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Design Proposal for Luyang Sea Crossing in Phase I Project of Yang Shan Deepwater Port Chapter IVChapter IVDesign Proposal of Bridge4.1 Layout DesignThe layout design of the bridge is in accordance with the proposals stated in the solicitation document. Six no of horizontal curves, with maximum straight length 5.75 km and minimum radius of 1000m, are placed within the 28 km boundary. The bridge layout plan is shown in the figure 4.1-1.Figure 4.1-14.2 Profile DesignThere are several physical constraints in the profile of Lu Yang Sea-Crossing Bridge as listed below:(1) Headroom Requirement at Principal NavigationThe free height of the principal navigation opening is larger than 35m respectively. The maximum design water level is 3.48m and thus the minimum bridge soffit level shall be higher than 38.48m. The principal navigation opening is located at chainage K17+623.(2) Headroom Requirement at Auxiliary NavigationThe free height of the auxiliary navigation opening is larger than 24m respectively. The maximum design water level is 3.48m and thus the minimum bridge soffit level shall be higher than 27.48m. The principal navigation opening is located at chainage K6+120.(3) Headroom Requirement for Non-navigation Openings BridgeTo maintain sufficient headroom for the peak tidal level 3.73m (100yrs return period), soffit level of the non-navigation bridge shall be higher than 9.0m.(4) Headroom Requirement for Marine EmbankmentThe headroom requirement for the bridge crossing over the original embankment at Lu Chao Port is larger than 2.5m. The top level of the original embankment is about 6.5m and thus the bridge soffit level is about 9.0m. In addition, the headroom requirement for the bridge crossing over the new embankment at Lu Chao Port is larger than 5.0m. The top level of the new embankment is about 8.0m and thus the bridge soffit level is about 13.0m.In order to satisfy the above constraints and provide a safe and comfortable riding condition, the general arrangement of the bridge is designed with reference to the relevant standards. The key design issues are list in the table 4-2-1. Table 4-2-1Key Design IssuesItemsUnitRequired ValueAdopted ValueMax.Gradient%520Min Radius of Convex Curvem450011000Vertical CurveConcave Curvem3000300004.3 Bridge Deck Cross-Sectional ArrangementLu Yang Sea-Crossing Bridge Project is designed based on the dual two lanes expressway design standard. The bridge deck sectional arrangement includes:1.0m(Clash Parapet) + 3.75m(Hard Shoulder) + 23.75m(Carriageway) +0.5m(Marginal Strip) +2.5m(Central barrier) + 0.5m(Marginal Strip) + 23.75m(Carriageway) + 3.75m(Hard Shoulder) + 1.0m(Clash Barrier)The total deck width is 28m as shown in figure 4.3-1.Figure 4.3-1The cross-fall is 2% and super-elevation will be provided where horizontal curve is smaller than 2500m.When the dual two lanes carriageway cannot satisfy the traffic demand during the late operation period, the hard shoulder can be revised to carriageway and thus the dual two lanes carriageway can become a dual three lanes carriageway. The bridge deck sectional arrangement includes:1.0m(Clash Parapet) + 0.5m(Marginal Strip) + 33.75m(Carriageway) +0.5m(Marginal Strip) +2.5m(Central barrier) + 0.5m(Marginal Strip) + 33.75m(Carriageway) + 0.5m(Marginal Strip) + 1.0m(Clash Barrier)The total deck width is 28m as shown in figure 4.3-2.Figure 4.3-24.4 Design Criteria of Bridge General ArrangementThe design proposal of the Lu Yang Sea-Crossing bridge project should be prepared in consideration of the project character, site condition and relevant experience in bridge construction project. The design criteria are listed as below: (1) In consideration of the practical, cost-effective, safe and aesthetic requirement and the advanced technology used in similar projects, the bridge shall be designed to match the project character and the navigation requirement. In addition, structure scheme of non-navigation opening bridge shall be cost effective and meet the tidal requirement.(2) The site condition is adversely affected by the heavy wind and tide, therefore construction work within marine area shall be minimized by utilizing the prefabricated, standardized and massive construction method. Working efficiency, construction duration and site safety is the prime concern of the project.(3) The structural design of the sea-crossing bridge shall fully consider the adverse effect due to the surrounding marine condition. Durable construction materials with necessary protective measures shall be adopted in order to ensure the safety and serviceability within the service life.(4) The geotechnical condition of Lu Yang Sea-Crossing Bridge Project is not very good. Very thick layer of soft material was found within the proposed site area. Thus suitable type of bridge structure shall be adopted to effectively minimize the foundation construction work.(5) The design shall fully consider the aesthetic effect and structural scale. The proposed bridge shall harmonize with the surrounding environment. Adequate environmental protective measures shall be provided.(6) The structural form of the sea-crossing bridge shall be continuous with few movement joints, in order to maintain better ridding conformance.(7) The sea-crossing bridge is considered to be located within the marine area, therefore durable structural form shall be adopted to minimize the future maintenance.4.5 General Design Concept of the Sea-crossing Bridge 4.5.1 Location Feature of the BridgeLu Yang Bridge crossing the Hang Zhou Bay is 28km wide. The bridge at the northern area will found on plane and smooth sand/slited clay breach which is about 3.0km wide at level 2.0-2.0M. The southern marine area is about 25km wide. The seabed is plane and smooth, at level -10 -13m.There are two navigations within the bridge area. The principal navigation located at chainage K17+623m which is 17.7km from the Lu Chao Port original embankment. It is constructed for the 5000T container ship. The auxiliary navigation located at chainage K6+120m which is 6km from the Lu Chao Port original embankment. It is constructed for the 1000T cargo vessel.The Sino-Japan seafloor cable will cross bridge at the principal navigation while the Shengsi Maji Mountain Harbour seabed cable will cross the bridge at auxiliary navigation.4.5.2 Bridge sectional divisionAccording to the topographical and navigational condition at the bridge location, the bridge can be divided into five sections from north to south. These five sections are: north approach bridge, auxiliary navigation bridge, middle approach bridge, principal navigation bridge and south approach bridge. In the middle approach, there is an opening span at the middle of the bridge.The total length of the approach bridges is 26.950km, which covers a large area. The length of the approach is about 95.8% of the overall length of the bridges. These are the main points of this design scheme. According to the topography and the alignment of the approach locations, the bridge can be classified to the zones: beach area, high pier in water and low pier in water.In considering the water depth requirement for the ships during the construction period, the demarcation between water and beach areas is in accordance with the differences in the foundation construction schemes and defined at reduced level 2.0m. In this scheme, for the beach area, reduced level of the seabed is at -2.0m above and the level at 2.0m below is the water zone.The limit of the non-navigation area will be at +19.0m at the deck level. For the sections with deck level lower than +19.0m, they are classified as low pier zone and above +19.0m as high pier zone.For the Luyang Sea Crossing sectional division, see Figure 4.5-1.Figure 4.5-14.5.3Selection of Bridge Type(1) Approach Bridge at beach area: This includes the land area at the north of Lu Chao Port sea bank, the ground level is at 2.0 (under reclamation, expected reclaimed level at 4.0M) and the total length about 3,000m. In this area, the scheme will be short spans concrete bridge in respect to economy, technique and sea bank requirement taken into account. The beach area at the south of new sea bank will be affected by the sea tides and therefore both the land and sea construction equipments cannot be accessible. The construction method should adopt a trestle or floating bridge on the sea for the ease of access. For the bridge in this area, the considerations should be in the respect of construction method, construction time and bridge cost-effectiveness. Also, the span length should be short. (2) Low pier area inside the water for the approach bridgeThe length of the lower pier area for the approach bridge inside water is 20.35km, which occupies the largest percentage of the whole bridge. The shape and layout of the bridge will govern the construction period and cost. By using the normal bridge structures and construction method cannot reach the requirement, and must adopt precast, standard and large structural components. The following are the considerations: Cost-effectiveness: Based on the economical reason, the span length should not be long but preferably short. Prestressed concrete structure will be appropriate because it is economic and durable. Effect to water flow: For the short span lengths, they will probably affect the water flow in the sea. Based on similar experience in previous projects, the preferable span length should be greater than 50m. Construction method: The site is located in a large sea with strong wind and high tides. The use of insitu concrete will not be feasible. The foundation and superstructure should adopt precast concrete structure components and large machinery to speed up the construction. The foundation will be on piles. In the presence of the soft stratum, the bearing stratum will be deep into the water. The preferable piling option would be large diameter driven pipe piles. For the superstructure, the structural components should be large and therefore the on site installation could be minimized. The most favourable construction method would be whole span precast installation. By using this method, the construction speed could be very fast and the construction time can be guaranteed. On the other hand, the whole-span lifting method also raises higher requirement to the lifting equipment, transportation, casting yard and temporary port. Therefore from the point of view of construction, the span length can not be to long as this may make the whole span precast construction difficult.(3) High pier area inside the water for the slip road bridgeThe high pier areas for the approach bridge are mainly distributed in the principal and auxiliary navigational channel and the total scope is about 3.5km. The average height of the deck level is about 30m. For this region, the use of whole span precast construction would not be suitable and precast segmental construction will be more appropriate. Due to the high pier and the compromise of the principal and auxiliary navigational channels, the span length cannot be too short in the high pier areas. Also, due to the increase in the sub-structures, the use of short spans will not be economical. Therefore, we should compare the span length from 70m-100m.(4) Bridge for Principal Navigation ChannelThe principal navigation channel can adopt either one void for two ways navigation or two voids for two ways navigation (each void for one way river traffic). (i) By using the one void for two ways navigations, the net width of the void will be 300m. Considering the space requirement for foundation and collision barriers, the main span could not be less than 370m. The side span lengths shall be determined by structural and aesthetic requirements.For span length of about 370m, main structural form can be cable stayed, arch, suspension and trussed bridge, in which cable-stayed would be the most competitive. In a wide sea with strong wind, the installation of arch bridge will be very difficult. Steel trussed bridge will be uneconomical and the maintenance works is difficult. Also, the construction of large anchor for the suspension bridge in the soft ground under deep water would not be feasible.Therefore, if the main channel adopts single void with two-way navigation, the bridge structural form would be cable-stayed which is most appropriate among the various types.(ii) For the single void single navigation, by adopting two singles voids, the clearance for navigation will be 170m. With the requirement of foundation and collision barriers, the main span length cannot be less than 200m. The side span lengths shall be determined by structural and aesthetic requirements. For span length 200m the bridge types can be rigid frame, cable stayed, arch and steel truss, among which the rigid frame would be the most competitive. In a wide sea with strong wind, the installation of arch bridge will become very difficult. On the other hand, the steel truss is expensive and has the problem of big maintenance work.Therefore, in the single navigation single void option, it is proposed to carry out the alternative study based on the structure type of continuous rigid frame.In view of the two above-mentioned navigation methods, an alternative study has been undertaken, for final determination of the bridge type.(5) Bridge for Auxiliary Navigation ChannelThe auxiliary navigation channel bridge can adopt either single void two ways or single void single way.(i) For the single void one-way navigation, two navigational spans shall be set and each void should have a clearance width of 100m. With the requirement for foundation and collision barriers taken into account, the span length cannot be less than 140m. (ii) For the single void two-way navigations, the clearance width of the void should be 180m. With the requirement of foundation and collision barriers taken into account, the span length cannot be less than 200m, and the side span lengths shall be determined by structural and aesthetic requirements.Bridge types that can suit the 140-200m span length include cable stayed, rigid frame, arch etc. For the bridge over auxiliary navigational channel, we shall consider in the respect of cost, difficulty in construction, innovation of the structures and construction period in the comparison.(6) Opening BridgeThe opening bridge will be located at the middle of the non-navigation section between the principal navigation and auxiliary navigation. Its span is 50m. With the duct and cable crossing and construction method taken into account, vertical lifting bridge and horizontal swing bridge have been studied and compared.4.6 Bridge LayoutAccording to the topographical and navigation conditions of the bridge site, the bridge can be divided into the following sections from north to south:(1) North Approach Bridge (k0+000K5+900)The scope of the north approach bridge starts from north coast to the auxiliary navigational channel, spanning over the old and new sea bank and beach area of Lu Chao Port, with a total length of 5900m. They can be divided into three parts: Land Section, length about 2730m Beach Section, outside the bank, river bed level 2.0-2.0m, length 350m Water Section, outside the bank inside the water, river bed level 2.0-10.0m, length 2820mIt is proposed to use 88 spans of 35m prestressed concrete beam for above land section and beach section. For the water section, 30 spans of 70m prestressed concrete beam and a series of 9x80m prestressed continuous concrete box girder will be adopted.(2) Auxiliary Navigation Channel Bridge (K5+900K6+340)Since the void clearance of the auxiliary navigational channel bridge is 100m, it is proposed to adopt the prestre