven into soil
- and lagging (wood boards) between each
- shoring system-keeps earth out as we dig
Methods for holding earth back during excavation
Shoring-holding dirt back - typically temporary, but may have to stay if adjacent to existing building or deep
Soldier beams
Sheeted excavation (steel sheets driven into ground- excavate between)
Trenches (modular, reusable system that is temporary instead of shoring )
Benched excavation
Soil mixing (create walls for excavation-dig holes, fill with cement, water and soil mix to create strengthened barrier wall)
Slurry walls ( used with soft earth or high ground water - economical )
Tie beam vs grade beam
The beams only tackle horizontal load. Grade beams can handle vertical roads like it a column or wall is on top)
Shallow frost protected footing
Run insulation underground next to fasting to use buildings heat to keep soil from freezing - used when we don’t excavate below frost line
Caissons
Drilled and filled - deep foundation
Can go all the way to bedrock - high bearing capacity
Can be 12’ in diameter
Sometimes 2x height of structure
Work in cohesive soils ( clay)
