Subsidence

Question 1

What are the three zones of mine subsidence (rock features)

Answer 1

top - bottom
bending zone; sheared zone; caved zone

Question 2

What is the caved zone

Answer 2

it can be 10 times the mining height and is a function of the geology and mining height

Question 3

What is the sheared zone

Answer 3

contained near vertical shear failures through intact rock; shear on vertical joint planes; major horizontal bedding

Question 4

what is the bending zone

Answer 4

multiple regions of major strata bending plane shear and usually discontinuous (some vertical fracturing)

Question 5

What are the four divisions of surface subsidence

Answer 5

surface zone, constrained zone, fractured zone and caved zone
(top to bottom)

Question 6

What are the site conditions for conventional

Answer 6

*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

Question 7

What are the subsidence or subsidence effects

Answer 7

deformation of the ground mass surrounding the mine due to the mining activity

Question 8

What are the subsidence impact

Answer 8

physical changes to the ground and its surface caused by subsidence effects

Question 9

the disadvantages of DMR method

Answer 9

*only predicts maximum values of subsidence
*it only gives the approximate shape of the subsidence profile for a single isolated panel

Question 10

What does the amplitude of subsidence depend upon

Answer 10

*width to depth ratio panel
*mining geometry
*seam thickness
*overburden characteristics
*local geological structures
*in situ horizontal structures

Question 11

What happens to valley closure when the distance between the valley and panel reduces

Answer 11

valley closure increases

Question 12

What happens to valley closure trends when there is multiple longwalls

Answer 12

the valley closure increases to a larger amount

Question 13

What happens to subsidence when mining away from the valley

Answer 13

it increases to a platue reduces slightly then increases
(overall trend of increase)

Question 14

What is the key to look at for any assessment

Answer 14

the stresses

Question 15

What are components to parametric analyses (UDEC)

Answer 15

*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

Question 16

What are the components for parametric analyses (3DEC)

Answer 16

*orientation of longwall relative to valley
*orientation of major horizontal stress with respect to velley as well as longwall advance

Question 17

Does mining parrellel or perpendicular to the valley have an impact

Answer 17

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

Question 18

What are methods of subsidence remediation

Answer 18

*injection grouting
*permeation grouting
*impermeable blankets or lining
*joint sealing

Question 19

What is injection grouting

Answer 19

holes are drilled through creek beds where a variety of grouts and filler materials are injected into the voids

Question 20

What is permeation grouting

Answer 20

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

Question 21

what are impermeable blankets and linings

Answer 21

installation of a completely water proof lining to pool the water and prevent water loss below. Choice of materials varies for cases

Question 22

What is joint sealing

Answer 22

When water is leaking from the pool it can be sealed using a variety of products some even applied in wet conditions