UPDATING THE NIOSH SUPPORT TECHNOLOGY OPTIMIZATION PROGRAM (STOP)

WITH NEW SUPPORT TECHNOLOGIES AND ADDITIONAL DESIGN FEATURES

Thomas M. Barczak, Research Physicist

National Institute for Occupational Safety and Health

Pittsburgh Research Laboratory

Pittsburgh, PA USA

ABSTRACT

The initial Support Technology Optimization Program (STOP),

Version 1.0, was released at the 19th Ground Control Conference.

This original program has since been updated to Version 2.3 which

was released in May, 2001. This paper describes the additional

features of Version 2.3, focusing primarily on the following three

aspects: (1) including uncontrolled convergence into the design

requirements for standing roof supports, (2) the addition of design

procedures for cable bolts as an alternative secondary roof support,

and (3) the addition of new standing roof support technologies.

Another new feature which should facilitate the development of

design criteria for standing roof support is the capability to define

ground reaction curves through convergence measurements alone

without having to make support loading measurements. There are

several other new features provided in Version 2.3 which are only

briefly addressed in the paper. These include: (1) additional graphics

capabilities to facilitate rapid assessment of support comparisons, (2)

an East-West designation for support selection to more accurately

provide cost and support availability data, (3) additional safety

measures including a safety factor to identify support design near the

peak support capacity, checks to see if the support dimensions comply

with aspect ratio requirements, and a measure of roof coverage for the

design layout of the support system. These new features of STOP

provide more capabilities to design and analyze secondary roof

support systems for conditions which could not be fully analyzed in

the original version of the program.

INTRODUCTION

The Support Technology Optimization Program (STOP) was

initially created and released in August 2000 (1). The program has

gained wide acceptance by the mining industry, providing both an

engineering foundation for support design as well as a means to

examine and compare new support technologies. STOP provides a

means to optimize roof support applications, and in so doing, helps

to ensure the safety of mine workers by preventing roof falls due to

improper support design. The safety of the mine workers is also

enhanced by providing comparative information on material handling

requirements for specific roof support products, allowing the user to

identify support technologies which minimize material handling

requirements. Since there are over 5,000 lost work days per year in

coal mines due to material handling injuries occurring during support

construction, material handling requirements are an important

parameter to consider in support selection.

The purpose of this program upgrade was to enhance its

capabilities for support design and to keep it up to date in terms of

available support technologies. The original version of STOP

allowed the user to define capacity requirements based on a specified

convergence, since passive standing roof supports develop load

carrying capacity only in relation to the closure of the mine entry.

The underlying premise in this design methodology is that the roof

support capacity is controlling the ground movements, and hence

roof stability. While this is often the case, there are conditions

where all the convergence cannot be controlled by the capacity of

secondary roof supports. Examples of convergence which typically

cannot be controlled by secondary supports includes floor heave and

pillar yielding. STOP can now accurately accommodate this

uncontrolled convergence behavior into the support design.

Several new standing roof support technologies have been added

to the program. These include: (1) Tekpak support developed by

Fosroc Inc, (2) Meshpack support developed by Strata Products

USA, and (3) RBS and Big John Props developed by American

Commercial Inc. The capabilities of these new support technologies

will be analyzed through the STOP. In addition to these standing

roof support technologies, design capabilities for cable bolts have

been incorporated into the program. 

A major part of support design is to be able to define the design

criteria. STOP has provided several options to facilitate the

definition of the design requirements, one of which is the Ground

Reaction Curve. The Ground Reaction Curve is the most powerful

design option in that it is a measure of the support and strata

interaction, which if known, allows one to design a support system

which will limit the convergence in the mine opening to a designated

level, and hence ensure stability of the mine entry based on in-mine

observations of ground behavior. In the original version of STOP,

this information could be inputted into the program provided

measurements of both support loading and convergence were

obtained. In the new version, only convergence measurements are

required, and the support loading, which is much more difficult to

measure underground, is estimated from the data base of support

performance obtained through laboratory testing of the supports.

This makes it much easier for the user to define ground reaction data,

and, therefore, to reap the benefits of its design capabilities.
Figure 1. Design criteria based on the performance of a 4-point

wood crib with an uncontrolled convergence of 5 in included

with a design convergence of 3 in.

Figure 2. The ACS support system fails to provide the required

capacity at 8 in of convergence.

Additional enhancements in the design capabilities of the program

include additional safety measures including a safety factor to identify

support design near the peak support capacity, checks to see if the

support dimensions comply with aspect ratio requirements to ensure

support stability, and a measure of roof coverage for the design layout

of the support system.

The purpose of this paper is to present these new capabilities,

provide some examples of their use, and to present the new support

technologies which have recently become available for secondary roof

support applications. 

NEW FEATURES IN STOP

The three most notable changes to the STOP are: (1) the

capability to include uncontrolled convergence into the design

requirements for standing roof supports, (2) the addition of design

procedures for cable bolts as an alternative secondary roof support,

and (3) the addition of new standing roof support technologies. 

Uncontrolled Convergence

As described in the Introduction, not all convergence can be

controlled by man made roof support structures. However, these

ground movements induce loading in standing roof supports, which

may at times damage the support, and hence should be considered in

the design of these support systems. Following is a description of

how STOP accommodates these uncontrolled ground movements into

the design of standing roof supports. 

First, the user can specify the amount of uncontrolled

convergence in any of the design criteria options. The timing of the

uncontrolled convergence is also part of the design consideration.

Two options are available: (1) Independent or (2) Concurrent. When

the Independent option is selected, the design convergence is set to

the controlled component of the convergence, and a security check is

made to see if the support can maintain the required capacity through

the total convergence, which is the sum of the controlled and

uncontrolled component. If the support cannot maintain the capacity

through this range of convergence, a warning is issued in the

Warnings box. Essentially, this option is saying that timing of the

uncontrolled convergence is such that it should not be counted on to

generate the required capacity of the passive roof support system to

maintain roof control, however, the support must be stable enough to

continue providing this necessary capacity to control the roof

deformation should floor heave or pillar yielding occur. 

Here is an example of independent, uncontrolled convergence.

A 100-ton Heintzmann ACS support is selected for analysis. The

design criteria are chosen based on the performance of a conventional

4-point wood crib support system, which has previously been

successfully utilized in this situation. Using the current support

system to establish the design criteria (figure 1), a load density of 11.6

tons/ft at 3 in of convergence is established for a double row of 4-

point cribs constructed from 6x6x36 in poplar timbers on a 96-in

spacing. It is also shown that an uncontrolled convergence of 5 in is

set. As seen in the design criteria summary at the bottom of the form,

the uncontrolled convergence timing is designated as Independent and

a security check is set up at 8 in of convergence equating to the sum

of the controlled (3 in) and uncontrolled convergence (5 in). Figure

2 depicts the performance window for the ACS support. It is seen

that the required spacing of a single row of ACS props to provide the

required 11.6 tons/ft at the design convergence of 3.0 in is 77.1 in.

However, as the Warnings box shows, the ACS support is in yield at

3 in of convergence and fails to provide the required 11.6 tons/ft at

8.0 in when the uncontrolled convergence is added to controlled

component. It is seen from the Ground Behavior and Support

Performance box that the ACS reaches its peak loading at about 2.25

in and sheds loads fairly quickly after reaching its peak load.

The other option is for the designation of the timing of the

uncontrolled convergence to be Concurrent. This means that it is

occurring at the same time as the controlled component of the

convergence and is thus acting to mobilize the support capacity to

provide roof control. The design convergence for the support

analysis is then set to the sum of the controlled convergence and the

uncontrolled convergence. In this case, the security check is set at

the controlled component of the convergence. The idea is to check

to see if the uncontrolled convergence did not occur, would the

support have the same or greater capacity as it would with the

uncontrolled convergence. 
Figure 3. Design requirements set at 14.9 tons/ft with at a design

convergence of 8 in including 5 in of uncontrolled (concurrent)

convergence

Figure 4. A conventional 4-point wood crib fails to provide the

required 14.9 tons/ft at 3 in of convergence

Figure 5. The Propsetter support on the other hand can provide

the required 14.9 tons/ft at both 3 and 8 in of convergence

Figure 6. Design criteria of 20.8 tons/ft established from a

Ground Reaction Curve at 8 in of convergence including 5 in

of uncontrolled convergence

The previous example of the 4-point wood crib support system as

the current support system is again used, except now the timing of the

uncontrolled convergence will be designated as concurrent and the

design convergence will include the 5 in of uncontrolled convergence.

As seen in figure 3, the load density requirement at 8 in of

convergence for the wood crib support system on a 96-in spacing is

14.9 tons/ft. Figures 4 and 5 depict the assessment of the current 4-

point wood crib (figure 4) and a Propsetter support (figure 5). The

wood crib system continues to provide greater support capacity as the

convergence continues (see the performance curve in the Ground

Behavior and Support Performance box). Hence, if the uncontrolled

convergence did not occur, the wood crib system at the 96-in spacing

would not provide 14.9 tons/ft at 3 in of convergence, and hence, the

wood crib support system fails the security check. The Propsetter on

the other hand, reaches its peak loading early in the loading cycle, and

although the support is yielding at 8 in of convergence, it provides the

required support capacity at 3 in of convergence as well.

Using a Ground Reaction Curve to define the design criteria

affords the user an additional capability with uncontrolled

convergence that is concurrent with the controlled component by

allowing the user to adjust the spacing to determine a spacing that

will make the support in compliance with the security check. Here

is an example. Again we will use a 4-point wood crib support

system for analysis. In this case, a hypothetical Ground Reaction

Curve is selected for the design criteria as shown in figure 6. The

design convergence is set at 8 in with 5 in of uncontrolled

convergence occurring concurrently with the controlled component.

The required support load density is 20.8 tons/ft using this ground

reaction data. It is seen from figure 7, that a double row of 4-point

wood cribs constructed from 6x6x36-in oak timbers will provide this

capacity when employed on a 115-in spacing. However, this system

also fails the security check at 3 in of convergence, meaning that if

the uncontrolled convergence (i.e., floor heave) did not occur, the

wood crib would not provide 20.8 tons/ft at 3 in of convergence.

However, by selecting the User Defined Spacing option in the

Support Layout (figure 8), it can be seen that at an 84-in spacing, the

same 4-point wood crib design provides 20.8 tons/ft and meets the

security check, meaning that at this spacing the support would

control the roof even if the floor heave did not occur.
Figure 7. Double row of wood cribs on a 115-in spacing

provides the required 20.8 tons at 8 in of convergence

but not at 3 in

Figure 8. Reducing the spacing of the 4-point crib system to 84 in

allows the system to meet the security check requirements

Figure 9. Separate design criteria for cable bolts can be provided

by activating the Edit button under the Design Basis - Cable

Bolts frame in the upper left corner of the window

Figure 10. Design criteria using a detached block

basis for cable bolts

Cable Bolts

A category for intrinsic support has been added to the support

selection module. In this category, cable bolts have been added as a

support selection option. The current methodology for cable bolt

design is based on a detached block approach using a shear or arch

type failure geometry (2). This criteria can be specified in the design

criteria window, where a separate design criteria section for cable

bolts is provided (figure 9). As an intrinsic support, the cable bolt

will only see roof loading, whereas the complete roof to floor closure

will be seen by a standing roof support system. Therefore, a separate

design criteria section is provided.

The Edit button (figure 9) can be pressed to activate the cable bolt

“detached block” design criteria. The design criteria for cable bolt

window (figure 10) is similar to that for standing support, except the

convergence criteria is changed to “roof displacement” and a safety

factor is included in the design requirements. The roof displacement

requirement is defaulted to 1 in, but the user can select any value.

This criteria sets a limit for the amount of roof displacement that is

permitted to occur before the cable bolt system provides sufficient

loading to put the dead weight of the roof mass into equilibrium.

The safety factor is similar to that computed for standing roof

support, except it is now used as part of the design requirement. The

safety factor is defaulted to 1.5, meaning that the ultimate capacity

of the cable bolt is 1.5 times the design load requirement necessary

to support the dead weight of the roof rock at the designated failure

height. In other words, the cable bolt load must not exceed 67 % of

the ultimate load capacity of the cable. The minimum acceptable

safety factor is 1.25, equating to a cable bolt being utilized at 80 %

of the ultimate capacity of the bolt. 

The Performance window for cable bolts is shown in figure 11.

The design approach for cable bolts in somewhat different than that

used for standing support. Since the cable bolt spacing is likely to

be fixed relative to the primary roof bolt spacing (most likely in
Figure 11. Performance window for defining a cable bolt system

and determining the number of cables and spacing pattern

necessary to satisfy the load requirements

Figure 12. Increasing the number of roof-bolt sets per cable set

to 2, allows 7 cables to be used in the 8-ft spacing to provide a

design closer to the minimum design requirements

Figure 13. When 3 cables per cable set are chosen, the

safety factor requirement is not met and a warning

is issued to this effect

between the roof bolt spacing), the design goal is to determine the

number of cables across the entry (equivalent to the number of rows

of supports in standing support evaluations) that are needed to satisfy

the design criteria. There are also options to consider in terms of the

cable layout or pattern of cable bolts used. First the user can select

the number of roof bolt sets in which the cable set will be employed.

A roof bolt set is defined as a set of roof bolts across the mine entry.

Specifying a single set of roof bolts means that the cables set must be

employed between every row of roof bolts and this pattern will

continue down the entry. On the other hand, if 2 roof bolts sets are

specified, then the cables must be employed in a spacing equivalent

to two rows of roof bolts. A cable set is defined as the number of

cables used in relation to the space option down the entry, which

again is defined by the number of roof bolts sets. The number of

cables per set is the parameter calculated by the program.

Some examples will help to clarify the cable design procedure

using STOP. The first requirement is to select the cable parameters

to be used in the design. These are shown in the upper left hand area

of the performance window. In this example, a 0.6-in diameter cable

bolt with a length of 14 ft and 5 ft of resin anchorage is selected for

evaluation. Other parameters selected include the hole size (1 in in

this case), and the plate options (6 in plate in this case). It is also seen

that the cable is put in without any pretensioning in this example.

Using the criteria displayed in figure 10, the cable bolt design

criteria for this example is 15.0 tons/ft at 1 in of roof displacement

with a safety factor of 1.5. As seen in figure 11, the standard roof

bolt spacing is set at the default value of 4 ft, and the number of roofbolt sets per cable set is set at the default value of 1. The program is

asked to calculate the required number of cables for these criteria, (the

Calculate radio button is pushed), and the program determines that 4

cables per cable set are needed (figure 11). Hence, the recommended

design is 4 cables across the entry spaced in between each row of roof

bolts. The Achieved Ground Control information provided on the

right side of the window shows that the load density of 15 tons/ft is

provided at 0.517 in of roof displacement and a safety factor of 1.95

in relation to the ultimate capacity of the support. The loaddisplacement performance of the cable bolt system relative to the

design requirements is also graphically shown in the bottom left area

of the window.

If the no. of roof-bolt sets per cable set is increased from 1 to 2,

then the available spacing of the cable set is 8 ft, and the program

computes that 7 cables are required in a pattern with 3 cables in the

first row and 4 cables in the second row (figure 12). With this

pattern of cables, the design requirements are met at slightly greater

roof displacement (0.591 in) and with less of a safety factor (1.71).

In essence, this design is moving closer to the minimum

requirements set forth in the design criteria by allowing a pattern of

7 cables in 8 ft as opposed to 4 cables every 4 ft. 

Instead of having the program compute the required number of

bolts, the user can define this. For example, if the no. roof-bolt sets

per cable set is set at 1, and the user-defined number of cables is set

at 3, then the safety factor drops to 1.46 which is below the

requirement of 1.5, and a warning to this effect in issued in the

Warnings box on the lower right area of the window (figure 13).
Figure 14. Pretensioning of a cable bolt can be used to reduce the

required roof displacement necessary to meet the load criteria

Figure 15. Cost and material handling data are also 

available for cable bolts

Figure 16. Performance information on the RBS prop

Other design options besides bolts per row are available to the

user when the program is computing the cable layout. One is to limit

the number of cables across the entry to a maximum of 4. This

limitation stems from installation restrictions with drilling the holes

for the cable bolts, and to some extent the practical limit of the area

of influence of a single cable bolt. When this option is chosen and

more than 4 cables are required to satisfy the design requirements, the

4 cable per row limit will reduce the safety factor and may reduce it

below the design requirements. The other option is to limit the

number of cables per row to an even number. Again this limitation

may be due to the hole drilling practices, particularly with a dualboom bolter. When this option is chosen, the safety factor is likely

to be increased since the number of cables will be rounded to the

nearest even number increment.

Pretensioning of a cable is also one of the design options. The

effect of preload is to essentially shift the performance curve to the

left, meaning that some of the deformation of the cable will be used

up by the pretensioning. From a ground control perspective, the

effect of pretensioning is generally to reduce the amount of roof

displacement required to achieve equilibrium of the rock mass by

building a more competent roof beam. The reduction in roof

displacement will be in proportion to the amount of active roof

loading applied by the pretensioning. If the pretensioning is too high,

the required safety factor limit will be exceeded and a warning will be

given to this effect. An example of pretensioning is shown in

figure 14.

As done with all of the standing supports analyzed in STOP, the

cable bolt design process also includes estimated cost and material

handling data. Figure 15 shows an example of this information.

Shown in the figure are the cost models used for the cable bolts.

It is seen that all components of the system (bolt, resin, and plate)

are included in the cost structure. The fixed cost of $0.25 per cable

in the construction model is to account for bit replacement.

New Support Technologies

In addition to cable bolts, several new standing roof support

technologies have been added to this version of STOP (Version 2.3

– April 19, 2001). These include: (1) RBS Prop, (2) Big John Prop,

(3) Tekpack, and (4) Meshpack. In addition to these new support

concepts, additional models have been added to the Star Prop,

Heintzmann Pumpable Crib, and the Tri-Log Crib. A brief analysis

of these new support technologies is provided through the

capabilities of STOP.

RBS Prop – The RBS Prop is a yieldable timber post. The yield

capability is provided by a specially designed head piece which sits

on top of a conventional timber post (figure 16). The head piece

consists of a threaded plastic section similar to a large bolt, that

threads into a steel shell lined with a threaded plastic sleeve. The

yield is provided by the shearing of the plastic threads.

As seen from figure 17, the load-displacement profile for the

RBS prop is similar to that of a conventional 4-point wood crib
Figure 17. Load-displacement performance plot of

RBS prop and wood crib

Figure 18. Spacing comparison for RBS prop and

4-point wood crib system

Figure 19. Design information on the Big John Prop

Figure20. Comparison of the RBS and Big John Props to a

conventional 4-point wood crib

Figure 21. Design information on the Tekpack support

constructed from (6x6x36 in) mixed hardwood timbers, although the

crib is slightly stiffer during the period when the load is controlled by

the shearing of the threads in the RBS prop. Hence, for convergence

control between 1.5 and 4 in, the RBS prop will require a tighter

spacing than would a conventional 4-point crib. Figure 18 shows one

example at a design load density requirement of 12 tons/ft at 2 in of

convergence achieved with a double row of supports.

Big John Prop – The Big John Prop utilizes the same threaded

plastic end piece as does the RBS Prop to provide controlled yielding

(figure 19). The difference in the two systems is that the Big John

utilizes cut sections of timber for the post instead of the round

sections used in the RBS Prop. The Big John Prop is currently

marketed with 2, 3, and 4 ply sections of timber measuring nominally

3.5 x 6 in in cross section. This provides for higher ultimate loading

capability since the ultimate capacity is controlled by the buckling

strength of the prop and the built-up sections of timber have a much

larger area than the 8-in-diameter timber post used in the RBS prop.

The load-displacement profile prior to full thread shearing is the same

as the RBS Prop since it is the same end piece (figure 20).

Tekpack Support – The Tekpack Support is marketed by Fosroc

Corporation and is very similar to the Pumpable Crib support

marketed by Heintzmann Corporation (figure 21). Both support

systems utilize a two-part specialized grout that is pumped into a

fabric bag which acts a form during pumping and provides sufficient

confinement to provide some residual loading capacity once the

material fractures during load application.
Figure 22. Design information on Meshpack support

Figure 23. Comparison of Pumpable crib, Tekpack, and

Meshpack supports

Figure 24. Using the program to define a ground reaction curve

from convergence measurements alone with support loading

calculated from the laboratory test data

Meshpack Support – The Meshpack support (figure 22) is another

support that is pumped in place using a fabric bag to act as a form.

Unlike the Pumpable Crib (Heintzmann Corporation) and the

Tekpack support (Fosroc), the Meshpack support marketed by Strata

Products USA uses a more conventional cementitious grout

consisting primarily of Portland cement and flyash. The two

component grout mixes used in the previously mentioned supports

require the water to be retained by the bag to interact with the grout.

In contrast, the Meshpack is a weeping system where the water is

allowed to weep (drain) out of the bag. The large volume of water

used is primarily for solids material transport during pumping and is

not fully used as an agent in strengthening the mix. Steel bands and

wire mesh provide additional confinement to the bag as seen in

figure 22.

The Meshpack is the strongest of the three pumpable supports

(Heintzmann Pumpable Crib, Fosroc Tekpack Support, and the

Meshpack) due to the inherent strength of the pumped material. It

also has the highest post failure strength, due in part to the extra

confinement provided by the steel bands and wire mesh. The

downside of this higher strength and larger residual load capacity is

that it cannot be maintained for as much convergence. As seen from

figure 23, the residual load in this laboratory test specimen lasted

through 8 in of convergence before a large load shedding event

occurred. At the writing of this report, this support is new on the

market and no field trials in active mines have yet been conducted.

MAKING IT EASIER TO DEFINE GROUND

REACTION CURVES

In the original version of STOP, the user had to input both the

measured support load and convergence to define data points for a

ground reaction curve at a particular mine site (3). Now the user can

define data points for determining the ground reaction curve by only

measuring and inputting the convergence in the mine associated with

a particular support application (figure 24). The program will use

this convergence measurement to calculate the estimated support

loading and resulting support load density for the layout of the

support system. It should be noted that the ground reaction will vary

depending on the location in the mine relative to the mining activity

as well as several other factors including geology and overburden

depth. The goal is to evaluate the ground behavior in the worse load

condition. For example, in a longwall tailgate, the convergence

measurements should be made at the tailgate corner, since the

abutment loading will be most severe at this location. The caveats

of measuring the convergence are explained in more detail in the

cited reference material number 3. This should facilitate the

development of ground reaction data since convergence is relatively

easy to measure, while the more difficult measurement of support

loading is no longer required.

ADDITIONAL FEATURES

East-West Support Settings

Some supports that are available in the East are not available in

the West. In addition, those that are available in both the East and

the West typically will have different costs associated with them,

particularly if the supports are made in the East and shipped to the
Figure 25a. Plotting of the support spacing

Figure 25b. Plotting of the normalized support costs

West. Even supports which are made and used in the West, such as

conventional wood cribbing, can have significantly different costs

than their Eastern counterparts due to differences in the cost of

materials (wood). In the new version of STOP, the costs and support

availability and various default settings are customized for eastern and

western mine applications. As part of the input, the user can select

which area of the country is relevant to the analysis.

Additional Graphics Capabilities

The original STOP (Version 1.0) allowed the user to plot either

the unit support load or the support system load density as a function

of convergence for any of the supports chosen for analysis.

Version 2.3 allows the user to chart any of the 24 different analysis

parameters. For instance, the normalized installed support cost per

foot of entry is shown in figure 25. This capability significantly

increases the visual graphics available for support analysis and helps

facilitate the rapid evaluation of support parameters.

Roof and Floor Bearing Strength 

The design criteria now includes the roof and floor bearing strength.

This is needed to see if the support load will cause the support to

punch into the roof or floor, which could significantly degrade the

capability of the support to maintain roof control. It should be noted

that default setting for both the roof and floor strength is 2,000 psi.

This may or may not be appropriate for a particular mine, so this

parameter should be updated by the user when establishing the

design criteria. 

Support Header and Footer 

The program also now allows the user to specify the header and

footer used with the support. Inputs are asked for the roof and floor

contact area. The user can input values or use the set of defaults

contained within the program which are believed to be representative

for that particular support. Roof coverage dimensions are also

provided. On occasion, these dimensions may be larger than those

used in the roof contact bearing area computation. For example, the

foot print of a wood crib is determined by the box area derived from

the length of the timbers, while the contact area is determined by the

actual timber contact area with the floor and hence will be much

smaller.

Warnings box

On each of the Performance windows for the various support

technologies, a Warnings box is shown on the bottom left portion of

the window just below the Achieved Ground Control area.

Messages are posted in this box pertaining to a variety of rules

relevant to a particular support. Some example messages include: 

< Support is in yield.

< Exceeds roof bearing strength.

< Exceeds floor bearing strength.

< Support is too short (poor aspect ratio).

< Skin-to-skin spacing exceeds W/2.

< The achieved convergence exceeds the design convergence.

Safety Factor

A load safety factor has been included under the Achieved

Ground Control box to provide insight into how close the loading

of the support is to its peak capacity for the recommended support

installation. The Safety Factor is the ratio of the maximum support

capacity to the actual support loading achieved using the current

design. The maximum support capacity is defined for each support

as part of the internal program data base. For supports such as wood

cribs that continue to build load through very large displacements,

the peak load is defined at 20% strain. When the support has yielded

(exceeded its peak loading), the safety factor will be the inverse of

the ratio of the peak load to the actual load and hence will be less

than 1. A safety factor of 1.0 means that the support is operating at

its peak capacity. This typically is not desirable since any additional

convergence will cause most supports to shed load. A safety factor

of 2.0 means that the support is at 50% of its peak supporting

capacity.

Aspect ratio checks

Checks are now make to see if the support dimensions comply

with rules established from laboratory testing. If not, a warning is

issued in the Warnings box that the support is too short. Aspect

ratio requirements for several commonly used support technologies

are as follows:
Conventional wood cribs – 4.3*

Link-N-Lock cribs – 4.0:1

Tri-Log cribs – 4.0:1

Link-N-X cribs – 3.0:1

Concrete cribs – 6.0:1

Can Support — 5.0:1

Pumpable crib – 4.0:1

CONCLUSIONS

The additional features incorporated into the STOP enhance the

design capabilities of the program. The three most noticeable

additions are the capability to incorporate uncontrolled convergence

into the design criteria for standing roof supports, the addition of

cable bolts as a support technology with design procedures to

determine the number of cables per row required to support a

detached roof block in suspension, and the addition of new standing

roof support technologies. 

Since standing roof supports are almost always passive roof

supports, convergence plays a major role in their design and

capability to provide adequate roof control. In the initial version of

STOP, it was generally assumed that the support capacity had a direct

bearing on the roof deformation and ultimately roof stability. While

this is generally the case, there can be convergence which is not

controlled by the capacity of the standing roof supports, most notably

convergence which is induced by floor heave and pillar yielding. The

uncontrolled convergence caused by these events will produce

deformation and loading of the support structure, just as the roof

deflection or controlled convergence. Hence, it is critical to know if

the support can survive these uncontrollable ground movements and

continue to provide the necessary capacity to control the mine roof.

In addition, it is important to know if the extra loading produced by

these uncontrollable ground movements will cause support loads that

will cause failure of the immediate roof or floor strata, and in doing

so, degrade the roof or floor stability or degrade the effective capacity

of the support. On the other hand, if the magnitude of the

uncontrolled convergence changes or is not present under all

conditions, then it should not be required in order to create the

support force necessary to control the mine roof. For this problem,

STOP provides a security check to see if the required support capacity

would be available at a reduced level of convergence, and if not,

allows the user to tighten the support spacing to determine what

support spacing would be necessary to provide the required support

capacity under these conditions.

The addition of the cable bolt design section provides another

type of roof support system that can be designed and analyzed in

STOP. Cable bolts are sometime used in lieu of standing support in

longwall tailgates and in other applications where the restriction of

space in the mine entry is an issue. STOP now provides design

capabilities for cable bolts in which unique design criteria can be

established specifically for cable bolts, and the required cable bolt

pattern that is necessary to satisfy these design criteria can be

optimally determined. Estimated cost calculations can be computed

and compared with standing supports.

The revolution of new standing roof support technologies

continues in 2001. Four new support technologies have been added

to STOP, keeping the program up to date with the very latest support

technologies. Each of these technologies were described with

examples in the paper, showing that viable new alternatives exist to

the multitude of choices for secondary roof support systems.

A key ingredient in any support design is to be able to define the

design requirements. STOP provides several options for doing this,

including the use of a Ground Reaction Curve, which is nothing

more than a measure of how the ground behaves relative to the

amount of support that is installed. In this new version of STOP, the

capability to define Ground Reaction Curves has been simplified.

Now, this information can be obtained by simply measuring the

convergence seen in the mine with a particular support application,

and the program will automatically compute the support loading and

thus eliminate the need for underground measurements of support

loading to determine the ground reaction information for that

support system. This should facilitate the use of this powerful

design methodology.

The other major modification incorporated in this new version

of STOP is the additional graphics capabilities. The program now

provides the user with the opportunity to plot or chart any of the

design parameters. This graphical analysis facilitates comparison

among the different support technologies, and in doing so, enhances

the capability to select the optimum support system for a particular

application.

REFERENCES

1. Barczak, T.M. Optimizing Secondary Roof Support with the

NIOSH Support Technology Optimization Program (STOP). In:

Proceedings of 19th International Conference on Ground

Control in Mining, Morgantown, WV, Aug. 8-10, 2000, pp. 74-

84.

2. Tadolini, S. C. and Trackemas, J.D. Cable Support for Longwall

Gate Road Stability. In: Proceedings of 14th International

Conference on Ground Control in Mining, Morgantown, WV,

Aug. 1-3, 1995, pp. 9-17.

3. Mucho, T.P., Barczak, T.M. and Dolinar, D.R. Design

Methodology for Standing Roof Secondary Roof Support in

Longwall Tailgates. In: Proceedings of 18th International

Conference on Ground Control in Mining, Morgantown, WV,

Aug. 3-5, 1999, pp. 136-148.