Rock Mechanics.pdf - Mining and Blasting

Figure 16.7 Geometry of vertical
shear surfaces in rectangular block.
CHIMNEY CAVING
For h − b sin ≤ d ≤ h, i.e. groundwater level intersects the stope hanging wall,
a similar calculation gives
QBCGF = Q1 − w tan ′ (h − d) 3
9 tan
When d ≥ h, no water pressures act on the block surface and
QBCGF = Q1
Similar calculations for the up-dip face DCGH lead to the result
QDCGH = a c ′ (h − b sin ) + k
2 tan ′ (h − b sin ) 2
− w
3 tan ′ (h − b sin − d) 2
for 0 ≤ d ≤ h − b sin , and
QDCGH = a c ′ (h − b sin ) + k
2 tan ′ (h − b sin ) 2
for d ≥ h − b sin .
The results for the down-dip face ABFE are
QABFE = a c ′ h + kh2
tan
2
′ (h − d)2
− w tan
3
′
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