Excavation 1 Flashcards
(21 cards)
What is trench excavation?
An excavation where length greatly exceeds depth, commonly used for buried services and strip foundations.
What is mass excavation?
Removing a large volume of soil from a limited area, e.g., for basements, building/bridge foundations.
What is cutting excavation?
Widespread removal of topsoil to make an even surface—used for temporary roads, highways, or agricultural leveling.
What is the purpose of trench excavation?
For laying foundations, pipes, and utility cables underground.
What factors influence trench technique and support?
Purpose
Ground conditions
Obstructions
Location
What steps should be followed before trenching begins?
1) Verify alignment and endpoints
2) Identify underground utilities
3) Set out trench
4) Prepare disposal plans
5) Gather tools and machines
6) Plan support systems
7) Ensure team is informed
What is benching in excavation?
Creating steps in trench walls to reduce height and prevent collapse.
What is shoring in trenching?
Installing supports to hold back soil in unstable or wet ground, protecting workers.
What is shielding in trenching?
Using trench boxes/shields to protect workers—not to hold soil back—especially in deeper or unstable trenches.
What is battering in excavation?
Sloping the trench walls at a safe angle to avoid collapse—used when the ground is stable.
What is the Zone of Influence in excavation?
The area around a trench affected by external loads—placing heavy machinery or spoil piles here can cause collapse.
How far must temporary spoil be from the trench edge?
At least 2 feet (0.61 m) from the edge, measured from base of the spoil.
What’s the risk with permanent spoil piles?
If placed too close to excavations, they can cause ground instability and safety violations.
What safety precautions should be taken around excavation sites?
Fence off and sign area
Guard and light area at night
Provide footbridges with rails
Use ladders
Avoid blasting/vibration nearby
What is Horizontal Directional Drilling (HDD)?
A trenchless method used to install underground services without open-cut excavation. Ideal for road crossings or urban areas.
Advantages of HDD?
Minimal surface disruption
Faster in congested areas
Environmentally friendlier
Reduced traffic impact
Disadvantages of HDD?
Higher initial cost
Not ideal for rocky/unstable soils
Requires skilled operators
Risks of HDD?
Ground heave or settlement
Fracturing of soil
Hitting unknown utilities
Drilling fluid loss (“frac-out”)
If a 1m deep trench is dug for a strip foundation on sloped land with 1m elevation difference, what’s the max depth needed at the high end?
2 meters deep at the higher point (1m slope + 1m trench depth)
What are implications of deeper trenches on sloped land?
Greater risk of collapse
More soil removal
More support systems required
Higher costs
More complex water drainage management
How can deep trenching on slopes be made safe?
Use stepped foundations
Add retaining walls
Use proper trench support
Consider engineering design review
