PRESENTATION TOPIC THE ROOF FALL IN UNDERGROUND MININGPRESENTATED BY NIAZ M SHAHANI-11MN69(31-03-2014)

DEPARTMENT: MINING ENGINEERING -MEHRAN UET JAMSHORO

CONTENTS

The Roof fall in Underground Mining

1. Introduction 2. Definition3. Causes 4. Parameters 5. Detection Methods 6. Prevention methods of Roof fall7. References

INTRODUCTION

A coal mine roof can be considered as a jointed bedded beam made up

of material with a finite compressive strength.

Depending on the horizontal stress and vertical surcharge loading

applied to the beam will collapse by either vertical shear along the

joints, bedding-parallel shearing leading to delaminating (a splitting

apart into layers) and the subsequent failure of thin layers.

Roof fall occurrence is a common ground control problem.

INTRODUCTION

INTRODUCTION CONT…

In some instances, it may cost as much to clean up a fall as it does to

mine actual coal.

The loss of revenues associated with downtime is not the only tragedy

involved but includes the loss of life.

roof is not dependent on the usual indicators of potential failure such as

presence of cracks and moisture.

In fact, in most cases of mine roof failure, the immediate roof condition

was rated as good or better, which gives little or no indication of pending

failure and collapse.

DEFINITION

It is simply defined as;

A coal mine cave-in especially in permanent areas such as entries.

OR

A “sudden fall of rock” from the roof inside the mines.

CAUSES OF ROOF FALL IN U/G MINING

Nearly all roof failures can be traced to 2 major causes:

The interaction of stresses in the roof, pillars and floor exceeded the

rupture of the roof rock strata;

Geologic disturbances in the immediate roof, such as slicken slides,

channel sands, transition zones, rider coal seams, kettle bottoms, cracks and

joints and the presence of water, are often associated with roof falls.

PARAMETERS OF ROOF FALL

The parameters studied included:

presence of cracks and water before the occurrence of fall,

sloughing of coal ribs,

floor heaving,

type of roof support (resin or mechanical anchor bolts),

distance to coal face, and

time of occurrence of fall after initial coal extraction

DETECTION METHODS OF ROOF FALL IN U/G MINING

There are two important methods of the detection of roof fall in

underground mining

 

1. Roof fall risk-assesment method

2. Roof fall risk management method

1. ROOF FALL RISK ASSESMENT METHODThere are four basic steps to evaluate roof fall risk-assessment method,

These are

1. Recognize and rate defective roof conditions that represent roof fall

hazards: This is accomplished with the RFRI hazard assessment

technique.

2. Determine the roof fall probability for specific roof conditions: This is

accomplished using qualitative analysis techniques where RFRI (roof

fall risk index) values were grouped into logical probability categories.

1. ROOF FALL RISK-ASSESMENT METHOD CONT…3. Evaluate the exposure of miners to roof falls in the study area.

4. Rank the roof fall risk for all active workplaces within the mine using

a risk matrix: Rating or ranking roof fall risks helps to identify what

areas should be monitored most closely by the mine operators and

miners alike. It is also critical for prioritizing the areas where

administrative and/or engineering controls are needed most to reduce

these risks.

2. ROOF FALL RISK- MANAGEMENT METHOD

When risks are ranked, mine operators have the opportunity to:

1. investigate strategic or tactical controls;

2. monitor the performance of the controls; and

3. modify them as needed, in an iterative process, thus continually

addressing the highest roof fall risk areas.

PREVENTION METHODS OF ROOF FALLMethods to provide the prevention of roof fall in underground mines are

to provide the proper supporting of the roof. These are wood Timbering

and Roof bolting.

Conduct frequent and adequate examinations of the roof, face, and ribs.

Be alert for changing conditions at all times. When hazardous conditions

are detected, danger off access to the area until it is made safe for work and

travel.

Share and discuss roof control plans with the miners on a regular basis.

For miner safety, assure that the roof control plan safety precautions are

followed.

REFERENCES

1. Methods for determining roof fall risk in underground mines (A.IANNACCHIONE, L. PROSSER, G. ESTERHUIZEN AND T. BAJPAYEE)

2. Mine Roof Condition and the Occurrence of Roof Falls in Coal Mines The Ohio Journal of Science. v84, n3 (June, 1984), 133-138, http://hdl.handle.net/1811/23010

3. SafeMiners.com (Training and Resources for Mine Safety)4. http://www.safeminers.com/?tag=fall-of-roof-or-back