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.