arch 3007 exam 2 - foundations

piles and caissons are usually installed in

clusters and "capped"

instead of a basement, a building might have a ______

crawl space

frost line

depth at which soil in a particular area no longer freezes

footings

distributes building loads widely and evenly to the ground

friction piles

don't bear on anything... friction of soil provides the resistance - driven in clusters

_____ is important to all retaining and foundation walls to lessen _______ that either wants to knock wall over or push water through it

drainage, hydrostatic pressure

earthquake loads

dynamic horizontal and vertical, whiplash

cofferdam

enclosure used to keep water back providing a dry environment for excavation or repair work

water table

flows through and around underground rocks forming tunnels and caves

_____ allows water to move more quickly to the _____ or drainage tile

gravel, weepholes

hydrostatic pressure

ground water lift (floating boat)

shoring

holds back excavation when building the foundation

plate load test

hydraulic arm with plate measures bearing and potential settlement

core borings

intact, cylindrical sections retrieved by digging or drilling

wind load

lateral (side), downward, and uplift

soil

may consist of superimposed layers, each containing a mix of types

differential settlement

means the building is sinking unevenly which can lead to serious problems - Tower of Pisa

uniform settlement

means the entire building sinks or subsides at an equal rate (as opposed to differential settlement)

two broad classes of soil

non-cohesive and cohesive

dynamic load test (test piles)

pipes or piles are driven into ground... how easy it is pounded into the ground

cap

serves as a footing for column or wall above and distributes loads across multiple piles or caissons

categories of foundations

shallow and deep

slab on grade

shallow concrete foundation supported by well-compacted soil in middle and thickened slab at edges (also rafts or mat)

earth pressure

soil push, freeze/thaw cycles

bearing capacity

soils resist the downward force of a building or a structure - different soils have different bearing capacities

piles

steel, concrete, or wood forcibly driven

end bearing piles

steel, concrete, or wood forcibly driven to reach stable strata

angle of repose

the angle at which soil can be sloped without caving or sliding

caisson disease

the bends

deep foundation

transfer loads to a point some distance below the substructure

shallow foundation

transfer loads to the earth at the base of column, slab, wall

drainage mat

used in addition to waterproofing

dead load

weight of building materials and fixed equipment

live load

weight of people, furniture, snow

settlement

(sinking) occurs in all buildings as soil consolidates

bracing

(tiebacks) keeps the shoring from collapsing

gabion wall

- a large gravity wall - wire mesh baskets filled with rocks

coarse sand and gravel

- coarse aggregate - un-consolidated rock fragments - excellent for drainage and foundations

caissons

- concrete cylinder poured into a large drilled shaft - reaches down into earth to find solid bearing (bedrock) - 18" to 8' diameters - bottom can be "belled" to make a type of footing to spread the load

non-cohesive

- course grained, large particles, includes gravels and sands - best for building foundations

types of bracing

- crosslot bracing - rakers - tiebacks

test pit

- digging a hole or open pit to examine soil or to find water table

sand

- fine and coarse - lose, granular rock / crystal - between silt and gravel - good drainage - coarse is good for foundation

clay

- fine ground, plate-shaped particles - expands and contracts with moisture

silt and organic

- fine, sedimentary material (sand, clay, organic material) - stable when dry, unstable wet

types of retaining walls

- gravity wall - cantilever timber - concrete block wall

retaining walls

- hold back soil where abrupt elevation changes are necessary for building or landscaping - don't support weight but must resist lateral pressure from soil and moisture

sump pump

- installed under basement slab in lowest corner - doesn't run unless heavy rain or snow melt - collects water and pumps it away to prevent basement flooding

foundation resists:

- lateral (overturning) forces from wind and earthquakes (whiplash) - expansion and compression from freeze and thaw - hydrostatic pressure

foundation piers

- minimum site intervention (excavation and drainage) - soil not good or no need for subsurface spaces - usually on sloped or wet sites - aesthetics (lightly touches ground)

rock and bedrock

- native, consolidated rock - great foundation, excellent bearing capacity - difficult to excavate

types of foundations

- piers - slabs - walls - piles and caissons

excavation

- removing soil to install foundations is required for all buildings - necessary to get to soil with appropriate bearing capacity - some excavation is for basement levels - also necessary to deal with the heaving and contraction of soil due to freezing and thawing

cohesive

- smaller, finer particles - includes silts and clays

types of shoring

- soldier beams and lagging - sheet piling (timber, steel, concrete) - slurry wall (a narrow, site-cast, concrete wall

post-tensioned slabs

- steel cables run through sleeves cast into the slab - concrete cures and then cables are stretched - process creates a "pre-cambered" slab - allows for thinner concrete and less rebar

soil profile

- taken to determine layers or make-up of the site - integrity of the building structure depends on the bearing and frictional capacity of that profile

foundation

- the lowest division of a building - the substructure - constructed wholly or partially below grade (always some degree of excavation) - transmits loads (live and dead) from the roof, floors, and superstructure down to the earth

slurry wall

- used in tight, soft soil locations where threat of collapse is high - idea is to first build 4 underground walls (box) then excavate the site (dig out inside of the box) - while digging the 4 walls, thick fluid (slurry) keeps the hole from collapsing - slurry is then replaced by concrete - site (inside the box) is then excavated

foundation walls

- used to go deeper to find better bearing, to get below frost depth, or to make a basement - the footing, foundation wall, and concrete slab are all poured separately

dampproofing

- when groundwater issues are mild - moisture resistant cement-plaster is sprayed, rolled, or troweled on

waterproofing

- when water issues are more critical - resists hydrostatic pressure pushing water through - applied as liquid, sticky sheets, loose mats/sheets