28th International Conference on Ground Control in Mining

Morgantown, West Virginia7/28/2009 – 7/30/2009

Coal Pillar Strength Based On The Ground Reaction

Curve– A New Approach

Kazem Oraee, Navid Hosseini, Mehran Gholinejad

Coal Pillars

Coal Pillars Strength Formula Holland-Gaddy (1964)

Bunschinger (1876)

Salamon-Munro (1967)

Coal Pillars Strength Formula Bieniawski (1967)

Bieniawski (1968)

Holland (1973)

Coal Pillars Strength Formula Oraee-Hosseini (2007)

Coal Pillars Bearing Capacity

Width to Height Ratio (W/H) Uniaxial Compressive Strength of Intact

Coal

Ground Reaction Curve (GRC)

Coal Pillars

Solid (Stiff) Pillars The solid pillars remain in elastic behavior

phase and support the applied loads with their inner-core

Yield Pillars The yield pillars reaching the plastic behavior

phase, and by creating a pressure arch, transfer the applied loads to the abutments on both sides

The Typical GRC for Coal Pillar

Displacement →

W/H

Rat

io →

Critical Point

Elastic Zone

Plastic Zone

Pillar Design for Tabas Coal Mine

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.020

2

4

6

8

10

Strain

W/H

Rat

io

Linear Phase (Elastic)

Non-Linear Phase (Plastic)

Coal Pillar Design Based on GRC

Linear Phase (Elastic)

Non-Linear Phase (Plastic)

Coal Pillar Design

Oraee-Hosseini (2007); Tabas Coal Mine, Iran

Linear Phase (Elastic)

Non-Linear Phase (Plastic)

ConclusionsThe presented new method, based on the GRC, can advantageously identify the elastic and plastic behavior phases and the critical point that is similar to yield point in the stress-strain curve, which denotes the transition of phase behavior. Therefore, this new approach can determine the elastic and plastic behavior phases of pillar based on the W/H ratio. Moreover, for each phase, a dedicated equation is presented. With measurement of coal pillar horizontal strain, that is done simply, and by using these new equations, the coal pillar strength is calculated accurately. Undoubtedly, the knowledge of coal pillar behavior phase with accurate estimation of coal pillar bearing capacity is the basis in coal pillar logical design. The new method for coal pillar design with applied approach is the general pattern in design of various pillars in underground mining methods elsewhere.

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