Development and Thinking of Tunnels and Underground Engineering in China in Recent 2 Years （From 2017 to 2018）（近2年我国隧道及地下工程发展与思考（2017—2018年））

The author gives an overview of the development of tunnels and underground engineering in China in the past two years, including railway tunnel, high speed railway tunnel, highway tunnel, metro tunnel, hydraulic tunnel and utility tunnel, and introduces some key and representative railway, highway and municipal tunnels projects, i.e. Muzhailing Tunnel on Lanzhou Chongqing Railway, Dangjinshan Tunnel on Dunhuang Golmud Railway, immersed tunnel of Hong Kong Zhuhai Macao Bridge, China Laos Railway Tunnel, Gaoligongshan Tunnel on Dali Ruili Railway, Yuelongmen Tunnel on Chengdu Lanzhou Railway, Tianshan Shengli Tunnel on Urumchi Yuli County High speed Railway, Shenzhen Zhongshan Passage, Su′ai Tunnel in Shantou, Ka Shuang Tunnel of Ertix River Water Diversion Project, Qianhai underground integrated hub in Shenzhen and underground integrated structure of Optics Valley Square in Wuhan. The author also introduces the development and progress in the fields of engineering investigation technology, BIM technology, mechanized and intelligent tunnel construction technology, shield/TBM manufacturing and remanufacturing technology, offshore immersed tube tunnel construction technology, non circular shield tunnel construction technology, tunnel big data platform construction technology, etc. According to the operation of series national strategies and planning such as Sichuan Tibet Railway, coordinated development of Beijing, Tianjin and Hebei, the Yangtze Economic belt, and the Guangdong Hong Kong Macao Greater Bay Area, following technical demands are proposed, namely, sea crossing tunnels, construction of complex and long distance tunnels, environmental protection technology for tunnel construction in ecologically vulnerable areas, development of large scale urban underground complexes, research and development of new materials in alpine environment, intelligent diagnosis of tunnel diseases and rapid repairs, intelligent disaster prevention of ultra long complicated tunnels and underground engineering, etc. Some thoughts and suggestions are put forward in two aspects of engineering construction management mode and mechanization supporting in combination with the development status of the industry.     

Key Design Technologies for Cutter Replacing of Super large  Slurry Shield under Atmaspheric condition: Case Studies of Shantou Gulf Tunnel and Shenzhen Chunfeng Tunnel（超大直径泥水盾构常压换刀设计关键技术——以汕头海湾隧道及深圳春风隧道为例）

By analyzing the application cases of super large diameter shield machine in the world and taking China Shantou Gulf Tunnel and Shenzhen Chunfeng Tunnel construction for examples, the problems encountered in the research and development and construction are proposed and the key technologies to solve a series of problems, such as cutterhead maintenance and cutter changing technology under high soil and water pressure, boring in long fractured zone, are explored. More specifically, the technologies mainly involve cutterhead design, atmospheric cutter changing, main drive with telescopic and swinging function, reliable sealing system, anti blockage technique by applying double crushers, which are of great significance to the development and application of super large diameter shield machine.     

Main Construction Technical Difficulties and Solutions of  Shenzhen Chunfeng Tunnel（深圳春风隧道主要施工技术难题与解决方案）

Shenzhen Chunfeng Tunnel is one of the shield tunnels under construction with the largest diameter in mainland of China. The whole tunnel passes through the coastal composite stratum, with rock from broken to integral, and the strength of some sections reaches 173 MPa. The tunnel under crosses the railway, subway, bridge and multiple buildings closely in a complex and sensitive environment. Combining the stratum situation and characteristics of large diameter shield machine, the problems that will be faced during the construction process, including low rock breaking efficiency of shield machine, discharge stagnation and jamming of the chamber, settlement control in sensitive environment, and impact of large diameter shield segment floating, cracking and construction on urban traffic, are analyzed. Based on the engineering experience, the following solutions are proposed: a shield rock breaking efficiency solution for the complete extremely hard rock section, settlement control measures for adjacent buildings and structures of shield driven tunnels, solutions for jamming and discharge stagnation of large diameter slurry shield, comprehensive measures for prevention and control of shield segment floating and cracking, and a slag treatment plan for downtown areas. Chunfeng Tunnel tests the wisdom of Chinese builders with its tremendous volume and strict construction standards, and it also has certain reference significance for other similar projects.     

The Current Status and Some Problems of Slurry Shield in China（中国泥水盾构使用现状及若干问题）

For recent ten years, the slurry shield tunnelling technology has been widely used in major underneath river/ocean tunnels and urban metro constructions in China. With the gradual maturity of the slurry shield technology, especially the large diameter slurry shield technology, the numbers of projects and shield machines have been among the highest in the world. However, great challenges arise during the construction of the slurry shield projects under complex geological conditions, such as the stability of the excavation face, cutting tool abrasion, opening the chamber and repairing the machine, slurry circulation with slag, and remanufacturing of the shield. Therefore, it is necessary to investigate the development of slurry shield construction technology in China. Based on typical cases of slurry shield projects, this study analysed the main problems of the slurry shield in the construction process and summarised the current experiences and key technologies. Considering the actual situation of the slurry shield technology, this study clarifies its development direction in China, which is significant to promote the development of the slurry shield technology in the world.     

Fully Prefabricated Assembling Technology of Tsinghuayuan  Tunnel in Beijing Zhangjiakou High speed Railway（京张高铁清华园隧道轨下结构预制拼装技术）

Tsinghuayuan Tunnel of Beijing Zhangjiakou High speed Railway is the first fully prefabricated high speed railway tunnel in China. The supporting structure, subrail structure, and subsidiary structure of Tsinghuayuan Tunnel are all prefabricated in the factory. The strength, deformation and stability of subrail structure are analyzed by numerical simulation method; a kind of three block type of subrail prefabricated structure is put forward according to prefabricated assembling technology; and the subrail space is used to ventilate and rescue under the stability condition. The connection between subrail structure and shield segment is the key to fully prefabricated assembling technology. By introducing the grouting technology and construction keys of subrail structure, the stress on subrail structure and shield segment can be balanced. The results can provide reference for similar projects in the future.     

Key Techniques for Construction of Sanyang Road Cross riverTunnel of Wuhan Rail Transit Line 7（武汉轨道交通7号线三阳路越江隧道施工关键技术）

The author focuse on the great challenges encountered during the tunneling process in the Wuhan Sanyang Road Tunnel, and the key techniques adopted to solve those problems. When tunneling in composite strata, engineers inevitably face problems such as inefficient excavation, excessive tool wear, excavation face instability and the risk of clogging. The TBM used in the project allows tool change under atmospheric pressure, which improves the efficiency of tool change and eliminated the risk of casualties during hyperbaric interventions. In terms of the tool wear and clogging, the authors propose technical solutions as follows: the optimization of the tool′s type and configuration, improvement of the central flushing system and chemical dissolution of clogging. The results indicate that through the countermeasures proposed, the tunneling efficiency can be improved effectively. They also reduce the cutter change frequency and eliminate the risk of TBM downtime. The technical achievements obtained in the construction of the Wuhan Sanyang Road Tunnel can provide technical reference for the construction of large diameter shield tunnels in composite strata in the future.     

General Design of Shenzhen Zhongshan River crossing Link Project（深圳至中山跨江通道工程总体设计）

Shenzhen Zhongshan River crossing Link is the first super integrated project in the world that consists of four different types of structures, i.e. ultra long and wide immersed tunnels, super large span sea crossing bridges, deep water artificial islands and undersea interchanges. The river crossing is designed for two way and 8 lane as per highway technical standards. Based on project characteristics and its technical difficulties, engineering solutions and the associated technology innovations have been listed as follows: (1) Proposed a design concept of standardization, industrialization, intelligence and project integration, and completed the study of overall design of Shenzhen Zhongshan River Crossing Link. An immersed tunnel with a combined steel shell and concrete composite structure is designed and the width of tunnel elements is from 46 to 55.5 m; Lingdingyang Bridge has been designed as a suspension bridge with a 1 666 m main span and two 270 m high main bridge towers. For West Island, a temporary enclosure caisson structure made of ultra large steel cylinders with a diameter of 28 m is designed to achieve a rapid artificial island formation. (2) Summarized the design and construction solutions related to combined steel shell and concrete structural immersed tunnel, the mix design, batching and concrete casting methods of high strength self compacting fluidized concrete, concrete quality check and inspection, design and construction of deep cement mixed (DCM) pile foundation for immersed tunnels, design and construction of large scale undersea dimensional transport interchange, flutter and wind stability design for super large span suspension bridge with monobox girders, and key techniques related to design and construction of offshore anchorage in deep sea. Furthermore, an equipment is developed and innovated for not only transport, also for installation of immersed tunnel elements to ensure the implementation of the project in an effective and economical way.     

Some Key Technical Issues on Construction of Ultra long Deep buried Water Conveyance Tunnel under Complex Geological Conditions（复杂地质条件下跨流域调水超长深埋隧洞建设需研究的关键技术问题）

For the water conveyance tunnels in the long distance water diversion projects constructed or planned in China, most of them have to pass through mountain areas with complex geological conditions, due to the constraints of route selection. These tunnels might face engineering problems such as harsh natural environment, high seismic intensity and steep terrain, leading to difficulties in construction and high operational risks. In this paper, some key technical issues on the construction of ultra long deep buried water conveyance tunnels under complex geological conditions are summarized into 5 aspects, namely, (1) exploration and testing techniques for deep buried tunnels, (2) prediction and prevention for large deformation and rock burst in the surrounding rock masses, (3) failure mechanism and anti faulting techniques of the surrounding rock masses and lining for tunnels crossing active faults, (4) synergistic load bearing mechanism and life cycle design theory for rock support system of deep buried tunnels, (5) disaster treatment for deep and long tunnels such as prevention of high pressure water inrush. The scientific and technical problems to be solved and their development directions are pointed out, which can provide some reference for engineering construction of ultra long deep buried tunnels.     

Achievements and Challenges of Tunneling Technology in China over Past 40 Years（中国隧道工程技术发展40年）

In this paper, the current situation of tunnel engineering in China is introduced, especially the achievements obtained in the field of tunnel construction since the reform and opening up over 40 years. The 34 708 km long traffic tunnel built after reform and opening up takes 96% of the total length. The challenges met and achievements obtained during the key tunnel projects construction in China are presented emphatically from the aspects of extra long tunnel, deep tunnel, large tunnel, tunnel at high altitude and tunnel in complex environment. It is pointed out that: the main technological challenges during extra long tunnel construction are the accuracy of geological investigation, rapid construction and running disaster prevention; the main challenges during deep tunnel construction are high geostress, high waterpressure and high geothermal; the large tunnel faces high design and construction challenges; the challenges during tunnel construction at high altitude are freezing thawing and hypoxia; but still, many tunnels have been built under complex environments, including karst, gas, high geostress, high waterpressure, expansive rock, etc., and many technological breakthroughs have been achieved. The development trend of tunnel projects in China is proposed from the aspects of investigation, design, construction and operation, turning the development speed into development quality. It is generally acknowledged that the tunnel engineering achievements in China over the past 40 years benefit significantly from the development of international tunnel technology. Meanwhile, the development of tunneling technology in China has also greatly contributed to the international tunnel engineering development.     

Key Construction Technologies for Overlapping Twisted Shield bored Tunnels in Weak Water rich Strata(富水软弱地层中麻花型盾构隧道群施工关键技术)

The project under study is an overlapping twisted shield bored tunnels in weak water rich strata. The purpose of the study is to solve the key technological problems in the construction of the project. The optimal construction sequence of the overlapping twisted shield tunnels is determined according to the engineering geological conditions, the surrounding working environment, and theoretical analysis on the spatial relationship of the four tunnels, and verification control are carried out via monitoring means. The tunnel construction is properly timed, smart self propelled movable support jumbo is adopted, and grouting reinforcement technology is used to ensure the construction safety of the overlapping twisted shield bored tunnels. The grouting pre reinforcement technology and the clay shock technology are adopted to ensure the safety of the surrounding buildings. The technologies for the construction of the overlapping twisted shield bored tunnels described in this paper is of great significance for the construction of similar overlapping tunnels with high shield launching/receiving risks and crossing under important structures with small clearance.     

State of art and Prospectives of Urban Utility Tunnels in China（我国城市综合管廊建设发展现状与未来发展趋势）

Based on the introduction of the history and typical projects, the state of art of urban utility tunnels in China are mainly discussed in terms of construction mode, planning and design, construction and operation management. Then the significant technologies used for utility tunnels in China such as the green construction concept, intensive planning/design concept, intensive planning/design method, formwork slipping technology, precast/assembly technology and BIM based intelligent management technology and so on are elaborated. Finally, prospectives of utility tunnels in China are presented.     

Innovation and Practice of Hard Rock TBM in China（我国硬岩掘进机的创新与实践）

In recent years, with the help of good national policy support, the design, manufacturing and construction technology for tunnel boring machine (TBM) in China have been greatly improved; but compared with foreign relatively proven technology, there is still a certain gap for domestic technology development and engineering application. Based on the situation analysis of research and application of TBM in China and abroad, the research work for TBM design is carried out according to the complex geological conditions of Gaoligongshan Tunnel on Dali Ruili Railway as follows. (1) The prototype disc cutter rock breaking and scaled disc cutter wearing experiment are carried out to provide reference for adaptable design of TBM cutterhead and key parameter calculation. (2) The TBM design scheme is discussed from the aspects of high efficiency rock breaking of cutters and cutterhead, TBM over excavation, integrated support system, etc. (3) Two kinds of advanced geological prediction technology, i.e. HSP method and RTP method, are researched. The study results can provide reference for design and manufacture of TBM with high adaptability in complex geology and construction application in Gaoligongshan Tunnel.     

Innovation and Practice of Parallel Dual mode Slurry/EPB Shield Construction Technology and Freezing Cutterhead Opening Technology（并联式泥水/土压双模式盾构施工技术与冷冻刀盘开舱技术的创新与实践）

Two major concerns have been drawn in the process of shield construction: one is the difficulty in selecting a shield machine; the other is the high risk of opening for cutterhead changing. Based on the existing shield systems, a parallel dual mode shield with freezing cutterhead is developed by optimising internal structure and equipment and carrying the freezing device. The dual mode shield construction technology and freezing cutterhead technology are successfully carried out on project cases including Guangzhou Metro Line 9, Guangzhou Metro Line 21 and 220 kV Shijing Huanxi Electric Tunnel (Xiwan Road Shisha Road Section). The parallel dual mode slurry/EPB shield not only has the functions and advantages of slurry shield and EPB shield but also can switch into slurry/EPB mode for different strata and environments easily. Thus, it can achieve rapid shield tunneling. By combining the shield with the freezing system, the soil around cutterhead can be frozen to provide conditions for chamber opening under atmospheric condition. Meanwhile, it is also compatible with dual mode shield.     

Design and Application of Double shield TBMs  for Urban Metro Tunnels（城市地铁双护盾TBM设计及应用）

With reference to the construction conditions and features of metro tunnels, the design features of double shield TBMs are analyzed and key issues to be considered and settled when a double shield TBMs is used for metro tunnel construction are proposed. The issues include cutterhead′s rock breaking capacity, small curve excavation, selection of backfill grouting technology and jamming prevention and release function in fault and fracture zone, etc., which all have a direct effect on the geological adaptability, tunnel lining quality and tunneling performance of double shield TBMs. Subsequently, the specific design and optimization scheme, which includes the design of cutterhead thick steel plates, tapered shield, monorail hoist and pea gravel backfill and cement slurry grouting, etc., are studied. The success of double shield TBMs in Shenzhen Metro project well proved its remarkable geological adaptability and advantages in efficient mechanized construction.     

Analysis of Adaptability of TBM in Trial Boring Stage of Super long Tunnel（超特长隧洞TBM集群试掘进阶段适应性分析）

The total length of the 2nd stage water transfer project in the northern area of Xinjiang of China is 540 km. The project consists of three tunnels, namely Xi Er (XE) Tunnel, Ka Shuang (KS) Tunnel and Shuang San (SS)〖HJ6.5mm〗 Tunnel, with lengths of 139.04 km, 283.27 km and 92.15 km respectively. All of these three tunnels have deep cover and are super long tunnels, and 95.6% of the total length of these three tunnels is constructed by TBMs. KS Tunnel is the longest water tunnel built or under construction in the world. In the paper, the trial TBM boring scheme and schedule of the water transfer project are introduced; the geological conditions revealed are statistically analyzed; and main project difficulties, i.e. durability of key equipment in long distance driving, passing through fault and fracture zones, water inrush, single head ventilation and transportation in long distance tunneling, anti slope drainage, and rock breaking efficiency and boring efficiency, are put forward. The adaptability of the TBMs used is analyzed from the aspects of adaptability to different surrounding rocks, adaptability to bad geological conditions and countermeasures, long distance ventilation and belt conveyor mucking and countermeasures, and TBM boring stability (such as equipment availability, boring time proportion, system malfunction and operation time). The following conclusions are obtained: (1) Accurate geological survey is the precondition of efficient tunneling. (2) The open type TBM can better adapt to Grade Ⅱ and Ⅲ of surrounding rocks, jointed and fractured zones and small faults; the adaptability of the TBMs used to the large scale fault fracture zones and water rich strata in this project is poor, and it needs to be improved in aspects of TBM equipment, supporting and construction technology. (3) The average availability of the TBM equipment in the trial boring stage is 89.9%, however, the malfunction rate of some ancillary equipment is high, particularly oil leakages occur to the main bearing seals; in order to achieve long distance tunneling, it is necessary to further improve the reliability and durability of the TBM equipment. (4) The average net boring efficiency in the trial boring stage is 296%, and TBM1 in Section Ⅱ of SS Tunnel achieves up to 45.2 % net boring efficiency; and highest monthly progress rate is 1 280 m, which created the highest record of the open type TBM boring in China. (5) TBM need to make great efforts to achieve 90% of the equipment system′s availability and over 40% of the tunneling efficiency.     

盾构隧道结构耐久性问题思考

Structural durability of shield tunnel lining is a trans scale problem from mesoscopic material to macroscopic structure. With increasing amount of shield tunnel construction in China, the issues related to structural durability become more prominent. In this paper, the typical applications of shield tunnel lining in China and other countries are introduced. The service conditions and diseases of shield tunnel lining structure are then analyzed. The factors affecting the structural durability of shield tunnel lining, such as material, design, environment, construction, management and maintenance, are summarized. The research results and progress related to structural durability of shield tunnel lining are then reviewed in terms of tunnel durability, durability evaluation and prediction, durability ensuring techniques. Finally, the existing problems and future research directions in structural durability of shield tunnel lining are discussed in terms of durability ensuring techniques, impact of diseases and accidents, tunnel evaluation and rehabilitation, arrangement of secondary lining and establishment of dynamic evaluation system for structural durability.     

锦屏二级水电站深埋特大引水隧洞关键技术

Seven tunnels across Jinping Mountain are arranged for Jinping Ⅱ Hydropower Station, with a total length of about 120 km. Among them, four headrace tunnels have a length of 16.67 km, an excavated diameter of 12.4-14.6 m, and a cover depth of 1 500-2 000 m in general. The maximum cover depth is 2 525 m, and the maximum external water pressure is more than 10 MPa. The tunnels are featured by great length, great depth and large diameter. It is the largest and most difficult among the underground tunnel groups built or under construction in China and even the world. With complex hydrogeological conditions and special topographical conditions along the tunnels, many challenging problems, such as rock burst under high in situ stresses, groundwater inrush in karst strata and failure of loading bearing structure, were encountered during construction. A great amount of groundbreaking studies were carried out regarding these problems. The key technical problems during construction of extremely large and deep tunnels were solved successfully. Safe and rapid tunnel construction and stable operation were achieved. The hydropower station started operation in 2014 and has been in a safe and stable operation state. The successful construction of headrace tunnels of Jinping Ⅱ Hydropower Station can provide some experiences and reference for deep tunnel projects in the world.     

Innovation and Prospect of Key Technologies of Immersed Tunnels in China（中国沉管法隧道典型工程实例及技术创新与展望）

In this paper, the application status of foundation trench excavation and navigation channel dredging, dry dock construction, element precasting, element transport, element mooring, element immersion, joint treatment and foundation treatment of several typical immersed tunnels in China are introduced. And then the Honggu Immersed Tunnel in Nanchang and subsea tunnel of island tunnel project of Hong Kong Zhuhai Macao Bridge are taken as examples; and some innovations of key technologies, i.e. key construction technology, element transport and immersed technology, differential settlement control technology for element immersion, subsea connection technology, and subsea space development and subsea harbor construction technology, are summarized for river crossing and sea crossing immersed tunnels. Finally, the development trends of immersed tunnels are prospected based on new technologies and equipments from the aspects of prolongation of immersed tunnel, field breakthrough, urban construction promoting and traffic demand adding of cities along rivers and seas. The results can provide reference for construction and popularization of immersed tunnels.     

Great Revolution in Maritime Transportation: Discussion on Preliminary Work and Operation Plan of Bridge/Tunnel Projects for Vacuum HTS Maglev Train at High Speed（畅想海上交通运输建设的伟大革命——真空高温超导磁浮高速列车桥隧工程前期工作与运行方案探讨）

The improvement in the operation speed of the transportation project means the progress and development of the construction technologies in transportation projects. In this paper, the following factors restricting the further improving of the speed of high speed railway are analyzed: as the operation speed increases, the trains in the dense atmosphere are subject to the wind induced resistance and various resistances caused by the friction between the wheels and the rails and by the irregularity of tracks, and the noise will also increase with a high power. Therefore, the economy and safety issues involved in the operation have become the main factors restricting the further improving of the speed of high speed railway. A scheme of vacuum pipelines of underwater vacuum tunnel and/or subwater bridge is proposed in this paper: the pipelines and cars are sealed and vacuated to form the quasi vacuum. The transportation system of the vacuum maglev train at ultrahigh speed with the HTS maglev technology can achieve the operation speed more than 4 times that of the existing HSR train (about 1 200 km/h). Key technologies for constructing the vacuum maglev tunnels/subwater bridges in respect of construction plans, vacuating and sealing, as well as maglev trains are introduced in this paper. The subjects to be further studied on the vacuum HTS maglev tunnels (pipelines) are analyzed from the aspects of technology, management, construction costs, operation expenses, candidate project, airtight materials for cars and evacuation in case of emergencies. It is recommended that "cross sea maglev train in vacuum tunnel" should be developed in the eco tourism project between the coastal cities and their neighboring islands and a series of necessary technical tests should be conducted during the trial operation, so as to obtain related experience. Based on the experience and lessons learned, the transportation system at ultrahigh speed may be implemented for strait crossing projects in China. Finally, a brief introduction to the research on HSR trains at ultrahigh speed in countries such as China, the United States and the Netherlands is presented in this paper. The development of vacuum pipeline transportation can drive the development of China′s transportation modes in a faster, safer and more energy efficient manner, facilitating the development of the fifth generation of transportation industry and its driving role in the social and economic development, and promoting the integration and progress of the economy of China or even the world at a higher speed.     

Construction Technologies for Tunnels in Special and  Complicated Geology of Lanzhou Chongqing Railway（兰渝铁路特殊复杂地质隧道修建技术）

Lanzhou Chongqing Railway is located in the uplift margin of the Tibetan Plateau, where the geological environment is very complicated and special. Based on numerical analysis and field tests, the physical and mechanical properties, micro structure, and complicated water related stability of the Tertiary sandstone are studied. A comprehensive dewatering system integrating deep surface wells and vacuum light well points in tunnel is used and the construction technique featured with advance reinforcement by horizontal jet grouting for the full face of aquiferous silty fine sand tunnels is invented to solve the problem of the Tertiary quick sand. In addition, the classification method for deformation potentiality in design and dynamic adjustment in construction of tunnels in high geostress soft rock is established, the deformation control technology combining active stress release and passive control according to the deformation mechanism is developed, an automatic real time monitoring system for operation is invented, and a complete technological system of design, construction, and operation management of soft rock tunnels is built. Moreover, the TBM equipment parameter design principles are put forward, the parallel lining and multi stage belt conveyor mucking system is researched, the phased ventilation technology is invented and thus the problem of safe and fast long distance construction by large diameter TBMs is solved. The technological achievements have filled in gaps and facilitated development of the tunnel construction technology.