Documents
Resources
Learning Center
Upload
Plans & pricing Sign in
Sign Out

MINING GROUTING a rational approach

VIEWS: 140 PAGES: 15

									                      MINING GROUTING: a rational approach

                                         W F Heinz1

Abstract:
Mining grouting in South Africa has always been associated with deep mines.
Certain techniques and equipment used are a result of the very high pressures
resulting from the large depths of South African Mines.
Some of the techniques specifically developed within the South African mining
environment are

1.      Precementation of deep shafts up to 2400m.
2.      Cover grouting to develop or sink under or through rock formations in safety.
3.      The successful impermeabilisation of rock masses with „thin, unstable”
        cement grouts.
4.      The conveyance of cement-sand slurries over many kilometres.

“Grouting is more an art than an engineering science”. This statement may be true
but in essence it has always been an admission of our lack of understanding of the
success of grouting. In recent years cement and chemical grouting have developed a
new dynamism driven by a better understanding of the grouting process, by an
improved understanding of the behaviour of grouting materials, by the development
of new grouting materials (micro fine cements) and techniques (jet grouting) and, of
course, by many new good publications (books and articles) and research on the
subject. Other factors such as environmental concerns and computers have also
contributed to this new dynamism in the grouting field.

  Many of these developments have been initiated in the civil engineering field such
as dam grouting, tunnelling, etc.; grouting in underground mining conditions is
conspicuously absent in research, development and literature. This paper presents the
development over many years and the State-of-the-Art of South African mining
grouting and endeavours to present a more rational evaluation and appreciation of
the achievements of the early grouting engineers. It also presents a more rational
approach in grouting particularly for mining conditions, keeping in mind recent
developments in grouting engineering and possible developments in future.

1. INTRODUCTION

About 50% of the world‟s gold has been mined in South Africa over the previous
century. Gold production was first recorded in 1871 in the Northern Transvaal. The

1
 Chairman, Rodio South Africa Pty Ltd., P O Box 714, Halfway House, 1685, South Africa.
Email: rodio@rodio.co.za



                                               1
Witwatersrand Basin, the richest gold field in the world, was discovered in 1886 near
Johannesburg.

However, the South African gold mining industry has been declining steadily in
recent years. In 1910 gold production was 234.25 tons. In 1970 South Africa
produced 1000.4 tons of gold which was approximately 80% of the entire world
production, during 2002 South Africa produced slightly less than 400 tons which was
approximately 25% of the world production.

Mining was originally confined to a 70km belt along the reef outcrops of the
Witwatersrand basin. Today gold is mined up to 4,000m below surface. ERPM in the
East Rand passed the 3,000m mark 45 years ago and reached a world record of
3,428m below surface in 1959. At present investigations are underway to evaluate
the exploitation of ultra-deep ore bodies down to 5,000m below surface.

By necessity the access shafts have been extended deeper and deeper. During the
early 60‟s, 2,000m was thought to be the maximum depth of a shaft. In the 90‟s the
length of the winch was extended to 3,000m; Western Areas South Deep Shaft is
currently the deepest shaft in the world at 2,994m.

The problems associated with deep gold mines have resulted in extraordinary
achievements. The extreme heat (rock temperature up to 60°C) and pressure
encountered at depth, the hardness of the rock, the ever-present underground water,
gases (methane and hydrogen sulphide) etc. all required innovative solutions.

Grouting using mainly cement slurries was introduced at a relatively early stage in
the development of the gold field; without the cementation technique the enormous
development of the Gold Mining Industry would probably never have taken place.

2. HISTORICAL BACKGROUND

Cementation or mining grouting developed during the previous century. Innovation
and development was driven by the economic upswing of the coal and gold mining
industries during the beginning of the 20th century and technical problems related to
mining.

The contributions of South African mining engineers in the field of grouting in
mining and construction has been greatly underestimated.

Mining cementation relates mainly to two fields: shaft sinking and underground
cementation for water control and sometimes strength improvements.

Some of the first precementation work was executed by Portier in France in 1864,
however, the South African cementation techniques are closely related to the name
Albert Francois, a brilliant Belgian mining engineer.

Francois developed his cementation process in 1896 for the purpose of shaft sinking.
However, Francois‟ most important contribution was the invention of a high pressure



                                         2
cementation pump (see Fig. 1) and the realization that cement at high pressures (up
to 5,000 lb/sq inch, 350 kg/cm²) can be introduced into the minutest fissures in rock
formations. The process was first brought to England in 1911 and was applied at the
Hatfield Colliery in Yorkshire. Subsequently the Francois Cementation Process was
applied with great success in many English collieries particularly in Yorkshire and
the Midlands in the years following WWI (World War I).

Francois‟ involvement on the South African gold fields commenced in 1917. In 1914
Francois offered his services to a Johannesburg mining house but it was only two
years later when significant water inrushes occurred (4,500,000 gal/day,
20,457m³/day) at ERPM that Francois was requested to assist. At ERPM 26 th cross
cut south, water was struck and in the 30 level west drive, water was encountered
unexpectedly at high pressure. (Krynauw, 1918). The Francois Cementation Process
was successful. The same process was used to create a grout curtain underneath an
arch dam in the Mazoe Valley, Rhodesia in 1918; again the process proved
successful.




In 1917 the Francois Cementation Syndicate was formed; two years later this was
changed to the Francois Cementation Company (Africa) Ltd as a wholly owned
subsidiary of the parent company in the UK. Today the company still operates
successfully as Cementation-Skanska.

By the end of 1918, the Francois Cementation Process was well established; the
following projects had been completed successfully: Comet Deep (ERPM), 26 th cross
cut, 30th level West Angelo Deep 28 th West Dam, 29th West Cross cut; Geduld
Proprietary Mine Ltd: 2 nd and 3rd level South, 4th level South Drive; Daggafontein
Mine No 2 Shaft and No 4 Shaft, Brakpan Mines. In addition the Rand Water Board
Pumping Station and the Mazoe Dam in Southern Rhodesia were successfully
grouted and repaired with this process.

The Francois Cementation process was described by Krynauw (1918), who worked
closely with Albert Francois during 1917, as follows:



                                         3
“An essential condition in the introduction of cement into fissures and cracks is that
the injection should be done under a considerable pressure, the object being, firstly,
to overcome the contra pressure of water present in the fissure; secondly, for the
purpose of forcing the cement as far as possible into the minute cracks, and, thirdly,
for the purpose of squeezing out the superfluous water from the cavity which is being
filled with cement pulp, and thus leave the cement in a condition most suitable for its
rapid and efficient setting.”

After the discovery of the Witwatersrand Goldfields, it was soon realized and
verified that the gold bearing reefs continued below the water bearing dolomites. In
1910 the West Rand Estates Ltd located a shaft site commonly known as Pullinger
near the centre of the Venterspost mining area. It was a circular shaft; sinking began
in 1910, the shaft was lined with German Haniel and Lueg‟s cast iron tubbing and
was abandoned in 1911 at a depth of 97ft (29.5m) as two of the most modern electric
pumps at the time could not cope with the inrushes of 208 000 gal/hour (946m³/hour)
and several mud rushes.

Subsequent applications which successfully established the Francois Cementation
process for shaft sinking in South Africa were the sinking of Daggafontein Mines
(no. 2), West Springs No. 1 and two circular shafts at the Brakpan Mines. At
Vogelstruisbult GM in 1934 the cementation process was significantly improved by
using more modern drilling methods.

During earlier cementation projects at Daggafontein and West Springs long diamond
drilling holes up to 200ft (61m) were drilled. The holes were drilled inclined,
eighteen holes were drilled for a 45ft by 8ft shaft. At Vogelstruisbult GM for the first
time percussion equipment was used to drill the cementation holes. At Venterspost
this method was further improved to drill 40ft (12m) cementation cover holes to
allow a 30ft (9m) advance.

However, a milestone was achieved by sinking Shafts No. 1 and No. 2 at the
Venterspost Gold Mining Company. After the failure of the Pullinger shaft in 1911 it
was decided in 1934 to use cementation for sinking the new shaft in the vicinity.
Cementation work at Venterspost was divided into three phases (Allen and Crawhall,
1937/38):

    a) “The pre-treatment of fissured dolomite free from decomposition.
    b) The stabilisation of sand and wad deposits occurring in the upper zones of
       the dolomite.
    c) The correction of errors arising from insufficiently intensive ground
       preparation.”

The sinking of these two shafts was remarkable for several reasons:

   1. For the first time it was shown that the cementation process was successful
      under the most hazardous conditions where previous attempts had failed such
      as sinking through dolomite AND



                                           4
   2. For the first time a shaft was sunk through “Wad” (hydrated manganese
      oxide), which is low in density, highly compressible and, except for the
      absence of fibres, not unlike peat and often water logged. Wad occurs in large
      horizons in the upper strata in dolomite. In some zones it was necessary to
      place a concrete mat 2 to 4 ft in thickness to be able to effectively treat this
      material. The cementation process for this material was what would today be
      termed a combination of the “Soil-Frac” method and compaction grouting.
      Crawhall states that: “the muds have proved themselves amenable to
      cementation, and the effect of injections is to squeeze the soft ground near the
      shaft into such a compact condition that it is impervious to the vast volume of
      water impounded in similar ground outside the immediate area of the shaft.
      This produces a stable enough condition to permit excavation. More usually the
      cement builds up in ever thickening layers from some plane of weakness, but is
      also found to cut through the mud dividing it into innumerable compartments
      separated by films of cement.”

In parallel to these important advances in the mining grouting field, civil engineering
cementation advanced rapidly driven by the great dam building era in Europe,
particularly in Switzerland, Italy and Spain.

Several geotechnical companies specializing in cementation works were founded
during this era; timeously for the purpose of entering the great era of dam and tunnel
construction.

During the 20 years leading up to WW II, many important innovations and new
grouting techniques were developed. The now well established Lugeon water test
was developed by Maurice Lugeon (Lugeon 1933), the tube-à-manchette was
invented, the split spacing technique became common place. The Hoover Dam
(Simmonds, 1953) with its specific grouting problems also contributed significantly
to this field. The essential elements of present day dam grouting techniques had been
developed by the end of the thirties.

By 1946 batching plants had been developed, producing large volumes of high
quality cement slurries for dam grouting activities such as grout curtains and rock
consolidation e.g. at Mattmark (Blatter, 1961)

In the early phases of development of the Orange Free State Goldfields (OFS
Goldfields) during the fifties, civil engineering grouting techniques developed for
dams, tunnels and foundations were applied successfully in the mining field.

Now for the first time, civil engineering grouting methods were applied with effort to
mining engineering problems. The most notable techniques introduced were high
speed, high shear mixing of cement grouts, the use of packers at large depths,
improved grouting pumps and mixers, high volume automatic batching plants, more
advanced control and monitoring equipment but possibly most importantly the
introduction of grouts with higher densities i.e. smaller w:c ratios.




                                           5
The Orange Free State Goldfields were discovered in 1938. Development was
interrupted by WW II but expansion continued rapidly after the war. During some
years in the fifties, more than 30 deep shafts were at various stages of development
in South Africa. At present (2003) shafts and mines are being closed and the OFS
goldfield has been reduced to a few shafts only.

While the underground cementation process had matured by the fifties, pregrouting
of deep shafts received a new impetus during the development of the OFS goldfields.
Some notable precementation work was executed at Harmony (Newman, 1956),
President Brand (Mudd, 1959), FSG, Western Deep levels (1960), Hartebeestfontein
and Buffelsfontein.

The precementation at Buffelsfontein in 1961 was the first precementation executed
by utilizing large automated batching plants using high speed/high shear mixing,
“thicker” mixes and packers at depth.

3. SHAFT SINKING
In the shaft sinking context grouting is applied to:

       a) Pregrouting or precementation of shafts
       b) Cover grouting during shaft sinking

Sometimes a shallow grout curtain is constructed around the shaft collar. As this
would require a typical dam grouting technique, we disregard this application for the
purpose of this paper.

a) Pregrouting or precementation of shafts

Pregrouting or precementation of deep shafts prior to sinking has been applied in
South Africa since the fifties, with considerable success. Geological and
geohydrological considerations are decisive parameters determining success or
failure of a precementation, indeed its desirability, economically and otherwise. The
following information and data is required:

1) Comprehensive and exhaustive collection of geological information and data
   relevant to the project. In particular
   a) Geological data, logs of all boreholes at the site and in the vicinity of the
       project
   b) Aerial photographs and magnetic surveys to detect possible faults and dykes,
       infrared photography in dolomitic terrain.
   c) Analysis of prominent joints and fissure patterns.
   d) Compilation of information on water: water tables (perched), quality,
       direction and flow of water.

2) Characteristics and values of the in situ stress filed.
   a) Hydrofracturing data which will provide direction and value of stresses.
   b) Determination of hydrofracturing stresses and possibly determining of similar
      values for existing fractures, weak joints etc.



                                            6
Benefits of pregrouting of shafts can be summarised as follows:

1) It increases the safety of the sinking operation.
2) It minimizes the inflow of water and gas;
3) It minimizes the time lost due to additional grouting operations (cover grouting)
   during sinking and hence minimizes standing time of costly shaft sinking crews
   and equipment;
4) It provides improved rock strength for excavations in the immediate vicinity of
   the shaft area (grouted fissures have been found up to 60m from the pregrouted
   shaft);
5) It provides detailed information of the geology of the proposed shaft site and
   possibly information on ore grades in the shaft vicinity;
6) It reduces the number of intermediate underground grout stations during shaft
   sinking operations.
7) It allows the mine to start mining earlier in some cases several months, which
   should result in earlier positive cash flow from mining operations.
8) Ideally pregrouting is done outside the shaft perimeter with no interference
   between the sinking teams and the pregrouting teams or contractor.
9) Shaft sinking is an expensive operation, hence time allowed for supporting
   activities such as grouting during sinking operations though critical, are often
   curtailed to the detriment of the final result. Pregrouting minimizes this
   possibility.

Pregrouting can be done before sinking commences or during sinking. If done during
shaft sinking the pregrouting holes should lead the sinking operation by several
hundred metres.

Grouting Pressure

During recent years much progress has been made in determining allowable grouting
pressures for shaft pregrouting projects.

The role of fluids and slurries in fracture propagation has been researched intensively
in recent years.
The most significant contributions in this field result from oil and gas fields
development (Cleary, 1997). The production of oil and gas fields is enhanced by
hydraulic fracturing. Therefore, fracturing is well researched and most importantly
its parameters can be determined in situ. Therefore, hydrofracturing can be used to
determine in situ allowable pressures to be applied to pregrouting. (Cornet 1992,
Smith 1987).

The first consideration concerns the water table. This will determine the minimum
pressure required to move slurries into the rock formation.

Current practice in pregrouting of deep shafts in South Africa uses a sealing pressure
at a certain depth of 2,5 times the in situ nominal hydrostatic pressure at that depth
i.e. as determined from the in situ acting water table (See Figure 2.)



                                          7
For the typical case where the water table is several hundred metres below the
surface, this rule seems to be reasonable. If in addition one considers that typically
underground water pressures are found to be two thirds of the nominal hydrostatic
level as determined from the in situ water table – then this rule results in grouting
operating pressures which are safely below the hydrofracturing pressure.

The maximum sealing pressure used at Western Deep Level no. 2 shaft (Muller,
1960), was 1,0 lb/sq in/ft to about 750 ft and 1,7 lbs/sqin/ft below 3000ft.
In oil well terminology this is termed the fracture gradient where values range from
0,45 lb/sqin/ft to 1,15 lb/sqin/ft with typical averages around 0.8 lb/sqin/ft (Smith
1987). These values refer to host rocks of oil and gas typically sedimentary rocks.




Figure 2: Grouting Hydrofracture Criteria



                                            8
Figure 2 illustrates that the pregrouting pressure in the no- hydrofracture zone may
be too low to achieve proper grout penetration. In the absence of other effects,
fracturing quickly seeks out and attains an orientation perpendicular to the minimum
stress direction, this is the path of least resistance where least work is required to
propagate the fracture. Also fractures can strongly interact with each other by
disturbing the stress field in which the other fracture grows. (Cleary, 1989).

Firstly it is imperative to achieve the depth of the shaft in safety. Secondly water
inflow must be minimized and depending on the cost, reduced to negligible flows
also with a view to operating the shaft at minimum cost. Thirdly it is advantageous to
create a strengthened zone around the shaft to improve safety during sinking and
later operations and maintenance. Finally, all these requirements are to be fulfilled at
an acceptable cost.

In order to achieve this, pressures have to be sufficient to obtain adequate penetration
at the same time controlling hydrofracturing which may open fissures and fractures
that may be difficult to close again by grouting.

Current practice to grout the formation up to 2.5 times the hydrostatic head seems
reasonable to 1,250m. A rough guide would indicate the use of 70% of the
hydrofracturing pressure in order to remain largely within the elastic deformation of
the rock formation. State-of-the-Art requires doing proper hydrofracturing tests in the
formations at the site, this will furnish the stress field, direction of the minor
principal stress, fracturing pressure, possibly permeability and above all fracturing
parameters of pre-existing fractures and weak planes.

Financial and technical benefits of pregrouting are often questioned; although some
examples shown in Table 1 of early pregrouting projects clearly show the advantages
of pregrouting of shafts as opposed to only cover grouting (grouting operations
during sinking).

Table I: Pregrouting/Cover Grouting

                                                     Cement Absorption
           Shaft                Depth     Pregrouting Cover    Pregrouting         Cover
                                 (m)         (tons)    (tons)      (%)              (%)
President Brand 2D Vent         1402          1468      576         72               28
Harmony No. 2                   1687          734        61         92               8
Stilfontein Toni Shaft          1303          609       501         55               45
Kinross No. 1 & No. 1A          1681          7761       93         99               1

Table I shows that time savings can be achieved although in some cases such as Toni
Shaft (Stilfontein G.M, now closed) economic advantages are not as obvious.




                                           9
b) Cover drilling during shaft sinking

In earlier shaft sinking operations at the beginning of the 20 th century, cover grouting
utilized (Jeppe, 1946) diamond drilled holes up to 200ft. The holes were drilled at a
slight angle to the vertical so that they ended some 7 to 9 ft outside the perimeter of
the shaft e.g. in a 45ft by 8ft shaft 18 holes were drilled.

The rate of diamond drilling was rather slow especially in cherty dolomite e.g. at
Vogelstruisbult G.M the depth of the cover holes was 126ft, drilled at an average of
3ft/day (MacWilliam, 1935). As progress was too slow it was decided to drill
percussion holes initially to a depth of 15ft; the shaft was then sunk 11ft. Rapidly
these percussion holes were extended to 20ft and eventually 30ft. After cementation
of the 30ft holes, the shaft was advanced 27ft.

Today most shafts are circular, sometimes the stretched circular shaft is used where a
short flat usually less than 10% of the shaft diameter is introduced between two
semicircles. Irrespective of whether a shaft has been pregrouted, the Mines and
Works Act requires that holes are drilled and grouted ahead of excavation to prevent
blasting into uncontrollable quantities of water which could flood the shaft.
Furthermore, it is desirable to have a dry shaft
        a) to avoid an increase in relative humidity of the incoming mine ventilation
             system
        b) to avoid degradation of the shaft steelwork and
        c) to reduce ventilation and pumping power requirements over the life of the
             shaft.

Hence the importance of proper cover grouting procedures.
State-of-the-Art practice is to drill eight to twenty-four holes (depending on shaft
diameter) up to 50m but typically 36m at 75° to 85° below the horizontal and so
spaced and raked that the toe of each hole overlaps the collar of the succeeding hole
on the pitch circle circumference. This results in a truncated cone of spiral boreholes
at least one of which will intersect randomly orientated planar fissures drawn through
the cone. These rounds are repeated every 30m so that the shaft is always at least 6m
inside cover.

Grouting under these conditions is still very much an artisan job, where decisions on
thickening procedures are made on site at the face. Slurries with W:C ratios of 6:1 to
4:1 are used to start the grouting. Thickening the slurry is relatively fast as time is of
essence during shaft sinking, grouts of W:C ratios of 1:1 to even thicker are used if
no pressure is achieved.

Cover grouting has one major drawback in that cementation and sinking cannot be
done at the same time. A major part of the time may have to be spent on grouting,
and as grouting time is a function of geological conditions and hence is difficult to
estimate and control, grouting may be rushed at the expense of the quality of sealing.




                                            10
4. UNDERGROUND CEMENTATION

Underground cementation originally developed by Francois and successfully applied
in many mines was at the time described as follows:

       1.      Diamond bore holes were drilled and on completion if cementation
               was found to be necessary, a casing or pipe with high pressure valves
               attached was inserted into the hole and cemented securely into
               position.
       2.      A cement pump was then run with a thin mix of about 3% for as long
               as 15 shifts unless the fissure had been closed in the meantime. The
               mix was then thickened to 10%, if pump pressure did not increase the
               mixture was again thickened to 30% with the addition of sawdust.
               (Cowles 1930).
       3.      The pump pressure was invariably increased by these means after
               which the mixture was thinned and pumping was continued until the
               hole was sealed.
       4.      The cement was allowed to set for a few hours, the hole was then
               redrilled. If the fissure was not completely sealed, the process was
               repeated until the fissure was sealed.

The basis for this approach was described by Voskule (1930) as follows:

“It is a well-known fact that a thin solution of cement and water, under normal
conditions, sets very slowly. When high pressures are applied the cement settles out
of the mixture and sets hard in a comparatively short time as an incrustation on the
walls of the container or cavity; this process being repeated as more mixture is
injected. In this way the cavity, the fissures and exits from the cavities are reduced in
size, thus increasing the pressure required to displace with cement and drive out the
excess of water. From subsequent examination of cemented strata it appears that the
exits eventually become choked up and the surplus water has to be pressed out
through an increasing thickness of cement filter, thus giving rise to the very high
pressures required towards the completion of the injections.”

In earlier days (before 1910) cavities and fissures were merely filled by gravity with
the mixture. No attempt was made to increase the percentage of cement to water after
the cavities had been filled. Sometimes small hand pumps were employed.

Today‟s standard and understanding of the grouting process would regard this
procedure as technically unsound and time consuming, hence uneconomical.
However, in fairness to the original pioneers in the mining grouting field, the
procedure described by Voskule (1930) was successful; hence the motivation of this
paper to present these early successes in order to facilitate a more rational evaluation
of these techniques.




                                           11
Grouting with thin, unstable slurries

Current civil engineering grouting philosophy requires thicker rather than thinner
grouts or more correctly stable grouts rather than unstable grouts.

The ideal grout should behave like water and have negligible viscosity and yield
stress during the dynamic phase i.e. during penetration; only thin grouts behave in
this way; also the ideal grout requires instant strength once it has reached its final
position and is required to perform its task. The final in situ quality of “thin” grouts
as well as the danger of hydrofracturing at higher pressures during grouting are the
concerns regarding thin grouts.
“Thick” or dense grouts choke fissures. Therefore, the tendency today is to use
grouts as thick as possible (not to choke fissures) and as stable as possible and
attempt to reduce the flow parameters such as viscosity and yield stress by adding
superplastisizers.
The most important limiting factor of "thick" grout is penetration. Where, for
economical reasons, penetration of many metres is essential, grouts should be as thin
as empirical tests will justify. However, much thinner ratios than W: C 4:1 are not
justified, particularly as rheological parameters do not change significantly for
slurries thinner than W: C 2:1 for particulate suspensions.

It is important to realise that “stable” grouts are really grouts stable under
gravitational forces only. Practically all cementitious grouts are unstable at high
pressures. In “Ultra Deep Grout Barriers” (Heinz, 1993) the author introduced the
concept of static and dynamic phase grouting.

Stable means either sedimentation is so slow that it is almost negligible or thixotropic
action, hydration or other reactions and possible forces prevent sedimentation.

It is helpful, indeed necessary, to distinguish between STATIC PHASE grouting and
DYNAMIC PHASE grouting of particulate suspensions.
The ideal static phase of cement grouting is the measuring cylinder where
sedimentation is predominantly influenced by:
         gravity, very low particle velocity, stationary continuous phase, some particle
         interference.
In contrast, in the dynamic phase of cement grouting the sedimentation process is
predominantly regulated by:
         High velocity resulting from high pressures, forces which change the
         direction and value of the resultant force on the particles in contrast to gravity
         only, different velocities between the suspended particles and suspending
         phase, selective sedimentation (pressure filtration).
Both phases require control and manipulation. It is incorrect to assume as is typically
done that if the static phase is “stable” the dynamic phase is also “stable”. Stable in
the dynamic phase requires the properties of the grout to remain similar before and
after moving through the rock mass.

High pressure mining grouting is dynamic phase grouting and hence is
fundamentally different from static phase grouting.



                                            12
Recent mining grouting practice has tended towards “thicker” slurries, however, the
basic technique of pumping thin grout first is still utilised.
Typically water is pumped for two to three hours. This will give the artisan an
indication of the transmissivity of the rock formation. This will be followed by “thin”
grout approximately W:C 6:1, whereupon the slurry is thickened to attempt to obtain
pressure.

5. CHEMICAL GROUTING

While cement grouting is still widely used in underground, mining applications,
chemical grouting has increasingly supplemented and in some cases even replaced
cement as a sealer of water and methane carrying rock formations.

Although AM9 was used successfully for water control underground at Kinross, this
was soon discontinued because of its toxicity. At present mainly two types of
chemical grouts are used (brand names): Polygrout and Supergrout.

Polygrout is a polyurethane that is water activated. Polygrout comes in two forms
(both pure liquids). One is soluble in water as well as water activated and sets as low
as 5% in solution. The other Polygrout is water activated but not water soluble.

Both set to a rubber like consistency and expand up to 3 times their volume when
setting. Polygrout is in many ways the ultimate grout. It has no solids, sets in 1
minute to 60 minutes in virtually any water, and it is acid resistance. It can be used to
seal small leaks to huge fissures.

The disadvantages of Polygrout are its relatively high price (80 times the price of
normal OPC) and the fact that it cannot be redrilled as it is too “rubbery”. Its main
advantage is the reaction with water hence its effectiveness in stopping large water
inrushes.

Supergrout is a “cementitious” type grout setting hard like cement. It is a modified
oxychloride inorganic grout. Bentonite can be added to modify the flow properties
and to help sealing. Supergrout A is a liquid and Supergrout B is a powder. The
powder is mixed into the liquid and is ready to be pumped. Normal grouting
equipment can be used.

Supergrout has less solids than cement and is more colloidal in size, so it exhibits
superior penetration of fissures, and is used throughout the goldfields and platinum
mines of SA to seal methane as well as water. Supergrout sets in about 4-6 hours at
room temperature but is temperature sensitive and sets in about half that time
underground.

Supergrout is reasonably priced (20 times the price of normal OPC) and is easy to
use with normal grouting equipment; it can also be redrilled easily.




                                           13
6. CONCLUSION

The achievements of the early mining grouting engineers in South Africa and
elsewhere at the beginning of the previous century, were quite extraordinary.

A deciding factor in the development of high pressure grouting in deep mines was
the invention of the high pressure cementation pump by Albert Francois over 100
years ago.

Discovery and development of the gold fields in South Africa and the particular
problems encountered in deep mines were the driving forces of the developments in
mining grouting

Mining grouting techniques as developed in South Africa and other mining countries,
have often been criticized, in some cases even been denounced as “black art”. These
critics have little understanding of the actual grouting techniques and have certainly
not studied the successes achieved in this field. Indeed the successes are the most
important justification for the application of these mining grouting techniques.

Grouting with thin, unstable cement slurries is possibly the most criticized and
controversial element of mining grouting, nevertheless it is still being applied at
present with success. Practically all particulate suspensions are unstable at high
pressures.

In an endeavour to reconcile civil engineering and mining grouting, it is helpful,
indeed necessary to define a new concept viz. static and dynamic phase grouting
described in the paper. Somewhat akin to the characterization of hydraulic flow by
the Reynolds number, this new concept attempts to redefine the fields of application
and the limits of these phases and highlights the need to include pressure, rock and
fissure characteristics as well as slurry properties in the parameters that determine
successful grouting procedures.

7. REFERENCE LIST

Allen, W. & Crawhall, J.S. (1937). “Shaft-Sinking in Dolomite at Venterspost.”
Papers and Discussions, Association of Mine Managers of the Transvaal.

Biccard Jeppe, C. (1946). “Gold Mining on the Witwatersrand.” Papers and
Discussions, The Transvaal Chamber of Mines, South Africa.

Blatter, C.E. (1961). “Vorversuche und Ausführung des Injektionsschleiers in
Mattmark.” Schweizerische Bauzeitung, Heft 42, 43. Oktober.

Cleary, M.P. (1997). “Technology Transfer for Hydraulic Fracturing.” www.gri.org

Cleary, M.P. (1989). “Effects of Depth Rock Fracture.” Proceedings ISRM-SPE,
International Symposium, Balkema.



                                           14
Cornet, F.H. (1992). “The HTPF and the Integrated Stress Determination Methods.”
Pergamon Press. (HTPF: Hydraulic test on preexisting fracture)

Cowles, E.P. (1930). “Underground Cementation.” Third Empire Mining and
Metallurgical Congress, Johannesburg.

Heinz, W.F., (October 1993) “Extrem tiefe Injektionsschürzen/Ultra Deep Grout
Barriers” Proceedings, International Conference on Grouting in Rock and Concrete,
Salzburg, Austria.

Krynauw, A.H. (1918). “Cementation Process Applied to Mining – Francois
System”. The Journal of the Chemical, Metallurgical and Mining Society of South
Africa. Johannesburg, South Africa.

Lugeon, M. (1933). “Barrages et Geologie.” Lausanne. Reimpression photostatique
1979. Poligrafico Pedrazzini, Locarno.

MacWilliam, K.J. (1931 – 36).” Notes on Cementation at Vogelstruisbult Gold
Mining Areas, Limited.” Papers and Discussions, The Transvaal and OFS Chamber
of Mines, South Africa.

Mudd, R.A. (1958 - 59). “Some Notes on Pre-grouting at President Brand Gold
Mining Company, Ltd.” Papers and Discussions, The Transvaal and OFS Chamber
of Mines, South Africa.

Muller, T.F. & Skeen, C. (1952) “Shaft-Sinking on the Virginia and Merriespruit
Mines.” Papers and Discussions, Association of Mine Managers of the Transvaal.

Newman, S.C. (1956 - 57). “Pre-cementation at No. 2 Shaft, Harmony Gold Mining
Company, Ltd.” Papers and Discussions, The Transvaal and OFS Chamber of Mines,
South Africa.

Simmonds, A.W. (1953). “Final Foundation Treatment at Hoover Dam.” Vol. 118 of
the Transactions of the ASCE.

Smith, D.K. (1987). “Cementing” SPE Monograph, Society of Petroleum Engineers.

Voskule, G.A. (1930). “The Cementation Process.” Third Empire Mining and
Metallurgical Congress, Johannesburg.




                                        15

								
To top