F3 - Excavation and Shoring practices - LT #1 and LT #2 Flashcards
Topsoil is:
Organic material, not allowed under footings
What material has the smallest particle size?
Clay
The distance from the surface to the rock can be measured by a geotechnical engineer using a:
Seismic test - sending shockwaves through the soil.
What supports the shore when a shore supports the wall of a building?
Jacks on a mud crib
Where is a needle beam placed?
Through the wall of the building underpinned.
Supported by blocks underneath and jacks on mud cribs from excavation side.
What two types of underpinning are placed in spaced sections under an original footing?
Part of the old footing may need to be trimmed away to make it easier to place concrete, this is
Leg and Leg under leg underpinning
OR
Bolting shores on jacks and putting under a whaler
Regulations for excavations are contained where:
Part 20 of the OHS Regulation.
Excavations at what depth, do not require shoring?
4 feet in depth.
Which excavations require an engineer?
1) Deeper than 20 feet
2) Adjacent to building or other structures
3) Subject to vibrations (near roadway or factory)
4) Subject to hydrostatic pressure (groundwater seeping into excavation)
5) Being dug on sloping ground steeper than 1 V to 3 H
Before any worker enters an excavation over 4 feet in depth, the excavation must:
Suitably shored, or have its sides safely sloped or benched.
If the sides of an excavation cannot be sloped, they must be supported with:
shoring
Instead of shoring, excavations can be safely sloped to protect workers. Maximum slope is:
3 RUN to 4 RISE (0.75 to 1V) Approx 53 degree)
The most common practice of benching is:
Making a series of cuts up to 4 feet in depth. Each cut has an adjacent horizontal bench at least 1.5 times wide.
For hard and solid soil, what type of shoring is required?
The timber shoring in this soil type usually consists of simple upright and cross braces. Walers may not be required.
Soils likely to Crack or Crumble require what kind of shoring?
Looser needs more support.
Planking used to form the sides of timber shoring, is spaced closer together and supported by walers and cross braces.
Soft, sandy, filled, or loose soil requires what kind of shoring?
Planks installed tight together.
Supported by both walers, cross braces.
Largest size and closest spacing of walers and cross braces.
Unstable soil requires what kind of treatments?
An engineer must determine the safe slope.
How deep must a trench be before trench shoring is required?
At least 4 feet
A trench is defined as:
An excavation no wider than 12 feet.
When a trench is too wide or too irregular for pre-fab shoring, what is used?
Timber and plank shoring is used.
Trench width is divided into two categories, which are?
over 6 feet and under 6 feet
Which direction is timber shoring installed from?
Installed from the top down, as it is unsafe to enter an unshored trench
Skeleton shoring is:
Spaced apart uprights, walers and cross bracing/
Used for trench depth up to 15 feet in type A and B soils
Close and Tight shoring is:
Skeleton shoring, but uprights are tighter together.
Plywood shoring is:
Plywood substitutes upright planks, (a long as the trench is not more than 9 ft deep)
Upright planks installed 600 mm OC, all plywood seams are covered by uprights or walers, cross braces do not bear directly on the plywood.
Telescope shoring is:
Installed when the trench is deeper than the longest available planks.
Hydraulic rams must be fitted with steel locking pins that:
hold the sides of the shoring apart if the hydraulic lines are broken
Shoring is installed from the top down and removed from:
The bottom up
Safe entrance and exits must be provided within ____ Feet of the worker locations. Crossings must be at least ___ Wide
Entrance and exits - Within 20 feet, Crossings must be at least 20 Inches Wide and equipped with guards if trench is more than 4 feet deep.
Uprights of shoring in a trench cannot slope more than:
15 degrees outward.
End Shoring must:
Needs to be sloped, shored, or have the area equal to the depth restricted from entry.
End walers can be used at end of shoring
Of matching size can be used, as long as they bear on the side walers.
Wider end shoring must be designed by:
Professional Engineer
End shoring is not required if:
The trench is narrower than the required upright spacing.
How is a trench backfilled?
Place fill from the bottom of the trench up to the bottom of struts and stringers, remove lower struts and stringers, fill. Repeat. until all is removed.
When bulk shoringThe sides of excavations need to be shored when the cut is more than
1.2 (4 feet) deep. Require an engineer as well.
Deep excavations are usually only supported with:
Rock anchors.
What is a rock anchor?
Drilled into side of excavation, used to bolt a shoring system to the face of excavation.
What is sheet piling?
Interlocking sheet piling can be used as shoring. It is used for excavations up to 4.5 meters (15 ft) deep.
When forming a bridge, what forming would be used?
Sheet piling, AKA Cofferdam. Another use for sheet piling is for creating permanent retaining walls.
What are soldiers?
Wide flange steel beam along the perimeter of the excavation. Spaced 1.8 m to 3.7 m apart. Next 75 mm to 10 mm thick lumber is inserted between the flanges, spanning soldier to soldier.
For excavations up to 400 Feet deep what kind of slurry is used?
Concrete slurry walls are often used. These walls are from 450 mm to 1500 mm (18” to 60” thick and can be shoring and foundation.
Does concrete displace the bentonite slurry when concrete is placed in a concrete slurry wall?
Yes
What are steel H beams used for a concrete slurry wall called?
Soldier beams
When must shoring be inspected?
At the beginning of each workday, during the day, and at the end of the day double check everything is still secure
List four situations where a professional engineer is required to design the excavation and shoring procedure.
1) Subject to vibration (Near a major roadway or factory)
2) Subject to hydrostatic pressure (groundwater)
3) Being dug on sloping ground steeper than 1V3H
If shoring is not used, what is the steepest slope that the sides of an excavation can be left at?
0.75:1
What is the meaning of hydrostatic pressure?
Water that is under pressure
Which part of the WorkSafeBC OHS regulation provides specifications for excavations?
Part 20
What would be a safe horizontal slope for an excavation that is 8 ft. deep?
6 horizontal (.75: 1V)
Process of adding sections of foundation under an existing foundation is called what?
Underpinning
How is soil testing done?
Digging test hole or drilling core samples
Fill under foundations of gravel or sand is layered how much?
Placed in 100 mm to 150 mm Layers
Needle beams are supported by:
Under the building on blocks and on building side by jacks on mud cribs
What is jacked cylinder underpinning?
Jacking steel cylinders down to adequate bearing. Soil in the cylinders is then removed using high pressure water jets.
Cylinder filled with concrete and capped with bearing plate.
Column and wedges are used between the bearing plate and old foundation
Maximum depth for benching cuts vertically is:
4 feet, horizontal is at least 1.5 times as wide
Soil Types A, B, and C
Type A - Hard and Solid
Type B - Likely to crack or crumble
Type C - Soft, sandy, filled, or Loose soil
Design for shoring based on:
Trench depth, width, and soil stability type.
What is required at the end of the trench?
Sloped, shored, or have the area equal to the depth restricted from entry.
What is the best way to remove vertical planks from the trench?
Using chains attached to the uprights and a backhoe or crane to pull them out
What is a Raker strut?
The bulk shoring type is used to support shoring similar to one side of the trench shoring system. The ends of steel rakers can be set in concrete bearing blocks instead of mudsills.
