Excavation Stability

Question 1

What are the two key areas of slope stability analysis

Answer 1

safety and dilution control

Question 2

Can equilbrium be both stable and unstable

Answer 2

Yes

Question 3

Look at Excavation response diagram

Answer 3

Done

Question 4

How does stress associate in direction around an excavation

Answer 4

stress has to go around the excavation

Question 5

What changes with excavation size

Answer 5

an increase in area increases the stability issues in the area requiring more ground support. There are larger instabilities over a larger area.

Question 6

Can excavation increase be unintentional? how?

Answer 6

indirect size increase can come from ore breaking and lead to an increase in size

Question 7

How do two excavations interact

Answer 7

through a zone of influence

Question 8

What can be caused by two excavations interacting

Answer 8

secondary stress distribution

Question 9

What is assumed if ribs are highly damaged

Answer 9

all stress is placed within one tunnel

Question 10

wat is assumed when ribs are in a good condition

Answer 10

that the stress state shadow and stress distribution has been redistributed and is stable

Question 11

What needs to be understood to determine the equations used

Answer 11

failure regions for each of the tunnel shapes in an environment

Question 12

When is a flat roof better

Answer 12

when there is relatively high horizontal stress and the strata is layered

Question 13

What can be used to mitgate the stress experienced

Answer 13

cannot change the stress but can change the excavation shape orientation

Question 14

What is the optimal excavation shape decision based on for a hardrock mine

Answer 14

when boundary stresses are relatively low compared to rock mass strength use the concept of equalising the compressive stresses

Question 15

What is not a reasonable basis for coal or weak rock when deciding the excavation shape

Answer 15

if the in situ stress are high enough to induce a significant amount of failure in the rock surrounding the excavation then the elastic stress may no longer be a reasonable basis for excavation design

Question 16

What did fairhurst suggest should be considered

Answer 16

choosing an excavation shape where high compressives stresses are concentrated at the corners for the zone of overstressed rock to be limited in extent and confined by the surrounding rock mass

Question 17

What are the main input parameter for the stability graph method

Answer 17

Modified stability number (N)
Shape factor - hydralic radius (HR)

Question 18

What is hydraulic radius used to show

Answer 18

dimensions of the stope

Question 19

What are the spanning classifications of:
tunnels
stope surfaces

Answer 19

one way spanning as long length compared to width

two way spanning

Question 20

What is shape factor

Answer 20

used to account for the shape and size of the opening

Question 21

What is the stability of tunnels controlled by

Answer 21

span
it is the one thing that controls it irrespective of infinite other dimensions

Question 22

What is stress factor A

Answer 22

the ratio of intact rock strength to induced stress

Question 23

What is joint factor B

Answer 23

assess the the joint forming a shallow oblique angle with the face are most likely to become unstable
while joints that are perpendicular are more likely to have high levels of stability

there is a table showing the categories

Question 24

What is gravity factors C

Answer 24

it determines the most likely mode of failure of the block in two categories:
gravity driven - gravity fall and slabbing
sliding failure

Question 25

for block caving what does laubschers caving chart use for the empirical relationships

Answer 25

rock mass quatlity, undercut geometry, and induced stresses

Question 26

what are the laubschers chart two key parameters

Answer 26

Mining rock mass rating
Hydraulic radius

Question 27

What happens if the caving hydraulic radius is too small

Answer 27

the cave will arch and wont fall

Question 28

What are the limitations of the laubschers caving assessment

Answer 28

*it is based off case studies
*doesnt include structures such as faults
*doesnt explicitly consider stress induced damages and deformation

Question 29

What are stability graph methods limitations

Answer 29

*inadequate fill
*corners - designed and accidental
*intersections
*discrete shear structures

Question 30

what are the 4 types of numerical modelling

Answer 30

*finite element method
*aba case
*DN - discrete this is a realworld
*Particle base
*Map3D uses boundaries

Question 31

What are the three pillars of geotechnical engineering

Answer 31

*rock mass quality
*stress
*equations (shape and size control)