68
International RILEM Conference on Materials, Systems and Structures in Civil Engineering
Conference segment on Service Life of Cement-Based Materials and Structures
22-24 August 2016, Technical University of Denmark, Lyngby, Denmark
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69
International RILEM Conference on Materials, Systems and Structures in Civil Engineering
Conference segment on Service Life of Cement-Based Materials and Structures
22-24 August 2016, Technical University of Denmark, Lyngby, Denmark
SERVICE LIFE DESIGN AND ASSESSMENT FOR CONCRETE
STRUCTURES IN HZM SEA LINK PROJECT FOR 120 YEARS
Kefei Li
(1)
, Dongdong Zhang
(1)
, Quanwang Li
(1)
(1) Civil Engineering Department, Tsinghua University, Beijing, China
Abstract
The ongoing mega project of Hong Kong – Zhuhai-Macau (HZM) sea link project consists of
sea bridges of 28.8km, an immersed tube tunnel of 6.8 km and two offshore artificial islands.
One of the major challenges of this project is to ensure a service life of 120 years for the
concrete structures in a rather aggressive marine environment. This paper gives a
comprehensive presentation on the durability design and the durability assessment for the
concrete elements and structures in the project. For the durability design, the general
philosophy and approaches are given for the concrete elements, and model-based design is
conducted for the carbonation-induced and chloride induced corrosion of steel rebars. The
durability requirements are obtained from this model-based design process. During the
construction phase, the durability requirements are represented by quality control parameters,
and in-situ tests are performed to collect the data for these parameters. On the basis of the
statistical properties of these parameters, the achieved durability extent of concrete elements
is evaluated through a systematic durability assessment process. On the basis of the
assessment results, a preliminary maintenance planning is formulated for the service life
1. Project
introduction
The HZM project links the cities of Zhuhai and Macau on the South-eastern coast of China
mainland and the city of Hong Kong (HK) across the water region of Ling’ding Ocean. The
total length of project is near 36km, consisting of sea bridges of 28.8 km, two offshore
artificial islands and an immerged tube tunnel of 6.8 km. The traffic capacity is 6 lanes in dual
direction with a design speed of 100km/h. The design working life of the whole project is 120
years [1]. The preliminary study of project began from 2008 to 2010, the detailed study phase
started from 2010 and construction works are expected to end in 2017. The general view of
HZM project is illustrated in Figure 1.
70
International RILEM Conference on Materials, Systems and Structures in Civil Engineering
Conference segment on Service Life of Cement-Based Materials and Structures
22-24 August 2016, Technical University of Denmark, Lyngby, Denmark
Figure 1: General view of HZM sea link project
The sea bridges consist of four navigable spans and non-navigable spans of 28.8km. The
structure for the three navigable spans is cable-stayed bridge while the Hong Kong side span
adopts continuous beam structure. These spans are connected by 110m non-navigable spans
of continuous beam with steel box-girder. Except for the pylons and auxiliary piers in the
navigable spans, all the piers and the bearing-platforms of sea bridges are prefabricated in
segments and assembled in place. The immerged tube tunnel is made of concrete, consisting
of four in-place segments (112.5m each) and 27 prefabricated segments (180m each). The
cross section of the tunnel tube is 38m 11.4m with wall thickness of 1.5m. The prefabricated
segments of immersed tunnel are made in factory near the project site and transported to the
project site by floating-sinking method. Two artificial islands are constructed serving as the
connections between the sea bridges and the immersed tunnels. The area of artificial islands is
nearly 200,000 m
2
, constructed with the help of cofferdam made from sand-filled steel tubes.
The HZM project is exposed to the subtropical marine monsoon climate. The annual average
temperature is between 22.3~23.1ºC. The annual average humidity is between 77%~80% with
large seasonal variation. The sea water salinity is 32.9 for eastern part and 25.4 for western
part (bottom on sea bed), and lowest salinity is recorded as 8.1 and 10.4 for eastern and
western regions. The concentration of Cl
-
in sea water is between 10700~17020 mg/L and the
sulfate ions (SO
4
2-
) between 1140~2260 mg/L. The pH values of sea water are between
6.65~8.63. On the basis of hydrology data, the exposure zones are evaluated as: atmospheric
zone (>+6.26m), splashing zone (+6.26m~-0.40m), tidal zone (-0.40m~-2.10m) and
immerged zone (<-2.10m).
2. Durability design for 120 years
2.1 Design philosophy
For the concrete structures exposed to the marine environments of project site, the possible
deterioration mechanisms include: the carbonation-induced corrosion of reinforcement steel