Stability Assessment of Mining Excavations: the Impact of Large Depths

Figures & Tables

Parameters	Comments
Hkr=Re pen2∗γ${{H}_{kr}}=\frac{{{R}_{e\,pen}}}{2*\gamma }$	H – depth of excavation site, m;
	_kr H– critical depth, m;
	R_{c pen} – penetrometric compressive strength, MPa;
HHkr≤1$\frac{H}{{{H}_{kr}}}\le 1$	γ – specific weight of overlying strata. 0.027, MN/ m³;
WL=∑hi∗ϒi∑hi${{W}_{L}}=\frac{\sum{{{h}_{i}}*{{\Upsilon }_{i}}}}{\sum{{{h}_{i}}}}$	n – fracture intensiveness coefficient (– );
	l_s – number of fractures in roof (– );
	l– number of strata in roof (–); _w
nlslw$n\frac{{{l}_{s}}}{{{l}_{w}}}$	W_L – roof lithology index( – );
	h_i – thickness of the ith rock layer, m;
W _L – n >0	r_i – reduction coefficient for the ith layer, related to lithology: sandstone – 1.0; siltstone – 0.77; claystone – 0.66; coal – 0.72.

Parameters		Cross-cut C-1	Eastern guideline	Airway cross-cut W-1	Raise gallery Z-VII	Bypass S of IIz shaft
Depth, m		1,290	1,050	950	950	1,075
R_c roof, MPa	Penetrometer	38.1	40.5	27.8	23.3	51.0
	Laboratory	67.9	70.2	52.9	56.2	50.7
RQD, %		6.6	43.7	14.6	13.7	85.4
Number of strata in roof		13	12	9	3	6
Number of fractures in roof		36	27	7	10	2
Range of crack zone, m		6.5	8	0.7	4.7	1
Maximal force on dynamometers, kN		187	222	299	120	0
Maximal tensile force in instrumented rock bolt, kN		277	281	150	255	229
Maximal dislocation of extensometer anchors, mm		–	60	72	–	1.6
Change of principal stresses, MPa		–	0.8	0.61	1.44	0.44
Change in height and width of yielding	h	–	0.01	0.46	0.27	–
support arches in relation to nominal dimensions, m	w	0.84	0.13	0.22	0.06	–

Parameters	Variant
	I	II	III	IV
HHkr$\frac{H}{{{H}_{kr}}}$	<1	≥1	<1	≥1
W_L – n	>0	>0	≤0	≤0
Final result	Possible insignificant loading and deformation of yielding arch support	Possible significant loading of roof bolting support	Possible significant loading and deformation of yielding arch support	Possible significant loading and deformation of yielding arch support and loading of roof bolting support