This paper summarizes a number of large-scale infrastructure construction projects in China in recent years, such as Qinghai-Tibet Railway, Shenzhen Metro, Shanghai River-crossing Tunnel and other underground projects.
The construction and smooth implementation of the Qinghai-Tibet Railway provides a good experimental basis for solving the underground engineering construction in the plateau frozen soil area. At the same time, the construction of urban subway project also poses a new challenge to solve the underground engineering construction in complex urban geological environment; However, the construction of large bridges, river-crossing tunnels and offshore facilities makes the underwater underground engineering construction face higher technical requirements. The construction and completion of a series of large-scale infrastructure facilities have greatly promoted the technical level of underground engineering construction. Summarizing and perfecting these new technologies and other technical achievements in underground engineering construction in time will provide good technical support and guarantee for the future underground engineering construction and will greatly promote the underground engineering construction in China. Based on the technical achievements of underground engineering construction in some large-scale infrastructure projects in China in recent years, such as Qinghai-Tibet Railway, Shenzhen Metro and Shanghai River Crossing Tunnel, this paper introduces this new technology and provides reference for similar projects in the future.
1 new construction technology of underground engineering in frozen soil area
The Golmud-Lhasa section of the Qinghai-Tibet Railway is over 1 100 kilometers long, crossing the Qinghai-Tibet Plateau with the highest altitude in the world, known as the roof of the world and poor construction conditions. It is also 1 time in the world to build a railway in high-altitude frozen soil area, which has no mature construction experience and high technical content.
1. 1 construction technology of bored piles in permafrost regions
The key technology is to reduce all kinds of heat generated in the construction process, such as friction heat of drilling, heat of backfill soil and hydration heat of cast-in-place pile concrete. In order to avoid the sudden change of temperature field of foundation soil around the pile, which will cause the foundation soil around the pile to heat up and melt in a certain range. At the same time, due to the seasonal changes in permafrost regions, the seasonal melting layer on the surface will produce frost heaving force with the seasonal changes, and eliminating these frost heaving forces is also a key point of bored piles.
In order to reduce the influence of construction heat on frozen soil area and form a new state of thermal balance as soon as possible, after pouring concrete for bored piles in frozen soil area, the construction above the pile cap can only be carried out after a stage of heat exchange process. Generally, the heat exchange time is 60 days, and after 60 days, the pile foundation can be considered to be basically stable.
During the use of pile foundation, frost heaving force will be generated due to the change of frozen soil season. According to the position and direction of frost heaving force acting on the foundation surface, it can be divided into three types: tangential frost heaving force, horizontal frost heaving force and normal frost heaving force (see figure 1). Horizontal frost heaving forces cancel each other out, and the main damage of frost heaving to the project is tangential force and normal force. In engineering construction, the following measures can be taken to prevent the pile foundation from frost heaving: ① To avoid the pile foundation from normal frost heaving force, bury the pile foundation to a certain depth below the natural upper limit of frozen soil; (2) Bury the steel expansion cylinder at least 0.5m below the upper limit of frozen soil, the inner diameter of the casing is larger than the pile diameter by 10cm, and apply residual oil on the periphery of the casing to reduce the hydrophilicity of the outer surface, so that it is not necessary to disassemble the casing after the pile is completed; ③ Use high pile caps as far as possible, and drill and expand bottom piles in areas with severe frost heaving; (4) backfill the outer side of the pile casing and the bottom of the low pile cap with coarse-grained soil mixed with residual oil. The above measures can effectively reduce the tangential frost heaving force and lifting frost heaving force of frozen soil on casing (see Figure 2); ⑤ Dry drilling with rotary drilling rig to ensure the correct hole position and verticality of drilling; ⑥ Using low-temperature early-strength durable concrete, the problem of slow strength growth caused by low-temperature pouring of concrete is avoided.
1.2 frozen soil tunnel construction technology
There is little experience for reference in the construction of permafrost tunnels on the plateau. Its core is to minimize the influence of temperature rise on frozen soil and avoid construction disasters and operational hidden dangers caused by freezing, compression, settlement and frost heaving.
The compressive strength of frozen soil is very high, and its ultimate compressive strength is even equivalent to that of concrete. The compressive strength of frozen soil drops sharply after melting, which leads to hot melt settlement and frost heaving in the next cold season, which often leads to the instability of engineering buildings and is difficult to repair.
When the temperature of water-bearing loose rock and soil drops to 0℃, ice is produced, which is the main sign of freezing state. When water turns into ice, its volume increases by about 9%, which makes the soil frost heave. When the soil freezes, not only the water in the original position freezes into ice, but also under the action of osmotic force (suction), the water will move from the unfrozen area to the freezing front, where it freezes into ice, making the frost heave of the soil more intense.
In the process of freezing, the volume of water turning into ice increases, which causes water migration, ice precipitation, frost heaving and soil skeleton displacement, thus changing the structure of soil. In the process of melting, the displacement of soil particles will inevitably fill the space where ice melts and discharges, resulting in melting and consolidation, which will cause the local ground to move down, that is, hot melt settlement (hot melt settlement).
In order to avoid hot melt settlement in tunnel construction, the key technology of frozen soil tunnel construction is to do a good job of heat preservation measures.
Tunnel thermal insulation construction technology mainly includes: optimizing the construction of open tunnels and openings in cold season, and adding sunshade and thermal insulation shed during excavation to block the influence of solar radiation energy on frozen soil. The main tunnel adopts weak blasting and smooth blasting technology to reduce the disturbance and overbreak of frozen soil. After excavation, the scattered ice cubes in the arch (wall) interlayer are removed and the concrete is sprayed quickly to seal the rock surface. Adopt rail transportation to reduce waste gas pollution in the tunnel and reduce ventilation times and air volume; In warm season, measures such as night blasting ventilation and cooling fan ventilation are adopted to control the tunnel face temperature below 5℃ and minimize the frozen soil melting circle outside the excavation section of the cavern. The whole length of the tunnel is paved with "waterproof layer, insulation board and waterproof layer" to block the disturbance of frozen soil caused by temperature change in the tunnel after the completion of the tunnel and ensure the safety of operation.
The main factors affecting the frost heaving of soil are soil type, water content and freezing conditions. After long-term experiments, cryologists have proved that the frost heave of coarse-grained soil is very small or even absent, while that of fine-grained soil is generally very large. When the water content of soil is large, the frost heaving phenomenon is serious. When the water content of soil is less than a certain value, the frost heave rate of soil is zero. In order to prevent frost heaving from affecting the engineering structure of open-cut tunnel and portal, rich frozen soil, saturated frozen soil and soil-bearing ice layer within the influence range of frost heaving of open-cut tunnel and portal slope are excavated, and coarse-grained soil is used for filling, and the water content of coarse-grained soil is strictly controlled, and waterproof and drainage facilities are made after filling.
Engineering example: Huo Feng frozen soil tunnel of Qinghai-Tibet Railway is 65,438+338 m long, which is the highest frozen soil tunnel in the world. The upper limit of permafrost is 1 ~ 1.8m, and the thickness of permafrost is 100 ~ 150m ... All caves are located in permafrost. In the construction process, fully grasp the engineering characteristics of frozen soil, adopt excavation techniques such as grouting pipe shed, grouting anchor rod and smooth blasting in the tunnel, comprehensively use coarse-grained soil to replace the covering layer of open-cut tunnel, set up multiple insulation layers in the whole length and section, and adopt technologies such as insulation, temperature control, oxygen supply, concrete spraying and information monitoring, so as to shorten the thawing period of frozen soil to the maximum extent, rebuild a new thermal balance system of frozen soil tunnel, and meet the requirements of safe, high-quality and efficient construction.
In addition, the temperature protection measures in frozen soil areas include the construction technology of riprap ventilation subgrade, the construction technology of laying insulation board on high-temperature fine-grained soil subgrade, and the construction technology of high-temperature fine-grained soil hot rod subgrade. These measures can greatly reduce the influence of foundation bearing capacity on frozen soil.
2 new technologies for subway and river-crossing tunnel construction
With the rapid development of urbanization in China, the traffic pressure in big cities is increasing day by day, and large-scale urban subway construction is inevitable. There are more and more urban cross-river tunnels planned along the Yangtze River. This kind of engineering construction is often large in scale, with harsh construction environment and complicated construction technology. The following briefly introduces several new construction technologies.
2. 1 Pile foundation underpinning technology in subway construction
Pile foundation underpinning is inevitable in subway construction. The research on underpinning technology of large axial force pile foundation in Shenzhen Metro Department Store Square has solved the main key technical problems of underpinning of large axial force pile foundation, and enriched the construction technology of pile foundation underpinning project.
Pile foundation underpinning is a common form of underpinning technology application in China. The core technology of pile foundation underpinning lies in the load conversion between the new pile and the old pile, which requires that the deformation of the underpinning structure and the new pile be limited to the allowable range of the superstructure during the conversion. In view of the above deformation control, underpinning mechanism can be divided into active underpinning and passive underpinning. Active underpinning is mainly to load the new pile and underpinning structure before the old pile is cut off, so as to eliminate the deformation of some new piles and underpinning structures and limit the deformation of piles and structures after underpinning within the allowable range. This technology is applied in the case of large axial force and strict structural deformation requirements. Passive underpinning is to transfer the load to the new pile in the process of dismantling the old pile, and the deformation of the pile and structure after underpinning is difficult to control. This technology is suitable for small tonnage and lax structural deformation control. The underpinning project of the pile foundation of the Department Store Plaza building in Guo Mao Laojie section of Shenzhen Metro has many underpinning piles (6 piles), large axial force (18000kN), large pile diameter (2000mm), poor geological conditions, high underground water head, deep underpinning position (2 floors underground) and complicated service environment (vibration influence when crossing the subway in the middle). At present, there is no similar large axial force underpinning at home and abroad.
Due to the limitation of direction and minimum radius (Rmin=300m), the first phase line of Shenzhen Metro must pass under the skirt building of Department Store Plaza. Therefore, the problem of pile foundation underpinning arises. There are 22 floors in the main building of the department store plaza, 9 floors in the skirt building and 3 floors in the basement. It is a frame beam shear wall structure, and the foundation is an independent pile foundation with end-bearing piles. The standard bearing capacity of the pile tip bearing layer (strongly weathered layer) is 2700kPa, and the maximum diameter of the pile body is 2000 mm According to the floor, it is estimated that the maximum design axial force of the underpinning pile is about 18900kN.
The tunnel runs through the department store square, Shennan East Road and Huazhong Hotel. Due to the influence of the location of the excavated tunnel and its superstructure, some piles are in or near the tunnel, so it is necessary to underpinning six podium piles on the 9th floor of the department store plaza (the pile diameter is 2000mm, and the bearing layer of the pile foundation is all in the bedrock below the tunnel structural plane), and the maximum axial force is 18000kN.
According to the structure, foundation form and operation space of the department store plaza, the underpinning of the pile foundation of the department store plaza is in the form of beam underpinning structural column, and the newly added underpinning pile is manual digging pile. The whole underpinning project is carried out on the third floor underground.
According to the deformation requirements of high-rise structures, the podium pile foundation adopts active underpinning. During underpinning, a loading jack is arranged between the underpinning beam and the new pile, which makes the upper structure have a small amount of jacking displacement, and at the same time, most of the settlement displacement of the new pile is preloaded during jacking. The load acting on the original structural pile is transferred to the new pile through the underpinning beam through active loading, and the top increment of the original pile (column) and the settlement of the new pile are also effectively controlled. After manually digging a hole to the bottom of underpinning beam, pile cutting will be carried out step by step. After the pile is cut, the tunnel is excavated, the lining is deformed stably (during which the jack device is adjusted in time), and the underpinning beam is connected with the new pile to form a permanent structure, thus completing the underpinning. The whole process of pile foundation underpinning and tunnel construction is strictly monitored and measured to ensure the structural safety.
Through strict calculation and construction operation, through technical research, the technical problems such as pile foundation excavation and support, underpinning and beam replacement, pile foundation interception, and force conversion in weak strata have been solved, ensuring the safe and normal use of underground pipelines such as high-rise buildings, shopping malls and squares.
The underpinning principle of pile foundation in this project is shown in Figure 3.
2.2 Horizontal freezing method in river-crossing tunnel construction
Freezing method is a special construction method for connecting passage of underground tunnel, which uses artificial refrigeration technology to turn water in stratum into ice and natural soil into frozen soil to increase its strength and stability, isolate the connection between groundwater and underground structures, and carry out connecting passage construction under the protection of freezing wall.
Refrigeration technology is completed by three circulating systems with freon as refrigerant. These three circulation systems are Freon circulation system, brine circulation system and cooling water circulation system. Three refrigeration circulation systems form a heat pump, which transports geothermal energy in low-temperature brine to Freon circulation system through freezing holes, then to cooling water circulation system through Freon circulation system, and finally to the atmosphere through cooling water circulation system. With the continuous flow of low-temperature brine in the stratum, the water in the stratum gradually freezes, forming a frozen soil column centered on the frozen pipe, which expands continuously, and finally the adjacent frozen soil columns are connected into a whole, forming a frozen soil wall or frozen soil curtain with a certain thickness and strength. The principle of horizontal freezing reinforcement is shown in Figure 4.
In actual construction, freezing holes are drilled horizontally, freezing pipes are erected, and salt water is used as heat transfer medium for freezing. Generally, freezing equipment is installed at the construction site to cool unfrozen liquid (usually salt water) to -22 ~-32℃. Its main features are:
(1) can effectively isolate groundwater, and the water content >: 10% water-bearing, loose and unstable stratum can be constructed by freezing method.
(2) The shape and strength of frozen soil curtain can be flexibly arranged and adjusted according to the construction site conditions and geological conditions. The strength of frozen soil can reach 4 ~ 10 MPa, which can effectively improve work efficiency.
(3) Freezing method has no pollution to the surrounding environment, no foreign matter enters the soil and low noise.
(4) There are many factors that affect the strength of frozen soil. Frozen soil is a rheological property, and its strength is related to both the origin of frozen soil and stress characteristics. The main factors affecting frozen soil are freezing temperature, soil water content, soil particle composition, loading time and freezing speed.
The key technologies of freezing construction include:
(1) Determine the main technical indicators of freezing, that is, determine the salt water temperature, the average temperature of frozen soil wall and the frozen soil strength during the active freezing period and the maintenance freezing period according to the actual working conditions.
(2) Layout and construction of freezing holes, that is, according to the plane size and structural stress characteristics of the connecting channel, the layout and design of freezing holes are carried out, and the deflection of freezing holes is fine-tuned according to the segment reinforcement diagram, and the outward deflection angle of the aperture is controlled within the range of 0.5 ~ 10.
(3) Design the refrigeration station, actively maintain the refrigeration construction, calculate the refrigeration capacity, and select the refrigeration unit according to the needs of refrigeration capacity.
(4) The construction method and sequence of excavation and construction of communication channel.
(5) Construction monitoring.
Shanghai Dalian Road Crossing River Tunnel Project consists of two tunnels, east and west, with a connecting passage between them. Both tunnels are located at the bottom of Huangpu River, about 400m apart. The connecting channel (1) is located on the west bank of Puxi, with the distance between the centers of the east-west line tunnels of 35.705m, the tunnel height difference of 3.565m and the clear distance of the connecting channel of 25.665m The connecting channel (2) is located on the bank of Pudong, with the distance between the centers of the east-west line tunnels of 27.575m, the tunnel height difference of 0.345m and the clear distance of the connecting channel of17. In order to ensure the construction safety of the passage, freezing method is adopted. Engineering practice shows that the freezing construction technology of connecting passage has the advantages of fast freezing speed, high frozen soil strength, good curtain uniformity, high anti-leakage performance, close combination with tunnel segments, safe and reliable construction and so on. It can ensure the safety and reliability of the construction of the river bottom communication channel under the conditions of long distance, large depth and high confined water. Melting settlement is an inevitable situation in freezing construction, and it can be compensated and reduced by reserving grouting holes in tunnels and communication passages in time. In the construction of several connecting channels, its superiority and social and economic value have been fully demonstrated.
2.3 Construction technology of underground excavation of the middle hole in the three-arch and two-column structure of subway station.
With the development of urban subway and rapid rail transit in China, more and more big cities are building subways. Because most of the sections that the subway passes through are bustling commercial areas, some sections are affected by demolition costs, traffic occupation, underground pipeline protection, ancient cultural relics protection and environmental protection. However, the open excavation (cover excavation) of the subway station is restricted, so the underground excavation method can only be used for construction, which leads to the appearance of underground excavation of the subway station.
Ciqikou Station, Tiantan East Gate Station and Chongwenmen Station of Beijing Metro Line 5 adopt the comprehensive supporting construction technology of three arches and two columns underground excavation method, which ensures the quality and safety of the project, completes the construction task on schedule and obtains good social benefits. This technology is suitable for the construction of underground parking lots, underground shopping malls, long-span highways and railway tunnels, such as long-span double-layer underground excavation stations and multi-arch tunnels with poor self-stability of surrounding rocks.
Technical characteristics of underground excavation method in station construction;
(1) CRD (diaphragm) method completed the excavation of the middle tunnel and formed the initial supporting system of the safe middle tunnel.
(2) Complete the bottom plate, bottom beam, steel pipe column, middle plate, top beam and middle arch of the middle tunnel, form a stable middle tunnel supporting system, bear the main load of surrounding rock, and provide safe conditions for side tunnel excavation.
(3) CRD method is adopted to symmetrically complete the excavation of the side tunnel.
(4) Dismantle the temporary initial supporting system and complete the secondary lining construction of the side tunnel.
(5) In the process of system transformation, reasonably determine the segment length and add steel supports at the same time.
(6) Give full play to the role of monitoring and measurement, and use information to guide construction.
The technical principle of underground excavation station tunnel construction method: divide the long-span tunnel with poor geology into three parts, and each part is divided into strips to ensure the safety during excavation. First, a temporary structure is formed at the initial stage of the tunnel, and a permanent lining structure is applied in the temporary structure to form a central stable support to bear the main load of surrounding rock. Then, each block of the side hole part is excavated symmetrically, and finally the whole structure is formed. In the process of system transformation, steel supports are added according to the monitoring situation. Its technological process is as follows: construction preparation → advanced pipe shed → grouting reinforcement → excavation of all parts of the middle tunnel → laying waterproof layer → bottom plate and bottom beam of the middle tunnel → column → middle plate of the middle tunnel → top beam and middle arch → advanced pipe shed → grouting reinforcement → excavation of all parts of the side tunnel → dismantling temporary partition wall → laying waterproof layer → bottom plate of the side tunnel → side wall and middle plate → side arch → grouting behind the secondary lining. The subway station with three arches and two columns is constructed by underground excavation method, as shown in Figure 5.
Ciqikou Station is the interchange station between Beijing Metro Line 5 and the planned Beijing Metro Line 7. The station is180m long, 21.87m wide and 4.933m high. The building area of the station is 12244.2m2, and the main coverage depth of the station is 9.8 ~10.3m. The station is a double-deck island structure with three arches and two columns. The underground 1 floor of the station is the station hall floor, with reserved passages to realize the transfer with Line 7, and the second underground floor is the platform floor. This method was adopted in the station construction, which ensured the safety and quality of the project construction and achieved success.
3 Underwater foundation construction technology
3. 1 offshore foundation engineering construction
With the construction of infrastructure, there are more and more offshore projects such as sea-crossing bridges. A number of planned and under-construction bridges, such as Bohai Bay, Changjiang Estuary, Hangzhou Bay (under construction), Lingdingyang at the Pearl River Estuary and Qiongzhou Strait, have brought new challenges to the construction of offshore infrastructure. It is an inevitable trend to use large diameter and long foundation piles in large-scale sea-crossing and river-crossing projects, and structural steel pipe piles, temporary steel liners and temporary steel pipe piles on offshore platforms will be widely used. All these put forward new requirements for pile drivers. The piling boat equipped with high pile frame, powerful power system for hanging piles, high-energy piling hammer and advanced offshore piling GPS measurement and positioning system can successfully complete the task of piling by hammer at sea.
Broadly speaking, offshore pile sinking system includes ship combinations such as piling ship, pile carrier, anchor ship, tugboat and traffic boat. Judging from the pile sinking process of steel pipe piles, the piling boat is the main body of steel pipe piles, which mainly consists of the following parts: hull system (including hull, anchoring system and power system), pile frame and its suspension system, hammer sinking system (including piling hammer and replacement piling), GPS measurement and positioning system for offshore pile sinking, etc. In particular, GPS can automatically collect and process data when the construction ship is located far from the shore, reflect the current and designed position of piling in the form of graphics and numbers, facilitate the operator to adjust the position of the ship for construction piling, and automatically generate piling reports and playback data, which brings convenience to offshore piling.
The positioning of offshore pile sinking is realized by "GPSRTK measurement and positioning system for offshore pile sinking", as shown in Figure 6.
Three GPS receivers installed on the piling ship receive the fixed frequency data links transmitted by the reference stations established on land and in the sea as reference data for positioning. Its working principle: during positioning, the position, direction and attitude of the hull are controlled by RTK through the GPS mobile platform fixed on the piling ship, and the position of the pile body at a certain elevation relative to the pile frame of the hull is determined by two prism-free rangefinders fixed on the ship, so as to calculate the actual position of the pile body at the designed elevation and display it on the computer screen of the system. By comparing with the design coordinates, move the ship and correct it until the deviation meets the requirements. The inclination of the pile body is controlled by the pile frame. According to the scale drawn on the pile by the red horizontal beam emitted by the prism-free rangefinder, the elevation of the pile top is calculated systematically. Before specific positioning, input the design center coordinates, elevation, plane torsion angle and other parameters of the pile to be positioned into the computer. When positioning, the display screen can display real-time pile position data and graphics, as well as the designed pile sinking position and deviation. The commander of the piling boat can direct the piling boat to locate correctly according to the displayed relevant information.
This technology is suitable for the sinking construction of structural steel pipe piles, temporary steel liners and temporary steel pipe piles on offshore and river platforms, and has the following obvious advantages: ① it can be used in the sea areas with bad sea conditions; (2) It can adapt to the pile sinking construction of super-long and large-diameter steel pipe piles; ③ The construction of inclined piles with different inclination angles and plane deviation angles can be satisfied; ④ Steel pipe piles can pass through different soil layers; ⑤ The measurement and positioning are simple and quick, and the accuracy meets the requirements; ⑥ Short construction period (diameter 1.6m, and the whole construction process of a single steel pipe pile with a length of 80m only takes 2.5h). This has been practiced in the Hangzhou Bay Bridge project under construction.
3.2 Sinking construction technology of double-wall steel cofferdam without guiding ship
There are two weak links in foundation construction that affect the progress of the project, namely, the bored pile foundation of steel sheet pile cofferdam and the sinking of open caisson to grass-roots foundation, and the waterproof cofferdam installed at the top of open caisson at grass-roots level is generally weak, and the arrangement of pumping process in cofferdam is limited by the construction water level; (2) Embedding open caisson foundation into rock stratum to remove weathered rocks is very labor-consuming and time-consuming, especially in deep-water rapids, and the progress of the project directly restricts the safe flood crossing of the whole foundation. Comparatively speaking, the bored pile foundation of double-wall steel cofferdam adopts waterproof structure of double-wall steel cofferdam, which absorbs the advantages of the above two construction structures. In essence, it is a building structure combining a circular floating shaft with a waterproof cofferdam, which can bear greater inward or outward water pressure. Generally speaking, the arrangement of foundation construction process is not affected by seasonal water level changes.
Double-walled steel cofferdam is composed of inner plate wall and outer plate wall, which are connected by rigid support. Because there is a cavity between the two board walls, the bottom is closed by the annular blade feet, which has the ability of self-floating. When the bottom section floats, according to the lifting capacity of the equipment, the slab wall can be raised section by section, the counterweight can be injected into the cavity, and it can be sucked by a mud suction machine to make it sink until the steel cofferdam sinks to the design position, and it can be kept stable by pouring underwater bottom sealing concrete, and then the bored pile construction can be carried out according to the design requirements.
The sinking construction of double-wall steel cofferdam without guiding ship is adopted. Because the huge guiding ship and connecting beam system are cancelled, the wind force and current force borne by the anchorage system are greatly reduced, thus simplifying the configuration and construction of anchorage equipment, speeding up the construction progress and saving steel and water equipment. At the same time, the double-walled steel cofferdam structure is a floating open caisson, which is not only convenient to float in place, but also can bear large water pressure and overcome the disadvantage of sand turning at the bottom when sinking. Moreover, the cofferdam sucks mud and sinks in place in a short time, so the construction is safe. It is especially suitable for water construction projects with high navigation conditions, narrow construction area, sandy clay and pebble soil layer, and it is impossible to set guide boats.
This technology was applied to the underwater foundation construction of Luzhou Yangtze River Bridge on Longnan Railway in Sichuan, which successfully completed the task of deep-water foundation construction and ensured the completion of the bridge on schedule. For similar deep-water foundation construction, it has extensive popularization and application value.
4 conclusion
China's vast territory, vast territory, different natural geographical environment, different soil quality and strong regional underground engineering make underground engineering construction very different and complicated. Continuous innovation combined with different engineering characteristics is the basis of improving underground engineering construction technology. This paper introduces several new technologies of underground engineering construction completed in China in recent years, hoping to inspire underground engineering construction. On this basis, on the one hand, actively promote the application of these new technologies, and more importantly, constantly innovate on the basis of application, so that China's underground engineering construction will continue to step up to a new level.
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