F-3 Site Layout Excavation and shoring practices Flashcards
Grading
refers to the surface of ground on the job site.
Grade also means _____
Slope. 2% grade means that the grade drops 2mm vertically for every 100mm traveled horizontally
Soil classifications
soils are classified by their particle size
Soil testing
important for determining foundation design and for estimating building costs. can be done by test samples and drilling core samples
Underpinning
when excavating deeper then the foundations of an adjacent building, care must be provided to maintain bearing for the buildings foundation. the process of adding sections of foundations under and existing foundation is called under pinning
Temporary support
temporary support of an existing building can be provided by a series of beams placed through the wall of the building being underpinned. the beams are known as needle beams and are supported under the building on blocks, or in pits on mud crimps
Permanent support
once supported, footing under the footings are made. sometimes existing footings need to be trimmed to put concrete in. this is known as leg to leg underpinning
Excavations that require shoring
the depth of the excavation is what determines the shoring and sloping requirements
Worksafe BC regulations with shoring
normally excavations under 1.2 meters (4ft) in depth do not require shoring.
Engineered excavations
needed if
- deeper then 20 feet
- adjacent to buildings or other structures
- subject to hydrostatic pressure ( water seeping into excavation)
- being dug on sloping ground steeper then 1 vertical to 3 horizontal
Sloping requirements
instead of shoring small excavations can be sloped. maximum slope is 3 horizontal to 4 vertical
Benching requirements
Series of benches (stairs) down into an excavation. vertical cuts are 4 feet
Type A: Hard and solid soils
Need least support. the timber shoring in this type of soil usually consists of simple uprights and cross braces.
Type B: soils likely to crack or crumble
these are looser and require more support.
Type C: soft, sandy filled or loose soil
soft and loose soils will constantly slough into the trench if not held back with solid planking.
Timber and plank shoring (trench shoring)
this method is used when the trench is too big.normally it would be metal shoring but these wooden ones are made custom for big trenches.
planks may be spaced if soil is stable but must be close fitting if the soil is loose.
Timber shoring is slow to instal and must be installed from the top down.
Simple shoring
trenches less then 2.4m (8Ft) in hard and solid soil are aloud to be built without walers. cross braces and uprights are spaced no more then 6 feet apart
Skeleton shoring
constructed with uprights, walers, and cross braces. type A and B soils trenches 15 ft
Close and tight
when uprights are required to be tight together
Plywood Shoring
plywood can be used for uprights only if the trench is less than 2.7m (9ft). must be 3/4. upright planks are installed 24”OC
Telescopic shoring
when the trench is deeper then the longest available planks. each section of planks must have at least two cross braces
Prefab shoring
fasted and safest way to shore. pre made units that are lifted into trench by equipment digging them.
Steel cage shoring
most common type of pre fab shoring. metal frames with solid sides. can be adjusted.
Hydrolic shoring
type of prefab shoring. incorporates a hydraulic system.
