Site Flashcards
Buoyant upload forces
when underground water pushes up on a building
plastic limit
how much water a soil can absorb before starting to expand
liquid limit
how much water until a soil starts flowing
Shear strength (for soil)
soil shear strength is the resistance of particles sliding over each other due to friction or interlocking and possible cementation or bonding
- Densely packed coarse grain solid exhibit higher shear strength
- Loosely packed coarse grained soils exhibit less shear strength
- Smaller grained soils (sand clay silt) have and even lower shear strength and can carry less building
most to least competent earth materials for supporting a building
Most to least competent for supporting a building: Gravel, Sand, Silt, Clay
Clay changes its structural behavior most over time
Clay is cohesive aka relies on stickiness for strength, sand and gravel are frictional
strategies for excavation
Soldier beams, sheeting, shoring, benched excavation
Soil mixing
excavation strategy
mix cement and water with soil along perimeter, forming columns of strengthened soil
Slurry wall
excavation strategy
While a trench is being excavated to create a form for a wall, it is simultaneously filled with slurry (usually a mixture of bentonite and water). The dense but liquid slurry prevents the trench from collapsing by providing outward pressure. Once a particular depth of trench is reached, a reinforcing cage is lowered into the slurry-filled pit and the pit is filled with concrete from the bottom up using tremie pipes. The heavier concrete displaces the bentonite slurry, which is pumped out, filtered, and stored in tanks for use in the next wall segment, or it is recycled
how to deal with excavating under the water table
Watertight enclosure (bathtub)
Pump water out of the excavation or next to the excavation
what to consider when deciding what foundation to build?
Soil bearing capacity, construction schedule, contractors recent experience, cost, groundwater conditions, effect on adjacent buildings, frostline depth
wall footing
type of spread footing
also called a strip footing, has a crawlspace or basement
column footing
type of spread footing
good for point loads, may need to brace them to eachother at grade with grade beams
can do cantilevered or combined footings with it
combined footing is good for dealing with property lines
slab on grade
type of spread footing
low loads, don’t have to worry about frost
mat foundation
type of spread footing
a continuous slab resting on the soil that extends over the entire footprint of the building, thereby supporting the building and transferring its weight to the ground
can handle heavier loads than slab on grade
floating foundation
type of spread footing
boxlike rigid structures set at such a depth below ground that the weight of the soil removed to place it equals the weight of the building; thus, once the building is completed, the soil under it will bear the same weight
when do you use piles vs caissons?
when there is no cohesive soil
pile cap
transfers load to a group of piles
minipile or helical pile
use to shore up an existing building where excess vibration associated with ramming piles would be a problem or in or near a building where quiet is desired and the ramming noise would be disruptive or anywhere where large amounts of soil displacement wont fly
reasons to underpin an existing foundation
Building renovation makes new building heavier
Existing foundation was never sufficient and needs to be improved
Adjacent sitework weakened you foundation
ways to improve an existing foundation
Extend the foundation to some deeper strata with more competent support
Make the foundation wider so that it rests on more soil
Improve the earth with imported fill or grout
3 types of foundations you can add to existing foundations
new foundation footing beneath existing
underpinning with new piels below
minipiles below
how do you keep a basement dry?
- Well maintained gutters, roof drains, downspouts
- Some place to discharge roof water far away and downhill of the building
- Sloped site away from the building to bring the surface rainwater away
- A break in the soil so that water that would otherwise press against the foundation wall will instead drop (uses drainage mat or gravel fill)
- A perforated pipe to accept the water and carry it on
blindside waterproofing
installed before the foundation and foundation wall. The waterproofing membrane is applied to the soil support (i.e. shoring, sheet pile, slurry wall, rocks, neighboring building) and then concrete or shotcrete is applied against the membrane.
good if there is a closely neighboring building