Bureau of Mines Report of Investigations/ 1984 

Use of a Sodium Silicate Gel 

Grout for Plugging Horizontal 

Methane- Drainage Holes 

By David C. Oyler 

UNITED STATES DEPARTMENT OF THE INTERIOR 
UNITED STATES DEPARTMENT OF THE INTERIOR 

William P. Clark, Secretary 

BUREAU OF MINES 

Robert C. Horton, Director 
Library of Congress Cataloging in Publication Data: 

L 

Oyler, David C 

Use of a sodium silicate gel grout for plugging horizontal methanedrainage holes. 

(Report of investigations ; 8843) 

Supt. of Docs. no.: I 28.23:8843. 

1. Coalbed methane drainage. 2. Grouting. 3. Sodium silicate. 

I. Title. 11. Series: Report of investigations (United States. Bureau 

of Mines) ; 8843. 

TN23.U43 [TN305] 622s[622'.8] 83-600297 

I 

I 
CONTENTS 

Page 

Abstract ....................................................................... 1 

Introduction ................................................................... 2 

Acknowledgments ................................................................ 3 

Grout design ................................................................... 3 

Grouting method ................................................................ 5 

Plugging operations ............................................................ 6 

Preparation .................................................................. 6 

Grouting ..................................................................... 10 

Results ........................................................................ 13 

Costs .......................................................................... 18 

Discussion ..................................................................... 19 

Conclusions .................................................................... 20 

ILLUSTRATIONS 

Outline of Federal No . 2 Mine. 1980. and locations of the multipurpose 

borehole and Honey Run air shaft ......................................... 3 

Six-day-old Hayward Baker grout mixes ..................................... 5 

Grout mix 5C with 6 pct diatomaceous earth ................................ 6 

Bureau-designed compression packer used to seal horizontal holes .......... 7 

Schematic of method used to plug horizontal holes ......................... 7 

Water flushing of hole 2 .................................................. 8 

Second view of hole 2 during flushing operation ........................... 9 

Vicinity of multipurpose borehole showing locations of horizontal holes ... 9 

Hole 2 after mine-through. April 10. 1980. showing calcite lining the 

lower half of the hole ................................................... 10 

Three-compartment tank truck at multipurpose borehole site ................ 10 

Grout pumping and metering equipment ............................... ....... 11 

Pressure curves and grouting records of horizontal holes .................. 12 

Hole 2 five days after being grouted .................................... 14 

Hole 1. view away from the borehole at location B ......................... 15 

Hole 1. view toward the borehole at location C ............................ 15 

Grout film in the coal cleat near hole 1 .................................. 16 

Hoies 8 and 8P. location H ................................................ 17 

Hole 8 .................................................................... 17 

Hole 8P ................................................................... 17 

TABLES 

1 . Composition of sodium silicate grout mix used to plug horizontal holes .... 4 

2 . Horizontal hole grouting data ............................................. 12 

3 . Grout costs ............................................................ 18 
UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

~aume' 

centimeter 

centipoise 

foot 

cubic foot 

gallon 

gallon per 

hour 

inch 

kilogram 

kilopascal 

pound 

m3 /hr 

per minute 

m3/min 

minute 

min 

mm 

PCt 

vol pct 

wt pct 

pound per square inch, 

gauge 

meter 

cubic meter 

cubic meter per hour 

cubic meter per minute 

minute 

millimeter 

percent 

volume percent 

weight percent 

year 
USE OF A SODIUM SILICATE GEL GROUT FOR PLUGGING HORIZONTAL 

METHANE-DRAINAGE HOLES 

By David C. Oyler ' 

ABSTRACT 

Methane-drainage holes must be completely filled by grout before mining to prevent the emission of large quantities of gas during minethrough, which would constitute an explosion hazard. In November 1980, 

seven horizontal holes at the multipurpose borehole, a small-diameter 

shaft drilled as a Bureau of Mines coalbed methane-drainage installation on the property of the Federal No. 2 Mine, Monongalia County, 

WV, were plugged using a sodium silicate gel grout. This report describes the grout mix and the use of the grout at the multipurpose 

borehole, and discusses the results observed upon mine-through of the 

holes in early 1981. Cost data for the sodium silicate grout are also 

presented. 

~echanical engineer, pi ttsburgh Research Center, Bureau of Mines, pi ttsburgh, PA. 
INTRODUCTION 

Since the 19601s, the Bureau of Mines 

has been experimenting with the use of 

holes drilled horizontally in coalbeds to 

remove methane gas ahead of mining. As 

the technology and equipment used have 

become more sophisticated, the average 

length of the holes drilled and thus the 

average gas flow per hole (other factors, 

such as the depth of the coal seam, being 

equal) has increased. 

There has been a concern as to the risk 

of mining into a horizontal hole that 

would bleed large quantities of methane 

(up to 8.5 m3/min or 300 ftJ/min) directly onto the cutting head of a mining machine. Since this would greatly increase 

the probability of an ignition--a totally 

unacceptable risk--a means of plugging 

the methane-drainage holes before minethrough had to be developed. 

In 1976, the first attempt was made to 

plug horizontal methane-drainage holes 

before they were mined through. These 

holes were located at the bottom of the 

Honey Run air shaft, on the property of 

the Federal No. 2 Mine.2 The Honey Run 

holes were plugged3 using a grout made 

from a mixture of cement, fly ash, and a 

f luidifier, known as 1nteraid,4 of a type 

commonly used by grouting companies. All 

holes but one had 381nm (1.5-in) diameter 

polyvinyl chloride (PVC) plastic pipe inserted in them; the longest hole (648 m 

or 2,126 ft) had a 25.4-mm (1-in) metal 

pipe in it. 

To assure pumpability and to prevent 

premature set up of the grout, the grout 

2~ields, H. H., J. Cervik, and T. W. 

Goodman. Degasification and production 

of Natural Gas From an Air Shaft in the 

Pittsburgh Coalbed. BuMines RI 81 7 3, 

1976, 23 pp. 

3~ul, G. N., and J. Cervik. Grouting 

Horizontal Drainage Holes in Coalbeds. 

BuMines RI 8375, 1979, 16 pp. 

4~eference to specific products does 

not imply endorsement by the Bureau of 

~ines. 

designed was high in excess water, consisting of a sack of cement (42.6 kg or 

94 lb) and a sack cf fly ash (34 kg or 

75 lb) added to each 0.057 m3 (15 gal) of 

water used. Into this mix was added 1.1 

kg (2.5 lb) of fluidifier. It was assumed that sufficient pumping times and 

pressures would allow the excess water to 

be squeezed into the fracture system of 

the coalbed and leave the holes full of 

solids. However, in most of the holes a 

layer of water, caused by the separation 

of excess water and solids in the grout, 

built up at the top of the hole. In the 

long hole at Honey Run, the grout was not 

pumped all the way around to the collar 

of the hole, which left sections of the 

hole unplugged. Also, some plugging of 

the grout lines still took place despite 

the precaution of using a thin, fluid 

grout. 

Since the Honey Run shaft project, cement grouts with less excess water and 

larger percentages of fluidifier have 

been used with better results. The use 

of larger diameter (38-mm or 1.5-in) pipe 

has reduced the high friction losses that 

may have been a contributing factor to 

the poor plugging job done on the 648-m 

(2,126-ft) hole at Honey Run. Since 

1977, 381nm 1 in) PVC pipe has been 

used for plugging and in some cases this 

pipe has been installed immediately after 

drilling. However, there have been some 

doubts about the effectiveness of cement 

grouts. When the time came to begin 

planning to plug the seven horizontal 

methane drainage holes in the multipurpose borehole, a Bureau of Mines methanedrainage demonstration installation located in a specially drilled shaft on the 

property of the Eastern Associated Coal 

Corp. Federal No. 2 Mine (fig. 1) ,5 the 

personnel of the Mine Safety and Health 

5~ields, H. H., S. Krickovic, A. Sainato, and M. G. Zabetakis. Degasification 

of Virgin ~ittsburgh Coalbed Through a 

Large Borehole. BuMines RI 7800, 1973, 

27 PP* 
The cooperation and efforts of the Peduti, electrical engineer, Eastern Asmanagement and personnel of the Hayward sociated Coal Corp., and Mr. Robert RuBaker Co. Odenton, MD, and Eastern Asso- bright of Hayward Baker Co. were invaluciated Coal Corp. (Fairview, WV) Federal able. The author would also like to 

No. 2 Mine are greatly appreciated. In thank John Prichard, mechanic, Federal 

particular the efforts of Mr. John No. 2 Mine, for his help in flushing the 

Veitch, resident engineer, and Mr. Frank horizontal holes. 

GROUT DESIGN 

In September 1980, a contract was 

awarded to Hayward Baker of Odenton, MD, 

for the development and emplacement, in 

the horizontal holes at the multipurpose 

borehole, of a sodium silicate grout. 

Hayward Baker had available a setting 

agent, and the major task of development 

was then to tailor the grout for use in 

horizontal methane-drainage holes. 

Sodium silicate is a mixture of sodium 

oxide (Na20) and silicon dioxide (Si02) 

in various proportions (Na20:xSi02). It 

is a solid with a low solubility in hot 

or cold water, but it can be dissolved in 

saturated steam at 517 to 689 kPa (75 to 

100 lb/in2g). Although it can be purchased in many Na20-to-Si02 ratios, the 

most commonly used ratio is Na20:3.22 

Si02. This solid material is then commonly dissolved in steam to give a liquid 

of specific gravity 1.4 (11.67 lblgal) 

and a viscosity of 206 cp.6 This mixture, known variously as a 40 ~e', grade 

40, or type N sodium silicate, was the 

material actually mixed with water in 

the grout tests and in the grouting 

operation. 

6~iamond Shamrock Corp. (Cleveland, 

OH) . Sodium Silicate Handbook. 1979, 

55 PP. 
The requirements for a grout for use in 

horizontal holes are-- 

1. A low shrinkage so that no void 

spaces will form as the grout sets. 

2. A set time long enough to allow 

placement of the grout, generally from 1 

to 8 hr, depending upon allowable pumping 

rates for the grout and hole length. 

3. A low viscosity so that the grout 

can be pumped long distances (150 to 610 

m or 500 to 2,000 ft are typical). 

The material need not have a high compressive strength, but since sodium silicate gels have an inherently low strength 

this was also of concern. 

There were two lines of development 

that could have been pursued. The development effort could have been concentrated on a low-solids grout that would 

be squeezed into the fracture system and 

seal there, but which would shrink in the 

hole; or a high-solids grout that would 

not shrink, but would probably not enter 

the fracture system as easily. The decis ion was made to concentrate upon low 

shrinkage grout. 

It has been common practice in the 

grouting industry to add cement to 

the sodium silicate grout as the solid 

material to reduce shrinkage. However, 

the cement reduces the set time of the 

sodium silicate grout to minutes or even 

seconds. Since this created problems in 

grout placement, the use of cement as an 

additive to the grout was rejected. However, straight sodium silicate gels had 

too high a shrinkage so a compromise between a low-solids and zero-solids grout 

was made and mixes with various quantities of diatomaceous earth were tested. 

The diatomaceous earth acted as a relatively low-cost filler. It had little 

effect upon the viscosity and density of 

the grout and it slightly increased the 

strength of the grout. The addition of 

diatomaceous earth also reduced the set 

time of the grout, but this effect was 

small enough that it was acceptable. 

Figure 2 shows the effect of increasing 

quantities of diatomaceous earth on the 

shrinkage of a particular grout mix. The 

three samples shown in the photograph are 

all of the same mix used to grout the 

horizontal holes. Only the percentage of 

diatomaceous earth has been varied from 

sample to sample. Sample 4C has 2 pct, 

sample 5C, 6 pct, and sample 6C, 10 pct 

diatomaceous earth by weight. 

The mix of sample 5C was the mix finally chosen for use in the horizontal 

holes. The composition of this grout, 

known as Geloc-4, is given in table 1. 

The organic reactant listed in the ingredients is the setting agent and is a 

proprietary material. The TX-100 is a 

surfactant (detergent) that allows an 

easier mixing of the water and the sodium 

silicate. 

TABLE 1. - Composition of sodium silicate grout mix 

used to plug horizontal holes 

NAp Not applicable. 

'~vera~e for the 7 holes. 

2~pecific gravity 1.4; 40 ~e: 

3~olume after being mixed in water. 

Material 

Sodium silicate2.. ... Water................ 

Diatomaceous earth... 

Organic reactant..... 

TX-100 surfactant.... 

Total........... 

Mix design 

wt pct 

40 

49.4 

6.0 

4.5 

.1 

100.0 

Actual mix1 

vol pct 

33.6 

58.3 

3.4 

4.7 

.1 

100.1 

wtpct 

41.1+0.3 

48.12 .2 

5.8 

4.9 

.1 

NAP 

vol pct 

34.6+0.4 

56.8+ .2 

33.3 

5.22 .4 

.1 

NAP 
to adhere to the wall of a hole even after shrinking. It has a viscosity only 

slightly higher than that of water, making it easy to pump. As mixed in the 

laboratory its set time was about 30 min, 

which was marginal for the longest hole 

der the cooler field conditions. The 

compressive strength of the grout was 

also quite high for sodium silicate mixtures, as can be seen from figure 3 

where the grout easily supports the 

weight of a pencil placed in it. 

GROUTING METHOD 

It was initially planned to pour grout 

down one of the 1021nm (4-in) diameter 

steel lines originally used to pipe gas 

from the bottom of the shaft to the surface, to a high-pressure hose at the bottom of the shaft. A union would then 

be used to connect the hose to a grout 

header that was in turn connected to mechanical compression packers that were 

part of the gas piping system. Highpressure valves were to be used on each 

side of the union to allow the flow of 

grout to be shut off after a hole was 

filled. It was necessary to plan for the 

use of 12.7-mm (0.5-in) diameter grout 

pipe in the holes because the 32m 

(1.25-in) ID pipe of the packers (fig. 4) 

in the 76-mm (3-in) holes would not allow 

the passage of the coupling of any pipe 

larger than 12.7 mm (0.5 in). 

This was a compromise from the 19- 

(0.75-in) pipe recommended by Hayward 

Baker. It meant that friction losses in 

the pipe while pumping grout at the 

planned rates of 3.6 to 4.5 m3/hr (16-20 

gallmin) would be very high. Had the use 

of a cement grout been planned, the friction losses would have been too high to 

allow the use of 12.7-mm (0.5-in) pipe. 

To decrease the friction losses, the direction of grout flow was changed from 
FIGURE 3. - Grout mix 5C with 6 pct diatomaceous earth, 6 days after mixing. 

PLUGGING 

PREPARATION 

Preparations for grouting the horizontal holes were begun early in September 

1980. One of the two 102- (4-in) steel 

gas-flow lines from the bottom of the 

shaft to the surface was disconnected 

from the receiver tank underground, and 

from the 152m (6-in) gasline on the 

surface, to allow BQ wireline drill rod 

to be run inside it by personnel from the 

Federal No. 2 Mine. The drill (46m or 

1.812-in ID) rod was used to carry the 

grout instead of the 102m (4-in) pipe, 

in order to decrease the amount of grout 

stored in the vertical line at any time. 

Had a smaller pipe been readily available, it would have been used rather than 

the BQ pipe. 

g 

the actual grouting operation, the highpressure hose was connected to the side 

line as shown in figure 5, and the 12.7- 

mm (0.5-in) plastic pipe in the hole was 

the gas and water return line. 

OPERATIONS 

During the week of September 29, 1980, 

12.7- (0.5-in) ID schedule 40 PVC pipe 

was inserted into the horizontal holes. 

Although the holes had been drilled over 

8 yr earlier (May-July 1972), the pipe 

was run into holes 1, 4, 6, and 8 with 

few difficulties (fig. 8). Some tight 

spots were encountered in hole 2, caused 

by loose coal in the hole at about 180 to 

198 m (600-650 ft) from the collar of the 

hole. The pipe had to be worked through 

the tight areas by repeatedly pulling it 

out several meters and then shoving it 

back in forcefully. It was later discovered that this pipe had broken, five 

joints (15 m or 50 ft) from the far end, 

probably owing to the harsh treatment 

given it while working it to the back 

of the hole. Pipe counts while running 
A High-pressure hose 

B Vert~caline pressure gage 

C Greasef~tt~ng 

D 1 3-cm(b2-in) valve 

E Control valve (high pressure) 

F 5-to 2.5-cm (2-to I-in) reducer 

G Quick d~sconnect flttlngs 

H Hole pressure gage 

1 Hole shut In valve 

J 5-cm(Z-in) tee 

K All threod 13-cm (I/2-in) nipple 

B L Bushing w~th threads chased 

M 1.3-cm (b2-in) PVC threod to socket adapt 

N Grout return polnt 

0 7.6-crn (3-in) packer 

P Packer rubber 

Q 7.6-cm (3-~n) horizontal hole 

PLAN VIEW R 1.3-cm(l/2-1n) PVC plpe 

- Grout path 

FIGURE 5. - Schematic of method used to plug horizontal holes. 
FIGURE 6. - Water flushing of hole 2. 

the pipe also made it appear that the 

pipe in hole 7 had been separated, but 

when the pipe was removed from the hole 

later it was found to be intact and 

was re-inserted without difficulty. The 

greatest problems were encountered in 

inserting pipe in hole 5. In the initial 

attempts pipe could not be pushed past a 

depth of 47 m (155 ft). 

In mid-October 1980, a crew with a 

hand-held air drill worked to clean out 

hole 5. The original records from 1972 

indicated that the hole had been drilled 

into roof rock at 42 to 45 m (140-148 ft) 

and had been terminated at 47 m (155 ft). 

The hole had then been sidetracked at 21 

to 34 m (70-110 ft). It appeared that 

the PVC pipe had entered the sidetrack. 

During the cleanout operation, the drill 

pipe followed the main hole and had no 

difficulty in reaching the end of the 

hole at 152 m (500 ft). The PVC pipe, 

however, still followed the sidetrack. 

To finally get the PVC pipe past the 

sidetrack, it was necessary to thread it 

through the drill pipe. After this was 

done, the PVC ran freely to the end of 

the hole. When hole 5 was mined through 

(fig. 8, locations L and M) it was found 

that the hole had actually been sidetracked twice, but since mining advanced 

only 29 m (94 ft) from the collar of the 

hole, it was not possible to confirm 

the lengths of the sidetracks or determine which sidetrack the PVC pipe had 

entered. In 1982 an area south of location L (fig. 8) was mined but hole 5 

could not be found, possibly because it 

had been drilled in roof rock. 

The final preparations for grouting 

were made on November 5 and 12. On November 5, hole 2 was flushed out with water by connecting a surface line to the 

BQ rod and using a hose to connect the BQ 
in background. 

rod to the 12.71nm (0.5-in) PVC pipe underground (figs. 6 and 7). Water was 

then circulated in the hole through the 

12.7- (0.5-in) PVC pipe and out the 

annulus of the hole, to the floor of the 

shaft. 

Hole 2 was flushed on November 5 because of the five joints of pipe that had 

broken free. [This was determined by inspection of the hole in 9 Right (fig. 8, 

location A) where the hole had been mined 

through inadvertently in April 1980. ] 

After the five broken joints had been removed, it was found that pipe could be 

pulled out but not pushed in. The hole 

was flushed on November 5 in an attempt 

to clean out broken coal, which was assumed to be wedging the pipe in the hole. 

The attempt was unsuccessful and hole 2 

was later grouted with the back 15 m (50 

ft) of hole having no pipe in it. 

g ppy 

each hole, just before each was flushed 

with water. No broken pipe was found in 

any other hole. 

The rest of the holes were flushed with 

water on November 12 in the same manner 

as hole 2 was flushed, with the exception 

that a 1521nm (6-in) vent tube was placed 

at the return line of each hole to carry 

gas coming from the holes to the shaft 

air exhaust line. All of the other six 

holes were flushed uneventfully and with 

little return of solid material, except 

hole 4. 

In hole 4, which was producing between 

60 and 80 pct of the gas being drained 

from the shaft in the last few months, 

large quantities of coal were seen in the 

form of dust and small lumps. In addition, flakes of calcite, similar to those 

seen in hole 2 when it was accidentally 

cut into in April 1980 (fig. 9), were observed in the returning water. [In hole 
FIGURE 10, - Three-compartment tank truck at multipurpose borehole site, 
FIGURE 11. - Grout pumping and metering equipment. 
6 

B 

2 

1229-1305 hr 

11/13/80 

600 

400 Total volume, 

159m!(419 gal) 

20 40 60 

1158-1245 hr 11/14/80 E 

11/14/80 \ 

80 g 

V) 

0 20 40 60 0 20 40 60° 

TIME, mln 

8... 

TIME, rnin 

'~ssumes a grout pumping rate of 3.5'0.17 m3/hr (15.75'0.75 gallmin) and '0.5 min 

accuracy in determining the time of grout return. 

2~ncludes a sidetrack assumed to be 15 m (50 ft) long. 

KEY 

o Vertlcal line pressure 

A Hole pressure 

62 Grout return (hole stui in 

with~n 2 minl 

3.40 

H Control valve opened 

Pumping at surface 

Hole valve open 

2.62 

FIGURE 12. - Pressure curves and grouting records of horizontal holes. Activity times are expressed 

on the basis of a 24-hr clock. 

693 

169.5 

556 

17 

.77 

204 1.01 

40 

268 

82 
As the grout returned through the much 

smaller 12.71nm (0.5-in) PVC pipe, the 

hole pressure rapidly increased, primarily because of the pressure drop in the 

PVC pipe. Once the grout had returned, 

the control valve was gradually opened 

and the hole and vertical line pressures 

equalized. Grout was also poured on the 

floor of the borehole for 1 to 2 min after returns were obtained in order to remove any water-contaminated grout before 

the hole was shut in. 

Pumping was usually continued until a 

grout volume of 2.5 times the calculated 

hole volume had been pumped. At that 

time, mixing of grout at the surface was 

discontinued and the grout remaining in 

the BQ pipe was allowed to flow into the 

hole until the hole pressure dropped to 

around 345 to 480 kPa (50-70 lb/in2g). 

The hole was then shut in and preparations were made to move to the next hole. 

This technique evolved during the grouting operation, and it can be seen that 

the pressure-flow curves for holes 5, 6, 

7, and 8 (fig. 12) do not match this description exactly. 

Hole 6 was the first hole grouted. 

While grouting this hole it was found 

that no definite endpoint existed at 

which a hole would no longer accept 

grout, or at which the pumping pressure 

would rapidly increase. The grouting 

operation was shut down relatively early 

in hole 6, but because of the uncertainty 

in the condition of the grout in the 

holes, larger volumes were pumped into 

the other holes. 

Grout was pumped into hole 8 in two 

separate stages because the initial diatomaceous earth-water mixture was used up 

and more had to be mixed in the surface 

tanks before more grout could be mixed 

and pumped. It should be noted that 

grout was still flowing into hole 8 under 

relatively low pressure (270 to 760 kPa 

or 40 to 110 lb/inZg) at between 60 and 

80 min elapsed time even though the set 

time of the grout was about 55 to 65 min. 

(This was partially because the grout 

mixing was done at temperatures just 

above freezing, which slowed the setting 

reaction.) Much of the previously set-up 

grout may have been either in the fracture system of the coalbed or coating the 

walls of the hole, but not blocking the 

hole. The continuous mixing method used 

may have allowed grout to be pumped in 

the hole long after the set-up time of 

the first grout pumped had passed. Recent work by Bader, and Krizek, and Baker7 suggests that sodium silicate grouts 

may not completely set up as long as they 

are kept in motion. They report increases in set time, during pumping, of 

from 2 to 7 times as compared with samples not kept in motion. 

Holes 6, 8, and 7 were grouted (in that 

order) on November 13. On November 14 

the remaining four holes were completed 

and owing to the experience gained on the 

previous day, the methods used were much 

more uniform. Once all of the equipment 

and personnel were in place and ready, ,it 

was possible to grout a 150-m (500-ft) 

hole in about 30 min. The changeover to 

the next hole required about 5 min. 

RESULTS 

On November 19, shortly after the holes 

were grouted, a trip was made to the Federal No. 2 Mine to inspect hole 2 where 

it had been mined through in April 1980 

(fig. 8, location A). A packer had been 

inserted to seal the hole just before the 

grouting operation was begun. When the 

valve on this packer was opened, the hole 

was found to have some pressure in it and 

some wet grout was forced out of the hole 

(fig. 13). With the valve shut, pressures of 41 kPa (6 1b/inzg) built up in 

10 min, but there was little flow of gas 

and no water flow from the hole. 

Hole 1 was the first hole to be mined 

through (fig. 8, locations B and C), 

7~ader, T. A, R. J. Krizek, and W. H. 

Baker. Injection and ~istribution of 

Silicate Grout in Sand. Proceedings of 

the Conference on routing in Geotechnical Engineering. Am. Soc. Civil Eng., 

New York, 1982, pp. 540-563. 
FiGURE 13. - Hole 2 five days after being 

grouted, location A (fig. 8), Note wet grout in 

the valve. 

on February 5, 1981. Hole 2 was mined 

through (fig. 8, locations D, E, and F) 

in several locations between February 5 

and 18. 

Figures 14 and 15 are photographs of 

hole 1, taken on February 18, 1981, looking respectively away from and toward the 

shaft (fig. 8, locations B and C). The 

grout appeared to be in good condition, 

and no void spaces were noted in the 

hole. The condition of hole 2 in the locations where it was inspected was similar. At location G (fig. 8) grout was 

also observed in the fracture system of 

the coalbed about 0.6 m (2 ft) from hole 

1. Figure 16 is a photograph of the 

gp, 

outby rib was observed (location J) there 

appeared to be little or no void space in 

the grout there. There was also a film 

of water flowing from the outby sides of 

the holes, but no water flow from the inby sides. Hole 7 was inspected at location K (fig. 8), and the condition there 

was found to be similar to that of holes 

8 and 8P. 

The most important observation was that 

there was no gas flowing from any of 

the holes, on either rib. These observations indicate that, when wet (in unmined 

coal), the grout maintains its initial 

volume and acts as a seal to prevent gas 

flow. The grout does not appear to stop 

water flow, but this may actually be an 

8~odium silicate grouts are a milky 

white color, but the diatomaceous earth 

added to the grout made it a beige or tan 

color. Once exposed to air, the grout 

dries to an off-white color that makes it 

difficult to distinguish it from rock 

dust. 
FIGURE 15. - Hole 1, view toward the borehole at location C (fig. 8). 
FIGURE 16. - Grout film in the coal cleat near hole 1. 

advantage since the water flow appears to 

prevent the grout from drying out. As 

the grout dries, it becomes a chalky, 

low-density material which shrinks and 

loses its ability to prevent gas from 

flowing. However, the likely places for 

drying and shrinking to take place are in 

already isolated blocks of coal, which 

peared that the volume of grout in the 

holes inspected on March 3 had decreased. 

On the virgin (and usually wet) rib, water flow was observed from all of the 

holes (fig. 8, locations B, D, J, K, and 

L). No gas flow was observed either from 

holes on the ribs on the isolated pillars 

or from holes on virgin ribs, even in 

places where gas and water could be seen 

and heard flowing from the rib itself. 
FIGURE 18. - Hole 8, same location as figure 17. FIGURE 19. - Hole 8P, same location as figure 17. 

A final inspection of the holes was points using mine spad and steel tape 

made on June 17, 1982, after mining had surveys. Hole 4 was found at only one 

progressed sufficiently to cut through location. Hole 5 could not be located in 

the far ends of most of the holes. Dur- either of two anticipated locations, afing this inspection trip, each of holes ter passing through a 73- (240-ft) bar1, 6, 7, and 8 was located at least two rier pillar. The June 1982 inspection 
confirmed the results of the 1981 inspec- the inspected portions of the holes were 

tions. Grout in the holes remained sol- in pillars isolated by mining from virgin 

id, without voids, and no gas flow was coal, no seepage of water was observed 

observed from the holes. Since most of from the holes. 

COSTS 

On a unit volume basis, the contractor 

costs for placing the grout averaged 

$1,490 per cubic meter ($5.65 per gallon) in 1980 dollars. This includes the 

contractor's labor, equipment, and cost 

of the materials used. Table 3 gives the 

material costs. These costs were for an 

experimental procedure. If this type of 

grouting was done on a routine basis, it 

is possible that the unit cost could be 

reduced. 

TABLE 3. - Grout costs1 

Along with the contractor costs there 

were additional personnel costs for 

grouting preparations and for the actual 

grouting operation. Because a close accounting of this time was not kept and 

because some of the actual time was spent 

in what were essentially research activities, no attempt has been made to determine the actual hours. Instead, an estimate has been made of the number of hours 

required to perform a particular operation, under normal conditions, on a 150- 

(500-ft) hole. These estimated times are 

as follows, in hours: Insertion of plasMaterial I Unit I Amount tic pipe in a hole, 1.5 hr; assembly and 

actant, and surfac- grouting a hole, 1.0 hr. These times are 

tant. .. .4,156.7 gal.. 1 $1.50 1 $6,235.05 based upon the use of a two- or threeSodium silicate, reDiatomaceousearth I I person crew working underground (an encost hookup of a grout header, 1.0 hr; flushing of a hole with water, 1.0 hr; and 

2,400 lb.. 

Total material cost. 

NAp Not applicable. 'in 1980 dollars. 

Overhead. . . . . .l5 pct . . Total.. . . . . . . . . . . 

The material cost for the sodium silicate grout, not including overhead 

charges, was $425 per cubic meter ($1.61 

per gallon). This compares to a cost for 

a cement grout (42 kg or 94 lb cement, 

0.019 m3 or 5 gal of water, and 0.91 kg 

or 2 lb of fluidifier) of $310 per cubic 

meter ($1.17 per gallon) (assuming $5.00 

per sack of cement and $1.98 per kilogram 

of fluidifier). 

.I75 

NAp 

This direct comparison is somewhat misleading, however, since the sodium silicate grout has a greater tendency to enter the coalbed. It may require two or 

three times as much sodium silicate as 

cement grout to fill a hole. Additional 

costs are also incurred with the use of 

sodium silicate for special services and 

equipment, not necessary in cement grouting, to mix and pump the grout. 

441.00 gineer or supervisor and one or two 

6,676.05 laborers). 

NAp 

NAP Since the work was also done from the 

bottom of a shaft, additional personnel 

had to be kept on surface at all times. 

These included the hoistman, a topman for 

safety, and a fireboss, who was occasionally used underground as an additional 

laborer when needed. Therefore, every 

hour worked on the holes required 2 or 3 

employee-hours of labor by underground 

personnel and 3 employee-hours by surface 

personnel. It is possible that the size 

of the underground crew could be cut to 

two persons for all but the grouting 

operation, with only a slight loss of efficiency. The flushing operation was 

performed in 1 day by an engineer and the 

fireboss. The surface crew at that time 

consisted of the hoistman and a topman. 

However, during the grouting operation it 

is recommended that a three-person crew 

be used in order to avoid slowups and 

confusion. 

1,001.41 

7,677.46 
DISCUSSION 

Table 2 shows the total volumes of 

grout pumped into each hole and gives an 

estimate of the quantity of grout required to fill a hole. The total quantity pumped was determined by meters on 

Hayward Baker's pumps. Corrections were 

also made for grout stored in the vertical line or grout added from the vertical 

line. This value is probably accurate to 

k0.04 m3 (10 gal). The volume required 

to fill a hole was estimated from the 

time required to obtain grout returns 

and a steady pumping rate estimated by 

Hayward-Baker. The estimated pumping 

rate was 4.3 m3/hr (15.75 gallmin). 

Again corrections were made for grout 

stored or left in the line during the 

period measured. The flow rate measured 

by Hayward Baker is probably accurate to 

'5 pct, and the time measurement is accurate to within '0.5 min. 

The measured quantities of grout 

pumped, to the time of grout return, appear to have been close to the hole volumes except in the cases of holes 4, 7, 

and 8. In all cases the quantitites were 

larger than the estimated hole volumes. 

For each of holes 4, 7, and 8, the overruns were around 35 pct. It would have 

been reasonable to expect a higher overrun in the grout volume required to fill 

hole 8, since some grout could have 

flowed to hole 8P, but the overrun was no 

higher for that hole than for 4 or 7. 

This indicates that grout did not begin 

to migrate to hole 8P until the pressure 

in hole 8 began to rise. A 35-pct overrun, however, is not particularly high so 

it appears that the volumes of sodium 

silicate grout required to fill a hole 

can normally be expected to be close to 

the hole volume. This can probably be 

attributed to the low pressure actually 

required to pump the grout into a hole. 

From the lower pressure curves in figure 12, it can be seen that the maximum 

pressures required were 100 kPa (15 lb/ 

in2g). Once the hole pressures reached 

550 to 830 kPa (80-120 lb/inZg), large 

quantities of grout began to enter the 

coalbed. In contrast, the pressure required to obtain returns of cement grouts 

in a 3003 (1,000-ft) hole are typically 

600 to 900 kPa (90-130 1b/inzg), and 

pressures up to 3,500 kPa (500 lb/inZg) 

have been used in an attempt to force the 

excess water in the cement grouts into 

the coalbed. Sodium silicate grouts, 

because of their low viscosity, appear to 

require much lower pressures in order to 

fill a hole, and once pressures of 400 

kPa (60 1b/inzg) are reached, grout will 

begin to enter the coalbed. 

Volumes of grout between 1.85 and 3.4 

times the holes volume were pumped into 

the holes. The largest quantity was 

pumped into hole 8 and a large portion of 

this, 0.36 of the hole volume, went to 

fill hole 8P. As mentioned earlier the 

actual volumes required to obtain returns 

were never more than 1.35 times the hole 

volumes. In the case where only 1.85 

times the hole volume was pumped, hole 6, 

the hole was still found to be full upon 

interception by mining. To insure that 

holes are filled, it appears that between 

1.5 and 2.0 hole volumes of grout would 

typically be sufficient. The only question remaining is whether the grout in 

the hole or the grout in the cleat stops 

the flow of gas.9 There was some evidence for both mechanisms, but the evidence was not convincing or strong for 

either. Because the hole must be filled 

in any case, there would only be a cost 

saving from reduced material costs if excess grout volumes over the hole volume 

were not required. 

9~lobod, R. I,. , and E. J. Burcik. 

Method of Sealing Coal Against Methane 

Emission. U.S. Pat. 3,845,632, Nov. 5, 

1974. 
CONCLUSIONS 

From the results of the plugging and 

mine through of the holes at the multipurpose borehole it can be seen that 

sodium silicate grouts can be very effective in plugging horizontal methane 

drainage holes. It also appears that sodium silicate can be pumped past blocked 

or partially collapsed portions of a hole 

to fill those areas that cements may not 

be able to enter. However, there are a 

number of problems and questions remaining in the use of this material: 

1. The cost of the grout. 

2. The cost of placement of the grout. 

3. The short set-up times. 

4. The proprietary nature of the 

material. 

5. The lack of understanding of the 

grout's mode of action. 

Although the cost estimates for portland cement and sodium silicate grouts 

given in this report are nearly equal, it 

should be remembered that the portland 

cement costs are inflated by the use of 

the large quantities of fluidifiers required to fill a long hole, which may not 

be needed in short holes. Also, as used 

in the multipurpose borehole, 2.5 times 

the estimated hole volume of sodium silicate grout was required, while probably 

no more than 1.5 times the estimated hole 

volume of cement would be required. Further research may show that less sodium 

silicate is required, but at present the 

probability of higher sodium silicate 

grout material costs must be a serious 

consideration. 

personnel trained in their use. Most 

mine personnel are also at least familiar 

with portland cements and their properties. It then requires more complicated 

equipment and greater expertise to use 

sodium silicate than cement, all resulting in higher costs. 

Another major difficulty with sodium 

silicates is their short set-up times. 

The grout designed for this project had a 

nominal set-up time of 25 to 30 min in 

laboratory tests. The actual set-up time 

in the field was 55 to 65 min. 

These short set-up times make it difficult to grout the 300- to 600- (1,000- 

to 2,0004 t) long holes that are being 

more frequently drilled. Portland cements, on the other hand, can be designed 

with set-up times of 4 to 8 hr (although 

with their higher viscosities and consequently slower pumping rates, the advantage is not quite as great as at first 

glance). However, recent work cited earlier in this report indicates that sodium 

silicates may actually have very long set 

times while being pumped. If this is the 

case, then sodium silicates may actually 

have an advantage over cements in this 

respect. 

At present the only sodium silicate 

that has been proven effective is the 

grout mix shown in table 1. The setting 

agent is a material proprietary to Hayward Baker. Although other companies may 

have equally effective grouts, only experiment and testing will determine which 

grouts are applicable. In the meantime a 

lack of competition or local availability 

may make the use of sodium silicates more 

expensive. 

The costs of placing the sodium sili- Finally, the lack of knowledge as to 

cate are also likely to be much higher. the true mode of action of the grout 

Sodium silicate must be pumped as sepa- makes it necessary to use larger quantirate components, in carefully measured ties of grout to insure that the operaquantities, before mixing. This requires tion is effective. 

the use of several accurate pumps and