Xiaobailou to Xiawafang Tunnel Project of Tianjin Metro 1 Line?

Xiaobailou-Xiawafang Tunnel Project is an important part of Tianjin Metro 1 Line (newly built section). Located in the central area of Tianjin, the shield machine basically advances under sections such as Nanjing Road and Dagu South Road. The area along the line includes Xiaobailou business district, important business center in Hexi area and main office area in Tianjin. Among them, Wang Zhongshan's old residence (brick and wood structure) with a century-old history is located on the axis of the tunnel, with major buildings such as China Construction Bank and Asia-Pacific Building (under construction) on both sides, and many large-diameter and high-pressure municipal public pipelines are laid above the tunnel.

The total length of Xiaobailou-Xiawafang tunnel is 2087.699 meters, and the left and right communication passages are located at DK16400.000m. The tunnel has an outer diameter of 6.2m, an inner diameter of 5.5m, and a segment width of1.0m.. The design strength of the lining is C50, and the whole ring segment is divided into 6 blocks, consisting of 1 capping block (f), 2 adjacent blocks (l) and 3 standard blocks (b). The longitudinal and circumferential directions are connected by M30 bending bolts; Elastic gaskets (EPDM and water-swellable rubber) are used for waterproofing of segment joints.

Second, the engineering geological conditions

The soil layers in this tunnel area are mainly Quaternary artificial fill layer (artificial accumulation Qml), the first continental layer (riverbed-floodplain sediment Qc3al), the first marine layer (shallow sea sediment Q24m), the second continental layer (riverbed-floodplain sediment Q 14al) and the third continental layer of Quaternary Pleistocene (riverbed-floodplain sediment Q/).

Shield mainly passes through ④, ④3, ⑤ and ⑤ 4 soil layers. See table 1 for physical and mechanical indexes of soil layer.

Table 1 physical and mechanical indicators

Third, the shield machine

The articulated earth pressure balance shield in herrick, Germany, is an advanced shield machine in the world at present. The shield has a diameter of 6390 mm, a total length of about 48 meters, a main length of 8.47 meters and a weight of about 300 tons. The shield machine * * * has 32 jacks (divided into 16 groups) with a stroke of 2. 2 meters. The thrust of a single jack is 1078 kn. The total thrust is 345 1 100 kn. 14 articulated jack with travel of150mm. Shield assembler has 6 degrees of freedom and can move in all directions; Screw machine power 1 10kW, diameter 700mm, maximum torque 190kNm. The shield is also equipped with a segment feeder, which can hold three segments. The total power of shield machine is about 1000kW. Because the hinged part is added to the shield, the cutting of the support ring and the cutting of the support ring on the tail of the shield form a living body, which increases the sensitivity of the shield, makes it more convenient to control the tunnel axis in the construction process, and greatly improves the situation of segment outer arc breakage and segment water seepage.

Fourth, shield construction technology

1? Shield tunneling

(1) Clip Art of Portal Website

Before the shield goes out of the hole, the 800 mm thick underground continuous wall (its structural form is two rows of main reinforcement, transverse reinforcement and connecting reinforcement) should be chiseled to expose the reinforced soil outside, and then the construction will be formally promoted.

When digging a hole, first set up a steel scaffold in the hole circle; Put wooden strips in front of the cutter head to protect the cutter head from being broken when removing the concrete block; Drill five holes (evenly distributed) in the hole to observe the external soil. If the soil is in good condition, the concrete of the portal will be chiseled into pieces. First, the internal and external steel bars are chiseled out, and the internal steel bars are cut off, leaving the external steel bars. Drill 1 hanging holes in each concrete, clean up the concrete fragments falling at the bottom of the hole ring, then cut off the external steel bars one by one in the order of first down and then up, and hang out the concrete blocks.

In order to reduce the loss of positive soil, the excavation of portal should be carried out continuously and the operation time should be shortened as much as possible. The whole process is supervised by a full-time safety officer, and the sealing device on the hole is tracked and inspected by a special person, so as to remove the sundries and concrete fragments in the hole and protect the sealing device.

② Soil reinforcement

The soil in front of the tunnel is reinforced by Φ 800 @ 600 deep mixing pile, and between the deep mixing pile and the underground continuous wall is reinforced by Φ 600 high-pressure jet grouting pile. The plane size of reinforcement is 7.4m (width) ×25.4m (length), and the pile depth is 18. 197m, in which the upper 5.5m is a weak reinforcement area and the rest is a strong reinforcement area. After reinforcement, the soil strength Qu is more than or equal to 0.8 MPa.

2. Set the structural parameters of the hole.

(1) Balanced earth pressure setting

According to the geological conditions of the tunnel exit section, P=0. 182MPa is calculated by the water-soil cost-effective formula, and Pa≈0. 168MPa is calculated by the water-soil calculation method (Rankine earth pressure theory). Considering that the shield needs to pass through the reinforced soil at the exit stage, the initial equilibrium pressure is 0. 175MPa.

In practice, according to the feedback of ground deformation, the value of equilibrium pressure is changed to 0.20MPa (according to the formula of cost-benefit of water and soil, under the geological conditions of Tianjin, the value of transverse static equilibrium pressure coefficient k0 is about 0.9 ~ 1.0). Therefore, it can be used to calculate the positive equilibrium pressure in the future propulsion process.

3. Promote construction

(1) tunnel axis control

The shielding jack is divided into four areas: up, down, left and right. By adjusting the regional oil pressure, the resultant force of all jacks and the resultant force of resistance acting on the shield form 1 couple, which is beneficial to control the propulsion axis.

The position of tunnel axis is controlled by the horizontal and elevation deviation of shield. The deflection direction of shield should be adjusted according to the position of shield tail and ring segment, that is, the deflection of shield should be controlled according to the length difference between left and right jacks and upper and lower jacks.

The gap between the shield tail and the looped segment is theoretically 45 mm, but it is controlled within 50 mm in actual construction. Because the distance from the shield incision to the shield tail is generally about 5m, the position of the incision is the position where the shield tail will reach, so it is very important to control the shield posture for the loop axis of the segment. But the back of the shield is a ring-shaped section, so the position of the ring-shaped section directly affects the rectification of the shield. In addition, the poor posture of the shield will also cause the segment to be squeezed at the tail of the shield, resulting in damage and water seepage. Therefore, the control of shield posture and segment assembly are complementary.

② Control of ground deformation

(1) ground deformation caused by shield propulsion.

When the set equilibrium pressure P0 is less than the measured earth pressure P 1, that is, the equilibrium pressure is lower than the normal earth pressure, resulting in overbreak and ground subsidence; When P0 "p1,that is, the equilibrium pressure is higher than the normal earth pressure, resulting in under-excavation and ground uplift. Therefore, the rotating speed or advancing speed of the screw machine should be controlled to control the deformation of the ground soil in front of the shield.

② Ground deformation caused by synchronous grouting.

The sector block is assembled at the rear of the shield. The segment diameter is 6.2m, while the shield diameter is 6.39m.. There are 1 ring with a width of 95 mm, which is the building gap of shield construction. If this building gap is not filled, the surrounding soil will move to this gap, which will cause ground subsidence, so synchronous grouting must be used to fill the building gap in shield tunneling.

The theoretical building spacing of each propulsion ring is 1.87m3, and the grouting quantity of each ring is generally 150% ~ 250% of the building spacing. The pressure at the pumping outlet should be controlled according to different depths and soil quality, generally about 0.3MPa.

See Table 2 for cement slurry mixture ratio, and the consistency of cement slurry is 9 ~ 1 1 cm.

③ Ground monitoring

Ground monitoring is used to reflect ground deformation, and ground deformation information is one of the important conditions to guide construction. Shield propulsion parameters need to be formulated according to ground deformation information, so timely and accurate feedback is needed.

(3) segment assembly

The tunnel is assembled by six precast reinforced concrete segments, and the annular form is vertical insertion of small caps. The quality of segment assembly directly affects the final forming quality of tunnel, so the following points must be controlled during segment assembly:

(1) During segment assembly, the flatness of lining torus should be strictly controlled, the torus advancing amount should be determined according to the slope of tunnel axis, and the segment ellipticity should be controlled according to the actual measurement;

(2) Strictly control the circumferential and longitudinal compactness of the segment after looping;

(3) Before the segment waterproof treatment, the segment must be torus and end face cleaned, and then waterproof rubber strip paste;

(4) During the assembling process, it is necessary to remove the garbage and sundries at the assembling site at the tail of the shield, and at the same time, it is necessary to pay attention to the correctness of segment positioning, especially the positioning of the first segment will affect the overall quality after it is looped and its relative position with the shield;

⑤ According to the measurement report of the whole ring and the gap between the segment and the shield shell, fully adjust the segment assembly posture in time by using the hinge device;

⑥ After assembling each segment, extend the jack and control it to the required jacking force, and then assemble the next segment, thus completing the assembly of a ring;

⑦ After each segment is assembled, adjust the ellipticity of the ring in time to meet the requirements, and then adjust the jacking force of the jack to prevent sudden change of shield posture;

⑧ Strictly control the flatness of torus, control the steps of adjacent segments, and prevent segments from breaking at the joint of adjacent segments;

Pet-name ruby torus propulsion is controlled, and the perpendicularity between segment torus and tunnel design axis is often detected. When segment propulsion exceeds the control amount, wedge should be used to correct it to ensure that segment torus is perpendicular to tunnel design axis;

Attending control adjacent ring height difference, not beyond the allowable range; Control the rotation of segment, and correct the rotation direction and amount of segment in time.

The annular segments are connected by longitudinal and circumferential bolts, and the tightness of the connection will directly affect the overall performance and quality of the tunnel. Therefore, after each annular segment is assembled, tighten the longitudinal and circumferential bolts connecting the segments in time; When advancing the next ring, the longitudinal bolts should be tightened under the action of jack jacking force; After pushing the ring segment out of the frame, the longitudinal and circumferential bolts must be tightened again.

Verb (abbreviation of verb) construction summary

1. The central elevation of the tunnel between Xiaobailou and Xiawafang of Tianjin Metro 1 line is basically in the silty clay layer of -9 ~ -9~- 13m, which is suitable for shield tunneling. However, this section is the first marine layer and the second continental layer, and the soil layers interact with each other, and the upper and lower soil layers change greatly, and the local soil is sandy. Therefore, the shield is driving.

2. According to the measured equilibrium pressure during shield tunneling, the static equilibrium pressure coefficient of the earth side is 0.9 ~ 1.0 by feedback calculation, and the equilibrium pressure calculated by this value is close to the actual earth pressure, which is convenient for controlling the ground deformation.

3. When the shield is advancing at this elevation section, the thrust is basically 10000 ~ 12000 kn, and the advancing speed is about 4cm/min.

4. Through construction control and auxiliary measures, most ground deformation can be controlled within the range of 5 ~-10 mm. ..

The construction methods and technical measures adopted in Xiaobailou-Xiawafang Tunnel of Tianjin Metro 1 Line can provide reference for other tunnels in Tianjin Metro (using shield method).

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