A key focus for Perry Infrastructure was the microtunnelling industry, in particular the hard rock market. The company realised that machines currently available had some limitations and the company set out to identify these limitations and overcome them.
Perry Infrastructure turned to Herrenknecht, the German based manufacturer of tunnelling and microtunnelling equipment. Jim Perry and Robbie Ashton met with their technical staff in Sydney in early 2004, and several months later Jim Perry was asked by Herrenknecht to travel to Germany to discuss the design and evolution of a new machine, the AVT600. At this stage 800 man hours had been put into the concept design of this innovative machine by Herrenknecht.
Jim Perry’s market for many years was Sydney, and he had drilled many thousands of metres of the highly abrasive Hawkesbury Sandstone. This knowledge, together with Herrenknecht’s vast resources and technical expertise, was used to design a machine that could cut through hard rock while it pushed an encasing pipe as it progressed.
The majority of rock microtunnelling in Australia is carried out using “free boring” techniques, which see an open hole drilled through the rock, not pushing the product pipe or encasing pipe. This method allows the drillers to withdraw their drill rods and cutting head to replace worn cutters.
The downside of free boring is the risk of passing through a lens, or dyke, of soft formation clay or sand which may allow the boring head to pass but then causes a collapse behind the microtunneller. With the hole behind the machine collapsed the borer cannot be withdrawn and the borer cannot drill ahead as it relies on laser guidance from the launch shaft for its direction. Usually the only option is to retrieve the borer by excavating from the surface, which is not always a desirable option as the shaft may be quite deep in rock, and immovable objects such as a freeway or railway line may be above the bore.
Following extensive design and testing of the machine in the factory in Germany it is now being transported to Australia. The new Herrenknecht AVT600 is a high powered laser guided microtunneller with “grunt”. It is designed to drill up to 200 m in length in rock up to 80 MPa in strength. The machine has 60 kN of torque at the face and is driven by 300 mm augers with 100 mm hex drives. The augers and inner tubes have been manufactured in Australia by Perry Infrastructure.
The machine is capable of installing a 750 mm steel casing as it progresses. It possesses hydraulically retractable wing cutters. The cutting assembly is located within an inner housing that is positively located in the lead section of 750 mm casing. Should the outside wing cutters, the gauge cutters, wear in the abrasive sandstone the wingcutters are hydraulically retracted at the press of a button. Once the wing cutters are retracted they can fit within the encasing pipe.
The machine is designed like a mini tunnelling machine with two sets of 30 tonne capacity hydraulic grippers holding the inner shell against the 750 mm casing. Once the wingcutters are retracted the grippers are released and the entire drill string and machine are retracted to the launch shaft using the continuous flight augers.
The worn cutters are replaced and the drilling assembly re-inserted through the 750 mm casing pipe that has remained in position. The machine is located in the correct position using witness marks and cameras feeding information to the driller’s console. The hydraulic grippers are then actuated and the wing cutters extended to their full cutting diameter. Drilling can then continue.
The machine is expected in Australia in April, 2005. Herrenknecht has identified many overseas markets that can utilise this machine once it has been trialled and proven by Perry Infrastructure.
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