MINE DESIGN WORK REPORT No. 2

8/7/2019 MINE DESIGN WORK REPORT No. 2

1/15


2/15

MN 415 MINE DESIGN: SURFACE MINE DESIGNMT.ELIBARRI GOLD DEPOSIT GEOTECHNICAL MODELLING

2.5. Laboratory rock analysis and results

Summary of Rock strength lab analysis was conducted by Douglas and PartnersConsulting Company (DPCC) as outlined below.

2.5.1. Rock mass strength

Table 1: Defect friction angleConsultant Lithology Defect Friction angle ()

Peak ResidualLower Lower

DPCC Metasediments

Shist/joint 31 24

DPCC Granodiorite Joints 34 25DPCC Faults Shear 17.5 5.5

Table 2: Uniaxial Compresive StrengthLithology UCS range

(MPa)UCS mean(MPa)

STD (MPa) Classification

Metasediments

15 77.5 43.7 29.4 High

Granodiorite 29 109.6 63.7 32 High

Table 3: Rock mass StrengthRock mass zone UCS Test

(MPa)

Cohesion

(kPa)

Friction

angleLower bound weatheredmetasediments

3 52 24

Mean weathered metasediments 6 95 31Lower bound Fresh Metasediments 17.5 230 37Fresh mean metasediments 30 430 41Lower bound granodiorite 20 360 55Mean granodiorite 40 690 60Fault zones 29 23

Table 4: Rock Quality Designation (RQD)Lithology Range (%) Mean (%) Rock Quality

Metasediments 20 - 60 30 PoorGranodiorite 30 - 70 50 Poor/Fair

Granodiorite fault 0 - 20 10 Very poor

2.6. Summary of Rock mass

i. Weathered metasediments are typically high to moderately weathered,low strength and poor quality

ii. Weathered granodiorite is typically high to moderately weathered, verylow strength and poor quality.

iii. Fresh metasediments are typically high strength and poor to fair quality


3/15


iv. Fresh upper granodiorite is typically high strength and poor to fair quality

v. Fresh lower granodiorite is typically high strength and fair quality

vi. Fault zones are typically highly weathered, extremely low strength andvery poor quality

3.0. GEOTECHNICAL MODELLING

The geotechnical modelling of the Elibarri Gold deposit that was carried out is outlinedin steps as followed;

3.1. STEP 1: PROJECTION OF X- SECTIONS ON TO PLAN VIEW.

There are 7 X-sections all together taken from the first assignment and we used thesesections to project the sectional view of the ore deposits of H-zone and K- zonerespectively on to their Plan view as shown in appendix A . For the 7 sections refer to

Appendix B . Also Longitudinal sections X-X and Y-Y are used (See Appendix C )Method used to project the sections is the Coordinate System to transfer the outlineof the sectional view of the ore deposits on to the plan view. This is done by taking theupper bound coordinate and lower bound coordinate of the ore deposit of both H-zoneand K-zone and plotting these points of coordinates with respect to the coordinates of the plan view. Then these points were connected forming the outline of the deposit onplan view.

The possible pit outline as drawn on plan view was just an assumed outline drawnfollowing the shape of the outline of the ore deposits.

3.2. STEP 2: PROJECTION OF GEOLOGICAL STRUCTURES ONTO PLANVIEW.

The projecting of geological structures on to the plan view was done in a similarmanner as with the X-Sections. So the method used is again the Coordinate System.

The structures projected are mainly the faults namely; Cross-faults A & B strikingNortheast and dipping Northwest at 60 o angle and H-Fault, Upper K-fault and Lower K-Fault all three striking Northwest and dipping Northeast with dip angles of 37 o, 52 o, and54 o respectively. Refer to plan view appendix A .

3.3. STEP 3: DIVIDING THE ORE DEPOSIT ON PLAN VIEW INTODIFFERENT SECTORS.

The division of the two distinct ore deposits the H-zone and K-zone was done based onthe following criteria;

i. Altitude- (location of ore deposit at depth with respect to surface topography),that is from the X-Sections it can be seen that H-zone is located at loweraltitude and K-zone at higher altitude.

ii. Geology of the deposits

iii. Structural orientation (dip direction and angle) with respect to the Pit slopeorientation.

iv. Possible mining sequence.


4/15


The deposit was divided into 4 sectors namely ; GK, JT, GT and AB . From the abovecriteria GK and AB are located at lower altitude with mainly granodiorite as thedominant and persistent rock type in H-zone and JT and GT are located at high altitudewith two distinct geology, the metasediments and granodiorite are assumed to bepersistent throughout the K-zone deposit. See Appendix A .

Within these 4 sectors the analysis of pit slope design identified two directions of pitslope as per the 4 sectors with respect to the orientation of the fault structures.Stability analysis carried out will based on these pit slopes.

In GK the two pit slopes are; Lihir slope and Ok Tedi slope

In JT the two pit slopes are; Wafi golpu slope and Pogera slope

In GT the two pit slopes are; Mt. Kare slope and Misima slope

In AB the two slopes are; Ramu slope and Yandera slope

3.4. STEP 4: STEREONET PROJECTION OF THE FAULT STRUCTURES.

Basically stereonet projection of structures is done to identify potential failures andmodes of failure such as plane, wedge etc within a pit slope triggered by the presenceof geological structures for slope stability analysis. Stereonet is important as complexgeological information of structures like discontinuities can be represented easily andinterpreted and understood easily when carrying out stability analysis.

In plotting the fault structures the main parameters to consider and used are; dipdirection and dip angle of the structures and the pit slopes. The main instrument used

is the stereonet.Simply the general procedure in plotting stereonet graphs are as follows;

i. Trace the Stereonet graph on a tracing paper or other suitable paper

ii. Then place the traced stereonet graph on to the original graph. Make sure alignthe directions on the graph properly with 0 o to 360 o on the traced graph with theoriginal graph.

iii. Marked the dip direction given eg, 315 o/60 o on the direction given on thecircumference of the graph and rotate it to align that 315 o with the west to east line(270 o-90 o). (Note if the dip direction is on the left part of the stereonet graph alwaysrotate it to 270 o and if on the right side of the graph always rotate it to 90 o).

iv. Then on that W-E line count 60 o to the centre of the stereonet graph and draw anarc or curve line joining the north to south line as drawn already on the stereonetgraph.

v. Finally rotate the graph back to its original position on the stereonet graphaligning with 360 o-180 o line.


5/15


Figure 1: A stereonet graph

The possible optimum pit slope angle selected for each of our 4 sectors is based on;

the angle and dip direction of the fault structures

the rock mass strength with respect to the friction angle.

That is, for sector GK and AB the pit slope angles are 54 o and 45 o respectively wasselected based on the friction angle of mean weathered metasediments (31 o), meangranodiorite (60 o) and lower bound granodiorite (55 o) since the dominant rock in H-zoneis granodiorite assuming the stability considering rock mass strength will be influencedby the strength properities of granodirite but little influenced by oxidizedmetasediments, and adjusting the angle to a suitable optimum one considering thefaults orientation with respect to pit slope orientation.

For sector JT and GT their pit slope angle are 48o

and 45o

respectively was selectedbased on two friction angle of 41 o for Fresh mean metasediments and 60 o for Meangranodiorite. Since in K-zone the deposit is situated in two rock types, and assumingthey are persistent through the entire deposit and the stability of slope will beinfluenced by the strength properties of the two rocks and adjusting the angle to asuitable pit slope angle by taking an overall pit slope angle of the two friction angles.

The dip directions of each pit slopes of the 4 sectors are taken with respect to thedirection in which the pit is to be designed or cut . See Appendix D.

Selection of possible optimum pit slope From the X-sections

Sector GK- section F-F,

Sector JT- section A-A


6/15


Sector GT- section G-G

Sector AB section E-E


7/15



8/15


3.5. STEP 5: SLOPE STABILITY ANALYSIS

Stability analysis will be done as per the pit slopes within each sectors of the deposit.As the deposit is composed basically of rock geology the likely type of failure modesthat are associated with the rock geology is planar failure and wedge failure. The mainmethods used here to conduct slope stability analysis are;

i. Conventional methods; which involve stereonet plotting and Kinematic approach

ii. Numerical methods; which involve Limit Equilibrium methods of calculatingfactor of safety for Plane, wedge or circular failures.

Figure 2: (a) Criteria for Plane failure to occur (b) Criteria for Wedge failure to occur

That is conditions for plane failure in (a) are;

a. Dip direction of plane = dip direction of slope face 20 o

b. Dip angle of plane < dip angle of slope face

c. Dip angle of plane > friction angle of plane

The conditions of Wedge failure in (b) are;

a. Azimuth /dip direction of intersection = dip direction of slope face (to daylightslope face)

b. Plunge/dip of intersection < dip of slope face

c. Friction angle < plunge/dip of slope face.

d. Inequality; friction angle< plunge angle< slope face angle

3.5.1. SECTOR GK

3.5.1.1. Geological information


9/15


(Note; section F-F and longitudinal section Y-Y was used to obtained the information)

Sector GK covers the northern part of the H-zone of the deposit. There is basically twotype geology evident in that sector; the upper geology is composed of oxidizedmetasediments and granodiorite dominate the lower part but is composed of both freshwhere no fault is intersected and faulted where faults are intersected.

Table 5: Summarized dataGeology/Rockmass zone

Extent/Depth

Groundwater

Weathering

Meanfrictionangl

e,

RockQuality

Strength

Oxidizedweatheredmetasediments

0-110m Yes (within30m-70m)

Yes 31 Poor Low

Freshgranodiorite

110m-190m

No No 60 Fair High

Weathered,faultedgranodiorite

190m-480m

No Yes(high)

55 Poor Low

Freshgranodiorite

480m-1110m

No No 60 Fair High

3.5.1.2. Slope Stability Analysis

3.5.1.2.1. Lihir slope

The main fault observed is Cross-fault B striking NE and dipping NW at 60 o. By plottingthe stereonet graph, there were no potential failure modes identified in that slope sincethe fault will dip into the slope as it dips in opposite direction. Therefore the slope isSTABLE .

3.5.1.2.2. Ok Tedi slope

The types of faults present are; Cross-fault B striking NE and dipping NW at 60o

andLower and Upper K-Faults striking NW and dipping NE at 52 o and 54 o respectively.Stability analysis carried out using stereonet identified no potential failure modes. Thuscross-fault B will dip into the slope face and the two K-faults will dip at approximately90 o to the slope face and into the rock mass. Thus generally the slope is STABLE.

3.5.1.3. Recomendation

Generally Sector GK is STABLE.


10/15


3.5.2. SECTOR JT


(Note; section A-A and longitudinal section X-X was used to obtained the information)

Covers the northern part of the K-zone ore deposit with two basic geology namely;metasediments (oxidized, weathered and faulted) and Granodiorite (fresh andweathered due to K-Faults).

Table 6: Summarized dataGeology/Rock masszone

Extent/Depth

Groundwater

Weathering

Meanfrictionangle,

RockQuality

Strength


0-100m Yes(within30m-70m)

Yes 31 Very poor Low

Freshmetasediments

100m-500m

No No 41 Poor Moderate

Freshgranodiorite

500m-780m

No No 60 Fair High

Weatheredgranodiorite

780m-1110m

No Yes (fairlyhigh)

55 poor Low


3.5.2.2.1. Wafi golfu slope

The main fault observed is Cross-fault B striking NE and dipping NW at 60 o. By plottingthe stereonet graph, there was no potential failure modes identified as the fault dips inopposite direction at an angle to the slope face. Therefore the slope is STABLE.

3.5.2.2.2. Pogera slope

The main fault observed is Cross-fault A striking NE and dipping NW at 60 o. By plottingthe stereonet graph, there was no potential failure modes identified as the fault dips inopposite direction at an angle to the slope face. Therefore the slope is STABLE.


11/15


3.5.2.3. Recommendation

Generally Sector JT is STABLE.

3.5.3.SECTOR GT


(Note; section G-G and longitudinal section X-X was used to obtained the information)

Covers the southern part of the K-zone ore deposit with two basic geology namely;metasediments (oxidized, weathered and faulted) and Granodiorite (fresh andweathered due to K-Faults)


Extent/Depth

Groundwater

Weathering

Meanfrictionangle,

RockQuality

Strength



Yes 31 Poor Low

Freshmetasediments

100m-520m

No No 41 Poor High

Freshgranodiorite

520m-590m

No No 60 Fair High

Weatheredgranodiorite

590m-1110m

No No 55 poor High


3.5.3.2.1. Mt. Kare slope

The main fault observed is Cross-fault A striking NE and dipping NW at 60 o. By plottingthe stereonet graph, there was a potential Plane failure mode identified. However, thefailure will not take place since the criteria and condition for the failure mode notsatisfied or met. The cross-fault dips in the same direction as the slope face but;

Dip angle of fault > dip angle of slope face; hence, fault is located inside theslope faceDip angle of fault > friction angle of slope face; hence, fault is located inside thefriction circle(Note: slope dip direction=315 o and dip angle = 45 o)


12/15


Thus, the slope is stable but since one condition is met, the dip direction, stabilitystrategies are established for future analysis if any conditions are met such as;

Monitoring of ground movement and ground water condition

3.5.3.2.2. Misima slope The main fault observed are Cross-fault A striking NE and dipping NW at 60 o and Lowerand Upper K-Faults striking NW and dipping NE at 52 o and 54 o respectively. By plottingthe stereonet graph, there was a potential failure mode identified as Wedge failure( intersection where sliding will occur has dip direction=010 o and dip angle =45 o).

However, probability of failure to occur is very low and failure will not occur since thecriteria and conditions for failure are not met. That is;

Azimuth dip dip direction of the slope facePlunge of intersection > dip of slope face, hence it is located inside the greatcircle of slopePlunge of intersection > friction angle, hence it is located inside the friction circleFriction angle> plunge of intersection > slope face angle(Note: slope dip direction=335 o and dip angle = 45 o)

Therefore the slope is stable .

3.5.3.3. Recomendation

Generally from the slope stability analysis carried out for the two slopes Mt. Kare andMisima it is concluded that sector GT is STABLE.

3.5.4.SECTOR AB


(Note; section E-E and longitudinal section Y-Y was used to obtained the information)

Covers the southern part of the H-zone ore deposit with two basic geology namely;metasediments (oxidized, weathered) and Granodiorite.


Extent/Depth

Groundwater

Weathering

Meanfrictionangle,

RockQuality

Strength

Oxidizedmetasediments


Yes(30m-70m)

31 Poor Low

Freshgranodiorite

with orebody

190m-420m

No No 60 Fair High


13/15


enclosedWeatheredgranodiorite

220m-410m

No Yes(highly)

55 poor Low


3.5.4.2.1. Ramu slope

The main fault observed are Cross-fault B striking NE and dipping NW at 60 o and H-Fault, Lower and Upper K-Faults striking NW and dipping NE at 37 o, 52 o and 54 orespectively. By plotting the stereonet graph, there was a potential failure modeidentified and the failure mode is a Wedge failure and Plane failure. There are twopossible intersection where sliding may take place identified ( refer to Appendix D,sector AB)

i. Intersection 1; dip direction= 008 o and dip angle = 35 oii. Intersection 2; dip direction= 024 o and dip angle = 47 o

However, probability of wedge failure to occur is very low and failure will not occursince the criteria and conditions for failure are not met. That is;

Azimuth dip dip direction of the slope facePlunge of intersection > dip of slope face, hence it is located inside the greatcircle of slopePlunge of intersection > friction angle, hence it is located inside the friction circleFriction angle> plunge of intersection > slope face angle

However, plane failure will occur since;Dip angle of H- fault < dip angle of slope face; hence, fault is located outsidethe slope face

Dip angle of H- fault < friction angle of slope face; hence, fault is located insidethe friction circleDip direction of H-Fault = dip direction of slope face(Note: slope dip direction=065 o and dip angle = 45 o)

Therefore the slope is stable for wedge but unstable for Plane failure . To be moreconfidence if it will fail or not the factor of safety for plane failure is calculated tobe = 2.6

3.5.4.2.2. Yandera slope

The main fault observed are Cross-fault A striking NE and dipping NW at 60 o and Lowerand Upper K-Faults striking NW and dipping NE at 52 o and 54 o respectively. By plottingthe stereonet graph, there was a potential failure mode identified and the failure modeis a Wedge failure and Plane failure. There are two possible intersection wheresliding may take place identified ( refer to Appendix I, sector AB)

iii. Intersection 1; dip direction= 008 o and dip angle = 35 oiv. Intersection 2; dip direction= 024 o and dip angle = 47 o

However, probability of wedge failure to occur is very low and failure will not occursince the criteria and conditions for failure are not met. That is;

Azimuth dip dip direction of the slope face


14/15


Plunge of intersection > dip of slope face, hence it is located inside the greatcircle of slopePlunge of intersection > friction angle, hence it is located inside the friction circleFriction angle> plunge of intersection > slope face angle

However, probability of plane failure to occur is high since;Dip angle of H- fault < dip angle of slope face; hence, fault is located outsidethe slope faceDip angle of H- fault < friction angle of slope face; hence, fault is located insidethe friction circleDip direction of H-Fault = dip direction of slope face(Note: slope dip direction=315 o and dip angle = 45 o)

Therefore the slope is stable for wedge but unstable for Plane failure. So to be moreconfidence if it will fail or not the factor of safety of plane failure is calculated to be =2.6

Therefore since FOS = 2.6 > 1 (standard FOS =2.5) slope Yandera and Ramu are safe.

But for future stability of the two slopes to experience Plane failure if triggered bymining activities or nature like earthquake and for safety purposes stability monitoringstrategies are establish such as;

Monitoring of ground movement and ground water conditionUsing supports like rock bolts and other slope stability methods to stabilize theslope.

CALCULATION OF FACTOR OF SAFETY FOR PLANE FAILURE FOR RAMU SLOPEAND YANDRA SLOPE

FOS = Resisting force/ Sliding force = c.A + W Cos . tan/ W Sin

Area 1 = ABCE = 100m x 300m = 30000m 2


15/15


Area 2 = CED= bh/2 = 300x300/2 = 45000m 2

Total area = A1 +A2 = 45000 + 30000 = 75 000m 2

Area 3 = FBD = bh/2 = 400x300/2 = 60000m 2

Area of sliding block = 75000-60000 = 15000m 2

Volume of sliding block = 15000m 2 x 1m = 15000m 2

Weight of sliding block = 15000m 2 x 26.98kN/m 3 = 404700kN

FOS = Resisting force/ Sliding force = c.A + W Cos . tan/ W Sin

= [(960kPa x15000m 2) +( 404700 x Cos 45 o x tan 55 o)] /(404700 x Sin 45 o)= 2.6

Documents

MINE DESIGN WORK REPORT No. 2