TECHNICAL | MECHANISED TUNNELLING


1 REFERENCE PROJECT: HONG KONG – WATER MAINS IMPROVEMENT


The pipejacking project in Hong Kong is part of the larger water mains improvement project with an overall length of 56km, involving installation of new pipelines, and surveying and rehabilitation of existing pipelines with diameters of up to DN 1400. The project is owned by the Water Supplies Department. Victory Trenchless Eng. Co. Inc (VTEC) was awarded a contract


to install a 107m-long section of pipeline on Wood Road in the Wan Chai area. Pipejacking was selected as the preferred method to install the section on 153m constant radius. Geology along the alignment is granite with UCS up to 200MPa. A 3m-long steel pipe was selected for the installation, able to


support the higher jacking loads. An additional benefit of the welded steel pipes for hard rock is the capability to counteract the roll.


Due to the hard rock condition and small diameter (only OD 960mm), an AVN 800 HR was selected. The cutterhead was equipped with conical 317mm cutters with TCI inserts. Due to the


high abrasivity of the rock, the cutting wheel was armoured with additional protection plates, especially in the rim area and additional hard facing in all critical zones. The machine had installed power of 90kW, enabling cutting wheel rotation of up to 26rpm @ 260 l/min and a maximum torque of 55kNm. As typical for Hong Kong, space on site was limited which resulted in challenges, not only for the machine assembly but regular pipe extension and welding, with an average welding time of 2-3 hours. An extremely compact launch shaft design was chosen (3.5m x 6.5m). The works were undertaken in 2020. During the initial period of the drive and learning curve, the cutting wheel drive was adjusted, including replacing the hydraulic pump in the control container to enable a higher cutting wheel rotation speed of up to 26rpm. The pipejacking was completed over 60 days, including several idle days. Average daily progress was 4m. Given the abrasivity of the rock, there was only moderate wear of the cutting tools (see Figure 9).


2 REFERENCE PROJECT: HUNUA 4 WATER MAIN, NEW ZEALAND


The Hūnua 4 watermain project is the largest water pipeline project undertaken in New Zealand for many years. The project involves over 30km of 1.3m to 1.9m-diameter steel pipeline in Auckland. A Herrenknecht AVN 2500 (OD 3,025 mm) was tunnelling in basaltic rocks with a UCS up to 135MPa. Thanks to a dedicated hard rock cutting wheel design (see Figure 10), an average penetration rate of 8mm/rev was accomplished. This resulted in a best weekly performance of more than 137m and a record drive length of 1,296m, which was the longest single drive in the southern hemisphere by a pipejacking MTBM of this size.


equipped with a stronger main bearing, higher torque,


triple the thrust jacking loads, and greater penetration rates in hard rock. The design of its cutting wheel and tools have


been fundamentally changed, employing an adapted multi-ring, conical cutting wheel design using tungsten carbide inserts (TCI) cutters. The equipment also offers high wear resistance and, as shown on utility projects already internationally, the machine can perform drives up to 200m in length without interventions. After tests, the AVN 800 HR had its first operational


trial drive on a 34m-long bore in Clara mine, Germany. Rock strengths up to 140MPa were successfully handled. Peak performance of the machine was 35mm/min. Technical improvements on the AVN 800 HR:


● For rock with high UCS: up to 200MPa ● High wear-resistance of TCI cutter discs ● Extended drive length: up to 200m ● Torque: 55kNm ● Increased rotation speed of cutting head: up to 26 rpm @ 260 l/min


● Compact jacking frame to achieve a small launch shaft of Ø 3.2m


● Operation by standard control container C20 possible ● Flushing ring (with remote-controlled ball valve): fine particles kept from annulus


● Extension kit OD 1,295mm with rock cutting wheel, up to 80MPa possible


22 | January 2024


See Figures 1a and 1b. A project example with AVN 800 HR was the Water


Main Improvement Project in Hong Kong, in 2020, where the new machine design handled abrasive hard rock conditions (see box panel-1). For the smaller diameters of AVN 400 to AVN 600, a


new rock cutterhead generation has been designed with tricone cutters, having a comparable wear-resistance to the TCI offer on the AVN 800 HR. The new generation of small diameter slurry machines will enhance possibilities for microtunnelling in rock, working with alternative methods like E-Power Pipe® Pipe®


and Direct – and helped by a new jet pump system for slurry


discharge, down to 450mm (18”) diameter – to give wider options on projects, such as for underground cable or pipeline installations. It should be noted, however, that the AVN 800 HR


is not restricted to hard rock geology but can be equipped with a standard or mixed soil cutting wheel as ground conditions vary on different drive sections, and alignments, of a utility tunnel. Another trend in trenchless, small diameter tunnels


for alignments to go deeper, especially for sewers. There are two key reasons for this trend: first, to get below the increasing number of utility services in urban settings; second, municipalities want more gravity flow in their sewers rather than building and operating so many pumping stations.


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