Chapter 10 - Geohazards and risk

Question 1

what is attenuation?

Answer 1

the loss of energy experienced by a wave shown as a reduction in amplitude as it propogates through a material

Question 2

what is it called when the amplitude gets smaller over distance?

Answer 2

geometric dispersion

Question 3

what rocks have high attenuation?

Answer 3

unconsolidated sands and gravels

Question 4

what is it called when solid acts as a liquid as a result of seismic acitivity?

Answer 4

liquefaction

Question 5

how is earthquake intensity measured?

Answer 5

Mercalli scale

Question 6

what are some things that happen to buildings during earthquakes?

Answer 6

part of building breaks
‘pancaking’ floors separate
pipe break
landslides

Question 7

intensity decreases with distance
magnitude stays the same

Answer 7

just memorise this :)

Question 8

how does one calculate the return period?

Answer 8

numbers of years on record +1 / number of recorded events

Question 9

building designs to reduce the impact of earthquakes?

Answer 9

• height that does not match natural frequency with EQ FRQ
• avoid irregular/asymmetrical designs
• avoid ornamentation
• absorbant material

ground base/isolation

shear walls

felxible piping

absorbing sway - controlled rocking frame system

Question 10

how do you predict using science?

Answer 10

‘worst case scenario’

nearest active fault
largest earthquake
estimate return period
assume epicentre
calcualte ground motion

Question 11

methods of predicting earthquakes

Answer 11

physical properties
stress - cracks (lowers water + tilting)
animal behaviour
radon emissions - uranium in granite with short half life
seismic gap model

Question 12

idk smthg about tsunamis

Question 13

how do you reduce energy of wave tsunami edition?

Answer 13

maintain coral reef health
,maintain costal trees and vegetation
prohibit building
buildings with no permanent accommodation on ground floor

Question 14

what are examples of 1:1 clays?

Answer 14

kaolinite

Question 15

what are examples of 2:1 clays?

Answer 15

smectite , illite, vermiculite

Question 16

what are the layers of clays?

Answer 16

sheets of silica tetrahedra
aluminium octahedral sheets

Question 17

what clay mineral is common for indsutry under smectite?

Answer 17

montromillite

Question 18

which clay type expands?

Answer 18

smectite
(ish vermiculite)

has high shrink-swell capacity

Question 19

what are mitigating techniques for clays?

Answer 19

foundations below WT
continuous raft foundation
drainage system
tree removal
alter chemistry

Question 20

how to you change the chemsitry of clay?

Answer 20

Iron fixing bacteria (smectite)

Question 21

what subsidence is there due to mining?

Answer 21

shallow mining
deep mines more predictable (modern)
longwall mining

Question 22

what are some holes that form from rainfall?

Answer 22

crownhole - human activity
sinkhole - cave system

Question 23

how to reduce impact of sinkholes?

Answer 23

avoid karst terrain
drainage
reomforce foundations
ground survey techniques

Question 24

what causes mass movement?

Answer 24

increasing mass
increasing slope
decreasing friction

Question 25

classify mass movement by velocity?

Answer 25

heaves (slow)
slides (fast dry)
flow (fast wet)

Question 26

what forms as a result of a rock fall?

Answer 26

talus

competent rocks falling along planes is called translational slides

Question 27

what is it called when clay falls?

Answer 27

slumps (incompetent rocks are isotropic)

Question 28

mechainical properties of rock strenght?

Answer 28

composition
consolidation
water content
joints/cracks

Question 29

what units is stress?

Answer 29

MPa

Question 30

what is strain?

Answer 30

deformation of rock

Question 31

what is the Uniaxial compressive strenght test?

Answer 31

cylindircal core samples placed in hydraulic press and load slowly increased until sample fails

Question 32

what are the relative strenghts of crystal rocks?

Answer 32

compressive > shear > tensile

Question 33

what is the equation for lithostatic pressure?

Answer 33

density x gravity x height

Question 34

what makes faults so weak?

Answer 34

infilled with clay (weak when wet)
different rocks either side (react to loads unequally)

Question 35

what makes bedding planes weak?

Answer 35

fine materials settle out
change in rock = change in properties (encourage water permeating)

Question 36

what are the 5 stages of invesitgation for engineering?

Answer 36

1 - prelim research
2- geological survery
3 - geophysical survey
4 - borehole and excavation
5 - testing soils and rocks (mech prop)