Subsidence Flashcards
What are the three zones of mine subsidence (rock features)
top - bottom
bending zone; sheared zone; caved zone
What is the caved zone
it can be 10 times the mining height and is a function of the geology and mining height
What is the sheared zone
contained near vertical shear failures through intact rock; shear on vertical joint planes; major horizontal bedding
what is the bending zone
multiple regions of major strata bending plane shear and usually discontinuous (some vertical fracturing)
What are the four divisions of surface subsidence
surface zone, constrained zone, fractured zone and caved zone
(top to bottom)
What are the site conditions for conventional
*relatively flat surface topography
*seam is level
*free of major geological rock mass
*does not contain extremely strong and extremely weak strata
*regular pattern working
What are the subsidence or subsidence effects
deformation of the ground mass surrounding the mine due to the mining activity
What are the subsidence impact
physical changes to the ground and its surface caused by subsidence effects
the disadvantages of DMR method
*only predicts maximum values of subsidence
*it only gives the approximate shape of the subsidence profile for a single isolated panel
What does the amplitude of subsidence depend upon
*width to depth ratio panel
*mining geometry
*seam thickness
*overburden characteristics
*local geological structures
*in situ horizontal structures
What happens to valley closure when the distance between the valley and panel reduces
valley closure increases
What happens to valley closure trends when there is multiple longwalls
the valley closure increases to a larger amount
What happens to subsidence when mining away from the valley
it increases to a platue reduces slightly then increases
(overall trend of increase)
What is the key to look at for any assessment
the stresses
What are components to parametric analyses (UDEC)
*influence of longwall location relative to a valley
*influence of horizontal stress
*influence of valley slope angle
*influence of mining factors
*influence of valley shape
*influence of geological structure around valley
What are the components for parametric analyses (3DEC)
*orientation of longwall relative to valley
*orientation of major horizontal stress with respect to velley as well as longwall advance
Does mining parrellel or perpendicular to the valley have an impact
Yes it can have a significant difference to the valley closure and max subsidence.
Parallel will have larger valley closure and subsidence
Perpendicular will reduce the valley closure and max subsidence
What are methods of subsidence remediation
*injection grouting
*permeation grouting
*impermeable blankets or lining
*joint sealing
What is injection grouting
holes are drilled through creek beds where a variety of grouts and filler materials are injected into the voids
What is permeation grouting
uses grouting and filling materials into an individual pool or stream done in a way that the voids in the creek bed will be blocked to stop the water pentrating the underlying strata
what are impermeable blankets and linings
installation of a completely water proof lining to pool the water and prevent water loss below. Choice of materials varies for cases
What is joint sealing
When water is leaking from the pool it can be sealed using a variety of products some even applied in wet conditions
