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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: email@example.com 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
"MINING GROUTING a rational approach"