Wet shotcrete trial

摘要

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/m~3 and 8 kg/m~3 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/m~3 UnitsLafarge 42.5 Duratech 500 kgCondensed silica fume 40 kgRayton Sand 1.558 TonDelvocrete stabilizer 10 3.6 litresGlenium 27CH 5.4 litresMeyco TCC 735 5 litresWater 230 litresMeyco SA 160 25 litresFibre 8 kgCement/Water Ratio 2.35 - Water/Cement Ratio 0.43 - Flow 615 mmIf 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 machines 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 percent with regard to this project.