Golder Associates Pty Ltd Suite 7, Level 1, 132-138 Pacific Highway, Charlestown, New South Wales 2290, Australia (PO Box 724 Charlestown NSW 2290) Tel: +61 2 4946 2700 Fax: +61 2 4946 2711 www.golder.com Golder Associates: Operations in Africa, Asia, Australasia, Europe, North America and South America A.B.N. 64 006 107 857 Golder, Golder Associates and the GA globe design are trademarks of Golder Associates Corporation. 1.0 INTRODUCTION The NSW Division of Resources and Energy (DRE) have responded to Airly Mine concerning the Modification Application (DA162/91 – Mod 3). It is understood that the area involved is related to Golder Associates (GA) Reports 127621105-093-Rev0 and 127621105-109-Rev1; these reports address pillar stability and subsidence assessments for the proposed workings in 103 Panel, 121 Panel, 122 Panel, 200 Area Extension, 205 Panel, 100 Cross Panel and 420 Panel. In this report, a response is made to the DRE comments, which are attached for convenience as Appendix A. The DRE state that: “It proposed to manage impacts to cliff lines and rock formations in the EPZs by adopting an arbitrary pillar design factor of safety, nominally greater than two (FOS>2)”. “EPZ” stands for Environmental Protection Zone, which the Development Consent states “…are to be adequately protected so as to avoid adverse structural or visual impact caused by mining”. The original definition of the area of the EPZs related to a mining layout that envisaged total extraction. Also, the DRE have commented that: “Notwithstanding the lack of a detailed final mine plan in the EA there is uncertainty as to the long- term stability of parts of the proposed workings, for the following reasons: The EA and related geotechnical assessments have not adequately considered the effects of geotechnical conditions on pillar performance, particularly roof and floor conditions. Additional information sought from the proponent indicates potentially poor roof conditions which it appears has not been considered in the pillar stability assessments in the EA; The proposed pillar width to height ratio will be as low as 4.2:1 for some pillars. This ratio is too low for pillars that are intended to be stable long-term. Additionally, poor roof conditions may adversely affect the width to height ratio and hence stability, particularly over time; and It is noted that over a certain depth of cover remnant pillar sizes formed using the criteria in EA may be regarded as non-conforming under current safety legislation. In order to address the above comments, it is firstly necessary to outline the design methodology adopted for bord and pillar workings at Airly Mine. DATE 27 August 2014 REPORT No. 127621105-137-Rev0 TO David King, Senior Mining Engineer, Airly Mine, Glen Davis Road, Capertee, NSW 2846. RESPONSE TO DRE LETTER CONCERNING MODIFICATION APPLICATION (DA162/91 – MOD 3)
Transcript
Golder Associates Pty Ltd
Suite 7, Level 1, 132-138 Pacific Highway, Charlestown, New South Wales 2290, Australia (PO Box 724 Charlestown NSW 2290) Tel: +61 2 4946 2700 Fax: +61 2 4946 2711 www.golder.com
Golder Associates: Operations in Africa, Asia, Australasia, Europe, North America and South America
A.B.N. 64 006 107 857 Golder, Golder Associates and the GA globe design are trademarks of Golder Associates Corporation.
1.0 INTRODUCTION
The NSW Division of Resources and Energy (DRE) have responded to Airly Mine concerning the Modification Application (DA162/91 – Mod 3). It is understood that the area involved is related to Golder Associates (GA) Reports 127621105-093-Rev0 and 127621105-109-Rev1; these reports address pillar stability and subsidence assessments for the proposed workings in 103 Panel, 121 Panel, 122 Panel, 200 Area Extension, 205 Panel, 100 Cross Panel and 420 Panel. In this report, a response is made to the DRE comments, which are attached for convenience as Appendix A.
The DRE state that: “It proposed to manage impacts to cliff lines and rock formations in the EPZs by adopting an arbitrary pillar design factor of safety, nominally greater than two (FOS>2)”.
“EPZ” stands for Environmental Protection Zone, which the Development Consent states “…are to be adequately protected so as to avoid adverse structural or visual impact caused by mining”. The original definition of the area of the EPZs related to a mining layout that envisaged total extraction.
Also, the DRE have commented that:
“Notwithstanding the lack of a detailed final mine plan in the EA there is uncertainty as to the long-term stability of parts of the proposed workings, for the following reasons:
The EA and related geotechnical assessments have not adequately considered the effects of geotechnical conditions on pillar performance, particularly roof and floor conditions. Additional information sought from the proponent indicates potentially poor roof conditions which it appears has not been considered in the pillar stability assessments in the EA;
The proposed pillar width to height ratio will be as low as 4.2:1 for some pillars. This ratio is too low for pillars that are intended to be stable long-term. Additionally, poor roof conditions may adversely affect the width to height ratio and hence stability, particularly over time; and
It is noted that over a certain depth of cover remnant pillar sizes formed using the criteria in EA may be regarded as non-conforming under current safety legislation.
In order to address the above comments, it is firstly necessary to outline the design methodology adopted for bord and pillar workings at Airly Mine.
DATE 27 August 2014 REPORT No. 127621105-137-Rev0
TO David King, Senior Mining Engineer, Airly Mine, Glen Davis Road, Capertee, NSW 2846.
RESPONSE TO DRE LETTER CONCERNING MODIFICATION APPLICATION (DA162/91 – MOD 3)
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2.0 PILLAR STABILITY
2.1 Pillar Design Issues for Subsidence Control
To control subsidence above coal pillar workings, long-term pillar design should take into account the following possible issues and subsidence mechanisms:
pillar instability (e.g., pillar strength and load), immediate pillar floor and roof stability and the potential for bearing failure, overburden strata spanning capability and panel dimensions (i.e. primarily the span of the extracted area and depth).
2.2 Pillar Factor of Safety and the Probability of Stability Concept
The assessment of pillar stability requires the determination of pillar load, strength and an appropriate Factor of Safety (FoS), which is defined as: Factor of Safety = Pillar Strength
Pillar Stress
The FoS concept is commonly applied when the potential for pillar collapse or failure is being analysed, as it can generally be related to the probability of failure occurring. The pillar stability assessment for Airly have utilised the most recent UNSW pillar strength equations (Salamon et al, 1996) for Australian coal pillars with w/h ratios of >5, as follows:
115
29.063.27
5.2
11.022.0
51.0
h
w
hwm
ms
where:
σs = strength (MPa) w = minimum pillar width (m) h = roadway height (m) Θ = a dimensionless ‘aspect ratio’ factor for rectangular pillars defined by
Salamon et al, 1996 For pillars with width to height ratios of ≤ 5 the pillar strength is determined as follows:
( ) 51.0
84.0s h
w6.8
Θ=σ
A probability of stability of 99.9% is attained at a Factor of Safety of 1.63, see Figure 1, and further increases in FoS have minimal effect, as the probability of stability curve approaches 100% asymptotically. From a risk management perspective, increasing the FoS beyond 1.63 can only reduce the failure probability by <0.1%. It is emphasised that the FoS relates to the overall panel situation, rather than that of individual pillars. The consequences of panel collapse are a primary consideration, as these determine the acceptable probability of failure, which in turn allows an appropriate FoS to be determined. For example, prudent risk management suggests that the probability of failure for long-term first
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workings panels beneath sensitive surface structures should be negligible. In Australia, long-life critical pillars (e.g. in main headings and for the protection of surface infrastructure) are often designed to a FoS of ≥ 2.11, which equates to a nominal failure probability of one panel in a million, based on the UNSW power law strength equation (Salamon et al, 1996). This reduces the probability of failure to a level that would be considered acceptable in other key fields of public interest. It is important to note that the South African and Australian databases from which the UNSW pillar design formulae were derived cover a broad range of roof and floor materials, including mudrocks, coal, siltstones and sandstones. Therefore, these materials and the variability in pillar strength that may be associated with them are implicitly recognised and largely catered for in the FoS approach. Uncertainty associated with the natural variability in coal measures strata often prohibits design to low FoS values. Geological variability partly accounts for the scatter in the population of failed pillar cases and usually necessitates design to FoS values of >1.5, equivalent to low failure probabilities. Back analysis indicates that incidences of pillar instability traditionally associated with weak floor, for example, can very often be explained in terms of ‘conventional’ empirical design criteria, notably in terms of FoS and pillar w/h ratio, as will be discussed in Section 2.3. Similarly, the database encompasses pillars in a significant number of seams in different geotechnical environments; consequently the existence of pillar weaknesses is very largely reflected and implicit within the variability in the failed and intact pillar cases, such that these weaknesses are again very largely catered for by adopting appropriate FoS values. It should also be understood that the nominal probability of failure is related to the life-time of the pillar database that underpins the empirical design methodology; currently this averages approximately fifty years (i.e. of the order of 100 years of coal pillar history is available). The annualised probability of failure (a concept more commonly applied in engineering practice) is therefore about one-fiftieth of the nominal failure probability. In summary, it should be clear from Figure 1 that provided the workings under consideration are designed to a minimum system FoS of around 1.6, it is necessary to look beyond this concept to obtain any further assurance of long-term stability that may be required. An issue requiring particular consideration is the w/h ratio of the pillars, which is discussed in detail in the following section. 2.3 The Importance of Pillar Width to Height (w/h) Ratio
The role of increasing w/h ratio in enhancing coal pillar stability has long been known. Back analysis of case histories from South Africa, Australia and elsewhere has shown that w/h ratio exerts a major influence on coal pillar strength. At low w/h ratios (<3) overloaded coal pillars tend to fail in a brittle, uncontrolled fashion, whereas at greater w/h ratios (>4) the overloaded pillars demonstrate a more plastic form of deformation: significant displacement may still take place in the form of roof to floor convergence, as well as rib spall, but the pillar core remains confined and tends to retain its load carrying ability, generally without failing in the commonly understood sense. This was illustrated by Madden (1987) with laboratory UCS tests on sandstone discs during the initial practical development of the squat pillar formula (he used sandstone because coal samples are more heterogeneous and difficult to prepare). It was also shown by Das (1986) in tests on Indian coals, see Figures 2a and 2b. The potential impact of localised geological structures, such as faults, also diminishes rapidly as pillar w/h ratio increases, as illustrated schematically in Figure 3. International coal industry experience confirms the importance of w/h ratio to stability; incidences of collapse are concentrated at low w/h ratios, even in known weak floor environments.
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Furthermore, back analysis of the results of in situ coal pillar tests from South Africa indicates that the post-peak modulus (stiffness) of actual pillars becomes positive (i.e. suggesting strain hardening behaviour) once the w/h ratio exceeds 4.1, as seen in Figure 4. In other words, even if the coal is heavily fractured, the overall pillar does not fail in the commonly understood sense; a creep event becomes the likely worst-case scenario.
Pillar width to height ratio, applied in conjunction with other design criteria, such as FoS, is a useful indicator of design reliability. This is illustrated in Figure 5, which presents the FoS versus w/h ratio relationship for a combined database of failed South African and Australian bord and pillar panels, plus a database of highwall mining failed pillar cases (Hill, 2005). These three databases are highly complementary in nature, reflecting the experiences of their respective industries. For example, the Australian data provides insight with regard to pillar behaviour at relatively high w/h ratios and furnishes the failed case at the w/h ratio of 8.2. In contrast, the South African industry has a high proportion of mining geometries with lower w/h ratios, which is partly reflected in the maximum w/h ratio of only 3.7 for a South African failed case. Similarly, the highwall mining failed pillar cases cover the lower end of the range of w/h ratios, from 0.6 to 1.4. There are no failed cases in the combined database with a w/h ratio of greater than 8.2, even at a very low FoS, and there is only one failed case at a w/h ratio of >5. The highest FoS assigned to a bord and pillar collapse is 2.1 and this was associated with a w/h ratio of only 2.2. Although there are failed highwall mining pillars with Factors of Safety of >2, all of them have pillar w/h ratios of <2. A limit envelope can be defined for the database of failed cases, illustrated by the curve and given by the following equation:
w/h ratio = 22.419e-1.148*(Factor of Safety)
Beyond this envelope, there is no precedent for failure within the three databases. It is worth noting that the exclusion of the highwall mining pillar data would not materially change the shape of this limit envelope. In the case of long life (>5 years) pillars, if it is reasonable to assume that the pillars are, or will at some point in the future, be subjected to full tributary area loading, then it is generally considered prudent to design the pillars to be outside (i.e. above) the envelope defined by this equation, even though there are many examples of stable pillars that fall within it. Furthermore, in the case of critical, long-life pillars, it is considered prudent to allow an additional margin beyond this curve. GA generally suggests a 20% margin, which is defined by the second (i.e. outer) curve in Figure 5 and the following equation:
w/h ratio = 26.903e-0.957*(Factor of Safety) 2.4 Summarised Composite Design Criteria based on FoS and w/h Ratio
As previously indicated, coal pillar design criteria should reflect the specific requirements and nature of the workings (e.g. short-term production panel, as opposed to long-life pillars with surface protection constraints). The approach adopted by GA in Australia can be summarised as follows (Hill, 2005):
A. Short-term production workings, with considerable local knowledge: design may be within the failed pillar database limit envelope, under controlled circumstances.
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B. Short-term production workings (general): design on the basis of being beyond the failed
pillar database limit envelope. C. Key underground workings, for example main headings, with medium to long-term
serviceability / stability requirements: design on the basis of the limit envelope plus 20% (i.e. the outer database curve).
D. Underground workings beneath critical, highly sensitive surface structures and / or features
(e.g. key infrastructure, such as railways / waterways): design on the basis of a minimum w/h ratio of five (i.e. squat pillars) with a minimum nominal FoS of 2.11 according to the Salamon et al 1996 formulae (i.e. a probability of failure of ≤ 1 in a million).
These criteria are summarised in Figure 6. They are considered guidelines and it is important that specific attention be given to the geotechnical / mining environment, including historical experience of ground behaviour in the seam under consideration. A subsequent review of long-term pillar stability issues and the associated design considerations concluded that these design criteria remain appropriate for Australian conditions (Hill, 2010). In Strata Engineering Report 09-001-AIR-4 (SEA, 2010), the partial extraction situation at Airly Mine was considered analogous to “key underground workings” (i.e. Category C above); long-term stability is required for surface protection, although in this case the surface features were not in general considered in the highest category of “critical infrastructure”. The Category C approach has been applied to the mine workings developed at Airly to-date, without incident. However, for preliminary design purposes, the cliff lines were not a specific focus. Subsequently, in the Subsidence Impact Assessment (SIA) for the Airly deposit (GA Report No. 127621105-003-R-Rev2, 2013), a minimum FoS of 2.11 was also adopted for pillars underlying “cliff line zones” defined by GA, noting the following:
The cliff line zones defined by GA are contained within and are less extensive than the EPZs originally stipulated for a total extraction layout.
As previously indicated, a FoS of 2.11 equates to a nominal probability of panel failure of one in a million.
A geotechnical assessment of the Airly deposit for the purpose of assessing partial extraction options did not identify roof or floor materials that would be considered unusually weak and that might otherwise necessitate the adoption of alternative / more conservative pillar design criteria (SEA, 2012).
Experience of mining the Lithgow Seam does not indicate that floor stability is likely to be an issue for pillar stability at the depths of cover involved at Airly.
The mine has operational controls for responding to poor ground that limit pillar splitting / quartering.
The impact of the varying topography in the context of practical bord and pillar design is the application of average panel Factors of Safety that significantly exceed the design minima.
3.0 ADDITIONAL COMMENTS
The issues raised by DRE are further addressed as follows.
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3.1 Potentially Poor Roof Conditions
As noted in Section 2, the databases from which the UNSW pillar design formulae were derived cover a broad range of roof and floor materials and the variability in pillar strength that may be associated with them are implicitly recognised and largely catered for in the FoS approach. Nevertheless, as noted in previous reports to Airly (e.g. SEA Report No. 09-001-AIR-10, 2012), it is considered appropriate to address levels of geological structure and weak roof conditions that are considered atypical / abnormal. In that regard, the mine undertakes mapping prior to splitting / quartering of pillars. In areas of structure, the following guidelines have been recommended:
No splitting should be undertaken with a horizontal distance of 35m of any reverse (thrust) fault or dyke.
No splitting should be undertaken in a pillar intersected by a normal fault with a throw >0.5m.
No splitting should be undertaken in a pillar intersected by two or more normal faults with individual throws >0.2m.
As a result, atypical / abnormal strata conditions not catered for in the general FoS approach are addressed on an individual pillar level, rather than within the general pillar geometry guidelines. 3.2 Inadequate Pillar Width to Height Ratios
Final pillar width to height ratios range from 4.1 upwards, with associated high Factors of Safety. To assist in assessing the conservatism of the designs, these are plotted in terms of the GA design nomogram on a panel by panel basis in Figures 7a to 7l. All designs plot satisfactorily on or above the design curve recommended for long-term stability (i.e. as Category C or above).
Furthermore, the coal pillars in each panel can be expected to perform as a system, rather than independently. It is therefore also worth noting the following typical ranges of FoS for each of the panels:
Panel FoS
103 3 to 4
200 Extension 4 to 6
205 (Option 1) 3 to 5
205 (Option 2) 2 to 4
100 Cross (Opt. 1) 4 to 6
100 Cross (Opt. 2) 2 to 3
420 (Opt. 1) 3 to 5
420 (Opt. 2) 2 to 4
121 (Opt. 1) 3 to 6
121 (Opt. 2) 3 to 6
122 (Opt. 1) 3 to 6
122 (Opt. 2) 3 to 6
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“Option 1” refers to pillars formed on 35m square centres with splitting / quartering, whereas “Option 2” refers to pillars formed on 20.5m by 35m centres, with splitting only.
Given the various combinations of w/h ratio and FoS, the pillars are considered adequately dimensioned to ensure long-term stability.
DRE state that poor roof conditions may adversely affect the width to height ratio and hence pillar stability, particularly over time. The nature of the database, roof conditions at the mine and controls for limiting splitting / quartering in the presence of structure have been noted previously.
It should be understood that the South African and Australian databases employ a combination of nominal (design) and actual (as built) dimensions, which will differ in practice. As with geological variability, geometrical discrepancies are therefore inherent within the database and contribute to the spread of values, such that it is generally considered prudent to design to Factors of Safety of significantly greater than 1.
Salamon and Oravecz 1976 addresses this issue as follows:
“Since the pillar strength formula was derived from practical mining data, in which similar discrepancies were inherent, a safety factor, chosen on the basis of the previous discussion, will largely take into account the errors arising from this source”.
Note that the ‘previous discussion’ refers to Factors of Safety of ~1.6.
Furthermore, it is important to understand that the database, empirical strength formulae and the associated probabilities of stability are not founded on the likely actual pillar geometry at the moment of collapse. It is simply not rational to base an assessment on what the actual pillar geometry may have become after a period of time or may be at some point in the future. To take this approach across the whole of the database (even if it could be rationally undertaken, which it cannot) would simply mean that smaller and/or higher coal pillars would be associated with higher probabilities of stability. In other words, assessing coal pillar stability on the basis that some unquantified (and frequently unquantifiable) deterioration may take place over time to change the actual pillar dimensions amounts to ‘double dipping’ of factors already inherently accounted for within the database and is not logical.
By way of illustration, take the following worst case example of a split and quartered pillar on (final) 17.5m square centres at a depth of 110m, mined at a height of 2.8m and with a representative roadway width of 6m (allowing for breakaways):
Design FoS = 2.0 (note that the pillar is not in a cliff line zone as defined by GA)
Design w/h ratio = 4.1
Design probability of pillar stability = 99.9993% (note that the average pillar FoS for the panel is substantially higher, with a higher associated probability of panel stability)
If an average of 0.3m of top coal ply falls from the roof of the unsupported area in the medium to long-term, then the average final height is 2.9m and the situation becomes as follows:
Final FoS = 1.9
Final w/h ratio = 3.9
Final probability of pillar stability = 99.9993% (i.e. rationally, the probability of stability remains unchanged)
Local experience of pillar splitting and quartering to-date suggests that top coal ply failure in the unsupported area is typically very limited. Also, general experience of mining the Lithgow Seam at the depths involved indicates that long-term roof deterioration tends to be very limited, even in the
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absence of roof support. Finally, it should be noted that the underpinning database of failed bord and pillar panels is dominated by cases involving levels of roof support that would be considered very limited to negligible in current Australian terms. Long-term coal pillar stability is not a function of the installed level of roof support.
The issue of potential long-term deterioration of workings leading to eventual failure is an important consideration, particularly if surface features warrant protection. In the Australian and South African databases, apart from one uncertain Australian case (i.e. at between 80 and 170 years) the maximum recorded time interval from mining to subsequent pillar failure is 52 years and the median time to failure is five years.
Expressed in the context of pillar FoS and width to height ratio values, it can again be shown that the likelihood of failure reduces markedly with time and is related to pillar stability, see Figures 8a and 8b. Referring to Figure 8a, it can be seen after an elapsed period of 20 years, there are no cases of pillar collapse at FoS values of >1.5. After 40 years, there are no failure cases at FoS values of >1.4. Referring to Figure 8b, it can be seen after an elapsed period of 10 years, there are no cases of collapse involving pillars with width to height ratios of >3. After 40 years, there are no failure cases at w/h ratios of >2.
The industry databases illustrate that the majority of failures occur within a short time of mining, due either to inappropriate design or some form of local anomaly. As time progresses, the actual likelihood of failure decreases and those collapses that do occur involve designs that would be considered increasingly marginal. There is no evidence to suggest that pillar failure becomes inevitable or even more likely over time. On the contrary, the historical data suggests that pillar deterioration (e.g. associated with spall and weathering) tends to a limit over time.
3.3 Non-conforming Pillars Under Current Safety Legislation
Coal pillar sizes in New South Wales (NSW) are regulated primarily by Clause 88 of the NSW Coal Mine Health and Safety Regulation (CMHSR) 2006, which contains a long-standing provision that the plan dimension of a coal pillar should be not less than one-tenth of the cover depth or 10m, whichever is the greater. It is understood from discussions with the mine that there is no intention to apply for exemption from this provision and as such, all pillars will conform to the minimum width requirement. 4.0 CONCLUDING REMARKS
This report addresses the issues raised by the DRE. Finally, if DRE has an alternative approach or design rationale with regard to any of these issues (particularly pillar width to height ratio), it could be considered worthwhile to seek a meeting on the matter. Yours sincerely,
GOLDER ASSOCIATES Pty Ltd
Bob Trueman
Principal Mining Engineer
David Hill
Technical Director
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References
Das, BM (1986). Influence of Width to Height Ratio on Post-failure Behaviour of Coal. International Journal of Mining and Geological Engineering, 4:79-87.
Galvin, JM, Hebblewhite, BK, Salamon, MDG and Lin, BB (1998). Establishing the Strength of Rectangular and Irregular Pillars. Final Report for ACARP Project C5024.
Goler Associates (2013). Subsidence Predictions and Impact Assessment for Airly Mine. GA Report No. 127621105-003-R-Rev2 to Airly Mine.
Golder Associates (2014). Pillar Stability and Subsidence Assessments for the 103 Panel, 200 Area Extension and 205 Panel. GA Report No. 127621105-093-R-Rev0 to Airly Mine.
Golder Associates (2014). Pillar Stability and Subsidence Assessments for the 205 Panel Extension, 100 Cross Panel, 420 Panel, 121 Panel and 122 Panel. GA Report No. 127621105-109-R-Rev1 to Airly Mine.
Hill, D.J. (2005). Coal Pillar Design Criteria for Surface Protection. Proceedings of Coal2005, AusIMM, Brisbane. Hill, DJ (2010). Long-Term Stability of Bord and Pillar Workings. Paper presented at the Third International Workshop on Coal Pillar Mechanics and Design, Morgantown, W. Va.
Madden, BJ (1987). Coal Pillar Design – Can Increased Extraction be Achieved Safely? Mine Safety and Health Congress, Johannesburg.
Madden, BJ and Hardman, DR (1992). Long-Term Stability of Bord and Pillar Workings. Proceedings of the Symposium on Construction over Mined Areas, Pretoria.
Salamon, MDG, Galvin, JM, Hocking, G and Anderson, I (1996). Coal Pillar Strength from Back-Calculation. Strata Control for Coal Mine Design, UNSW. Final Project Report, No: RP 1/96. Joint Coal Board.
Salamon, MDG and Oravecz, KI (1976). Rock Mechanics in Coal Mining. Chamber of Mines of South Africa.
Strata Engineering (2001). A Review of the Geotechnical Design Aspects Highwall Mining Based on a Back-Analysis of Australian Experiences. Report No. 00-001-RCH/1 to Roche Mining.
Strata Engineering (2010). Design of Partial Extraction Layout for Airly Mine. SEA Report No. 09-001-AIR-4 to Airly Mine.
Strata Engineering (2012). Pillar Stability in 101 and 200 Areas. SEA Report No. 09-001-AIR-10 to Airly Mine.
Strata Engineering (2012). Geotechnical Assessment for Proposed Partial Extraction Layout Options. SEA Report No. 09-001-AIR-12 to Airly Mine.
0.87 201 50
1.22 901.26 931.3 95
1.38 981.63 99.92.11 100
Engineer: D. Hill Client: Airly MineDrawn: B. Richardson Title:Date: 26.08.14
