From the end of last year to the beginning of this year, the Central Urban Work Conference, the Provincial Urban Work Conference, and the Provincial Housing and Urban-Rural Development Work Conference were held successively, all emphasizing the construction of urban underground utility tunnels. Previously, the State Council also issued the "Guiding Opinions on Promoting the Construction of Urban Underground Utility Tunnels," clearly proposing the construction goals for urban underground utility tunnels. To this end, our journal invited Zhang Mingsheng, a senior engineer at the Shaanxi Provincial Institute of Urban and Rural Planning and Design, to interpret the planning and construction of urban underground utility tunnels in our province.

Reporter: First, please popularize the meaning of urban underground utility tunnels.

Zhang Mingsheng: Urban underground utility tunnels, as the name implies, put all existing above-ground overhead lines and various underground pipelines into an underground utility tunnel, and place them in the tunnel according to the technical requirements of each specialty. Underground utility tunnels are divided into trunk utility tunnels, branch utility tunnels, and cable tunnels. Urban underground utility tunnels are also divided into single-compartment, double-compartment, triple-compartment, and quadruple-compartment according to the width of urban roads and the number of pipeline types. The number of compartments is set according to needs. Generally, the comprehensive cost of a single compartment is 30-50 million yuan; double compartment 60-100 million yuan; triple compartment 100-150 million yuan.

Reporter: Why has the state paid special attention to the construction of urban utility tunnels in recent years? What is the difference between building underground utility tunnels and previous underground pipe networks?

Zhang Mingsheng: First, with the continuous advancement of science and technology, the continuous improvement of urban living environment, people's lives, and national strength and financial resources, urban functions are increasingly improved. At the same time, the contradiction between resource scarcity and the ecological environment urgently needs to be resolved. To this end, the Party Central Committee and the State Council have issued a series of policy documents at the national level to publicize and support the planning and construction of underground utility tunnels.

On September 6, 2013, the State Council issued the "Opinions of the State Council on Strengthening Urban Infrastructure," clearly proposing to carry out pilot projects for urban underground utility tunnels, and to fully launch pilot projects for underground utility tunnels in 36 large and medium-sized cities across the country within 3 years; small and medium-sized cities should build a number of utility tunnel projects according to local conditions; new roads, new districts, and various parks should simultaneously plan and construct underground utility tunnels; old urban areas should combine old city renovation and development to build underground utility tunnels. In June 2014, the state also mentioned the requirements for pipelines entering utility tunnels in the new urbanization plan. In the same year, the State Council issued relevant guiding opinions and revised and issued the technical specifications for underground utility tunnel engineering. At the same time, it issued the "Guidelines for the Preparation of Urban Underground Utility Tunnel Planning" and the "Investment Estimation Indicators for Utility Tunnel Engineering." The provincial government also issued the "Implementation Opinions of the Shaanxi Provincial Government on Strengthening Urban Infrastructure."

Second, through decades of construction and development, various pipelines in municipal infrastructure have increased, and "zipper projects" continue to appear. Strong and weak current lines are shaped like spider webs, seriously affecting the appearance of the city. It is imperative to bury strong and weak current overhead lines underground.

Traditional underground pipelines use direct burial. The positions of various pipelines are determined by the plane positions specified in the engineering planning of the master plan, regulatory plan, or detailed plan, and are approved by the planning department. Previously, underground pipelines included water supply, drainage (rainwater, sewage), heating, gas, etc.; above ground there were overhead lines, strong current, weak current (telephone, television, mobile communications, etc.). Now, with the expansion of city scale and population, these pipelines can no longer meet the requirements on the road plane. In addition, due to professional technical requirements (such as spacing, etc.), underground pipelines are buried deeper and deeper, and they also affect each other.

Underground utility tunnels put various above-ground and underground pipelines into a fully enclosed reinforced concrete box culvert. Of course, the pipelines entering the tunnel must be determined through demonstration based on technical conditions, engineering geological conditions, engineering investment, and other factors.

Reporter: At what stage is the planning and construction of urban underground utility tunnels in our province currently? What are the advantages and difficulties in planning and construction?

Zhang Mingsheng: At present, about 1000 km of underground utility tunnels have been built nationwide. Our province has only built a part in Xi'an, Yan'an, and Baoji, with a total scale of about 26.5 km, including 7.4 km in Xi'an, 6.0 km in Baoji, and 13.1 km in Yan'an. In addition, most other urban areas mainly have underground pipelines and direct burial laying.

From 2015 to 2016, all cities in the province (cities at or above the prefecture level), as well as Yangling and Xixian New Area, have completed special plans for underground utility tunnels and all have passed technical review. Currently, the Provincial Department of Housing and Urban-Rural Development is carrying out survey and research work for applying for the second batch of national pilot cities and provincial pilot cities, and plans to complete the application work by the end of April this year.

Currently, from the central to local levels, leaders attach great importance to the planning and construction of underground utility tunnels, and cities have relatively strong confidence in building underground utility tunnels. However, there are many various underground pipelines, each acting on its own, without unified management. In addition, underground space has not been uniformly planned and utilized, and there are many problems. In new roads, development zones, various parks, and old city renovation, the conditions for building underground utility tunnels are basically mature. It is conditional and necessary for cities to selectively build underground utility tunnels.

Of course, the construction of urban underground utility tunnels involves all aspects. I believe that there are currently three problems in the construction of urban underground utility tunnels in our province: First, large investment. Government investment, PPP models, private capital, etc., financing is a major difficulty. Second, engineering construction involves technical issues such as coordination and connection of various systems and specialties in engineering land use. Third, after the underground utility tunnels are completed, further exploration is needed in management and operation.

Reporter: How should underground utility tunnels be built in old urban areas?

Zhang Mingsheng: Old urban areas have high building density, narrow roads, concentrated population, and prosperous commerce. Building underground utility tunnels is indeed somewhat difficult. For old urban areas, it is generally considered in conjunction with old city renovation, and more cable tunnels with small cross-sections can be considered. If underground utility tunnels must be built, then it must be determined after demonstration from technical and economic aspects.

As mentioned earlier, underground utility tunnels are generally divided into trunk tunnels, branch tunnels, and cable tunnels. Cable tunnels connect with users, and in implementation, the tunnel and various user pipelines must also be well connected.

Reporter: What are the connections between urban underground utility tunnels and sponge cities?

Zhang Mingsheng: There are two aspects to the connection between the two: On the one hand, in terms of ground plane layout. Because of less demolition, easy construction, relatively small traffic impact, and small engineering investment, both are generally placed under green belts. However, large trees in green belts have a greater impact, and underground utility tunnels have many ancillary equipment on the ground (feed ports, ventilation openings, inspection holes, safety escape openings, etc.), which may affect the green landscape. On the other hand, in terms of vertical elevation. The elevation of underground utility tunnels and the ground at 2.5-3.0 m is conducive to various cross-road pipelines and plant growth, but from the investment of built underground utility tunnels, for every 1.0 m deeper burial, the cost per 1 km increases by about 10 million yuan.

Reporter: Underground pipelines are invisible to ordinary people, and even if seen, they cannot be understood. So we also want to know, from planning and design to construction and other links, how is quality supervised? How can the construction of urban underground utility tunnels withstand the test of time?

Zhang Mingsheng: Technically, urban underground utility tunnels can be roughly divided into three major parts: the main engineering part, the pipeline part, and ancillary facilities. According to the classification of utility tunnels, there are three types: main tunnels, branch tunnels, and cable tunnels. Their construction projects have large investment, high technical difficulty, and complex management and maintenance. Therefore, the engineering construction requirements are relatively high, and it must be carried out completely in accordance with basic construction procedures. At the design level, there must first be planning, research, preliminary design, and construction drawings. Each stage must undergo technical review and approval by the competent unit. Construction must be tendered, and the winning unit must strictly follow the construction technical specifications of each specialty. Construction quality is supervised by on-site supervision, and there is also acceptance by the quality inspection department. The main part of the utility tunnel has a service life of 100 years, and other pipeline projects have a service life of 10-20 years depending on the care of maintenance and management. Underground utility tunnels are livelihood projects involving all walks of life and thousands of households. Quality first, safety first.

Reporter: During the "13th Five-Year Plan" period, what are the expectations for the planning and construction of urban underground utility tunnels in our province? After completion, can we say goodbye to "zipper roads"?

Zhang Mingsheng: This year's provincial urban work conference and provincial housing and urban-rural development work conference clearly require that during the "13th Five-Year Plan" period, the province should build 100 km of urban underground utility tunnels and 500 km under construction. All cities in the province should select 2 cities each as pilot cities for underground utility tunnels and sponge cities. According to the construction scale of underground utility tunnels during the "13th Five-Year Plan," there is still a certain gap to avoid "zipper roads." However, according to the requirements for underground utility tunnel construction, in old urban areas, combined with renovation, underground utility tunnels will be built. As the pace of utility tunnel construction accelerates, the "zipper road" phenomenon will become less and less, and the city's appearance will become cleaner and tidier. In the near future, we will definitely say goodbye to "zipper roads."