Week 7: Hazard & Risk (brief), Geotech, TUNNELLING

Question 1

Risk = _____ x _____

Answer 1

Risk = LIKELIHOOD x IMPACT

Question 2

What are some ways engineers have designed buildings to withstand earthquakes?

Answer 2

• Vibration control: resistance to horizontal bending
• Base control: (ex. anti-earthquake rubber bearings at the base)
• Dampers, isolators, compensators

Question 3

Equation for the weight of a rock about to slide down a slope:

Answer 3

Weight = V x p x g

Where V is the volume of the rock body, p is the density of the material (kg/m^3), and g is the gravitational acceleration, 9.8 m/s^2.

Question 4

In mathematical terms, what is the shear force of the rock sample on the slope? (Hint: it might help to draw an FDB and picture which way the shear force acts on the rock)

Answer 4

Shear force:

S = Wsin(theta)

Where W is the weight of the sample of rock, and theta is the angle of the slope.

Question 5

In mathematical terms, what is the normal force of the rock sample on the slope? (Hint: it might help to draw an FDB)

Answer 5

Normal force:

N = Wcos(theta)

Question 6

Factor of Safety = x/y

What is x, and what is y?

Answer 6

x denotes the resisting forces, while y represents the driving forces.

Factor of safety = Resisting Forces / Driving Forces

Question 7

What two factors are the Resisting Forces dependent on?

Answer 7

Cohesion and friction

Question 8

In mathematical terms, what is the extended equation for the Factor of Safety for slope stability?

Answer 8

FoS = R/S

(cA + (Wcos(theta) - U)(mu) / Wsin(theta)

Where cA is the cohesive force, U is the water force (pressure within pores), and mu is the coefficient of friction,

Question 9

How does removing water and drainage mitigate landslide occurrence?

Answer 9

Increase cohesive forces (internal friction) and reduce pressure on the rock body (increasing effective normal stress).

Question 10

List three ways to mitigate landslides.

Answer 10

• Engineered debris flow damns and channels
• Draped meshes/catch fences
• Structural stabilization (walls)
• Scaling
• Protection sheds
• TUNNELLING

Question 11

What are the positive and negative impacts of using CLAY as structural material?

Answer 11

+ = impermeable, can make great liners in engineered landfills.

• = weak and soft when moisture is high, foundations can be unpredictaible.

Question 12

What are the negative impacts of using SILT as structural material?

Answer 12

• Sensitive to frost heaving/ice lense formation

- Foundations are weak (ex. leaning tower of Pisa)

Question 13

What are the positive and negative impacts of using SAND as structural material?

Answer 13

+ = good drainage and strength, low water means suction golds grains together.

• = sensitive to water content, especially in earthquakes

Question 14

Void ratio (e) = ____ / _____

Answer 14

Void ratio (e) = VOLUME of VOID / VOLUME of SOLIDS

Question 15

Porosity (n) = _____ / _____

Answer 15

Porosity (n) = VOLUME of VOID / TOTAL VOLUME

Question 16

Water content (w) = _____ / _____

Answer 16

Water content (w) = WEIGHT of WATER / WEIGHT of SOLIDS

Question 17

Describe the process of “consolidation”.

Answer 17

The delayed compaction of grains due to slow escape of pore water.

Question 18

List two solutions for building in permafrost.

Answer 18

• use foundations on insulting piles (wood, non-metal materials)
• build on a thick gravel pad (or styrofoam)
• cooling pipes or heat dissipation devices
• build stilts extending 0-15m into ground

Question 19

Describe the anatomy of a well-engineered damn, from the middle to the outside.

Answer 19

1. Clay core (impermeable)
2. Sand/silt (filter retains the clay)
3. Sand and gravel (shell to dissipate water pressure and provide strength)
4. Boulders (protects the slope)

Question 20

List two types of soil foundations.

Answer 20

• Piers (solid columns that extend into the soil until rock is reached, to keep building steady)
• Friction piles (increased friction between the soil and columns)
• Raft/floating foundation (increased surface area, like snow shoe)
• Foot clamps (feet extend from column once dug into ground)

Question 21

List three things tunnels are used for.

Answer 21

• Services (water, elec., sewer)
• Water transfer
• Hydroelectricity
• Mining
• Road and rail
• Pedestrians
• Sports facilities
• Storage
• Science
• Ships?!

Question 22

Where is Canada’s oldest tunnel located?

Answer 22

Brockville, bruv.

Question 23

List two examples of tunnelling techniques.

Answer 23

• Road header machines
• Drill and blast
• Tunnel boring
• Cut and cover
• Multiboom drilling rig

Question 24

What is the biggest tunnel boring machine, and where is it located?

Answer 24

Big Bertha (17.5m in diameter), Seattle