2016 3rd International Conference on Engineering Technology and Application (ICETA 2016) ISBN: 978-1-60595-383-0

1 INTRODUCTION

With the continuous development of city construction and the expansion of city scale, urban traffic problem gradually become main factors that hinder the urban development. However, urban rail transit is one of the main ways to ease the pressure of urban traffic [1]. The main body structure of urban rail transit in the operation period of nearly a hundred years would inevitably encounter some of the role of natural disas-ters. With the large-scale development and utilization of urban underground space, the deformation of soil can be very large when a strong earthquake happened in the big city, which leads to serious damage to some weak links in the underground structure and serious impact on the overall safety of the underground struc-ture. Meanwhile, due to the wide range of subway, the site conditions are complex and varied, which mainly include the differences of soil, sand liquefaction, soft soil seismic subsidence, subsidence, structural cracks and shore slip. These factors affect the seismic action of underground structures directly in earthquake, and

they have important influence on underground struc-ture [2-4].

Generally, the underground structure is bound by the surrounding soil, and has good anti-seismic per-formance. But the phenomenon of multiple seismic disasters was indicated that the existing underground structure was not safe enough, and sometimes even be in serious danger [5,6]. For example, in the 8.1 mag-nitude earthquake in Mexico in 1985, the phenomenon of separation and destruction of the lateral wall and the surface of the earth’s surface which built on the soft foundation was occurred [7]. In 1995, the 7.2 magnitude earthquake in Japan caused the most seri-ous damage to Kobe city underground structures in history. Subway, underground parking garage, under-ground tunnels, underground commercial streets and a lot of underground structures were damaged seriously [8]. Especially in the subway station and the subway tunnel, there was a total of 5 subway stations and about 3 km of the subway tunnel, which was the most serious damage to the subway station [6]. In 1999, Taiwan earthquake with a magnitude of 7.3 also caused a certain influence on the underground struc-ture, which the fracture of tunnel lining was the most

Anti-seismic Analysis and Study for the Joint Structure Between Running Tunnel and Tunnel and Subway Station

Guizhou Tian* School of Civil and Transportation Engineering, Hebei University of Technology, Tianjin, China Tianjin Real Estate Group Co., Ltd, Tianjin, China

Chuan Zhao Tianjin Real Estate Group Co., Ltd, Tianjin, China

ABSTRACT: Based on a subway section in Tianjin city, the MADIS finite element software was used to nu-merical simulation analyze the subway station joint section. The research results show that the stress of segment joints of shield segment wells are significantly higher than the standard section of the stress; the bending moment and sheer force of the shield shaft end wall in the floor and the negative floor location are large, so measures should be taken to strengthen the structure of this point; axial force of the maximum and minimum values are in the open mouth of the shield, and they all meet the requirements of structural stress. The seismic structural measures during design and construction for Tianjin area are summarized, and the research results can provide reference for the subway station structure and tunnel seismic design.

Keywords: anti-seismic analysis; numerical simulation; running tunnel; shield construction; subway

*Corresponding author: 2296014849@qq.com

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and followed by hole slope collapsing slide; the posi-tion of the Chelungpu fault on the west side of the footwall and other areas, to the Sanyi No. 1 railway tunnel in the damaged tunnels was the most serious, resulting in orbit distortion, lining crack and drop off phenomenon, and leading to the disruption of moun-tain line railway for 17 days [9]. These are greatly enhanced people’s emphasis on underground structure seismic design [10-14].

These are greatly enhanced with the rapid develop-ment of the economy of Tianjin, and especially several Tianjin Metro lines are being built at the same time, which has led to the development of the new round of Tianjin city. The anti-seismic stability of underground structures has important effect on the normal use and safety of underground structures, safety of surface structures, as well as the city flood control and other geological disasters. Therefore, it is urgent to carry out the anti-seismic design of the subway station and tun-nel structure in Tianjin area.

2 ENGINEERING SITUATION

Taking a section of Tianjin Metro as the research background, the full length is 630.9 m of the right line, and the full length is 632.8 m of the left line. Interval minimum radius of curve is 400, the maximum longi-tudinal slope is 30%, the shield method is carried out, segment diameter is 6.2m, thickness of segment wall is 0.35m, ring width is 1.2m and interval thickness of overlying soil for 21.0~29.0m. The soil layer of the interval shield tunnel is mainly composed of silty clay and silt, and the shield is buried deeply in the 23.3m. Even the wall is T-shaped and is connected to the wall. The ground is not reinforced and the lifting conditions of the shield machine are not available.

The ground is not reinforced according to the na-tional standard “Chinese motion parameter zoning map” (GB18306-2001), this field peak ground accel-eration is 0.15g (basic intensity is VII degree), the corresponding ground acceleration is 1.287 to 1.491m/sec2. According to the “code for anti-seismic design of buildings”, this site is not beneficial for the anti-seismic. The type of surface groundwater of this field is quaternary pore phreatic water. The under-ground water in the silty sand and silty soil hosted in the second continental layer has a little pressure, which is the micro confined water. Embedded deep within the scope of 5 m, the temperature of ground-water changing with the temperature, the temperature of 5 m below, along with the depth increasing slightly, general is 14~16°C.

3 COMPUTATIONAL MODEL

MADIS finite element software was used to establish 3D model, 280m was selected as seismic wavelength

along the direction of the line. Took the stress form of the station end segment into consideration, station structure was added into the model, interval computa-tional model was established according to the half wavelength (140m) along the direction of the line, and 20m was selected in the station computational model along the direction of the line. Frame structure model was adopted for the top, middle, bottom and the side wall of the station, while displacement response method of the beam-spring model for shield tunnel segment was used. End constraint by using angle of slide bearing, segment by plate elements, segment indirect head with an axial spring, rotation spring and shear spring model method.

In the whole calculation model, the shield segment in horizontal and vertical directions are under spring boundary condition. In the longitudinal direction, the sliding angle constraint of the support was adopted for the free end. Spring boundary condition was used for the end wall and the side wall in well shield model. In the longitudinal direction, the sliding angle constraint of the support was adopted for the free end, and verti-cal displacement constraint conditions were used in the roof around. The finite element model was shown in Figure 1.

Figure 1. 3D finite element model.

4 RESULTS AND DISCUSSION

In order to reflect the force situation of standard sec-tion and interval end segment, the comparison of the standard section (select point was 50m from the sta-tion) and interval end segment (select point was 1m from the station) was made. The results are as follows: (1) The internal force of segment connected with the

shield well, the result was shown in Figure 2. The calculation results show that the maximum posi-tive moment of standard segment stress was 163.5kN.m in segment 123.75 degrees site (blue), the maximum negative moment was -246.2kN.m, in the segment 191.25 degrees site (red), and the maximum sheer force of the segment stress was 177.9kN in the segment of 180 degrees site (red) and the maximum axial force of the stress segment was 3710.7kN in the 90 degrees site (red), the maximum deformation was 6.507mm. After accounting for the reinforcement of the segment, the segment stress can meet the require-ments of stress under seismic conditions.

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(2) The internal force of standard segment, the result was shown in Figure 3.

The calculation results show that the maximum positive moment of segment stress on the shield well connection was 109.3kN.m in segment -45 degrees site (blue), the maximum negative moment was

122.3kN.m in segment 90 degrees position (red), the maximum shear force was 264.1kN in the segment -56.25 degrees site (red), the maximum axial force of segment stress was 5535.8kN at the 90 degrees posi-tion (red), the maximum deformation was 1.966mm. After accounting for the reinforcement of the segment,

(1) Segment bending moment diagram (2) Segment shear diagram

(3) Segment axial force diagram (4) Segment deformation diagram

Figure 2. The internal force diagram of duct piece connected with joint of the shield well.

(1) Segment bending moment diagram (2) Segment shear diagram

(3) Segment axial force diagram (4) Segment deformation diagram

Figure 3. The internal force diagram of standard duct piece.

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the segment stress can meet the requirements of stress under seismic conditions.

Compared with the stress of connection segment shield shaft and the standard segment, the stress is higher than the standard section of the structure. (3) The internal force of shield shaft at the connect-

ing point, the results were shown in Figure 4 to Figure 6.

Figure 4. The bending moment diagram of shield tunnel.

The negative bending moment of shield well end wall at the position of bottom plate and the negative two-plate were larger, the value was 1833 kN.m~ 2030 kN.m, and the structure has been strengthened in this position. The maximum bending moment of the positive moment occurred in the center of the negative three layers, and the maximum value was 1302.4kN.m, which satisfied the structural require-ments. A larger unit force was at the right end of the opening hole on the left side of the shield, the value was 1805.2kN.m, the others were in the range of 21.17 ~ 811.7kN.m, except for the largest unit, all meet the structure requirement. A larger unit force was at the left end of the opening hole on the right side of the shield. The value was 1518.8kN.m, the rest was rang-ing from 339.1kN.m to 882kN.m, except for the larg-est unit, and they meet the structure requirement.

Figure 5. The shear force diagram of shield tunnel.

The negative sheer force of shield well end wall at the position of bottom plate and the negative two-plate were larger, the shear force was 1540.9kN.m~2016 kN.m, and the structure has been strengthened in this position. The sheer force of the rest was smaller which can meet the structural requirements. The shear force on the left side of the shield openings was in the range of -1246.8 ~ 1258.8kN, and all units were able to meet the requirements of structure. The shear force on the right side of the shield hole was ranging from 1265.6kN to 920.2kN, and all units were able to meet the requirements of structure.

Figure 6. The axial force diagram of shield tunnel.

The maximum and minimum axial force value of the shield shaft end wall appeared at the mouth of the shield openings. The axial force on the left side of the shield hole was 16.41 ~ 5101.1kN, and it meets the requirements of structure. The axial force on the right side of the shield hole was 238.1 ~ 3824.6kN, it meet the structure requirement. So the shield tunnel has a good anti-seismic performance in this area.

5 TIME-HISTORY ANALYSIS OF INTERVAL AND THE STATION END

5.1 Calculation model

The finite difference software FLAC 3D was used in the calculation and the three-dimensional model was used in the analysis of the Jiefang bridge station and the section of the bridge. According to the finite ele-ment calculation principle and computing power, and considering the effects of boundary conditions, the scale of calculation model was confirmed rationally. In the model, the length was 127.6m (direction of vertical line), the width was 40m (along the direction of the line), and the high was 81.2m. The grid and body structure of the model are shown in Figure 7, and Figure 8.

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Figure 7. The grid of model.

Figure 8. The body structure of the model.

5.2 Unit constitutive and parameters

Solid element was adopted to simulate the soil, the Moore - coulomb model was used in the constitutive model; linear elastic constitutive was used to simulate the concrete materials; the shell element simulation was used in lining process; the linear elastic constitu-tive model was used in the constitutive model; the structural parameters were shown in Table 1.

Table 1. Structure parameter.

Name of structure

Elasticity modulus E (MPa)

Poisson ratio μ

Unit weight γ (KN/m3)

Station struc-ture

30000 0.2 25

Shield seg-ment

34500×0.75* 0.2 26

Note: * 0.75 was the stiffness reduction factor of the shield segment  under  the  influence  of  the  girth  and  longitudinal seam.

5.3 Boundary conditions and seismic waves

When the calculation was in static, the boundary con-dition was static, In front and back, the left and right and the bottom surface are respectively bound to the vertical displacement of the surface, and the upper surface is free; when the calculation was in dynamic, the bottom surface using a viscous boundary, all around using the free-field boundary, and Rayleigh damping was used for damping. The peak acceleration

of seismic wave was 0.1485g, and the filtering and baseline correction were carried out. The acceleration time history curve is shown in Figure 9 along the X direction.

Figure 9. The acceleration time-history curve.

5.4 Calculation results of internal force

Figure 10. Segment bending moment diagram (Nm).

Figure 11. Interval displacement diagram.

The results shown in the above figures indicate that with the interval away from the station structure, in-terval internal force decreases, and the contrary trend of the displacement. It shows that the structure of the station has a displacement constraint on the interval, the greater the stiffness, the greater the internal force generated by the earthquake. At the end of the inter-val, the interval stiffness is small, which can be de-formed by strata. Therefore, the internal forces are small. The deformation joints should be set at the junction of the interval tunnel and the station structure.

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6 ANTI-SEISMIC MEASURES OF TIANJIN METRO AREA STRUCTURE

(1) The selection of interval bit line and both ends of station in initial design should avoid seismic and dangerous areas; the position of interval tunnel and station structure joints, interval contact on both sides of the channel and soil properties dra-matically change, should be set deformation joint.

(2) In order to increase the vertical stiffness of the section, the section uses the staggered joint as-sembly, the structure of staggered joint assembly performances a better longitudinal structural ri-gidity compared with through seam assembly, and the structure of through seam assembly re-flects better flexible features.

(3) For shield tunnel in soft soil layer, an appropriate increase in the grouting material layer parameters and grouting layer thickness, increase the cohe-sive force between soil and the segment, and re-duce the relative sliding between the lining and soil.

(4) Setting elastic gasket, rubber sealing to ease the stress concentration of segment and joint and im-prove the anti-seismic performance of shield tunnel.

(5) Foundation reinforcement treatment is adopted for the station head position with large force of the shield tunnel and improves their elastic mod-ulus, which can greatly reduce the effect of the surrounding soil layer on the structure and the joint force, and has significant effect of vibration reduction.

(6) In order to meet the conventional load, connect-ing bolts between shield segments should adopt the small stiffness; in order to reduce the disloca-tion between segments, concave convex mortise end segment should be set.

7 CONCLUSIONS

(1) Numerical simulation analysis was used to study the interval of the standard segment, shield well connected segment and shield shaft end wall. The analysis results show that, the interval shield tunnel has better anti-seismic performance.

(2) Marking comparison of the segment stress be-tween shield well connection and standard inter-val, the results indicate that the stress of segment joints of shield segment wells are significantly higher than the standard section of the stress.

(3) The negative bending moment and sheer force of shield well end wall at the position of bottom plate and the negative two plate are larger, which shall be to take structural measures to strengthen; the maximum and the minimum value of the axi-al force appeared at the mouth of the shield openings, they all meet the structural require-ments.

(4) Taking Tianjin Metro as an example, the an-ti-seismic structural measures during the design and construction of metro are summarized.

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