Application of shield construction in Tianjin subway?

The following is the application of shield construction brought by Zhong Da Consulting in Tianjin Metro for your reference.

By introducing the important parameters in the shield construction of Tianjin Metro 1 Line and the protection schemes and measures for the environment, especially the important structures, it is explained that it is reasonable and practical to introduce the shield method into the section construction of Tianjin Metro.

Construction method belongs to "trenchless" technology in underground engineering, and its selection and application are influenced by specific soil engineering geology, hydrogeological conditions and other related factors. Geological data show that Tianjin is located in the alluvial plain, and the soil layers are mainly the first continental layer, the first marine layer, the second continental layer, the third continental layer, the second marine layer and the fourth continental layer of the Quaternary Pleistocene, mainly silty soil and silty clay soft soil. From the geological conditions, Tianjin subway is more suitable for shield construction. Therefore, the introduction of shield method solves the influence of Tianjin metro section construction on the surrounding environment, and the project cost is lower than that of mining method.

Combined with the actual situation in Tianjin, this paper introduces the application of shield construction in Tianjin subway project.

1 overview

The shield section of the new section of Tianjin Metro 1 Line is divided into three sections: Xiaobailou Station-Xiawafang Station, Xiawafang Station-Nanlou Station and Nanlou Station-Tucheng Station, with a total length of 3 440 m ... The top of the structural section is buried 6 ~ 12m, and the tunnel body is mainly located in the first marine layer, the second continental layer and the third continental layer of the Quaternary upper Pleistocene. The inner diameter of the tunnel is 5500mm, and the segment thickness is 350mm. The third section adopts the construction technology of one-way propulsion, no stopping and no turning around.

According to the geological conditions in Tianjin, EPB shield machine is adopted in all three blocks. Shield machines from Herrick Company of Germany and Kawasaki Company of Japan were adopted in this construction, and certain technical parameters were obtained through engineering practice. The specific application situation is that the German Herrick shield machine is used in Xiaobailou Station-Xiawafang Station and Xiawafang Station-Nanlou Station, and the Japanese Kawasaki equipment is used in Nanlou Station-Tucheng Station.

Combined with the construction of Xiaobailou Station-Xiawafang Station, this paper introduces the application of shield method in Tianjin subway from the following aspects.

2 Selection of shield machine

The selection of shield machine is mainly based on the stratum engineering geology and hydrogeology of the project area and the line conditions of the project (including the line types of horizontal and vertical tunnels, environmental conditions along the line, underground obstacles, etc.). ), and the mechanical properties of the shield machine. Combined with the characteristics of uniform saturated soft stratum in Tianjin area, the EPB shield machine with wide applicable stratum range, advanced and reasonable technology and mature application in other areas is adopted.

3 shield propulsion construction parameter setting

(1) setting of equilibrium pressure value

According to the calculation, when the shield passes through the reinforced area, the value is about 0.17 MPa; This value is about 0.20 ~ 0.24 MPa when the normal section is advancing.

(2) Thrust setting of shield machine

In actual construction, when the shield passes through the reinforcement area, the value is about10000kn; In normal section, the value is about 10000 ~ 13000 kn.

(3) promoting the setting of unearthed quantity

Theoretical excavation per ring =(π×D2×L)/4=32.05m3/ ring.

The actual excavation amount of shield tunneling is controlled at 98% ~ 100%, and the excavation amount when passing through the reinforcement area is about 32m3/ ring. When the normal section is advancing, the excavation amount is about 3 1 ~ 32 m3/ ring.

(4) Setting of propulsion speed

The advancing speed of the reinforcement area should be controlled at about 10mm/min; Under the premise of ensuring that the ground deformation meets the design requirements and specifications during normal propulsion, the propulsion speed is basically 30 ~ 50 mm/min. In general, 8 ~ 10 cycles can be advanced every day, with the fastest 20 cycles per day and the slowest 5 cycles per day.

(5) Cutter head oil pressure setting

The soil in the reinforcement area is hard, the progress is slow, and the cutter head oil pressure value is high, generally16 ~18 MPa; After leaving the reinforcement area, the shield machine advances normally, and the oil pressure value is basically 14 ~ 16 MPa.

4 ground deformation control

There are two main factors that affect the surface deformation: shield propulsion, synchronous grouting and supplementary grouting behind the wall.

(1) Ground deformation caused by shield advancing

The shield machine used in this section is earth pressure balance shield. The setting range of the balance pressure P0 is

(hydraulic pressure, active earth pressure) < P0< (hydraulic pressure, passive earth pressure)

Taking the matching of equilibrium pressure and normal earth pressure as the control objective, the measured earth pressure value P 1 is compared with P0 value, and the corresponding spoil management is carried out according to this pressure difference. The control flow is as follows:

When P0

When P0 >; Pi, the balance pressure of shield machine is higher than the normal earth pressure, which leads to under-excavation and ground uplift;

When P0=Pi, the shield machine advances normally.

Therefore, the balance pressure control of shield machine directly leads to the deformation of ground soil in front of shield machine.

(2) shield propulsion

The diameter of shield is 6.39m, and the diameter of segment is 6.2 m. If the building gap after shield construction is not filled, the surrounding soil will move to this gap, resulting in ground subsidence. Synchronous grouting and post-grouting of lining wall in shield propulsion are the main means to fill the gap between soil and segment ring, control ground deformation and reduce later deformation, and are also important processes in shield propulsion construction.

① Synchronous grouting

Theoretical building spacing of each ring:1.0π (6.392-6.22)/4 =1.87m3.

Outer diameter of shield: φ 6.39m; Outer diameter of segment: φ 6.2m

The grouting quantity per circle is generally 150% ~ 250% of the building cracks, that is, the synchronous grouting quantity per circle is 2.81~ 4.68m3. The pressure at the pumping outlet should be controlled according to different depths and soil quality, generally around 0.3MPa.

See table 1 for the slurry mixture ratio.

② Grouting behind the wall

When the shield is pushed to a special section and there are buildings or pipelines that need to be protected on the ground, the grouting behind the wall can be adjusted in time according to the actual situation and the monitoring information of stratum deformation. Slurry can be double liquid slurry, and the pressure value, quantity and specific position of grouting depend on the actual situation, and the general grouting pressure is 0.3 ~ 0.4 MPa.

See Table 2 for mud ratio.

5 Main construction technical measures

(1) Strictly control the shield construction parameters.

In order to ensure the shield advancing along the design axis, the following measures must be taken to control the earth pressure, advancing speed and incision excavation, and to minimize the fluctuation of equilibrium pressure. At the same time, in the process of curve propulsion, considering the pressure difference in front of the cutter head, it is necessary to synchronously adjust and control the oil pressure values of the left and right sections and the stroke of the left and right propulsion jacks to make them advance along the design axis. The specific measures are as follows: ① Observe and adjust the balance pressure of shield machine in time according to the excavation amount and system monitoring equipment; (2) According to the unearthed soil quality and the stratum revealed by the geological report, predict the positive earth pressure in advance, and raise or lower the balance pressure of the shield machine in time; (3) Strictly control the pressure and excavation amount of the earth bin to prevent over-excavation and under-excavation; (4) according to the mechanical properties of the soil and the mechanical properties of the shield machine, the forward movement distance of the cutter head is controlled; ⑤ Accelerate the assembly speed of each ring and reduce the stay time of shield machine in soft soil; ⑥ During normal propulsion, the speed should be controlled at 2 ~ 4cm/min. When passing through the building, the propulsion speed should be controlled at about 65438 0 cm/min.

(2) Strictly control the amount of rectification.

The curve propulsion of shield is actually on the tangent of the curve, so the key to the propulsion is to ensure the control of the shield head. During curve construction, the ring of shield driving construction is rectification, which must be measured frequently and rectified frequently, and the amount of rectification should be as small as possible each time to ensure that the torus of wedge block is always in the radial vertical plane of curvature radius. Control and master the amplitude of rectification of shield at one time, so as to make rectification as uniform and stable as possible and reduce the influence of rectification on surrounding soil. At the same time, under the good condition of ensuring the deformation control in front of the shield, the shield construction should be balanced and uniform to reduce the impact of shield construction on the ground.

The segment assembling position should be strictly controlled in curve segment construction. If the segment position is not ideal, and the bent segment can't meet the deviation rectification, it is necessary to use cork wedge to make the segment in the ideal position and ensure the shield axis.

(3) control the grouting behind the lining

When advancing, the quality, quantity, position and pressure of the grout should be strictly controlled, and the grouting parameters should be adjusted at any time according to the deformation monitoring in the construction process. If necessary, grouting behind the wall should be used for control. In the process of construction, the method of linkage between propulsion and grouting is adopted. When the grouting can't meet the requirements, the shield propulsion will be suspended to prevent the deformation of the soil.

During grouting, the following points should be noted to ensure the grouting effect:

① Control the grouting time to ensure that grouting measures are taken at the best time;

(2) According to the soil conditions, determine synchronous grouting, semi-synchronous grouting or post-push grouting and rear grouting;

③ According to different soil conditions (soil quality, earth pressure, pressure, water pressure, etc.), determine the synchronous grouting pressure and grouting quantity. ) and excavation conditions;

(4) Take measures to prevent the injected slurry from leaking from the joint between the shield tail and the segment of the working face;

⑤ According to the filling effect and purpose (whether seepage prevention is considered or not), the secondary grouting shall be adopted appropriately; ⑥ Ensure the quality of grouting materials and the suitability of grouting technology.

Although the design axis is a smooth curve, in the process of actual propulsion, the excavation axis must be a broken line, and the excavation amount outside the curve is large. This will inevitably lead to soil loss outside the curve, and the gap between buildings will increase during the excavation process. Therefore, in the process of filling the construction gap by synchronous grouting, it is necessary to strengthen the grouting quantity outside the curved section and reinforce the outer soil at the same time, so that the outer soil can give the segment enough support, reduce the horizontal displacement of the tunnel and ensure the shield to advance smoothly along the design axis.

(4) Remedial measures for overweight buildings and strengthening ground tracking grouting.

When the shield passes through important sections, the monitoring and analysis of ground deformation should be strengthened, and the propulsion parameters should be adjusted in time. If the deformation of the ground building exceeds the warning range, it is necessary to carry out double liquid grouting behind the wall through the segment grouting hole in the tunnel, and carry out ground tracking grouting to protect the building.

6 construction difficulties

(1) construction of shield crossing "Wang Zhongshan's former residence"

Between Pukou Road and Nanjing Road, there is a century-old "Wang Zhongshan Old Residence" (brick-wood structure) above the shield axis, which is located on the natural foundation with a brick wall foundation of1.0m. In order to protect this building, strict requirements are imposed on the shield propulsion axis and ground deformation control. In order to control the key points, the above technical measures were taken in the construction, and the following measures were also taken.

(1) Strengthen ground tracking grouting.

Because "Wang Zhongshan's former residence" is very sensitive to deformation, when the shield passes 200m in front of the building, the grouting flower tubes that can be grouted repeatedly are buried in advance along the periphery of the building, and a certain number of monitoring and control points are arranged. When the shield passes through the building, if the deformation of the ground building exceeds the warning range, it is necessary to carry out double liquid grouting behind the wall through the segment grouting hole in the tunnel, and carry out ground tracking grouting in time to adjust and control the settlement of the building. Only ground grouting measures are more effective and direct for protecting buildings.

According to the relationship between the building and the line, the flower tube can be repeatedly grouted along the periphery, with the spacing of 1.5m and the buried depth of 8 ~ 10m. See Table 3 for the proportion of main mud materials.

(2) Static leveling monitoring.

According to the plane layout and foundation form of the building, combined with the plane relationship between the structure and the line, monitoring communication pipes are buried in every corner and the middle of each side of the structure.

Due to proper construction measures and feedback from construction informatization, the final settlement is-10.4mm, which is completely controlled within its allowable settlement range (according to inference and analysis, the maximum settlement of "Wang Zhongshan's former residence" is about 25mm), ensuring the safety of celebrities' former residence.

(2) Crossing the brick sewage culvert

The brick culvert has a section size of 2.35m×2.35m and is located at the intersection of Dagu South Road, Di Wei Road and Jianshan Road in Hexi District, Tianjin. The overall direction of the brick culvert is Di Wei Road, oblique to Dagu South Road. According to the investigation, the Korean side was built in 1958 and is still in use today. The buried depth of the tunnels at the intersection of South Korea and the left and right line tunnels from Nanlou Station to Tucheng Station is 13.224m and 13.596m respectively. The square culvert is located below 3m underground, and the clear distance from the tunnel is about 8.246m.

According to theoretical calculation and analysis, the settlement of the square culvert should be controlled within 20 mm. When crossing the underground structure during construction, the ground settlement and deformation caused by shield tunneling should be basically controlled within 5 ~ 20 mm by taking the following measures:

(1) According to the data of automatic monitoring equipment for shield propulsion and ground monitoring, adjust the front pressure of shield in time and control the propulsion speed reasonably;

(2) Strictly control the pressure and excavation amount of the earth bin to prevent over-excavation and under-excavation;

(3) Control the change of shield propulsion posture, maintain balanced and uniform construction, and reduce the disturbance to the stratum. The tunnel body of the shield tunnel at the square culvert is located on the radius curve of 300 meters, and the shield posture and the single rectification range are controlled to make the rectification amount uniform and stable, so as to reduce the influence of rectification on the surrounding soil;

④ Control the slurry quality, grouting pressure and grouting quantity of synchronous grouting to reduce the deformation of soil after shield advancing.

7 conclusion

(1) Small radius construction was considered in the selection of shield, so the articulated shield with rectifying jack device was selected. Adjusting the position of shield tail can improve the relative position between shield tail and segment, so as to facilitate the assembly of segment and better control the propulsion axis of tunnel.

(2) It is very important to control the ground subsidence by adjusting the opening rate and pressure of the cutter head. Practice has proved that the settlement can be well controlled within the design range by taking auxiliary measures.

(3) For the key parts in construction, strengthening monitoring and ensuring the realization of information construction is an important means to achieve the expected goal.

For more information about project/service/procurement bidding, and to improve the winning rate, please click on the bottom of official website Customer Service for free consultation:/#/? source=bdzd