Lassonde Mineral Engineering -...

M1N565S - Design and Support of Underground Mine Excavations

UNIVERSITY OF TORONTO FACULTY OF APPLIED SCIENCE & ENGINEERING

Lassonde Mineral Engineering

M1N565S Design and Support of Underground Mine Excavations

M1N565S Winter 2017

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

Wed, April 20, 2017 Pierre Lassonde Chair in Mining Engineering

2.00 - 4:30 PM AM

GB-405

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 is 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


Question 1: (30 points)

You have been assigned to review the pre-feasibility study for the "Raiders of the Lost Gold" Mine. The orebody strikes E-W and dips 800 to the north. The entire thickness of the orebody (24 m measured horizontally) is to be mined.

The following recommendations were obtained from the preliminary stope design.

Stope height: 30 m Stope length: 21 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 "XYZ Consultants".

BACK HANGING-WALL

Rock Mass Classification Mm Typical Max Mm Typical Max

ROD 58 65 72 45 50 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) 140/1800

500/1650 850/0000

Compressive strength (MPa) 100 ± 30 150 ± 20

Major principal stress (MPa) 100 15

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

im

KI

50

i1i

BE

OF


Stable Zone -

/ Caved Zone

no 5 10 15 20 25 Hydraulic radius (m)


3

M!N565S - Design and Support of Underground Mine Excavations


On November 30, 2016 the "Aladdin Sane" mine in Northern Quebec reported a FOG associated with large seismic event: 21:44:14 Surface Sensor 2.2 Mn

Mining Info: Blasthole Stoping; Development Opening Type: Excavation drift; Opening Size: H = 5 m W = 8 m; Max Span Diameter: 10 m; Depth: approx. 1600 m.

Damage Info: Failure Conditions: 5 tonnes dislodged.

Geology: Rock type: Felsic Gneiss; Description of Rock mass: Irregular, fractured, slabbing. Structural Geology: unfavourable rock conditions; #2 Fault projected.

Ground Support: Resin rebar on back and walls (1.8 m length, 1.4 m x 1.4 m pattern); plates torn off. Bolts ok Mining Screen on back and walls (#7 4" x 4") failed. Two rebars had plates turn off, two push plates ripped off screen.

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

LL



The "D.B. Cooper" Mine in Oregon is operated by the Columbia River mining company. You have been given the mandate to determine the cause of a reported ground fall at the 600 m level on March 16, 2017. 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.

Conduct a back 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.

Note: Intact Rock: y = 28 kN/m3 cyc = 150 ± 15 MPa v = 0.30 E = 75000 ± 20000 MPa Dominant Joint Set: JRC =2; c = 1.2 kPa p = 300 Q (based on limited visual observations) = 12; RMR = 70 - 78 (1 foot is equal to 0.3048 m)

5



Provide a description of different forms of corrosion observed in underground mines in both atmospheric and aqueous conditions.

Provide a description of atmospheric corrosion and identify the controlling factors.

A high stress mine in Northern Ontario has a well designed and implemented micro seismic system. The seismic data are treated to provide a series of technical information that the mine uses to develop its mine seismicity management strategy.

Please discuss the significance of the constructed b value chart and any information that you can infer.

b = 1.5

E 10

I -2.5 -2.0 -1,5 -1,0 '0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0

Local Magnitude

Provide a summary of the basic components of shotcrete.

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

Propose a suitable ground support strategy for ground displaying extreme structural defined squeezing in a hard rock mine in the Canadian Shield. Explain and justify your rational.

6


Potentially Useful Information:

QRQDJ w

J, 'a 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.

I. 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 J ). For portals, use (2.0 x J,).

3. Joint Roughness Number Jr

a) Rock-wall contact. And h) rock-wall contact bejhre 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.

7


4. Joint Alteration Number (r I Ja

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 befire 10 cms 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. montrnorillonite (continuous, but < 5 mm 6-12 8-12 thick ). Values of Ja 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/cm2)

Jw

A Dry excavations or minor inflow, i.e. < 5 lit/mm. locally <1 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 ci,) Weakness zones intersecting excavation, which mciv 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)

10

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

50

B

3


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 /c9, O0/O SRF

H Low stress, near surface >200 <0.01

J Medium stress, favourable stress condition 200-10 0.01-0.3 1

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 Stabbing 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[ [10, reduce 0 to 0.5 0 where cy, =

unconfined compression strength, cT , and 23 are the major and minor principal stresses and co = 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 H).

c) Squeezing rock, plastic flow of incompetent rock under the injluence of high rock pressure

no/(Yc 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 H>300 Q"'- Rock mass compression strength can be estimated from q = 7 y 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 Jr1 classification is applied to the joint set or discontinuity that is least tavourable for stability born trorn the point of view of orientation and shear resistance (where t = (T,, tan' (Jr/Ja).

/14 1 .1 1/) .10 100 .100 1,000

Rook Moon Quality

Rook Mono Quality 22., Z-o J' J, Jo 500

'where 0 - Trrorrel Quality lndeo RQD - Bock Qoollig Dnoigrrolion

In - Jont 5r,l Nonthe, Jr = Joint Rhrrenr

Jo = Joint Alinrotion Jo - Joint Wote, Condition

SRF - Stress Reduction Factor

Reinforcement Categones

Uncopported 2. Spot Bolting 3 Syrtnnrotrc Boiling 4 Sonoric Boiling orrd Uornirriorceo 5hotcrnon, 4-10 cnn) 5 Fibnr-Re,nlorcnd Shorororo and Bolting, 5-9 or,, S Fiber-Reinforced Shotcrnto and Boiling, 9-12 ott 7 Frber'Rernforced Shotcrnto rod Boiling, 12-15 3 Fber-Reirrforced Slrotcrnte >15

Rnrrrlorced Rib. of Shotorere and Bolting 9. Coot Concr,,te lining

LKI

0.

0

31

ff


0 5 10 15

Ratio ouniaxial strength to induced stress al

Difference in strike

or 1 1 1 1 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

10

6 0 U

h 5 4

ws

2

11

7

I


Failing

\ stope surface

Slabbing

10 20 30 40 50 60 70 80 90

Inclination of critical joint

10 20 30 40 50 60 70 80 90

Inclination of stape surface a

11

0.40

51 0,35

- 0.30

005


1 2 3 4

(RQD/Jn)

Hydraulic radius

5 6 7 8

Assumed lower

L boundary Loose for n arch

0.75 L zone

Ve

Assumed lower Loose boundary ZOM for natural arch

ifomed arch

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

L = 1.40 + 0.184w L = 1.60+ JO+0.00I2w2

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

diagram. L/s> 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 CO = excavation span L = bolt length T = applied tension to the bolt bearing capacity of bolt

12


H Wedge susceptible to slide along a discontinuity or along Wedge susceptible to fall under the effect of gravity the intersection of two discontinuities

W(f sin )6— cos /3 tan( o) - cA

B(cosa tamp +,f sin a)

R = cA + W cos /3 tan q

N= PV T

s < 3e w~!L+1.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 B = orientation of the sliding surface R = resistance to sliding e = joint spacing = excavation span s = spacing between bolts T = applied tension to the bolt L = bolt length B = load bearing capacity of the bolt

13


Minimum bolt density 085 0,70 0.65 0.55

with mesh (bolts/ml)

Minimum bolt density with reinforced 0,65 0.50 0.45 0.40 shotcrete (bolts/m2)

Reinforced shotcrete 100 n irn, 75 mm 50 mm thickness

Walt support coverage fo floor Mid-drift Shoulder

0.01 0.04 0.1 0.2 0.4 1 4 10 40 100

Rock mass quah ROD

quality Q=(---) x (r J. j-) x (-)

14


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

VtciI Stt.is I0 0 113 20 30 40 0 0 10W

0 10 20 30 40 40MPg 13-

16

- -

0-

2cl13 l

4130 086 Mtht MPm

l0O

1003-

120 120G

- \ N

\ \ \ \ \ \ \

\ \

2G0

M*mrn, 143, laf

0zO 22 40 P P 80 0 10 30 4 0 60 40 60 WS

x04 8

8

333

I-

0,0422 4hn I2 0141,013348 101m

4CC

94 1 - 1404

34 -

9 8

4 4 8 N00-

Q\ \ MOO 4

'4840 \, 44 44

119t I4804'

15


Expansion shell 20 mm in charecter

000

z -4

20))

I

55 mm. 16o kN)

41)0

Epamion shell 20 m

a diamtcr (1)

z 1110mm. 217 kN)

O r 1)' I) 00 50 4)4 0 50 100 10 20(1

Dkplaccnient (mm) Shear d00accmcnt (mm)

(2) 0

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.

400 Cement rebar 21) mm _______________ 41)1) Cement rchar 20 mm

in diameter

— II • I

in diameter

I t F

:7

z

f

\ 140 mm 20

:

t4 mm 199 kN)

U icj io 200

D:splaccment imm) Shear dftspiacemcnt Initial

al hI

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

-:Spl

it set ht

E

Split set he It SS46

SS46 Eqi] 200 ? 20(1

58 mm. 160 kN)

IX) CO 5I kN

ISO 100 1) 51) 00 50 100

DispLacement (mm) Shcar displacement 1m111 I

hl

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

16


100 1mntiata tt

II I -Iou

Inflatable bolt 38mm

EU 100

t59mm. 179 k N )

0 1) 50 I 00 150 200 o 54) 1)1) 150

Displaccmcnt minI Shear dop1accment (mmI

(a)

Load displacement behaviour of a 38-mm inflatable bolt under pull and shear loads.

4141) ________________________

fwtn strand cable 400 Twin st ca and ble

2x12.7 mm tndmmetcr L II I 2 I27 mm in diameter

t oo

3 Z Il34 mm, 233kN)

-00

11-10 100

0 -0 1110 1-0 790 1 I) lit) LAO

LSlaccmcnt tram) shear dispiacementi nimi

Load displacement behaviour of a twin strand cable under pull and shear loads.

oo 100

20)

7 mmx

M-10 - 200

) !FD-Bolt 022-1

: 1) Bolt section: 22 mm 1500mm

50 liii) 151O 200 250 I) 50 01) 150 200 250

Displacement lmm Displacement (mm

D-Bolt and test results of a bolt section of 22 mm x 1 .5 m: a) static pull test results of rock bolts, and (b) dynamic test result.

17

:00


1000

100

1.0

0.1

Stable Zone --

__________

Caved Zone

101 5 10 15 20 25 Hydraulic radius (m)

10


'



On November 30, 2016 the "Aladdin Sane" mine in Northern Quebec reported a FOG associated with large seismic event: 21:44:14 Surface Sensor 2.2 Mn

Mining Info: Blasthole Stoping; Development Opening Type: Excavation drift; Opening Size: H = 5 m W = 8 m; Max Span Diameter: 10 m; Depth: approx. 1600 m.

Damage Info: Failure Conditions: 5 tonnes dislodged.

Geology: Rock type: Felsic Gneiss; Description of Rock mass: Irregular, fractured, slabbing. Structural Geology: unfavourable rock conditions; #2 Fault projected.

Ground Support: Resin rebar on back and walls (1.8 m length, 1.4 m x 1.4 m pattern); plates torn off. Bolts ok Mining Screen on back and walls (#7 4" x 4") failed. Two rebars had plates turn off, two push plates ripped off screen.

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.

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