The reporter learned from the 5th International Conference on Underground Space 2017 held on September 21 that the feasibility study for Qingdao's highly anticipated second subsea tunnel project has been basically completed. The preliminary plan is for the Huangdao end to connect to the Shugang Expressway, and the Qingdao end to land near the mouth of the Haipo River. The total length is 15.8 kilometers, with a two-way six-lane standard and a design speed of 80 km/h.
　　Underground Space Holds an "Academic Feast"
　　The conference was themed "Collaborative Development and Utilization of Urban Underground Space," with 4 domestic and international academicians and 12 top international experts attending in Qingdao. Among them, Qian Qihu, an academician of the Chinese Academy of Engineering and a professor at the Army Engineering University, delivered a keynote report titled "Developing and Utilizing Urban Underground Space to Treat Urban Diseases." Qian Qihu believes that Qingdao is at the forefront of the country in the development and utilization of underground space.
　　The reporter learned that the International Conference on Underground Space was first held in Beijing in 2003, and subsequently held in Shenzhen, Nanjing, and other cities. It is the highest-level and most prestigious underground space academic conference in China, and this is the first time it has been held in Qingdao. "The decision to hold this conference in Qingdao is not only because Qingdao has achieved good results in underground space research and practice in recent years, but also an affirmation of Qingdao's deployment of deep-sea and deep-earth and urban strategies," said a relevant person in charge of the organizer with a smile.
　　Qian Qihu and Ray Sterling, Chairman of the International Associated Research Centers for Urban Underground Space, respectively led domestic and international academicians and experts to "dissect" in simple terms the theories and practical achievements contained in classic underground space development cases such as China's longest subsea highway tunnel—the Qingdao Jiaozhou Bay Tunnel, the world's longest subsea tunnel—the design of Norway's Rogfast subsea tunnel, and Japan's development and utilization of deep underground space. In addition, the conference also held an international expert technical seminar on Qingdao's second subsea tunnel and the underground road projects along the Qianhai coastline. It is reported that in the future, as the preliminary research work on Qingdao's second subsea tunnel unfolds, multiple intercity rail transit projects are under construction, and multiple subway lines are opened successively, Qingdao will have more underground space development projects put into construction and operation.
　　Building Expressways into Underground Space
　　"As a comprehensive investment group directly under the municipal government, Qingdao Conson Group has actively explored the comprehensive development and utilization of urban underground space. In 2007, construction started on the Qingdao Jiaozhou Bay Tunnel to solve the cross-sea traffic problem between the two sides of Jiaozhou Bay, with remarkable results," said Qu Liqing, Chief Engineer of Qingdao Conson Development (Group) Co., Ltd. Over the past six years, the traffic volume of the Jiaozhou Bay Tunnel has continued to rise, with an average annual growth rate of 24%. The peak daily traffic volume increased from 29,000 standard vehicles/day in 2011 to 85,000 standard vehicles/day in 2017, nearly saturated. Building a second subsea tunnel to better promote interaction between the two sides of Jiaozhou Bay has become increasingly urgent. Based on this idea, in May 2014, Qingdao Conson Group completed the pre-feasibility study report for the second subsea tunnel and passed the special evaluation organized by the municipal government. In May 2017, the feasibility study work for the second subsea tunnel project was comprehensively carried out.
　　Exhaust pollution, environmental damage, traffic congestion... How should these "urban diseases" be solved? Developing and utilizing underground space may be an effective way. Qian Qihu pointed out that from a technical perspective, underground space above 100 meters can be built, and even 2-3 levels can be constructed. "At the end of the last century and the beginning of this century, developed countries had already begun building underground expressways and underground logistics systems. Currently, 6 international seminars on underground logistics systems have been held, and many countries have begun to pay attention to this system." Qian Qihu believes that underground rail transit, underground expressways, and underground logistics systems for freight are trends in using underground space to solve traffic problems.
　　According to reports, the traditional port collection and distribution mode is mainly based on highway container truck transport, which requires crossing the city, with passenger and freight traffic affecting each other. Port land collection and distribution traffic needs to cross the city in large quantities or occupy urban road resources, bringing problems such as traffic congestion and environmental pollution. As an important national port city, how should Qingdao solve the problem of port transportation? Qian Qihu mentioned in his report that an underground container logistics transportation system can be built, innovatively adopting a new collection and distribution mode to alleviate traffic congestion and achieve energy conservation and emission reduction.
　　"In the large underground space of Shandong, Qingdao occupies a huge share. Shandong and Qingdao are at the forefront of the country in the development and utilization of underground space, and China's development and utilization of underground space has already been at the forefront of the world," Qian Qihu said. It is worth mentioning that Qian Qihu also expressed expectations for the development of Qingdao's underground space. He hopes that Qingdao should contribute to solving urban diseases for major cities around the world, beautifying and greening cities, and play a good exemplary role.
　　According to research, the second subsea tunnel is positioned as another all-weather cross-sea channel connecting the east and west banks of Qingdao, with two-way six lanes, a design speed of 80 km/h, mainly for passenger vehicles, while also accommodating freight traffic functions. Compared with the 7.8-kilometer length of the Jiaozhou Bay Tunnel, the length of the second subsea tunnel has doubled, reaching 15.8 kilometers, of which the sea section is 11.1 kilometers long.
　　The complex geological conditions and large undulations of the bedrock surface in the area are one of the construction difficulties of the second subsea tunnel. The tunnel will cross the large-scale Cangkou Fault on the Qingdao side, with granite on one side and sedimentary rock on the other. The surrounding rock conditions vary greatly, and the geological conditions with many types of rock and complex lithology require the use of multiple construction methods in combination and simultaneous advancement in tunnel construction, which is a great challenge for the construction organization design.
　　In addition, due to the ultra-long design, ventilation and disaster prevention and rescue also require special research. To this end, the division of ventilation sections, the setting of ventilation shafts, the calculation of rescue distances, the design of evacuation plans, and the operation of sound and light alarm systems and photoelectric guidance systems will all be discussed in depth during the design and construction stages.
　　Cross-Jiaozhou Bay traffic is one of the key nodes of Qingdao's overall transportation. At present, Qingdao has completed and started construction of four cross-sea channels, namely the Jiaozhou Bay Tunnel, the Jiaozhou Bay Bridge, Metro Line 1, and Metro Line 8.