p

qy 

to several weeks of active fire fighting. Time is most Seals should be located first in areas where the least number 

portant when constructing seals, and miners may be placed of seals are needed and the sealed area should be large enough 

great risk during construction. Even when mine fires are for hot, combustible gases to expand without endangering the 

~cessfully sealed, experience has shown that there is a high miners who are building the seals. The bottom, ribs and roof 

jbability of an explosion within 72 hours of sealing. There- should be firm and above potential flood levels. Seals should 

8, a seal should be capable of withstanding explosion be constructed in a level area, preferably below the elevation 

etpressure shortly after construction. of the fire, and they should be placed in areas where the roof 

,Controlling a fire by reducing the exchange of oxygen is sufficiently supported. 

pires surrounding the fire area quickly with barriers ca- Storing sealing materials at key locations prior to the 

kle of withstanding moderate-strength explosions as the occurrence of a fire can significantly minimize construction 

@ained atmosphere transitions from the fuel-lean to fuel- delays and greatly reduce the burden on the miners who would 

kcondition. Once the fire becomes established, the chances be required to move and place these materials at the sealing 

[successful in-mine sealing decreases rapidly with each location while wearing self-contained breathing apparatus. 

p that passes. Also, communication with the surface should be maintained 

$ priori planning for sealing is paramount to successfully to all sealing areas, and the miners constructing the seals 

Fjtrolling an underground fire and for rapidly constructing a should be able to retreat swiftly to safety. 

$during mine recovery. Rapid sealing of a mine section If the decision is made to seal a section of a mine, the 

puld be part of normal mine planning and layout. In the quicker the seals are built, the less exposure to miners. As 

btof afire, having developed sealing strategies can signifi- part of an effective sealing operation, materials should be 

I 

Y 

Preprint number 03-010, presented at the SME Annual Meeting, Feb. 24-26, 2003, Cincinnati, Ohio. Original manuscript 

5 accepted for publication April 2004. Discussion of this peer-reviewed and approved paper is invited and must be submitted 

toSMEPublicationsDept.priortoSept.30,2005.Copyright2004,SocietyforMinig,Mefa//urg~andExp/oratioo,//nc. 
concrete-block seal, it is difficult to uniformly load or completely fill the gap between the top of the seal and the mine roof 

with mortar; thus the effectiveness of vertical arching becomes critical. In the field, most of the standard-type block 

seal strength comes from the rib-to-rib arching action. An 

alternative design concept is based on improving the arching 

action by providing better coupling between the seal and the 

mine roof, which can be done by preloading the seal with 

pressurized grout bags. 

To address these issues, the following organizations participated in a joint research effort: NIOSH's Pittsburgh Research Laboratory (PRL), Strata Products Inc., RAG American Coal Company, FOMO Products Inc., Burrell Mining 

Products International Inc. and HeiTech Corporation. The 

project's purpose was to evaluate the strength characteristics 

and air-leakage resistance of a preloaded wood crib seal 

design, alightweight cementitious Omega block' seal design 

and a design consisting of a series of grout-filled bags. These 

seals were specifically designed for rapid construction and 

quick setting as compared to the more standard method of 

constructing a mortared concrete block seal design hitched or 

lReference to specific products is for informational purposes and 

does not imply endorsement by NIOSH. 

ft) gas ignition zone. An electric fan 

motor housing was used to mix the 

the ignition zone. 

A sample line within the ignition zone was used to co 

ously monitor the gas concentrations using an infrared 

lyzer. In addition, samples were collected in evacuated 

analyses verified the infrared anal 

methane in air. Three electrically 

triple-point configuration equally spaced acro 

end) of the entry, were used to ignite the flammable natur 

and air mixture. Barrels filled with water were located 

ignition zone to act as turbulence generators to achie 

projected 140-kPa (20-psi) pressure pulse. The pressure 

generated by the ignition of this methane-air zone gen 

resulted in static pressures ranging from -1 50 kPa (-22ps 

crosscut X-1,129 kPa (-19 psi) X-2 to -1 15 kPa (-17 ps 

X-3 the most outby seal. 

To ensure that all of the seal designs woul 

a 140 kPa (20 psi) explosion pressure pulse, 

coal dust was used for several of these tests in addition t 

natural gas ignition zone. The coal dust was loaded 

shelves that were suspended from the mine roof on 3-rn 
of the data-gathering stations to an underground 

room off C-drift and then to an outside control 

high-speed, 64-channel, PC-based computer dataiaition system (DAS) was used to collect and analyze the 

is system collected the sensor data at a rate of 1,500 

per second over a five-second period. The data were 

rocessed using LabView and Excel software and outed in graphic and tabular form (discussed in the "Exploand air-leakage test results" section). The reported data 

averaged over 10 ms (15-point smoothing). 

leakage determinations. An important factor to be conr any seal design is its impermeability, or its ability 

ze air leakage from one side of the seal to the other. 

urements of the air leakages across the seals were conted before and after each of the explosion tests. A wooden 

ework with brattice cloth or curtain was erected across C 

outby the last seal position. This curtain effectively 

Led the ventilation flow, which resulted in a pressurized 

on the C-drift side of the seal. By increasing the speed of 

-level LLEM main ventilation fan while in the blowe, the resultant pressure exerted on the seals increased 

proximately 0.25 kPa (1-in. H20) for the lowest fan 

setting to nearly 1.0 kPa (3.7-in H20) for the highest fan 

explosion evaluations, the use of pressurized grout bags in 

conjunction with the use of an easily applied adhesive along 

the wood crib joints has been effectively demonstrated to 

provide several advantages when constructing underground 

coal mine seals. One advantage is the time required for seal 

construction compared with the standard-type solid-concreteblock seal and other mortared block seal designs. 

With the construction materials located at the site, it 

requires approximately seven hours for two miners to stack 

and glue the wood cribs, about 1.5 hours to fill the packsetter 

bags and about 45 minutes to foam and coat both sides. By 

comparison, two miners require about 60 to 70 hours to 

complete a mortared standard-type concrete block design. 

Additionally, wood crib seals are near full strength within 24 

hours of completion and do not require the 28-day cure 

period of mortared block seals. This quick construction and 

cure time is particularly beneficial when installing seals to 

isolate a fire zone and/or a gob area prone to spontaneous 

combustion. 

The use of hardwood cribbing reduces materials-handling 

requirements, which may further reduce injuries that are 

typically associated with handling the smaller, yet heavier, . 

standard-type solid-concrete block. The hardwood cribbing 

timbers, 150- x 130- x 760-mm (6- x 5- x 30-in.), are commonly used for roof support for many eastern mines. Finally, 
Crosscut 1. The packsetter bags along the mine roof 

injected first (starting at the center and working 

the wood cribs are dimensionally consistent throughout and 

allow for easy construction with interlayer glueing. particular order. When injected with grout, 

Figure 2 shows a schematic and Fig. 3 is a photo of a overlapped both sides of the wood crib wa 

completed wood seal that was placed in Crosscut 1. The 150- mm (3 in.). 

x 60-mm (6- x 2.5-in.) half timbers were used to overlap the 

vertical seams. Two 13-mm-wide x 760-mm-long (0.5- x 30- 

in.) beads of Handi-Stick adhesive were applied to each between the bags and the mine roof to fill 

timber between rows, and two 13-mm wide beads were sealant was then applied by hand to the 

applied to the vertical sides of each piece. Approximately one the wood crib seal and then covered with brattice 

1-L (32-02) can of Handi-Stick adhesive provided twocourses Several pieces of 25- x 150-mm (1- x 6- 

of wood crib coverage. The glue starts to set within 3 rnin and 

cures to full strength in 24 hours. During the seal construction 

at LLEM, the mine temperature dropped to 4°C (40°F), perimeter of the brattice w 

making it difficult to keep the glue warm during application. used to adhere the brattice to the riblroo 

For optimal performance, the glue should be stored and used front and back of the seal were then spra 

at temperatures above 10°C (50°F). to cover the bratticelfo 

The packsetter bags, as manufactured by Strata Products (Fig. 4). A construction time of appro 

Inc., Marietta, Georgia, were similar in design to the bags used worker-hours) was required. Because this was a pro 

during a previous seal evaluation program (Weiss et al., seal design and modifications to the construction proces 

2002). The dimensions of the packsetter bags can vary de- required, it is anticipated that the construction time 

pending on the seal design thickness and construction tech- decrease for future seal installations. 
he low-viscosity Bloc-bond was applied to all block-to- I! lock interfaces to a mortar joint thickness of about 6 mm 

P ,25 in.). 

The 60-mm gap between the last course and the mine roof 

filled with 25- x 200-mm-long (1- x 8-in.) rough-cut 

ds aligned lengthwise from rib to rib. One row of these 

ds wasplaced in the middle of the top seal course with two 

of additional boards place symmetrically on each side of 

nterrow, with the lengthwise board edges flush with the 

hby and outby side of the seal. Each row of wood was wedged 

about 300-mm (12-in.) centers and the gap between the 

kd ges and board rows filled with Bloc-bond. A 6-mm- (0.25- 

!.-)thick coating of Bloc-bond was then applied to both faces 

@&he seal. Seal construction was completed in 9.5 hours (28.5 

hiorkerhours). The Bloc-bond achieves 13.8-MPa (2,000-psi) 

'pmpressive strength within the first 24 hr. 

borehole is required to allow 30-mm (1.25-in.) PVC lines to 

convey the accelerator and cement slurry. This remote pumping location is especially beneficial when several seals are 

required and where the handling of material is difficult. The 

pumpable bag seal design (Fig. 7) was constructed by positioning six 760-mm- (30-in.-) diameter cylindrically shaped 

column bags (with sewn in reinforcement rings or bands 

spiraling around the circumference of the bags) equally across 

the crosscut. 

Each bag was held in place to the mine roof using four 

PVC adjustable pogo sticks; nylon straps were used to secure 

the pogo sticks in place during the grout-injection process to 

ensure that the pogo sticks would not bow. These column 

bags were separated approximately 120 to 150 mm (5 to 6 in.) 

apart with the end bags approximately 100 mm (4 in.) from 

each rib. No hitching was required with this seal. The 

material used within each bag was a two-component 

cementitious grout. Equal quantities of accelerator (90 bags 

of PacBent 120 Accelerator - M-PB20-Acc) and cement (90 

bags of Blue Circle Special Cement Pacset 140 Cementitious 

- M-PS30-Cem manufactured by Rockfast Mining Products) were used to fill the column bags. The average bag 

MTechcolumn bag pumpable seal. The HeiTech pumpable 

9s that were used in this study are primarily used for ground 

Bpport in longwall mining. They provide improvement in 

round-support capability as well as reduced material hanling. 

The pumping site for multiple seals can be located in excess 

f3,000 m (10,000 ft) away and on the surface. For a surface 

mping station, aminimum of a 101.6-mm- (4-in.-) diameter 
g8 p

weight for both the accelerator and cement product was 25 kg 

(55 Ib). The bags were grout-injected using a 2.15:l powder 

to water ratio; i.e., 100 kg (220 lb) of AcceleratodCement 

mix to 212 L (56 gal) of water. A total of 2,245 kg (4,950 lb) 

of PacBent accelerator powder and an equal amount of the 

Pacset cement powder were used with approximately 4,770 

L (1,260 gal) of water. 

Based on the powder-to-water ratio used during this construction, HeiTech estimated the compressive strength of the 

grout to be in the 41- to 55-MPa (600- to 800-psi) range. 

Subsequent analyses of six batch samples showed an average 

compressive strength of 41.2 f 4.3 MPa (597 f 63 psi). Four 

mixers were used during the grout-injection process - two 

for each powder. An Edeco Mindeb single-action pump was 

used to inject the grout components into the bags. The pumping distance was approximately 60 m (200 ft). This singleaction pump injected -4 L (1 gal) of the accelerator slurry on 

the first cycle followed by -4 L of the cement slurry on the 

second cycle; these components were then left to mix within 

the bag. 

Each of the six bags was initially filled with 300 mm (12 

(250 cfm). 

The preexplosion air-leakage rates (Table 1) through a& 

of the three seal designs were within the acceptable gulb 

lines. I 

Wood seal preloaded with grout bags. The pressure EIJ# 

LVDT displacement data measured during the LLEM Tqt 

#396 on the preloaded wood crib seal are shown in Fig. @ 

Within 0.45 sec, the pressure on the seal rose to about 150m 

(22 psig), and the center of the seal showed a permand 

center displacement of -20 mm (0.75 in.). The wood crib#& 

design with the packsetter bags survived the explosion w& 

no significance evidence of any outward damage. Portionat$ 

the perimeter sealant on each side of the seal at the packsew& 

bag and sealfroof interface were also dislodged during h 

explosion. 

Post-explosion air-leakage measurements showed that thJB 

wood crib seal design with the packsetter bags maintain4 

minimal leakages (2.1 m3/min at 0.17 kPa or 73 cfm at 0.7 i& 

H20) as listed in Table 2) and well within the acceptable rate@ 

Therefore, this design would continue to serve its intfunction to limit air movement into and out of a seal area. 

Thd-preloaded wood crib seal was also subjected t~y 

second slightly stronger explosion (LLEMTest #399). Wa 
center of the seal showed a permanent displacement of nearly 

40 mm (1.5 in.). Even though the seal shifted 40 mm, the postexplosion leakage (1.5 m3/min at 0.25 kPa or 53 cfm at 1 .O in. 

H20) remained within acceptable limits. 

Conclusions 

?his research effort was designed primarily to determine the 

eength characteristics of the three seal designs for use in 

tapid sealing operations during a mine emergency or recovery 

Idtuation. The program objective was to determine the ability 

td newly constructed seal designs to withstand a pressure 

Ise of at least 140 kPa (20 psi) while still maintaining 

ant resistance to air leakage within 24 hours after 

e wood seal utilizing the quick-setting grout-filled 

acksetter bags, the Omega low-density block seal without 

, and the HeiTech design with a series of interlocking 

le grout bags can be constructed in less than 12 hours 

withstood 140-kPa (20-psi) explosion pressure. 

hese seal designs use existing ground support and stopg materials, require minimum power and compressed air 

construction, do not require conventional rib hitching and, 

st importantly, can reduce exposure time for coal miners 

ng sealing and mine recovery operations. 

0.2 0.4 0.6 

Time, s 

Figure 11 -Pressure and displacement histories recorded 

on the HeiTech seal. 

Acknowledgments 

The authors thank RAG American Coal Company in 

Waynesburg, Pennsylvania, for providing the seal constmction materials and labor for the wood crib seal; Ed Barbour, 

sales and marketing manager, and Joe Atkins, application 

technician, of StrataProducts Inc., Marietta, Georgia, for their