Demonstration of remote mine 


seal construction 


T.A. Gray 


Engineering manager, GAI Consultants, Inc., Monroeville, Pennsylvania 


M.A. Trevits 


Research physical scientist, NIOSH, Pittsburgh, Pennsylvania 


L.M. Crayne 


Construction manager, Howard Concrete Purnpirig Co., Cuddy, Perlnsylvania 


P. Glogowski 

GAI Consultants Inc., Monroeville, Pennsylvania 

Abstract 

Mine seals cart be remocely consrrt~cred in underground coal mines through vertical boreholes wherr 

direct uccess to a fire is impossible or considered to be too dangerous. This method has great merit because the boreholes can be drilled to specific mine areas, urtd the seals can he positioned close to a fire 

zone. The technology, however. can be Iurgely ineffective if ike conslructed seals do not provide effecrive 

barriers to aiflow or if they cannot he used to inzpocrnil water and orher inert murerials. L7nforhmarely, 

1-10 viable alternatives exist ro seczling the entire mine at the ground surface. Full-scale remote mirte seal 

construction research is being coridzlcted at the National Institure for Occupational SMety und Health's 

(NOSHj Lake Lynn Luboratory (LLL). Under this effort, Howard Concrere Pumping Cornpan): and 

G.4l Consulrants Inc, have joined forces to evaluare a potentially significant improvemenr to the czlrrenr 

srare of the art. This puper covers the development of novel technc~logyfi>r remote mine seal constrnction, 

the evalr~arion ofthe matericils used, the co~tsrruction prircrice and the follow-up restirtg. 

Introduction jointly by NOSH and MSK4 in 2001, and this need resulted 

>line fires constitute one of the greatest threats to the health and in a three-phase N'IOS~.Iresearch project (NOSH? 2001 j. In adsafety of those working in the undergroundmine envirunmnenl. dition, MSHA agreed to senre as a cooperator in this effort. 

IZrorn199L through 2000 there were 76 underground coal mine Yh~lseOne involved the qualitative review of existing 

fires and 61 underground metalJrion~necal mine fires reported technology used to remotely construct mine seals. The review 

to the Mine Safety and Heath Administration (MSHA.2003). included materials used to construct mine seals, including ceIn the early stapes of a mine fire. miners try to fight the fire if rnent and polyuretharic foam. and an analysis of he available 

possible with water, foam, dry chernicd powder: rock dust or material mixing technologies (surface versus downhole mixing) 

sand. This practice, hcrwever, can place nlulers dangerously (Trevits and Urosek, 2002). 

close to the fire zone and is typically only effective in the very Phase TWOof the research (ongoing through December 

early stages ofarniile 6re. Wleil a mine fire gowsoutof control 2004) involves the remote construction of mine seals at 

and is tooda~lgerous to fight directly. the nre arenis oftensealed LLL. The services of ~bward Concrete Pumping Company 

to limit the inflow of oxygen and contain the !ire. Mine seals iHoward), Cuddy, Pe~lnsylva~lia, were contracted by NIOSH 

can be bujJt by miners underground. but such efforts become to construct the seals for Phqse Two. GAI Consultants, Inc., 

problcmaric when underground conditions become unsafc for (G.AI) of Monroeville. Pennsylvania. provided technical exreasons including the potential for a mine explosion. pertise to Howard for remote seal design and for developing 

An cflective solution when underyound access is irnpos- the implementation procedure. 

sible is to build airtight mine seals remotely through vertical Pluzse Threeof the research was tentatively planned to begin 

boreholes. The nerd to evaluate; improve and develop new sometime after January 2005 (pending approval and funding). 

technology to remotely construct mine seals was identitied l'he work involves a held demoustration at an actual mine siw 
N 

New 

Workings 

0 

I 

400 

V - U-Seal InstallationArea 

Figure 1-Layout of the Lake Lynn Laboratory Mine. 

~igure2 -Underground layout of the seal construction 

site. 

where a mine seal will be remotely constn~ctedfollowed by an 

in-mine physical evaluation. This paper dcscribes thc dcvelopmenr of novel technology for remote mine seal construclion 

as developed during Phase Two. evaluation of the materials 

used. construction practices and follos-up testing. 

Project plan 

The objective of tl~isproject was to develop a specialty grout 

product and a method for placing the product through a borehole into a mine opening to form a mine seal at a reasonable 

cost. Several additional engineering design consnaints were 

imposed by NOSH and included the following: 

the methodology developed must be capable of being 

deployed quickly; 

the mine seai must be capable of being rapidly installed; 

the marerial used rnllsr be locally availabl:; 

the seal must be made of noncombustible material; 

the grour material must be of a consistency to allow 

placement in a free space without excessive I3ow if 

the mine is open and unobstructed but have flowable 

characteristics should the mine opening contain roof fall 

debris. cribbing, equipment or conveyor structures; 

the grout and the methods of application must facilitate 

mine roof-to-Roar and rib-to-rib closure: and 

the seal must be strong enough to withstand the force of 

a mine explosion, up to 110 kPa (20 psi). 

?he work was conducted at LLL.The Lake Lynn Laboratory is a highly sophisticated unde~groundand surface iaboratory located about 100 km (60 miles) southeast of Pittsburgh, 

Pennsylvania, and 16km i10miles) northeast of Morgantown, 

West Virginia. where large-scale explosion trials, mine fire 

research and a myriad of other mine safety and health research 

programs are conducted. The underground workings are sized 

to match those of commercial mines, thus malung tllem true, 

full-scale test galleries. Movable bulkheads permit the 'setup 

of single-entry, triple-entry and longwall face coniigurations 

for experiments (NIOSH, 1999) (Fig. 1). 

Previously. a 152.1-mm- (6-in.-) diameter cased borehole 

was completed in the first crosscut between the B and C Drifts 

of the experimental mine, and it was determined that this 

borehole was suitable for the seal construction work (Fig. 2). 

The thickness of the overburden in the area of the borehole is 

about 60 m (200 ft). The crosscut in the mine measured 5.8 rn 

(19 ft) wide, 13.2m (40 ft) long and 2.1 m (7 ft) high. The floor 

sloped on the order of a 1.13% gradient. A second borehole, 

located about 9 m (30 ft) away, was available for viewing the 

mine seal installation through use of a downhole video camera. 

In-mine to surface commul~jcationwas facilitated through the 

use of a mine pager phone system. 

Grout material. Constructing an effective mine seal through 

a single borehole is a difficult engineering challenge: The 

grout mixture c.mnot be too fluid or it will flow away from 

the borehole. If the grout mixture is too stiff, it will tehd to 

build quickly form.ing a mound at the bortom of the borChole 

and mill not How and fill the mine roof-rib areas. The Howarcl/GAl team determined that two different gout placement 

techniques, and grout mixes were needed to meet this desigr! 

challenge. It was decided that the first macerial to be placei 

in the mine would fill most of the open space. This was also 

the less costly component of the, fill material and would help 

to lower the overall cost of the seal. The design of the bulk-fill 

material for the mine seal called for fiy ash, Portland cement 

and a 2A (-1.9-mm,-3!4-in.) crushed limestone aggregate. A 

conventional concrete admixture was used to accelerate the set 

of the 9-0111.The material was bIended to achieve a pumpable 

mixture that had adequate suength and rapid setting properties. The amount of By ash added was sufficient to produce 

a mix thn~could be pumped to the borehole, travel down the 

borehole without segregation and provide a moderate degree 

of flowahili~.Once the grout was in place, the aggregate 

would provide sufficient shear resistance for the grout to be 

somewhat immobile until the mix set. Typical initial set time 

for tllis mixture could be achieved in 15 to 20 minutes and 

would support foot uaffic in 30 to 45 minutes. 

The second material to be used to fill any remaining opzn 

space above the bulk fill along the roof-rib line was a hvo-part 

gout blend that was developed with the assis~inceof Master 

Builder's Concrete Products Laboratory in Cleveland, Ohio. 

Tine basic groilt was to be a blend of .4S'I?\.I Class-F fiy ash . 

and Portland cement. The initid testing of the gout indicated 

that a conventional shotcrcte accelerator would not produce 

suficient stiifening in the desired time frame. Additionally, it 
clid not exhibit suitable rheological and hardeni~zg properties 

required for the grout appIicadun. Further testing determined 

that Master Builder's TCC system was more effective iu 

providing the desired grout chllracteristics than convenrional 

admixtures. 

The hiaster Builder TCC System, is rnade up of two-parts. 

Pan X improves the pumping ch3r:icteristics and provides 

a reaction plat.form for Part B, and it is added just prior to 

injection into dlr pump. ['art B is a liquid, high performance 

shotcrete and grout accelerator that reacts with PartA to create 

an immediate stiffening of the g~out. Part B is.itdded at the 

spray nozzle via astream of air that transports the gout to the 

mine roof-and-rib surface. The reaction between the Pal: A and 

Part B arimixtu-res essentially provides the initial st-Lffeninp 

through a flocculation process that is unrelated to the shemical hydration of the cement products in the grout. Therefore, a 

concrete accelerator was also added at the nozzle to accelerate 

the hydration process. Tl~e adclition ir-F the accelerator along 

with the cement content of the grout fac~litated rapid strength 

development of the in-place grout spray. 

To improve the stiffen in^ propzstiesoftht: grout and produce 

the required stickiness for the grout spray to adhere to the minz 

roof-and-rib areas, the cvater content of die n6x was adjusted 

while retaining the fluidity andpumpabiliry ot'tbe rnis through 

the addition of a high-range water-reducing additive. 

As the nlate~ial development phase progressed, it became 

appnrent the aoiform. consistent blendir~gof tl~econsrituents in 

the sprayed grout was critical to the goutperfonnance. The final 

portion of the grout rnis design work focused on a sensitivity 

study ihat itler~iified the grout's reaction to dzviations in the 

blending process. [t was concluded that ic would be necessilq 

to very n~iely metcr the ingredients in thc grout mix to achieve 

~hzdesired pert'o~-~~mct: frorn the sprayed prout. 

Grout placement techniques. As rnentio11ed above, the HowerdIGX1 team cletenninzd that cwo grout placer~~ent techniques 

were needed. It was be1ievc.d thar placement of the bulk till 

would fonn a mound below the borehole and would leave an 

open space near the mine roof-rib area. Therefore, i\ second 

placement technique w:a needecl to address the remaining 

open areas. 

The first process was designed to use a technique very similar 

to that used when placing bulk grout with a tremie pipe. The 

concept c:illed for the bottom of the injection casing to be slotted to facilirr~te some directional control of the grout stream. 

The bulk srour malerial ~vould be placed in separatc lifts with 

cime bertveen lifts to allow the material to begin to stiffen. The 

seco~id placement technique required the use OF two smngs of 

pipe (one inside of the or,her) to convey two streams of material 

to a spray nozzle. The spray nozzle permitted the ble~lcling of 

the two-part goo accelemror mix while allowing sufficient air 

velocity ro transport the grout t the mine roof-and-rib areas. 

A spray nozzle was dcsigned by GAI for this purpose (refer 

to Fig. 2j. In both techuique.~, an on-site volumetric mixing 

plant w:is used to blend the gout mistme. The bulk grout 

was pumped to the borehole using a positive displacement 

pump and the spraycd grout was moved to the borehole using 

11con\:enrional grour pttrnp 2nd compressed air. 

Mine seal construction 

Priortoctjnstruceng the mine seal atLI-L, amodel ~nirieopening 

was construct~d at How;lrd's fxiliry in Cuddy. Pennsylvania. 

The model minc opening was constructed for testing mddirect 

observation of the performance. of the do\vnhole nozzle and 

pumpirig equipment. Tlie model rnine operling condsted of n 

Figure 3 -Spray nozzle.. 

Figure 4 -View of the model mine. 

small excavation in a hillside (Fig. 43. The roof of the model 

mine was formed usingcrane matsso adrill rig coultl be locared 

over the mine void to hold the pipe for the spray nozzle. 

The eqilipmertt necessary for a test was assembled at the 

demonsuation site, and 3 small quantity. i.e., 3.8 m3 ( 5 cu yd!. 

of test material was mixed in a concrete transit mixer truck. 

Material was sprayed into the model mine void and the results 

of the test were evaluated. During the spraying proccss, several adjustments to the admixture formulation were made as 

well as air transport velocities and spray rotational velocitjl. 

Samples of the gi:out were prepared for strength evaluation 

and time-of-set. From the information collected during the 

inicid demonstration. modifications were made to the nozzle 

and the drill rig used to support the pipe s~ring. Clanpes were 

also made to the cement content, admistuses and additive ratios 

to improve stickiness, time-of-set and application uniformity. 

Some laboratory work was alsoconducred to improve the prout 

blends by modifying admixtures and addi~ive ratios. After additional shop trials and modifications to the equipment, a second 

full-scale surface demonstration was conducted to evaluate the 
Figure 5 -Underground view of bulk fill material for seal 

No. 1. 

Figure 6 -Elbow for bulk fill placement. 

impact of the modifications to the materivls and equipment on 

the characteristics of the resultant grout mix. The result of this 

demonstration was used again to modify materials.equipmenr 

and equipmen1 usage. 

Mine Seal No. 1.On July 19.2002. I-Toward mobilized their 

mixing, pumping and injection equipment to 1-Ib. The equipment included a volumetric mixer batch plant, cement storage 

silo. water tanks, group pumps, air compressor, a drill ri,o and 

miscellaneous support equipment such as trucks and loaders. 

Initial opemtioi~s included calibrating the batch plant so that a 

u~iiform flow of bulk material could be mixed to produce a raLe 

of approximately 23 mj (30 cu yd) of material per hour. 

On July 22, 2002: placement of the bulk fill for seal No. 1 

was initiated i~sing anlixture composed of 3.4 crushed limestone agpegate, fly ash and cement. This mixture was pumped 

into the mine opening using a string of casing. Bulk fill was 

purnped over different time intervds with a pause beween 

intervals ro allow the in-place grout to stiffen. This process 

was used in an atrrmpr to control the extent of lateral material 

flow out of the mine cross-cut areas. The pumping time and 

Figure 7 -Underground view of elbow placing bulk fill. 

the pause intervals were determined by visual observarion via 

a downhole video camera and colnmunicarion with the mine 

pa-ger phone. Pumping was tenhinated after approximately 86 

rn" (I .l2 cu yd) of material had been placed into the crosscut 

(Fig. 5). Underground examination revealed that the mine 

opening had not been completely sealed (open spaces were 

observed at the mine roof-and-rib areas), and some of the bulk 

fill material had flowed into the adjacent mine areas. 

Adual, string of drill pipe and casing affixed with the spTay 

nozzle was then placed into the borehole in preparation for the 

second part of the mine seal construction. On July 23: 2002, 

pumping began ro complete consmiction of the mine seal. 

Unfortunately, after only a few minutes of pumping, a critical hose failed on the surface and the pumping operation was 

terminated. Under~mund examination of the sprayed areas 

indicated that the spray mixture did not stick to the mine rib 

areas and flowed away. Also, because minimal space, about 

300 mm (12 in.) between the bulk fill and the bottom of the 

borehole was available, it was decide to remove 450 mrn (1 8 

in.) of bulk fill material below the bottom of the borehole to 

provide sufficient space for follow-up backfilling work. 

The disappointing results of the spray nozzle application 

indicated that additional work was needed to further refine the 

material mix components before the spray nozzle was used 

agajn. In the interim, afrer reviewing the progress made during 

the placement of the bulk fill, it was decided to fit the end of 

the casing string of pipe with an elbow to provide a means of 

directior~allycon troll in^ the placement of grout material (Fig. 

6). It was also thought that this elbow configuration could 

facilitate roof-rib closure with the bulk fill material. 

On Augusc 2.3002. a newly designed elbow was lowered 

into the rmne opening from the surface borehole. Once the 

elbow was positioned in the mine opening. pumping of the 

seal marerial began using a 2A limestone ag-pegate, fly ash 

and cement mixture. Compressed air was added to the now 

stream to facilitate movemenr of the material towards the mine 

rib areas.This material was pumped into select locations along 

the mine rib areas in an attempt to fill the mine opening (Fig. 

7j. Pumping was terminated after approximately 75 m 3(100 

cu yd) of material had been placed into the crosscut and after 

the elbow became plugged. 

Underground exanlination revealed that the mine opening 

had not been completely sealed. some of the material hac 
Figure 8 -View of fill placement at model mine. 

Rowed beyond the crosscut and Into the adjacent mlne areas. 

Tne area directly below the horehole and in the immediate 

vicinity of the elbow had been completely sealed to the nlinc 

roof. Several unsuccessful attempts were made to dislodge the 

plug in the elbow, but it was ultimately decided to terminate the 

construction of mine seal No. 1 and remove the elbow from the 

hole. In general. before the elbow became plugged, significant 

progress had been made towards filling the mlne opening. ,A 

subsequent meeting with Howard1G.U team revealed that additlond design and demonstration work was necessary before 

installation of scal No. 2 could begin. Later, mine seal No. 1 

was removed from the LLL site using permissible explosives 

and permissible blasting techniques. 

On October 8,2002. a test of the spray nozzlc was successfully conducted at the Howard model minc site. During the 

10-m3(13-cu yd) test,engineers were able to successfully spray 

and build up material on the mine rib areas. The material was 

sprayed to an estimated thickness of 300 to 380 mm (13, to 15 

in.) on the mine rib areas (up to the roof) with no build-up on 

the floor below the spray nozzle assembly (Fig. 8). This was 

a much different outcome as compared to that seen during 

previous tests and during the construction df mine seal No. 1. 

The GAI engineers attributed the successful outcome of this 

test to adjustments in thc equipment used to conuol material 

feed and a significant improvement of the material mix. 

Mine Seal No. 3. On October 8. 2003, the Howard/GX team 

initiated the remote installation of mine seal No. 3- at LLL. 

Pumping of the first part of the remote seal (bulk material) 

began using a sand. fly ash and cement mixture. This material 

was pumpud into the mine opening using the elbow. The bilk 

material was pumped in a series of lifts to fill the mine opening. Pumping was terminated after approximately 43 m3 (55 

cu yd) of material had been placed in the crosscut. It should 

be noted that crr~nmunication with underground personnel was 

required to orient the elbow and complete the construction of 

the base. 

Underground examination revealed that the minc opening 

had not been completely sealed. However, the seal material 

was placed to within 0.16 m (1.5 ft) of the mine roof below 

the borehole and within 0.76 to 0.9 rn (7.5 to 3 ft) of the mine 

roof near the rib areas (Fig. 9). It was decided to remove an 

additional L53 mm (6 in.) of material below the bottom of the 

Figure 9 -View of bulk fill placement for seal No. 2 

Figure 10 -Surface test of spray grout system. 

borehole to allow sufficient room to test the capability of the 

spray nozzle. 

On October 14. 2003, a 7.6-m3 (10-cu yd) surface test of 

the final component of the seal mixture !fly ash, cement and 

accelerators) was conducted ilt LLL (Fig.10). The result of the 

test showed that the mixture would perform as required (little 

to no slump). Adual string of drill pipe and casing affixed with 

the spray nozzle was then placed into the 152.4-mm- (6-in.-) 

diameter borcholo in preparation for the second part of the 

seal construction. 

On October 15.2003, the second part of the mine seal was 

installed using the spray nozzle. The material was spayed in 

a back-and-forth motion along the mine rib areas to f 11in the 

gaps. Interaction benveen observers underground and engineers 

on the surface ensurcd that the nozzle was aimed in the proper 

direction. Good mine roof-and-rib contact was made with the 

sprayed material. The problematic corner areas at the mine 

roof-rib intersection were filled before the grout began to build 

up and migate towards the spray nozzle (Fig. 11). 

Filling of the remaining area near the borehole was accomplished by lowering the spray nozzle into the wet material 
Figure 11-Underground view of spray nozzle during seal 

No. 2 construction. 

Figure 12 -Underground view of mine seal No. 2 from 

the B-Drift. 

below the llozzlc and hen rotating the spray node through a 

360" arc. Eventually, the material built up around the nozzle 

and closed the mine opening (Fig. 12). In all, a total of 17.2 

m"22.5 cu yd) of sprayed material was used to close the mine 

opening. An underground examination showed that the mine 

seal material (both bulk and sprayed material) had flowed about 

3.7 m (13 ftj from the borehole towards the B-Drift and only 

about 2.7 m (9 ft) from the borehole towards the C-Drift. The 

shape of the seal approximated atruncatedpj~amid whose base 

measured 5.8 m (1 9 ft) wide (the width of the cross cut) by 6.4 

m (21 ft) deep and whose top measured 5.8 m (19 ft) wide (the 

width of the cross cut) by 0.9 to 1.5m (3 to 5 ft) deep. 

Material and mine seal tests 

Lnconiined compressive tests were conducted on 76-mm- (3-

in.-) diameter cylinder samples (cylinder area =4.560 mrn2= 

7 07 sc] in.) that were collec~ed during the construction of seal 

Nos. 1 and 2. Some samples were collected on the surface from 

equipment tanks and others were collected undergmund as the 

material was being placed in the mine void. The results of the 

tests are shown in Table 1.As can be observed in the table, the 

compressive stren,oth of the bulk fill material is substantially 

higher than that of the sprayed fill material. The reason for 

the lower compressive strength of the svayed material is that 

the sprayed mix does not contain simd and had air bubbles 

trapped jn the mixture. 

Although the major thrust of this research effort was aimed 

at development of material mixes and mine seal construction 

techniques, the benefits of constructing the seal at the LLL 

facility included the option of testing the seal's ability to 

confine mine air and also to withstand the forces of a mine. 

explosion. Air-leakage tests were conducted by building a 

frame on one side of the mine seal and covering that frame 

with brattice cloth. Nex~, an opening was made in the brattice cloth the size of an anemometer to facilitate'air velocity 

measurements. Once this work was completed, airflow in the 

mine was adjusted to produce a desired differential pressure 

and the air leakage through the seal was measured. Air-leakage 

tests were conducted on mine seal No. 2. and the results are 

shown in Table 2 (Weiss, 2003). 

Prior to conducting the air-leakage tests, several approxinlateiy 25.4-mm-(1-in.-) diameter holes were observed in the . , 

seal near the mine roof area. Therefore, the air-leakage values 

observed in the table were not totally unexpected. 

To conduct the explosion test? a known quantity of methane 

gas was injected in the end of the C-Drift near the crosscut 

where the seal was installed. This area was temporarily closed 

with a frame and brattice cloth to confine the gas. The gas was 

diluted with air to achieve an explosive concenuation. Thegas 

was then i-gnited producing an explosion. An explosion test 

was conducted on mine seal No. 2 on November 24,2003. 

The mine seal withstood a pressure of 124kPa (18 psi) with 

no visible signs of damage (Weiss, 2003). 

Research findings and recommendations 

The overall objective of the work was to determine if a mine 

sed could be constructed remotely from the ground surface. 

This objective was achieved as a seal was successfully built 

through a borehole and was confined to the crosscut of the. mine 

opening. The technology used ro build the seal was tested and 

the correct material mix design was developed. The results of 

follow-up testing showed that a strong and robust seal was 

construcLed as required in the design constraints. The issue 

of air leakage can be addressed by slowing the rotation of the 

spray nozzle to allow for a more substantial build-up of seal 

material. As an additional remedy. it may also be possible to 

insert the spray nozzle into the observation borehole and spray 

the entire face of the seal to close and fill any holes. 

Resulcs of he work todate suggest that this remote seal 

construction system may have merit for isolating a mine fire. 

This technique however does rzquire additional mals because 

considerablzcommun~cationwith the subsurface personnel was 

nceded to achieve rib-to-rib and roof-to-floor closure. One of 

the fundamental keys to successful in-mine construction is the 

ability to directly observe the progress ofconstruction. Because 

tl~iswas a research and demonstration project, cornmunicadon 

between thesurface operation and the underground seal locarion 

was permitted. This will not be the case when a mine fire OCcurs. Additional research istherefore proposed to furtherrefine 

the construction method. A mine seal should be constructed a[ 

LLL without voice conlmunication with the surface. The only 

means of observing the progress of construction should be via 

the nearby borehole equipped with a downhole video camera 

with sufficientresolution capabilities and lighting. Experienc" 

gained during tnis work also sugpesls that a downhole laser 
Table 1-Results of compressive strength tests on cylinder samples. 

I Seal 1 Bulk Fill1 Seal 1 Bulk Fill2 Seal 2 Bulk Fill3 Seal 2 Spray Fill" - I

Comp.. Cornp.. 

Age, strength, Age, strength, 

days psi IMPa) days psi 

'Sampl~born rnerer~alounped on Juiy 22. 20CZ. 

'Sdmoled iron rna!srtal punpzd on A~~gus:?.2002 

or radar imaging device should be constructed that ofizrs 

real-time imdgi.ng and .is capable of penetrating smoke. dust 

or the fog that tends to form in the mine opening as the seal 

material be,' olns to set. 

X 152.4-rnrn (6-in.) borehole was used during the trials at 

LLL, and the downhole equipmen1 was desi~ned to meet this 

necd.The issue of working with this equ.ipment in smaller diameter boreholes should be addressed along with the hctthatdeeper 

overburden depths will i~ndoubtedly be encountered. Perhaps 

nn additional spray nozzle should be constructed to facilitate 

remote seal construction in small-diameter boreholes. 

Finally* it is su~~estecl that this technolo~y should be further

evaluated through construction of a mine seal at LLL in a mine 

entry that is obstructed with debris (roof fall materid) and mine 

structures (possibly cribbing, trackor~on\~eyor suucturzs~.This 

zpproach will test rhe ability of the seal material to How around 

obstructions and still form a seal while closely matching the 

conditions most likely found in an underground mine. 

Acknowledgments 

The authors recognize John Urosek and Clete Stephan. 

MSHA, for input and support throushour the design and 

conduct of this research project. Spccial thn&s are also go to 

Eric Weiss and the NOSH staff at the LLL fac~lity for their 

Comp.. Cornp.. 

Age, strength, Age, strength 

davs . psi days psi 

3$arr.p~ecirorri niararlal pl~npctdan Oct~ker8.2902 ... -5arnpld frorli material purnoed 2n Gmter 15. 2C03 

Table 2 -Results of air-leakage tests on mine seal 

Air leakage rate, cu Wmin 

professionalism, dediclition and assistance in the conduct of 

this research effort. 

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