+, sEHVIcCe fl 

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Public Health Service 

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health CENTERS FOR 

CDC DISEASE CONTROL 

AND PREVENTION 
DISCLAIMER 

Mention of company names or products does not constitute endorsement 

by the National lnstitute for Occupational Safety and Health 

Copies of this and other documents are available from 

Publications Dissemination, EID 

National lnstitute for Occupational Safety and Health 

4676 Columbia Parkway 

Cincinnati, OH 45226-1 998 

Fax number: (513) 533-8573 

Telephone number: 1 -800-35-NIOSH (1 -800-356-4674) 

E-mail: pubstaft@ niosdtl .em.cdc.gov 

Cover photo: Reir~forced cer~zerztitiozis senl irzstr.umerzted 

with trarzsducers nrzd nccelerorneters to nlcnsure 

displacement of the senl dzrrirzg nrz explosion test nt tlze 

Lake Lynn Experirnerztal Mine. (Plzoto by I(erzrzet1z L. 

Cashdollar, NIOSH Pittsburglz Research Laboratory.) 
Report of Investigations 9647 

Evaluation of Reinforced Cementitious Seals 

By Eric S. Weiss, Kenneth L. Cashdollar, I. Verne S. Mutton, 

Deepak R. Kohli, and William A. Slivensky 

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Public Health Service 

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health 

Pittsburgh Research Laboratory 

Pittsburgh, PA 

August 1999 
International Standard Serial Number 

ISSN 1066-5552 
ILLUSTRATIONS 

PlanviewoftheLLEM .................................................................... 4 

Seal test area in the LLEM ................................................................. 4 

Linear variable displacement transducer (LVDT) and acceleron~eter attached to a seal ................... 5 

Support posts and instrumentation on thc back side of a seal ....................................... 6 

Pressurized entry for leakage determination rates across the seals ................................... 7 

Brattice in place for seal leakage test ......................................................... 7 

Construction of second wall of plug seal in crosscut 1 ............................................ 9 

Completed plug seal in crosscut 1 ............................................................ 10 

Construction of Meshblock seal in crosscut 2 ................................................... 10 

Completed Meshblock seal in crosscut 2 ...................................................... 11 

Construction of Meshblock seal in crowcut 4. showing reinforcing bars anchoring it to the ribs and roof .... 12 

Construction of Meshblock seal in crosscut 4 ................................................... 12 

Construction of Meshblock seal in crosscut 4 ................................................... 12 

Completed Meshblock seal in crosscut 4 ...................................................... 12 

Construction ot Meshblock seal in crosscut 3. showing reinforcing bars anchoring it to the ribs and roof .... 12 

Construction of Meshblock seal in crosscut 3 ................................................... 13 

Completed Meshblock seal in crosscut 3 ...................................................... 13 

Completed stopping in crosscut 3 ............................................................ 14 

Pressure traces as a function of distance in C-drift for LLEM test 347 ............................... 15 

Pressure traces as a function of distance in C-drift for LLEM test348 ................................ 16 

Pressure data for stopping 5. showing time of stopping failure fix- LLEM test 348 ...................... 17 

Remains of stopping 5 after LLEM tcst 348 .................................................... 18 

Pressure and impulse data for seal 4. showing time of seal failure for LLEM test 348 ................... 18 
ILLUSTRATIONS-Continued 

Page 

Remains of seal 4 after LLEM test 348 ........................................................ 19 

Remains of seal 4 after LLEM test 348 (closeup view near wall) .................................... 19 

Pressure and impulse data for seal 3 for LLEM test 348 ........................................... 19 

Front (C-drift) side of seal 3 after LLEM test 348 ............................................... 20 

Back (B-drift) side of seal 3 after LLEM test 348. showing crack pattern marked with white chalk ......... 20 

Back (B-drift) side of seal 2 after LLEM test 348. showing crack pattern marked with white chalk ......... 20 

Pressure traces as a function of distance in C-drift for LLEM test 349 ............................... 21 

Pressure and impulse data for seal 3. showing time of seal failure for LLEM test 349 ................... 21 

Remains of seal 3 after LLEM test 349 ........................................................ 22 

Remains of seal 3 after LLEM test 349 (closeup view near wall) .................................... 22 

Back (B-drift) side of seal 2 after LLEM test 349. showing crack pattern marked with white chalk ......... 22 

Pressure traces as a function of distance in C-drift for LLEM test 350 ............................... 23 

Pressure traces as a function of distance in C-drift for LLEM test 351 ............................... 23 

Pressure data for stopping 3. showing time of stopping failure for LLEM test 351 ...................... 24 

Data for the middle LVDT on seal 3 for LLEM tests 347. 348. and 349 .............................. 24 

Data from middle accelerometers on seals 2. 3. and 4 for LLEM test 348. along with their Fourier transforms 33 

TABLES 

Lake Lynn Experimental Mine explosion tests .................................................. 5 

Guidelines for air leakage through a seal ...................................................... 8 

Seal and stopping construction data .......................................................... 9 

Air leakage measurements before the first LLEM explosion test .................................... 14 

Air leakage measurements between the first (No . 347) and second (No . 348) LLEM explosion tests ........ 16 

Air leakage measurements between the second (No . 348) and third (No . 349) LLEM explosion tests ....... 20 

Air leakage measurements after the fifth (No . 351) LLEM explosion test ............................. 23 

Tecrete seals evaluation in the Lake Lynn Experimental Mine: pressure data, test 347 ................... 28 

Tecrete seals evaluation in the Lake Lynn Experimental Mine: pressure data. test 348 ................... 29 

Tecrete seals evaluation in the Lake Lynn Experimental Mine: pressure data. test 349 ................... 29 

Tecrete seals evaluation in the Lake Lynn Experimental Mine: pressure data. test 350 ................... 30 

Tecrete seals evaluation in the Lake Lynn Experimental Mine: pressure data. test 35 1 ................... 30 

Tecrete seals evaluation in the Lake Lynn Experimental Mine: flame arrival time data .................. 31 

Tecrete seals evaluation in the Lake Lynn Experimental Mine: LVDT data. test 347 .................... 32 

Tecrete seals evaluation in the Lake Lynn Experimental Mine: LVDT data. test 348 .................... 32 

Tecrete seals evaluation in the Lake Lynn Experimental Mine: LVDT data. test 349 .................... 32 

Tecrete seals evaluation in the Lake Lynn Experimental Mine: LVDT data. test 350 .................... 32 

Tecrete seals evaluation in the Lake Lynn Experimental Mine: LVDT data. test 351 .................... 32 

Tecrete seals evaluation in the Lake Lynn Experimental Mine: failure data. seal in crosscut 4. test 348 ...... 34 

Tecrete seals evaluation in the Lake Lynn Experimental Mine: failure data. seal in crosscut 5. test 348 ...... 34 

Tecrete seals evaluation in the Lake Lynn Experimental Mine: failure data. seal in crosscut 3. test 349 ...... 34 

Tecrete seals evaluation in the Lake Lynn Experimental Mine: failure data. new stopping in crosscut 3. 

test351 ............................................................................... 35 
UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

cfm cubic foot per minute ~n ' square meter 

cm2 square centimeter 111 ; cubic meter 

ft foot m '/inin cubic meter per minute 

ft2 square foot ln ln millimeter 

ft3 cubic foot M Pa megapascal 

ft/s foot per second ms lnillisecond 

g/m3 gram per cubic metel- m is meter per second 

hr hour m/s2 ineter per second squared 

Hz hertz psi pound (force) per square inch, gauge 

in inch ps ia pound per square inch, absolute 

in H20 inch of water ps I-s pound per square inch - second 

kg It i lograln s second 

ltHz It ilohertz t ton (metric) 

km ltilolneter t/h ton (metric) per hour 

ItN-s kilonewton second V dc volt, direct current 

k Pa ltilopascal degree Celsius 

kPa-s ltilopascal second degree Fahrenheit 

m meter yo percent 
325-mm-thick seal that was tesled 27 hr after completion against this 

 140-kPa explosion pressure, a special 

requirement of the test program. This seal survived explosions with pressure pulses up to 300 kPa (43 psi). 

The 2.3-m-high by 325-mm-thick Meshblock seal survived three explosion tests with overpressures up to 

455 kPa (66 psi) and satisfied the air leakage criteria. 

A I ,200-mm-thick plug seal was constructed of two Gunmesh formwork walls in-filled with shotcrete and 

a 3,450-kPa (500-psi) strength Aquablend core. This plug seal survived three explosions with pressure pulses 

ranging 11-om 150 lo 430 kPa (-22 to 62.5 psi) with no measurable postexplosion air leakage. Two Gunmesh 

stoppings with thicknesses 01' 40 and 75 inln withstood explosion overpressures of 23 and 115 kPa, 

respectively. Anchoring all seal and stopping designs into the roof, ribs, and floor with steel "rootbolts" 

provided very effective boundary constraint that is critical to the performanceofstructures subject to explosion 

overpressures. 

'Mining engineer, Pittsburgh Rcccarch Laboratory, N:ltional Institute For 0ccupation:ll Saft~y and Health. Pittsburgh, PA. 

'~esearch physicist, Pittsburgh Research Laboratory, National lnstitt~te fol-Occupational Safety and Health. Pittsburgh, PA. 

'Mining engineer, New South Wales. Australia. 

'~lectrical engincer, Pittsburgh Research Laboratory, National I~ist~tute for Occupational Safety and Health, Pittsburgh, PA. 

'~h~sical science technician. Pittsburgh I<eseawh Lnhol-atory. N:~lional Institute for Occul~ational Safety and Health, Pittshurgh, PA. 
resistant seals in the Luke Lynn Expel-imcntnl Minc (LLEM). 

In 1993, Tecrete Inclustrics introcluccd a Meshhlock systcm 

of seal construction in Austc~liiun coal ~nincs. This scal systcm 

provicied a monolithic structure hut coi~lcl Ilc conlrt~.~~c~ccl on a 

continuous basis. Mcshhlock ia ;I [I-aclc numc 1.01. it lorm 

comprised of licavy metal wire iund metal scrccn [liar is ~~scd to 

contain the shotcretc in u scal. Details ol'thc Mcshhlock systcm 

can be found in the "Mcshhlock Seals" section ol' this I-cpo~-1. 

Previous research I Barzegar 1996nl hits sIlo\vn that the 

boundary conditions (at the intcrt;~cc kctwccn ~hc scol iuncl thc 

mine roadway) influence the ability 01' [he scal to resist 

horizontal overprcssurcs. Stil'l'ness ol' the immcdiatc 

surrounding roadway material ~und thc 1'ix;ltion ol'thc seal at this 

interfaceare the most in~por~i~nt l'i~ctors that in1'1i1cncc horizontal 

load resistance I'or imy given seal clesign. Stccl "rooll~oltlr" iu-c 

an integral par1 01. cnch Mcslnhlock sc;~l tlcsi:_.n. ~)l-ovicliny an 

effective anchor to the I-ool', rills, ant1 flool-. I'lnc Icgislarion in 

Queensland at the time tlicac scal tlclrigns wcrc i~itroclucccl to 

the Australian coal mining industry in 1993 ~.ccluircd that 

permanent seals he ahle LO wit1ist;uncl a pressure 01.345 kPa and, 

in seams prone to spontaneoils conihustion, that lhcy be 

installed quickly. A piuticulnr lia~iu-d in gassy untlcryround 

coal mines occurs when n section ol the workings is scalcd 

cxplosion gallery, which is a concrete tunnel 2.7 m in di~unetcr 

iund 5.7 m' in cross section. A 250-mm-thick Meshblock scal 

tlcsign constructed within the concrete tunnel withstood eight 

~ncthiuic explosions with ovcrpressu~-cs ti-0111 85 to 500 kPa. 

This scal was I'ully instrumented to provicle time-related 

~~~'c\st~re iund disl~laccment measurements. These data were 

LISCCI to I'ind LI suitable computer model IBarzcgar 1996bl that 

rcl'lcctcd the response of the wall ~~nder dynamic loads and the 

incrcnscd load capacity due to the stability and strength ol'the 

stccl holts. This research provided a basis for the construction, 

instrumentation, and cxplosion testing of several Tccrete seal 

designs in the LLEM. 

In Inrc 1996, PRL began acollaboration on a research project 

with Tccrctc Industries and BHP Australia Coal to investigate 

the capnhility of various seal and stopping dcsipns to mcct or 

cxccctl the I-ccluirements of the Queensland Dt-parr~nent ol' 

Mines and Energy's "Approved Standal-d Sol- Ventilation 

Conlrol Devices." This standard was the result of deliberations 

and investigations by Task Group 5, which was formed by thc 

rcco~nnicndnlir,n ofthe Warden's Inquiry concerning the Moura 

No. 2 Minc cxplosion [Roxborough 19971. Task Group 5 was 

charged with the reassessment of the regulatory provisions for 

explosion-rcsist~~nt seals and the investigation of mine inerting 

tcclinicli~cs. The research program in the LLEM tcsted scal 

clcsigns within a range of overpressures to match the 
EXPERIMENTAL MlNE AND TEST PROCEDURES 

MlNE EXPLOSION TESTS 

All of the explosion and ail- Icakagc dctcrminntiot~ tests on 

the various seal designs wcrc conelucted in 111c LLEM I Matles 

et al. 1983; Triehsch ancl S~lpko 14901. which is loc:~tcd 

approximately 80 km southcast ol'l'it~sl~i~rgli. I~CLII-~;~i~-cl~;~~lce, 

Fayette County, PA. Tlic LLEM is one ol'tlic wo~-lcl's Ior.c~~iost 

mining lahot-ntories l0r conclucting largc-scale safety ;uitl hci~lth 

I-esearch. The LLEM is i~nicluc in that it can simulate current 

U.S. coal mine gco~netrics for a variety 01' mining sccn:u-ios, 

includilig multiple-entry roo~n-:uid-l>illi~r mining ant1 longwall 

mining. 

Figure I shows a l>l;ui vicw ol'thc LLEM. The unclergrot~nd 

entries consist 01' npl7roximatcly 7,630 m ol workings 

developed in the mid- l9(70s 1'01- the co~iimercial cxtri~ction 01' 

limestone and 2,286 m 01' ontrics clcvclol7ccl by rho I'ornlcr 

USBM in 1980-8 1 I'or reseal-cli [Mattes ct al. lOX.3 1. Thcsc 

more recent entries arc dc1,ictcd. rn I'igurc I. ;IS cl~-~lta i\ tIi~.oi~yli 

D, each of which arc -520 m long iuntl closet1 :\I the inhy cncl, 

and drift E, which is 153 m lony and connccls ell-il.ts C iuitl D. 

The dimensions of the drills and crosscuts arc typical 01'1iiodern 

[J.S. gco~nctrics li11- coal mine entries iuicl ri~rigc I'rom 5.5 to 

h.0 nl wick and arc approxi~n;~tcly 2 m high. The LLEM was 

clcsignccl to withstand explosion overprcss~~rcs 01' 1117 to 

-700 kt's (-. I00 psi). 

Figure 2 shows an expanded vicw ol'thc scal test area in ~lic 

multiple-entry seelion ol' llic LLEM. All 01 the scc~ls ~uicl 

stopl-li~igs were consrructcd in llic crosscuts hctwccn the H ant1 

C-clril'ts. All ol'tlic crosscuts wcl-c al,l2roximatcly 2 m high hy 

(> nl witlc. The roof height in one section 01' crosscut 3 was 

c~iI;~rgcd to more closely rcl~rcscnt tlii~l ol' typici~l Australii~n 

unclcl-ground coal mincs. Derails on tlic scals arc I'ouncl in the 

scctio~i 011 "Constn~ction 01' Seals ancl Stop17ingsM later in this 

rcl30rL 

13cl'orc ci~ch cxplosion tcst, u (30-t Iiytl~.ni~lic;~lly o,cr;~tcd, 

track-mounted, conct-ctc and stccl hulkheat1 was positionctl 

across 1:-clril't Lo contain Ihc cxplosiori prcssurcs in C-clril'l. 

Nearly I0 m' ((,(,I I.{') ol' natural gas ( 97'A mctli;~nc) was 

~~llcctccl into the closed cnd ol' C-drilt. An clcctl-ic la11 witli ;III 

cxpl(:sion-l~rool'~~iotor h~~siliy WAS LISC~ to 11iix the n;~t~~r;~l ?;IS 

\vitli 111c air in ~hc ignition zone. A plastic cli~~phr~~gnl was i~scd 

ro contain the niltural gas and ail-mixturc wilh~n the I-il-st 14.3 In 
Scale, m // 

Bulkhead 

1 ~est seal 

Data~gathering statlon 

1 Crosscut 

Figure 2.-Seal test area in the LLEM. 

of the entry, resulting in a -2 10-~n' gas ignition zone. A sample 

line within the ignition zone was used to continuously monitor 

the gas concentrations using an infrarcd analyzer. In addition, 

samples were collected in evacuated test tubes and sent to the 

PRL analytical laboratory for more accurate analyses using a 

gas chromatograph. The analyses verified the infrared analyzer 

readings of -9% methane-air. Three electrically activated 

matches, in a triple-point conrigul-ation across the face (closed 

ed) ote ety, wee used to gte te aabe atuagas 

and air mixture. Barrels filled with water were located in the 

gas ignition zone to act as turbulence generators to achieve the 

projected 138-kPa (20-psi) pressure pulse. 

Details on this first explosion test (LLEM test 347), as well 

as the other tests, are found in table 1. In previous methaneonly gas explosion tests, the pressure pulse generated by the 

ignition of the methane-air zone generally resulted in static 

pressure pulses ranging from -152 kPa at crosscut 1 to 

- 1 15 kPa at the most outby seal (in some instances as far outby 

as crosscut 5, or 150 m from the ignition source). Explosion 

studies have shown that the explosion pressure pulse decays 

less rapidly with distance in the larger LLEM entries (- 1 3-m2 

cross section) than in smaller entries such as those in PRL's 

Bruceton Experimental Mine (-5-m2 cross section), presumably 

because of the smaller surface-to-volume ratio in the LLEM 

[Sapko ct al. 19871. 

To achieve an explosion pressure pulse significantly in 

excess of 138 kPa, coal dust was used outby the gas ignition 

zone in C-drift. The coal dust was loaded onto shelves 

suspended from the mine roof at 3-m increments outby the 

ignition zone. During the second cxplosion test (LLEM 

lest 348), a 64-m-long zone of coal dust was used in addition to 

the gas ignition zone. The pulverized coal dust (Piusburgh 

Seam bituminous) was loaded onto the shelves to provide acoal 

dust concentration of 100 g/~n'; this assumed a uniform 
To achieve the low explosion pressures (<70 kPa) necessary 

to evaluate a stopping design during the fourth and fifth tests 

(LLEM tests 350 and 351), the length of the gas ignition zone 

was reduced from 14.3 m to only 8.2 m from the closed end of 

C-drift, giving an ignition volume of 1 15 m'. During the fourth 

test, 8.2 m' (290 ft') of natural gas was injected within the gas 

zone, giving a methane concentration of -7%. When ignited, 

the resulting gas explosion produced an average overpressure 

of approximately 25 kPa (3.5 psi). During the fifth test, 9.0 m' 

(319 ft') of natural gas was used and resulted in an explosion 

overpressure of about 40 kPa (6 psi). 

INSTRUMENTATION 

Each drift has 10 environmentally controlled data-gathering 

stations (shown in figures 1 and 2) inset in the rib wall. Each 

data-gathering station houses a strain gauge pressure transducer 

and an optical sensor to detect the flame arrival. The pressure 

transducer is perpendicular to the entry length and therefore 

measures the static pressure generated by the explosion. The 

pressure transducers were from Dynisco, Viatran, or Genisco. 

They were rated at 0-100 psia, with 0-5 V output, infinite 

resolution, and response time <I ms. The flame sensors used 

Two additional types of sensors were used during this seal 

evaluation program: linear variable differential transducers 

(LVDTs) and accelerometers. These two types of sensors are 

shown attached to the back (B-drift side) of a seal in figure 3;7 

'AII photographs in this report are by Kenneth L. Cashdolln~., Eric S. Weiss, 

or William A. Slivensky of the NIOSH Pittsburgh Research Laboratory. 

Texas Instruments Type LS400 silicon phototransistors, with Figure 3.-Linear variable displacement transducer (LVDT) and 

a response time on the order of microseconds. These accelerometer attached to a seal. 
acceleration. This electric charge is proportional to the motion 

and, for this program, can be related to the acceleration of the 

seal during the explosion tests. 

The main bodies of the LVDTs and the amplifiers for the 

accelerometers were attached to steel posts located behind the 

seals, as shown in figure 4. The square cross-section posts were 

bolted to the roof and floor. The main cylindrical body of each 

LVDT was held by an aluminum block (figure 3). The movable 

thin rod extending from the LVDT was attached to a small plate 

that was epoxied to the back face of the seal or stopping. Each 

accelerometer was also attached to the back of the seal with a 

quick-setting epoxy putty. The accelerometer signal cables 

were connected to the battery-powered amplifiers located in the 

two instrumentation boxes attached to the backs of' the two 

posts (see figure 4). These sensors were then interfaced to the 

nearest data-gathering station. 

During the first test, the four seals and the stopping in 

crosscut 5 were each instrumented with thrcc LVDTs and two 

accelerometers on the B-drift side (the side opposite to the 

explosion). An accelerometer and LVDT were installed at the 

exact center (midheight and midwidth) of the B-drift side of 

each seal and stopping (referred to as "middle" in the tables in 

appendix C). These are the sensors below the instrumentation 

box on the left post shown in figure 4. A similar set of sensors 

was installed at midheight and quarter-width (halfway between 

accelerometers were removed so that they would not be 

destroyed. 

The sensor data gathered during the explosion tests were 

relayed from each of the data-gathering stations to an 

underground instrument room off C-drift and then to an outside 

control building. A high-speed, 64-channel, PC-based 

computer data acquisition system (DAS) was used to collect 

and analyze the data. This system collected the sensor data at 

a rate of 1,500 samples per second over a 5-s period. The data 

were then processed using LabView, Excel, and PSI-Plot 

software and outputted in graphic and tabular form, which is 

shown and discussed in the "Explosion and Air Leakage Test 

Results" section later in this report. The pressure and flame 

sensor data were also collected by a VAX computer system and 

outputted as plots. All of the previous seal evaluation programs 

[Greninger et al. 1991; Weiss et al. 1993a; Weiss et al. 1993b; 

Weiss et al. 1993~; Weiss et al. 1996; Weiss et al. 1997bl relied 

on visual readings of the raw pressure transducer traces on 

analog strip charts and/or VAX computer plots to determine 

peak pressure values. The recently installed PC-DAS and 

software used during this program enhanced the data analyses 

through the capability of expanding the time and pressure 

scales, thereby differentiating the actual explosion pressure 

pulse from other noise spikes. The reported pressure data were 

avcraged over I0 ms (1 5-point smoothing) or 20 ms (3 I-point 
Figure 6.-Brattice in place for seal leakage test. 
formwork system, except for the 1,200-mm-wide plug seal, 

which had Gunmesh and shotcrete walls to contain the wet-mix 

core. Meshblock is the Tecrete trade name for a form 

comprised of heavy (4-mm-diam) metal wirc and metal screen 

that is used to contain the shotcrete in a seal. Details of the 

Meshblock system can be found in the "Meshblock Seals" 

section later in this report. The two stopping designs, one of 

which was tested in the first part of the program, were both 

constructed using Gunmesh formwork and shotcrete. Gunmesh 

is the Tecrete trade name for a form composed of a mesh and 

wire backing reinforced with a grid of 4-mm-diam wire, 

providing a means to contain and support sprayed shotcrcte 

material. Details of the Gunmesh formwork can bc found in the 

"Gunmesh Stoppings" section later in this report. 

The shotcrete was applied within the formwork with the drymix process using a REED Lova 215 pneumatically operated 

gunite machine. This recently developcd shotcrete machine 

supplied by REED Manufacturing, Chino, CA, was used in all 

seal and stopping constructions using the dry shotcrete process. 

The minus 5-mm aggregate and cement dry mix was designed 

to be cast into the Meshblock formwork and was also suitable 

for spraying as a shotcrete onto Gunmesh formwork. The 

prebagged dry shotcrete mix was fed into the hopper of the 

diam bull-hose, which provided the 10 m7/min (350 cfm) 

necessary to operate this machine when using a 38-mm-diam 

shotcrete hose. When handling these cementitious products, all 

material safety data sheet (MSDS) instructions should be 

adhered to by operators. 

A summary of the data for the four seals and two stoppings 

is found in table 3. Construction details for the seals and 

stoppings are found in the following sections of this report. Thc 

seals were constructed in rheLLEM under conditions analogous 

to those that may be encountered during seal construction in an 

actual underground coal mine. As in the installation of any seal 

design, all loose material had to be removed from the seal 

construction site, leaving competent strata. In the LLEM, the 

150-mm-thick concrete slab floor within each crosscut had been 

laid on gravel, and its stiffness would influence the ability of 

each seal design to resist horizontal loads. Therefore, the floor 

was drilled at 600-mm centers across the center line of thc 

intendcd seal and injected with a grout to provide greater floor 

stiffness. The mine air temperature during the 2-week 

construction period (January 28-February 10, 1997) ranged 

from 9 to 15 "C (48 to 59 OF) and averaged 10.5 "C (5 1 OF). 

Thc relative humidity ranged from 50%) to 74% and 

averaged 59%. 
techniques of a Gunmesh stopping is presented in the 

"Gunmesh Stoppings" section later in this report. Aquablend is 

the trade name for a low-density, pumpable, cementitious 

product. The entry size in crosscut 1 at the plug seal location 

was approximately 5.43 m wide by 1.95 m high. The first 

Gunmesh stopping required 1,837 kg of Quikrete MB500 

shotcrete to provide an adequate coverage of the Gunmesh. 

This prevented leakage of the wet-mix core material during the 

subsequent injection process. Figure 7 shows the construction 

of the Gunmesh form for the second stopping. This stopping, 

closest to C-drift and located about 1,168 mm (46 in) from the 

first stopping, was sprayed from the C-drift side with 2,3 13 kg 

of the Quikrete MB500 shotcrete. A 600- by 600-mm window 

through this second stopping provided the opportunity to clean 

shotcrete rebound from the interior floor of the plug seal after 

the second stopping was shotcreted. This window was 

subsequently sealed with shotcrete before the wet mix was 

added. Steel spacers located approximately 1,300 mm from the 

floor and spaced across the crosscut at 600-mm centers 

provided lateral support to the two stopping walls, which were 

subjected to a hydraulic head by the Aquablend wet mix. 

After completing these two stoppings (form walls), 

contractors from Alminco Pty. Ltd. injected 7,393 kg of 

Aquablend wet-mix slurry between the two stopping walls 

height) to the higher inby end of the seal. The last injection 

port was pressurized until refusal of the placer at 1.38-MPa 

slurry pressure. This ensured that the slurry level was in direct 

contact with the mine roof. Figure 8 shows the completed plug 

seal. 

Figure 7.-Construction of second wall of plug seal in crosscut 1. 
MESHBLOCK SEALS 

Three Meshblock and shotcrete seals ranging from 175 to 

325 mm thick were constructed in crosscuts 2 through 4 

between B- and C-drift in the LLEM (see figure 5). They 

ranged in thickness from 175 to 325 mm. One crosscut was 

mined to a height of nearly 3 m to simulate the height of entries 

found in a typical Australian coal mine. Summary data for the 

seals are presented in table 3. 

Roof and floor bolts were installed on 600-mm centers, and 

rib bolts were installed on I -m centers, which formed a vertical 

plane at the center line of each seal. These 24-mm-diam steel 

bolts were 1.2 m long and fully encapsulated with polyester 

resin capsules (16-s setting time) within the 600-mm-deep, 

30-rnm-diam holes. The concrete floor was chiseled to a depth 

of approximately 20 mm, providing a key and a level footing 

for each seal. The bolts provided a rigid attachment of the seal 

to the rock strata, which assists the seal in resisting horizontal 

loads. It must be noted that the test environment in the LLEM 

is one of solid, nonyielding strata. 

The Meshblock formwork consisted of a U-shaped frame 

formed as a folded grid of 4-mm-diam steel-wire framework 

(square grid pattern on 152-mm centers) (figure 9). A 3-mmaperture steel-mesh screen encloses the sides and is an integral 

part of this formwork, enabling the shotcrete nozzleman to 

examine the flowing shotcrete material. The Meshblocks were 

laid horizontally in rows in which the ends were butted to each 

other and secured by plastic or wire ties. Normally, two rows 

of Meshblock were erected at a time and cast with shotcrete 

(figure 9). The cycle was repeated until seal completion. There 
- -. 

t 2 

Figure 10.-Completed Meshblock seal in crosscut 2. 
Figure 12.-Construction of Meshblock seal in crosscut 4. 

Figure 15.-Construction of Meshblock seal in crosscut 3, 

Figure 13.-Construction of Meshblock seal in crosscut 4. showing reinforcing bars anchoring it to the ribs and roof. 
Figure 17.-Completed Meshblock seal in crosscut 3. 

GUNMESH STOPPINGS 

Two stopping designs were constructed in the crosscuts 

between B- and C-drift in the LLEM using Gunmesh formwork 

that was erected and then in-filled with sprayed shotcrete. The 

construction is similar to that of the walls constructed for the 

plug seal in crosscut 1 (figure 7). In the stopping erected in 

crosscut 5, both formwork and shotcrete were supplied by 

Tecrete Industries. The Tecrete MB500 (similar to the Quikrete 

MB500) is a mixture of cement and minus 5-mm aggregate 

shotcrete supplied in 25-kg bags and applied with the REED 

Gunrnesh stopping within crosscut 5. The Gunmesh formwork 

was cut using bolt cutters to fit the contours of the entry. The 

mine strata on both sides of the stopping were sealed with 

shotcrete. The formwork had a depthlthickness of 50 mm, 

which meant that an additional 25-mm thickness of shotcrete 

was sprayed to provide the total stopping thickness of 75 mm. 

At the stopping, crosscut 5 was 5.79 m wide by 2.22 m high. 

The compressive strength of the shotcrete used in this stopping 

was 37 MPa after 7 days and 50 MPa after 28 days. 

As part of a low-pressure explosion test program, a second 

Gunrnesh stopping was erected in crosscut 3 on March 4, 1997 

(after the seal in crosscut 3 was destroyed during LLEM 

explosion test 349), using the Gunmesh formwork. Due to a 

shortage of shotcrete, no additional coating was applied to this 

stopping beyond the -40-rnm thickness of the Gunmesh 

formwork (figure 18). The size of crosscut 3 at this stopping 

location was 5.88 m wide by 2.10 m high. Generally, to satisfy 

the requirements of the Queensland Department of Minerals 

and Energy "Approved Standard for Ventilation Control 

Devices," Gunmesh construction techniques are used in 

applications that require explosion overpressure ratings of 14, 

35, and 70 kPa (2, 5, and 10 psi). Totals of 5,239 kg and 

1,948 kg of shotcrete were sprayed on the 75-mm-thick and 

40-mm-thick stoppings, respectively. A significant fraction of 

this material was lost by passing through the Gunmesh 

formwork or as rebound. 
the explosion tests are found in thc appendices. Summary Table 4.-Air leakage measurements 

tables of static pressure data are in appendix A. The table for before the first LLEM explosion test 

each explosion test lists the static prcssurcs at the various Air leakage rate, m3/min, station locations and the interpolated static pressures at the at pressure differential ofseals. A summary table of flame arrival times at the various Location 0.03 0.28 0.53 0.93 

stations for each exelosion is in amendix . . B. Thesc llame kPa kPa kPa kPa 

arrival times were used to calculate the average flame spccds in Seal in crosscut 1 . . . . . 0.0 0.0 0.0 0.0 

Seal in crosscut 2 . . . . . 0.0 0.0 0.0 0.8 table I. Summary tables of LVDT data arc in appendix C. Seal in crosscut 3 . . . . . 0.0 0.0 0.0 0.0 

Examples of the accelerometer data for LLEM test 348 are Seal in crosscut 4 . . . . . 0.0 0.0 0.0 0.0 

shown in appendix D. The plots on the left side of figure D-I 

show the raw accelerometer data on a greatly expanded time 

scale. On the right side of the figure are the corresponding 

Fourier transforms of the data. Analyses of the failure1 

destruction of the seals and stoppings arc in appendix E. The 

LLEM explosion tests are individually discussed in detail in the 

following sections. 

Before the first explosion test, the four scal designs (in 

crosscuts 1 through 4) and the one stopping design (in 

crosscut 5) were evaluated Ibr air leakage resistance. The four 

differential pressures listed in table 4 correspond to the four 

speeds of the main ventilation fan in the LLEM. As table 4 

indicates, virtually no air leakage could bc detected through any 

of the four seal designs for pressure differentials up to nearly 

1 kPa. The 75-mm-thick Gunmesh stopping design in 

crosscut 5 exhibited no air leakage up to 0.28-kPa pressure 

Stoppinq in crosscut 5 . . 0.0 0.0 1.2 1.8 

FIRST EXPLOSION TEST 

On February 11, 1997, the first explosion test (LLEM 

test 347) was conducted in C-drift of the LLEM approximately 

27 hr after the completion of the 2.74-m-high by 325-mm-thick 

Meshblock seal in crosscut 3. The ignition of the 210 m3 of 

-9.0% methane-air zone at the closed end of C-drift generated 

peak static overpressures at the seal and stopping locations 

ranging from 160 kPa at the 325-mm-thick Meshblock seal in 

crosscut 2 to 115 kPa at the Gunmesh stopping in crosscut 5. 

These pressure values are based on a 10-ms time average 

(15-point smoothing) of the raw pressure signals from the 

PC-DAS. Figure 19 shows the pressure traces at various 

distances down the entry for explosion test 347. These pressure 
0 0.5 1 .O 1.5 2.0 2.5 

TIME AFTER IGNITION, s 

Figure 19.-Pressure traces as a function of distance in C-drift 

for LLEM test 347. 

traces in figure 19 and in subsequent figures have also been 

averaged over 10 ms. The complete listings of the peak 

pressures (P,,,,,) at the various transducer locations for LLEM 

test 347 are in table A-1 for both 10- and 20-ms averaging. 

Also listed in table A-1 are the interpolated static peak 

pressures at each of the seals and the stopping for this test. The 

10- and 20-ms time-averaged pressure data, the pressure-time 

integrals (JPdt), and the P,,,,,, times are from the PC-DAS using 

LabView, Excel, and PSI-Plot software. This PC data analysis 

system allows the data traces to be expanded in time and 

pressure so that the peak values can be read precisely. 

Adclitionally, table A-1 lists the visual pressure readings from 

the VAX computer plots, which are at a similar scale to the 

plots in figure 19 and thus cannot be read as precisely. The PC 

and VAX pressure readings, however, show good agreement 

within measurement error. 

E'ostexplosion observations following the first explosion test 

revealed that the four seal designs withstood the explosion 

pressure pulse with little or no outward damage except for a 

few vertical and/or horizontal hairline cracks on each of the 

Meshblock seal designs. A I .6-mm-wide center vertical crack 

extending from the mine roof to the floor was observed on the 

fror~t wall of the 325-mm-thick Meshblock seal in crosscut 3 

after the explosion. The depth of this crack was unknown. It 

was also uncertain if this crack was due to the explosion 

pressure pulse or to shrinkage of the shotcrete material, because 

this seal was tested after only a 27-hr cure period. A similar 

crack had developed on the 325-mm-thick Meshblock seal in 

crosscut 2 approximately 2 days after the seal was completed 

and well before the first explosion test. The crack in the 

crosscut 2 seal was observed on both sides of the seal and was 

attributed to the not uncommon problem of shrinkage 

sorn~etimes associated with cementitious-based products. 

The 75-mm-thick Gunmesh stopping design in crosscut 5 

also withstood the pressure pulse, but exhibited two horizontal 

cracks that extended across the entire front face (C-drift, or 

explosion side) of the stopping-one across the top section of 

the stopping about 150 mm down from the roof and the second 

across the center portion of the stopping. A chipped-out section 

of the center of this stopping on the C-drift wall indicated 

localized compression failure of the shotcrcte, with the entire 

structure very close to failure. No cracking was evident on the 

back side of this stopping. The data from the LVDTs (see 

appendix C) on the Gunmesh stopping recorded a maximum 

displacement of about 25 mm during the explosion. The 

maximum displacement (see appendix C) of the thicker 

Meshblock seals for LLEM test 347 was only 1.8 mm for the 

325.-mm-thick seal in crosscut 2 (160-kPa peak pressure); 

2.7 mm for the similarly thick, but larger cross-section 

Meshblock seal in the 2.7-m-high crosscut 3 (1 35-kPa peak 

pressure); and 8.4 mm for the 175-mm-thick Meshblock seal in 

crosscut 4 (1 20-kPa peak pressure). The 1,200-mm-thick plug 

seal in crosscut 1 revealed only negligible displacement 

(-0.1 mm) when subjected to a peak pressure pulse 01 

approximately 150 kPa. These LVDT data show that, 

as expected, the displacements were greater Sol- the thinner seals 

or larger cross-section seals. The more detailed LVDT data for 

test 347 (table C-I) show that the largest displacement (within 

expcrimental error) for each individual seal occurred at the 

middle LVDT; similar or smaller displacements occurred at the 

other LVDTs. Postexplosion air leakage rates (table 5) across 

each of the seal and stopping designs l'ollowing the fir\[ 
LLEM as a means to evaluate them against highel

 impulse 

loadings. Thecalculatedprcss~~re-time intcgral for the plug scal 

in crosscut 1 was approximately 41 kPa-s, giving a total 

impulse of 435 kN-s. 

In order to more fully evaluate the strengths of the seals and 

the stopping and to generate data to assist in the tievclopment 

of a numerically basccl design tool for explosion seals, 

successive and more intense explosions were required. 

SECOND EXPLOSION TEST 

On February 18, 1997, a sccond explosion lest (LLEM 

test 348) was conducted against the seal and stopping designs. 

The ignition of the mcthane Lone (sa~ne as for the first 

explosion) with thc addition of the 64-m-long zone of 

suspended pulverized coal dust (I 00 g/m3) gcneralctf a stalic 

pressure pulse throughout thc tcst Lone that rangcd f om a high 0 0.5 1.0 1.5 2.0 2.5 

of 385 kPa at the 175-mm-thick Meshblock seal in cl-osscut 4 TIME AFTER IGNITION, s 

to a low of 300 kPa at the 2.7-111-high, 325-mm-thick Figure 20.-Pressure traces as a function of distance in C-drift 

Meshblock seal in crosscut 3. The prcssul-e rrnccs a1 various for LLEM test348. 

distances down the entry are shown in figure 20. The f',,,,,, and 

JPdtdata at the various transducer and seal locations fol-LLEM exceed the desired level of 240 kPa. The unexpecledly high 

test 348 are listed ill table A-2, Based on a pl-evious seal prcssure pulse generated during this second test luay have been 

evaluation program in the LLEM Llsing a similar gas and dLlst due to very low humidity conditions compared to the high 

zone, it was anticipated that the ,-yak pressure i,lllsc would no1 humidity of the earlier evaluation program. Lower humidity 
e pug seacosscut 

ad te esbocseas 

crosscuts 2 and 3 showed little or no apparcnt cla~nagc. 

The LVDT data i0r the 75-mn-thick Gunmesh stopping in 

crosscut 5 showed a displacement of >60 mm prior to failure 

(table C-2). The time ol' Ihilure was detcrminetl I'rom the 

LVDT data (see table E-2). The pressure data (10-ms time 

average) from the two transduccrs on each side ot'this stopping 

are shown in figure 2 1. Thc two 131-cssure trttccs were aligned 

by matching the positions ol'peak pressul-c at (he two stations. 

The resulting time scale at the position ol' tlic stopping was 

TIME AFTER IGNITION, s 

Figure 21.-Pressure data for stopping 5, showing time of 

stopping failure for LLEM test 348. 

The seals in crosscuts 1, 2, and 3 survived the second 

explosion (LLEM test 348). The 325-mm-thick Meshblock 

seals in crosscuts 2 and 3 were exposed to peak pressure pulses 

of 3 15 and 300 kPa, respectively. The plug seal in crosscut I 

was exposed to a 330-kPa peak prcssure pulse. Maximum 

displacements of the three surviving seals wel-c 6.6 mm for the 

crosscut 3 Meshblock seal in the high roof area, 2.4 mm for the 

crosscut 2 Meshblock seal, and 0.5 Inm for the plug seal in 

crosscut I (table C-2). The pressure and impulse data from the 

two tr:unsrIucers on either side of the 2.7-m-high seal in 

crosscut 3 (75 rn from the face) are shown in figure 26. As in 

the previous figures, the pressure peaks were aligned and the 

tinicscale was interpolated. the pressure-time integral dataand 

the impulse data reported in appendix A were calculated from 

the main pressure pulse, up to 1.5 s in figure 26. The sccond, 

smaller reflection pressure pulse (I .5 to 2.6 s in figure 26) was 

not included. Therefore, the pressure-time integral l'or seal 3 

was -94 kPa-s and the impulse was - 1,500 kN-s based on an 

interpolation of the data from the two transduccrs. Summary 

press~~e and impulse data for seal 3 and the other seals f'or 

LLEM tes[ 348 are presented in table A-2. 

The plug seal in cl-osscut I and thc Mcslihlock seal in 

cl-osscut 2 survived LLEM explosion test 348 with little or no 

apparent damage, except for a few additional vertical and 
(I) \ 

 in crosscut 3 after the explosion. The vertical center crack 

4 30 observed on the front wall of the seal in crosscut 3 atier the first a explosion test was more pronounced following the second tcst. 

Figures 28 and 29 show the postexplosion back (B-drift) sides 

of the Meshblock seals in crosscuts 3 and 2, respectively. Thc 

patterns of small cracks on the two seals are outlined in white 

chalk. Figure 28 also shows the wood framework used to hold 

500b8~~~III-+ 

- 

the brattice cloth for the air leakage tests. The minor tension '!' .* 

5 400 - cracks on the B-drift side of seals in crosscuts 2 and 3 show a 

yield linc mechanism wherein the seal is divided into a series of m 

a elastic plates forming a roof-to-floor arch. The resistance to 

-20 bending loads from the explosion is provided by the stiff -0 

a surrounding rock, which provides a reaction to the arch formed \ 

in the wall. When the C-drift central portion ot'the seal can no 

longel- sustain the high compressive load and the shotcrcte 

crushes, failure is by snap-through of the seal and stopping; this 

0.66 0.68 0.70 0.72 0.74 0.76 0.78 0.80 occurrcd with the 175-mm-thick seal in crosscut 3 and thc 

TIME AFTER IGNITION, s 75-mm-thick stopping in crosscut 5. Table 6 shows that the air 

Figure 23.-Pressure and impulse data for seal 4, showing leakage tests on the surviving Meshblock seals in crosscuts 2 

time of seal failure for LLEM test 348. and 3 were wcll within the established guidelines even up to 
TIME AFTER IGNITION, s 

Figure 25.-Remains of seal 4 after LLEM test 348 (closeup view Figure 26.-Pressure and impulse data for seal 3 for LLEM 

near wall). test 348. 
Figure 28.-Back (B-drift) side of seal 3 after LLEM test 348, 

showing crack pattern marked with white chalk. 

pressure differentials of 0.9 kPa. The plug wnl sliowctl no 

evidence of any air Icakagc. 

THIRD EXPLOSION TEST 

On February 26, 1997, the third ancl largest explosion test 

(LLEM test 349) was conduc(ecl against the rcnlaininy seals in 

crosscuts 1,2, and 3. The ignition of the mcthane and coal cl~~st 

zone (same as for the second cxplosion test, cxccpt that ~licoal 

dust concentration was incre~isccl to 200 gcncra(cc1 a pcak 

static pressure pulse !ranging I'rom 595 kPa at the 2.7-m-high 

Meshblock seal in crosscut 3 to 430 kPa at thc plug scnl in 

crosscut I. Figurc 30 shows tlie prcssurc traces at the \titrious 

instrument stations in C-dl-il't for this third cxplosion tcst. Peak 

Seal in crosscut 4 ........... (I) (I) (I) (I) 

Sto~~inq in crosscut 5 ........ (I) ('1 (I) (I) 

'Destroyed by pressure pulse. 

~x~cssurcs and jPdt data at thc val-ious tr:uns~luccr ant1 seal 

locations I'or LLEM test 349 are listccl in tahlc A-3. For this 

tcs~, thcl-c were signil'icant differences in the prcssurc rcadin~s, 

tlcpcnding on thc amount ol' smoothing. This was cspucially 

I~LIC :I( the stations from 71 to 123 m, where tlie time at pcak 

~XCSSLIIX was very short. 

Postcxplusion observations revealed that [he 2.74-ni-liigli, 

325-~111-thick Meshblock :;cal in crosscut 3 was co~iiplctcly 

tlcstroycd by this higher pressure p~~lsc gcncl-atccl cluring thc 

tliil-(1 cxplosion tcst. This seal design withsloocl two prcvio~~s 

cxplosion tcsts at ~~ressures of 135 and 300 kPa. Prior to failure 

ofscal3 during this third explosion tcst, the LVDTdala showed 

21 ~naximum displacclnent of > 15 mni ((able C-3). The Linic ol' 

I'ailurc lor this seal was determined t'iclrn the LVDT data 

(tahlc E-3). The pressurc and impulse clata from the two 

tl-ansduccrs on cithcr side of this seal are shown in I-igure 3 1. 

The pck ppr-cssu1-e pulse was --595 kPa :it crosscul 3. This sctil 

I'i~ilcd at -90 ms after pcak pressure. The total inipi~lsc up to 

the tinle ol'l'ailure was .-XU0 kN-s. The rcniai~ls olscal 3 xu 

shown in figures 32 and 33. The rcinl'orcing har-s rcmi~incd 
0 0.5 1.0 1.5 2.0 2.5 

TlME AFTER IGNITION, s 

Figure 30.-Pressure traces as a function of distance in C-drift 

for LLEM test 349. 

embedded in the roof, ribs, and floor, but they had been bent by 

the force of the explosion. Part of the seal remained attached to 

the ribs (figure 33). This indicates that failure occurred at the 

middle of the seal rather than at thc interface with the mine ribs 

and roof. 

TlME AFTER IGNITION, s 

Figure 31 .-Pressure and impulse data for seal 3, showing time 

of seal failure for LLEM test 349. 

Very little outward damage was evident on the two surviving 

seals after LLEM explosion test 349, except for some additional 

minor horizontal yield line cracks. A maximum displacement 

of - 1 1 mm was recorded from the LVDT on the crosscut 2 

Meshblock scal as it was subjected to a 455-kPa pressure pulse. 

As expected, the maximum displacement was at the middle 

LVDT, with smaller displacements for the upper and right 

LVDTs. The maximum displacement from the LVDTs was 

< 1 mm l'or the plug seal that was subjected to a pressure pulse 

of 430 ItPa. Figure 34 shows the crack pattern (outlined in 

white chalk) on the B-drift side of the seal in crosscut 2 after 

LLEM test 349. The horizontal yield line cracks observed after 

the second explosion test (figure 29) have now extended 

horizonlally across the center of the seal and angled diagonally 

into the corners (figure 34). This is an expected pattern of yield 

lines for a confined vertical rectangular structure subject to 

horizontal load. 

Due to scheduling limitations, the postexplosion air leakage 

evaluat~ons were not conducted until after the last two low-level 

explosion tests were conducted. The air leakage evaluations 

after the fifth test showed that the plug seal in crosscut 1 had no 

detectable air leakage even at pressure differentials up to 

0.9 kPa (table 7). The 325-mm-thick Meshblock seal in 

crossc~lt 2 also exhibited low air leakage rates that were well 

within the established guidelines. 
Figure 32.-Remains of seal 3 after LLEM test 349. 

Figure 33.-Remains of seal 3 after LLEM test 349 (closeup view Figure 34.-Back (B-drift) side of seal 2 after LLEM test 349, 

near wall). showing crack pattern marked with white chalk. 
Table 7.-Air leakage measurements after the fifth (No. 351) 

LLEM explosion test 

Air leakage rates, m3/min, 

at pressure differential of- Location 0.14 0.35 0.51 0.90 

kPa kPa kPa kPa 

Seal in crosscut 1 . . . . . . . 0.0 0.0 0.0 0.0 

Seal in crosscut 2 . . . . . . . 0.0 0.7 0.8 1.2 

Seal in crosscut 3 . . . . . . . (I) (' ) 

'Destroyed by pressure pulse. 

I FOURTH AND FIFTH EXPLOSION TESTS 

The remaining two low-pressure explosion tests were 

conducted to evaluate a second Gunmesh stopping design that 

was constructed in crosscut 3 alter seal 3 was destroyed during 

LLEM explosion test 349. This 40-mm-thick Gunmesh 

stopping was installed at a location in crosscut 3 with a mine 

roof height of approximately 2 m (closer to C-drift than the 

seal, which had been in an enlarged part of the crosscut). The 

fourth, explosion test (LLEM test 350) was conducted on 

March 1 1, 1997. The ignition of the 1 1 5-m7 zone of 

7.1 a/o methane-air generated a peak pressure pulse of 23 kPa at 

the Glunmesh stopping location in crosscut 3 during this fourth 

explocion test. Figure 35 shows the pressure traces at the 

various instrument stations in C-drift for the fourth test. 

Postexplosion observations following the fourth test revealed 

no outward damage to the stopping, except for a vertical 

hairline crack on the front wall (C-drift, or explosion side) of 

the stopping. The Gunmesh stopping experienced a maximum 

displacement of slightly over 13 mm as recorded by the LVDTs 

0 0.5 1 .O 1.5 2.0 2.5 

TlME AFTER IGNITION, s 

0 0.5 1.0 1.5 2.0 2.5 

TlME AFTER IGNITION, s 

Figure 35.-Pressure traces as a function of distance in C-drift Figure 36.-Pressure traces as a function of distance in C-drift 

for LLEM test 350. for 1-LEM test 351. 
mounted on the back of the stopping. No air leakage 

evaluations were conducted after this fourth explosion test due 

to time limitations. 

The fifth explosion test (LLEM test 351) was conducted on 

March 12, 1997. This was the final test of the Tecrete seal 

evaluation program. The gas ignition zone was 1 15-m3 of 

7.7% methane-air. Figure 36 shows the pressure traces at the 

various instrument stations in C-drift. The pressure and 

impulse data from the two transducers on either side of this 

stopping are shown in figure 37. This explosion generated a 

peak pressure pulse of -39 kPa at the Gunmesh stopping 

location in crosscut 3 based on an interpolation of the data from 

the two transducers. This pressure pulse destroyed the 40-mm- o 1 I I I I I JO 

thick Gunmesh stopping. A maximum displacement of about 0.90 0.95 1.00 1.05 1.10 1.15 1.20 1.25 

TlME AFTER IGNITION, s 28 rnrn was recorded by the LVDTs prior to the failure of the 

stopping (table C-5). Because the stopping was destroyed, no Figure 37.-Pressure data for stopping 3, showing time of 

stopping failure for LLEM test 351. air leakage evaluations were possible. 

DISCUSSION 

The LVDTs were very useful in evaluating the movement of 

the seals and stoppings caused by the explosion pressures. 

Examples of the displacement (deflection) data from the middle 

LVDT on the seal in crosscut 3 are shown in figure 38. In the 0 

first explosion test (LLEM test 347), there is only a small 

deflection (-3 mm) of the LVDT as the seal was exposed to a I I I 1 

static pressure of 135 kPa. There is a peak deflection of -7 mm 

44 

8p~ 

measured by the LVDT as the seal was exposed to a pressure of 

300 kPa during LLEM test 348. The middle LVDT measured 

a deflection of 2 15 mm before the seal was destroyed at just E 4- 

E 

before 0.8 s during LLEM test 349, which had a maximum z explosion pressure of 595 kPa. The other LVDTs on seal 3 0 

showed similar deflection data, as listed in the tables in i= 04 I I I I 

appendix C. By comparing the LVDT data in figure 38 with X 

the pressure data in figures 26 and 3 1, the effects on the seal 2 16 W 

n can be studied as a function of time. The seal started to detlect 

shortly after the arrival of the leading edge of the pressure pulse Iin both tests. Maximum deflection occurred at peak pressure. 

12- 2 

In LLEM test 348, the seal deflection gradually decreased as the 

pressure returned to ambient. In LLEM test 349, the seal and 

the LVDT were destroyed while still at maximum deflection; 8 

thus, any data after 0.8 s were meaningless. 

Examples of the accelerometer data for LLEM test 348 are 

shown in figure D-1. The plots on the left side of the figure 4 

show the raw accelerometer data for the seals in crosscuts 2, 3, 

and 4 on a greatly expanded time scale. On the right side of the 

figure are the corresponding Fourier transforms of the data. 0- 

0.4 0.8 1.2 1.6 

The raw data show an oscillation that is mostly symmetric TlME AFTER IGNITION, s 

about zero, with only a slight net positive component. The 

Figure 38.-Data for the middle LVDT on seal 3 for (A) LLEM test Fourier transforms of the accelerometer data indicate the natural 347, LLEM test 348, and (C) LLEM test 349. 

vibration frequencies of the seals. For example, the Fourier 

I I C1 I I 

- 

- 

- 

- 

- 

- 

- 

- 

I I I 
transform of the data for the middle accelerometer on the seal 

in crosscut 2 for LLEM test 348 showed multiple strong peaks 

between 90 and 1 15 Hz. The Fourier transform of the data for 

the accelerometer on seal 3 showed multiple strong peaks 

between 50 and 80 Hz. The Fourier transform of the data for 

the accelerometer on seal 4 showed a strong peak at <20 Hz and 

another strong peak between 45 and 60 Hz. In general, the 

Fourier transforms of the accelerometer data showed that the 

stiffer seals (i.e., those that were thicker and/or had a smaller 

cross section) had higher natural frequencies. In principle, the 

data from the LVDTs and accelerometers are complementary. 

If the LVDT displacement data are differentiated twice with 

respect to time, the result should be the accelerometer data. 

This was tested for the middle LVDT on seal 3 for LLEM 

test 348. The LVDT displacement data were first smoothed at 

15 points. Then, the resulting second derivative was 

qualitatively similar to the accelerometer data, except for some 

increased baseline noise due to the remaining intrinsic noise on 

the LVDT trace. 

Prior to the completion of this report, a brief summary of the 

test program and results was reported at the Queensland Mining 

Industry Health and Safety Conference [Mutton and Downs 

1 9971 in September 1997. 

CONCLUSIONS 

Explosion-resistant seals, such as those evaluated in this 

report, provide protection for underground coal miners by 

isolating them from the effects of explosions that might occur 

in the gob or other worked-out areas of the mine. Although this 

research project was funded by and conducted primarily for the 

Australian mining industry, the knowledge gained will also 

benefit the U.S. mining industry. The four reinforced 

cementitious seal and stopping designs developed by Tecrete 

Industries were evaluated by PRL in its Experimental Mine at 

Lake Lynn Laboratory for strength characteristics and air 

leakage resistance. These full-scale designs were air-leakage 

tested, then subjected to a series of explosions. One primary 

objective was to determine if the seal and stopping designs were 

of sufficient strength and leakage resistance to meet or exceed 

the requirements of the Queensland Department of Mines and 

Energy "Approved Standard for Ventilation Control Devices" 

and the requirements of U.S. mining regulations. The second 

objective was to gather data for use in the development of a 

model that will be used to optimize future seal designs in terms 

of strength and economics based on roadway conditions and 

required pressure rating. Both of these objectives were 

successfully achieved during this program. 

All seal and stopping designs withstood the first explosion 

test. The static pressure exerted on the two 325-mm-thick 

Meshblock seals and the I ,200-mm-thick plug seal ranged from 

135 to 160 kPa (with the values rounded to the nearest 5 kPa, 

as noted in appendix A). The 175-mm-thick Meshblock seal 

(located farther from the face) was subjected to a lower pressure 

of - 120 kPa. Air leakage resistance data were also well within 

the guidelines established for this program. The special 

requirement of this program to design a seal capable of 

withstanding a 138-kPa explosion overpressure within -24 hr 

after construction was also satisfied. The 2.74-m-high, 

325-mm-thick Meshblock seal design was tested 27 hr after 

construction and withstood the - 138-kPa explosion pressure 

while maintaining negligible leakage rates. 

Successively higher level explosion tests were then 

conducted. The 175-mm-thick Meshblock seal failed during an 

explosion with a peak pressure of -385 kPa (-56 psi). The 

325-mm-thick, 2.74-m-high Meshblock seal design survived a 

peak pressure of -300 kPa (-43 psi) and failed during a 

stronger explosion with a peak pressure of -595 kPa (- 86 psi). 

The 1,200-mm-thick plug seal and the 325-mm-thick, 2.26-mhigh Meshblock seal withstood the most intense explosion test, 

which generated peak pressures at the seal locations of 

-430 kPa (-62.5 psi) and -455 kPa (-66 psi), respectively. 

Results from the testing of the Gunmesh stoppings showed 

that the 75-mm-thick structure withstood an explosion 

overpressure of - 1 15 kPa (- 17 psi) while maintaining air 

leakage resistances well within the established guidelines for 

this program. This stopping later failed during an explosion 

with a peak pressure of -385 kPa (-55 psi). The 40-mm-thick 

stopping w~thstood an explosion overpressure of -23 kPa 

(-3.4 psi) alnd later failed during an explosion with a peak 

pressure of -39 kPa (-5.6 psi). 

The development of the high-explosion resistance in the seal 

and stopping designs can be attributed to the lateral restraint 

provided by the surrounding strata, the high strength of the 

shotcrete material, and the reinforcing "rootbolts" and 

Meshblock. The use of fully encapsulated 24-mm-diam steel 

bolts embedded 600 mm into the roof, ribs, and floor and 

extending into the seal and stopping designs provided increased 

restraint at the seal-to-strata interface. An important aspect 

demonstrated by these tests is that seal height is of major 

importance I o the seal's ability to resist explosion overpressure. 

This was evident during the testing of the two 325-mm-thick 

Meshblock seal designs wherein one was constructed in an 

entry enlarged to a height of 2.74 m and the other in an area 

2.26 m high. The 2.74-m-high seal was close to failure at 

-300 kPa (-43 psi) as shown by the crack patterns (figures 27 

and 28); the 2.26-m-high seal withstood -455 kPa (-66 psi) 

with only minor yield line cracking apparent (figure 34). 

The data provided by the LVDTs and accelerometers will aid 

in the development of numerical models to assist in seal design 

to meet current requirements and to enable future improvements 

to these structures. Further study, however, is needed to 
, Qp

providing the MB500 shotcrete material and Paul E. Sulman, 

U.S. Sales Manager, of REED Manufacturing for his assistance 

with the shotcrete machine. Richard Adasiak of R. G. Johnson, 

Inc., organized help for building the stopping in crosscut 3. 

y, pp

installation of sensor mounting equipment and wiring. 

REFERENCES 

Apte VB, Green AR, Pearson RD [I 9951. A test repol7 on the performance 

of a concrete explosion stopping in a large tunnel. WorkCovcr Authority, 

Londonderry Occupational Safety Centre report No. TR 13047, June 1995. 

Barzegar F [1996a]. Thlee-di~ncnsional finite elcnient analysis of Lake 

Lynn Experimental Seal Walls (for Tecretc Intlustlies Pty. Ltd.). Sept. 1996. 

Barzegar F [1996b]. Three-dimensional finite cle~nent analysis of a 

shotcrete mine seal. Tecrete Industries Pty. Ltd., January 1996. 

CFR. Codc 111 I~ctlertrl repk~fir~ns. Washington. DC: U.S. Government 

Printing Officc, Oilice of the Fedel-al Rcgisler. 

Greninger NB, Weiss ES. Luzik SJ, Stephan CR [l991]. Evaluation of 

solid-block and cetnentitious foam seals. Pittshurgh. PA: U.S. I>cpartment of 

the Interlor, Bureau of Mines, RI 9382. 

Mattes RH. Bacho A. Wade LV [l9X?]. Lake Lynn Labor:~tory: construction, physical dcscription, and capability. Pittshurgh. PA: U.S. Department of the Interior, BUI-eau of Mines, IC 891 I. 

Mitchell DW [1971]. Explosion-proof bulkheads: present practices. 

Pittsburgh, PA: U.S. Department or the Inlerior. Bureau of Mines, RI 7581. 

Mutton VS. Downs ML) 119971. Explosion testing of Tecrete mine seals. 

In: Proceedings of the Queensland Mining Industry Health ant1 Safety 

Conference. Yeppoon, Queensland. Australia: pp. 07- 108. 

Roxborough FF [1997]. Anatomy of a disaster: the explosion at Moura 

No. 2 coal mine, Australia. Mining Techno1 79(906):37-43. 

Sapko MJ, Weiss ES, Watson RW [1987]. Size scaling of gas explosions: 

Bruceton Expel-imental Mine versus the Lake Lynn Mine. Pittsburgh, PA: 1J.S. 

Department of the Interior, Bureau of Mines, RI 9 136. 

Stcphan CR [1990a]. Construction of seals in underground coal ~nincs. 

Pittsburgh, PA: U.S. Department of Labor, Mine Safety and Health 

Atlministmtion, industrial Safety Division (ISD) report No. 06-2 13-90, Aug. I. 

1990. 

Stcphan CR [1990b]. Omega 384 block as a seal constl-uction ~iiaterial. 

Pittshurgh, PA: U.S. Department of Labor, Mine Safety and Health Administration, Industrial Safety Division (ISD) report No. 10-3 18-90, Nov. 14, 1990. 

Triebsch G, Sapko MJ [1990]. Lake Lynn Laboratvry: a state-of-the-art 

mining xscarch laboratory. In: Proceetlings of the lnte~national Symposium 

on Unique Underground Structures. Golden, CO: Colorado School of Mines, 

Vol. 2, 1~1). 75-1 to 75-21. 

Wcics ES, GI-eninger NB, Perry JW, Stephan CR [I993a]. Strength and 

leakage evaluations for coal mine seals. In: Proceedings of the 25th International Conferenceon Safety in Mines Research Institutes. Pretoria, Kepuhlic 

of South Africa: Conference Papers for Day One, pp. 149-161. 
Weiss ES, Greninger NB, Slivensky WA, Stephan CR [1993b]. Evaluatioi~ 

of alternative seal designs for coal mines. In: Proceedings of the 6th U.S. Mine 

Ventilation Symposium. Salt Lake City, UT: University of Utah, Chapter 97, 

pp. 635-640. 

Weiss ES, Greninger NB, Stephan CR, Lipscomb JR [1993c]. Strength 

characteristics and air-leakage determinations for alternative mine seal designs. 

Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, RI 9477. 

Weiss ES, Slivensky WA, Schultz MJ, Stephan CR, Jackson KW [1996]. 

Evaluation of polymer construction material and water trap designs for 

underground coal mine seals. Pittsburgh, PA: U.S. Department of Energy, 

RI 9634. 

Weiss ES, Mutton IVS, Cashdollar KL, Kohli DR [1997a]. Evaluation of 

Tecrete-reinforced cementitious seals. Final report for Memorandum of 

Agreement No. 14-09-0050-3739. 

Weiss ES, Slivensky WA, Schultz MJ, Stephan CR [1997b]. Evaluation 

of water trap designs and alternative mine seal construction materials. In: 

Dhar BB, Bhowmick BC, eds. Proceedings of the 27th International 

Conference on Safety in Mines Research Institutes. Vol. 2. New Delhi, India: 

Oxford & IBH Publishing Co. Pvt. Ltd., pp. 973-981. 
APPENDIX A.-SUMMARY TABLES OF STATIC PRESSURE DATA 

FOR LLEM EXPLOSION TESTS 

Table A-1 .-Tecrete seals evaluation in the Lake Lynn Experimental Mine: 

pressure data, test 347 (February 11, 1997) 

TRANSDUCER 

Distance, Time of Pmax visual Pmax P,ax Pressure-time 

ft (m) reading, 10-ms (1 5-pt) avg, 20-ms (31 -pt) avg, integral IPdt, Pmaxp s ~si ~si 1kPa) osi fkPa) DSI-s (kPa-s) 

13 (4.0) ........... - -35 - - - 34 (235) - - 

Location and Pmax visual Pmax pmax Pressure-time 

distance, ft (m) reading, 10-ms (1 5-pt) avg, 20-ms (31-pt) avg, integral J Pdt, 

DSI DSI (kPa) ~si (kPa) wsi-s &Pa-s) 

Seal in crosscut 1 : 59 (1 8.0) ......... - 22 -22 (150) -22 (150) -6 (-41) 

Seal in crosscut 2: 156 (47.7) ........ 23.0 23.5 (160) 22.0 (150) 5.3 (36) 

Seal in crosscut 3: 246 (75.0) ........ 18.5 19.5 (135) 18.5 (130) 4.3 (30) 

Seal in crosscut 4: 355 (1 08.2) ....... 18.0 17.0 (120) 16.0 (110) 3.4 (23) 

Sto~~inq in crosscut 5: 452 (137.8) ... 17.0 17.0 (115) 15.5 (1 05) 2.4 11 7) 

NOTE.-Visual pressure readings from VAX plots are *1 psi; PC LabView pressures are to nearest 0.5 psi (5 kPa). 

Pressure-time integral is calculated up to the time that the pressure trace returns to -0 psi; it does not include the second 

(reflected) pressure pulse. 
Table A-2.-Tecrete seals evaluation in the Lake Lynn Experimental Mine: 

pressure data, test 348 (February 18, 1997) 

TRANSDUCER 

Pmax Pma, Pressure-time Distance, Time of 10-ms (1 5-pt) avg, 20-ms (31 -pt) avg, integral J Pdt, ft (m) prr,ax, s wsi (kPa) DS~ IkPa) DSI-s (kPa-s) 

757 (230.7) ........... 3.118 19.0 (130) 18.0 (1 25) - - SEAL/STOPPING 

Pmax Pmax Pressure-time Location and 

10-ms (1 5-pt) avg, 20-ms (31 -pt) avg, integral JPdt, distance, ft (m) wsi (kPa) ~si /kPa) mi-s (kPa-s) 

Sealincrosscut1:59(18.0) .......... 48.0 (330) 4'7.5 (330) 16.6 (1 15) 

Seal in crosscut 2: 156 (47.7) ......... 45.5 (31 5) 44.0 (305) 16.0 (1 10) 

Seal in crosscut 3: 246 (75.0) ......... 43.0 (300) 42.0 (290) 13.6 (94) 

Seal in crosscut 4: 355 (1 08.2) ........ '55.5 (385) '53.0 (365) 33.3 3(23) 

Stoppinq in crosscut 5: 452 (137.8) .... '53.5 (370) '50.0 (345) 3l .3 3(9) 

'Two peaks of equal height. 

'Destroyed. 

"ntegral up to time of failure. 

NOTE.-PC LabView pressures are to nearest 0.5 psi (5 kPa). 

Table A-3.-Tecrete seals evaluation in the Lake Lynn Experimental Mine: 

pressure data, test 349 (February 26, 1997) 

TRANSDUCER 

Distance, Time of PTnax Pmax Pressure-time 

ft (mj 10-ms (1 5-pt) avg, 20-ms (31 -pt) avg, integral J'Pdt, P,,,,x, s -- DS~ (kPa) r~si (kPa) wsi-s (kPa-s) 

13 (4.0) ........... 2.990 86.5 (595) 85.0 (585) - - 

757 (230.7) ......... 3.1 10 15.0 (100) '4.0 (95) - - 

SEALISTOPPING 

Location and pr,,ax pmax 

Pressure-time 

distance, ft (m) 10-ms (1 5-pt) avg, 20-ms (31 -pt) avg, integral JPdt, 

~si (kPa) r~si (kPa) ~si-s IkPa-s) 

Seal in crosscut 1: 59 (1 8.0) ........ 62.5 (430) 57.0 (390) 16.0 (110) 

Seal in crosscut 2: 156 (47.7) ....... 66.0 (455) 62.0 (425) 15.2 (105) 

Seal in crosscut 3: 246 (75.0) ....... '86.0 (595) '74.5 (51 0) 27.3 '(50) 

'Destroyed. 

'integral up to time of failure. 

NOTE.-PC LabView pressures are to nearest 0.5 psi (5 kPa). 
ft (m) reading. 10-ms (15-pt) avg. 20-ms (31 -pt) avg, integral SPdt, 

p,. s osi osi (kPa) osi (kPal osi-s (kPa-s) 

13 (4.0) ............. 3.450 10.5 10.7 (74) 10.7 (74) - - 59 (1 8.0) ............ 3.230 - 6.2 (43) 6.0 (42) 2.06 (14.2) 

84 (25.6) ............ 3.250 6.0 6.3 (44) 6.3 (43) 2.07 (14.3) 

134 (40.8) ............ 3.31 0 6.0 5.9 (41) 5.8 (40) 1.73 (1 1.9) 

184 (56.1) ............ 3.330 6.0 6.1 (42) 6.0 (41) 1.55 (10.7) 

234 (71.3) ............ 3.370 6.0 5.8 (40) 5.7 (39) 1.28 (8.8) 

304 (92.7) ............ 3.395 5.0 4.9 (34) 4.8 (33) 0.82 

- (5.7) 

403 (1 22.8) ........... 3.470 3.5 3.7 (26) 3.6 (25) - 501 (152.7) ........... 3.550 2.5 2.7 (19) 2.6 (18) - - 598 (1 82.3) ........... 3.620 2.0 2.0 (14) 1.9 (13) - - 

757 (230.7) ........... 3.940 2.0 1.8 (12) 1.7 (1 2) - - SEAL/STOPPING 

Location and P,. , visual '',,a, p, Pressure-time 

distance, ft (m) reading, 10-ms (15-pt) avg, 20-ms (31-pt) avg, integral [Pdt, 

osi WSI (kPa) osi IkPa) osi-s IkPa-s) 

Seal in crosscut 1 : 59 (18.0) ........... 6 6.2 (43) 6.0 (42) 2.06 (14.2) 

Seal in crosscut 2: 156 (47.7) .......... 6 6.0 (41) 5.9 (41 1.65 (1 1.4) 

New stoppinu in crosscut 3: 246 (75.0) . . 6 '5.6 (39) '5.5 (38) '0.88 '(6.0) 

'Destroyed. 

'Integral up to time of failure. 

NOTE.-Visual pressure readings from VAX plots are 21 psi; PC LabView pressures are to nearest 0.1 psi (1 kPa). but 

uncertainty is approximately k0.2 psi. 
APPENDIX 6.-SUMMARY TABLE OF FLAME ARRIVAL TIMES 

FOR LLEM EXPLOSION TESTS 

Table B-1 .-Tecrete seals evaluation in the Lake Lynn Experimental Mine: 

flame arrival time data 

Flame sensor Flame arrival time, s 

distance, Test Test Test Test Test 

ft (m) 347 348 349 350 35 1 

13 (4.0) . . . . . . 0.286 0.261 0.308 -0.74 0.52 

84 (25.6) . . . . . . 0.495 -0.52 0.524 1.24 0.96 

1 34 (40.8) . . . . . . 0.531 0.563 0.569 ND (7 

184 (56.1) . . . . . . 0.573 0.610 0.615 ND ND 

234 (71.3) . . . . . . (I) 0.652 0.630 ND ND 

304 (92.7) . . . . . . (I) 0.694 0.664 ND ND 

403 (122.8) . . . . . ND 0.759 0.77 ND ND 

598 (182.3) . . . . . ND 1.18 ND ND 

ND No detectable signal. 

'Signal was el V. 

NOTE.-Flame arrival time corresponds to 2 1 -V signal on flame sensor; data 

are relative to ignition time. 
APPENDIX C.-SUMMARY TABLES OF LVDT DISPLACEMENT DATA 

FOR LLEM EXPLOSION TESTS 

Table C-1 .-Tecrete seals evaluation in the 

Lake Lynn Experimental Mine: 

LVDT data, test 347 

(February 11, 1997) 

Table C-3.-Tecrete seals evaluation in the 

Lake Lynn Experimental Mine: 

LVDT data, test 349 

(February 26, 1997) 

Maximum Location and displace- instrument ment, mm 

Maximum Location and displace- instrument 

ment, mm 

Seal in crosscut 1: 

LVDT Upper ...... 0.1 

LVDT Right ...... 0.1 

LVDT Middle ..... 0.1 

Seal in crosscut 2: 

LVDTUpper ...... 1.8 

LVDT Right ...... 1.5 

LVDT Middle ..... 1.8 

Seal in crosscut 3: 

LVDT Upper ...... 1.5 

LVDT Right ...... 2.1 

LVDT Middle ..... 2.7 

Seal in crosscut 4: 

LVDT Upper ...... 5.7 

LVDT Right ...... 7.2 

LVDT Middle ..... 8.4 

Stopping in crosscut 5: 

LVDT Upper ...... 12 

LVDT Middle ..... 2 5 

Seal in crosscut 1: 

LVDT Upper ....... 0.7 

LVDT Right ....... 0.5 

LVDT Middle ...... 0.5 

Seal in crosscut 2: 

LVDT Upper ....... 3.0 

LVDT Right ....... 6.6 

LVDT Middle ...... 10.8 

Seal in crosscut 3:' 

LVDT Upper ....... 215 

LVDT Middle ...... 215 

'Destroyed. 

Table C-4.-Tecrete seals evaluation in the 

Lake Lynn Experimental Mine: 

LVDT data, test 350 

(March 11, 1997) 

Table C-2.-Tecrete seals evaluation in the 

Lake Lynn Experimental Mine: 

LVDT data, test 348 

(February 18,1997) 

Maximum Location and displace- instrument ment, mm 

New stopping in crosscut 3: 

LVDT Upper .......... 10.8 

LVDT Middle ......... 13.2 

LOC " 

ment, mm 

Seal in crosscut 1 : 

LVDT Upper ....... 0.5 

LVDT Right ....... 0.3 

LVDT Middle ...... 0.4 

Seal in crosscut 2: 

LVDT Upper ....... 1.8 

LVDT Right ....... 2.4 

LVDT Middle ...... 2.4 

Seal in crosscut 3: 

LVDT Upper ....... 3.6 

LVDT Right ....... 4.2 

LVDT Middle ...... 6.6 

Seal in crosscut 4:' 

LVDT Upper ....... >15 

LVDT Right ....... >15 

LVDT Middle ...... >15 

Stopping in crosscut 5:' 

LVDT Middle ...... >60 

'Destroyed. 

Table C-5.-Tecrete seals evaluation in the 

Lake Lynn Experimental Mine: 

LVDT data, test 351 

(March 12, 1997) 

Maximum Location and displace- instrument ment, mm 

New stopping in crosscut 3:' 

LVDT Upper .......... 2 5 

LVDT Middle ......... 2 8 

'Destroyed. 
APPENDIX D.-EXAMPLES OF ACCELEROMETER DATA 

FOR LLEM EXPLOSION TEST 348 

I ACCELEROMETER FOURIER TRANSFORM 

-50 

0.65 0.70 0.75 0.80 0.85 0 50 100 150 200 

TIME AFTER IGNITION, s FREQUENCY, Hz 

I Figure D-1.-Data from middle accelerometers on seals 2,3, and 4 for LL-EM test 348, along with their Fourier transforms. 
The peak pressure experienced by the stopping in crosscut 5 was 53.5 psi (370 kPa) at -0.760 s. The pressure at failure of thc 

stopping was -5 1 psi (-352 kPa) at 0.765 s. The pressul-e-time integral up to seal failure was - 1.3 psi-s (-9 kPa-s). The crosssectional area of the stopping in crosscut 5 was 139 ft' ( 12.9 m'); lhercfore, the total impulse JPAdt up to seal failure was I 16 kN-s. 

Seal in Crosscut 3 

Table E-3.-Failure data for seal in crosscut 3, test 349 

(February 26, 1997) 

Max~mum Time of seal failure, s Position displacement 

I \ln~ mm LVDT Accelerometer 

Upper . . . 15 0.769 - Mlddle . . . . . 15 0.769 - 

The peak pressure expc~.icnccd by the seal in c~.osscut 3 was 86 psi (595 kPu) a1 -0.68 s. The pressure at failurc of thc seal was 

-32 psi (-220 kPa) at 0.769 s. Thc prcssure-time integral LIP to seal l'uilure was -7.3 psi-s (-50 kPa-s). The cl-oss-sectional ;II-ca 

of the seal in crosscul 3 was 172 ft' ( 16.0 m'); lhcreli)re, the total impulsc JPAdt up to seal failure was 800 kN-s. 
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