TECHNICAL REPORT - Cabanga Evironmental€¦ · Report Prepared for: Mr. K. Badenhorst Project...

GeoMech Consulting (Pty) Ltd Metallurgical Resources Consulting (Pty) Ltd, Schurvekop Feasibility Study RE Investigation – GEOM10-2017-01 Email: [email protected] Cell: (+27) 82 413 2641

Report Prepared for: Mr. K. Badenhorst Project Manager Metallurgical Resources Consulting (Pty) Ltd 5 Northumberland Midstream Centurion 1692

Geomech Consulting (Pty) Ltd Report No. GEOM10-2017-001

SCHURVEKOP FEASIBILITY STUDY ROCK ENGINEERING REPORT

20 MAY 2017

Number of Pages Inclusive: (31) Report Compiled by: Mr. D. Lees Senior Rock Engineer

TECHNICAL REPORT Ref. No. GEOM10-2017-001

mailto:[email protected]


Contents

a. INVESTIGATION AREA ........................................................................................................................... 5

b. BOREHOLE POSITIONS .......................................................................................................................... 6

c. GENERALISED STRATIGRAPHY .............................................................................................................. 7

d. SURFACE ELEVATION ............................................................................................................................ 8

e. UNDERGROUND ACCESS ...................................................................................................................... 8

f. IDENTIFIED RESERVE AREAS ON THE NO. 2 AND 4 LOWER SEAMS ...................................................... 9

g. MINING TECHNICAL ............................................................................................................................ 11



EXECUTIVE SUMMARY At the request of Mr. K. Badenhorst, Project Manager, 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 and No. 2 Seam 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 cutoff 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 an geotechnical information, it is recommended that additional drilling and geotechnical testing be conducted in these areas to verify the rockmass 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 No. 4 Lower Seam and No. 2 Seam in the northern portion of the project area will have to be superimposed. Additional investigations using numerical modeling techniques could be conducted to confirm / refute the need to superimpose the barrier pillars on the Two (2) seams in this portion of the project area.



1. INTRODUCTION

At the request of Mr. K. Badenhorst, a geotechnical report has been compiled for inclusion in the Schurvekop Feasibility Study 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 Schurvekop project lies immediately west / north-west of the existing Forzando South mine which is owned by Exxaro Resoureces. The project area is located approximately 15 kilometers 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 No. 2 and 4 Lower Seams in the Schurvekop area have been conducted previously, the results of which were used in this investigation and the compilation of the subsequent report.

2. INFORMATION PROVIDED

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

• Survey information as detailed below: o An electronic (.dxf) file including the following drawing layers:

▪ Reserve areas on both the No. 2 and 4 Lower 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.



3. GEOTECHNICAL INVESTIGATION

a. INVESTIGATION AREA

The Schurvekop project area is indicated in Figure 3-1 below.

Figure 3-1. Schurvekop Project Area. There are Two (2) economically minable seams within the Schurvekop project area i.e. the No. 4 Lower Seam and the No. 2 Seam. The following cut-off criteria were applied to both of these Two (2) seams to identify the mineable reserve areas:

• Minimum mining height (seam thickness) 1.65 m.

• Minimum mining depth (overburden thickness) 20 m. In Figure 3-2 and Figure 3-3 the theoretical mining areas on the No. 4 Lower Seam and the No. 2 Seam respectively are illustrated based on the above criteria.

Figure 3-2. No. 4 Lower Seam, Theoretically Minable Area.

SCHURVEKOP

SEPTEMBER 2009

Legend

No. 4 Lower Seam Mineable Area

.



Figure 3-3. No. 2 Seam, Theoretically Minable Area. As can be seen from Figure 3-3, the mineable portion of the No. 2 Seam is expected to be located towards the center of the project area with the No. 4 Lower Seam theoretically minable in the majority of the project area (Figure 3-2).

b. BOREHOLE POSITIONS

A significant number of boreholes have been drilled within the Schurvekop mining area to date as indicated in Figure 3-4 below.

Figure 3-4. Boreholes Drilled in the Schurvekop Area and Surrounds.

SCHURVEKOP

SEPTEMBER 2009

Legend

No. 2 Seam Mineable Area

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SK042

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SEPTEMBER 2009

Legend


No. 2 Seam Mineable Area

.



c. GENERALISED 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 its based in places. No. 2 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 its based in places.



d. SURFACE ELEVATION

There is up to a 55 m increase in surface elevation in a north-easterly direction across the project area, Figure 3-5.

Figure 3-5. Surface Elevations in the Schurvekop Project Area.

e. 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 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 3-6 below. The responsibility of designing the boxcut based on the updated geotechnical information for this area has been sub-conracted 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 3-6. Current Planning with regards to the Position of the Boxcut and Surface Infrastructure at Schurvekop.

f. IDENTIFIED RESERVE AREAS ON THE NO. 2 AND 4 LOWER SEAMS

An initial investigation into the mineability of the No. 2 and No. 4 Lower 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 No. 2 and No. 4 Lower Seams during this investigation:

o Minimum mining height of 1.6 m, o Maximum mining height of 2.8 m, o Minimum overburden thickness of 30 m,

These criteria have subsequently been revised as documented in Section 3a of this 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 cutout distance, (this may however 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 minable. Based on these assessments, areas on both the No. 2 Seam as well as the No. 4 Lower Seam within the theoretically minable areas illustrated in Figure 3-2 and Figure 3-3 above were deemed to be minable or un-minable. Illustrated in Figure 3-7 and Figure 3-8 below are the mining layouts on the No. 4 Lower Seam and the No. 2 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 3-7. No. 4 Lower Seam, Proposed Mining Layouts.

SCHURVEKOP

SEPTEMBER 2009



Figure 3-8. No. 2 Seam, Proposed Mining Layouts.

g. MINING TECHNICAL

3.g.1. CONTAMINATION. 4 Lower Seam Indicated in Figure 3-7 above is the area on the No. 4 Lower 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 No. 4 Lower Seam:

o In the proposed mining areas, the immediate roof of the No. 4 Lower 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%.

o The immediate roof thickness is noted to be significantly thinner in the south-western, western and north-western portions of the reserve.

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

o In areas in which laminated sandstone / siltstone and / or shale are expected to form the immediate roof higher levels of contamination can be anticipated.

o 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.

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

o There is a sandstone parting which is of significant thickness and occurs within the “minable” zone on the No. 4 Lower Seam in the southern portions of the reserve, similar to Forzando South which will have to be negotiated.

o In the majority of the Schurvekop area the immediate No. 4 Lower Seam floor is noted to consist of an interlaminated sandstone-siltstone.

SCHURVEKOP

SEPTEMBER 2009



o 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.

2 Seam Indicated in Figure 3-8 above is the single area identified as theoretically mineable on the No. 2 Seam 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 No. 2 Seam:

o All areas within the mineable area on the No. 2 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.

o The percentage of sandstone in the immediate roof based on the available information isn’t expected to drop below 80 %.

o 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.

o In the majority of the Schurvekop area the immediate No. 2 Seam floor is noted to consist of either a dark Siltstone or a Shale.

o 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.

3.g.2. Overburden and Mining Depth. No. 4 Lower Seam Indicated on Figure 3-8 below is the 4 Lower Seam’s overburden thickness for the entire Schurvekop area with the proposed No. 4 Lower Seam mining layouts super-imposed on top of that.

Figure 3-8. The Schurvekop Area illustrating the thickness of the No. 4 Lower Seam’s Overburden.

SCHURVEKOP

SEPTEMBER 2009

Legend

S4LOB20mto30m

S4LOB30mto40m

S4LOBLessthan20m

S4LOBmorethan40m


.



The depth at which mining is proposed to take place on the No. 4 Lower Seam ranges from a minimum of 20 m to a maximum depth of in the region of 67 m as indicated in Figure 3-9 below.

Figure 3-9. Statistics based on the Geological Grids indicating the range, minimum, and maximum value for the expected No. 4 Lower Seam’s overburden thickness in the proposed mining areas.

2 Seam Indicated in Figure 3-10 is the statistical analysis including the range, minimum, and maximum values for the expected No. 2 Seam’s overburden thickness in this area based on the geological grids. The depth at which mining is proposed to take place on the No. 2 Seam ranges from a minimum of approximately 35 m to a maximum depth of in the region of 97 m.

Figure 3-10. Statistics based on the Geological Grids indicating the range, minimum, and maximum value for the expected No. 2 Seam’s overburden thickness in the proposed mining areas. 3.g.3. Roof Strata & Roof Support. 4 Lower Seam As stated in Section 1 on Contamination above the following is true of the No. 4 Lower Seam and No. 2 Seam’s immediate roof:

o The immediate roof of the No. 4 Lower 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 %.

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



o 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.

o All areas within the mineable area on the No. 2 Seam 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.

o The percentage of sandstone in the immediate roof based on the available information isn’t expected to drop below 80 %.

o 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.

o 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.

o Two (2) types of systematic roof support will be required when mining on the No. 4 Lower Seam and the No. 2 Seam at Schurvekop i.e. roof support designed based on beam formation principles and systematic support designed on suspension principles.

o These areas are illustrated in Figure 3-11 and Figure 3-12 below for the No. 4 Lower Seam and the No. 2 Seam respectively.

o 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 (3) 0.9 m or 1.2 m long roofbolts installed per row with rows spaced a maximum distance of 2.0 m apart.

o 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.

o The 1.2 m long roofbolts must be installed in an 1 120 mm long, 25 mm diameter hole, with a single 23 mm x 600 mm resin capsule.

o 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 (4) 1.5 m long roofbolts installed per row with rows spaced a maximum distance of 1.5 m apart.

o 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.

o 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 3-11. No. 4 Lower Seam recommended Roof Support Design Principles.

SCHURVEKOP

SEPTEMBER 2009

Legend

No. 4 Seam Beam Creation Support

No. 4 Seam Suspension Support



Figure 3-12. No. 2 Seam recommended Roof Support Design Principles.

3.g.4. Structure. Included below in Figure 3-13 and Figure 3-14 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 (2) such structures intersect. Additional specialized support as well as changes to the mining dimensions and methods may be required when mining in such areas.

SCHURVEKOP

SEPTEMBER 2009

Legend

No. 2 Seam Suspension Support



Figure 3-13. Illustration of the position of the geological structures identified through geophysics relative to the theoretical mining areas on the 4 Lower Seam.

Figure 3-14. Illustration of the position of the geological structures identified through geophysics relative to the theoretical mining area on the 2 Seam.

SCHURVEKOP

SEPTEMBER 2009

Legend

SillEdgeorDykeProbable

DataSillNearSurface

DataLineament

PossibleDykeStefaans

ProbableDykeStefaans

SCHURVEKOP

SEPTEMBER 2009

Legend

SillEdgeorDykeProbable

DataSillNearSurface

DataLineament

PossibleDykeStefaans

ProbableDykeStefaans



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 (2) identified mining seams. Included in Figure 3-15 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 3-16 below.

Figure 3-15. A plan indicating the positions at which the D2 Dolerite Sill is expected to intersect the 4 Lower Seam (Blue), as well as its anticipated zone of influence.



Figure 3-16. A Geological Cross-section along the line A-A’ in Figure 3-16 above, indicating the position of the Dolerite Sill relative to the 4 Lower and 2 Seams. 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 No. 4 Lower Seam as well as the No. 2 Seam and the D2 Dolerite Sill. The distances between the No. 4 Lower Seam and the No. 2 Seam and the D2 Sill are illustrated in Figure 3-17 and Figure 3-18 below respectively. From Figure 3-16 above as well as Figure 3-17 and Figure 3-18 below it is evident that the D2 Sill will migrate from below the No. 4 Lower Seam in the south to above the No. 4 Lower Seam in the north in the southern portion of the Schurvekop reserve area. As a result of the intersection of the sill and the No. 4 Lower Seam 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 3-17. Position of the D2 Dolerite Sill relative to the No. 4 Lower Seam.

SCHURVEKOP

SEPTEMBER 2009

Legend

4lsftod2sr

Elevation

0 - 72,85

-5 - 0

-10 - -5

-28,014 - -10

-53,23 - -28,014

4lsrtod2sf

Elevation

40,665 - 61,85

10 - 40,665

5 - 10

0 - 5

-44,075 - 0

-65,26 - -44,075



Figure 3-18. Position of the D2 Dolerite Sill relative to the No. 2 Seam. 3.g.5. Bord Width. A bord of 6.8 m has been used in the design calculations. Core of the immediate roof above the No. 4 Lower Seam 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 cutout 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.

SCHURVEKOP

SEPTEMBER 2009

Legend

2lsftod2sr

Elevation

0 - 99,07

-5 - 0

-10 - -5

-21,01 - -10

-21,01

2lsrtod2sf

Elevation

60 - 92,07

10 - 60

5 - 10

0 - 5

-32,56 - 0



3.g.6. Pillar Design. For the purposes of the pillar design within the Schurvekop project area, both the No. 4 Lower Seam as well as the No. 2 Seam have been sub-divided into design areas as indicated in Figure 3-19 and Figure 3-20 below. It can be noted from these Two (2) figures that the No. 4 Lower Seam has been divided into Five (5) design areas and the No. 2 Seam into Four (4). Based on the average mining depth and height in each of these areas a recommended average pillar center has been calculated and is recommended for the Main Developments as well as the Secondary Panels in Table 3-1 below.

Figure 3-19. Pillar Design Areas for the No. 4 Lower Seam.

SCHURVEKOP

SEPTEMBER 2009

Legend

No. 4 Lower Seam Pillar Design Area 1





.



Figure 3-20. Pillar Design Areas for the No. 2 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)

SCHURVEKOP

SEPTEMBER 2009

Legend

No. 2 Seam Pillar Design Area 1




.



Limitations to the Salamon & Munro Pillar Strength Formula

• Pillar widths should be in excess of 5.0m

• w:h ratio should exceed 2.0.

• At shallow depths, (< 40m) the formula is very sensitive to even small variations in pillar widths. Guidelines have been drafted for workings shallower than 45m.

• Pillar width to height ratio less than 5.0.

• Applicable to seams shallower than 150m.

• 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 (𝜎) of a coal pillar is given by the following power formulae:

𝜎 = 𝐾𝑤𝛼ℎ𝛽 Where:

w and h represent the pillar width and the mining height respectively. K and, 𝛼 and 𝛽 and are determined by statistical analysis.

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

K= 7.176, 𝛼=0.46, 𝛽= -0.66 A revision of the coal pillar strength for South African coal seams, which includes revised values for 𝛼 and 𝛽 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, 𝛼=0.6126, 𝛽= -0.7554 These values for 𝛼 and 𝛽 have been used in the calculation of the pillar strength according to the Coaltech formulas in Error! Reference source not found. 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 factor of safety (FOS) can be calculated using the formula:

FOS=σ/q The factor of safety (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 Error! Reference source not found. 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 centers per mining area as include in Table 3-1 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 3-1. Pillar Safety Factor and Size Calculations in the various mining areas on the No. 4 Lower Seam and No. 2 Seam at Schurvekop.

Seam Area Panel Type Center 1 (m)

Center 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


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


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


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


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


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


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


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



3.g.7. MultiSeam. Mining at Schurvekop is expected to be conducted on both the No. 4 Lower Seam as well as the No. 2 Seam. As a result of this fact and the recent changes to the planned mining layouts on the No. 4 Lower Seam and No. 2 Seam, multi-seam mining is expected to be conducted across a large portion of the reserve area. The areas in which multiseam mining may occur are illustrated in Figure 3-21 below.

Figure 3-21. Areas in which the mining on the No. 4 Lower Seam and No. 2 Seam could most likely overlap as well as the contour lines representing the parting between the Two (2) seams divided by 1.5. Also, illustrated in Figure 3-22 above are contour lines which indicate the value of the thickness of the parting between the No. 4 Lower Seam and No. 2 Seam divided by 1.5. Safety hazards have been known to occur in multiseam bord and pillar layouts if the seams being mined are in close proximity and not superimposed. Guidelines for multiseam 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 center distance, C, and the bord width b. The general guideline regarding multiseam superimposition is as follows:

• If the parting distance is less than 1.5 times the pillar center distance then the barrier pillars should be superimposed,

• If the parting distance is less than 0.75 times the pillar center distance then the in-panel pillars should be superimposed.

SCHURVEKOP

SEPTEMBER 2009

Legend

Multi-Seam Areas

2to4part_1_5

Elevation

24 - 38,45

22 - 24

20 - 22

19 - 20

18 - 19

17 - 18

16 - 17

15 - 16

14 - 15

4,17 - 14

.



Figure 3-22 shows a flow chart for designing multiseam workings.

Figure 3-22. Multiseam design guideline flow chart. What then becomes evident from the contour lines included in Figure 3-21 above, taking into account the recommendations of the multi-seam guidelines included above, is that wherever the pillar center distance, based on the pillar design calculations included in Section 3.g.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 (2) 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.

H Depth FIXED hs Seam height w Pillar width SF Safety factor OPTIONAL h Mining height b Bord width

SELECT h & b SELECT SF FOR CRITICAL SEAM

CALCULATE w & C

(using Salamon or Squat pillar formula)

MULTI SEAM

DESIGN FLOW CHART e% AREA EXTRACTION v% VOLUME EXTRACTION C PILLAR CENTRE DISTANCE P PARTING BETWEEN SEAM b BORD WIDTH w PILLAR WIDTH n No. OF PILLARS IN THE PANEL C

B CENTRE DISTANCE OF BARRIER PILLARS W

B BARRIER PILLAR WIDTH

IS PARTING > 1,5 C

NO NEED TO SUPERIMPOSE BARRIERS

OR PANEL PILLARS

SUPERIMPOSE BARRIERS

IS PARTING >0.75C. APPLY LIMITING

DISTANCE CRITERIA

NO NEED TO SUPERIMPOSE

PANEL PILLARS

PANEL WIDTH FIXED THEREFORE PILLAR WIDTH DIMENSIONS GIVEN BY

n.w + (n+1)b = C B - W B

PARTING > 2b

IS DESIGN A MINIMUM SF

OF 1,7 SUPERIMPOSE PANEL

PILLARS

ARE SELECTED SF's LESS OR EQUAL THAN

1,4 FOR COMBINED h OF BOTH SEAMS AND INDIVIDUAL SEAMS MINIMUM SF OF 1,8

INPUT

IS SEAM DEPTH < 40 m

SELECT h & b AND CALCULATE w & C

ACCORDING TO SHALLOW DEPTH GUIDELINES

e%<75, SF>2,1, w>6,5 m, w/h>2,2

YES

NO

NO

NO

YES

YES

LESS THAN CRITICAL LIMITING

DISTANCE

GREATER THAN CRITICAL LIMITING

DISTANCE SELECT SF SELECT b, h

CALCULATE w (using Salamon or Squat pillar formula)

CALCULATE e% CALCULATE v%

POSSIBLE PARTING FAILURE

END

YES

YES

NO

YES NO

NO



4. CONCLUSIONS AND SUGGESTIONS

The following conclusions and suggestions are made, based on the investigation which has been conducted into the feasibility of mining the No. 4 Lower Seam and No. 2 Seam in the Schurvekop project area via underground mining methods:

• Mining of both the No. 4 Lower Seam and No. 2 Seam in the Schurvekop project area is deemed to be theoretically viable.

• Based on the suggested cutoff criteria of a minimum mining height of 1.65 m and mining depth of 20 m the No. 4 Lower Seam and No. 2 Seam 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 No. 4 Lower Seam 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 rockmass 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 (2) seams has been sub-divided into pillar design areas and a recommended average pillar center 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 center 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 rockmass gained from the drilling which was conducted in the proposed area.

• Due to the fact that multiseam mining is proposed for a significant portion of the mining area, it is important that the multiseam design guidelines for the pillars and their superimposition are complied with.

• The barrier pillars on the two (2) mining seams will have to be superimposed in the northern portion of the reserve area based on the multiseam 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.

Should you have any further queries please feel free to contact myself at the following locations: Cell. (082) 413 2641, or Email. [email protected]. Yours Sincerely Geomech Consulting (Pty) Ltd Per: Duncan Lees (Senior Rock Engineer)



5. REFERENCES

a. Canbulat, I., and Madden, B.J., (2005). Shallow Depth Mining Considerations. SAIMM. 3rd Southern African Rock Engineering Symposium.

b. Salamon, M. D. G and Oravecz, K. I. (1976) Rock Mechanics in Coal Mining. Chamber of Mines of South Africa PRD. Series No. 198.

c. Van der Merwe, J. N. and Madden, B. J. (2010). Rock Engineering for Underground Coal Mining, Second Edition. SAIMM Special Publications Series 8.

d. 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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