Development of a Continuous Mining System for Semi-Steep Potash Seams

7/24/2019 Development of a Continuous Mining System for Semi-Steep Potash Seams

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Development of a Continuous Mining System for Semi-Steep Potash Seams

Jrgen Chon

RWTH Aachen University, Institute of Mining Engineering I (BBK I)

Per N. Martens


Ludger Rattmann


Franz X. Spachtholz

K+S AG, Germany

Thomas Jacob

K+S AG, Germany

Abstract

For tabular semi-steep deposits almost no standardized mining method is available. Due to the

ambition of a more sustainable utilization of deposits such as semi-steep potash deposits, alternative

mining concepts are getting more and more into the focus of the German potash mining industry.

Recently a project as part of a strategic research initiative to analyze potential applications for cutting

technology in German potash mines is launched in this context.

The following paper deals with the development of mining concepts for cutting technology in semi-steep deposits as a part of this initiative. The major problem in deposits with an inclination (dip) of

20 to 60 is a dip that is too steep for the straight forward use of mobile equipment or regular belt

conveyors on the one hand and on the other hand not sufficiently steep enough for gravity flow. Thus,

if one would intend to use mobile equipment, the core challenge is to find a suitable mine design

trying to reduce the inclination in the roadways to an acceptable level. In order to do so, different

alternative mine designs are developed and discussed.

The most suitable mine design is identified by means of a benchmarking analysis comparing new

continuous mining concepts and the commonly applied drilling and blasting method. In addition, 3D

models of these new mining concepts are presented. Furthermore, a performance matrix for different

cutting machines is developed in order to compare several cutting rates under various conditions.

Finally, a case study is carried out to apply the new mining concept to a representative mining area.


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Biography

Jrgen Chon graduated from RWTH Aachen University in 2008 with a diploma degree in Mining

Engineering. His diploma thesis dealt with technical and economical optimization of alternative

mining methods for continuous miner in a German rock salt mine. He is currently working as a junior

researcher at the Institute of Mining Engineering I (BBK I) since 2008. He is involved in various

environmental projects on tailings disposal and mine backfill in German potash mines. His core

responsibility focuses on a research project in cooperation with K+S AG, which comprises feasibility

studies on the applicability of cutting technology in various areas of German potash mining, e.g. mine

development, extraction and mining methods.


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Paper

Introduction

Continuous cutting technology represents one of the most efficient extraction methods in underground

mining operations. There is a wide range of continuous underground mining equipment for mechanicalextraction, e.g. shearer, borer miner, roadheader, continuous miner and bolter miner. Internationally, in

hard coal and potash mining cutting technology is considered to be state of the art.

However, whereas drilling and blasting is still the most widely applied extraction method in German

potash mining, applications of cutting technology come increasingly into focus due to technological

advancements and consequently increases in productivity.

The development of a continuous mining system for semi-steep potash seams is part of a strategic

research project, which currently is being conducted by the Institute of Mining Engineering I (BBK I)

at RWTH Aachen University in cooperation with K+S AG. It comprises feasibility studies on the

applicability of cutting technology in various areas of German potash mining, e.g. mine development,

extraction and mining concepts in general. Within the project, both framework conditions for the

application of cutting technology as well as mining concepts under various deposit conditions are

being developed.

The strategic research project for the applicability of cutting technology in German potash mines

comprises:

International benchmarking on state of the art of cutting technology, haulage systems and

mining methods in potash mining

Detailed process and cost analyses of current mining operations

Analysis of basic conditions for the applicability of cutting technology in potash mining

Analysis of possible applications and mine development concepts

o Cutting technology for extraction of semi-steep depositso Rapid development of mine roadways

o Combined extraction methods (cutting technology combined with drilling and

blasting)

Development of 3D models for the new mining concepts

Roadmaps, Recommendations, Outlook

The results of the strategic research project studies are going to be the basis for the implementation of

cutting technology in German potash mines.

Development of a Mining Concept for Semi-Steep DepositsApproach. The primary objective of the studies conducted is the development of mining concepts

using cutting technology for mine development and extraction as an alternative to the currently applied

drilling and blasting technology. With particular emphasis on the deposit characteristics, mining

concepts are developed along the process chain (cutting, loading and hauling) as well as potential

solutions provided for related processes (e.g. mine development, mine ventilation, roof support, etc.).

Currently, the following mining methods are mainly used in international potash mining:

Room and Pillar Mining

Stope and Pillar Mining

Sublevel Stoping

Cut and Fill Mining

Shrinkage Stoping

Longwall Mining

Solution Mining


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For tabular deposits with an inclination from 0 to 20 (flat) and for inclined deposits from 60 upwards

(steep), a choice of these standard mining methods can be applied. At an inclination range from 20 to

60 (semi-steep) almost no standard mining method can be applied because the minimum inclination

for gravity flow starts at 60 and the maximum inclination for mobile equipment and belt conveyors is

considered to be 20. Figure 1 provides an overview for tabular deposits and possible mining methods

depending on the inclination.

Figure 1: Mining methods for tabular deposits depending on the inclination [1]

Within the scope of this project the challenge is to develop mining concepts for semi-steep deposits

with an inclination ranging from 20 up to 60. Therefore, in a first step, the main aim is to reduce the

inclination in roadways down to a value which is acceptable for extraction machines as well as for

mobile equipment and belt conveyors from a technical and economic point of view. Accordingly, the

geometric relations have to be presented first.

Figure 2 illustrates the angular relationships between an inclined roadway and an inclined deposit. Theangle !represents the real inclination of the roadway. The dip angle "represents the real inclination of

the deposit and angle #(dip-adjustment-angle - DAA) is the angle between the strike and the roadway.

For a given deposit the DAA depends on the inclination of the deposit and the maximum inclination of

the roadway. Hence, the DAA is a major parameter for the panel layout. To depict an inclined

roadway in an inclined deposit into a mine map the angle relationship #= arcsin(sin(!) /sin (")) is

applied. With the help of the DAA it is possible to develop panel layouts under various dip conditions.

Figure 2: Principal drawing for used mine maps [1]

60

20

R&P

Longwall

Cut and

Fill

Standard Cases

Standard Cases

Exceptional

Cases

90

0

sin (!) = c/x

sin (") = h/c ! sin (!) = h / sin (") / h / sin (#) ! ! = arcsin (sin (") / sin (#))sin (#) = h/x

# = Dip angle (roadways in deposit) [/degree]

" = Inclination of the deposit [/degree]

! = Dip adjustment angle for roadways in deposit level [/degree]


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Figure 3 shows a theoretical example of a panel layout in a semi-steep deposit (average inclination

25). The general mining direction is downwards. Access to the panel is provided by an entry drift,

which is developed at a DAA of 33.5 within the deposit and which leads to an inclination of the

roadway of 13.5. At the end of this entry drift the actual panel layout starts. Within the panel the

inclination of the mains is reduced to 8.5 by means of a DAA of 20.5. For layout purposes and in

order to stay within the panel, the direction of the mains changes every 500 m. Fully-loaded standard

mobile haulage equipment can operate economically up to this dip of the mains. The main extraction

takes place in horizontal rooms/stopes with a length of approx. 500 m, starting from the mains. The

development of the mains and the mineral extraction in the horizontal rooms/stopes are carried out

simultaneously. The mineral is extracted by means of a continuous miner and is then transported to a

feeder breaker by means of dump trucks.

Figure 3: Mining concept for a semi-steep deposit (principal drawing) [1]

It is also possible to modify this layout depending on the deposit conditions and concession boundaries

for best-possible deposit utilization. Figure 4 shows different variations of possible panel layouts with

either horizontal/diagonal rooms/stopes and dipping main drifts or diagonal/horizontal rooms/stopes

and horizontal main drifts. The rooms/stopes are being developed between development drifts

(2-drift-systems), which have the same inclination and the same development direction.

Figure 4: Variations for panel layouts (principal drawings) [1]

500 m

1,0

00m

Inclination of the Deposit: 25

Inclination Development Drifts (in deposit): 8.5 = 15% ! != 20.5

Inclination Entry Drift: 13.5 = ! != 33.5

500 m

Main Development Drift

(3-Drift-System)

DirectionofMining

Rooms/

Stopes

Entry Drift

(3-Drift-System)

2,000 m

33.5

Feeder Breaker and

Conveyor Belt

20.5

20.5

400m


(3-Drift- System)Development Drift

(2-Drift- System)

400m


(3-Drift- System)

Development Drift

(2-Drift- System)

Horizontal Rooms/Stopes

Rooms/Stopes

Rooms/Stopes

Development Drift

(2-Drift- System)


(3-Drift- System)

Development Drift

(2-Drift- System)


(3-Drift- System)

Rooms/Stopes

Rooms/Stopes

Horizontal Rooms/Stopes

Diagonal Rooms/Stopes Diagonal Rooms/Stopes


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An alternative option to mineral transport within the potash seam would be the development of a

separate horizontal haulage level underneath the deposit, thus necessitating the integration of ore

passes between the seam and the haulage level. However, the roadways required would most probably

have to be developed in surrounding rock, which usually would be uneconomical.

In a next step and in order to facilitate the general comprehension for different mine design

alternatives some of the most suitable concepts are visualized (3D models). Figure 5 shows a mining

concept in which the rooms/stopes are being developed in horizontal direction. Consequently, the

parallel main development drifts have to be developed within the deposit staggered at different

elevations. The arrangement, development direction and number of cross-cuts between the parallel

main development drifts may vary due to rock mechanical considerations.

Figure 5: Mining concept for a semi-steep deposits (3D view) [1]

Example: Semi-Steep Panel of a Pilot Potash Mine

In a further step the aforementioned considerations are applied to planning of a specific future semi-

steep mining area at a given mining operation. The future panel is located at the south-east border of

the mine field, which is delimited by two geological faults (see Figure 6).

Figure 6: Pilot potash mine (mine map) [2]

Geological information is used to create a 3D-model in Surpac of the future mining area. This

model is linked up with the existing mine models of the operation (see Figure 7).

Saltdome

Panel

Plan View


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Figure 7: 3D model of the panel in Surpac [1]

Based on this model preliminary mining concepts are compared. After identifying the optimum

location for the entry drift and after a detailed planning of the roadheading sequence for these drifts, a

mining concept, optimized according to the framework conditions as mentioned below, is developed.

The mining concept includes the roadheading sequence for the panel mains and the extraction of therooms/pillars as well as a comparison to the drilling and blasting method. Furthermore, cost models

are part of the investigation. The major framework conditions are as follows:

Inclination: 20 to 33

Average thickness: 5 m

Rock Strength: 25 to 30 MPa

Arch shaped main drifts, reinforced with rock bolts (0.25 bolts/m$)

Maximum depth: 1,200 m

Required minimum thickness of the overlying rock salt layer is 35 m

Max. 20 % of the pillars height may consist of carnallitic rock

No entry area in the west of the panel (hazard of spontaneous gas release)

Max. inclination of 13.5 (24 %) for main development drifts

Max. inclination of 15.5 (28 %) for drifts/stopes in working areas

Restrictions due to mining climate regulations (KlimaBergV)

Isolated operation requires a large volume of fresh air

Extraction rate: 5,000 to 6,000 t/d

Entry Drift System. Accessing the panel from the north is not possible because of gas release-related

hazards in conjunction with an insufficient thickness of the protective rock salt layer in the roof.

Hence, the operation has to start in the southern part of the mine. Access to the panel is achieved via a

3-drift-system within the potash seam with a vertical offset of the drifts ranging from 10 to 15 m. It is

not deemed feasible to develop three parallel drifts at the same level due to rock mechanical

considerations as the footwall layers consists of carnallitic rock and the roof of anhydrite rock (seeFigure 8).

Figure 8: Entry drift (3-drift-system / side view) [1]

8 m

5m

1m

46,3 m!

25,0

Anhydrit-Formation

Carnallitit-Formation

20m

20 m

5m

2,9m!

6m !

37,4m!

37,4m!

37,4 m!

6 m!

2,9m!

2,9 m!

6 m!

46 %

Continuous Miner

+ Roadheader

Drilling +

Blasting

Deposit

Panel


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The entry drift is developed in north-easterly direction with a total length of 720 m and a dip angle of

13.5. The cross-section of a single drift amounts to 46.3 m$. The entry point into the panel lies at a

depth of -850 m. A plan view of the entry drift is shown in Figure 9.

Figure 9: Entry drift (plan view) [1]

Mining Concept. Several concepts and alternatives for mining the panel are investigated. After

considering the advantages and disadvantages and a resulting comparison of possible mining methods

regarding the parameters flexibility, productivity, mining costs (investment and operating costs) and

the possibility of selective mining, the room and pillar mining method is chosen and adapted. Figure10 shows a conceptual, qualitative comparison where red boxes indicate a nonfulfillment of a

parameter, yellow color indicates difficulties to match the required parameter and green color means

full achievement of the parameter.

Figure 10: Comparison of possible mining methods for the panel [1]

Figure 11 shows two variations for the panel layout as described before. The horizontal direction of

the main drifts (3-drift-system / green) can be considered as the main advantage of Alternative 1.

Disadvantageous effects are the more acute angles between the main development drift and an

additional 2-drift-system (also in terms of rock mechanics) and between the rooms/stopes and the

cross-cuts. The mining panel extends in eastern direction. Due to this, mine ventilation and

infrastructure would also become more complicated. In the case of diagonal rooms/stopes less acute

angles arise in the main development drifts and cross-cuts. As a result Alternative 2 is chosen, also

because of better deposit utilization and better access to future panels in the North-East.

Figure 11: Panel layouts (principal drawings) [1]

Mining Method Flexibility Productivity Inc lination 20-33 Investment Costs Operating Costs Selective Mining

Room and Pillar

Longwall Mining

Cut and Fill Mining

Comparison of Mining Methods

Depth: -1.300 m

Contour Lines

Concession

Boundary

Einfallen BF13

Depth: -1.300 m

Contour Lines

Concession

Boundary

Einfallen BF13No Entry AreaNo Entry Area

Entry Drift

(3-Drift-System)

Entry Drift

(3-Drift-System)

Alternative 1 Alternative 2


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Equipment Selection. Since the main development drifts (long lasting drifts) have to be arch shaped a

continuous miner (CM) in combination with a roadheader (RH) is selected as possible mining

equipment. Due to the cutting geometry of the CM which leads to rectangular drift profiles, an

additional RH is required to cut the arch. Therefore, a combination of both machines has to be taken

into consideration. For developing the rooms/stopes a continuous miner is used solely since an arch

shaped cross-section is not required. The selected machines are shown in Figure 12.

Figure 12: Equipment selection [3]

Creating a Performance Matrix.The manufacturers usually give an overview of the theoretic cutting

performance of their machines. In order to create a realistic value of the net cutting performance a

performance matrix is developed. In this respect the terms gross cutting performance and netcutting performance, availability as well as utilization are defined.

The gross cutting performance, as specified by the manufacturer, is a performance figure, which can

be achieved under optimal conditions in a test setup. It has little in common with the performance

achieved during operation. With the aim of achieving a net cutting performance value input parameters

and basic factors (as shown below) are an integral part of the matrix. Neither the cutting cycle nor the

overall roadheading cycle is taken into account in the gross cutting performance, e.g. the auxiliary

process time due to movement and alignment of the machine, the raising and lowering of the boom,

etc.. The compressive strength of the mineral, floor condition and mining depth have great influence

on the net cutting performance. Since mining machines under given conditions have to work with an

inclination, the inclination is considered as a factor of influence on the cutting performance.

Considering all these factors of influence, the net cutting performance of the machines is considerably

lower than what is specified by the manufacturer. Another important factor to be considered is

machine idle time associated with change time of haulage equipment. Work organization (particularly

in terms of haulage) and the movement of the machine are other input parameters. The input

parameters are entered into the performance matrix with values ranging from 0 to 1. To determine the

inclination and rock strength parameter, empirical values are used for evaluation. Experience in rock

salt mining has shown that at rock strength in the range of 20 MPa the cutting performance decreases

by 3 % per MPa (case example). Hence, the loss of cutting performance at a rock strength of 30 MPa

is 30 %, which results in a factor of 0.7 (70 %). It is assumed that the cutting performance decreases

per percent of inclination. All other parameters are expressed by their percentage (e.g. 1 = 100 %;

0.93 = 93 %; etc.). These factors are multiplied by the gross cutting performance to determine the

approximate cutting performance during operation.

MB 770 (~35 m2) Recutting withMT 520 (~11.3 m2)

Technical Data

Cutting Height max.: 7.1 m

Cutting Width max.: 10.3 m

Installed Cutting Power: 315 kW

Cuttable Rock Strenght: up to 35 MPa

Negotiable Gradients:

Incline/Decline: +- 20 gon (18)

Max. Cross Gradient: +- 8 gon (7)

Technical Data

Cutting Height: 4.9 5.5 m

Cutting Width: 6.6 7.2 m

Installed Cutting Power: 400 kW

Cuttable Rock Strenght: up to 35 MPa

Negotiable Gradients:

Incline/Decline: +- 20 gon (18)

Max. Cross Gradient: +- 8 gon (7)

Drift Cross-Section

8 m

5m

1m

CM (35 m!)RH (11.3m!)

7 m


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The following figure shows a Sandvik Continuous Miner type MB 770. The gross cutting performance

is given with approx. 388 t/h by the manufacturer. Applying parameters and basic factors into the

performance matrix results in an approximate cutting performance of 153 t/h during operation at an

inclination of 15 % (8.5) and a rock strength of 25 MPa.

Figure 13: Performance matrix for a continuous miner MB 770 (case example) [1]

Result.Based on the calculated performance data and the specification of the roadheading sequence,

the development of the entry drift of the panel is going to take 0.6 years using cutting technology

(continuous miner and roadheader) and 0.8 years using drilling and blasting technology. Cost models

indicate that development of the main drifts using drilling and blasting technology is about 45 %

cheaper than cutting technology. For the extraction in the rooms/stopes cutting technology is 40 %

cheaper as compared to the conventional method. Hence, it is recommended to use drilling and

blasting technology for the development of the mains and cutting technology for extraction in the

rooms/stopes.

Outlook

Cutting technology is widely applied in international potash mining. Both standardized and specially

developed machines are in use. In conjunction with a suitable mining method these machines are able

to achieve high production rates and will therefore continue to remain an integral part of potash

mining. Further improvements regarding cutting machines are expected in the near future, e.g. by theuse of high voltage, modified haulage systems as well as automation possibilities. Also a combination

of the cutting technology and the conventional drill and blast method is possible.

References

[1] Martens, P. N.; Rattmann, L.; Chon, J. (2011). Potentials of Cutting Technology in German

Potash Mining Feasibility Studies. Unpublished manuscripts, Final Reports, Institute of

Mining Engineering I (BBK I), RWTH Aachen University, Germany.

[2] K+S AG (2011). Unpublished presentation.

[3] Sandvik Mining and Construction GmbH (2011). Retrieved from http://www.miningandconstruction.sandvik.com/

Gross Cutting Performance 388,55 [t/h]

Input Paramete rs

Cutting Cycle 0,83 !(0,1]

Net Cutting Performance 1 : 322,50 [t/h]

Availability 0,90 !(0,1]


Utilization 0,90 !(0,1]


Inclination 15,00 [%]


Haulage System 0,85 !(0,1]


Working Organisation 0,95 !(0,1]


Basic Factors

Rock Strength 25,00 [MPa] Net Cutting Performance: 153,29 [t/h]

Floor Condition 1,00

Depth 1,00

Performance Matrix for a Continuous Miner MB 770

Documents

Development of a Continuous Mining System for Semi-Steep Potash Seams