OPTIMIZING SECONDARY ROOF SUPPORT WITH THE NIOSH SUPPORT TECHNOLOGY

OPTIMIZATION PROGRAM (STOP)

Thomas M. Barczak, Research Physicist

National Institute for Occupational Safety and Health

Pittsburgh Research Laboratory

Pittsburgh, PA

ABSTRACT

The decade of the 90's brought an unprecedented increase in the

development of innovative technologies to provide more effective

and easier to install roof support in underground mines. To facilitate

the application of these technologies to improve mine safety,

National Institute for Occupational Safety and Health (NIOSH)

developed the Support Technology Optimization Program (STOP).

STOP is a window’s based software program that provides mine

operators with a simple and practical tool to make engineering

decisions regarding the selection and placement strategy of these

various standing roof support technologies. This program includes

a complete data base of the support characteristics and loading

profiles obtained through safety performance testing of these

supports at the NIOSH Safety Structures Testing Laboratory.

Support design criteria in the form of the required support load

density at a specified convergence can be established from four

options: (1) a data base of measured ground reaction data from

various mines or ground behavior information inputted by the user,

(2) determination of loading requirements based on a detached roof

block or rock failure height, or (3) criteria based on the current roof

support system, and (4) arbitrary criteria set the by user. Using these

design criteria, the program will determine the installation

requirements for a particular support technology that will provide the

necessary support load density and convergence control.

Optimization routines are also available to determine the most

efficient support design for a user specified support installation. In

addition to these performance measures, STOP can be used to

compare material handling requirements and installation costs.

Comparisons among the various support technologies are easily

made including graphical analysis of relevant support parameters.

This paper describes the STOP and its application to optimize

standing secondary roof support systems. 

ACKNOWLEDGMENT

The author wishes to acknowledge the effort of Mr. Dave

Conover, NSA Engineering Inc. Dave was the programmer

responsible for developing the window’s based program for STOP.

The STOP architecture evolved over a year of effort going through

several pain staking revisions to form the final product that is now

available through the NIOSH web site. It is to Dave’s credit that this

program has been completed within the budget constraints of the

project and with such high quality of workmanship. 

INTRODUCTION

Secondary support provides additional roof support in the event

of failure of the primary support system. When properly designed,

secondary support will also assist the primary support in controlling

the integrity of the immediate roof beam. Hence, roof support should

be thought of as a three-part system: (1) the remaining coal pillars

which provide control of the overburden weighting; (2) the primary

support system consisting of the roof bolts which help to form a more

competent roof beam and in the case of mechanical bolts attach the

immediate roof beam in suspension to the more stable main roof

rock, and (3) the secondary roof support system which consists of

standing roof support and intrinsic support elements that are

designed to control the deformation of the immediate roof and handle

the additional abutment loading in retreat mining, such as longwall

mining where the tailgate is frequently supported with various

secondary roof support systems. It should be noted that the STOP in

its present form is limited to the evaluation of standing roof support

systems. 

Engineering design is applied primarily to size the pillars to

account for load variations due to depth of cover, active mining

zones, and the quality of the roof rock. Computer programs such

ALPS and ARMPS are valuable tools in designing pillars for various

mining scenarios (1, 2). There is no universally accepted design

criteria for primary support (roof bolts), although recent research by

National Institute for Occupational Safety and Health (NIOSH)
indicates that there may be some fundamental criteria to define

conditions where current primary support densities are inadequate.

The Wood Crib Performance Model (3) was developed in 1994 to

provide engineering design for conventional wood cribs, which were

the dominant form of secondary support at the time. The Wood Crib

Performance Model determined the supporting capability of various

conventional wood crib configurations and matched this capability

to user-defined load and convergence criteria. More recently, a

design methodology for standing secondary roof support in longwall

tailgate applications was developed, which incorporates measured

ground reaction data into the formulation of the load and

convergence design criteria for standing roof support systems (4, 5).

In the past 5 years, there have been 16 new standing roof

support systems developed for use as secondary roof support. These

new support systems not only provide superior roof support, but

many provide material handling advantages as well. The Support

Technology Optimization Program (STOP) was developed by

NIOSH to allow mine operators to compare these various support

systems and to optimize the application of both new standing roof

support technologies as well as conventional wood and concrete crib

support systems. Although STOP can be considered as an upgrade

of the original Wood Crib Performance Model, it is built on a

windows-based architecture and has several enhanced features that

were not available in the previous Wood Crib Performance Model.

These include: (1) selection from a data base of currently available

standing roof support systems for evaluation, (2) synopsis of

pertinent design and installation criteria for each support system, (3)

description of the performance characteristics including photographs

of the support loading profile showing the condition of the support

as it deforms, (4) name and phone numbers for the support

manufacturers, (5) ground reaction curve support design criteria

where the laboratory support performance can be matched to a curve

corresponding to the ground behavior as opposed to a single (load

and convergence) data point as was done in the wood crib model, (6)

enhanced optimization algorithms that determine the support design

which is most efficient for the user-specified support installation

requirements, or the installation requirements for user-defined

support load density and convergence requirements, (7) material

handling and cost information for each support, and (8) graphical

displays of the support system capability.

It is important to understand that although there are now a wide

variety of support choices, each of these support systems have a

unique performance profile. Simply replacing one support system

with another will not provide equivalent ground control. Most of the

new support technologies provide superior supporting capability,

which may allow wider spacings of the support to be used if the goal

is to provide equivalent support capability to that of a conventional

wood crib support system. STOP will determine the spacing

requirements that will provide equivalent support capacity. This is

one way that STOP can optimize the use of a particular support

system. STOP can also provide important information regarding the

benefits of increasing the support load density. Using measured

ground reaction data, STOP will determine: either the convergence

that can be expected from a certain support design installed on a

user-selected spacing, or the support spacing required to limit the

convergence to a certain level. 

This information can be very useful when petitioning Mine

Safety and Health Administration (MSHA) for approval to use an

alternative support technology. Without this information, MSHA

will typically require a trial section where the alternative support

system can be observed before full approval is granted. In longwall

mining, this means that one might have to wait for a full panel of

mining before implementing a new support technology. Likewise,

variations in the placement strategy or implementing a change in

support design can be delayed until a trial section is observed

without an engineering basis to justify such a change. Hence, STOP

can be included as another part of the overall process that MSHA

may utilize in approving a roof support plan. While it may not be the

sole deciding factor, it can provide critical engineering data that will

facilitate a decision regarding the implementation of these new

support technologies.

This paper will introduce the STOP, describe the architecture of

the program, and provide several examples of how it can be used to

optimize the design and use of secondary roof support technologies.

STOP can provide an engineering foundation to ensure that

inadequate support designs as well as ultra conservative support

applications are avoided. Safety will be improved by proper

matching of the support performance to the mine conditions which

will reduce the likelihood of roof falls and blocked escapeways.

Material handling injuries associated with support construction are

known to account for about 5,000 lost work days per year in

underground coal mines (6). STOP can help to define the material

handling advantages of alternative support technologies that use

lighter weight materials or systems that can be installed with the aid

of mechanical assist. The use of these support technologies can

significantly reduce material handling injuries. 

PROGRAM ARCHITECTURE

The program is a windows-based architecture. The Main Menu

allows the user to control the flow through the program if desired.

This window is always shown, and can be accessed through each of

the primary program segments. The main menu contains these six

modules:

File – The File window contains file management subroutines that

allows the user to create new files, open and close existing files, and

exit from the program. The File Menu also allows the user to set the

path for storage of several photographs that are incorporated into the

program for visual display of the support performance.

Information – The Information window can be thought of as a

general information center. The various support technologies are

categorized in six groups: (1) conventional wood (crib) supports, (2)

engineered timber supports, (3) conventional concrete crib supports,

(4) yieldable concrete supports, (5) steel supports, and (6) additional
Figure 1. Window for establishing design criteria based on a

ground reaction curve

Figure 2. Window to establish design criteria based on

detached roof block

supports. From this list and the embedded sub menus, the user can

select a specific support and learn more about the support through

several other program buttons. Keypoints provides a description of

the support, design and installation considerations, performance

characteristics of the support, and manufacturer or supplier contact

information. Performance displays the loading profile of the support

with photographs that depict the deformation and associated support

loading. NIOSH Testing Laboratory describes the Mine Roof

Simulator and makes reference to the safety performance testing

protocols through which the performance characteristics of the

support were determined. Reference/Bibliography contains relevant

reference material pertaining to the selected support system.

Design Criteria – The Design Criteria window is where the load and

convergence design criteria for the support system are formulated.

The requirement is to define the required support load density in

terms of tons of support capacity per linear ft of entry advance and

at what convergence this support capability is to be provided. There

are 4 different ways to establish these design criteria in the program:

(1) ground reaction curve, (2) detached block, (3) current support

system, and (4) arbitrary 

criteria. 

1. The Ground Reaction Curve (figure 1) allows the user to define

the support load density and convergence criteria from in mine

measurements of the ground behavior (convergence) associated

with various support systems (4, 5). Essentially, the ground

reaction concept implies that the convergence in the mine entry

is controlled by the magnitude of the support resistance.

Generally, the convergence decreases with increasing support

load density. Hence, if measurements of convergence are made

with two or more support systems of varying stiffness, then a

ground reaction curve can be established for that particular

mine. The user can define a ground reaction curve or use one

from the data base established from various mine sites which is

maintained in the program. Once a ground reaction curve is

defined, the program will determine the required spacing for a

particular support system that will provide the support load

density consistent with the ground reaction curve at a particular

convergence. 

2. The Detached Block window is shown in figure 2. The support

load density requirements are established by calculating the

weight of a detached block of roof rock above the mine entry.

The failure height can be input by the user or estimated from the

quality of the roof rock (Coal Mine Roof Rating) using an

approximation developed by Unal (7). The volume of the block

is also influenced by the shape of the failure. Options include

either an arch or a vertical shear failure at the pillar boundaries.

Two options are available for determining the convergence

criteria. If ground reaction information is available, this

information can be used to help define the convergence criteria.

In terms of the ground reaction curve, there is a critical

convergence where failure of the roof occurs. This could be

used to define the convergence criteria for the detached block,

the idea being that the support should put the roof rock mass

into equilibrium before the critical convergence is reached. If

this option is selected, the convergence is defaulted to the

maximum convergence on the ground reaction curve, but the

user can change this input if desired. In the absence of ground

reaction information, the user can simply input a convergence

criteria (allowable displacement before roof weight is supported

in equilibrium).

3. The Current Support System allows the user to define the design

requirements based on the performance of the current support

system (figure 3). There are two options available. One, if a

ground reaction curve is available, then the program will

determine where the current support system falls on the ground

reaction curve, and set the support load density and

convergence requirements to that point. For the second option,

the user must define an allowable convergence which should be

based on some in mine measurements. The support capacity

and resulting load density for the support spacing will be

calculated from the load-displacement profile for the support as

determined from tests in the Mine Roof Simulator or other

laboratory data.
Figure 3. Window to establish design criteria based on current

roof support system.

Figure 4. Window for selecting support

types for design and analysis.

Figure 5. Window for designing the support system and

determining the installation requirements to achieve

the design criteria objectives

4. Arbitrary Criteria simply allows the user to set the support load

density and convergence criteria to any arbitrary set of values.

Support Evaluation -- The Support Evaluation module is the heart

of the support design process. Any of a variety of support systems

contained in the program data base can be selected for design and

analysis (figure 4). Selecting the Design feature calls a subroutine

which allows the user to control relevant design parameters and/or

pick from the available design (models) for a particular support type

(figure 5). The user must also input the number of rows to be used

in the support placement. The program will then calculate the

required spacing of the supports to achieve the desired support load

density at the designated convergence, or the user can select a

support spacing and the achieved convergence will then be

calculated for the user-defined support installation. An optimization

algorithm is also included in which the program will determine the

support design or model which most closely matches the design

criteria (support load density at designated convergence). Also

included in the Support Evaluation module are analyses of the

installed support costs and the material handling requirements for the

support.

Comparison – The Comparison module provides comparison of the

selected and designed supported systems. There are three windows

in the Comparison module: (1) Comparison, (2) Summary, and (3)

Plot. The Comparison window describes the support layout (number

of rows and support spacing) and has a tabular listing of various

design parameters for each support system. The parameters are

grouped into categories: (1) ground control, (2) costs, and (3)

material handling. The user can pick any one of the selected support

systems to use a baseline system for comparison purposes. The

Summary window summarizes the support design parameters for

each support system. The Plot window allows the user to plot the

support performance (unit support load or support load density) as

a function of convergence and graphically compare the various

support systems as shown in the example in figure 6. Ground

reaction data can also be displayed on the plots to show the

convergence control provided by the various support systems relative

to the ground reaction curve.
Figure 6. Graphical analysis of selected support systems showing

support load density as a function of convergence

Main Window

Miscforms

File Open

File Save

Bmp Path

Help

References

About

Info Center Criteria Basis Support Select Comparison (3)

Design

considerations Failure stages

Design details:

GRCurve,

Detach block,

Current case,

Arbitrary

Table of

defined

GRcurves

GRpoints

Add new

support

Performance Material

handling

& costs

Plot setup

Optimization Wood

select

Next Next Next

Disclaimer

Figure 7. Flow diagram showing program control.

Help – A context-sensitive help file is available to facilitate the

operation of the program and interpretation of the results. The Help

file can be called from each window or from the main menu.

Using the Program

Generally, the program control guides the user through a logical

sequence of operations to facilitate the design and implementation of

a roof support system. Figure 7 is a diagram of this program flow.

The Information Center is shown on start up. Here, the user

can explore the various support technologies that are available,

examine relevant design and installation considerations, and observe

the failure stages of the various support structures. The Next button

transfers control to the Design Criteria module to a window where

the user must select the basis for establishing the design criteria,

choosing one of the following options: (1) detached block, (2)

ground reaction curve, (3) current support system, or (4) arbitrary

criteria. Control is then transferred to the appropriate window for the

chosen design criteria and the user then defines the support load

density and convergence design criteria in that window. Once the

design criteria are established, control is transferred to the Select

Supports window. It is here where the user picks the supports to

evaluate. There are several options available: (1) Add allows the user

to select a new support, (2) Delete to delete a support from

consideration, (3) Duplicate to duplicate a support, which can be

helpful when you want to reevaluate a support design with a few

minor changes, and (4) Rename to simply rename the support. 

After a support type is selected, control is transferred to a

window where the user can define the appropriate support design

parameters. Once the user defines the support design, the program

calculates two outputs: (1) Achieved Ground Control where the

convergence control provided by the support system and the support

load density are displayed and (2) Installation Requirements where

the number of rows and required support spacing are provided. For

most supports, under the Support Specifications, there is also an

Optimization button. Clicking on the Optimization button causes the

program to transfer to an optimization window where the user can

select a support spacing and number of rows and the program will

calculate the support model or design that most closely matches the

required convergence and support load density previously

established in the design criteria. The optimization algorithm
Figure 8. An example of the loading profile display

available in the Information Center

depends on which spacing option was selected in the support

specifications window. If “Calculate the required spacing” option

was selected, the optimization routine will select a support design

that will meet the design criteria at less than the specified maximum

spacing. If the “User-defined spacing” option is selected, then the

program will determine a support design that will meet the load

density requirement at a convergence less than the design

convergence.

Once the support system is defined and the installation

requirements (number of rows and spacing) are determined, then

control is transferred to the materials handling window where the

support costs and material handling requirements can be defined and

examined. A set of default values are included in the program that

are considered to be representative of the various support

technologies at the present time, however, the program allows the

user to modify any of these parameters. In particular the cost

parameters may be mine specific and time dependent to some degree.

These default values will be updated periodically on the web site

version, but the user should contact the support manufacturers to

receive the latest cost information. Finally, the Next button transfers

control to the Comparison module where the various support

systems can be compared to one another.

EXAMPLE APPLICATIONS OF STOP

Examining the Loading Profile of a Support System

In the Information Center of STOP, photographs of each

support during its loading phases are shown when the Performance

button is clicked. The load-displacement curve for the support is

shown with a line to designate the displacement that corresponds to

the photo in the window. Photos are typically shown at 2-in

increments in support displacement. An example for the Propsetter

support is shown below (figure 8). 

Optimizing the Use of Conventional Wood Cribs

Historically, conventional wood cribs have been used

extensively for secondary roof support. A common support system

is a double row of 4-point cribs constructed from 5x6 in (crosssectional dimensions), 30-in-long, mixed hardwood timbers. STOP

can be used to evaluate alternative designs and show that 9-point

cribbing can be more cost-effective. The procedure to conduct such

an analysis would be as follows:

1. Review the design information on conventional wood cribs in

the Information Center.

2. Choose Current Support Systems for the basis for selecting the

design criteria. Enter the entry width and height. Since no

supports have been defined yet, the program will transfer

control to the Select Supports window. Clicking on the Add

option will transfer control to the support menu where wood

cribs can be selected. 

3. Control will be transferred to the Wood Crib Specifications

window where the wood crib parameters are defined. Enter the

wood crib specifications (timber width, timber thickness, timber

length) and select the mixed hardwood species to establish the

wood strength. Input the number of timbers per layer. After

confirming the support design, Ok transfers control to the Select

Supports window. 

4. Hitting Ok here then transfers control to the Design Criteria

window, where the current wood crib design is featured. You

will now need to enter a value for the spacing of the supports,

number of rows, and enter a convergence to establish the

support load density design criteria. In this example, a spacing

of 81 inches for a double row of cribs and a convergence of 4.0

inches was chosen.

5. When control is transferred back to the Select Supports window,

the user has the option to examine the support material handling

and costs (by clicking on the Design and Costs button).

6. After reviewing the material handling and cost information, the

control will be transferred back to the Select Supports window,

where the alternative support designs are entered and evaluated

accordingly. One way to accomplish this is to duplicate the

current support and simply change the number of timbers per

layer from 2 to 3 and the number of rows from 2 to 1. The

program will then calculate the required spacing of single row

of 9-point cribs that will provide the same load density as that

of the double row of 4-point cribs.
Figure 9. Comparing the installation costs of various

wood crib designs (5x6x30 in timbers with 5-in

side placed down)

Figure 10. Same analysis as shown in figure 9 except the wide

side of timber (6-in side) was placed down to establish the

interlayer contact among adjacent timbers

Figure 11. Evaluation of engineered timber support systems as a

replacement to conventional wood cribbing

Figure 9 documents the result of one such analysis, comparing

the installed cost of a double row of 4-point cribs on an 81-in centerto-center spacing with that of single row of 9-point cribs on a 92-in

spacing. Both support systems, with cribs constructed from 5x6x30

in mixed hardwood timbers, provide 10.5 tons per ft of support

capacity at 4 in of convergence. Also included in this analysis is a

double row of 4-point cribs constructed from all oak timbers instead

of mixed hardwoods. Note that in this analysis, the narrow side of

the timber (5-in side) was placed down to establish the interlayer

contact.

Figure 10 illustrates the same comparison except that the cribs

are constructed with the wide-side-down (6-in side) instead of the

narrow side down (5-in side) as was done in the previous example.

The results clearly show the benefits of maximizing the support

capacity by increasing the contact area with the wide-side-down

construction.

Replacing Conventional Wood Cribbing with Engineered

Timber Supports

In recent years, numerous alternative timber supports have been

developed. These supports are engineered to provide improved

loading characteristics compared to conventional wood cribbing.

For this example, the goal is to replace a conventional wood crib

design with engineered timber supports and provide equivalent

support capability in terms of support load density at a specific

convergence. The procedure for designing these engineered timber

support applications is basically the same as in the previous example

except the alternative supports are chosen for analysis instead of

conventional wood crib designs.

The baseline case for this example is the same as that chosen in

the previous example: double row of 4-point, mixed-hardwood cribs

on a 116-in spacing providing 10.52 tons per ft of support capacity

at 4 in of convergence. The alternative supports chosen for this

example are: (1) 24-in Link-N-Lock, (2) 30-in Link-N-Lock, (3)

Hercules HM-9(308) crib, and (4) 30-in Tri-Log crib. Figure 11

shows the installed support cost per ft of entry for support systems

designed by the STOP to provide equivalent support loading to that

of the baseline conventional wood crib support system. The

installation requirements are also shown. As seen in figure 11, all

four of the engineered timber support systems are able to reduce the

installed support cost considerably without sacrificing support

capability. 

Increasing the Support Load Density to Reduce

Entry Convergence

The objective of increasing the support load density is to

improve ground control by allowing less roof movement to occur.

If the ground reaction at a particular mine is known, then support

systems can be designed to provide any measure of convergence

desired. The following example (figure 12) is based on a ground

reaction curve selected from the program’s data base. Using this

curve, the convergence is reduced from 4 in, achieved with two rows

of conventional 4-point, mixed-hardwood cribs on a 97-in spacing,

to 2 in with alternative support designs. 
Figure 12. Analysis of support system options when the

convergence requirement is reduced from 4 to 2 in.

1. Review the design information on the various support

technologies in the Information Center.

2. Choose Ground Reaction Curve for the basis for selecting the

design criteria. In the Ground Reaction form, the Emerald

ground reaction curve is chosen. Input 4.0 in for the design

convergence and the program will determine the required

support load density that is consistent with the ground reaction

curve. In this case, it is 10.50 tons per ft. 

3. Control will then be transferred to the Support Selection

window. Wood cribs are chosen for the support type.

4. Control will then be transferred to the Wood Crib Performance

window, where parameters for a 4-point wood crib are defined.

The program will then determine the installation requirements

for this crib design. The program proceeds to the Costs

window. The default settings for the wood crib are reviewed

and modified as needed. The program then computes an

installed cost per ft of entry for this support design. 

5. Control is then transferred to the Comparison module where the

performance parameters for this support system can be

reviewed.

6. The Comparison window is then closed by transferring control

back to the Main Menu. Here the Design Criteria is activated

and the Ground Reaction Curve criteria is again selected. The

Emerald curve is again chosen. Now the design convergence is

changed to 2.0 in.

7. Control will then be transferred back to the Support Selection

window. Now the various alterative support technologies can

be selected and designed in the respective Performance

windows. 

8. When the support designs are completed, the Comparison

window will now show the baseline wood crib system at 4 in of

convergence and the alternative support design performance

measures at 2 in of convergence.

Replacing Timber Supports with Other Alternatives

There are several alternatives to timber supports. The STOP can

be used to evaluate these various alternatives and make comparisons

based on equivalent support capability or show the advantages of

alternative placement strategies with superior roof support systems.

The following example will show how these alternative support

technologies can be designed relative to the current roof support

system using available ground reaction data. The process begins by

selecting the Current Support System for design basis. For this

example, the current roof support system is a double row of 4-point

wood cribs. Hence, the user selects wood cribs as the support type

and then enters the appropriate data in the Wood Crib Specifications

form to define a 4-point crib constructed from 6x6x36 in oak

timbers. The center-to-center support spacing is entered (108 in in

this case) and the number of

Table 1. Comparison of alternative support technologies as replacements

for conventional wood cribbing.

Design Requirements: Support Load Density =15.25 tons/ft Convergence = 3.4 in

Support type Design specifics Installation requirements Achieved convergence

control, in

Achieved support

No. rows Spacing load density, tons/ft

Wood Cribs 4-pt (6x6x36 in oak timbers) 2 108 3.4 15.25

Pumpable Crib 30 in 1 116 0.91 25.23

ACS Pizza Headplate 2 133 2.61 19.74

The Can 24in diameter 2 138 3.4 15.25

Stretch Prop timber ft/hd boards 3 61 3.4 15.25

1

Since this particular support begins to shed load prior to the design convergence of 3.4 in, the peak support loading was used to

determine the support spacing and achieved support load density which occurs below the design convergence. This is the preferred

application design for these supports since the support capacity at the peak loading would control the convergence prior to yielding. 
Figure 13a. Comparing the number of supports per

supply car for conventional wood cribbing

and three alternative support technologies

Figure 13b. Comparing the supports constructed per

shift for conventional wood cribbing and three

alternative support systems

Table 2. Support systems determined by the optimization routine for user -define support installation parameters.

Design Requirements: Support Load Density = 16.67 tons/ft Convergence = 3.0 in

Support type Optimized design

User specified installation

requirements Achieved convergence

control, in

Achieved support load density,

tons/ft

No. rows Spacing

Wood Cribs 9-pt (5x5x30 in timbers) 2 96 2.8 17.6

Link-N-Lock 36 in 1 96 2.6 18.5

Tri-Log Cribs 30-in standard 2 96 1.6 22.5

Propsetter 10-in diameter 2 96 2.6 18.4

The Can 24 in 2 96 1.6 22.5

support rows (2 in this case). The design convergence and support

load density are determined by clicking on the Set using GR curve,

where it is shown that the current support system intersects the

chosen ground reaction curve at 3.34 in of displacement and provides

a support load density of 15.25 tons/foot. Table 1 compares several

alternative support systems that provide equivalent or improved

support capability.

Using the Optimization Routines to Select the Best

Support Design

The previous examples have shown how STOP will determine

the required support spacing that is needed for a user-specified

support design. The optimization routines allow the user to specify

a support spacing and number of rows of support elements, and the

program will determine which support design best fits the load and

convergence design criteria. For the example shown in table 2, the

design criteria of 16.67 tons per ft of entry at 3 in of convergence

was established from a Ground Reaction Curve chosen from the

program data base. Then various support types are selected for

evaluation. When the Optimization button in the Performance form

is selected, the user will define the installation requirements (number

of rows and support spacing) and the program will determine the

support model which most closely matches the design criteria (16.67

tons/ft at 3 in of convergence in this case). Since the installation

spacing and number of rows are specified, the achieved convergence

will vary depending on the support type chosen. Table 2 documents

some examples of optimized supports as determined by the STOP. 

Evaluating Material Handling Aspects of Support Design

Surveillance data shows that material handling injuries are

common in support construction, causing several thousand lost work

days each year. Hence, part of the support selection process should

be the material handling requirements. Figure 13 is an example of

data derived from STOP for four support systems: (1) Pumbable

Crib, (2) Alternative Crib Support or ACS, (3), Propsetter, and (4)

conventional 4-point crib. As seen from this analysis (figures 13a13c), there are significant material handling advantages in using the

alterative support technologies compared to conventional wood

cribbing. 
Figure 13c. Comparing the construction work for conventional

wood cribbing and three alternative support systems

CONCLUSIONS

Historically, wood cribs have been used as secondary roof

support in underground mines. The Wood Crib Performance Model

was developed by the U.S. Bureau of Mines in 1994 to provide an

engineering foundation for the design and applications of these

supports. In the past few years, many new support technologies have

been developed by various roof support manufacturers. These

innovative support technologies provide superior roof support and

reduced material handling requirements in many cases. However,

each has its own performance characteristic, hence they all need to

be employed differently in order to provide equivalent roof support.

STOP was developed to provide a more comprehensive support

design program than that provided by the old Wood Crib

Performance Model. Not only does STOP include all of the new

support technologies that have been developed, it also allows for

application of a new design methodology based on a measured

ground reaction curve at a particular mine site. Also included in

STOP are a comprehensive material handling assessment and cost

evaluation for each support system. STOP is a window’s-based

program that is user-friendly and very flexible to provide engineering

solutions for various secondary support applications.

STOP can be used to determine the installation requirements for

an alternative support technology that will provide equivalent

support as compared to the mine’s current support system or an

installation that will provide a specified support load density at a

designated roof convergence. The optimization routines in the

program will select the most efficient support design for the userspecified criteria. 

STOP utilizes performance data developed by NIOSH through

safety performance testing in the unique Mine Roof Simulator load

frame. Each of these support systems have been evaluated through

a rigorous testing protocol that simulates in mine service conditions.

Photographs of the support condition at various stages of loading are

also included in STOP. These photographs help to provide an

appreciation for the limitations of the support, and can be used to

assess the general loading conditions when these profiles are

observed underground.

STOP can provide some much needed engineering to secondary

roof support. This can be very helpful when petitioning MSHA for

approval to use an alternative support technology or making changes

in application such as increasing the support spacing. By proper

engineering of the support relative to the ground reaction,

convergence can be controlled to a predetermined level. This will

allow an operator to optimize the support application and provide a

margin of safety in roof stability that will reduce the likelihood of

roof failure without the need for excessive roof support. Likewise,

this will remove the uncertainty in the support design and prevent the

application of inadequate support that can lead to roof falls. Finally,

STOP will allow mine operators to fully consider the material

handling aspects of support design in the selection process, and by

doing so reduce the incidence and severity of material handling

injuries.

REFERENCES

1. Mark C. Analysis of Longwall Pillar Stability (ALPS): An

Update. In proceedings of the Workshop on Coal Pillar Mechanics

and Design. U.S. Department of Interior, Bureau of Mines,

Information Circular 9315, 1992, pp. 238-249.

2. Mark C, Chase FE. Analysis of Retreat Mining Pillar

Stability. In proceedings of the New Technology for Ground Control

in Retreat Mining. U.S. Department of Health and Human Services,

Center for Disease Control, National Institute for Occupational

Safety and Health, Information Circular 9446, 1997, pp. 17-35.

3. Barczak TM, Gearhart DF. Engineering Methods for the

Design and Employment of Wood Cribs. U.S. Department of

Interior, Bureau of Mines, Information Circular 9361, 1993, 34 pp.

4. Mucho TP, Barczak TM, Dolinar DR, Bryja J, Bower J.

Design Methodology for Standing Roof Support in Longwall

Tailgates. In Proceeding of the 18th International Conference on

Ground Control in Mining, 1999, pp. 136-148..

5. Barczak TM, Mucho TP, Dolinar DR, Bryja J, Bower J.

Longwall Tailgate Support, Consideration, Design, and Experience.

In Proceedings of the Longwall USA, 1999, pp. 79-105. 6. MSHA.

Data from the Mine Safety and Health Administration computerized

data base on mine injury and accidents. Accessible through the

MSHA web site. 

7. Unal E. Empirical Approach to Calculate Rock Loads in

Coal Mine Roadways. In Proceedings of the 5th Annual Conference

on Ground Control in Mining. WV University, 1986, pp. 234-241.