Excavation Stability Flashcards
What are the two key areas of slope stability analysis
safety and dilution control
Can equilbrium be both stable and unstable
Yes
Look at Excavation response diagram
Done
How does stress associate in direction around an excavation
stress has to go around the excavation
What changes with excavation size
an increase in area increases the stability issues in the area requiring more ground support. There are larger instabilities over a larger area.
Can excavation increase be unintentional? how?
indirect size increase can come from ore breaking and lead to an increase in size
How do two excavations interact
through a zone of influence
What can be caused by two excavations interacting
secondary stress distribution
What is assumed if ribs are highly damaged
all stress is placed within one tunnel
wat is assumed when ribs are in a good condition
that the stress state shadow and stress distribution has been redistributed and is stable
What needs to be understood to determine the equations used
failure regions for each of the tunnel shapes in an environment
When is a flat roof better
when there is relatively high horizontal stress and the strata is layered
What can be used to mitgate the stress experienced
cannot change the stress but can change the excavation shape orientation
What is the optimal excavation shape decision based on for a hardrock mine
when boundary stresses are relatively low compared to rock mass strength use the concept of equalising the compressive stresses
What is not a reasonable basis for coal or weak rock when deciding the excavation shape
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
What did fairhurst suggest should be considered
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
What are the main input parameter for the stability graph method
Modified stability number (N)
Shape factor - hydralic radius (HR)
What is hydraulic radius used to show
dimensions of the stope
What are the spanning classifications of:
tunnels
stope surfaces
one way spanning as long length compared to width
two way spanning
What is shape factor
used to account for the shape and size of the opening
What is the stability of tunnels controlled by
span
it is the one thing that controls it irrespective of infinite other dimensions
What is stress factor A
the ratio of intact rock strength to induced stress
What is joint factor B
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
What is gravity factors C
it determines the most likely mode of failure of the block in two categories:
gravity driven - gravity fall and slabbing
sliding failure
for block caving what does laubschers caving chart use for the empirical relationships
rock mass quatlity, undercut geometry, and induced stresses
what are the laubschers chart two key parameters
Mining rock mass rating
Hydraulic radius
What happens if the caving hydraulic radius is too small
the cave will arch and wont fall
What are the limitations of the laubschers caving assessment
*it is based off case studies
*doesnt include structures such as faults
*doesnt explicitly consider stress induced damages and deformation
What are stability graph methods limitations
*inadequate fill
*corners - designed and accidental
*intersections
*discrete shear structures
what are the 4 types of numerical modelling
*finite element method
*aba case
*DN - discrete this is a realworld
*Particle base
*Map3D uses boundaries
What are the three pillars of geotechnical engineering
*rock mass quality
*stress
*equations (shape and size control)
