Wet shotcrete trial. by A.D. Storrie* and P. Bartlett* Introduction. Synopsis

Transcription

1 by A.D. Storrie* and P. Bartlett* Introduction Synopsis An underground wet shotcrete trial was completed last year to determine the effectiveness of wet shotcrete as an alternative support mechanism to dry shotcrete in the kimberlite environment. The wet shotcrete was manufactured at the underground batch plants, transported to site using an agiecar and transferred to the shotcrete pump. The wet shotcrete is pumped to the nozzle where compressed air at 7 bar and an accelerator, Meyco SA 160, is added and enables the shotcrete to be placed successfully onto the tunnel wall. No tunnel guard was previously placed on the sidewall and hangingwall. Geotechnical testing indicates that the Grace fibre performed extremely well with the energy absorption tests at 7 kg/m3 and 8 kg/m3 where both achieved over the mine requirement of 750 joules. The Grace fibre and wet shotcrete mix also achieved a compressive strength in excess of 55 MPa, well above the 45 MPa requirement for Premier Mine. The recommended wet shotcrete mix design is therefore based upon: Material/ Criteria Quantity/m3 Units Lafarge 42.5 Duratech 500 kg Condensed silica fume 40 kg Rayton Sand Ton Delvocrete stabilizer litres Glenium 27CH 5.4 litres Meyco TCC litres Water 230 litres Meyco SA litres Fibre 8 kg Cement/Water Ratio 2.35 Water/Cement Ratio 0.43 Flow 615 mm If the wet shotcrete system is implemented there is a potential for Premier Mine to make major savings. In South Africa there are two suitable wet shotcrete machines available for the mining industry, the Spreymec, manufactured by Tamrock and the Fermel/Meyco wet shotcrete machine. The Spreymec is a fully imported machine. The Fermel component is manufactured in South Africa and the Meyco shotcrete components are imported and supported by MBT (Master Builder Technologists) in South Africa. The Fermel/Meyco machine is assembled in South Africa. Premier Mine has allocated some R2,100,000 towards the implementation of the wet shotcrete system. If implementation is successful there should be an internal rate of return gain of 76% with regard to this project. De Beers Premier Mine has been looking at upgrading the underground support criteria through improved shotcrete mix designs, mechanization of support placement, increased quality control and increased safety. The reasoning behind the planned change of support philosophy has been driven in part by the swing-over of the BB1E undercut to an advanced undercut with development following in a de-stressed zone. Requirements from the Premier Mines C-Cut have also changed Premier Mine s support philosophy. The B-Cut and C-Cut development will subsequently require support implementation to follow directly behind the development of any excavation with the aid of a semiautomatic wet shotcrete machine. However, in order to facilitate this change in support philosophy wet shotcrete has had to prove itself as a competent form of support that is able to marry itself successfully into the development cycle. Kimberlite is hygroscopic and the water used in the shotcrete mix is drawn out of the shotcrete into the kimberlite. This results in decomposition at the kimberlite/shotcrete interface, weakening the rock strength of the kimberlite and nullifying or reducing the effectiveness of shotcrete as an interbolt support medium. The problem has been addressed by spraying a sealant onto the kimberlite as soon after development of an excavation as possible. The sealant prevents water entering the kimberlite. The application of the sealant obviously adds time and cost to the support cycle. If the wet mix shotcrete can be designed to eliminate a need for the sealant at the interface this would be a considerable advantage. * De Beers Premier Mine The South African Institute of Mining and Metallurgy, SA ISSN X/ First presented at SAIMM Colloquium: Shotcrete and membrane support, Apr The Journal of The South African Institute of Mining and Metallurgy JULY

2 Why wet shotcrete? Although the dry shotcrete product is a third of the price of wet shotcrete, wet shotcrete does have major advantages. The wet shotcrete advantages include: - Rebound of the product is reduced to 5 10% with wet shotcrete, compared to 15 35% with dry shotcrete With dry shotcrete, rebound of fibre can be as high as 35% compared to 5 10% for wet shotcrete The dust created when placing shotcrete is significantly reduced with a wet application compared to a dry application Thicker shotcrete layers can be applied with wet shotcrete when doping products and accelerators are added. Dry shotcreting does not allow for this benefit Greater quality control can be achieved when manufacturing wet shotcrete with effective cube test auditing of shotcrete at the batching plant and on site. Follow up in situ core testing can also form part of the auditing system. With and dry shotcrete used together, it is impossible to conduct core tests or manufacture cubes for compressive strength testing. Ultimately the mine is solely dependent on the ability of the batch plant operator and the shotcrete nozzle operator for quality control Flow testing the wet shotcrete mix at source gives good quality assurance and control prior to dispatching the product for final placement With dry shotcrete, due to variations in aggregate wetness prior to application, the water dosage is varied proportionally. Although the nozzle operator may be extremely efficient, the chance of error, resulting in the over or under wetting of the shotcrete is greatly increased. This deficiency will reduce the strength of the shotcrete Both applications of wet and dry shotcrete lend themselves to mechanization. The dry shotcrete system requires a greater infrastructure. Water pipes to site would be required for the final mixing of water with shotcrete on placement. Where possible water is not permitted in a kimberlite environment due to the decaying nature of kimberlite when water is added The placement of wet shotcreting lends itself to mechanization and will therefore result in a reduction of overall cost through increased productivity Dry shotcrete requires a large workforce to place shotcrete support. Fewer people are required to place a similar quantity of wet shotcrete Less shotcrete is required with a wet application due to the shotcrete following the profile of the tunnel. With welded, large voids between the kimberlite surface and the are created. An increased quantity of dry shotcrete is required to fill and cover this void A semi-robotic wet shotcrete machine does not expose the operator to unsupported ground and is therefore considerably more safe than Premier Mine s current dry shotcrete operation. Premier Mine s shotcrete requirements Added to the advantages indicated above, Premier Mine primarily requires that wet shotcrete must prove itself as a valid and effective form of support in the kimberlite environment. The wet shotcrete process must also form an integral part of the development schedule and cycle. Shotcrete strength requirement of 45 MPa and energy absorption rate of 750 joules is required. The energy absorption of the wet shotcrete is gauged according to the EFNARC plate test, which is designed to determine the energy absorbed from the load/deformation curve as a measure of toughness. This test is designed to model more realistically the biaxial bending that occurs underground at Premier Mine. Wet shotcrete mix designs for Premier Mine In the Greater Cullinan district there are two sand aggregate suppliers. The one, Rayton sand, is presently contracted to supply Premier Mine with sand. The other Richter sand have no contract with Premier Mine. The grade analysis varies between Rayton and Richter sand, with Rayton producing the finer of the two products, Examples 1 and 2 and Table I. After conducting a series of cube tests, it was identified that the coarser Richter sand is more suited to the wet shotcrete process, Table II. TEL: (011) SOILS & MATERIALS TESTING FAX: (011) P.O. BOX 227, MARAISBURG, 1700 e mail: lab@geopractica.co.za GRADING ANALYSIS - SHOTCRETE AGGREGATES Client PREMIER MINE Location SHOTCRETE MIX DESIGNS (RAYTON SAND) Data 2000/06/09 Test No 459b Job No Checked By EB Percentage Passing SIEVE ANALYSIS Values are expressed as a percentage of the total sample Sieve Total Size Passing (mm) (%) Particle Size (mm) Example 1 Rayton sand grading analysis 190 JULY 2001 The Journal of The South African Institute of Mining and Metallurgy

3 Client PREMIER MINE Location SHOTCRETE MIX DESIGNS (RICHTER SAND) Data 2000/06/09 Test No 458 Job No Checked By EB Percentage Passing TEL: (011) SOILS & MATERIALS TESTING FAX: (011) P.O. BOX 227, MARAISBURG, 1700 e mail: lab@geopractica.co.za GRADING ANALYSIS - SHOTCRETE AGGREGATES SIEVE ANALYSIS Values are expressed as a percentage of the total sample Sieve Total Size Passing (mm) (%) Particle Size (mm) Example 2 Richter sand grading analysis Table I Sand density details Description Rayton Sand Richter Sand Loose Bulk Density Compacted Bulk Density Apparent Relative Density With Master Builder Technologists, one of the world leaders in shotcrete technology, provided the additives in conjunction with Azalcon s cementitious material and Premier Mine s already established deliverables. To this end wet shotcrete testing at Premier Mine was based upon the following: Lafarge 42.5 ordinary Portland cement Azalcon HT33 is a cementitious type hydraulic hardening material consisting of selected fly ash, Portland cement special activators and additives Delvocrete admixture is used to stabilize the hydration process by forming a protective barrier around the cement particles Glenium 27 CH admixture is added to reduce the water/ cement ratio required in the shotcrete mix Meyco TCC 735 admixture is added to enhance the quality of shotcrete in a plastic and hardened state. This ensures improved hydration characteristics and reduces the shrinkage and increases binding, density and compressive strength Meyco SA160 accelerator is added to accelerate the early strength of the shotcrete while at the same time limiting the decrease in final strength Condensed silica fume 90 (CSF), an extremely fine material and is a by-product from the silicon metal industry and is used as a cementitious compound in the shotcrete matrix. CSF acts as a filler and helps the hydration process and increases shotcrete density and strength and reduces shotcrete rebound, permeability and the amount of water that can bleed from the shotcrete. CSF can be used in powder form, however, a slurry format is recommended for health reasons Rayton sand Richter sand Synthetic Industry HPP S 50 Fibre, a 50 mm-length monofilament polypropylene is manufactured with waves throughout. The waves are designed to improve the bonding between the matrix and the fibre Grace Concrete Products, Grace Structural Fibre, a 50 mm-length synthetic polymer blend of polypropylene and polyethylene. During the mixing process with the fibre fibrillates and deforms, creating a greater bonding area between the matrix and the fibre. The fibre has a tensile strength of 550 MPa and Modulus of Elasticity of 4.3G Pa. The development of a successful wet shotcrete for kimberlite Premier Mine has looked at various types of shotcreting in the past with varying degrees of success. The Azalcon wet shotcrete trial During 1999 a wet shotcrete trial with Azalcon s cementitious material, HT33, resulted in failure. The failure was due in part to the use of an unskilled workforce in conjunction with an incorrect starting up and closing down procedure with the wet shotcrete machinery. Due to the nature of the kimberlite and its ability to absorb water, Premier Mine s policy has demanded that no washing down of surfaces be undertaken before placing shotcrete or impermeable membrane. This hindered the trial considerably by creating a dust interface between the shotcrete and the kimberlite and in turn contributed to the failure of the shotcrete as a form of support. The water content was not locked within the shotcrete rapidly enough to prevent the kimberlite from absorbing the water and allowed the kimberlite surface to decay into a clay type surface. The already partially decayed nature of the kimberlite also resulted in the tunnel guard membranes, inability to render itself effectively to the kimberlite to form a good bond. To place wet shotcrete an air pressure of 7 bar is preferred; during the trial an average mine air pressure of 4 bar was achieved. This shortfall in compressed air resulted in insufficient compaction of shotcrete onto the kimberlite surface. All these factors contributed to the ultimate failure of the wet shotcrete trial, Figure 1. The Journal of The South African Institute of Mining and Metallurgy JULY

4 Table II Geopractica mix design cube test results Design Sand Cementitious Cementitious CSF Glenium Delvocrete Meyco TCC 735 Water Days Compressive Flow type type content (kg) 27CH (litres) stabilizer 10 (litres) (litres) Liters Strength (MPa) (mm) 1 Richter HT Repeat Richter HT Richter HT Rayton HT Rayton HT Flow too wet 5 Richter HT Richter HT Repeat Richter HT Rayton HT Repeat Rayton HT Richter 42.5 OPC Richter 42.5 OPC Richter 42.5 OPC Repeat Richter 42.5 OPC Rayton 42.5 OPC Rayton 42.5 OPC Rayton HT Although the Azalcon trial was unsuccessful valuable lessons were learnt it was important to build upon this knowledge. For the Azalcon trial a worm and stator pump was used, Figure 2 and Figure 3. This worm and stator system is suitable for small contractor type operations but does not lend itself to a more automated and controlled environment. To develop Premier Mines understanding of wet shotcrete a more professional approach had to be taken. To achieve a more professional approach shotcrete specialists had to be utilized. Local aggregates with the best-known additives had to be used to develop various shotcrete mix designs before the underground trial began. To give the future trial the best chance of success the services of Master Builder Technologists, providers of shotcrete additives and shotcrete expertise were utilized. Geopractica, consulting geotechnical engineers were used for the duration of the trial. Machinery, which lends itself to mechanization, automation and to Premier Mine s environment had also to be utilized for the duration of any future shotcrete trial. The wet shotcrete pre-trial Following initial laboratory wet shotcrete design testing at Geopractica four mix designs were identified for the underground pre-trial on a reduced scale; two linear metres per design, Table III. HPP S 50 fibre was used in all four-mix designs. Past experience with earlier wet shotcrete trials had proved unsuccessful, it was therefore considered prudent to conduct the pre-trial before any major expense had been laid out. The equipment utilized for the trial was also considered to be of major importance. Without going to the major expense of a completely automated wet shotcrete machine with onboard compressor, shotcrete pump and accelerator pump it was necessary to utilize the complete range of machinery, a 450 CFM diesel compressor, a Putzmeister shotcrete pump with an onboard accelerator pump, Figure 4. Premier Mine s batch plants, although suited to mixing whilst utilizing a larger aggregate, are not ideally suited to mixing wet shotcrete. The paddle bushes are well worn and therefore have little resistance. This resistance is needed to mix the sand at the extremities of the batching plant bowl. The result of this is that ninety per cent of the wet shotcrete is mixed by the batch plant whilst the remainder is mixed by the agiecar, Figure 5. Although the bowl and paddle shortcomings would cause difficulties if allowed to continue with a wet shotcreting production phase, the batching plant did not pose a major difficulty for the trial as a technologist was present for the duration of the trial. Wet shotcrete stalactite formations on tunnel hangingwall Wet shotcrete fall of ground Figure 1 Azalcon wet shotcrete hangingwall photographs Shotcrete slabbing 0.75m2 192 JULY 2001 The Journal of The South African Institute of Mining and Metallurgy

5 Shotcrete wet mixing trough Worm and stator feed box Shotcrete and compressed outlet Shotcrete intake Compressed air intake Azalcon wet shotcrete nozzle Shotcrete feed Shotcrete intake Shotcrete, accelerator and compressed outlet Worm and stator pump and mixing unit Compressed air intake Stater clamps holding steel sleeve and worm screw thread Shotcrete intake Figure 3 Azalcon wet shotcrete nozzles Accelerator intake Feed trough and worm and stator Figure 2 Azalcon wet shotcrete equipment Connection to hose The sidewall and hangingwall were previously coated with tunnel guard; an impermeable membrane. Over a short time a layer of dust had built up over the tunnel guard. This dust was removed prior to the placing the wet shotcrete using a water and compressed air mix. Table III Mix design cube test results, costs and selection Design Sand Sand Cementitious Cementitious Condensed Glenium Delvocrete Meyco Meyco HPP fibre Total type type silica fume stabilizer TCC 735 SA 160 Content Cost/ Cost/ Cost/ 27CH Cost/ Cost/ Cost/ Cost/ Cost Cost Cube (R) Content cube (R) kg Cube (R) (litres) Cube (R) (litres) Cube (R) (litres) Cube (R) (litres) Cube (R) (kg) Cube (R) Cube 1 Richter HT R Repeat Richter HT R Richter HT R Rayton HT R Rayton HT R Richter HT R Richter HT R Repeat Richter HT R Rayton HT R Repeat Rayton HT R Richter OPC R1, Richter OPC R Richter OPC R1, Repeat Richter OPC R1, Rayton OPC R Rayton OPC R1, Rayton HT R The Journal of The South African Institute of Mining and Metallurgy JULY

6 450 CFM compressor Wet shotcrete pump and dosing machine Dosing pump The wet shotcrete was transported to site in one cubic metre increments using the Premier Mine agiecars. The wet shotcrete was then transferred into the shotcrete pump. The wet shotcrete was then pumped to the nozzle via a 50 mm rubber hose. At the nozzle, compressed air was delivered at a pressure of 7 bar in conjunction with an accelerator to place the wet shotcrete. Once the wet shotcrete had been placed, penetration with a finger became impossible after two minutes. After five minutes it became impossible to force a nail through the wet shotcrete. A driving force behind the success of all four-mix designs was the use of the SA160 accelerator, which helped to lock the water in the shotcrete and give high initial shotcrete strength. All four wet shotcrete mix designs were successfully applied to the sidewall and hangingwall, Figure 6. Despite all the wet shotcrete mix designs adhering to the sidewall and hangingwall successfully, the Azalcon HT33 product did not flow easily from the batching plant into the agiecars. The HT33 mix designs also started to cure and hydrate after a very short period. Once the HT33 wet shotcrete had been transported from the 630 m Level batching plant to the test site on 615 m Level, less than fifty per cent of the HT33 mix was able to flow from the agiecar unaided. Water had to be placed into the agiecar kettle in order to increase the fluidity of the mix. The adding of water therefore changed the design of the shotcrete and reduced the strength proportionately. Figure CFM compressor, shotcrete and dosing pump Poor mixing of sand, cement and water Lafarge 42.5 OPC with Rayton sand Batch plant shortcomings Batch plant quality control Figure 5 Batch plant shortcomings and quality control Wet shotcrete placement Figure 6 Lafarge 42.5 OPC with Rayton sand, wet shotcrete placement 194 JULY 2001 The Journal of The South African Institute of Mining and Metallurgy

7 From the four mix designs tested underground, core samples were taken, Table IV. However only cores taken from Rayton sand with OPC test cores gave satisfactory results. The cores taken from the remaining three panels were of poor quality due to the thickness of panels placed. The Rayton sand with OPC mix design results were however extremely good and recorded results averaging over 40 MPa. Despite the HT33 mix designs costing on average R per cube less than OPC per cube metre, it was decided to remove HT33 from further trial. The wet shotcrete trial For the wet shotcrete laboratory tests, Rayton and Richter sand and Lafarge OPC were used in conjunction with Grace and HPP S 50 fibre. The wet shotcrete materials for two duplicate EFNARC panels was manufactured in a mechanical drum mixer and placed into moulds. The standard panels, 1 m x 1 m and 100 mm thick were compacted using a tamping rod and by dropping from a height of 10 mm, 70 times. The panels were cured for five days prior to cutting to the correct size and placing into a curing bath until testing. For the underground trial Rayton sand, Grace and HPP S 50 fibre were used with Lafarge OPC. To ensure that there was as little interruption to the mine s operation, no changes to the underground batch plant system were required in order to cater for Rayton sand shotcrete design for the underground shotcrete trial. A technologist was employed at the batch plant to manufacture the wet shotcrete and to ensure that the correct standard was achieved. The machinery and process for the trial mirrored the lines of the previous trial. Four production level drawpoints were earmarked and sprayed with ten linear metres of wet shotcrete, each draw-point with a different quantity of HPP fibre or Grace fibre. Due to the 4 m x 4 m dimensions of the tunnel a scissors lift was utilized to give the nozzle operator the height to ensure that there was only 1 m between the nozzle and kimberlite surface. After cleaning the kimberlite surface with a mix of water and compressed air, shotcrete was placed successfully in all four draw-points. However, once the troughs were opened via blasting to mine standard, it became apparent that the required shotcrete thickness was not achieved, Figure 7. Following this development it also became apparent that no hand-held nozzle placement of shotcrete should be undertaken unless 100 mm plugs were used to guide the nozzle operator. Geotechnical results for the wet shotcrete trial The Richter sand results indicate: From cube tests, the HPP S 50 fibre with Richter sand performed better in compression than the Grace fibre with Richter sand, Table V and Figure 8 The Richter sand with HPP S 50 fibre energy absorption test results indicate an ability to sustain a greater load before failure than that achieved with Richter sand with Grace fibre, Table VI With the Richter sand being a more rounded aggregate, less water is required than with Rayton sand. The Rayton sand is coarse and consequently has an increased surface area; this increases the water demand Despite the Richter shotcrete design demanding more sand compared to the Rayton shotcrete design, for a similar quantity of cement per cubic metre, the water/cement ratio for the Richter design is less but delivers an increased compressive strength over and above the Rayton designs which require more water The Grace fibre has a lower density compared to the HPP fibre so for a given mass, one cube, Grace fibre requires a greater volume. The increased volume of Grace fibre and its fibrillating nature demands that, for a given flow, a greater volume of water is required when compared to the HPP fibre. This increased water demand ensures that the wet shotcrete remains pumpable, however, in turn the increased water/ cement ratio reduces the strength of the shotcrete mix Due to the Richter design formulated with HPP S 50 fibre and due to the shape and size of the aggregate, Remaining wet shotcrete, 30 mm thick Kimberlite hangingwall Figure 7 Wet shotcrete support after opening up the trough at a production drawpoint Table IV Wet shotcrete mix design core testing Design Sand type Cementitious Core Core Core Core Failure Measured compressive type number diameter (mm) length(mm) age (days) load (KN) strength MPa 1 Richter HT Repeat Richter 42.5 OPC Rayton 42.5 OPC Rayton HT The Journal of The South African Institute of Mining and Metallurgy JULY

8 Table V Richter sand and fibre reinforced wet shotcrete cube test results from laboratory trials Design Fibre Content Days Compressive Average 10 strength (MPa) (MPa) Grace Grace HPP S HPP S HPP S Compressive strength (MPa) Fibre content (kg/m3) Grace 50 mm laboratory Figure 8 Richter sand wet shotcrete cube results graph HPP S 50 mm laboratory both are able to key and develop a good mechanical bond. Indications suggest that the finer Grace fibre is less able to key sufficiently well to Richter sand, a wellrounded aggregate. If the cement content were increased the bond between the Grace fibre would increase while at the same time improving the ductility of the fibre reinforced shotcrete. It is not recommended to increase the cement content due the increased cost attached. The Rayton results indicate: The Rayton sand cube results were relatively inconclusive due in part to the variation in water content while mixing, however the results did show that both the HPP and Grace fibre performed well at 7 kg/m3, Table VIII and Figure 10 The Grace fibre performed extremely well in the energy absorption tests at 7 kg/m3 and 8 kg/m3 where both achieved over 750 joules, Table IX and Figure 11 Energy absorption rate (joules) Table VI Richter sand laboratory energy absorption test results Fibre Type HPP S 50 Test No Kg/m Energy Absorption = 775 J Fibre Type HPP S 50 Test No Kg/m3 ITASCA Corrected Energy absorption = 883 J Energy Absorption = 567 J Fibre Type HPP S 50 Test No ITASCA Corrected Energy absorption = 631 J 7.5 Kg/m Energy Absorption = 656 J Fibre Type HPP S 50 Test No ITASCA Corrected Energy absorption = 680 J 7.5 Kg/m Energy Absorption = 889 J Fibre Type HPP S 50 Test No Kg/m3 ITASCA Corrected Energy absorption = 940 J Energy Absorption = 799 J Fibre Type HPP S 50 Test No Kg/m3 ITASCA Corrected Energy absorption = 828 J Energy Absorption = 896 J Fibre content (kg/m3) Grace 50 mm laboratory HPP S 50 mm laboratory Figure 9 Richter sand laboratory energy absorption graph ITASCA Corrected Energy absorption = 978 J JULY 2001 The Journal of The South African Institute of Mining and Metallurgy

9 Table VII The recommended wet shotcrete design for Premier Mine Material/ Criteria Quantity/m3 Units Lafarge 42.5 Duratech 500 kg Condensed silica fume 40 kg Rayton sand ton Delvocrete stabilizer litres Glenium 27CH 5.4 litres Meyco TCC litres Water 230 litres Meyco SA litres Fibre 8 kg Cement/Water ratio 2.35 Water/Cement ratio 0.43 Flow 615 mm In comparison to the HPP S 50 fibre, Grace fibres, good performance could be as a result of the finer matrix of the Rayton sand while at the same time being a coarse aggregate and providing a large surface area. This large surface area increased the well-fibrillated Grace fibres ability to bond with the aggregate and cement more effectively. The HPP fibre was unable to match the bond achieved between Rayton sand and Grace fibre. It is therefore recommended that Premier Mine adopt the wet shotcrete mix design shown in Table VII. Wet shotcrete financial requirements The wet shotcrete material costs are considerably higher than those for dry shotcrete, Appendices 1A and 2A. However, less wet shotcrete material is required due to effective contouring to the tunnel profile, reduced rebound of shotcrete and reduced operational placement costs and increased productivity compared to dry shotcrete. Other major cost savings are achieved through the reduction of tasks. The introduction of fibre reinforced wet shotcrete eliminates the need for welded and tunnel guard. This task reduction therefore translates to a reduction of manshifts required to implement the support types, Appendices 3A and 4A. From 2001 to 2005 some 22,000m3 of wet shotcrete support will be required compared to 36,000m3 for dry shotcrete. There is a potential for Premier Mine to make major savings by introducing wet shotcrete. In South Africa there are two suitable wet shotcrete machines available for the mining industry, the Spreymec, manufactured by Tamrock and the Fermel/Meyco wet shotcrete machine. The Spreymec is a fully imported machine and is manufactured in Finland. The Fermel component is manufactured in South Africa and the Meyco shotcrete components are manufactured in Switzerland but supported by MBT (Master Builder Technologists) in South Africa. The Fermel/Meyco machine is assembled in South Africa. Premier Mine has allocated some R2,100,000 towards the implementation of the wet shotcrete system. If implementation is successful there should be an internal rate of return gain of 76% with regard to this project, Appendix 5A Conclusions The fibre reinforced wet shotcrete has proven itself as a competent form of kimberlite support and requires no welded or tunnel guard. The wet shotcrete system is also able to place 5 m3 of wet shotcrete per hour compared to 4 m3 per shift with dry shotcrete. Although the dry shotcrete materials, and tunnel guard is considerably less expensive to purchase it is extremely labour and time intensive. The dry system is also only as good as the personnel placing the shotcrete. Each shotcrete design is determined by the nozzle operator and is Table VII Rayton sand, fibre/wet shotcrete cube results: (a) underground trials, (b) laboratory trials Design Fibre Content Days Compressive Average 12 strength (MPa) (MPa) (a) Grace Grace HPP S HPP S Design Fibre Content Days Compressive Average 12 strength (MPa) (MPa) (b) Grace Grace Grace HPP S HPP S HPP S The Journal of The South African Institute of Mining and Metallurgy JULY

10 Compressive strength (MPa) Fibre content (kg/m3) Energy absorption rate (Joules) Grace 50 mm Underground Grace 50 mm Laboratory HPP S 50 mm Underground HPP S 50 mm Laboratory Fibre content (kg/m3) Figure 10. Rayton sand wet shotcrete cube test results (Compressive strength/fibre content) Grace 50 mm Laboratory Grace 50 mm Underground HPP S 50 mm Laboratory HPP S 50 mm Underground Table IX Rayton sand laboratory energy absorption test results Fibre Type Grace 50 mm Test No A 7 kg/m Energy Absorption = 473 J Fibre Type Grace 50 mm Test No B ITASCA Corrected Energy absorption = 496 J 7 kg/m Energy Absorption = 985 J Fibre Type HPP S 50 mm Test No a ITASCA Corrected Energy absorption = 973 J 7.5 kg/m Energy Absorption = 776 J Fibre Type HPP S 50 mm Test No b ITASCA Corrected Energy absorption = 607 J 7.5 kg/m Energy Absorption = 597 J Fibre Type Grace 50 mm Test No A ITASCA Corrected Energy absorption = 448 J 8 kg/m Energy Absorption = 750 J Fibre Type Grace 50 mm Test No B ITASCA Corrected Energy absorption = 1021 J 8 kg/m Energy Absorption =1058 J Fibre Type HPP S 50 mm Test No a ITASCA Corrected Energy absorption = 942 J 9 kg/m Energy Absorption = 786 J Fibre Type HPP S 50 mm Test No b ITASCA Corrected Energy absorption = 634 J 9 kg/m Energy Absorption = 604 J ITASCA Corrected Energy absorption = 748 J Figure 11. Rayton sand ITASCA energy absorption tests results therefore open to abuse and is impossible to monitor or quantify. Alternatively the wet shotcrete quality is determined by the batch plant operator and should be monitored, audited and policed by the technologist. The use of a semi-automatic wet shotcrete rig is also safe to operate, as the operator is not exposed to the area to be supported. The wet shotcrete rig also only requires one qualified operator, an artisan or fitter grade and two helpers to assist with the final preparation of the tunnel. From the Premier Mine wet shotcrete trial, the large tunnel dimensions proved too big for a hand-held wet shotcrete system. The hangingwalls were difficult to spray and therefore not completed to the required thickness. A wet shotcrete rig with a semi-automatic robotic arm is therefore recommended to place the shotcrete as required. From the trial, it was determined that a greater emphasis must be placed the importance of the manufacture of and the personnel supporting the system. Premier Mine therefore requires a dedicated technologist to ensure that a standard quality is achieved. Wet shotcrete rig and batch plant operators also need to be trained and educated on the importance and urgency related to manufacture, delivery and application of. Ultimately there needs to be a change in mindset on the importance of good quality. Without this support and urgency, it is not recommended that the mine transfer to the wet shotcrete system. However, for the future of the mine, both B and C Cut, it is imperative that the mine transfers to the wet shotcrete system. Once Premier Mine has implemented a wet shotcrete system that fulfils the demands required and has gained the necessary experience, the shotcrete mix designs must be adjusted to reduce the cost of materials. However, at this stage it is important to gain a good wet shotcrete database from which to build any future improvements. Recommendations Premier Mine has two choices: To continue with the tunnel guard, and dry shotcrete placement system Alternatively, it is recommended that Premier Mine purchases the Fermel/Meyco wet shotcrete rig which is 198 JULY 2001 The Journal of The South African Institute of Mining and Metallurgy

11 Appendix 1A CAPITAL SUPPORT TUNNEL TYPES FOR DRY SHOTCRETE TYPE 1 PRODUCTION TUNNEL (per metre of tunnel) TYPE 4 UNDERCUT TUNNEL (per metre of tunnel) TYPE 8 CONTACT ARCH SUPPORT (Undercut Level) 1,8 m gewi s 4 each welded 12 m tunnelguard 12 m (2 layers) shotcrete 12 m footwall 1.2 m total 1, TYPE 2 PRODUCTION DRAWPOINT (10 metres) 1,8 m gewi s 40 each , welded 120 m , tunnelguard 120 m , (2 layers) shotcrete 120 m , m anchors 23 each , bullnose 10 each , rope installation camelback 10 each , rope installation footwall rail 2 m , footwall 12 m , total 26, TYPE 3 PRODUCTION TROUGHS (per metre of tunnel) 1,8 m gewi s 4 each welded 12 m tunnelguard 12 m (2 layers) Shotcretel 12 m total 1, TYPE 5 UNDERCUT INTERSECTION (per metre of tunnel) 6 m anchors 5 each , bullnose 40 each rope installation tunnelguard 0 m (2 layers) Shotcretel 0 m total TYPE 6 WASTE ROCK SUPPORT 1,8 m gewi s 4 each welded 12 m shotcrete 4.4 m total TYPE 7 CONTACT ARCH SUPPORT (Extraction Level) 1,8 m gewi s 0 each welded 0 m ,8 m gewi s 4 each welded 12 m tunnelguard 0 m (5 metres) tunnelguard 12 m yielding 11 each , (2 layers) arches total tekseal 83 m , * All the above costs are material costs only footwall 0 m * Scribing materials for contact arch support excluded * D.A.S. to be used for roadways in rim tunnels total 79, Description Rate Unit Unit Cost Cost Efficiency Man shifts 1,8 m gewi s 0 each welded 0 m yielding 5 each 5, , arches tekseal 42 m , footwall 6.6 m , total 38, TYPE 9 REHABILITATION on average per 5 m Description Rate Unit Unit Cost Cost Efficiency Man shifts site 1 each preparation strip 5 m slipe 5 m , lash 5 m tunnel 0 m guard 1,8m gewi s 40 each , welded 0 m tendon 20 each straps shotcrete 0 m mm total TYPE 9 ARMCO Description Rate Unit Unit Cost Cost Efficiency Man shifts tunnel 14.1 m guard 1,8m gewi s 4 each welded 14.1 m ARMCO 0.2 m 25, , erect 5.6 m , back fill (25 MPa) shotcrete 12 m mm footwall 1.2 m total considerably less expensive than the Spreymec and is well supported by wet shotcrete specialists. However, before the implementation of the wet shotcrete system can commence the following is required. - The batch plants must be upgraded to such an extent that a good mixing process is achieved and all weighing or measuring systems are accurate and easy to read whether or not any wet shotcrete system is to be introduced - The batch plant operators must receive extensive on-the-job training in the manufacture of and in plant maintenance, (this would need to be well supported by Management). Those who were considered unsuitable to manufacture after a one-week training period must be replaced with operators that are more competent - The wet shotcrete rig must be operated by a artisans or a fitter. Once identified, the operator must receive a two-week induction course on a mine where the machine is operational. The operator must also receive extensive training from the supplier of the machine at Premier Mine on how to use, clean and maintain the rig - After a two-month period the supplier of the wet shotcrete rig must audit the operation and give more training where necessary. Acknowledgements The Premier Mine Projects Department is grateful to the The Journal of The South African Institute of Mining and Metallurgy JULY

12 Appendix 2A CAPITAL SUPPORT TUNNEL TYPES FOR WET SHOTCRETE TYPE 1 PRODUCTION TUNNEL (per metre of tunnel) TYPE 4 UNDERCUT TUNNEL (per metre of tunnel) TYPE 8 CONTACT ARCH SUPPORT (Undercut Level) 1,8 m gewi s 4 each shotcrete 12 m , footwall 1.2 m total 2, TYPE 2 PRODUCTION DRAWPOINT (10 metres) 1,8 m gewi s 40 each , shotcrete 120 m , m 23 each , anchors bullnose 10 each , rope installation camelback 10 each , rope installation footwall rail 2 m , footwall 12 m , total 30, TYPE 3 PRODUCTION TROUGHS (per metre of tunnel) 1,8 m gewi s 4 each shotcrete 12 m , total 1, ,8m gewi s 4 each shotcrete 12 m , total 1, TYPE 5 UNDERCUT INTERSECTION SUPPORT 6m anchors 5 each , bullnose 40 each , rope installation total 5, TYPE 6 WASTE ROCK SUPPORT 1,8 m gewi s 4 each shotcrete 4.4 m total TYPE 7 CONTACT ARCH SUPPORT (Extraction Level) 1,8 m gewi s 0 each yielding 11 each 5, , arches tekseal 83 m , footwall 0 m total 79, Description Rate Unit Unit Cost Cost Efficiency Man shifts 1,8m gewi s 0 each yielding 5 each 5, , arches tekseal 42 m , footwall 6.6 m , total 38, TYPE 9 REHABILITATION on average per 5 m Description Rate Unit Unit Cost Cost Efficiency Man shifts site 1 each preparation strip 5 m slipe 5 m , lash 5 m ,8m gewi s 40 each , tendon 20 each straps shotcrete 0 m mm total TYPE 9 ARMCO Description Rate Unit Unit Cost Cost Efficiency Man shifts 1,8m gewi s 4 each ARMCO 0.2 m 25, , erect 5.6 m , back fill (25 MPa) shotcrete 12 m mm footwall 1.2 m total * All the above costs are material costs only * Scribing materials for contact arch support excluded * D.A.S. to be used for roadways in rim tunnels following for permission to publish Premier Mine General Manager, Mr Hans Gastrow Premier Mine Mining Manager, Mr Malcolm Lotriet General Manager Mining, Mr Tony Gutherie General Manager Geotechnical Engineering, Mr Alan Guest. The Projects Department is also grateful to the following for their contributions Geopractica Consulting Geotechnical Engineering Master Builder Technologists South Africa Grace Concrete Products South Africa Azalcon. 200 JULY 2001 The Journal of The South African Institute of Mining and Metallurgy

13 Appendix 3A B-Cut LOM for 2001 SBP Base manpower case for dry shotcrete Date 23 March 2001 Life of mine base case support requirements for dry shotcrete B-Cut LOM for 2001 SBP Base material case for dry shotcrete Date 23 March 2001 Year Level support metres Tunnel metres-blue Tunnel metres-waste Contact metres Manshifts 1,887 1,450 1, Level support metres Tunnel metres-blue Tunnel metres-waste Draw point metres Trough metres Contact metres Manshifts 2,494 1,977 4,389 1, Level support metres Tunnel metres-blue Tunnel metres-waste Contact metres Manshifts 4,512 5,574 2, Level support metres 0 Tunnel metres-blue Tunnel metres-waste Draw point metres Trough metres Contact metres Manshifts 1,940 7,637 3,871 6,205 2, Level support metres Tunnel metres-blue Tunnel metres-waste Draw point metres Trough metres Contact metres Manshifts 1,474 2,128 2, GRAND TOTAL 2,794 4,169 2,514 1, Total manshifts required 12,307 18,765 14,629 7,500 2,001 0 Year Level support metres Tunnel metres-blue Tunnel metres-waste Contact metres Material cost (R) 553, , , Level support metres Tunnel metres-blue Tunnel metres-waste Draw point metres Trough metres Contact metres Material cost (R) 854, ,371 1,327, , Level support metres Tunnel metres-blue Tunnel metres-waste Contact metres Material cost (R) 1,375,840 1,863, , Level support metres Tunnel metres-blue Tunnel metres-waste Draw point metres Trough metres Contact metres Material cost (R) 625,402 2,725,369 1,207,697 1,853, , Level support metres Tunnel metres-blue Tunnel metres-waste Draw point metres Trough metres Contact metres Material cost (R) 489, , , GRAND TOTAL 2,794 4,169 2,514 1, Material cost (R) 3,899,172 6,418,490 4,469,988 2,274, ,010 0 Appendix 4A B-Cut LOM for 2001 SBP Base manpower case for wet shotcrete Date 23 March 2001 Life of mine base case support requirements for wet shotcrete B-Cut LOM for 2001 SBP Base maretial case for wet shotcrete Date 23 March 2001 Year Level support metres Tunnel metres-blue Tunnel metres-waste Contact metres Manshifts Level support metres Tunnel metres-blue Tunnel metres-waste Draw point metres Trough metres Contact metres Manshifts , Level support metres Tunnel metres-blue Tunnel metres-waste Contact metres Manshifts 1,430 2, Level support metres 0 Tunnel metres-blue Tunnel metres-waste Draw point metres Trough metres Contact metres Manshifts 795 2,653 1,616 2, Level support metres 0 Tunnel metres-blue Tunnel metres-waste Draw point metres Trough metres Contact metres Manshifts GRAND TOTAL 2,794 4,169 2,514 1, Total manshifts required 3,965 6,721 5,459 3, Year Level support metres Tunnel metres-blue Tunnel metres-waste Contact metres Material cost (R) 1,066, , , Level support metres 0 Tunnel metres-blue Tunnel metres-waste Draw point metres Trough metres Contact metres Material cost (R) 1,069, ,230 1,777, , Level support metres Tunnel metres-blue Tunnel metres-waste Contact metres Material cost (R) 3,496,601 5,653,124 1,939, Level support metres Tunnel metres-blue Tunnel metres-waste Draw point metres Trough metres Contact metres Material cost (R) 835,480 3,402,887 1,578,833 2,440, , Level support metres Tunnel metres-blue Tunnel metres-waste Draw point metres Trough metres Contact metres Material cost (R) 588, , , GRAND TOTAL 2,794 4,169 2,514 1, Material cost (R) 7,057,043 11,563,414 6,956,511 3,012, ,446 0 The Journal of The South African Institute of Mining and Metallurgy JULY