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M1N565S - Design and Support of Underground Mine Excavations

J UNIVERSITY OF TORONTO FACULTY OF APPLIED SCIENCE & ENGINEERING

Lassonde Mineral Engineering

M1N565S Design and Support of Underground Mine Excavations

M1N5655 Winter 2018

Final Exam: John Hadjigeorgiou Ph.D., P.Eng., ing., FCIM, ICD.D

Tuesday, April 17, 2018 Pierre Lassonde Chair in Mining Engineering

6.30 - 9:00 PM

Please answer all questions on the exam sheet provided. If required, you can use the back pages for additional space.

Note the presence of potentially useful reference information at the end of this document.

Colour images of the Fall of Ground (FOG) of question 2, and a copy of the stability graph are attached at the end of this document. Please submit with your examination booklet.

Question 1 /30 Question 2 /15 Question 3 /25 Question 4 /30 Total 100

Student Name: Student No:

1

M1N565S -Design and Support of Underground Mine Excavations

Question 1: (30 points)

You have been assigned to review the pre-feasibility study for the "Blues Brothers" Mine. The orebody strikes N-S and dips 850 to the east. The entire thickness of the orebody (25 m measured horizontally) is to be mined.

The following recommendations were obtained from the preliminary stope design.

Stope height: 35 m Stope length: 25 m

The preliminary mine design did not allow for cable-bolting of the hanging-wall.

You have access to the following information from the report prepared by "Belushi & Aykroyd Mining Consultants".

BACK HANGING-WALL

Rock Mass Classification Min Typical I Max Min Typical I Max

RQD 52 70 72 48 54 80

Jn Two joint sets + random Three joint sets

Jr Critical set is undulating and smooth

Critical set is planar and rough

Ja Minor surface staining Slightly altered joint walls

Critical joint set(s)

(dip/dip direction) 150/1800 60°/I 65°

850/0000

Compressive strength (MPa) 120 ± 30 130 ± 20

Major principal stress (MPa) 100 135

Assess the stability of the flat back and the hanging wall of the stopes. If you think appropriate, revise the proposed design, suggest alternate stope dimensions that will result in stable conditions and maximize the mine's annual ore production.

If you think applicable, propose a preliminary cable bolt pattern for the stope back. Justify your assumptions and recommendations.

Clearly state the limitations associated with your analysis.

Submit all calculations and design charts for further review.

2

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On March 11 2017 the "Big Lebowski" mine in Northern Ontario reported a FOG following a development round blast and a stope blast.

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Mining Info: Blasthole Stoping; Development Opening Type: Excavation drift; Opening Size: H = 5 m W = 4.6 m; Max Span Diameter: 5.6 m; Depth: approx. 1800 m.

Damage Info: Failure Conditions: 2.6 tonnes dislodged in first blowout, 1.5 tonnes dislodged in second.

3


Microseismic System: Reported a series of events 2:49:10 Surface Sensor 0.7 Mn 4:01:49 Surface Sensor 0.3 Mn 4:02:15 Surface Sensor 2.0 Mn 4.02:34 Surface Sensor 1.1 Mn

Geology: Rock type: Felsic Gneiss; Description of Rock mass: fractured Structural geology fault and unfavourable rock mass conditions. Joint/Fault: Close to #3 fault projection, close to #3 fault projection, close to waste rock.

Ground Support: Resin rebar on back and walls (1.8 and 2.4 m length, 1.2 m x 1.2 m pattern); Mining Screen on back and walls (#7 4" x 4"); straps.

Desribe all your actions from the moment you have been advised of the FOG. Prepare an immediate follow up action plan for this drift.

Propose a potentially more appropriate ground support strategy for similar ground conditions and excavation size.

Justify your reccomendations.

4

BOLT 13



You have been retained by he "Butch Cassidy and the Sundance Kidd Mine" in Utah to investigate the cause of a reported ground fall at the 800 m level on February 41h 2018. Following a site visit the ground control engineer drew the following sketch where she superimposed the observed failure pattern on the ground control standard for this location. Drift dimensions are drawn to scale.

/

iu.i 5 ,JóT L\7/ XL 70• '00'- \ 90' 80*

0.

. LJO

All. LT SPACING Lim X Lim

/\_1l

SCREEN 2CM FRill XLT 1

F%.00R l}I 10Th 2.00 __________ ______

VALLS 1.00 1LTS 1.0K FRil FLIXR

This was accompanied by the following information:

The mining crew installed #6 rebar (19.5 mm) 1.5 m long in the sidewalls and 1.8 m long in the back. Surface support was composed of galvanised weld mesh screen 2.7 m x 1.5 m. The ground support standard for this haulage drive did not require the installation of bolt 4 and 10. In this case, these bolts were not installed.

The GCMP indicated the following ground conditions for the zone in which the FOG occurred: Intact Rock: y = 34 kN/m3 cyc = 150 ± 15 MPa v = 0.30 E = 75 000 ± 20 000 MPa Q (based on core logging) = 12; RMR (Based on visual observations = 65).

5


Based on limited laboratory testing during the feasibility study joints were characterised by c = 1.2 kPa and p = 300 kPa. The ground control engineer suggested that the JRC of the observed joints was between 2 and 4.

Conduct aback analysis in order to determine the success and appropriateness of the installed system. Propose an interpretation for the cause(s) of this failure. Prepare and propose any remedial measures that would contribute to avoiding such problems in the future.

Please state clearly any assumptions that you make and justify your analysis and methodology while acknowledging the limitations of your analysis.

6



a) A new mine in the Northwest Territories is investigating the use of wet-mix shotcrete. Discuss the advantages and limitations of wet-mix as opposed to dry-mix shotcrete.

b) Provide a description of aqueous corrosion and identify the controlling factors in an underground metal mine. How will this affect the longevity of ground support?

c) Provide a description of the following: P and Swaves. Magnitude-Time History analysis Frequency—Magnitude Relation of Events (b Value)

d) Discuss the performance under static and dynamic loads of an energy absorbing bolt. Provide two distinct applications where the use of energy absorbing bolts may be warranted. Provide appropriate examples.

e) Discuss the potential advantages of using different types of fiber-reinforced shotcrete.

f) Provide a description, of the various continuum numerical methods and summarize their applicability and limitations as mine design tools.

7


Potentially Useful Information:

Q RQD Jr Jw

J,, J. SRF

Type of excavation ESR A Temporary mine openings etc 3-5 B Vertical shafts: (i) circular section 2.5

(ii) rectangular/square section 2.0 C Permanent mine openings, water tunnels for hydro power (exclude high pressure 1.6

penstocks), pilot tunnels, drifts and headings for large excavations etc. D Storage rooms, water treatment plants, minor road and railway tunnels, surge chambers, 1.3

access tunnels, etc. (cylindrical caverns?)

E Power stations, major road and railway tunnels, civil defence chambers, portals, 1.0 intersections etc.

F Underground nuclear power stations, railway stations, sports and public facilities, 0.8 factories etc.

1. Rock Quality Designation RQD A Very poor 0-25 B Poor 25-50 C Fair 50-75 D Good 75-90 E Excellent 90-100 Note: Where ROD is reported or measured as * 10 (including 0), a nominal value of 10 is used to evaluate Q. RQD intervals of 5, i.e. 100, 95, 90, etc. are sufficiently accurate.

2. Joint Set Number J,, A Massive no or few joints 0.5-1.0 B One joint set 2 C One joint set plus random joints 3 D Two joint sets 4 E Two joint sets plus random joints 6 F Three joint sets plus random joints 9 G Three joint sets plus random joints 12 H Four or more joint sets, random, heavily jointed, 'sugar cube', etc. 15 J Crushed rock, earthlike 20 Note: For intersections, use (3.0 x Jo). For portals, use (2.0 x Jo).

3. Joint Roughness Number Jr

a) Rock-wall contact. And b) rock-wall contact before 10 cm shear A Discontinuous joints 4 B Rough or irregular, undulating 3 C Smooth, undulating 2 D Slickensided, undulating 1.5 E Rough or irregular, planar 1.5 F Smooth, planar 1.0 G Slickensided, planar 0.5 Note: Descriptions refer to small scale features and intermediate scale features, in that order. C) No rock wall contact when sheared H Zone containing clay minerals thick enough to prevent rock-wall contact 1.0 J Sandy, gravelly or crushed zone thick enough to prevent rock wall contact 1.0 Note: i) Add 1.0 if the mean spacing of the relevant joint set is greater than 3m. ii) Jr = 0.5 can be used for planar slickensided joints having lineations, provided the lineations are oriented for minimum strength.

M1N565S — Design and Support of Underground Mine Excavations

1 4. Joint Alteration Number a) Rock-wall contact (no mineral fillings, only coatings)

A Tightly healed. Hard. Non-softening, impermeable tilling. i.e. Quartz or - 0.75 epidote

B Unaltered joint walls, surface staining only 25-35 1.0 C Slightly altered joint walls non-softening mineral coatings, sandy 25-30 2.0

_______ particles, clay-free disintegrated rock. etc

D Silty-, or sandy-clay coatings, small clay-fraction (nonsoftening) 20-25 3.0 E Softening or low friction clay mineral coatings, i.e. kaolinite. mica. Also 8-16 4.0

chlorite, talc, gypsum and graphite etc., and small quantities of swelling clays. (Discontinuous coatings, 1-2mm or less in thickness)

b. Rock wall contact bejore 10 cins shear F Sandy particles, clay-free disintegrated rock. 25-30 4.0 G Strongly over-consolidated, nonsoftening clay mineral fillings 16-24 6.0

(continuous, < 5mm thick)

H Medium or low over-consolidation, softening, clay mineral fill., 12-16 8.0 (continuous, <5mm thick)

J Swelling clay fillings, i.e. montmorillonite (continuous, but < 5 nun 6-12 8-12 thick ). Values of J1 depend on percent of swelling clay-size particles, and access to water, etc.

c) No rock wall contact when sheared. KLM Zones or bands of disintegrated or crushed rock and clay (see G, H and J 6-24 6,8

for clay conditions) or 8-12

N Zones or bands of silty- or sandy clay, small clay fraction. (non- - 5.0

______ softening)

OPR Thick, continuous zones or bands of clay ( see G, H and J for clay 6-24 10, 13 or conditions) 13-20

5. Joint Water Reduction Factor Approx. water pres. (kg/ m2)

Jw

A Dry excavations or minor inflow, i.e. < 5 lit/mm. locally <I 1.0 B Medium inflow or pressure, occasional outwash ofjoint fillings 1-2.5 0.66 C Large inflow or high pressure in competent rock with unfilled

joints

2.5-10 0.50

D Large inflow or high pressure considerable outwash of fillings 2.5-10 0.33 E Exceptionally high inflow or pressure at blasting, decaying with

time

>10 0.2-0.1

F Exceptionally high inflow or pressure continuing without decay >10 0.1-05 Note: Factors C to F are crude estimates. Increase Jw if drainage measures are installed. Special problems caused by ice formation are not considered.

6. Stress Reduction Factor I SRF

(1) Weakness zones intersecting excavation, which may cause loosening of rock mass when tunnel is excavated.

A Multiple occurrences of weakness zones containing clay or chemically disintegrated rock, _very _loose _surrounding _rock _(any _depth)

tO

B Single weakness zones containing clay, or chemically disintegrated rock (excavation depth < 50m)

5

C Single weakness zones containing clay, or chemically disintegrated rock (excavation depth> 50m)

2.5

D Multiple shear zones in competent rock (clay free), loose surrounding rock (any depth) 7.5 E Single shear zones in competent rock (clay free), (depth of excavation < 50m) 5.0 F Single shear zones in competent rock (clay free), (depth of excavation> 50m) 2.5 G Loose open joints, heavily jointed or sugar cube'(any depth) 5.0

M!N565S — Design and Support of Underground Mine Excavations

Note: Reduce these values of SRF by 25 - 50% if the relevant shear zones only influence but do not intersect the excavation. b) Competent rock, rock stress problems o/ai 70/Oc SRF H Low stress, near surface >200 <0.01

J Medium stress, favourable stress condition 200-10 0.01-0.3 K High stress, very light structure. Usually

favourable to stability, may be unfavourable to wall stability

10-5 0.3<0.4 0.5-2

L Moderate slabbing after> 1 hour in massive rock 5-3 0.5-0.65. 5-50 M Slabbing and rock burst after a few minutes in

massive rock 3-2 0.65-1 50-200

N Heavy rock burst (strain burst) and immediate dynamic deformations in massive rocks

<2 >1 200-400

Note: For strongly anisotropic virgin stress field (if measured): when 5[ a ,/a, [10, reduce to 0.5a0 where ac =

unconfined compression strength, a, and are the major and minor principal stresses and ao = maximum tangential stress. Few case records available where depth of crown below surface is less than span width. Suggest SRF increase from 2.5 to 5 for such cases (see 1-I).

C) Squeezing rock, plastic flow of incompetent rock under the influence of high rock pressure

SRF

0 Mild squeezing rock pressure. 1-5 5-10 P Heavy squeezing rock pressure >5 10-20 Note: iv) Cases of squeezing rock may occur for depth i-i> ° Q' 3 Rock mass compression strength can be estimated from g 7 ' Q '' (MPa) where y = rock density in gm/cc d) Swelling rock: chemical swelling activity depending upon presence of water. R Mild swelling rock pressure 5-10 S Heavy swelling rock pressure 10-15

Note: Jr and J > classitication is applied to the joint set or discontinuity that is least tãvourable for stability both from the point of view of orientation and shear resistance (where r = cy,, tan' (Jr/Ja).

Rock Clasoes

C F £ 0 C B A

EceponoUy Exoerrrnly ,ry Veo Eoreooy

Poor Poor -oor

20

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1.5

_Q XJO

Rook Moss Q0>Jy --

QD Rook Moos Occolity 0- !2. .

w4r,r 0 - Tonnd Qoolty lod,.o ROD Ro>k 0oo1ity D,nigrrotion

in - joint Sot Nonrbor Jr = joint Rooghness

Jo - joint Alrerot,00 - joint Wot,, Cond ition

SRF - Stress Redontion Factor

Reinforcement Categories

Ijr,oppoc ted 2 Spot Bolting 3 Systnrrroro Rolting 4 S r sterrrooc Boning Iced Uoreiniorc,d Shorcoete. 4-10 cm)

Fiber-Reinforced Shctcrete and Roltmrrg, 5_2 cm 0. Fb,r'Remnforo,d Shotcrete and Roing, 9-12 cm 7 Fbom-Rermkn nod Skotcmeto and kotirrg, 2-15 co R. Fiber-Re,rmforced Skorcrete, >15 on.

Reinforced Ribs 0) Skotcrere and belting 0 Cost Connors, Imnmrmg

10


1.0

0.8

0.6

0.4

02

0 0 5 10 15

Ratio of uniaxial strength to induced stress

90' Difference in strike 1.0

0

.00 -

0.9 .- - 0

— .- •0• .

0.8 —

CQ / I-

/ c 0.7

/ 45•/

0.6 0• /

/ /

00

/ 0.4 30,.

/ 0.3 /

0 I-I /

/ 0.2

0.1

01 I I I I I I I I

0 10 20 30 40 50 60 70 80 90

Relative difference in dip between the critical joint and the slope surface

11


Falling

\ Slope surface

a

Slabbing

III 4 ! 11

0 10 20 30 40 50 60 70 90 90

Inclination of sropc surface a

8

7

6 .2. U

5

4

3

2

1

10 20 30 40 50 60 70 80 90

Inclination of critical Joint

12

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M!N565S - Design and Support of Underground Mine Excavations

0,40

0.35

0.30

NJ 0

0

C,) a.

0.05

1 2 3 4 5 6 7 8 (RQD/Jn)

Hydraulic radius

Moderately jointed rock Heavily jointed rock mass Use non tensioned bolts Use friction or tensioned rock bolts

L=I.40+O.184w L = 1.6O + l .O + O.0012 w2

Bolt lengths can be reduced based on the above In order for a compression zone to be developed:

diagram. LIs> 2 s < 3e 0.5B<T<0.8B Shotcrete and wire mesh reinforcement necessary

e = joint spacing B = load bearing capacity of bolt s = spacing between bolts (0 = excavation span L = bolt length T = applied tension to the bolt hearing capacity of bolt

13

M!N565S - Design and Support of Underground Mine Excavations

0)

Wedge susceptible to slide along a discontinuity or along Wedge susceptible to fall under the effect of gravity

the intersection of two discontinuities

N - W(f sin /' - cosfl tan ç) - cA

N =

B(cosa tan ço+fsina) T

s ~ 3e R=cA+Wcos/i tan çb co2!L+t.Om 2<f<5

N = number of bolts a. = angle between the plunge of the bolt and the

W = weight of the wedge normal to the sliding surface

f = safety factor c = cohesive strength of the sliding surface

A = surface area along the sliding plan = angle of friction of the sliding surface

13 = orientation of the sliding surface R = resistance to sliding

e = joint spacing (o = excavation span

s = spacing between bolts T = applied tension to the bolt

L = bolt length B = load bearing capacity of the bolt

14


Minimum bolt density 0,85 0.70 0

.

65 b.55 with mesh (bolts/m2)

Minimum bolt density with reinforced : 065 0.50 0.45 0.40 shotcrete (bolts/m2)

Reinforced shotcrete 100 mm: 75 mm 50 mm thickness

Wall support coverage . To floor Mid drift Shoulder

4- 0.01 0.04 0.1 0.2 0.4 1 4 10 40 100

Rock mass quality Q=(_D)

x () x sRF74

15

0'C0e I1Il"1I I

43 10 20 30 43 30 00 10 00 MPS

4


Pre-mining stresses at some hard rock mines in the Canadian Shield

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00 20 30 40 50 W

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0 0.0266 MPiJ,o ±0004

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16


400 Ecpaimim shell 20 mm in thameter

300 344)

200 3 200

155 mm, 160

1443

(000000

14)14

Epamicn be)42l) mm

Eqi]

_

n thameter

4 4 mm, 217 kNI

I) 4

0 54) I 00 I'1) 010 t) 1 0 150 24)0

I)4,bccment ImnIl Shear dispExment ImmI

dl 04

Load displacement behaviour of a mechanical bolt under pull and shear loads. The symbols "o" and "x" refer to failure in the plate and bolt shank, respectively.

Cementrchar2O mm Cement rcbar2() mm

4, in diameter I n diameter I I t I

304) 300

z

200 (47 mm, 199kN)

100 fl

(40 mm, 2O5L)

1410

1140 ISO

Displacemn (mml hcar dIsplacement mimI

al 1 110

Load displacement behaviour of a cement fully-grouted rebar under pull and shear loads.

-4K)

E

__

SpOtset bolt I I Sp1i1 et bolt

5546 _____________

3(X) 304)

Z.

200 200 41l mm, 6OkN)

=

443

I kN

Ii 1) 50 104) 5) .1X3 4 104) 150

Displacement (mm) 'hcar displacement (mm 4

a) 64

Load displacement behaviour of a Split set under pull and shear loads.

17

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Stable Zone - - - - - - - - -

Caved Zone

5 10 15 20 25 Hydraulic radius (m)

Student Name: Student No:

19



On March 11 2017 the Big Lebowski" mine in Northern Ontario reported a FOG following a development round blast and a stope blast.

1 - .•t * -

-

•-'

,. -..,

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Mining Info: Blasthole Stoping; Development Opening Type: Excavation drift; Opening Size: H = 5 m W = 4.6 m; Max Span Diameter: 5.6 m; Depth: approx. 1800 m.

Damage Info: Failure Conditions: 2.6 tonnes dislodged in first blowout, 1.5 tonnes dislodged in second.

3

lassonde mineral engineeringexams.skule.ca/exams/bulk/20181/min565s_2018_designand...please answer...

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