Design Method and Construction Technology in Tunnel Engineering under Complex Geological Conditions

Abstract

Over the past 40 years of reform and opening up, China’s railway tunnel construction industry has made great progress. The completed railway tunnels account for nearly 90% of the total length of China’s railway tunnels. At present, China’s tunnel construction technology is relatively advanced, but with the development of tunnel engineering in the southwest, railway tunnel construction is facing a series of major and complex geological problems. This chapter mainly introduces the tunnel design theory and method, support structure system, construction technology, and equipment under complex geological conditions. In addition to the technical problems and challenges faced by the current railway tunnel engineering, this chapter puts forward the development of active support collaborative control concept and technology, digital survey and design, intelligent construction, and intelligent operation and maintenance, so as to provide a useful reference for promoting the development of tunnel engineering.

1. Introduction

In the twenty-first century, China’s railway tunnel engineering has developed rapidly. Especially with the construction of high-speed railways and intercity railways and the implementation of the national “western development” strategy, railway tunnels show that the requirements due to high construction standards and complex geology, and complex special tunnels are gradually increasing, The scale of urban tunnels in complex environment and underwater tunnels crossing rivers and seas has increased rapidly. The completion and opening of these tunnel projects have made outstanding contributions to traffic and economic development. At the same time, there has been an accumulation of a large number of scientific and technological achievements and practical experience in railway tunnel engineering.

After 40 years of development, China’s railway tunnel has made great progress in basic theory, design method, construction technology, and equipment development. It has made major achievements and breakthroughs in high-speed railway tunnel, large-section loess tunnel, underwater tunnel, and TBM tunnel in complex and dangerous mountainous areas. It has significantly improved the technical level of railway tunnel construction and demonstrated the international influence of China’s railway tunnel construction [1]. However, with the advancement of national major railway construction and the construction of underwater tunnels across rivers and sea, China’s railway tunnels are also facing technical challenges in structural durability, the construction of large buried deep and ultra-long railway tunnels in high sea uplift seismic areas, large-diameter shield high water pressure long-distance construction, and safe operation of tunnel engineering. Therefore, combined with the current needs of tunnel engineering construction, this chapter summarizes and analyzes the tunnel engineering design methods and construction technology under complex geological conditions, and puts forward the direction of development and prospect according to the technical problems and challenges faced by the current railway tunnel engineering.

2. Theory and method of railway tunnel design

Since the 1980s, China has always adopted the standard design and analogy design methods based on experience. In recent years, China’s railway design has incorporated the concepts of “New Austrian Tunneling Method [2],” “Norwegian method [3],” and “New Italian method [4].” At the same time, a semi-quantitative approach to railway tunnel design has been developed, which incorporates information about the complex and diverse terrains, and the geological and climatic conditions affecting China’s railway tunnels. Structural design has changed from allowable stress method to probability reliability method based on limit state, and numerical simulation methods based on finite element and finite difference have also begun to be applied to structural design. Tunnel design quality has been greatly improved, and tunnel design ideas have also undergone major changes. There is a shift in design from one that relies solely on the lining bearing to those that rely on the surrounding rock. Many studies have been carried out in the aspects of surrounding rock stability evaluation and classification, and surrounding rock deformation control design. Finally, a tunnel construction method with Chinese characteristics based on active control of surrounding rock deformation was formed, which greatly promoted the development of railway tunnel design theory and methods [1].

2.1 Design method based on surrounding rock stability evaluation and classification

The standard design and analogy design of railway tunnel in China are mainly based on the evaluation and classification of surrounding rock stability. The stability of surrounding rock is directly related to the safety of tunnel construction and is the core issue of design and construction. After a lot of engineering practice and analysis, it is proposed to take the self-stability of surrounding rock as the index and formulate a unified surrounding rock classification standard, as shown in Table 1, which has guided the design and construction practice of railway tunnel for a long time.

Surrounding rock level		Stability description of surrounding rock at all levels
Basic level	Subclass
I	—	The surrounding rock is stable, no collapse, and rockburst may occur
II	—	If the exposure time is long, local small collapses may occur, and the damage is mainly due to falling blocks, the side walls are stable, and the roof of the gentle rock layer with poor interlayer bonding is easy to collapse; the temporary self-stabilizing span is 17–20 m
III	III 1	When the arch is not supported, a small collapse can occur, the side wall is basically stable, and the blasting vibration is too large and easy to collapse; the temporary self-stabilizing span is 14 ∼ 16 m
	III 2	When the arch is not supported, a small collapse can occur, the side wall is basically stable, and the blasting vibration is too large and easy to collapse; the temporary self-stabilizing span is 10–13 m
IV	IV 1	When the arch is unsupported, it can collapse greatly, and the side wall sometimes loses its stability; the temporary self-stabilizing span is 7–9 m
	IV 2	When the arch is not supported, it can cause a large collapse, and the side wall sometimes loses its stability; the temporary self-stabilizing span is 5–6 m
V	V 1	The surrounding rock is easy to collapse, and if it is not handled properly, there will be large collapse, the side wall often has small collapse, and the surface is prone to subsidence or collapse to the surface during shallow burial; the temporary self-stabilizing span is 3–4 m
	V 2	The surrounding rock is easy to collapse, and if it is not handled properly, there will be large collapse, the side wall often has small collapse, and the surface is prone to subsidence or collapse to the surface during shallow burial; the temporary self-stabilizing span is less than 3 m
VI	—	The surrounding rock is easy to collapse and deform. When there is water, the soil and sand often gushing out together with the water. When buried shallowly, it is easy to collapse and penetrate to the surface; there is no self-stability

Table 1.

Sub-classification and stability of surrounding rock of railway tunnel [5].

However, in the actual construction process, the surrounding rock revealed by excavation does not correspond to the basic level of surrounding rock, so it is difficult to judge on-site, and it is easy to have weak or strong support parameters. In recent years, railway builders have carried out a lot of scientific research and test work to improve and strengthen the quantitative classification of surrounding rock. By refining the basic quality index of surrounding rock (BQ) and the elastic wave velocity range of surrounding rock with different lithologies, the concept of surrounding rock sub-grade is proposed, and the surrounding rock of grades III, IV, and V is divided into two sub-grades, respectively. The index combination corresponding to each sub-grade is the sub-grade division standard. Finally, the BQ value range corresponding to each sub-grade surrounding rock is determined, which well guides the design and construction of railway tunnel. The sub-grade and stability of railway tunnel surrounding rock are shown in Table 1.

The surrounding rock classification method of railway tunnel has been relatively perfect. The measurement while drilling technology such as advance drilling parameters has developed rapidly, and the intelligent construction technology of tunnel has been continuously promoted. It would be possible to establish a method to map rock mass quality indicators based on drilling parameters, and then dynamically and automatically quantify and interpret the grade of surrounding rock.

2.2 Design method for deformation control of surrounding rock

The research team of high-speed railway tunnel surrounding rock stability control technology led by Zhao Yong and others [1] innovatively proposed a set of tunnel construction technology methods with Chinese characteristics. Its principle is that on the premise of ensuring the stability of surrounding rock, small tremie advance grouting, reasonable lining support, and other means are used to control the deformation of surrounding rock, give play to the coordination between the support structure and the surrounding rock structure, make full use of the self-supporting capacity of surrounding rock, and form a fast and durable tunnel stability structure system. As shown in Figure 1, advance reinforcement is used to prevent surrounding rock collapse and control the scope and extent of damage to the excavation surface. The initial support structure bears all additional stresses released by the surrounding rock due to excavation to help the surrounding rock share the load. As a safety reserve, the secondary lining shares part of the load with the primary support.

Figure 1.

Schematic diagram of the control design principle of the full deformation process of the tunnel.

This method considers that the surrounding rock of the tunnel is composed of “shallow surrounding rock” and “deep surrounding rock.” The surrounding rock in the loose area needs to be supported in time for the load of this part of the surrounding rock. Outside this range, the surrounding rock with good overall stability and capable of bearing the stratum load is called “deep surrounding rock.” It is composed of “loading layers,” which start from the shallow surrounding rock interface and appear alternately [1].

2.3 Design method of mechanized large section of tunnel

The tunnel construction team of the Hubei section of the Zhengwan High-speed Railway has carried out scientific research and field practice related to the construction of large-scale mechanized large-section tunnels. In summary, the relevant methods of railway tunnel mechanized large-section design and construction are explained as follows [6, 7].

In terms of mechanized supporting design, it covers four operation areas: advance support, excavation, initial support, and secondary lining, which are divided into basic supporting and reinforced supporting according to the perfection of the configured machinery. Advance support is one of the auxiliary measures to ensure the stability of the excavation face of the tunnel, which is taken ahead of the excavation of the tunnel face. The main methods are pipe shed, small conduit, horizontal jet grouting pile, etc. Excavation refers to the work of loosening, breaking, excavating, and transporting soil or rock for mucking during the construction of tunnels. The initial support refers to the support carried out immediately after excavation, which generally includes shotcrete, shotcrete with anchor rod, shotcrete anchor rod, and steel frame combined support. Secondary lining is a formwork concrete or reinforced concrete lining applied inside the initial support during tunnel construction, and together with the initial support, it forms a composite lining.

In terms of construction method design, there are full-section methods and microstep methods. In the aspect of face stability evaluation, a combination of qualitative evaluation and quantitative evaluation is adopted, which is divided into three types: stable, temporary stable, and unstable.

In terms of advance support design, advance support measures (including surface shotcrete, advance small conduits, pipe sheds, surface anchors, advance grouting, etc.) are determined according to the results of the face stability evaluation. The engineering analogy method and the limit equilibrium method are used to analyze and determine the parameters. The design model of the tunnel face advanced support is shown in Figure 2, and the calculation formula is shown in formula (1) [8].

Figure 2.

Design model of advance support of the tunnel face. Note: L_e is the length of the unsupported section, m; θ₀ is the failure angle of the tunnel face; D is the height of the tunnel, m.

In terms of the design method of tunnel support, the load structure model is used for calculation. The surrounding rock pressure in the shallow buried and eccentric pressure sections is adopted according to the formula value of the tunnel design code, and the deep buried section is determined according to the measured value of deformation and stress.

$$K=\frac{P_1+{\beta }_1{\alpha }_1{F}_c}{{\beta }_2\left(F_w+{\alpha }_2{F}_q\right)}+{\beta }_3$$E1

where β₁, β₂, β₃ are coefficients related to the internal friction angle of surrounding rock; α₁ is the vertical deformation pressure reduction coefficient of the disturbance section in front of the tunnel face under the pipe shed support; α₂ is the cohesion increase coefficient of surrounding rock after pre grouting reinforcement of tunnel face; F_c is the cohesion force of the sliding surface, kN; F_q is the resultant force of vertical deformation pressure of the sliding body, kN; F_w is the self-weight of the sliding body, kN; P₁ is the bolt support force of the tunnel face, N; K is the stability coefficient of the tunnel face.

This method has now formed the standard for China National Railway Group Co., Ltd. (draft for approval in 2021). The promulgation of this standard will greatly promote the mechanization level of railway tunnel drilling and blasting construction and provide technical support for the intelligent construction of railway tunnels.

2.4 Total safety factor method for tunnel support structure design

Xiao Mingqing and his team summarized and proposed the “total safety factor method for tunnel support structure design” through years of tunnel engineering design, construction, and research [9]. The total safety factor is a factor used to simultaneously evaluate the overall structural safety of initial lining and secondary lining. The technical idea of this method is to regard the interaction relationship between the support structure and the surrounding rock as the relationship between the action force and the reaction force. The deformation compatibility between supporting structure and surrounding rock is not strictly considered, which greatly simplifies the problem to be solved. The judgment of whether the tunnel needs support and the calculation of the support force need to be determined after numerical analysis using various constitutive models that are consistent with the actual situation. The intrinsic safety and deformation of the support structure are calculated by the load structure model to realize the safety evaluation and quantitative design of the support parameters [10]. Figure 3 is a composite structure model formed by combining the three-layer structure of bolt-surrounding rock-bearing arch, shotcrete layer, and secondary lining. In it, the purpose of spray layer is to reinforce the tunnel structure and improve the stability and safety of the tunnel. The secondary lining is a molded concrete or reinforced concrete lining constructed on the inner side of the primary support, which forms a composite lining together with the primary support to achieve the effect of reinforcement support. Therefore, we use the model shown in Figure 3 to calculate the total safety factor and evaluate the safety of the tunnel support structure. The relevant calculation formula is as follows [11]:

Figure 3.

Calculation model of total safety factor method.

Construction stage (without secondary lining):

$${\mathrm{K}}_{\mathrm{c}}=\eta {\mathrm{K}}_1+{\mathrm{K}}_2$$E2

Operational stage:

When using durability anchors:

$${\mathrm{K}}_{\mathrm{op}}=\eta {\mathrm{K}}_1+\xi {\mathrm{K}}_2+{\mathrm{K}}_3$$E3

When using non-durable bolts:

$${\mathrm{K}}_{\mathrm{op}}=\xi {\mathrm{K}}_2+{\mathrm{K}}_3$$E4

where K_c and K_op are the total safety factor in the construction stage and operation stage, respectively; K₁, K₂, and K₃ are the safety factors of anchor-rock bearing arch, initial support, and secondary lining, respectively; η is the correction factor for the safety factor of the anchor rock bearing arch; ξ is the correction factor of the safety factor of initial support.

The total safety factor during the construction period is recommended as follows: when the sprayed layer is made of steel fiber reinforced concrete or with a steel frame, it is not less than 1.8, and when the sprayed layer is made of plain concrete, it is not less than 2.1. The recommended total safety factor during the operation period is: not less than 3.0 when the secondary lining is made of reinforced concrete, and not less than 3.6 when the secondary lining is made of plain concrete. A tunnel that satisfies the above-mentioned total safety factor is a safe and good tunnel. When the stress of a section of the spray layer or secondary lining composite structure is greater than the safety bearing capacity, it will reach the damage stage. At this time, if the offset distance of the axial force N is large and the steel bar is configured appropriately, large eccentric compression failure will occur. If the offset distance of the axial force N is small but the configuration of the steel bar is excessive, small eccentric compression failure will occur. The calculation model of large and small eccentric compression failure is shown in Figure 3(b) and (c).

This design method can easily calculate the safety factor of the tunnel at different stages, and it is hoped that it will be further improved through field measurement and model test, which provides a convenient calculation method for the quantitative design of the tunnel.

3. Tunnel construction technology

3.1 Informatization design and construction technology

In the 40 years of tunnel development in China, we have constantly summarized the practical experience of railway tunnel construction informatization, taking safety and quality management as the main line, and reference to domestic and foreign engineering construction informatization experience. An information-based design and construction technology based on advanced geological prediction and monitoring measurement has been formed.

The traditional advanced detection methods mainly focus on advanced drilling, seismic emission, electromagnetics, electrical methods, etc. In recent years, with the development of drilling equipment, advanced exploration technology has also been developed rapidly. Dozens of meters to thousands of meters can be achieved. At the same time, some new ideas of advanced tunnel geological prediction technology have been proposed, including tunnel-induced polarization technology, tunnel nuclear magnetic resonance technology, single-hole directional radar technology, and seismic wave water exploration technology. It has played a beneficial and positive role in promoting the advancement of advanced geological forecasting technology and improving engineering service capabilities. The three-pole bathymetric induced polarization method proposed by Shandong University, which can quantitatively estimate the water volume of water bodies within 30 m in front of the driving face, and the full-space transient electromagnetic method, which can identify and locate the water bodies within 80 m in front of the driving face, are suitable for quantitative detection in adverse geological conditions [12]. Important progress has been made in the field, especially the feasible method for estimating the water content of aquifers, and the establishment of a comprehensive advanced detection technology and system [13, 14]. The above achievements have been successfully applied in many projects with complex geological conditions, such as the Chengdu-Lanzhou Railway, the Chengdu-Kunming Railway, and the Beijing-Zhangjiakou High-speed Railway. It fully reflects the rapid development of advanced geological forecasting technology, which provides important support for the safe and efficient construction of railway tunnels in China.

Tunnel site monitoring and measurement is a key link in tunnel construction and the basis for realizing information-based design and construction. The traditional monitoring technology mainly relies on personnel entering the construction site and using traditional measuring tools for manual operation measurement; in recent years, with the proposal and development of automatic monitoring technology, automatic total station monitoring technology, optical fiber sensing technology, and 3D laser scanning technology have appeared. Digital close-up photography technology, monitoring technology based on the Internet of Things, etc., greatly improve the accuracy of monitoring and measurement, and provide reliable basic data for tunnel informatization construction.

Information-based design and construction technology is currently the mainstream of railway tunnel construction. Data on the geology, the surrounding rock dynamics, and the support status are obtained through advanced geological prediction, monitoring, and measurement. This approach makes it possible to sort and analyze the above-named data, assess the stability of the surrounding rock and support structure system, determine the support parameters, and construction methods that are more consistent with the surrounding rock dynamics, and guide on-site construction. In recent years, with the development of information-based design and construction technology, intelligent construction technology has also been proposed. In 2020, tests and verifications were successfully carried out around the major subsystems of the intelligent construction collaborative management platform in four sections of Zhengwan High-speed Railway, including Gaojiaping, Baokang, Xingshan, and Xinhua, and the purpose of intelligent tunnel construction was initially achieved [15, 16].

3.2 Tunnel auxiliary construction method of drilling and blasting method

The auxiliary construction methods commonly used in railway tunnels in China mainly include advanced bolting, advanced small conduit grouting, advanced pipe shed grouting, advanced grouting in the cave and surface grouting, etc. With the development of drilling and grouting equipment, the work efficiency of auxiliary construction methods has also been greatly improved, especially the development of advanced grouting in the cave and surface grouting technology, which provide important technical means for dealing with mud (water) intrusion in the tunnel, strengthening weak, broken strata and landslides and other unfavorable geology.

The advanced grouting technology in the cave has wide applicability, strong pertinence, and flexible operation. With the development of engineering requirements and technology, the current main processes include forward segmented grouting, drilling and injection integrated backward segmented grouting, horizontal sleeve valve tube bundle fine grouting, and full hole one-time constant pressure and constant flow grouting, which can be reasonably selected according to different geological characteristics and reinforcement requirements. Influenced by the effect and technology of advanced grouting in the cave, the deep hole grouting technology outside the cave has developed rapidly in recent years. This technology is widely used in the advanced reinforcement of various weak, water-rich, and broken rock tunnels. The construction depth of grouting holes can reach 150 m. After reinforcement, the average monthly excavation footage of soft rock tunnels can reach 80 m [17, 18]. The advanced grouting in the cave and surface grouting are shown in Figures 4 and 5.

Figure 4.

Advance pre-grouting construction in the cave.

Figure 5.

Surface grouting construction.

The above technologies have been successfully applied in many projects such as Beijing-Shenzhen Passenger College, Ha-Mu high-speed railway, Menghua railway, Yinxi high-speed railway, Taijiao high-speed railway, Zhangjihuai railway, and so on.

In order to meet the needs of engineering grouting, the drilling and grouting machinery equipment have also made great development. The drilling equipment has been developed from the original tunnel drilling rig carried on the shoulder to the current crawler-type multi-functional drilling rig. The equipment is widely used in hydropower cofferdam construction, dam anti-seepage construction, highway slope anchoring, subway tunnel pipe shed support construction, airports, and deep foundation pits for high-rise buildings. Its construction efficiency and drilling capacity are greatly improved. At the same time, the grouting material has also developed from the traditional ordinary cement-based grouting material to the fast-hardening sulfate cement-based grouting material. This material has controllable setting time, high early strength, and strong dispersion resistance, which greatly improves the construction efficiency of advance grouting and the effect of water plugging and reinforcement.

In terms of grouting effect inspection and evaluation, on the basis of traditional analysis method, inspection hole method, excavation sampling method, displacement estimation method, etc., geophysical exploration methods such as in-hole imaging and cross-hole CT have been developed, so that the inspection of grouting effect is more intuitive and objective.

3.3 Mechanized large section construction technology of tunnel by drilling and blasting method

With the rapid development of high-speed railway in China, great progress has been made in the construction technology of high-speed railway tunnels. A new breakthrough has been made in the mechanized construction of drilling and blasting tunnels, and the mechanization of a single process has gradually shifted to the mechanized construction of all processes. The drilling and blasting method has evolved from manual blasting to drilling with rock drill jumbo or multi-arm drill truck. During the application of millisecond blasting, pre-crack blasting and smooth surface blasting technology, the entire excavation section is drilled, while blasting is either carried out simultaneously or at controlled and short intervals, to minimize vibration and other associated effects. The construction of mechanized large-section tunnels of Zheng-Wan high-speed railway and Cheng-Lan high-speed railway involved the construction of large-section excavations under surrounding rock conditions at all levels [7], as shown in Figure 6. The mechanization of the tunnel construction entails the main processes of operations such as excavation, initial support, waterproofing, and secondary lining. The main equipment includes rock drilling jumbo, bolt drilling rig, wet spraying manipulator, steel frame installation jumbo, self-propelled inverted arch trestle, etc., as shown in Figure 7. Rock drilling jumbo is a kind of rock drilling equipment used in tunnel and underground engineering. It can move and support multiple drilling machines to drill simultaneously. Anchor Drilling Rigs roadway bolt support equipment is used to improve support effect, reduce cost, speed up roadway formation, reduce auxiliary transportation volume, reduce labor intensity, and improve roadway section utilization rate. Wet spraying manipulator is a construction machinery designed and manufactured to replace manual spraying concrete in order to reduce labor intensity and improve working conditions. It has the functions of making the nozzle pitch forward and backward, swing left and right or circle, and the boom can be retractable, lifted and rotated to meet the construction requirements of shotcrete.

Figure 6.

Surface grouting construction. (a) Full-section method (including inverted arch). (b) Microstep method I (upper section inverted arch). (c) Microstep method II (including inverted arch).

Figure 7.

Schematic diagram of the whole process of tunnel mechanical supporting.

3.4 Tunnel construction technology of shield method

The shield method has strong adaptability to the stratum and can be applied to various strata such as clay, sand, bedrock, etc. It has obvious safety and economic advantages in the construction of urban railway tunnels and underwater railway tunnels. At the same time, in order to adapt to the complexity of geological conditions, shield equipment has been developed from the previous single-function earth pressure shield and mud-water shield to dual-mode and multi-mode shields.

The shield tunnel adopts the prefabricated segment assembly to form the lining structure in time, which ensures the safety, reliability, and high quality of the tunnel construction. The prefabricated assembly structure has the advantages of fast construction speed, good quality, and green environmental protection. Gradually popularize the application of prefabricated assembly structures, such as the Tsinghua Park shield tunnel of the Beijing-Zhangjiakou high-speed railway, and realize the fully prefabricated assembly of the under-track structure [19].

The segment is completed by the shield’s own assembly equipment, and the bottom structure is completed by the matching box culvert assembly machine, realizing the rapid assembly construction of the middle-box culvert and the side box culvert. The middle box culvert block and the block and the side box culvert block and the block are all sealed with EPDM rubber strips. The installation of box culvert and side box is shown in Figure 8.

Figure 8.

Box culvert and side culvert installation. (a) Central box culvert installation. (b) Side box culvert installation.

The tunnel constructed by this technology is clean and tidy in the tunnel, and the tunnel is completed at one time, which reduces the construction time of under rail structure and greatly improves the construction efficiency. It is the development direction of shield tunnel construction in the future [20].

3.5 TBM tunnel construction technology

The TBM method is a construction method for tunnel construction using a full-face tunnel boring machine. The hard rock TBM uses the disc cutter on the rotary cutterhead to squeeze and shear the rock, before picking up the stone slag using the bucket teeth on the rotary cutterhead. The slag is discharged to the main belt conveyor and transported it backwards, and then transports the slag to the outside of the tunnel through the traction slag truck or the tunnel continuous belt conveyor. It has the advantages of advanced technology, fast speed, one-time forming, good working environment, high safety, small disturbance to surrounding rock and small damage to natural environment. It enables the construction of deep buried long tunnel in complex geographical landform which is difficult to realize by traditional drilling and blasting method. It is one of the most advanced tunnel construction equipment [21]. China has successfully built Qinling Tunnel, Mogouling Tunnel, Taohuapu No. 1 Tunnel, Zhongtianshan Tunnel and West Qinling Tunnel by TBM technology. Through the joint efforts of domestic engineering construction, design, equipment manufacturing, and other related units, domestic TBM has been greatly improved in function, cost, reliability, automation, and geological adaptability, and can be applied to many fields of engineering and tunnels with different geological conditions. The full-face rock tunnel boring machine (TBM) has dominated the domestic and international market since the first domestic TBM was launched and successfully applied in 2014. It has laid a foundation for the wider application of TBM technology in railway mountain tunnel projects [22, 23, 24].

4. Development direction and prospect

The number and length of railway tunnels in China have ranked first in the world. The topography, geology, and regional environment are also the most complex in the world. The types, standards, and functions of tunnel engineering are complete, and the technical achievements are remarkable. However, with the high-quality development of China’s economy and the application of new technologies such as informatization, digitization, and intelligence, the development of railway tunnel has also ushered in new opportunities and challenges.

4.1 Improving the active support system of tunnel

With the popularity of tunnel construction concepts such as “New Austrian Tunneling Method [2],” “Norwegian method [3],” and “New Italian method [4],” the development of railway tunnel design theory and method has been greatly promoted. The tunnel engineering community has gradually realized that protecting and making full use of the self-supporting capacity of tunnel surrounding rock is the core idea of tunnel construction. From the perspective of mechanics, the essence of tunnel support is to change the excavated surrounding rock from two-dimensional stress state to three-dimensional stress state, So as to inhibit the relaxation development of surrounding rock and improve the self-stability of surrounding rock.

Active support means that the support should be set up in time before the surrounding rock relaxes, and the surrounding rock should be actively protected, strengthened, and improved, mainly through anchor (cables) and other supporting components to penetrate into the surrounding rock to form a combined arch effect and improve the surrounding rock. It can improve the continuity of the surrounding rock and enhance the shear strength of the surrounding rock, thereby maintaining and improving the self-supporting ability of the surrounding rock. It is hoped that through the construction of national major railway tunnel projects and in combination with scientific research and tests, the concept of tunnel active support will be further improved and popularized, and the technical system of railway tunnel construction with Chinese characteristics will be improved.

4.2 Research on key technologies of BIM and GIS in tunnel life cycle

BIM (Building Information Modeling) takes the relevant information data of the construction project as the basis of the model, establishes the building model, and simulates the real information of the building through digital information simulation. It has the characteristics of information completeness, information relevance, information consistency, visualization, coordination, simulation, optimization, and plotting. At present, the three-dimensional simulation in BIM is mainly used to check the conflict in the construction process and improve the communication efficiency of project management [25]. With the popularization and application of BIM technology in the world, in recent years, China’s survey and design units and construction units are also actively promoting the information construction based on BIM, and exploring the application of BIM Technology in the whole life cycle of Railway Tunnel Survey and design, construction, safety operation and maintenance. At present, it is leaping from the “modeling based” stage to the “multi-dimensional data application based” stage. However, BIM 3D information model has deficiencies in scale expression, consistent analysis, spatial unified benchmark, overall positioning and so on.

GIS (Geographic Information System) is based on spatial 3D visualization and spatial database technology. It is oriented to massive 3D geospatial data and integrates complete 3D spatial entities above, underground, and inside and outside the tunnel. It has powerful functions of spatial data storage, management, retrieval, and analysis. In addition, GIS can dynamically monitor and analyze environmental changes in different periods, and can also be developed to integrate data collection, spatial analysis, and decision-making processes into a common information flow. It significantly improves work efficiency and economic benefits, and provides technical support for solving urban tunnel construction problems and ensuring sustainable maintenance [26].

Therefore, combining BIM with GIS, integrating BIM model into GIS scene, and giving full play to their advantages can not only meet the accuracy requirements of different projects, but also reduce the measurement work, reduce the cost of spatial information collection, and realize the sharing and utilization of data [27]. This is the development direction of digitalization and informatization of tunnel engineering in the future [28].

4.3 Research on intelligent construction technology of railway tunnel

In recent years, with the continuous improvement of labor cost, the number of skilled construction technicians on the tunnel site has decreased year by year. The “machine instead of people” in tunnel engineering construction has become a realistic demand. Less people (or even unmanned) is the inevitable trend of tunnel engineering construction and development in the future. On the basis of the high integration of mechanization, dataization, informatization, and artificial intelligence, equipment (less internal combustion, more power, high efficiency, and capacity matching) that can adapt to the high altitude hypoxia environment is selected for hierarchical matching. At the same time, robots with self-perception, self-learning, self-decision, and self-implementation functions are developed to carry out intelligent operations in the main processes of tunnel construction. It is of great significance to build a full-life-cycle tunnel intelligent construction system with deep integration of mechanization and informatization to ensure safe and reliable construction [7, 16]. This is of great significance for improving construction efficiency, ensuring construction safety, and improving construction quality.

Based on the current demand for railway tunnel construction, technical level and development status, the development trend of railway tunnel intelligent construction technology is to implement intelligent construction system, continuously accumulate and improve tunnel design and construction methods under various geological conditions, and finally break through the theory of tunnel intelligent construction technology based on deep learning. Realize a self-learning and self-adaptive intelligent tunnel construction system. Subsequently, an intelligent tunnel construction system with dynamic perception, implementation analysis, accurate decision-making, and independent implementation is established to comprehensively promote and realize the intelligent tunnel construction.

At present, based on the mechanized large-section rapid construction technology of tunnel, the Hubei section of Zhengzhou Wanzhou high-speed railway has preliminarily constructed the intelligent construction technology system of high-speed railway tunnel, and has successfully carried out the site test.

4.4 New technologies for tunnel intelligent operation and maintenance

With the increase of railway tunnel engineering in China year by year, lining defects and diseases are also gradually increasing. The risk of safe operation of high-speed railway tunnel is prominent. The later tunnel operation and maintenance involve many problems, such as many personnel and equipment, complex road environment, high operation risk, difficult patrol inspection, etc. [29]. The maintenance demand of tunnel operation far exceeds the existing maintenance capacity. It is urgent to develop intelligent monitoring, operation and maintenance, and disease treatment technology of tunnel condition based on Internet of things technology [30]. It includes the research and development of structural health intelligent detection and monitoring system suitable for tunnel and underground engineering, tunnel condition evaluation intelligent decision system based on big data, efficient tunnel, and underground engineering maintenance technology and intelligent equipment.

The establishment of intelligent operation and maintenance system can improve the ability of information collection. With the help of mobile Internet technology and information standards, information transmission and integration can be accelerated. The use of artificial intelligence technology can enhance information mining capabilities and improve information collaboration capabilities. Thus, a set of information collection system, a set of network transmission system, a data processing center, an operation service platform, a collaborative service network, a set of technical and business standard system, and a set of responsibility traceability verification system can be formed. “Measurable, visible, controllable and usable” has been developed into “real-time monitoring, dynamic monitoring, intelligent control, timely service and accurate prediction” to provide guarantee for tunnel operation and maintenance management.

China has an extensive amount of tunnel construction in relation to most countries. The scale of tunneling is large. Based on years of research on operation and maintenance, the recommendation is to build a new “predictive” operation and maintenance system with full life cycle cost and performance as control indicators. At the same time, it is to develop integrated operation and maintenance technology equipment, rapid maintenance and reinforcement technologies, and multi-functional intelligent operation and maintenance management systems to achieve low-cost and highly efficient tunnel operation and maintenance management [30].

5. Epilogue

Over the past 40 years, the design method and construction technology of China’s railway tunnel engineering have made rapid progress and made great achievements while drawing on the advanced technology at home and abroad. However, there are many technical problems when dealing with ultra-long and deep-buried tunnels, long-distance submarine tunnels, and those in complex urban environments. These problems are mainly focused on areas pertaining to intelligent construction, operation and maintenance. Therefore, railway workers should pay more attention to the intelligent construction of tunnels in future, to promote greater development of railway tunnel construction.