Hangzhou Bay Bridgea
36 km shortcut between Shanghai and Ningbo
 |
Wang RENGUI
Civil Engineer CCCC Highwang
Consultants CO. Ltd.
85, Deshengmenwai
Street,Xicheng
District,(100088) Beijing
CHINA
wrengui@263.net |
Wang Rengui , born 1965, received his civil engineering degree from the South-East University Nanjing PRC.
 |
Meng FANCHAO
Civil Engineer CCCC Highwang
Consultants CO. Ltd.
85, Deshengmenwai
Street,Xicheng
District,(100088) Beijing
CHINA
mengfanchao@hpdi.com.cn |
Meng Fanchao , born 1959, received his civil engineering degree from the Chongqing Jiaotong University PRC.
Abstract:
The Hangzhou Bay Sea-crossing Bridge is the world’s longest bridge over ocean waters. Its total length is 36 km in total length, of which 35.7 km is bridge. A great number of new techniques, new materials, new equipment, and new theories were adopted in the overall design of Hangzhou Bay Sea-crossing Bridge due to the large scale of the project, as well as complex hydrological, meteorological, geological, and sea erosive conditions which provided impetus to the innovation of bridge technology and design in many regards.
Fig. 1 Location of the Hangzhou Bay Sea-Crossing Bridge
Key Words: Hangzhou Bay Sea-crossing Bridge General Design Innovation
1 PROJECT IN BRIEF
The Hangzhou Bay Sea-crossing Bridge is a component of the national trunk line in the highway network of China’s “Five and Seven arteries in south-north and east-west directions”. It provides the most convenient way across the Hangzhou Bay on the highway from Shenyang to Haikou. The bridge is also an important component of highway network proposal of “2 transverse and longitudinal trunk lines separately,
18 link roads, 3 loop highways and 3 road corridors” before 2010 in Zhejiang province, and thus will effectively connect the southeast cities of Ningbo and ZhouShan of Zhejiang province with Shanghai to reduce driving time to under two
hours.
The project starts from ZhengJiaDai of JiaXing city, crosses Hangzhou Bay and ends at ShuiLu Bay of Ningbo city (see Fig. 1). It consists of a north link road, north approach viaduct, north channel bridge, middle approach viaduct, south channel bridge, offshore platform, south approach viaduct, and south link road.
More than 70 special studies were carried out to provide scientific validation in preliminary design stage for the final plan of the bridge with regard to construction conditions, construction plan, safety, and durability of the structure. This provided a solid foundation for the successful implementation of the project.
2 MAJOR TECHNICAL CRITERIA
(1) Road Class: Dual 3 lane highway
Notes: All di mensions are in centime ters, the number in bracket is subgrade width of the link road, the number outside of the bracket is the bridge deck width.
Notes: All di mensions are in centime ters, the number in bracket is subgrade width of the link road, the number outside of the bracket is the bridge deck width.
Fig.2 Width of Subgrade and Bridge Deck
(3) Subgrade Width: 33 m for bridge deck ( not including the anchor and cable area),
35 m for link roads, see Fig. 2.
(4) Design Load: Vehicle-Exceeding Class 20, Trailer-Class 120.
(2) Design Vehicle Speed: 100 km/h for the sea-crossing bridge, 120 km/h for link roads on both banks.
(5) Maximum Longitudinal Grade: Less than 3%. (6) Crown Slope of Bridge: 2%;
(7) Design Flood Frequency: 1/300 for Bridge, 1/100 for link roads.
(8) Design Service Life: 100 years for south and north channel bridges, 60 years for approach viaducts.
(9) Design Standard of Wind Resistance: 100 year return period in operation, 30 years during construction.
(10) Navigational Standard: Design maximum navigational water level of 5.19 m is adopted for navigational clearance calculations (National elevation bench mark in 1985). The main navigational span of north channel is designed for the passage of 35000 ton vessels and the condition of building a deepwater port is considered. The navigational clearance is 325 × 47 m. The two subsidiary navigational spans on both sides of the main navigational span are designed for the passage of 1000 ton vessels. The main navigational span of the southern channel is designed for the passage of 3000 ton vessels. The navigational clearance is 125 × 31 m. The subsidiary span is designed for the passage of 300 ton vessels.
(11) Seismic Intensity : ?
3 NATURAL CONDITIONS
3.1 Meteorological Conditions
The Project Area belongs to the typical subtropical zone characterized by a mild, humid, rainy climate, frequent monsoons and four different seasons. The annual average temperature is 16? with the highest temperature of 28? in July and lowest temperature of 4? in January.
3.2 Landforms
The terrain on the north and south banks at the bridge location is level. The shore consists of side foreland at river mouth and tidal flats. The south bank is 9 km in width while the north bank is 1.5 km in width.
The terrain at the bay bottom is composed of scouring channels and tidal current ridges, rising mildly from east to west with a reduction in water depth. The average and maximum water depths are 10 m and 13.6 m respectively with a U-shaped trough deeper in the north and more shallow in the south.
Fig. 4 Horizontal and Vertical Alignment
3.3 Hydrologic Features
Hangzhou Bay is an informal semidiurnal tidal sea area with flood and ebb tides twice one day. The flood tide lasts longer than the ebb tide with a typical movement type of reciprocating flow. The observed maximum tidal velocity is close to 5 m/s, the maximum tidal range is almost 8 m and the tidal flow volume is about 1 × 1010 cubic meters. The content of sand and salt in the sea water is 1.25 kg/m3 and 10.8 g/kg respectively.
Hangzhou Bay is in a stable condition at the bridge location, characterized by scour in winter, silting in summer, scour in the north, and silting in the south.
3.4 Geological Conditions
The stratum at the bridge location is mainly composed of quaternary cover. It is wildly covered by quaternary stratum in addition to some buttes and monadnocks on north bank. Thick loose deposits of the quaternary stratum are mainly composed of clayey soil, sandy loam, muddy loam, silty sand, fine sand, gravel and medium-fine sand on south bank, with an average thickness of 130 to 220 m. The stratum belongs to coastal plain. The bedrock is ignimbrite on north bank and mudstone on south bank. The geological profile is shown in Fig.3.
The poor geological conditions are mainly composed of soft soil layer and the methane in shallow stratum. The soft soil layer is 8 ~ 45m in depth featured with high moisture, high compressibility, thixotropy-prone, low shear strength, and low capacity. The shallow sandy layer is prone to liquefaction. The methane in shallow stratum is distributed in lensoid-shaped 40-60 m deep sandy layer in the 10 km tidal-flat area.
3.5 Hydrogeological Conditions
The groundwater is mainly quaternary unconsolidated rock pore water which can be classified into phreatic water, micro-confined water and confined water at the bridge location. Phreatic water is mainly distributed in the sandy loam layer at sea bottom, of which the first layer phreatic water is 50 m in depth with the sandy loam and fine sand with moisture while the second layer is 80 m in depth with the medium-fine sand with moisture. The groundwater and seawater are weakly erosive.
4 MAJOR TECHNICAL CHARACTERISTICS
4.1 Large Scale
The bridge is 36 km in total length, of which 35.7 km is bridges over water. The large scale of the project creates new difficulties for bridge construction, operation, and management.
4.2 Poor Natural Conditions
Effective work time is only 180 days per year due to the complicated hydrological and meteorological conditions with high tide and torrential flow.
The geological conditions is comparatively poor. There are soft soil layers 50 m in thickness and methane in shallow strata within 10 km in the south shoal, which may have adverse effects on the construction of bridge foundations.
4.3 Poor Construction Conditions and Constraints
Construction conditions may be constrained due to the 9 km long tidal-flat area on south bank.
4.4 Tight Construction Period
The Project is proposed to be completed in 2008. The 70 m full-span prefabricated box girders of the 18 km long approachs have to be erected from water due to the constraints of vessels and equipment while the 50 m full-span prefabricated box girders of 10 km long approach in the tidal flat section on south bank must be transported and erected by trolley onto the bridge below. There is only one work face. The construction plan and organization must focus on making sure the bridge project can be complete in time even though the offshore operation distance is long and the work load is heavy.
4.5 Need for High Structure Durability and Aesthetics
The bridge is in a high erosive sea environment which will have substantial effects on the durability of bridge. Furthermore, the bridge is located in the highly developed economical district in the Yangtze delta, so a high standard of aesthetic design is required.
5 OVERALL DESIGN
Fig. 5 Prospective View of Hangzhou Bay Bridge
The overall design of the Hangzhou Bay Bridge consists of definition of the horizontal and vertical alignment, general layout, and aesthetic design.
The horizontal and vertical curves should be smooth. Long straight lines and small deflection angles must be avoided to provide a safe and comfortable psychological and physical sense and be harmonious with the roadside surroundings.
The horizontal alignment is affected by several factors, including the north bank link road, north bank sea embankment, inland harbor basin in the Zhapu port, north navigational channel, south navigational channel, transition section between bridge and link road on south bank, south bank sea embankment, south bank link road,
6 STRUCTURE DESIGN
Fig. 7 Photo of South Channel Bridge, Fig. 6Photo of NorthChannel Bridge
6.1 North Channel Bridge
The North Channel Bridge is 5-span continuous cable stayed bridge with a half floating system, diamond-shaped double pylons, and double cable planes. The span layout is 70+160+448+160+70 = 908 m (Fig.6).
The pylon is diamond-shaped to enhance the structure stiffness and wind-resistant stability. Bored piles of 2.8 m diameter and abutments with anticollision and energy-dissipating devices were used. The stays are anchored at the pylon through an integrated steel anchor box.
A flat steel box girder of 3.5 m in depth and 37.1 m in width is used. Girder segments of standard 15 m length were prefabricated in the factory. The stays are anchored to the box girder using anchorage plates.
Rectangular cross sections with rounded edges are used as subsidiary piers and transitional piers. Bored piles of 2.5 m and 2.8 m diameter and pilecaps are used for the foundations.
6.2 South Channel Bridge
The South Channel Bridge is a 3-span continuous cable-stayed bridge with A-shaped pylon, double cable planes, and steel box girder. The span layout is 100+160+318 = 578 m (Fig.7).
The A-shaped pylon enhance the structural capacity, stiffness, and wind-resistant stability. The pylon has a delicate and harmonious appearance. Bored pile of 2.8 m diameter and pilecaps with anticollision and energy-dissipating devices were used. The stays are anchored to the pylons using integrated steel anchor boxes.
A steel box girder of 3.5 m constant depth and 37.1 m width is used as the main girder. Segments of length 15 m are prefabricated in the factory. The stays are anchored to the steel box girder by anchorage plates.
The subsidiary piers and transitional piers have rectangular cross section with round edges. Bored piles of 2.5m and 2.8m in diameter and pilecaps are used for the foundations.
6.3 Approaches over Water
Fig. 8 Photo of Approach in Water
Fig. 9 Photo of Approach in Tidal-flat Area
Fig.10 Photo of Offshore Platform
A 70m span continuous box girder erected by full span hoisting is used for the approach spans over water. The hoisting weight is 2260 tonnes for one span. A rectangular cross section with rounded edges is used for the pier shafts and steel pipe pile plus pilecaps are used for the foundations (Fig.8).
6.4 Approaches over Tidal Flats
A 50m span continuous box girder structure is used in this areas. Prefabricated spans are transported by trolleys over the previously completed portion of bridge. The hoisting weight 1350 tonnes for one span. A rectangular cross section with rounded edges is used for the pier shafts. Bored piles plus pilecaps are used for the foundations.
6.5 Approaches over Land
The approaches over land are affected by many factors. Continuous box-girder spans of 80m, 60m, 50m, and 30m are used depending on the obstacles to be crossed and economic requirements. A rectangular cross section with rounded edges is used for the pier shafts. Bored piles plus pilecaps are used for the foundations.
6.6 Offshore Platform
The Hangzhou Bay Bridge extends for more than 30 km over water without any island or reef. An offshore platform will be built in the sea to improve efficiency and reduce the risk during construction. The platform covers 12000 m2 (Fig.10).
The offshore platform will serve as the living and working base for the offshore constructors during construction and also function as a relay station for offshore survey and communication. It can also serve as an offshore location for emergency rescue and maritime administration.
The offshore platform is designed with double floors using bored piles and steel pipe piles for the foundation. The first floor platform is a structure composed of prefabricated beams and slabs plus wet joints. The architectural design of the second floor will be carried out depending on its actual final purpose.
7 CONCLUDING REMARKS
The Hangzhou Bay Bridge is a large-scale project with complex construction conditions. The primary material quantities are given in Table 1. The exploration and design work was carried out by a joint venture of CCCC Highway Consultant (HPDI) Co., Ltd (General design, north channel bridge, south channel bridge, approaches in the high pier region, and offshore platform design) and China ZhongTie Major Bridge Reconnaissance and Design Institute Co., Ltd (approaches in the low pier region and link road design).