Bohai Strait cross- sea channel is a strategic project which connects Shandong Peninsula and Northeast regions, and it is very important for speeding up the economic development of the Bohai-ring and revitalizing the northeast old industrial base. Through a comprehensive analysis of the strategic value of Bohai Strait channel,the engineering solutions and investment and financing methods are planned. According to the analysis, the Bohai Strait project should adopt Lvshun—Penglai tunnel option, and the railway tunnel is the preferred solution, cars are carried by trains to cross the Bohai Strait tunnel;tunnel boring machine (TBM)+ drilling and blasting method is used in the construction of the tunnel,this method is feasible in our existing tunnel built and economic capacity, and the construction risk is acceptable. In accordance with cross-sea project of domestic and international and the characteristics of Bohai Strait cross-sea channel, the build-operate-transfer (BOT) financing model is suitable.
The Bohai Strait cross-sea passage is a long period,large investment construction project. It's an important problem about the investment, financing, and the return on investment (ROI) of the project. This paper,comparative analysis of the existing cross- sea channels at home and abroad, puts forward that Bohai Strait cross-sea channel can take build-operate-transfer (BOT) financing mode. The internal rate of return (IRR) of this project is about 9.63 %, higher than the social discount rate commonly, which indicates that the project has economic feasibility. In terms of revenue, this is a "multi-win" project for the government, public, investors and many other stakeholders.
The construction of the cross-sea channel of the Bohai Strait is a great project which is benefiticial to our country and people. Diversification of investment channels,especially to attract domestic and foreign private capital,is an important way to raise funds for the cross-sea channel of the Bohai Strait. The two most critical shortcomings of build-operate-transfer (BOT) modle are overcomed by means of public-private-partnership (PPP) model. They are too long preparatory work for the project and great risks of investors and lenders. PPP model is superior to the BOT model,more efficient than BOT, and is more rational for allocation of risks. Financing success of PPP model for the project is greater. Moreover,government can grasp decision-making power and control power of the project in the PPP model. PPP model can be learned in the cross-sea channel of the Bohai Strait.
Geological conditions of Bohai Strait is complicated. Meteorological conditions, topography, stratum lithology, geological structure, earthquake activity are directly related to the Bohai Strait cross-sea construction successful or not. Adopting the research method, a lot of engineering geological and hydrogeological data of the bohaistraitwere collected, and detailed analysis has been carried on, the regional stability evaluated. The bridge is not disadvantage of the all-weather horoughfare, for thick fog, high wind and the average gale in year days up to 67.8 days in Bohai Strait;because there are some islands and islets what keep a line along the longitude, the joining islands are choosed for the Bohai Strait cross-sea engineering construction to reduce the difficulty and cost of construction. There are the poor stability Quaternary stratigraphic and third strata mainly basalt, large pore structure,very uneven distributed and up to 70 m cover, and these two sets of strata have great influence on theoption of buried depth of the tunnel. To line of Penglai—Lvshun, there are not active faults in construction site, and the formation of relatively stable. These work can provide reference for the Bohai Strait cross-sea construction.
Bohai Strait settled cross-sea project is an important part of the national railway network and the highway. Settled cross-sea channel will be built to replace the existing ferry transport, to meet the growing transportation needs. Based on the study of meteorology,hydrology, geology of Bohai Strait,the preliminary comparison of bridge or tunnel scheme and tunnel line position are analyzed. According to the analysis, Bohai Strait cross- sea project should adopt the whole scheme, and Lvshun—Penglai tunnel line bit program is excellent, the line position in deep tunnels is optimum. Because there are many technical difficulties of highway tunnel, as well as construction costs and operating costs are high, therefore, the railway tunnel scheme is the preferred one,and cars are carried by trains to cross the Bohai Strait tunnel.
Aspects of bridge and tunnel are analyzed and their characteristics are compared,such as aviation and shipping, traffic capacity and driving comfort, road safety and climate adaptability,construction difficulty and project risk, etc. Technically, schemes of bridge and tunnel are both workable. Tunnel scheme is privilege to bridge scheme on aviation, shipping, climate adaptability, ecological environment and so on. While bridge scheme has advantages over tunnel scheme on traffic capacity, construction difficulty and risk, operating costs, driving safety, driving comfort, landscape and so on. Comparative evaluation index system for Bohai Strait cross-sea channel is structured by analytic hierarchy process. And weight coefficients of every index are calculated. Membership grade of every qualitative index is calculated by experts scoring method and membership grade of every quantitative index is calculated by membership grade function. Finally, model of fuzzy comprehensive evaluation is used to calculate comprehensive evaluation value of full bridge scheme, full tunnel scheme and combination scheme of bridge and tunnel. Comprehensive evaluation value of full tunnel scheme is maximum and the full tunnel scheme is the recommended scheme for Bohai Strait cross-sea channel.
Referring to the successful experience of subsea tunnels having been completed,the engineering analogy method can be adopted to design supporting structure form and parameters of Bohai Strait tunnel. Through the investigation and comparative analysis, composite lining is used. For all levels of the surrounding rock,corresponding combination supporting measures are adopted in the primary support design. Tunnel mainly adopts limited emissions scheme,and reduction factor method is used to calculate the water pressure on lining. In the stress analysis of lining structure, safety coefficients under different water pressure are analyzed,and the design parameters of secondary lining are preliminarily determined.
Through the analysis of factors affecting the durability of the tunnel structure,and according to the relevant engineering test results and the experience of design and construction technology, improving measures of the primary support and secondary lining durability of Bohai Strait tunnel were put forward. The durability design parameters of successfully built tunnel were analyzed. Combining with the actual situation of the Bohai Strait tunnel, the engineering analogy method was adopted to get the durability design parameters of the Bohai Strait tunnel. It could provide a strong guarantee to the fixed number of 100 years of the Bohai Strait tunnel.
The proposed Bohai Strait tunnel is a challenging project, and penetration rate of tunnel boring machine (TBM) is one of the keys. This paper made a contrast between the Clem Jones tunnel in Australia and the Bohai Strait tunnel,and introduced the specific energy used in the Clem Jones tunnel. During the construction of the Clem Jones tunnel, researchers made the analysis and forecasted about the TBM's penetration rate using the specific energy, which was identical to the practical construction very well. This paper concluded that the specific energy can be used in the Bohai Strait tunnel as well as the Clem Jones tunnel,which was based on the comparative analysis of the Clem Jones tunnel and Bohai Strait tunnel.
Bohai Strait crossing passage is a strategic project, which has a significant role in boosting the development of Bohai surrounding economic zone and East China. In the paper,the construction mode,longitudinal profile, construction methods and planning of Bohai Strait crossing passage is further studied on basis of the common concept of tunnel crossing Laotieshan waterway. It is proposed that the form of full tunnel with two underground stations built in backfilled ground in the sea should be adopted for Bohai Strait crossing passage and that the tunnel should be constructed by open tunnel boring machine (TBM) method, with drill and blast as the assisting method.
Bohai Strait tunnel is an important part of the national railway network and the highway;the construction of the crossing is significant. Based on the whole tunnel scheme of Bohai Strait, the location choice and construction technology of shafts in Bohai Strait subsea tunnel were researched in this paper. Through the analysis of the tunnel boring machine (TBM) life, Beihuangcheng Island and Beichangshan Island were selected as the locations for two shafts; and through the calculations of construction and operation ventilation and the research of the island sites,the feasibility of the shaft location choice scheme was demonstrated. According to the construction technology analyses of shafts in mine, railway tunnel and road tunnel,a molding method of drilling and blasting was used to construct the Bohai Strait tunnel shaft; the main measure of the construction of shaft topsoil should be plugging; the main technology program of the construction of base rock section should take the reasonable crack grouting technology.
The tunneling length of single face of Bohai Strait tunnel increases to 25 km due to the arrangement difficulty of the vertical shafts. The construction ventilation of Bohai Strait tunnel is studied in terms of ventilation mode selection, ventilation calculation and facility selection, on the basis of the existing devised program. In the end, the gallery-type ventilation method is proposed to solve the ventilation problem of the mentioned tunnel. The paper can provide ventilation technical support to the study on Bohai Strait tunnel.
The identification and estimation of construction risks of Bohai Strait tunnel are made by means of analytic hierarchy process (AHP) fuzzy comprehensive evaluation method, with the construction risks estimation of existing devised program of Bohai Strait tunnel as an example. The results show that the construction risk grade of Bohai Strait tunnel is grade Ⅲ. The key construction risks of Bohai Strait tunnel, including manufacturing of main bearing of tunnel boring machine (TBM), mud/water bursting and ventilation,are analyzed, and the countermeasures and problems to be solved are presented. The paper can provide reference for the construction program determination of Bohai Strait tunnel and for the planning,design and construction program of sea-crossing tunnels in the future.
In view of the shaft construction risk analysis of Bohai Strait tunnel, this paper determines risks during construction. Combining the risk weight analysis ranking,the sequence in turn from low to high is supporting structure failure risk, natural disaster risk and shaft excavation risk. Through risk assessment,we determine that the risk of water inrush and mud outburst is the key risk. Considering the influences of key risk and other risks on the shaft construction,we put forward response measures about shaft construction risk of Bohai Stiait tunnel from the geological forecast,shaft hoisting equipment selection and hoisting process control, shaft excavation risk control, natural disaster risk prevention, shaft supporting structure for quality control and the establishment of the shaft system construction,which provide guidance for the subsequent construction.
The operation of super-long subsea tunnel is a extremly complex system project,has larger uncertainty and safety risk. The procedure of risk assessment was explained in detail,and its application on Bohai Bay subsea tunnel project was proposed as a case study in this paper. Firstly, lots of different risk factors of the subsea tunnel operation were identified systematically, which involved water damage,tunnel lining crack, tunnel freezing,tunnel lining corrosion,tunnel earthquake disaster,the air pollution inside the cave,tunnel fire and the train derailment accident. Then,those operational risks were analyzed and assessed by the confidence index method and analytic hierarchy process, and were classified and discussed gradually according to the risk acceptance criterion. Finally,some topics about risk assessment on the subsea tunnel operational risk needed to the further research were high-lighted here.
This Issue
Dec 2013, Volume 15 Issue 12