multislice longwalling for thick seam extraction ... longwalling for thick seam extraction -...

Multislice Longwalling for Thick Seam

Extraction - Properties of Goaf in the Roof

and Gate Roads Behaviour

AusRock 2014: Third Australasian Ground Control in Mining Conference

5–6 November 2014, Sydney, Australia

Presenter: Stanisław Prusek Authors: Prusek S.,¹ Lubosik Z¹., Płonka M1., and Syrek B²

¹ Główny Instytut Górnictwa (GIG), Poland ² Katowicki Holding Węglowy SA (KHW), Poland

DEPARTMENT OF EXTRACTION TECHNOLOGIES AND MINING SUPPORT www.gig.eu 2

PRESENTATION OUTLINE

Some information on Central Mining Institute (GIG).

Some data on Polish hard coal mining industry.

General information concerning Thick Coal Seams Extraction.

Properties of Goaf in the Roof and Gate Roads Behaviour –

underground measurements.


Some information on Central

Mining Institute (GIG)


The Central Mining Institute (in Polish: Główny Instytut Górnictwa, in brief: GIG)

Research institute, established 1945,

Subordinates to the Minister of Economy of Poland,

Employees (2013) – 578 people, including 14 professors and 15 Assoc. Prof.,

Notifying Body No. 1453 of the European Union within the range of the

directives:94/9/WE (ATEX),98/37/WE (machinery), 93/15/WE (explosives for the civil use),

and explosion-proof safety according to the world certification system IECEx,

The Scientific Council holds full academic authorizations to grant the degree of

doctor and doctor habil., and to apply for the title of professor in mining (since 1961) and

environmental engineering (since 1998).


Basic areas of GIG activity

SOCIO-ECONOMIC STUDIES

OCCUPATIONAL SAFETY IN THE INDUSTRY

MATERIAL ENGINEERING

CERTIFICATION, ATTESTATION, INTEGRATED

MANAGEMENT SYSTEMS

MINING AND GEOENGINEERING

ENVIRONMENTAL ENGINNERING

TRAINING AND EDUCATION


An unique place for mining investigations in a real scale

Experimental Mine „Barbara”

COAL DUST EXPLOSION IN EXPERIMENTAL GALLERY


Some data on Polish hard coal

mining industry


Coal is the major fuel used for generating electricity in Poland.

About 86 % of electricity is produced in coal-fired power plants.


Location of Polish coal basins and coal production in Poland in 2013

Total – 142.3 Mt

Hard coal – 76.5 Mt

Lignite (brown coal) – 65.8 Mt


Production – 76.5 Mt,

(64.4 Steam coal, 12.1 Coking coal)

Number of underground mines – 30,

Employees – about 107 000 workers,

Extraction system –107 single entry retreat

longwalls were employed, 101 longwalls with

natural roof caving and 6 with hydraulic backfilling

Average extraction depth - 713 m.

Polish hard coal mining industry in 2013


Gas hazard

Fire hazard

Dust hazard

Seismic and rock burst hazard

Water hazard

Climatic hazard

Radiation hazard

The coal seams are mined in conditions of natural hazards:

Such mining conditions negatively

affect the costs of mining activity

of Polish companies


General information concerning

Thick Coal Seams Extraction


Among the methods commonly used for thick coal seams extraction the

following can be mentioned:

Single pass longwall (SPL)

Multi-slice longwall (MSL)

Longwall top coal caving (LTCC).

B.Hebblewhite, Morgantown 2013


In Poland Multi-slice longwalling (MSL) is employed

the coal seams are extracted in slices with:

roof caving, extraction from top to bottom

(descending order),

hydraulic backfilling, extraction from bottom to top

(ascending order),

combination of the above two systems (hybrid).

Underlying slice is mostly

mined after 2-3 years


Properties of Goaf in the Roof and

Gate Roads Behaviour –

underground measurements


IMPREX

PROJECT

Realized

in years

2008-2011


Multi-slice longwalling in KHW Company

data collected from 24 longwalls


Average values of coal beam thickness and coal UCS in the longwalls

operated under previously extracted upper slice of the seam


Underground measurements were carried out in three longwall panels

located in slices of seam 510

Longwall Name 02a seam 510 slice II

04a seam 510 slice I

XVII seam 510 slice II

depth, m 815-865 795-850 700-765

seam inclination, 0 4 4-6 4-6

longwall height (seam thickness), m 3.6 (5.5 – 7.95) 3.0 (6.6 – 7.95) 2.7 (4.0-4.47)

longwall length, m 220 270 140-170

longwall panel length, m 860 610 720

coal beam thickness, m 0.4-0.8 0.4-0.8 0.4


Scope of underground measurements

Location of measurement stations in longwall panel 02a,

seam 510, slice II

Ø96 mm – borehole

10 m long


Assessment of the strength parameters of the caving

goaf by means of the borehole hydraulic penetrometer.

Determination of the caving goaf structure by means of

the borehole endoscope (endoscopic methods).

Assessment of the strength parameters and goaf structure - employed devices

Head with

a needle

Hydraulic

pump

Console for measuring and

storing the pressure data


Results of measurements of goaf compressive strength

The average values of goaf

compressive strength obtained from

the boreholes drilled in :

longwall panel 02a:

test no 1 - 36.53 MPa



longwall panel 04a:



longwall panel XVII:



Example of the strength parameters of the caving goaf measured

by means of the borehole hydraulic penetrometer – longwall 02a

Raise 3’a Raise 4a


Assessment of the structure of goaf in longwall panels 02a,

04a and XVII performed by means of endoscopic method

In most investigated boreholes the goaf was intensively cracked


Vertical and horizontal convergence and floor heave in Raises: 3’a, 5a and 19

- values and trend lines


Load exerted on steel arches in Raises 3’a, 5a and 19

- values and trend lines


CONCLUSIONS

1. In the Polish hard coal mines in seams to be extracted in slices, i.e. ones with a

thickness of 4.5 m and more there are around 952.6Mt of coal which constitute that

part of the resources which may be economically extracted.

2. The Multi Slice Longwall System (MSLS) is already a commonly used method for thick

seam extraction in Poland.

3. In order to design a longwall under a previously extracted upper slice of the seam it is

necessary to determine the compressive strength of the caving goaf at the roof, its

quality and the load on the support.

4. High variability (from 0 to 80MPa) of the caving goaf compressive strength

assessments obtained by means of a borehole penetrometer led to the conclusion that

the results do not describe the caving goaf parameters but the parameters of rocks,

which form the caving goaf only. Hence the use of a borehole penetrometer to assess

caving goaf UCS is not recommended.


5. The most promising way to determine the roof conditions in longwalls under a caved

goaf seemed to be an assessment of the equivalent compressive strength and degree

of reconsolidation.

6. All boreholes into the goafs examined by means of the borehole endoscope were

cracked, some of them practically the whole length, but others in some zones only. It

can be concluded that the density of fissures reduces with the distance from the roof to

the gateroad.

7. The results of the gateroad stability measurements confirmed that in the workings

located under the goaf no large convergence or load were observed in comparison with

the workings located below the natural roof .

CONCLUSIONS


Thank you for your attention

Stanisław PRUSEK, Associate Professor

Head of Department of Extraction Technologies and

Mining Support

GIG

plac Gwarków 1

40-166 Katowice

Poland

[email protected]

phone: +48 32 2592423

fax: +48 32 2584425

mobile: +48 512293839

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