3 - Culvert Design Flashcards
(69 cards)
What is a culvert?
A structure that channels water through an obstacle, typically in a road or embankment.
What do the culvert and soil bear the weight of?
The roadway and the vehicles.
What is the difference between a bridge and a culvert?
A bridge has a larger span, with its own abutments and bears its own weight plus that of the traffic.
In the US, if a structure has a span of over 20 feet, what is it considered as?
A bridge
What are 2 properties of pipe culverts?
They are circular, cheap and easy to install.
Why are box culverts popular in road design?
The shape provides a rigid structure that is appropriate in areas with poor soil conditions
What do culvert inlets determine?
The flow rate through the culvert
What is the ‘invert’ of a culvert?
The bottom level of the opening
What is the ‘soffit’ of the culvert?
The top level of the opening
What is the wing wall of a culvert?
The wall of the culvert.
Why is scour protection needed at the culvert exit?
Water can be travelling much faster than the inlet.
In order to avoid erosion in the culvert, what speed does the water need to be kept below?
1.2m/s
What is material failure?
Since circular culverts are made from corrugated steel tubes, corrosion can be a cause of structural failure.
What are the 3 failure modes of culverts?
Material failure, erosion, buoyancy
How can buoyancy cause failure of a culvert?
Air can get trapped in a full-flowing culvert, resulting in a buoyancy force and uplift on the culvert.
Blockages can reduce the ability of the culvert to convey water, what is a solution to this?
Using screens, to catch the debris before it enters the culver, and also keep children safe.
What are the 3 solutions when dealing with a bendy stream?
1 - Place culvert at most straight part
2 - Realign the channel
3 - Widen the culvert and add head walls
Why is full flow in a culvert (surcharge) not desirable?
Increased risk of blockage
If the hydraulic grade line (HGL) is above the soffit level, where is hydraulic pressure exerted?
On the culvert soffit
What is the total head, H1 of the energy grade line (EGL) ?
H1 = z1 + y1 + v^2 / 2g
What is the hydraulic grade line (HGL)?
z1 + y1
What does the froude number determine?
Wether the flow is subcritical, critical or supercritical
What is the equation of the Froude number?
Fr = v / root (g*y)
What happens when Fr > 1?
The flow is supercritcal and is characterised as rapid