Lin, Ming (CCCC HZMB Island and Tunnel Project General Office) | Lin, Wei (CCCC HZMB Island and Tunnel Project General Office) | Van Stee, Joel (Trelleborg B.V.) | Peng, Xiaopeng (CCCC HZMB Island and Tunnel Project General Office)
The immersed tunnel of Hong Kong-Zhuhai-Macao Bridge (HZMB) contains 219 segmented joints, 60% of which are placed at water depth over 40m and each segmented joint is of circumferential length of approximately 90 m. To ensure the watertightness, the improvement of using the injectable waterstop was attempted and no leakage was found in the 5.664 km long tunnel up to now. The ways of improvement were elaborated in this paper and the conclusion drawn is that the effectiveness of watersealing can be achieved by looking at the system covering the structure and foundation of each tunnel element. Further, the elongation of the injectable waterstop that may lead to water passage was controlled by using permanent prestressing tendons longitudinally to confine the opening of the segmented joint
The waterproofness of the segmented joint of HZMB immersed tunnel has been a challenge, for over 3 km long section is located in water depth of over 40m (maximum water depth is approximately 46 m). Further, the segmented joints amounts to 219 in total and the length of each joint is as long as 90m. Comparatively, other immersed tunnels in the world has either shallower water depth or smaller cross-section (Rasmussen and Grantz, 1997); some minor leakages were reported by (Grantz et al., 1997), and as per the third author's experience of over 20 immersed tunnel, leakage through segmented joint has always been a concern. Nevertheless, no leakage has ever occurred at the segmented joints in HZMB tunnel from the commencement of installation of tunnel element in May 2013 to the completion of all installation in March 2017, and to now (June 2018).
With the consideration of tunnel's large scale and risk of this project, four rounds of waterstops were initially made for the segmented joint in the beginning of works, namely, polyurea + injectable waterstop + water expansion adhesive belt + Omega gasket. As a matter of fact, the work of water expansive adhesive belt is hard to be executed and is thus cancelled. The polyurea layer is vulnerable to fall off under the wave effect during towing of tunnel element. Therefore, the two key rounds of waterstops are injectable waterstop and the Omega seal.
Of these two, the injectable waterstop (also named after rubber-metal waterstop) is positioned outside thus being the initial round of waterstop of the segmented joint. The waterstop product of Trelleborg B.V. has been selected and applied. This type of waterstop has been developed and applied in immersed tunnel for around 30 years (Janssen, 1978: Grantz et al., 1997). The Omega seal is the secondary waterstop; its function is to stop the possible seepage water. In HZMB tunnel to improve the water sealing effect of the injectable waterstop a series of attempts have been made; they were introduced in this paper.
Lin, Ming (CCCC HZMB Island and Tunnel Project) | Lin, Wei (CCCC HZMB Island and Tunnel Project) | Su, Faqiang (CCCC HZMB Island and Tunnel Project) | Ning, Jinjin (CCCC HZMB Island and Tunnel Project) | Wang, Xiaodong (CCCC HZMB Island and Tunnel Project)
In Hong Kong-Zhuhai-Macao Bridge project the immersed tunnel element reached up to 76 000t in mass for sea transportation. The true water resistance during towing for such a large element had never been studied to author's knowledge. By the time 30 elements were installed, the towing team had formed a good cooperation and gained confidence in safe work. The first author, taking advantage of this rare opportunity, proposed and organized the towing test to find the actual water resistance and the corresponding velocity of tunnel element. Five tunnel elements transportation were involved. The test results of the water resistance and the relevant velocity were reported in forms of table and graph. It was also found that tunnel elements, being towed in the limited navigation channel, had its velocity increased with the increased towing force. However, when the velocity reached a certain threshold value, it ceased to increase. In addition, the test results were compared to that of the physical model test of scale 1:40, it was found that the results of the physical model testing underestimated the water resistance; the main reason of the difference is the scale effect.
The immersed tunnel of Hong Kong-Zhuhai Macao Bridge (HZMB) is made of 33 tunnel elements, each has a typical length of 180m and a mass of around 76,000 t (Lin, 2017; Lin, 2018).
Four tugboats were planned to tow thirty-three immersed tunnel elements at the early stage of the HZMB project, based on the findings of the scaled physical model test. Trial towing of a large barge, which has a similar mass of the tunnel element, was conducted as a construction preparation, it was found that six tugboats were needed rather than four. Then, for the first time towing, the author used eight tugboats, even with the “redundancy”, in the halfway the tunnel element and the tugboats did not advance but fell backwards by around 700~800m due to current. Obviously, the water resistance was underestimated and there is a difference of water resistance of the real towing work and that of the scaled physical model test.
Lin, Ming (CCCC HZMB Island and Tunnel Project) | Lin, Wei (CCCC HZMB Island and Tunnel Project) | Huang, Weimin (CCCC HZMB Island and Tunnel Project) | Ning, Jinjin (CCCC HZMB Island and Tunnel Project)
Thirty-three immersed tunnel elements of Hong Kong-Zhuhai-Macao bridge project had been installed in offshore condition without major accident: each typical element has a mass of around 76,000 t. In this paper, the author elaborated the special solutions and the critical details developed behind the work of plan, out-docking, towing, and mooring for immersion. Three work principles were learnt from this project, the redundancy design to the solutions, the rehearsal before real works, and the selection of appropriate timing and location in accordance with the detailed work plan.
In Hong Kong-Zhuhai-Macao Bridge project (HZMB), thirty-three (tunnel) elements with a large mass of 76,000t had been installed in offshore condition one after another from the year 2013 to 2017 (Lin, 2017) without a major accident. The HZMB tunnel is the longest roadway tunnel that has ever been built, even for shorter one accident during installation was not rarely seen; Walter (1997) presented some accidents learnt from US experience and Lars (2000) Øresund link. The thirty-five times installation (Lin (2017) reported that E15 had been installed for three times) with safety was thus not a coincidence. This paper elaborates the special efforts behind this good ending.
Among the works of installation of element in the HZMB project, the three steps of docking (warping) out, towing, and mooring for immersion were regarded as challenging works. To explain, the description starts with the completion of element production. Firstly, by inundation, element floated up with its position controlled by mooring lines that were connected to the winches on land. In times of installation, the element was then winched out through the dock gate. Then, to transport the element on the sea, the tugboats were used and tied to element by nylon ropes. Meanwhile, the mooring lines fixed on element were released to let element go. The towing distance is around 11 km. When element was towed to site, it needs to be moored again (i.e. connected with mooring lines which are anchored to the sea floor) for the subsequent operations of immersion and underwater connection. It can be seen that each element has to experience a transition state from the mooring in prefabrication yard to the mooring in tunnel site, the latter exposed to current and waves. Further, the natural water depth is shallow, so the element can only be towed in a confined channel (Fig. 1). If the element was out of control, severe consequence is expected: the project could suffer great loss in terms of cost penalty and time-delay, and the stranded element could block the already busy ship channel at Pearl River estuary.
Lin, Wei (CCCC HZM Island and Tunnel Project General Office) | Zhang, Zhigang (CCCC HZM Island and Tunnel Project General Office) | Liu, Xiaodong (CCCC HZM Island and Tunnel Project General Office) | Lin, Ming (CCCC HZM Island and Tunnel Project General Office)
The paper presents how the detailed design of immersed tunnel was conducted to ensure a reliable construction in a design-build contract. Hongkong-Zhuhai-Macau (HZM) immersed tunnel is determined to be a concrete-type tunnel with no external waterproof membrane in preliminary design, crack prevention is highlighted. Further, foundation was re-designed, and negative buoyancy during immersion was specified for safety. The unusual siltation on the gravel bed makes it impossible to place the tunnel element E15. Various monitoring work were carried out to find out the cause, and design report was made to client to solve the problem.
The Hongkong-Zhuhai-Macau (HZM) island and tunnel project is a design-build contract belongs to the 35.6 km Hongkong-Zhuhai-Macau link across sea. The project is for a vehicle highway of 100km/h design speed with double way six lanes. The design is required to meet the standards of both Mainland and Hongkong China whoever is higher. For example, design life is taken as 120 years as per Hongkong requirement rather than 100 years, lane width is taken as 3.75m from roadway standard of Mainland rather than Hongkongߣs. The contract mainly includes a 5.7 km long immersed tunnel and two artificial islands. The islands are for transition between undersea tunnel and bridges. A building is also included in the west artificial island, aiming for a landmark.
The immersed tunnel is made of 33 tunnel elements, each has a typical length of 180m and a mass of around 76,000t. The detailed design and construction starts in parallel from November 2011 and the project has a tight schedule of only 6 years. For, unlike bridge construction that can have as much work face as possible, there is usually only one work face for immersed tunnel, i.e. the tunnel element must be installed one by one. And the installation work exposed to sea loads, time window selection was needed, it was considered extremely challenging to complete the project on time.