Keywords: the application of pilot project in the design of pipe jacking machine for rectangular tunnel of urban underground traffic
With the rapid development of urban construction, traffic plays a more prominent role in urban construction and development. With the development and construction, cities are required to solve more underground pedestrian passages, such as subway station entrances and exits crossing pedestrian tunnels, urban underground pipelines and common ditches. Rectangular tunnels are the most economical. Therefore, the research and application of urban traffic rectangular underground tunnel boring machine is very necessary.
1, Development and Application of Rectangular Tunnel The earliest shield tunnel in the world is the Gongqiao Tunnel in London, England, and construction started on 1826. The tunnel section is a rectangle of11.4mx6.8m. Due to the flooding accident during manual excavation and construction, the 458m-long rectangular tunnel was excavated in 18.
Since 1970s, with the development of economy, the construction technology of shield machine has made a new leap. Especially in Japan, the demand of underground space development and utilization has promoted the further development of shield tunnel technology. After the replacement of steel in 1980s, countries all over the world set off the climax of developing shield tunneling machines with special-shaped sections, and successively carried out the experimental research and engineering application of shield tunneling machines for rectangular tunnels, elliptical tunnels, double-circle tunnels and multi-circle tunnels. From the analysis of the use function of the tunnel, it is found that the section forms of urban traffic pedestrian tunnel, underground common ditch and subway tunnel are the most suitable and economical, so the re-development and application of rectangular shield tunneling machine is of great significance.
Japan has carried out research on large-section rectangular shield construction method, which mainly solves the construction of crossing the railway under the overpass, assembling with steel pipes and then pouring concrete lining. The shallowest covering soil of shield construction is only 3. 198 1 year. Nagoya and Tokyo used 4.29mx 3.09m hand-dug rectangular shield to dig two ordinary trenches with a length of 534m and 298m ... Nagoya also used 5.23mx4.38m hand-dug rectangular shield to dig 1 rectangular tunnel with a length of 374m ... In short.
Shanghai Tunnel Construction Technology Research Institute started the research on rectangular tunnel from 1995, and completed the design of 2.5mx2.5m variable grid rectangular pipe jacking machine, rectangular tunnel test project scheme and engineering design through the topic discussion newsletter 1995. 1April, 1999, the EPB pipe jacking machine with 3.8mx 3.8m rectangular cutterhead developed by Shanghai Tunnel Construction Technology Research Institute was adopted in the construction of the rectangular passage at the entrance and exit of Shanghai Metro Line 3. The rectangular tunnel was started in mid-April and the second rectangular tunnel project was completed in early June. The project quality is excellent, and the normal operation of Shanghai Yan 'an East Road Tunnel and the safety of Lujiazui Road underground pipeline are ensured during the construction. The first rectangular shield tunnel in China completed the promotion of two tunnels in only 40 days, and the research, promotion and application of rectangular tunnel were successful.
2. Research on urban traffic rectangular underground tunnel boring machine 2. 1 The effective use area of rectangular section is more than 20% larger than that of circular section. The crosswalk in urban traffic requires depth, so the rectangular tunnel can better meet the requirements of crosswalk construction.
With more and more entrances and exits of subway stations, China will also develop urban underground pipeline common trench, and this kind of underground tunnel project is the most economical, so the research and application of rectangular tunnel can directly serve the needs of engineering construction and has broad application prospects.
2.2 Research Methods of Rectangular Tunnel Feasibility Study of Rectangular Tunnel The technical route of Liqu River is as follows:
(1) Digestion and absorption of foreign rectangular shield and rectangular tunnel projects;
(2) Assumption and design of rectangular pipe jacking test project;
(3) Technical and economic comparison, model scheme design and selection of rectangular pipe jacking machine;
(4) Development of rectangular pipe jacking machine for test and rectangular pipe jacking machine for engineering based on testing machine;
(5) Through the structural test, the stress distribution of rectangular reinforced concrete tubular joints can be understood, which provides a basis for improving the design optimization of tubular joints;
(6) Through the test project of 2.5mx2.5m rectangular tunnel, the construction parameters and rules of rectangular tunnel jacking are understood, which provides a basis for engineering application;
(7) Design the engineering application scheme and construction, complete the engineering application and study the construction method.
2.3 The design of rectangular pipe jacking machine is chosen because the rectangular pipe jacking machine with variable grid format has the advantages of relatively simple processing, low cost and quick installation, and valuable data can be obtained in the experiment.
2.3. 1 R&D design principle rectangular grid pipe jacking machine uses grid to cut the soil, which blocks the soil on the excavation surface, effectively preventing the soil in front from collapsing, and adopts manual excavation method for excavation. The nose is pushed forward by the main jack-up. The nose is divided into two sections, and the middle is connected by a correction cylinder. Both sides of the shell are provided with rotation correction devices, and the notch ring is provided with angle-variable notches, which can carry out a certain amount of overbreak, which is beneficial to the attitude control of the nose and ensures that the deviation of the tunnel axis is within the design range. The grid contains four variable grids, which can adjust the amount of soil entering the front of the machine head and help to control the stability of the soil in front.
2.3.2 Basic situation of design In order to ensure that there is a certain gap between the pipe joint and the soil, which is beneficial to form a ring with the soil, the section size of the nose is designed to be larger than that of the pipe joint. The main engine of the pipe jacking machine can be divided into two sections, which are connected by a rectifying oil cylinder. The seal between the front and rear sections adopts lip seal and supporting rubber ring, and the notch ring is provided with a notch with variable angle. A aperture ratio-adjustable variable grid is installed in the grid, and rotation correction devices are installed on both sides of the shell. This device can control the posture of the nose.
The main jacking device consists of 8 cylinders, U-shaped jacking iron, top ring, shim, underframe and steel backrest. Eight cylinders are divided into two groups, and four cylinders in each group are symmetrically stacked and fixed by a bracket with a split structure. The working stroke is 1450 mm, and each cylinder can be controlled independently. The straightening device is mainly used to control the deviation between the left and right axes and the upper and lower axes of the nose. The total correction force is 752t, and the correction angle is 2 degrees. The grouting correction system (fin grouting) is mainly used to correct the rotation of the machine head, and the correction torque can reach 2 10x2-420kn.
2.4 rectangular tunnel engineering test
2.4. 1 Overview of the test project The test project is located in Hangtou District, Nanhui County, Shanghai, with a jacking distance of 60m and a covering depth of 6.45m There is a small river at 10m on the north side of the jacking axis and a reinforced concrete main road in the site at 10m on the south side, as shown in figure 1 0m. The soil layers crossed by the pipe jacking machine are: traffic tunnel section. This interval consists of gray muddy clay and gray sandy silt. Through engineering tests, the design and selection of rectangular pipe jacking machine, rectangular pipe joint, joint type and water stop are verified. By collecting various construction parameters and working conditions records, the construction method of rectangular pipe jacking is studied. The engineering test has completed the key experimental research of the rectangular pipe jacking machine technology, collected the first-hand information and data, and accumulated the practical construction experience of the rectangular section tunnel excavation.
3. Application of Rectangle in Underground Pedestrian Passage of Urban Subway1In February, 1998, the research group put forward a rectangular pipe jacking construction scheme for No.5 entrance and exit of Lujiazui Station subway. Two 62m rectangular tunnels with a net inner diameter of 3mx 3m need to be built at the entrance and exit of Lujiazui Station of Shanghai Metro Line 2.
3. 1 development of combined cutterhead earth pressure balance pipe jacking machine 3.8mx 3.8m combined cutterhead earth pressure balance pipe jacking machine is based on the successful development and test of 2.5mx2.5m rectangular pipe jacking machine, aiming at the underground passage project of No.5 entrance and exit of Lujiazui Station of Shanghai Metro Line 2.
3. 1. 1 Selection of rectangular underground tunnel boring machine Combined with the engineering situation, through scheme comparison, taking into account the characteristics of compact structure, good reliability and simple operation, it is agreed that the full-face cutting earth pressure balance pipe jacking boring machine will be adopted in the project. The combined cutter head earth pressure balance pipe jacking machine uses a large knife head and a copying knife to cut the soil. By adjusting the rotating speed and jacking speed of the screw machine, the earth pressure of the soil bin is controlled to maintain the stability of the excavation surface. In order to ensure a certain gap between the pipe joint and the soil, which is beneficial to the mud collar, the cross-sectional size of the nose end is designed to be larger than the pipe joint. (The cross-sectional dimension of the nose outsourcing is 3.828mx3.828m, and that of the pipe joint outsourcing is 3.8mx3.8m).
3. 1.2 characteristics of rectangular pipe jacking machine with combined cutter type earth pressure balance. The main engine of the pipe jacking machine can be divided into two sections, and the middle is connected by 16 correction cylinders. The seal between the front and rear sections adopts two lip rubber sealing rings. The front cut the whole piece of soil with a big knife head and four copying knives. When the spiral conveyor is used for excavation, adjusting the rotating speed of the spiral conveyor can keep the balance of soil pressure in the soil bin and the stability of the excavation surface.
3.2. 1 the whole section cutting problem of rectangular pipe jacking machine If only one big knife disc is used for rotary cutting, the section cutting rate can only reach about 90%, and the four corners in the sail section of rectangular pipe jacking machine cannot be cut. In view of the complicated geological conditions, pipelines and environmental protection in Lujiazui area, and the fact that the nose needs to pass through the SMW reinforcement layer when entering and leaving the hole, a large knife head is used to cut off most of the soil in front, and a copying knife arranged behind the knife head cuts off the soil in four corners.
3.2.2 The rotation of the head of the rectangular pipe jacking machine is corrected by grouting technology, and the disc rotates forward or backward.
3.2.3 Control method of axis deviation of rectangular pipe jacking machine head According to the axis deviation azimuth and deviation amount, the deviation correction cylinders are grouped, and the expansion and contraction of the cylinders are controlled to make the front and rear shells form an included angle, thus changing the direction of the head and achieving the purpose of deviation correction. In addition, grouting can be used to rectify the deviation, or both can be combined to rectify the deviation.
3.3 Construction of Rectangular Tunnel Project The pipe jacking project at the entrance and exit of Lujiazui No.5 of Shanghai Metro Line 2 is located in Lujiazui Financial and Trade Center in Pudong. Entrance 5 is the originating well and entrance 4 is the receiving well, which are located on the north and south sides of the approach section of Yan 'an East Road Tunnel. The channel is composed of parallel pipes, each with a Zhang Liwei of 62.25m, a clear spacing of 2.2m, a slope of 0.2%, and an average covering thickness of 5.3m at the top of the pipe. All the canal structures adopt precast rectangular reinforced concrete pipe joints. The overall dimension of the pipe joint is 3 800x 3 800, the wall thickness is 40cm, the length of the pipe joint is 2 m, and the total consumption of the engineering pipe joint is 64.
3.3. 1 Pipe jacking axis control is a big problem for rectangular pipe jacking. In the normal jacking construction of pipe jacking, we must attach great importance to the control of jacking axis. After each pipe joint is jacked in, the attitude of the nose must be measured and corrected, and the correction amount should not be too large, so as not to cause great disturbance to the opening angle between the soil and the pipe joint.
3.3.2 Environmental Protection and Settlement Control As this project will pass through Lujiazui Road, Pudong approach section of Yan 'an East Road Tunnel and pipelines such as water pipes, gas pipes, rainwater pipes, sewage pipes, local telephone lines and power lines. Among them, the clear distance between the top of the pipeline and the middle 450 sewage pipe, the middle 1 000 and the bottom of the R tunnel, and the small 800 rainwater pipe is 1m, and the clear distance between the top of the pipeline and the bottom of the approach section of Yan 'an East Road Tunnel is 1.564m, as shown in Figure 5. In the process of jacking, it is very important to control land subsidence and implement environmental protection.
When the ground settlement around the tunnel is caused by the pipe jacking method, a copying knife device is adopted: the soil in four dead corners of the rectangular pipe jacking machine is cut, and all the soil in front is cut with a big knife disc. Set up settlement monitoring, data feedback, adjust construction parameters and implement information construction.
Controlling land subsidence has actually formed and realized environmental protection. However, the settlement of the approach section of Yan 'an East Road Tunnel in this project is controlled between 10 mm and-30 mm. Under certain conditions, guarantee measures must be taken to control the settlement and ensure the safety of the tunnel approach section.
3.3.3 Control technology of rectangular pipe jacking machine (1) strictly controls pipe jacking construction parameters to prevent over-excavation; (2) Strictly control the rectification of pipe jacking, and implement the principle of "rectification frequently and slowly" in the whole jacking process; (3) The jacking speed should not be too high. Try to achieve balanced construction, and the jacking speed should be controlled at around 15mm/min.
(4) During jacking construction, continuous and uniform grouting must be ensured, so that the gaps in the building can be filled quickly, and the stability of the upper soil of the pipe jacking pipeline can be ensured.
(5) To overcome the phenomenon of "returning to soil", besides injecting thixotropic mud into the nose to avoid the phenomenon of "returning to soil", it is also necessary to inject grouting into the upper part of the pipe joint in the outlet section during jacking, so as to fill the building gap caused by "returning to soil" at any time.
(6) Monitor the "sinking" or "floating" of the pipeline elevation behind the head of the pipe jacking machine. When the pipeline sinks seriously, grouting should be carried out at the bottom of the sinking part to prevent the ground from sinking.
4 conclusion
Rectangular shield tunnel is a new shield tunnel technology developed and applied abroad in 1990s. Because this technology has the advantages of large cross-section utilization rate, shallow soil cover and low cost, it can be used in urban traffic pedestrian tunnels, vehicle tunnels, underground pipeline common ditches and water diversion and drainage pipeline projects. The success of the rectangular tunnel engineering test indicates that the application of this technology in China has entered the substantive start-up stage, which fills the gap in the construction technology of rectangular pipe jacking in China, provides design basis and construction experience for the engineering application of this technology, and will have broad application prospects.
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