Report - SAHRIS | SAHRA & Rock...DELTA BEC | MINE ROCK ENGINEERING 6-6 6 GEOTECHNICAL AND ROCK...

Metallurgical Resources Consulting 5 Northumberland Avenue Centurion Midstream 1692

South Africa T +27 82 374 1553 +27 12 661 5421 E [email protected]

Report Pre-Feasibility Study (Volume 1) Mmakau Coal (Pty) Ltd

July 2017

Classification

Confidential

Pre-Feasibility Study Mmakau Coal (Pty) Ltd

DELTA BEC | GEOTECHNICAL AND ROCK ENGINEERING 6-ii

Executive Summary

Chapter 1 Introduction and Project Description

Chapter 2 Geology

Chapter 3 Mining

Chapter 4 Coal Characterization

Chapter 5 Coal Handling Preparation Plant

Chapter 6

Geotechnical and Rock Engineering Chapter 7 Stormwater Management Plan

Chapter 8 Infrastructure

Chapter 9 Discard Disposal

Chapter 10 Traffic Study

Chapter 11 Mine Water Balance

Chapter 12 Human Resources

Chapter 13 Capital Cost Estimate

Chapter 14 Operating Cost Estimate

Chapter 15 Project Implementation Plan

Chapter 16 Risk Assessment

Chapter 17 Economic Evaluation

Chapter 18 Conclusions and Recommendations

Chapter 19 Alternative Options


DELTA BEC | GEOTECHNICAL AND ROCK ENGINEERING 6-iii

Contents

6 GEOTECHNICAL AND ROCK ENGINEERING ................................................................................... 6-6 6.1 Geotechnical .............................................................................................................................. 6-6

6.1.1 Introduction ............................................................................................................ 6-6 6.1.2 Approach and Methodology ................................................................................... 6-6 6.1.3 Site Description...................................................................................................... 6-6 6.1.4 Available Information ............................................................................................. 6-6 6.1.5 Site Investigation ................................................................................................... 6-7 6.1.6 Test Pitting ............................................................................................................. 6-7

6.1.6.1 Rotary Core Drilling ................................................................................ 6-7 6.1.7 Geology, Climate and Seismic Risk ...................................................................... 6-7 6.1.8 Soil and Rock Profile ............................................................................................. 6-8

6.1.8.1 Transported Soil (Hillwash) .................................................................... 6-8 6.1.8.2 Residual Soil .......................................................................................... 6-9 6.1.8.3 Bedrock .................................................................................................. 6-9

6.1.9 Groundwater .......................................................................................................... 6-9 6.1.10 Laboratory Testing ................................................................................................. 6-9

6.1.10.1 Foundation Indicator Tests ..................................................................... 6-9 6.1.10.2 Compaction Characteristics Tests ....................................................... 6-10 6.1.10.3 Uniaxial Compressive Strength (UCS) Tests ....................................... 6-11

6.1.11 Geotechnical Considerations ............................................................................... 6-13 6.1.12 Recommendations ............................................................................................... 6-13

6.1.12.1 Founding of Structures ......................................................................... 6-13 6.1.12.2 Use of In-Situ Materials ........................................................................ 6-13 6.1.12.3 Excavatability ....................................................................................... 6-13 6.1.12.4 Slope Stability of Box Cut Excavation .................................................. 6-13 6.1.12.5 Soils Strength ....................................................................................... 6-14 6.1.12.6 Rock Mass Strength ............................................................................. 6-14 6.1.12.7 Slope Stability....................................................................................... 6-14

6.1.13 Conclusion, Interpretation of Results and Validity of Recommendations............ 6-15 6.2 Mine Rock Engineering ............................................................................................................ 6-16

6.2.1 Executive Summary ............................................................................................. 6-16 6.2.2 Introduction .......................................................................................................... 6-17 6.2.3 Information Provided ........................................................................................... 6-17 6.2.4 Geotechnical Investigation .................................................................................. 6-18

6.2.4.1 Investigation Area ................................................................................ 6-18 6.2.4.2 Borehole Positions ............................................................................... 6-20 6.2.4.3 Generalized Stratigraphy ..................................................................... 6-20 6.2.4.4 Surface Elevation ................................................................................. 6-21 6.2.4.5 Underground Access ............................................................................ 6-21 6.2.4.6 Identified Reserve Areas on the No. 2 and No. 4 Lower Seams ......... 6-22

6.2.5 Mining Technical .................................................................................................. 6-24 6.2.5.1 Contamination ...................................................................................... 6-24 6.2.5.2 Overburden and Mining Depth. ............................................................ 6-25 6.2.5.3 Roof Strata and Support. ..................................................................... 6-27 6.2.5.4 Structure ............................................................................................... 6-29 6.2.5.5 Bord Width ............................................................................................ 6-34 6.2.5.6 Pillar Design ......................................................................................... 6-34 6.2.5.7 Multi-Seam ........................................................................................... 6-40

6.2.6 Conclusions and Suggestions ............................................................................. 6-42 6.2.7 References .......................................................................................................... 6-43


DELTA BEC | GEOTECHNICAL AND ROCK ENGINEERING 6-iv

Tables

Table 6-1: Test Pit Summary .......................................................................................................................... 6-7

Table 6-2: Borehole Summary ........................................................................................................................ 6-7

Table 6-3: Foundation Indicator Test Results ................................................................................................ 6-9

Table 6-4: Compaction Test Results ............................................................................................................ 6-11

Table 6-5: UCS Test Results ........................................................................................................................ 6-12

Table 6-6: Typical UCS and Hardness Correlations. ................................................................................... 6-12

Table 6-7: Typical Effective Strength Properties of Soils ............................................................................. 6-14

Table 6-8: Derived Strength Properties of Soil Horizons .............................................................................. 6-14

Table 6-9: Typical Shear Strength Values of Rock Types ............................................................................ 6-14

Table 6-10: Design Slope Angles of Soil and Rock Horizons ...................................................................... 6-15

Table 6-11: Pillar Safety Factor and Size Calculations in the various mining areas. ................................... 6-39

Figures

Figure 6-1: Seismic Risk at the Site ............................................................................................................... 6-8

Figure 6-2: Slope Stability Model .................................................................................................................. 6-15

Figure 6-3: Schurvekop Project Area ........................................................................................................... 6-18

Figure 6-4: No. 4 Lower Seam, Theoretically Mineable Area....................................................................... 6-19

Figure 6-5: No. 2 Lower Seam, Theoretically Mineable Area....................................................................... 6-19

Figure 6-6: Boreholes Drilled in the Schurvekop Area and Surrounds. ....................................................... 6-20

Figure 6-7: Surface Elevations in the Schurvekop Project Area. ................................................................. 6-21

Figure 6-8: Position of the Boxcut and Surface Infrastructure at Schurvekop. ............................................ 6-22

Figure 6-9: No. 4 Lower Seam, Proposed Mining Layouts ........................................................................... 6-23

Figure 6-10: No. 2 Lower Seam, Proposed Mining Layouts......................................................................... 6-23

Figure 6-11: Thickness of the No. 4 Lower Seam’s Overburden. ................................................................ 6-25

Figure 6-12: Statistics for the Expected No. 4 Lower Seam's Overburden Thickness ................................. 6-25

Figure 6-13: Statistics indicating the expected No. 4 Lower Seam’s Overburden Thickness. ..................... 6-26

Figure 6-14: Statistics Indicating the Expected No. 2 Lower Seam’s Overburden Thickness. .................... 6-27

Figure 6-15: Statistics Indicating the Expected No. 2 Lower Seam’s Overburden Thickness. ................... 6-28

Figure 6-16: No. 2 Lower Seam Recommended Roof Support Design Principles. ..................................... 6-29

Figure 6-17: The Position of the Geological Structures on the No. 4 Lower Seam...................................... 6-30

Figure 6-18: The Position of the Geological Structures on the No. 2 Lower Seam ..................................... 6-30

Figure 6-19: Positions at which the D2 Dolerite Sill is Expected to Intersect the 4 Lower Seam (Blue) ...... 6-31

Figure 6-20: A Cross-Section Indicating the Position of the Dolerite Sill ..................................................... 6-32

Figure 6-21: Position of the D2 Dolerite Sill Relative to the No. 4 Lower Seam .......................................... 6-33

Figure 6-22: Position of the D2 Dolerite Sill Relative to the No. 2 Lower Seam .......................................... 6-33

Figure 6-23: Pillar Design Areas for the No. 4 Lower Seam ........................................................................ 6-34

Figure 6-24: Pillar Design Areas for the No. 2 Lower Seam. ....................................................................... 6-35

Figure 6-25: Mining Areas on the No. 4 Lower Seam and No. 2 Lower Seam ............................................ 6-40

Figure 6-26: Multi-Seam Design Guideline Flow Chart. ............................................................................... 6-41


DELTA BEC | GEOTECHNICAL AND ROCK ENGINEERING 6-v

Appendices (Volume 2)

Appendix 6.1 - Site layout plan with boreholes and test pit positions

Appendix 6.2 - Soil profile descriptions

Appendix 6.3 - Borehole core photographs

Appendix 6.4 - Laboratory test results

Distribution list

1 e-copy to Mmakau Coal (Pty) Ltd 1 e-copy to Exxaro (Pty) Ltd


DELTA BEC | MINE ROCK ENGINEERING 6-6

6 GEOTECHNICAL AND ROCK ENGINEERING

6.1 Geotechnical

6.1.1 Introduction

The main purpose of the geotechnical investigation at the proposed Project was to identify geotechnical

related considerations that may have an influence on the proposed infrastructure development; and provide

geotechnical related recommendations for the structures and the proposed box cut excavation.

6.1.2 Approach and Methodology

The investigations were conducted in April 2017 and comprised test pitting, rotary core drilling and

laboratory testing.

The test pit locations were spread across the site and positioned in the vicinity of the major civil structures

while the boreholes were mainly positioned in the proposed box cut area. Borehole R1 was positioned at

the box cut location, borehole R2 at the mine incline shaft access while borehole R3 was located at the

product stacker. The layout of the civil structures have been revised significantly after the investigation and

therefore the test pits and boreholes are not as “structure specific” as what was initially intended.

The test pits were excavated with a 20 tonne excavator to either the maximum reach (± 5 m) or at the point

of refusal. The test pits were profiled according to the standard methodology proposed by Jennings, Brink

and Williams (Jennings et al., 1993) and backfilled after completion of the soil profiling.

The three boreholes were drilled by a geotechnical drilling contractor and logged and photographed in

accordance with accepted standards (Brink and Bruin (Eds.) 2002).

To confirm the visual assessments of the engineering properties of the soil and rock a number of

representative samples were taken and submitted for laboratory testing.

The data gained by the aforementioned activities are presented in this report as follows:

Site layout plan with boreholes and test pit positions - Appendix 6.1

Soil profile descriptions - Appendix 6.2

Borehole core photographs - Appendix 6.3

Laboratory test results - Appendix 6.4

6.1.3 Site Description

The site is relatively flat slopping gently to the north and north-west, draining towards the Viskuile River

located to the north of the site, with a wetland and/or pan located to the west of the site.

The site is mostly situated on agricultural land and therefore the vegetation generally comprises dense veld

grass used for grazing or seasonal crop fields (planted with soya beans at the time of the investigation).

6.1.4 Available Information

The following information was available at the time of the investigation:

1: 250 000 scale geological map of East Rand (2628);

A layout plan of the proposed mine infrastructure development.



6.1.5 Site Investigation

As mentioned earlier, the investigation comprised the following:

Test pitting to evaluate the shallow geotechnical conditions;

Rotary core drilling to evaluate the deeper geotechnical conditions; and

Laboratory testing.

6.1.6 Test Pitting

The test pitting comprised the excavation of a total of twelve test pits located at points where the major civil

structures will be placed, reference is made to these structures in Table 6-1, the table also summarises data

gained from the test pits.

Table 6-1: Test Pit Summary

TEST

PIT NO

COORDINATES

(LO29 CAPE)

STRUCTURE AT TEST PIT

POSITION TOTAL

DEPTH

(m)

REMARKS

X Y INITIAL CURRENT

T1 2 907 032 -49 445 Admin and

workshops - 3,5 No refusal but slow progress in very stiff material

T2 2 907 180 -49 356 Admin and

workshops - 4,0 No refusal but slow progress in very stiff material

T3 2 907 125 -48 870 ROM stockpile - 3,5 No refusal but slow progress in very stiff material

T4 2 907226 -49 081

Materials

handling

workshop

- 3,5 No refusal but slow progress in very stiff material

T5 2 907447 -49 054 Stockpiles - 3,8 Refusal on very soft rock sandstone and siltstone

T6 2 907 429 -48 911 Processing

plant - 4,0 No refusal but slow progress in very stiff material

T7 2 907 602 -48 926 Thickener Pollution control

dam 3,5 Refusal on very soft rock sandstone

T8 2 907 760 -48 991 Weighbridge - 3,4 Refusal on soft rock sandstone

T9 2 907 797 -48 678 Discard dump ROM Stockpile 2,3 Refusal on very soft rock sandstone

T10 2 908 041 -48 808 Access control - 3,0 Refusal on very soft rock sandstone and shale

T11 2 908 268 -48 555 Access road Admin and

workshops 3,0 No refusal but slow progress in very stiff material

T12 2 908 279 -47 911 Access road Access road 3,5 Refusal on soft rock sandstone

6.1.6.1 Rotary Core Drilling

The rotary core drilling comprised the drilling of a total of three boreholes, two at the box cut location and

one at the product stacker location. The data gained from the boreholes can be summarised as follows:

Table 6-2: Borehole Summary

BOREHOLE

NO

COORDINATES (LO29

CAPE) STRUCTURE AT TP POSITION TOTAL

DEPTH (m) REMARKS

X Y INITIAL CURRENT

R1 2 907 589 -48 735 Box cut Box cut 40.0 -

R2 2 907 312 -48 784 Mine access - 20.2 -

R3 2 907 488 -48 974 Product stacker - 20.2 -

6.1.7 Geology, Climate and Seismic Risk

The published geological map of the area East Rand (2628) indicates that the site is underlain by

sandstone, shale and coal beds of the Vryheid Formation, Karoo Supergroup. This was confirmed by the

presence of shale and sandstone bedrock in the boreholes and test pits.



The area is classified as having a climatic N-value (after Weinert) of less than five, which indicates a humid

climatic region and chemical weathering as the main form of weathering.

SANS 10160-2011 (Part 4) show that the site does not fall within any of the active seismic zones of South

Africa (see figure below).

Figure 6-1: Seismic Risk at the Site

The SANS 10160-2011 (Part 4) code describes the requirements for seismic design when a site is located

in Zones I and II, but is silent on requirements when the site is located outside any of the identified seismic

hazard zones. It is therefore apparent that there is no specific obligation to design for horizontal seismic

acceleration for the site.

6.1.8 Soil and Rock Profile

From the test pits and boreholes, the soil and rock profile presents a combination of the following horizons:

Transported soil (Hillwash);

Residual soils;

Bedrock (Shale and Sandstone).

6.1.8.1 Transported Soil (Hillwash)

The transported soil or hillwash horizon dominates the upper 0,6 m of the profile at the site. The

composition for the horizon generally comprises a loose to medium dense, clayey and silty sand with a

pinhole soil structure. The upper 0.3 m of the hillwash contains abundant plant roots and has been

reworked extensively in the crop field areas. Some ferricrete development occur locally in the lower portions

of the hillwash horizons as noted in test pit T09 resulting in a gravelly material (nodular ferricrete).



6.1.8.2 Residual Soil

The residual soil underlies the hillwash and occurs typically below 0.3 m to 1.2 m depth (average depth of

0.6m). The residual is typically about 3 m thick and originated from the underlying shale and sandstone

bedrock. The material generally comprised sandy and/or silty clay and a variable degree of ferruginization

ranging from absent or only traces of ferricrete nodules to nodular ferricrete. This ferruginization or

ferricrete nodules results in a variable gravel component in the upper portion of the residual soil.

The ferricrete development is very prominent, however the degree of development is highly variable. The

ferricrete development ranges from traces of ferricrete nodules (less than 5 %) to slightly ferruginised

material (approximately 20%) and to moderately ferruginised material/nodular ferricrete (approximately

50%). The ferricrete development is typically in the upper portion of the horizon roughly between 1 m to 2 m

depth with an average thickness of 1 m.

This consistency of the horizon is quite variable and to a large extent influenced by the degree of

ferruginization. The consistency of the horizon is locally described as soft, however, a firm to stiff

consistency is typically described and generally, the consistency increase with depth. A slickensided and

shattered structure was noted in this horizon in some of the profiles and these structures are an indication of

a potentially expansive horizon.

6.1.8.3 Bedrock

The bedrock generally occurs from below a 3 m depth however was encountered from as shallow as 2.3 m

as in test pit T09 to as deep as 6.15 m in borehole R2.

The upper portion of the bedrock rock generally comprises highly and completely weathered, very soft and

soft rock, sandstone and shale to an average depth of 10 m below surface. From below a 10 m depth, the

rock conditions generally increase to moderately weathered soft rock and slightly weathered medium hard to

hard rock shale and sandstone. Coal seams were encountered at between 25 m and 32 m below surface.

The rock mass is generally closely to medium jointed and dominated by the near horizontal bedding joints of

the shale and sandstone. Other than these bedding joints; only very few sub-vertical joints were noted. The

spacing of these joints could not be determined, however, it is expected to be widely to very widely jointed.

6.1.9 Groundwater

The investigation was conducted towards the end of the rainy season and the soil profile was generally very

moist. Seepage was encountered in some of the test pits and signs of the formation of pedogenic horizons,

such as ferricrete, that is associated with perched seasonal water tables, was prominent in most of the soil

profiles.

6.1.10 Laboratory Testing

6.1.10.1 Foundation Indicator Tests

Representative samples of selected horizons were taken and submitted for foundation indicator tests. The

results of these tests can be summarised as follows (see Appendix 6.4 for detail test results):

Table 6-3: Foundation Indicator Test Results

TEST

PIT NO

DEPTH

(m) MATERIAL TYPE

SOIL COMPOSITION

GM

ATTERBERG LIMITS

ACTIVITY CLAY

(%)

SILT

(%)

SAND

(%)

GRAVEL

(%)

LL

(%)

WPI

(%)

LS

(%)

T3 0.3 - 0.7 Hillwash 13 19 67 1 0,76 23 10 5,5 Low

T3 1.0 - 2.0 Slightly ferruginised

residual shale 36 21 41 2 0,50 32 13 7,0 Low

T3 2.0 - 3.5 Residual shale 58 18 24 0 0,22 38 18 9,0 Low



TEST

PIT NO

DEPTH

(m) MATERIAL TYPE

SOIL COMPOSITION

GM

ATTERBERG LIMITS

ACTIVITY CLAY

(%)

SILT

(%)

SAND

(%)

GRAVEL

(%)

LL

(%)

WPI

(%)

LS

(%)

T5 0.6 - 2.0 Moderately ferruginised

residual shale 18 12 40 30 1,35 28 9 7,0 Low

T5 2.0 - 3.8 Residual shale 33 21 45 1 0,51 54 28 15,5 High


residual shale 27 24 40 9 0,69 47 17 10,0 Medium

T8 1.9 - 3.4 Residual shale 34 26 37 3 0,49 55 29 15,5 High


residual sandstone 20 13 52 15 1,03 28 10 7,0 Low

T9 1.6 - 2.3 Residual sandstone 10 15 71 4 1,21 26 7 6,0 Low

T11 0.4 - 0.8 Hillwash 21 14 58 7 0,87 23 8 4,5 Low

Legend GM = Grading modulus

LL = Liquid Limit

WPI = Weighted Plasticity Index

LS = Linear Shrinkage

Activity = Activity of the soil according to Van der Merwe’s method.

The results in Table 6-3 indicate that:

The hillwash generally comprises silty and clayey sand with moderate grading moduli. The weighted

plasticity index of the samples ranges between 8% and 10%, which indicates a plastic material.

These, together with the low to moderate clay content of 13% to 21%, are indicative of a plastic

material with a low potential expansiveness, according to the interpretation approach proposed by

van der Merwe;

The residual shale generally comprises silty sandy clay with low grading moduli. The weighted

plasticity index of the samples ranges between 18% and 29%, which also indicates a plastic material.

These, together with the moderate to high clay content values between 33% and 58% is indicative of

a plastic material with a potential expansiveness ranging from low to high, according to the

interpretation approach proposed by van der Merwe;

The ferruginised residual shale generally comprises silty sandy clay with gravel and a moderate to

very high grading moduli. The weighted plasticity indices of the samples are between 9% and 17%,

which indicates a plastic material. These, together with the moderate clay content values of 18% to

36% is indicative of a plastic material with a low to moderate potential expansiveness, according to

the interpretation approach proposed by van der Merwe.

The residual sandstone comprises clayey and silty sand with high grading modulus. The weighted

plasticity index of the sample is 7%, which also indicate a plastic material. This, together with the low

clay content value of 10% is indicative of a plastic material with a low potential expansiveness,

according to the interpretation approach proposed by van der Merwe;

The ferruginised residual sandstone comprises silty and clayey sand with gravel and a high

grading modulus. The weighted plasticity index of the sample is 10%, which indicate a plastic

material. This, together with the moderate clay content value of 20% is indicative of a plastic material

with a low potential expansiveness, according to the interpretation approach proposed by van der

Merwe.

6.1.10.2 Compaction Characteristics Tests

Representative samples of the soil horizons were taken to assess the compaction characteristics of this

material. The results of these tests can be summarised as follows (see Appendix 6.4 for detailed results):



Table 6-4: Compaction Test Results

TEST

PIT NO DEPTH (M) MATERIAL TYPE

OMC

(%) MDD

SWELL

(%)

CBR AT VARIOUS DENSITIES TRH

90% 93% 95% 98%

T3 1.0 - 2.0 Slightly ferruginised residual

shale 18,5 1670 0,3 0,8 1,5 2,2 2,9 NC

T5 0.6 - 2.0 Moderately ferruginised

residual shale 14,2 1929 0,9 2,1 3,2 4,2 6,4 NC

T8 1.9 - 3.4 Residual shale 15,3 1570 10,9 0,3 0,5 0,7 1,2 NC

T9 0.6 - 1.6 Slightly ferruginised residual

sandstone 10,2 1989 0,1 6,2 7,4 8,3 9,9 G10

T9 1.6 - 2.3 Residual sandstone 8,7 1973 0,3 6,8 9,8 12,5 18 G9

Legend OMC = Optimum moisture content

MDD = Maximum dry density (Mod AASHTO)

Swell = Soaked at 100% Mod AASHTO compaction

TRH = Material classification according to TRH14 guidelines

NC = No classification.

The test results in Table 6-4 indicate that:

The residual shale has very low maximum dry density and high optimum moisture content values.

The CBR swell value is high and the tests yielded very low CBR values at densities typically specified

in the field (93% to 95%). The material does not meet the requirements of a G10 material, according

to the TRH 14 (TRH14, 1987) guidelines, and is therefore only suitable for use as landscaping

material;

The ferruginised residual shale has low to moderate maximum dry density and high to very high

optimum moisture content values. The CBR swell values are low to moderate and the tests yielded

very low CBR values at densities typically specified in the field (93% to 95%). The material does not

meet the requirements of a G10 material, according to the TRH 14 (TRH14, 1987) guidelines, and is

therefore only suitable for use as landscaping material;

The residual sandstone has high maximum dry density and moderate optimum moisture content

values. The CBR swell value is low and the tests yielded low CBR values at densities typically

specified in the field (93% to 95%). The material is classified, according to the TRH 14 (TRH14,

1987) guidelines, as a G9 and is therefore suitable for use as subgrade and selected layer in road

pavement layer works and for low stiffness engineered fills;

The ferruginised residual sandstone has high maximum dry density and moderate optimum

moisture content values. The CBR swell value is very low and the tests yielded low CBR values at

densities typically specified in the field (93% to 95%). The material is classified, according to the TRH

14 (TRH14, 1987) guidelines, as a G10 and is therefore suitable for use as subgrade and selected

layer in road pavement layer works and for low stiffness engineered fills.

6.1.10.3 Uniaxial Compressive Strength (UCS) Tests

Representative samples of the rock horizons were taken to assess the strength parameters of this

underlying rock formations. The results of these tests can be summarised as follows (see Appendix 6.4 for

detailed results):



Table 6-5: UCS Test Results

BOREHOLE NO DEPTH (m) WEATHERING ROCK TYPE UCS (MPa)

R1 10.03-10.36 Slightly Shale 44.7


R1 16.67-16.98 Slightly Sandstone 68.9

R1 24.12-24.32 Slightly Sandstone 85.0

R1 27.10-27.34 Unweathered Coal 32.2


R1 37.90-38.10 Moderately Siltstone and shale 31.7

The UCS test results can be correlated with the rock hardness descriptors as listed in Table 6-6 (Brink and

Bruin (Eds.) 2002).

Table 6-6: Typical UCS and Hardness Correlations.

ROCK HARDNESS DESCRIPTION UCS RANGE (MPA)

Very Soft Rock Can be peeled with a knife. Material crumbles under firm

blows with the sharp end of a geological pick. 1 – 3

Soft Rock Can be scraped with a knife, indentation of 2 to 4 mm with

firm blows of the pick point. 3 – 10

Medium Hard Rock Cannot be scraped or peeled with a knife. Hand held

specimen breaks with firm blows of the pick. 10 – 25

Hard Rock Point load tests must be carried out in order to distinguish

between these classifications. 25 – 70

Very Hard Rock These results may be verified by uniaxial compressive

strength tests on selected samples. 70 – 200

Extremely Hard Rock These results may be verified by uniaxial compressive

strength tests on selected samples. >200

The test results in Table 6-5 and the correlations in Table 6-6 indicate that:

The slightly weathered shale has a UCS of between 44.7 MPa and 80,0 MPa which can be

classified as hard rock;

The slightly weathered sandstone has a UCS of between 68.9 MPa and 85,0 MPa which can also

be classified as hard rock;

The unweathered coal has a UCS of 32.2 MPa which can be classified as medium hard to hard rock;

The moderately weathered siltstone and shale has a UCS of 31.07 MPa which can be classified as

medium hard to hard rock.



6.1.11 Geotechnical Considerations

The following geotechnical related considerations may have an influence on the proposed development:

The hillwash material covering the site generally comprise silty and clayey sand, with a pinhole

structure and can therefore be expected to be potentially compressible / collapsible;

The residual materials at the site generally comprise sandy and silty clay with a shattered structure

which is indicative of potential expansive soils;

The highly to completely weathered shale very soft rock shale may slake when exposed. When

covered this material is deemed suitable for founding of lightly and moderately loaded structures;

Heavy loaded structures can be founded on the soft rock or medium hard rock shale;

The bedrock horizons at the site were generally horizontally bedded and no major joints sets (other

than the bedding) were recorded. The stability of the box cut slopes will therefore be dictated by the

bulk mass material properties of the various rock horizons.

6.1.12 Recommendations

6.1.12.1 Founding of Structures

It is understood that the bulk of the office and administration structures will comprise light weight pre-

fabricated structures, which will not result in significant foundation loading. These structures can be

founded on the in situ soils with nominal foundation preparations.

Single storey masonry structures, e.g. the change rooms, workshops and coal laboratory facilities can be

founded on conventional strip footings with compaction of the sandy horizons below founding level depth.

Articulation with movement joints and light reinforcement (rebar in foundations, mesh in surface beds and

brickforce in walls) may be required.

It is our understanding that a modular plant will be constructed with founding loads of less than 120 kPa.

Founding at depth, on the very soft rock shale or better, or soil improvement (construction of soil rafts by

replacement with compacted granular fill such as G7 quality material) will be required for these structures.

Recommendations that are more detailed can be provided when the final location and configuration details

of these structures are available.

6.1.12.2 Use of In-Situ Materials

In general the in situ soils comprise residual shale that does not meet the requirements of a G10 material

and only suitable for use as landscaping material. However, the residual sandstone was classified as a G9

or G10 and therefore suitable for use as subgrade material in road pavement layer works and for non-

structural fills and landscaping purposes.

6.1.12.3 Excavatability

Refusal or near refusal with the excavator was generally encountered between 2,3 m and 4,0 m depth which

can be classified as “soft excavation” according to SANS 1200D (SABS 1200D,1988). The highly

weathered shale material (to a maximum depth of 10 m) is expected to be classified as “intermediate”

excavations according to the SANS 1200D guidelines, whereas the underlying slightly weathered shale,

sandstone and coal is expected to be classified as “hard” excavations, which will required drilling and

blasting.

6.1.12.4 Slope Stability of Box Cut Excavation

As noted above, the bedrock horizons are generally horizontally bedded and no major joints sets other than

the bedding joints were recorded. The bulk or mass material properties of the various rock horizons will

therefore drive the stability of the box cut slopes.



To analyse the stability of the box cut slopes, the strength parameters of the soil and rock horizons were

derived as follow:

6.1.12.5 Soils Strength

Typical unit weights and shear strength values for drained groundwater conditions were utilised based on

USCS classifications of soil types found at the site. The published empirical correlations between USCS

and shear strengths are listed in Table 6-7 (Swiss Norm SN 670 010b, 1993).

Table 6-7: Typical Effective Strength Properties of Soils

USCS SOIL TYPE UNIT WEIGHT

(KN/M3)

FRICTION ANGLE

(DEGREES)

COHESION

(KPA)

SC Clayey sands, small percentage of fines 19.5 ± 2.0 32 ± 4 0

CL Clayey silt, inorganic, low to medium plasticity 20.0 ± 1.5 27 ± 4 20 ± 10

CH Clay, inorganic, high plasticity, fat clays 17.5 ± 1.5 22 ± 4 25 ± 10

The soil horizons were generally classified as a CL or CH material with a thin cover of SC material. From

the information in Table 6-7 and the soil profiles on site the following general shear strength parameters

were derived for the soil horizons.

Table 6-8: Derived Strength Properties of Soil Horizons

SOIL TYPES UNIT WEIGHT

(KN/M3)

FRICTION ANGLE

(DEGREES)

COHESION

(KPA)

CL and CH with some SC 20 20 15

6.1.12.6 Rock Mass Strength

Typical rock mass strength values for different weathering grades of the rock and rock types were derived

using the Hoek-Brown failure criterion (Hoek et al, 2002) and listed in Table 6-9 below.

Table 6-9: Typical Shear Strength Values of Rock Types

ROCK TYPE

DEPTH OF

HORIZON

(M)

UCS

(MPA) GSI

UNIT

WEIGHT

(KN/M3)

FRICTION ANGLE

(DEGREES)

COHESION

(KPA)

Highly to completely weathered shale 10 3 35 23 25 30

Slightly weathered shale 15 60 45 24 40 150

Slightly weathered sandstone 25 70 55 25 50 300

Unweathered coal 32 30 35 16 25 60

Slightly weathered shale 37 60 45 24 30 200

Moderately weathered shale 39 30 35 24 25 100

6.1.12.7 Slope Stability

The stability of the box cut was modelled to determine the stable slope angles of the various soil and rock

horizons while maintaining a minimum Factor of Safety (FOS) of 1.25. Benches (3 m wide) were included

on each of the material interfaces. The design slope angles for the various soil and rock horizons were

derived from the slope stability model as presented in



Table 6-10: Design Slope Angles of Soil and Rock Horizons

DEPTH RANGE (m) MATERIAL SLOPE ANGLE (V:H)

0 to 2,5 Residual soil 1V:1,5H

2,5 to 10 Highly weathered shale 1V:1H

10 to 15 Slightly weathered shale 1V:0,5H

15 to 25 Slightly weathered sandstone 1V:0,25H

25 to 32 Un-weathered coal 1V:0,5H

The slope stability model with the derived soil and rock parameters is shown in Figure 6-2 below:

Figure 6-2: Slope Stability Model

Abramson et.al. (2002) notes that the factor of safety (FOS) value “constitutes an empirical tool whereby

deformation stability performances are limited to tolerable amounts within economic restraints”. In addition it

is noted that typical non-seismic values are usually in the 1,25 to 1,5 range. The model depicted above is

deemed representative of the short term (temporary) condition during the development of the box-cut, for

which a minimum FOS in excess of 1,25 is deemed to be required. The long term drawdown of the ground

water table (as part of the mining operations) will increase the FOS value.

6.1.13 Conclusion, Interpretation of Results and Validity of Recommendations

The purpose of the geotechnical investigation was to provide an overview of the site and identify

problematic geotechnical considerations for a pre-feasibility study. The current investigation, which is based

on a preliminary geotechnical investigation, indicates that the site is deemed suitable for the proposed

development from a geotechnical perspective.

The level of results presented in this report, inclusive of soil and rock profiles, laboratory test results,

conclusions and recommendations are deemed suitable for budgeting purposes for the current feasibility

study and must be augmented by additional investigations during the detail design phase. The

recommendations presented in this report are indicative and must be reviewed and refined in the future

phases of the project.



6.2 Mine Rock Engineering

6.2.1 Executive Summary

The information which was utilized in the pre-feasibility study for the Schurvekop project has been re-visited

for the purposes of conducting a feasibility study investigation.

Based on the outcomes of the investigations conducted during the pre-feasibility and feasibility study

phases of the project and the available geological, geotechnical and mining information, the proposed

extraction of the No. 4 Lower Seam (“S4L”) and No. 2 Lower Seam (“S2L”) reserves within the Schurvekop

project area, using underground mining methods, is deemed to be feasible.

In this report, the recommended minimum systematic support and pillar dimensions have been detailed per

mining area along with the anticipated amounts of contamination.

Challenges are expected in areas in which the roof and floor strata as well as the coal seam itself are

impacted on by the effects of dolerite intrusions.

The minimum mining depth cut-off which has been applied in this investigation is 20 m. Although areas in

which the mining seam lies at depths of between 20 m and 30 m are deemed to be potentially minable

based on the available geological and geotechnical information, it is recommended that additional drilling

and geotechnical testing be conducted in these areas to verify the rock mass properties of the overburden

before mining is conducted in them.

Due to the fact that multiseam mining will be conducted in a significant portion of the Schurvekop project

area, the design guidelines for multiseam mining must be complied with. As a result, it has been found that

the barrier pillars on the S4L Seam and S2L Seam in the northern portion of the project area will have to be

superimposed. Additional investigations using numerical modelling techniques could be conducted to

confirm/refute the need to superimpose the barrier pillars on the two seams in this portion of the project

area.



6.2.2 Introduction

At the request of Mr. K. Badenhorst, a geotechnical report has been compiled for inclusion in the

Schurvekop Pre-Feasibility Study (“PFS”) document to be produced. It is important to note that due to the

lack of additional drilling conducted during this phase of the project, some of the recommendations included

in the pre-feasibility study report have not been able to be implemented, however, it is believed that they are

not critical for the feasibility study, but could rather form part of the operational phase of the Schurvekop

project.

The Project lies immediately west/north-west of the existing Forzando South mine which is owned by Exxaro

Coal Central (“ECC”). The project area is located approximately 15 km north-east of the town of Bethal and

55 km south south-east of Witbank. The Bethal-Middelburg tarred road lies just to the west of the area and

the Bethal-Hendrina tarred road passes along the extreme eastern edge of the area.

Various Geotechnical investigations into the possibility of mining the S2L and S4L in the Schurvekop area

have been conducted previously, the results of which were used in this investigation and the compilation of

the subsequent report.

6.2.3 Information Provided

The following information was provided by management and the relevant departments:

Survey information as detailed below:

An electronic (.dxf) file including the following drawing layers

Reserve areas on both the S2L and S4L seams

Surface infrastructure (existing and planned)

Proposed boxcut position and dimensions

Geological borehole positions

Surface contour elevations

Seam thicknesses

Overburden thicknesses and depth to floor

Geological borehole logs were requested and utilized as required

The grid exports from the geological model.



6.2.4 Geotechnical Investigation

6.2.4.1 Investigation Area

The Schurvekop project area is indicated in Figure 6-3 below.

Figure 6-3: Schurvekop Project Area

There are two economically minable seams within the Project area i.e. the S4L and the S2L seam. The

following cut-off criteria were applied to both of these two seams to identify the mineable reserve areas:

Minimum mining height (seam thickness) 1.65 m;

Minimum mining depth (overburden thickness) 20 m.

The theoretical mining areas on the S4L and the S2L seam respectively are illustrated based on the above

criteria.



Figure 6-4: No. 4 Lower Seam, Theoretically Mineable Area.

Figure 6-5: No. 2 Lower Seam, Theoretically Mineable Area.



As can be seen from Figure 6-5, the mineable portion of the No. 2 Seam is expected to be located towards

the centre of the project area with the No. 4 Lower Seam theoretically minable in the majority of the project

area (Figure 6-4).

6.2.4.2 Borehole Positions

A significant number of boreholes have been drilled within the Schurvekop mining area to date as indicated

below.

Figure 6-6: Boreholes Drilled in the Schurvekop Area and Surrounds.

6.2.4.3 Generalized Stratigraphy

The relevant geological information obtained from each of the boreholes within the Schurvekop Project area

was assessed and captured digitally.

No. 4 Lower Seam The depth of the seam varies from 8.0 m to 70 m below surface within the Schurvekop Project Area. It is

shallowest in the northern portions of the reserve area and never exceeds a depth of 70 m within the greater

reserve area. The thickness of the coal that can be mined ranges from 1.65 m to 3.84 m with an average of

2.6 m. The No. 4 Lower Seam is generally overlain by a relatively thick, competent Sandstone layer which is

cross-bedded and contains a “false” layer at it’s based in places.

No. 2 Lower Seam

The depth of the seam varies from 26.3 m to 99 m below surface within the Schurvekop Project Area. It is

shallowest in the northern portions of the reserve area and never exceeds a depth of 100 m within the

greater reserve area. The thickness of the coal that can be mined ranges from 1.65 m to 5.3 m with an

average of 2.1 m within the project area. The No. 2 Seam is also generally overlain by a relatively thick,

competent Sandstone layer which is cross-bedded and contains a “false” layer at it’s based in places.



6.2.4.4 Surface Elevation

There is up to a 55 m increase in surface elevation in a north-easterly direction across the project area, as

shown below:

Figure 6-7: Surface Elevations in the Schurvekop Project Area.

6.2.4.5 Underground Access

Initially it was proposed that access to the underground workings on the No. 4 Lower Seam would be via

either a boxcut or alternatively from the highwall of a small opencast operation. Due to environmental

constraints as well as logistical and financial challenges, however, it was decided during the pre-feasibility

stage of the project in 2013 that access to the No. 4 Lower Seam reserves will most likely be gained from

the existing underground workings on the No. 4 Lower Seam at Forzando South.

The current thinking has once again changed with access to the underground reserves now planned via a

boxcut close to the western boundary of the project area as indicated in Figure 6-8 below.

The responsibility of designing the boxcut based on the updated geotechnical information for this area has

been sub-contracted to a different mining consultant who will therefore be responsible for providing the

detailed design of the boxcut as well as the support requirements if any.



Figure 6-8: Position of the Boxcut and Surface Infrastructure at Schurvekop.

6.2.4.6 Identified Reserve Areas on the No. 2 and No. 4 Lower Seams

An initial investigation into the mineability of the S4L and S4L seams was conducted in early 2013. In this

investigation, various constraints were defined which were applied to both of the identified potentially

minable seams.

The following is a list of the basic criteria which was applied to the S2L and S4L seams during this

investigation:

Minimum mining height of 1.65 m;

Maximum mining height of 2.8 m;

Minimum overburden thickness of 30 m.

These criteria have subsequently been revised as documented in the report above. The ability to support

the immediate roof and create a stable beam was assessed based on basic support criteria and was

specified per mining area. The changes to the mining areas have, however, required that the recommended

systematic support patterns per area be revisited.

In all of these investigations it is important to note that it has been assumed that the material forming the

immediate roof i.e. coal, siltstone, or sandstone, will be stable, prior to the installation of support, over the

planned spans of the bord width and cut-out distance, (this may prove not to be the case and provision may

have to be made to reduce such spans during the mining process).



Each one of the existing boreholes within the Schurvekop area was subsequently assessed according to the

above criteria and classified as minable or not mineable. Based on these assessments, areas on both the

S2L as well as the S4L seam within the theoretically minable areas were deemed to be minable or un-

minable. Illustrated in Figure 6-9 and Figure 6-10 below are the mining layouts on the S4L and the S2L

seam respectively, which have been deemed to be theoretically mineable based on the outcomes of the

above investigations and based on the information provided by Phoenix Mine Planning (Pty) Ltd.

Figure 6-9: No. 4 Lower Seam, Proposed Mining Layouts

Figure 6-10: No. 2 Lower Seam, Proposed Mining Layouts.



6.2.5 Mining Technical

6.2.5.1 Contamination

No. 4 Lower Seam

Indicated in Figure 6-9 above is the area on the S4L Seam which is deemed as theoretically mineable

based on the information provided by Phoenix Mine Planning (Pty) Ltd and taking into account the available

geotechnical information.

Based on the available information the following can be stated regarding the contamination expectations on

the S4L seam:

In the proposed mining areas, the immediate roof of the S4L seam is described as either Sandstone,

or an interlaminated Siltstone-Sandstone with percentages of Sandstone always expected to be equal

to or greater than 50%;

The immediate roof thickness is noted to be significantly thinner in the south-western, western and

north-western portions of the reserve;

The thickness is noted to range between relatively thin laminations and more than 6.0 m across the

reserve area;

In areas in which laminated sandstone/siltstone and/or shale are expected to form the immediate roof

higher levels of contamination can be anticipated;

Areas where the immediate roof consists of a siltstone/shale which is less than 300 mm thick may not

be self-supporting during the mining operation and could be considered as contamination;

From the available information, only localized areas are anticipated at Schurvekop in which this might

be the case;

There is a sandstone parting which is of significant thickness and occurs within the “minable” zone on

the S4L seam in the southern portions of the reserve, similar to Forzando South which will have to be

negotiated;

In the majority of the Schurvekop area the immediate S4L seam floor is noted to consist of an

interlaminated sandstone-siltstone;

These interlaminated layers could break up due to the movement of heavy equipment and

contamination as a result of the deterioration of the floor could be expected.

No. 2 Lower Seam

Indicated in Figure 6-10 above is the single area identified as theoretically mineable on the S2L at

Schurvekop. As can be noted from the figure the area is continuous and is located in the central and

eastern portions of the reserve in the topographical seam low formed as a result of the basement

stratigraphy in this area. Based on the available information the following can be stated regarding the S2L

seam:

All areas within the mineable area on the S2L seam have the immediate roof described as either a

sandstone or interlaminated sandstone-siltstone or siltstone with a thickness ranging between 1.49 m

to greater than 10 m;

The percentage of sandstone in the immediate roof based on the available information isn’t expected

to drop below 80 %;

A “False” roof as is typically known to exist within the Forzando Complex can be expected which may

have an impact on the amounts of contamination experienced during mining;

In the majority of the Project area the immediate S2L floor is noted to consist of either a dark Siltstone

or a Shale;

Both of these layers are expected to be weak and will most likely break up on exposure to water and

as a result of the movement of heavy equipment and contamination as a result of the deterioration of

the floor could be expected.



6.2.5.2 Overburden and Mining Depth.

No. 4 Lower Seam

Indicated on Figure 6-11 below is the S4L overburden thickness for the entire Schurvekop area with the

proposed S4L mining layouts super-imposed on top of that.

Figure 6-11: Thickness of the No. 4 Lower Seam’s Overburden.

The depth at which mining is proposed to take place on the S4L seam ranges from a minimum of 20 m to a

maximum depth of in the region of 67 m as indicated in Figure 6-12 below.

Figure 6-12: Statistics for the Expected No. 4 Lower Seam's Overburden Thickness



Figure 6-13: Statistics indicating the expected No. 4 Lower Seam’s Overburden Thickness.

Figure 6-13: Statistics indicating the expected No. 4 Lower Seam’s Overburden Thickness.

No. 2 Lower Seam

Indicated in Figure 6-14 is the statistical analysis including the range, minimum, and maximum values for

the expected S2L overburden thickness in this area based on the geological grids. The depth at which

mining is proposed to take place on the S2L ranges from a minimum of approximately 35 m to a maximum

depth of in the region of 97 m.



Figure 6-14: Statistics Indicating the Expected No. 2 Lower Seam’s Overburden Thickness.

6.2.5.3 Roof Strata and Support.

No. 4 Lower Seam

As stated in the contamination section above the following is true of the S4L and S2L immediate roof:

The immediate roof of the S4L is described as either Sandstone, or an interlaminated Siltstone-

Sandstone with percentages of Sandstone always expected to be equal to or greater than 50 %;

The immediate roof thickness is noted to be significantly thinner in certain portions of the reserve;

In some portions of the reserve area the immediate roof is noted to consist of a

siltstone/shale/sandstone layer overlain by the No. 4 Upper Seam and more difficult mining conditions

and increased amounts of contamination can be expected when mining in such areas;

All areas within the mineable area on the S2L have the immediate roof of the described as either a

Sandstone or interlaminated Sandstone-Siltstone or Siltstone with a thickness ranging between 1.49

m and greater than 10 m;

The percentage of sandstone in the immediate roof based on the available information isn’t expected

to drop below 80 %;

A “False” roof as is typically known to exist within the Forzando Complex can be expected which may

have an impact on the amounts of contamination during mining;

Based on the available information it is suggested that the systematic roof support at Schurvekop will

have to be changed to suit the prevailing roof conditions;

Two types of systematic roof support will be required when mining on the S4L and the S2L at

Schurvekop i.e. roof support designed based on beam formation principles and systematic support

designed on suspension principles;

In areas in which systematic support is to be designed on suspension principles it is suggested that

the minimum systematic support will consist of three 0.9 m or 1.2 m long roofbolts installed per row

with rows spaced a maximum distance of 2.0 m apart;

The 0.9 m long roofbolts must be installed in an 820 mm long, 25 mm diameter hole, with a single 23

mm x 500 mm resin capsule;

The 1.2 m long roofbolts must be installed in a 1 120 mm long, 25 mm diameter hole, with a single 23

mm x 600 mm resin capsule;

In areas in which systematic support is to be designed on beam building principles it is suggested that

the minimum systematic support will consist of four 1.5 m long roofbolts installed per row with rows

spaced a maximum distance of 1.5 m apart;

The 1.5 m long roofbolts must be installed in a 1 420 mm long, 25 mm diameter hole with a single,

“Two-Speedie” 23 mm diameter x 900 mm long resin capsule;

It is suggested that if/when additional boreholes are drilled in these mining areas the information

obtained from them could be used to refine the above support recommendations.



Figure 6-15: Statistics Indicating the Expected No. 2 Lower Seam’s Overburden Thickness.



Figure 6-16: No. 2 Lower Seam Recommended Roof Support Design Principles.

6.2.5.4 Structure

Included below in Figure 6-17 and Figure 6-18 are subsequent images illustrating the positions of the

known geological features relative to the No. 4 Lower Seam and the No. 2 Seam respectively, based on

recently obtained geophysical data. As can be noted from these figures, dykes and/or sill intersections can

be expected on both the No. 4 Lower Seam (primarily in Block 1) as well as on the No. 2 Seam. Due to the

fact that such intrusive structures may not always have a vertical dip, the positions of such structures in the

figures below should be seen as approximate and the actual position of such structures on the mining seam

may not be in the exact position in which it is indicated.

Based on the experienced gained when mining on the No. 4 Lower Seam at Forzando South, burnt coal,

and slips as well as significant deterioration of the sandstone/siltstone in the immediate roof and floor can be

expected when mining in the vicinity of such structures, particularly where two such structures intersect.

Additional specialized support as well as changes to the mining dimensions and methods may be required

when mining in such areas.



Figure 6-17: The Position of the Geological Structures on the No. 4 Lower Seam

Figure 6-18: The Position of the Geological Structures on the No. 2 Lower Seam



In addition to the information available regarding geological structures based on the geophysical data,

additional information is available regarding the position of the D2 Dolerite Sill relative to the two identified

mining seams. Included in Figure 6-19 below is a plan which was previously compiled by the Total Coal

South Africa (TCSA) (Exxaro Resources (Pty) Ltd) Geology Department which indicates the expected

positions at which the D2 Sill will intersect the 4 Lower Seam.

The “Red” line indicates the devolatilized limit and therefore any mining which will take place beyond this

line will most likely be in burnt coal with poor roof conditions in which specialized support in the form of 1.8

m roofbolts, Osro-straps, wire mesh and cable anchors may be required. A cross-section was subsequently

drawn along the line A-A’ indicated in the South-Eastern portion of the figure.

The cross section itself is included in Figure 6-20 below.

Figure 6-19: Positions at which the D2 Dolerite Sill is Expected to Intersect the 4 Lower Seam (Blue)



Figure 6-20: A Cross-Section Indicating the Position of the Dolerite Sill

In addition to the information included above, a colour plot was compiled based on the grid exports from the

geological model, illustrating the distance between the S4L as well as the S2L and the D2 Dolerite Sill. The

distances between the S4L Seam and the S2L and the D2 Sill are illustrated in Figure 6-21 and Figure 6-22

below respectively.

It is evident that the D2 Sill will migrate from below the S4L in the South to above the S4L in the North in the

Southern portion of the Project reserve area. As a result of the intersection of the sill and the S4L in this

area a significant amount of the mining to be conducted in this area may prove to be in difficult mining

conditions and therefore additional boreholes to investigate the effects of the sill would be required. In areas

where the sill is anticipated to be within a distance of 5.0 m or less of either seam (illustrated in red in the

figures below) poor roof, pillar and floor conditions can be expected.

In areas where the sill is anticipated to be within a distance of between 5.0 m – 10 m of either seam

(illustrated in yellow in the figures below) poor roof, pillar and floor conditions could be encountered.

In such areas, specialized support in the form of 1.8 m long roofbolts, Osro-straps, wire mesh and cable

anchors may be required. It is suggested that if mining is to be conducted in these areas additional

investigations into the roof and pillar conditions in these areas could be conducted.

Such investigations could include, but not be limited to:

The drilling of additional geological boreholes at specific positions along the developments as well as

the geotechnical logging, sampling and testing of the borehole core obtained through the drilling

process.



Figure 6-21: Position of the D2 Dolerite Sill Relative to the No. 4 Lower Seam

Figure 6-22: Position of the D2 Dolerite Sill Relative to the No. 2 Lower Seam



6.2.5.5 Bord Width

A bord of 6.8 m has been used in the design calculations.

Core of the immediate roof above the S4L indicates, as detailed above, that the immediate roof consists of

either a Sandstone or an interlaminated Sandstone – Siltstone (80:20). This immediate roof, in conjunction

with the systematic support suggested above, is expected to form a beam in the immediate roof which will

be stable over 6.8 m. It is, however, possible that the immediate roof will not be stable over the suggested

6.8 m or over a typical cut-out distance of 12 m, and if this is found to be the case, changes to the mining

layouts and dimensions may have to be made in certain areas.

It was previously suggested that further investigation into the competency and stability of the immediate roof

be conducted during the Feasibility Study phase, however, additional boreholes were not available and

therefore during the mining phase the roof stability will have to be monitored and the bord widths adjusted if

deemed to be necessary.

6.2.5.6 Pillar Design

For the purposes of the pillar design within the Schurvekop project area, both the S4L as well as the S2L

been sub-divided into design areas as indicated in Figure 6-23 and Figure 6-24 below. It can be noted from

these two figures that the S4L has been divided into five design areas and the S2L into four. Based on the

average mining depth and height in each of these areas a recommended average pillar centre has been

calculated and is recommended for the Main Developments as well as the Secondary Panels in Figure 6-23

below.

Figure 6-23: Pillar Design Areas for the No. 4 Lower Seam



Figure 6-24: Pillar Design Areas for the No. 2 Lower Seam.

Pillar Strength

Salamon & Munro Pillar Strength Formula

Salamon & Munro conducted a statistical analysis of intact and collapsed pillar geometries and from this an

empirical formula was derived that was mostly used for the design of the coal pillars at Savmore Colliery.

This pillar strength formula is given as:

σ = Kwαhβ

Where:

w and h represent the pillar width and mining height respectively, in metres.

K, α and β were determined by statistical analysis.

K = 7.176 MPa,

α = 0.46

β = 0.66

66.0

46.0

.176.7h

wStrength

(MPa)

Limitations to the Salamon & Munro Pillar Strength Formula

Pillar widths should be in excess of 5.0 m;

w:h ratio should exceed 2.0;

At shallow depths, (< 40 m) the formula is very sensitive to even small variations in pillar widths;

Guidelines have been drafted for workings shallower than 45 m;

Pillar width to height ratio less than 5.0;



Applicable to seams shallower than 150 m;

Blast fracture damage is included in the formula; an adjustment should be made for continuous miner

(CM) cut pillars.

In the absence of blast damage, which is allowed for in the Salamon & Munro formula, continuous miner cut

pillars will have a larger safety factor. Thus, the pillar width can be reduced to have the same nominal

safety factor by:

46.2).2

1.(w

w

Where:

o = Safety factor for pillars cut by CM

= Safety factor originally calculated

wo = Blast damage (change in width) - avg. 0.2 – 0.3 deep

w = original pillar width

Pillar failures due to the mining of two or more seams were excluded from the database.

Van der Merwe (1998) states that the safety factor concept as set out by Salamon, Munro and

Madden does not explicitly cater for long term stability and thus cannot be used to predict the life of

the pillar.

Coaltech 2020 Seam Specific Pillar Strength Formula

A number of different pillar strength formulae exist, however, the Seam Specific formula developed by

Salamon et al. in 2006 under the auspices of Coaltech 2020 is thought to be the most relevant to the coal

pillars at Schurvekop.

As indicated above the strength ( ) of a coal pillar is given by the following power formulae:

Where:

w and h represent the pillar width and the mining height respectively.

K and, and and are determined by statistical analysis.

For conventional Salamon and Munro (1967) pillars strength formula (as indicated above):

K= 7.176, =0.46, = -0.66

A revision of the coal pillar strength for South African coal seams, which includes revised values for and

for different South African coalfields (Coal specific, Coaltech 2020), was conducted by Salamon et al.

(2006).

According to this revision, Witbank coal specific properties are used to calculate the pillar safety factors for

Kangra Coal, are:

K= 5.854, =0.6126, = -0.7554

These values for and have been used in the calculation of the pillar strength according to the Coaltech

formulas in Table 6-11 below.



Pillar Load.

Pillar load is determined through applying the cover load or Tributary Area Theory (TAT), where each

individual pillar is assumed to carry the weight of the overburden immediately above it. This assumption

applies where the pillars are of uniform size and the panel width is larger than the depth to the seam.

The pillar load (q) for square pillars can be calculated from the formula:

q = γHC2.w-2

Where:

(γ) is the average specific weight of the overburden rock =0.02488MPa/m.

H is the Depth to the seam floor in metres.

C is the coal pillar centre distances in metres.

w is the coal pillar width in metres.

Pillar Factor of Safety (FOS).

MacCourt et al. (1986) found that the calculation of the safety factor for a pillar yields a good indication of

the stability of the pillar. However, anomalies occur especially in shallow areas with weak roof strata.

The pillar safety factor is defined as:

loadPillar

strengthPillarSF

Therefore, the pillar FOS can be calculated using the formula:

FOS=σ/q

The FOS is related to the probability of a panel of pillars failing. A higher FOS, means the lower the

probability of failure.

The pillar stability assessment was conducted by means of the strength, load and safety factor calculations

documented in Table 6-11 below, which indicates the calculated pillar strengths, pillar loads and safety

factors in each of the identified areas.

For the purposes of the pillar strength and safety factor calculations both the Salamon & Munro pillar

strength formula as well as the Coaltech (2020) Seam Specific pillar strength formulas have been used for

comparative purposes.

The following minimum values for the Safety Factors are suggested in the various mining areas and have

been applied to calculate the recommended pillar centres per mining area as include in Table 6-11 below:

Main developments: 2.0;

Production panels: 1.6;

In areas where secondary extraction is planned: 1.8.

In areas in which mining will be conducted within a horizontal distance of 100 m of a surface structure or

feature, including an environmental restriction, an application to mine within the identified area should be

submitted along with a Geotechnical Risk Assessment.

In such a Risk Assessment, all of the relevant design guidelines would be documented but the following can

be considered as a guideline at this point in the investigation:



Buildings where people congregate: 2.5;

Provincial Roads: 2.5;

Power Lines: 2.0;

Pans: 2.0;

Farm Dams: 2.0.

The following additional minimum standards should be applied in the design of the pillars on both of the

mining seams:

Minimum width-to-height ratio of the pillars: 2.2 (If a rectangular pillar is to be mined, the smaller of

the two widths should be used in the calculation and not the effective width),

Minimum pillar width of 7.0 m.



Table 6-11: Pillar Safety Factor and Size Calculations in the various mining areas.

SEAM AREA PANEL TYPE CENTRE

1 (M)

CENTRE

2 (M)

AVG.

BORD

WIDTH (M)

AVG.

MINING

HEIGHT (M)

WIDTH/HEIGHT

(MIN) H (M)

LOAD

(MPA)

SALAMON

STRENGTH

(MPA)

SF SF

(CM)

COALTECH

STRENGTH

(MPA)

COALTECH

SF

AREAL %

EXTRACTION

No.

4 L

ow

er

Seam

Area 1 Main

Development 14,0 14,0 6,8 2,1 3,4 56,0 5,3 10,9 2,1 2,5 8,5 4,1 73,6

Secondary Panel 14,0 14,0 6,8 2,1 3,4 56,0 5,3 10,9 2,1 2,5 8,5 4,1 73,6

Area 2 Main

Development 14,0 14,0 6,8 2,2 3,3 52,0 4,9 10,6 2,2 2,6 8,5 3,9 73,6

Secondary Panel 14,0 14,0 6,8 2,2 3,3 52,0 4,9 10,6 2,2 2,6 8,5 3,9 73,6

Area 3 Main

Development 14,0 14,0 6,8 2,8 2,6 52,0 4,9 9,0 1,8 2,2 8,5 3,0 73,6

Secondary Panel 14,0 14,0 6,8 2,8 2,6 52,0 4,9 9,0 1,8 2,2 8,5 3,0 73,6

Area 4 Main

Development 14,0 14,0 6,8 2,8 2,6 40,0 3,8 9,0 2,4 2,9 8,5 3,0 73,6

Secondary Panel 14,0 14,0 6,8 2,8 2,6 40,0 3,8 9,0 2,4 2,9 8,5 3,0 73,6

Area 5 Main

Development 14,0 14,0 6,8 3,0 2,4 35,0 3,3 8,6 2,6 3,2 8,5 2,8 73,6

Secondary Panel 14,0 14,0 6,8 3,0 2,4 35,0 3,3 8,6 2,6 3,2 8,5 2,8 73,6

No.

2 S

eam

Area 1 Main

Development 16,0 16,0 6,8 2,2 4,2 89,0 6,7 11,8 1,8 2,1 9,2 4,2 66,9

Secondary Panel 14,5 14,5 6,8 2,2 3,5 89,0 7,9 10,9 1,4 1,7 8,7 4,0 71,8

Area 2 Main

Development 16,5 16,5 6,8 2,7 3,6 85,0 6,1 10,6 1,7 2,0 9,4 3,5 65,4

Secondary Panel 15,0 15,0 6,8 2,7 3,0 85,0 7,1 9,8 1,4 1,6 8,9 3,3 70,1

Area 3 Main

Development 16,0 16,0 6,8 2,8 3,3 79,0 6,0 10,1 1,7 2,0 9,2 3,3 66,9

Secondary Panel 15 15 6,8 2,8 2,9 79,0 6,6 9,6 1,4 1,7 8,9 3,2 70,1

Area 4 Main

Development 14 14 6,8 2,8 2,6 54 5,1 9,0 1,8 2,2 8,5 3,0 73,6

Secondary Panel 15 15 6,8 2,8 2,9 54 4,5 9,6 2,1 2,5 8,9 3,2 70,1



6.2.5.7 Multi-Seam

Mining at Schurvekop is expected to be conducted on both the S4L as well as the S2L seam. As a result of

this fact and the recent changes to the planned mining layouts, multi-seam mining is expected to be

conducted across a large portion of the reserve area.

The areas in which multi-seam mining may occur are illustrated in Figure 6-25 below.

Figure 6-25: Mining Areas on the No. 4 Lower Seam and No. 2 Lower Seam

Also, illustrated in Figure 6-25 above are contour lines which indicate the value of the thickness of the

parting between the S4L and S2L seam divided by 1.5. Safety hazards have been known to occur in multi-

seam bord and pillar layouts if the seams being mined are in close proximity and not superimposed.

Guidelines for multi-seam bord and pillar layouts were developed by Salamon and Oravecz in 1976.

Whether pillars are superimposed or not depends on the parting distance, Pt, in relation to the pillar centre

distance, C, and the bord width b.

The general guideline regarding multi-seam superimposition is as follows:

If the parting distance is less than 1.5 times the pillar centre distance then the barrier pillars should be

superimposed;

If the parting distance is less than 0.75 times the pillar centre distance then the in-panel pillars should

be superimposed.

Figure 6-26 shows a flow chart for designing multi-seam workings. What then becomes evident from the

contour lines Figure 6-25 above, taking into account the recommendations of the multi-seam guidelines

included above, is that wherever the pillar centre distance, based on the pillar design calculations included

in 6.2.5.6 above, is to be greater than the value of the contour line in which those pillars are located,

superimposition of the barrier pillars will be required.



This has been found to be the case in the northern portion of the Schurvekop project area where the parting

thickness is less than the required minimum value for superimposition not to be required and as a result the

barrier pillars on the two mining seams will have to be superimposed in this portion of the reserve.

Additional investigations could be conducted using numerical modelling techniques to verify the

requirements to superimpose the barrier pillars in this portion of the reserve based on the local geology.

Figure 6-26: Multi-Seam Design Guideline Flow Chart.



6.2.6 Conclusions and Suggestions

The following conclusions and suggestions are made, based on the investigation which has been conducted

into the feasibility of mining the S4L and S2L seam in the Schurvekop Project area via underground mining

methods:

Mining of both the S4L and S2L in the Schurvekop Project area is deemed to be theoretically viable;

Based on the suggested cut-off criteria of a minimum mining height of 1.65 m and mining depth of 20

m the S4L and S2L have been deemed to be minable across large portions of the Schurvekop area;

The areas in the northern portions of the investigation area in which the depth to the S4L is less than

30 m are deemed to be potentially mineable, however, it is recommended that additional boreholes will

be required in these areas to verify the depth of weathering and specific rock mass properties of the

overburden material before these areas are mined;

A minimum systematic support pattern has been recommended for the different geotechnical areas

identified on both of the mining seams;

The mining area on the two seams has been sub-divided into pillar design areas and a recommended

average pillar centre and bord width proposed per area;

It is important to note that the pillar width should not be less than the bord width at any stage, hence

the minimum recommended centre of 14 m despite the relatively high safety factor of the pillars in

some areas;

Challenging mining conditions area anticipated in areas in which dolerite structures in the form of

dykes and transgressive sills are within close proximity of the mining seam;

The boxcut design is to be compiled by the consulting geotechnical and civil engineers based on the

geotechnical properties of the rock mass gained from the drilling which was conducted in the proposed

area;

Due to the fact that multi-seam mining is proposed for a significant portion of the mining area, it is

important that the multi-seam design guidelines for the pillars and their superimposition are complied

with;

The barrier pillars on the two mining seams will have to be superimposed in the northern portion of the

reserve area based on the multi-seam guidelines. Numerical modelling investigations could be

conducted to either confirm or refute the requirement to superimpose the barrier pillars;

Anticipated levels of contamination have been estimated in this report based on the available

geological and geotechnical information.



6.2.7 References

Brink A.B.A. and Bruin R.M.H. (eds) (1990) Guidelines for Soil and Rock. Logging in South Africa, 2nd

Impression 2002. Proc. Geoterminology

Hoek, E., Carranza-Torres, C. and Corkum, B. 2002. Hoek-Brown criterion – 2002 edition. Proc.

NARMS-TAC Conference, Toronto, 2002, 1, 267-273.

Jennings, J E B, Brink, A B A and Williams, A B, Revised Guide to Soil Profiling for Civil Engineering

Purposes in Southern Africa. The Civil Engineer in S A, p 3-12. January 1973.

National Institute for Transport and Road Research, Guidelines for Road Construction Materials. TRH

14, Pretoria, CSIR, 1987.

SABS 1200D: 1988 Standardised specification for civil engineering construction. D: Earthworks, South

African Bureau of Standards, Pretoria.

Swiss Norm (or Standard) SN 670 010b. 1993. Bodenkennziffern / Coefficients caractéristiques des

sols. Translated from German / French: Typical Soil Properties.

Abramson, LW, Lee, TS, Sharma, S and Boyce, GM (2002) Slope Stability and stabilization Methods,

John Wiley & Sons Inc., New York.

Canbulat, I., and Madden, B.J., (2005). Shallow Depth Mining Considerations. SAIMM. 3rd

Southern

African Rock Engineering Symposium.

Salamon, M. D. G and Oravecz, K. I. (1976) Rock Mechanics in Coal Mining. Chamber of Mines of

South Africa PRD. Series No. 198.

Van der Merwe, J. N. and Madden, B. J. (2010). Rock Engineering for Underground Coal Mining,

Second Edition. SAIMM Special Publications Series 8.

Wagner and Madden (1984) 15 Years’ Experience with the Design of Coal Pillars in Shallow South

African Colliers: An evaluation of the Performance of the Design Procedures and Recent

Improvements. Design and Performance of Underground Excavations. ISRM/BGS, Cambridge, UK,

pp 391 – 399.

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