Mining managment work Essay Example

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Geography
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1. Determine minimum width of main trunk development panel pillars (required for life of mine, 7 heading panel).

Using the formula

Taking =7.49Mpa

Substituting relevant values

1. What issues need to be considered in sizing the barrier pillar adjacent to main development panel? Determine any minimum width criteria.

The issues put into consideration can be widely be classified as operational and geotechnical requirements.

The geotechnical requirements take into consideration the regional stability, the stability of local pillars and protecting of the integrity of adjacent roadways/infrastructure from abutment stresses.

Barrier stability is important as a minimum width criterion. The stability of the barrier may be evaluated in accordance to abutment loading that may be found through numerical modeling and an estimate of strength of barrier pillar.

The hydraulic performance of a barrier pillar design is another criteria and may be evaluated using published empirical designs methods. The methods are used in determination of hydraulic impoundments, estimating seepage through barrier empirically, and undertaking numeric strain modeling.

Using the dunes rule the minimum width can be given as

1. An eight heading bord and pillar panel is to be developed and then fully extracted to a line just short of the east /west development corridor. It will then stand for several years at least before any final extraction on the retreat from that area. What minimum sized pillars should be used in the panel and why? How far short of the east/west development should the panel stop? Comment on pillar sizes at this stop line.

The minimum sized pillars to be used are calculated from

The superincumbent length for eight heading bord and piller is 180/8= 10

Taking stress in each pillar as 7.49Mpa

Using the relationship

Substituting 7.49=

The pillar has a square section

1. 180m long wall panels are being mined, south of the development.(Assume 180m of long wall extraction panel exists to the east of the long wall block. Caving conditions in this old panel are unknown but suspect and the workings are flooded. What width of solid barrier should be left adjacent to the flooded old workings?

The width of barrier is calculated using Ash and Eaton Impoundment Formula which is the most convenient Hydraulic Impoundment Empirical Design Method where

D is the depth = 180+2.8=182.8m= 182.8/0.3048=600ft

1. Over LW panels 1-3 is a channel of massive competent sandstone, up to 50m thick and situated within 5m of the roof horizon. Experience at an adjacent colliery has shown that wide panels under the sandstone create major face stability problems. These can only be controlled by narrowing the panels to a maximum of 90m so that the sandstone spans across the panel width. Longwall face lengths must be therefore restricted to 90m in these panels. What cham pillar width should be used?

Taking stress in each pillar as 7.49Mpa

Using the relationship

Substituting 7.49=

The pillar has a square section

MINE8140 2014

Hard Rock Assignment (30%)

A new orebody is located in a high stress mining environment, and will be accessed via a decline connecting to the surface. You are the person responsible for assessing the support requirements for the access decline and assessing the stability of open stopes, and the corresponding geotechnical instrumentation program(s).

You task is to provide a formal technical report on the following issues.

(A) Access Decline: Support requirements and instrumentation for the access decline.

(B) Stope Stability: Assessing Stope Stability using the Matthews Stability Graph.

(A) Access Decline (15%)

The 5.5m wide decline will pass through the following geotechnical domains along its length. Your task is to ensure that the stability of the main excavation is to be maintained throughout the mine life, and that appropriate early warning is provided where any remedial work might be required.

Geotechnical Domains

— Domain 1: weak, wet, weathered rock requiring surface constraint,

— Domain 2: a region of squeezing ground exhibiting time-dependent closure,

— Domain 3: a highly stressed region,

— Domain 4: a heavily structured region.

Prepare the following for submission for all domains to your management for approval:

1. Use the Barton’s Q system, rule of thumb methods to assess the bolt length, spacing and surface support requirements. Use Kaisers “RMR-Stress” chart to study the mode of failure.

Support design chart showing Westside Q values.

From the chart the bold spacing and length are determined and are as in the table

 Classification V. Poor to Poor 1.0m to 1.3m 1.3 to 1.5m 1.5 t0 2.2m Very good Extremely poor
1. Write a three page (max) essay outlining the things you would consider in a ground control management strategy covering all four generic types of ground conditions, indicating potential sources/types of instability and mode of failure, and appropriate ground control responses to these;

Ground control methods are used in maintaining the risks linked to a variety of ground movement that are encountered in underground mines to a level which is acceptable. This are applicable to all the stages of the mine right from feasibility, during the mine operation and at the stage of mine abandonment. The methods of control to be adopted is determined by the type of interaction of the qualities of the rock mass with different types of mine planning and design methods.

Domain 1 exhibit a soft rock condition which is identifiable as a point that has unconfined compressive strength with a range of 0.5 to 25Mpa. The geological structure has negligible influence on ground control in domain 1 material type. The hazards that can be associated with this domain is pillar punching or foundation failure, collapse of the roof as a result of excess shear and bending stress and problems as a result of swelling clays.

. The size and shape of rock blocks which are potentially unstable will be dependant on the type of orientation exhibited by the materials, the continuity and the spacing of planes of weakness in the materials in addition to size, the shape and orientation. In this type of domain where there a strength of more than 25Mpa. The release of excessive pore water pressure in the materials with time is likely to result to the movement of the rock mass in the excavated areas and this is likely to result to the excavation being closed gradually. The chances of time related behaviours in rock mass need to be addressed for domains 2 in addressing important issues such as design of mine excavations, designing and installing of rock support and reinforcing as well as abandonment. These behaviours may also be exhibited in domain 4. (Nickson, 1993)Domains 2 and 3 failure is controlled majorly existence of geological structure and the effect of gravity

(c) Design an appropriate instrumentation program for application in these regions, as part of the ground control management plan, indicating type, design, approximate, monitoring strategies .

There are a variety of methods that are used in the estimation of the magnitude and the orientation of the stress field and this is accomplished by considering absolute stress levels or by looking at stress changes. This involves use of a variety of instruments as in table.

 Absolute stress measurement Change in stress instrument CSIRO Hollow Inclusion cell (3D) CSIRO Yoke gauge 2D Borehole slotter stressmeter CSIRO Hollow Inclusion cell (3D) Hydraulic fracturing method (2D) Flat or cylindrical pressure cell

Open Stope Stability Assessment (15%)

and the insitu horizontal stress is two times the vertical stress. 3 Stope design work is being undertaken for excavations located at a depth of 450m depth. The ore is in a 2m wide vein system which dips 65 degrees to the east. Geological bedding structures dip 45 degrees at Dip Direction of 270 degrees. The country rock has UCS of 120 MPa and RQD from 55 to 65. There are three joint sets, including discontinuities parallel to bedding. The bedding-parallel discontinuities are undulating and smooth with a thin (<1mm) chlorite infill. The other two discontinuity sets have the same infill type but a planar-rough texture. Open stoping between levels 30m apart is planned. Numerical modeling indicates that the maximum induced stress will be approximately equal to the in situ horizontal stress. The rock density is 2.55t/m

Using the design tables provided during the lectures answer the following questions:

1. On a sketch show the excavation, structures and the potential failure mechanism that you consider critical for analysis of this proposed excavation.

b) Select a Q’ value based on the data provided.

For USC of 120MPa; SRF = 1

RQD is 55 to 65 thus average = 60

= 9n3 joint sets J

The bedding-parallel discontinuities are undulating and smooth with a thin (<1mm) chlorite infill

= 1wDry excavation J

Q=

c) What stope length would you recommend (with explanation) using the modified Matthew’s stability method? (Show all assumptions and calculations)

Additional information required is the k-ratios and strength of material

Nickson, S.D (1993). Cable support guidelines for underground hard rock mine operations. M.Sc. Thesis, Dept. Mining and Mineral Processing, University

of British Columbia,..

Roberts, M.K.C(2002). Addressing the problem of joints sub parallel to pillar lines. Contract report number 2002–0339, Johannesburg. RSA..

Barton, N(1997). Rock mass characterisation workshop. Workshop notes.