Herrenknecht to Supply TBM for Castle Peak Cable Tunnel in Hong KongThe Castle Peak cable tunnel project was awarded by CLP Power Hong Kong Ltd to Dragages Hong Kong Ltd on 30th November, 2005. Click cn/64. The overall contract duration is 1,200 days, with the first 360 days allowed for land acquisition. A 5.25 m-diameter double shield hard rock TBM has been selected for tunnel excavation and the machine will be supplied by Herrenknecht. Visit www.herrenknecht.comThere will be five plus one key precast segments per ring. The precast segment moulds will be fabricated by Shanghai Tunnel Engineering Co. (STEC) in Shanghai and the 3,000 rings of precast segments will be produced by China State Construction Engineering (HK) Ltd in Shenzhen.Mucking-out of the tunnel will be carried out with conveyors to improve air quality inside the tunnel and to reduce the risk of accidents by minimizing plant movements. The TBM is expected to be delivered to site in February 2007 and excavation of the 4,500 m-long tunnel will start in May 2007 from the Castle Peak portal in the west after three months of TBM assembly. Visit www.stec.net and www.cscechk.com/main_e.htmThe tunnel will terminate in the east at a 38 m-deep Tuen Mun shaft comprising 13 metres of excavation in the soft ground and 25 metres of excavation in the rock. Diaphragm wall will be used to retain the soft excavation while bolting and shotcreting will be sufficient to retain the rock face.The solid geology of the tunnel alignment consists of two principal rock formations, the Tsing Shan granite and the Tuen Mun formation. The Tsing Shan granite forms the topographically high ground over the western (and major) section of the alignment. The granite is typically strongly deformed and re-crystallised, with NE-trending foliation and thin mylonite or schistose bands. The granite is divided into three textural varieties, medium-grained (gm), fine-to-medium grained (gfm) and fine-grained (gf), arranged in broad N-S trending bands, each with a width of 1 to 1.5 km at the alignment.The Tuen Mun formation (previously the Tsing Shan and Tuen Mun formations of the Repulse Bay volcanic group), comprises faulted, folded and metamorphosed sediments and lavas, outcrops in the foothills and lower-lying ground at the eastern part of the alignment. In the western part (Tsing Shan foothills) interbedded fine-grained quartzitic sandstone, metasiltstone and phyllite predominate, with subordinate andesitic tuff and conglomerate. Between the Tsing Shan foothills and Lung Mun Road, andesite and tuff are widespread, and metamorphosed siltstones are present. The topography and rock cover have been examined based on the geotechnical information available. The potential for soft ground is limited to areas of low topography (the Castle Peak portal, the valley at Ch 300, and Ch 4,240 to Ch 4,500 near the Tuen Mun shaft). Soft ground may also occur as seams of highly decomposed rock within major faults. At Castle Peak portal, the rockhead contours indicate that the tunnel will commence at Ch 20 in rock and that a 5 m rock cover is achieved at or before Ch 30. From Ch 30, the rock cover increases to 60 m at approximate Ch 190, before reducing to about 10 m at Ch 300, where the alignment passes under a valley associated with fault F1. The findings of borehole DH3 (Lam 2004) are not sufficient to confirm if soft ground will be limited to a narrow, steeply-dipping band of completely/highly decomposed material within the fault, or if a more extensive rockhead depression is present and further ground investigation will be required.From Ch 300 to 3,850, the ground rises steeply, and the topography along the tunnel alignment is generally in excess of +100 mPD, with bedrock occurring 0 m to 30 m below the ground surface. Drilling at faults F2, F3 and F4 by Lam in 2004 recovered a continuous, predominantly Grade II rock core, and did not reveal any major zone of weakness or soft ground at any of these locations. DH8 (at F4) penetrated 116 m vertical thickness of foliated and mylonitised Grade II granite, with thin seams of Grade IV rock found down to 80 m depth, and terminated in Grade II/I basalt. DH8 did not encounter a substantial zone of weak ground.From the Tsing Shan foothills toward Tuen Mun, the topography gradually decreases below +100 mPD to +6.5 mPD at the Tuen Mun shaft site. Rockhead levels are expected to drop below 0 mPD from Ch 4240, and to remain at levels of -10 mPD to -12 mPD between Ch 4,240 and Ch 4,500. The vertical alignment of the tunnel has accordingly been arranged to optimise excavation within rock, and to maintain a minimum rock cover of approximately one tunnel diameter. Visit www.bouyguesasia.com and www.clpgroup.com 33-34/06.