East Rail's Lok Ma Chau Spur Line Extension in Hong Kong Nears EndIn Hong Kong's Northern New Territories lies a 25 hectare site of agricultural lands and ponds. This is the Long Valley wetlands, a feeding and breeding ground for many bird species. In 2002, the Kowloon Canton Railway Corporation (KCRC) awarded a contract to the Dragages Hong Kong joint venture, including Bouygues Travaux Publics and its Hong Kong subsidiary Dragages Hong Kong Ltd, to build two strategically important railway tunnels under these wetlands. Click cn/34.The LDB 201 5.2 km tunnel contract is part of a 7.4 km spur line that branches off from KCRC's East Rail mainline and runs from Sheung Shui in the East to Chau Tau in the West, to tie in with a new border crossing into mainland China. The TBM had come from a previous Dragages tunnel project (DB 320) on the KCRC's West Rail, as did many of the personnel. Visit www.krcr.com and www.bouyguesasia.com TBM 'Mulan'The TBM, named after a fabled female Chinese warrior, was an NFM Technologies machine of 8.75 metres in diameter, 100 metres long with all its associated equipment included a refurbished cutter head constructed in Shanghai. After assembly, the TBM was ready to start the construction of the first 3.6 km bored tunnel on 15th September, 2003. The first portion of 1.7 km between Sheung Shui and Kwu Tung (KTU) was completed in five months including a difficult section of 400 metres of very strong volcanic tuff rock. The first break-out in the box of KTU, which forms provisional works for a future station, was held on 27th February, 2004. Visit www.nfm-technologies.com After one month of maintenance during the crossing of the 335 m-long box of KTU, 'Mulan' was ready to start the second portion of the down track tunnel towards Chau Tau. The D-wall of the extraction shaft in Chau Tau was broken through on 21st June, 2004. This was the halfway point of the project, the TBM completing the 3.6 km tunnel drive after nine months in the ground.After disassembling and moving back to the launching shaft in Sheung Shui, 'Mulan' was ready to start the up track tunnel on 20th August, 2004, only two months after the completion of the first tunnel. The team being then more familiar with the soil conditions allowed the JV to achieve a better performance. The 3.6 km of the second drive were executed in 7.5 months for a final breakthrough in Chau Tau on 8th April, 2005. East ApproachThe tie-in of the LDB 201 tunnels with the existing KCRC East Rail main line comprises 700 metres of cut-and-cover tunnels ramping down from the existing rails level to the TBM launching shaft. These approach tunnels needed to be constructed within a very narrow envelope of land between the nearby Dongjiang watermains and the busy San Wan Road. In addition, the existing rails needed to be diverted to allow the construction of the tie-in without impacting on the East Rail main line operations.Starting in March 2003, advanced works were well underway, including reduction of the width of San Wan Road, formation works to divert the existing main lines to an "interim" alignment, installation of new posts and portals. In December 2003, the mainline was successfully diverted in a number of stages to the temporary alignment and the railways protection frames erected to allow the construction works of the cut and cover to proceed within one metre of the rail tracks with no risk of endangering the safety of the public. Dragages Hong Kong was able at that time to start the construction of the East Lok Ma Chau down track cut-and-cover tunnel using sheet piles installation by Giken press-in method and RMD sliding metallic formworks. This part of the East Approach (EA) was completed in August 2004. Visit www.giken.com and www.rmdkwikform.netThe construction of the East Lok Ma Chau up track cut and cover was undertaken using the roof of the down track, as a working platform for a completion in March 2005. The completion of this stage of works allowed the joint venture to reinstate the East Rail tracks in their permanent location between October 2004 and June 2005. These reinstatement stage included an "Island stage" where works had to be performed between the East Rail lines in operation. Kwu TungKwu Tung is a small rural village close to the centre of the spur line. It is foreseen that in the future this area will undergo major redevelopment with the construction of a new town with a KCRC station. The scope of works was to construct the lower station platform.The first phase of the works was the construction of over 20,000 sq m of 800 mm-thick D-wall to form the 338 m-long and 29 m-wide box. This D-wall was constructed using both conventional clamshell grabs and "cutter" in five months. The excavation of 270,000 cu m of soil took 5.5 months with the installation of three layers of struts.The challenge of this part of the site was to achieve the base slab before 27th February, 2004 to allow the TBM to cross the box. To let the working trains reach the TBM, the construction of the down track cut and cover could only be resumed in July 2004 after the completion of the first tunnel in Chau Tau. The same sequence was applied to the up track cut and cover for a final completion in October 2005. The backfilling of 100,000 cu m of soil was completed on top of the box between October 2005 and April 2006.West ApproachA cut and cover similar to the East one was being formed within sheet piles and diaphragm walls to connect the extraction shaft receiving the TBM and the viaduct section of the spur line at the border crossing. The main difficulties of the construction of this cut-and-cover tunnel were the diversion of a stormwater drain channel intercepting the project and several relocations of the Lok Ma Chau Road on top of the boxes. These works took place between June 2003 and May 2005. Cross PassagesTo comply with the Hong Kong Fire Departments evacuation strategy, ten cross passages were required to be constructed between the two tunnels every 240 metres. These ten cross passages required ground treatment to ensure that the construction could be carried out safely and successfully.One of them was fully in rock stratum and required only fissure grouting. A second one close from Chau Tau was shallow enough and in soft ground to be realized by ground substitution using a clamshell grab. Five cross passages were treated from the ground surface by tubes a manchettes (TaMs) and jet grouting.The more specific three remaining ones were located under the environmentally protected Long Valley wetlands where no work from the ground surface was permitted. That is the reason why the joint venture proposed to implement the ground freezing solution from inside the tunnel. This was the first time such a technique had been used in Hong Kong.Thirty-two freeze pipes per cross passage were installed plus additional instrumentation tools. The freeze units were installed in three soundproof containers. The brine was chilled to -30°C into the freeze pipes. Once an ice ring of 2 m wide was firmly established, the tunnel segments were opened up, ready for excavation.Each cross passage required the removal of 60 cu m of frozen solid ground with no chance of collapse. The ground freezing and the construction of these three cross passages took place between October 2004 and March 2005.Ongoing ProgressDragages Hong Kong Joint venture achieved a very good performance as the two bored tunnels were achieved two months ahead of programme and the East Approach East Rail's tracks were handed over to the client five months in advance of schedule. This year Dragages Hong Kong is processing with all finishing works, surface road works around emergency access point (EAP) and ventilation buildings, and testing with KCRC and the different government departments (Fire Service, Building, Water Service…) for a final handover on 31st October, 2006.This project involved around 2,000 persons at the peak production with Hong Kong Chinese workers on surface sites, Nepalese workers on TBM section and mainland Chinese subcontractor for the segments precast factory. The staff on site included 30 expatriates from France, the UK, Australia, Canada, Finland, the Netherlands, etc. Around 60 subcontractors were working on this site. The main ones were Action Top, Arup, Atkins, BYME, Giken, Houtai, Hung Yip, Intrafor-Bachy Soletanche JV, Kanson, Kinwah, Mok Sum Kee, Shenzen Gangchuang, Tsai Huan Kee, Wader and Yongnam. Visit www.arup.com, www.atkins.com, www.giken.com, www.vsl-intrafor.com, www.soletanche-bachy.com, www.gcbm.cn/en/index.htm and www.yongnam.com.sg. The major suppliers were Pionneer, VSC, Palmieri and RMD. Visit www.palmierirocktools.com 21/06.