Foundations Flashcards
Differential Settlement
Must be avoided. When settlement occurs unevenly across a foundation.
Uniform Settlement
When a structure settles evenly across its foundation.
Dead Loads and Live Loads
Dead loads - weight of forces of the building itself (frame, floor, wall, ceiling, etc…)
Live Loads - weight of forces of loads within a building (people, furnishings, snow, etc…)
Soil Types
Rock
Sand
Silt
Clay
Soil Testing/Reports
Done before excavation begins. digging (shallow) and boring (deep). Samples taken to represent conditions over the site.
Testing for ultimate bearing capacity, permeability, and liquid/plastic limits.
Soils Report given to architect / engineer. The foundations are then designed by an engineer according to the estimated total load requirements of the building.
The report includes the results of both field and lab tests, recommended types of foundations for the site, recommended depths and bearing stresses for the foundations, and an estimate of the expected rate of settlement.
Excavation shorting
a structure that supports the sides of an excavation and protects against cave-ins
Bracing
Rakers - Straight boards that are angled against level ground and the walls of an excavation site.
Crosslot - Braces that run vertically and horizontally on an excavation site, but parallel and perpendicular to the ground.
Not as preferable to tie backs due to issues of mobility on site.
Soldier Beams/Lagging
Soldier Beams - Vertical beams used to support an excavation site.
Lagging - Horizontal beams used to support an excavation site.
Sheet Piling
Sheeting provides a safe work zone for foundation construction. It is needed to brace the soil and prevent it from caving into the zone of excavation.
Piling - driving into ground
Slurry Wall
A “clamshell” bucket follows concrete guide walls, digging a trench which will become the wall itself.
The trench is dug to required depth, through the slurry, which acts to retain the earth.
Reinforcing steel is lowered into the trench in sections.
Concrete is pumped into the trench, forcing the slurry out of the trench, to be stored and re-used.
After the concrete has cured, earth is excavated within the construction zone and tie backs are drilled through the slurry wall to further secure the wall.
Tie Backs
Tie backs are a commonly used method of bracing sheeting systems against soil and water pressure.
Dewatering
When excavation is carried out below the water table in the surrounding soil, the site must be dewatered.
Excavations must be kept dry and to this end the water table might be altered by pumping using well points placed around the site, or by building a watertight barrier that becomes a permanent foundation wall, extending down to impermeable soil.
Water Table
Level of water above the impermeable surface that pools underground
Substructure
Habitable portion of building above the foundation but below ground level.
Superstructure
Habitable portion of a building above the ground.
