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Field measurement analysis of the influence of double shield tunnel construction on reinforced bridge
Tunnelling and Underground Space Technology 81 (2018) 252–264
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Field measurement analysis of the influence of double shield tunnel construction on reinforced bridge
T
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Wang Zhea, Zhang Kai-weia,e, Wei Gangb, , Li Binc, Li Qiangd, Yao Wang-jinga a
Institute of Geotechnical Engineering, Zhejiang University of Technology, Hangzhou 310014, China Department of Civil Engineering, Zhejiang University City College, Hangzhou 310015, China c East China Survey and Design Co., Ltd, Hangzhou 430000, China d China Railway 19th Bureau Group Co., Ltd, Beijing 100176, China e Greentown Real Estate Construction & Management Group Co., Ltd, Hangzhou 43000, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Double shield tunnel Bridge pile foundation underpinning Foundation reinforcement Field measurement
Constructing subway systems by shield tunneling in urban area may require tunnels to cross through pile foundations of buildings and bridges, which will definitely affect existing structures. Therefore, it is of great importance to study the construction schemes and influence of shield tunneling on reinforcing and rebuilding bridges. Investigating the case of the double-line shield tunnel of Hangzhou Metro Line 2 crossing through Fengqi Bridge, this paper discusses the project of reinforcing Fengqi Bridge and analyses monitoring data before and after the shield body crosses the bridge. Modification of Fengqi Bridge involves expansion and reinforcement of the raft foundation and improvement of composite ground. Our research findings indicate that these enhancements can effectively decrease bridge settlement during tunneling and improve mechanical conditions of bridge structures. Meanwhile, shield tunnel construction cuts pile and causes pile foundation displacement, leading to settlements behind bridge abutment, deck surface, and pipelines. Settlement of pipelines even exceeds the allowable levels. In addition, due to differences in settling mechanism between pile foundation and soil, differential settlement occurs in both sides of the bridge head and consequently bridge bump arises.
1. Introduction Construction of intercity rail transit networks, such as subway systems, is flourishing around the world and has gradually become focus of urban infrastructure development. However, with no forethought to include metro lines in early city planning, a common challenge encountered is the crossing of new underground tunnels through pile foundation of existing structures like bridges. Crossing of this kind not only increases difficulty in tunnel construction, but may also endanger existing bridges in the ways of deformation of pile formation, settlement and cracking of bridge deck surface, or bridge collapse. Therefore, it is of great significance to study this burdensome situation in engineering practices. There are many investigations in the effect of tunnel construction on surrounding bridges around the world (Afifipour et al., 2011; Basile, 2014; Chen et al., 2011; Dias and Adam Bezuijen, 2015; Fang and He, 2008; Hong et al., 2015a; Hong et al., 2015b; Jongpradist et al., 2013; Li and Wei, 2015; Li et al., 2014; Liu et al., 2014; Liu and Zhang, 2014; Marshall and Haji, 2015; Ni, 2014; Park et al., 2015; Shen and Liu,
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2015; Soomro et al., 2015; Wei et al., 2013; Xiang et al., 2008; Xiao-jie et al., 2009; Xu et al., 2015; Yoo, 2013; Zhang and Chen, 2011; Zheng et al., 2015). Research approaches often employed are empirical equations, theoretical analysis, numerical analysis, model testing, and field observation. Li and Wei (2015) studied the settlement and deformation of piles and surrounding ground at different stages of the shield tunneling process of the new Changping Line (Beijing Metro). They collected and analyzed field monitoring results of measured bridge subsidence, soil pressure, and grouting quantity, and also settlement data of piles and ground. Some researchers carried out numerical analysis of tunnel–pile interaction (Dias and Adam Bezuijen, 2015; Fang and He, 2008; Hong et al., 2015b; Jongpradist et al., 2013; Li et al., 2014; Liu et al., 2014; Liu and Zhang, 2014; Marshall and Haji, 2015; Ni, 2014; Soomro et al., 2015; Xiao-jie et al., 2009; Xu et al., 2015; Yoo, 2013; Zhang and Chen, 2011; Zheng et al., 2015). Using theoretical analysis, Wei et al. (2013) found that erection of a double-O-tube (DOT) tunnel would result in additional load to the
Corresponding author. E-mail address: [email protected] (G. Wei).
https://doi.org/10.1016/j.tust.2018.06.018 Received 30 June 2017; Received in revised form 22 February 2018; Accepted 26 June 2018 0886-7798/ © 2018 Elsevier Ltd. All rights reserved.
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ground improvement, effects of shield tunneling on bridges merit further study. Our study centers on the case of shield tunneling of Hangzhou Metro Line 2 from Jianguo North Road Station to Zhonghe North Road Station, crossing through the northern side of Fengqi Bridge. With discussion of scheme of Fengqi Bridge modification, this paper focuses on analyzing field date to explore influence on bridge foundation piles by the shield tunneling process after pile underpinning and foundation/ ground reinforcement of that long-span bridge. Our analysis of actual measurements of bridge distortions during shield tunnel construction can indeed compensate many deficiencies of unilateral numerical simulation.
surrounding pile foundation. According to the plan of Shanghai Metro Line 10, interval tunnel from Liyang Road station to Quyang Road station has to cross through the group pile foundation of Shajinggang Bridge on Siping Road. Xu et al. (2015) conducted a series of theoretical analysis and numerical simulation on the entire construction process to explore the load transfer mechanism of bridge structure. Calculation results indicate that both bridge static and traffic live loads can be successfully transferred from pile foundation to raft after pile underpinning, and removal of obstructed piles during tunneling has very limited influence on bridge structure. Previous studies rarely focus on the technology for foundation reinforcement and pile underpinning of long-span bridges. There is also a lack of field monitoring data on actual deformation in bridges. Furthermore, with diversities in technologies for pile underpinning and
Fig. 1. Vrious views of tunnel crossing bridge foundation (unit: cm). 253
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Fig. 1. (continued) Table 1 Physico-mechanical parameters of soil layers. Layers number
Soil name
Water content (%)
Unit weight (kN/m3)
Compressive modulus (MPa)
Cohesion (kPa)
Friction angle (°)
②2 ③3 ③6 ③7 ④2 ④3 ⑥1 ⑦1 ⑦3 ⑧1 ⑨1 ⑩1 (12)1
Sandy silt Silt with sand silt Silt with sand silt Sandy silt Silty silty clay Clayey silt Silty silty clay Silty clay Silty clay Silty clay Silty clay Silty clay Fine sand
27.8 25.6 26.2 26.1 31.8 30.9 39.0 29.5 33.3 36.6 23.2 30.8 23.6
18.9 19.1 19.1 19.4 18.4 18.2 17.7 18.9 18.4 18.0 19.7 18.8 19.1
7.5 10.0 11.0 7.0 2.8 4.0 2.5 5.8 4.5 4.5 6.5 4.8 10.0
4.0 3.0 1.0 6.0 13.0 6.0 14.0 31.0 23.0 18.0 40.0 35.0 0.0
25.5 29.0 30.0 18.0 10.0 18.0 10.5 16.0 12.0 11.9 17.5 15.0 31.0
Fig. 2. The reinforcement plan view of A-A elevation 1:150 (unit: cm).
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Fig. 3. The reinforcement plan view of B-B elevation (unit: cm).
Fig. 4. Details of high pressure jet grouting pile (unit: cm).
2. Project overview
because of the location, complex surrounding environment, and large traffic flow. As a result, modifying and reinforcing the original bridge, with bridge deck widened to 36.4 m, emerges as the best choice to meet the requirements for shield tunneling. Shield construction across Fengqi Bridge requires covering the surface with soil of 6.1 m thick and grinding 4 rows of piles. Two rows are Φ100 cm bore-hole cast-in-situ piles, with the foundation concrete labeled C25 and Φ22 main reinforcements. The other two rows are Φ30 cm reinforced concrete piles, arranged in quincuncial shape, as shown in Fig. 1. There is a visible communication pipeline bridge, with a pipeline truss of 60 cm × 40 cm, on the north side of the bridge. In addition, a cast-iron water pipe of Φ50 cm is set up in the cantilever of the north side of the bridge, while a pipeline of 60 cm × 60 cm for electric power supply is located under the sidewalk on the south side.
2.1. Original Fengqi bridge With a total length of 43.3 km, Hangzhou Metro Line 2 is completely constructed underground with 33 stations connecting 6 districts, namely Yuhang, Gongshu, Xihu, Xiacheng, Jianggan and Xiaoshan. Its southern section is prearranged for the Linpu rail, while the northern portion is reserved for the Anji intercity rail. Based on the Metro Line 2 route plan, the subway tunnel between North Jianguo Road Station and North Zhonghe Road Station will cross through the Fengqi Bridge pile on Fengqi Road. Fengqi Bridge is 100 m away from the west side of the intersection of North Jianguo Road and Fengqi Road, and it is at a distance of 60 m from the well head at the western part of North Jianguo Road Station. The bridge is a single-span simply supported beam structure with two abutments, over a river of 20.54–23.62 m wide. Superstructure of the bridge consists of 20 m post-tensioned prestressing concrete hollow slab, and the beam is 95 cm high. Meanwhile, the substructure is light abutment with Φ100 cm bore-hole cast-in-situ pile foundation. Great difficulty in rebuilding Fengqi bridge exist
2.2. Engineering geological conditions The thickness of Quaternary stratum in the project area is about 50 m, and the surface layer at the site is miscellaneous backfilling ranging from 2.8 to 5.7 m in thickness. There are silt and sand layer of 255
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Fig. 5. Fengqi bridge site photo.
Observation of ground settlement is set up near the bridgehead, 1 m away from the closest bridge measuring point. Monitoring of abutment settlement and horizontal displacement are shown in Fig. 6(b). QC1 to QC8 are the measuring points of abutment settlement, while QS1 to QS8 are for tracking horizontal displacement of retaining wall. These observation points are laid out on both sides of the bridge abutment with an interval of 18 m, and the space among the points on each side is 8, 8, and 7 m, respectively. After the “U” structure is added and connected with the abutment, monitoring of abutment settlement and displacement is moved to the “U” structure. Lastly, Fig. 6(c) demonstrates configuration of measuring points for dike and pipeline settlement. QD1 to QD8 are the dike measuring points, installed on the north and south sides of the bridge. QD8 was faulty, and so no data were recorded during monitoring. QGX1 to QGX3 and QGXT1 to QGXT 3 track communication pipelines, while QGXJ1 to QGXJ3 surveil water pipelines. Pipelines are set up on both north and south sides of the bridge.
about 8.0–15.1 m thick in the alluvium in the subordinate Qiantang River. Most of the soil layers in the interval range are silt with sand, silt, and sandy silt, while some of which are silty clay, silty clay with silt, and silty clay, as shown in Table 1. 2.3. Scheme of Fengqi bridge modification 2.3.1. Design of bridge modification Since the interval shield tunneling crosses through the north side of Fengqi Bridge, alteration of the bridge involves moving bridge support in the superstructure 0.5 m toward the river channel so as to reduce the span of the existing bridge. A “U” structure is added to the lower part of the bridge as the expanding foundation, which is also connected with the original bridge abutment by planting bars, as presented in Figs. 2–4. Fig. 5 is a field photo of Fengqi Bridge. High-pressure rotary jet grouting piles with diameter of 800 mm and 15.5 m in length are used in underpinning. In area requiring strong reinforcement, jet grouting piles are arranged at the four corners of a square, with center spacing of 120 mm. On the other hand, piles in weak reinforcement area are configured in two ways, as 120 mm × 120 mm or 160 mm × 160 mm equilateral triangles. Layout of piles is presented in Fig. 4. Strong reinforcement is mainly arranged on both sides of the abutment, while other area only primarily involves weak reinforcement.
3. Results of field measurements and discussion 3.1. Analysis of deck subsidence Settlement data of bridge deck surface during construction of upline shield tunnel is presented in Fig. 7. Fig. 7(a) shows the relationship between bridge deck settlement and progress of the tunneling process with measurements from all deck observation points included, whereas Fig. 7(b), (c), and (d) shows, respectively, data from each of the three cross-sections of the deck settlement monitoring points. Fig. 7(e) demonstrates final settlement recorded at measuring points of the three cross-sections of bridge deck in relation to spatial arrangement of these points, as Fig. 7(f) displays the final spatial variation of the bridge surface. Similarly, Fig. 8 illustrates the relationship between bridge deck settlement and advancing rate of down-line tunneling. Here, a positive value of settlement signifies that the bridge surface is heaved, while a negative value denotes subsidence. Results presented in Figs. 7 and 8 indicate that measured settlement varies from −5.18 to 3.14 mm with crossing of the up-line tunnel, while the range of subsidence at deck surface is from −4.50 to 1.00 mm for the down-line tunneling process. Our field data also show that the bridge started to slant after construction of up-line tunnel, and the largest differential settlement reaches 6.74 mm. Differential subsidence grows with increasing distance of the measuring points from the tunnel, while bridge surface nearest to the tunnel has an uplift. Although the settlement variation during down-line construction is smaller than that
2.4. Measuring-point layout of Fengqi bridge With the purpose of investigating effects of shield tunneling on the bridge, we set up and conducted a series of monitoring, which mainly concern settlement of bridge deck surface, subsidence behind abutment, horizontal displacement of abutment, embankment subsidence, and bridgehead and pipeline settlement. According to Code for Monitoring Measurement of Urban Rail Transit Engineering GB50911-2013 (Chinese national standard), the allowable value of bridge deck surface and abutment subsidence is ± 2 mm/d and the cumulative value is ± 15 mm. Axis settlement must be no more than 3 mm/d, with the accumulated one less than 20 mm and allowable upheaval value of 7 mm. Maximum cumulative subsidence of pipeline is 30 mm, while the allowable settling rate is less than 2 mm/d with pressure, and 3 mm/d without pressure. Fig. 6(a) presents the layout of monitoring points for bridge and ground settlement. QCJ1 to QCJ12 are the measuring points of bridge settlement, arranged in three rows. Each row is 10 m from the other, while the distance between two points at each row is also 10 m. 256
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present measured results from all monitoring points tracking abutment settlement. Collected data on abutment subsidence from the first and second cross-section monitoring points are illustrated in Fig. 9(b) and (c), respectively, while Fig. 9(d) exhibits spatial variation of both crosssections of abutment. Likewise, relationship between abutment settlement and advancing down-line tunneling process is displayed in Fig. 10. According to Figs. 9 and 10, variation of observed abutment settlement ranges from −4.00 to 4.31 mm during up-line construction; when the range for down-line tunneling is from −1.68 to 2.93 mm. Settlement gradually emerges for abutment at most of the measuring points during up-line tunnel construction. On the other hand, nearly all measuring points record a heave at the beginning and then a subsidence in down-line tunneling. That is, in the case of down-line construction, the abutment is upheaved during the stage of shield crossing, and it then settles slightly, and eventually stabilizes after the passing of the shield body. Fluctuation in abutment settlement is more substantial in the tunneling process of up-line than down-line. As a whole, measuring points in up-line settle, while there is uplift at down-line observation points. The tunneling process affects abutment settlement in up-line and down-line differently. 3.3. Analysis of riverbank settlement monitoring results Fig. 11(a) and (b) depicts change in riverbank subsidence at various stages of tunneling of the up-line and down-line, respectively. Measured settlement at the riverbank ranges from −4.22 to 1.56 mm for up-line tunnel construction, while the variation is from −1.18 to 2.36 mm for down-line tunneling. Similar to variations in abutment settlement, all up-line observation points on the riverbank subside steadily, when most down-line measuring points show an initial upheave, followed by a settlement. Compared to the down-line process, our obtained data reveal a more sizable variation in riverbank settlement for the up-line tunneling. Overall, riverbank is noted to settle after crossing of the shield body in the up-line tunnel, while a heave is observed for most of the down-line measuring points. 3.4. Analysis of measured pipeline settlement Fig. 12 illustrates pipeline settlement during construction of shield tunnels. Subsidence data of all three pipelines at various stages of the tunneling process is presented in Fig. 9(a). Measurements form observations points at both bridge communication lines (QGX and QGXT) and water supply pipeline (QGXJ) are shown in Fig. 12(b)–(d) separately. Settlement of communication pipeline QGX varies from −2.77 to 1.6 mm during tunneling, while variation ranges from −7.92 to 0.68 mm and −7.17 to 0.92 mm for QGXT and QGXJ, respectively. Monitoring points QGX1 to QGX3 for tracking subsidence of communication line QGX are located right above the tunnel, and steady settlement is recorded during the stage of shield crossing. On the other hand, communication line QGXT exhibits more rapid subsiding, with QGXT1 settles at the fastest rate of 6.44 mm/d and QGXT2 at 5.18 mm/ d, both exceeding the allowable rate. Even after grouting, both sides of the pipeline still show vast differential settlement of 5.31 mm, and the pipeline eventually slants vertically. All measuring points of water pipeline QGXJ1 to QGXJ3 indicate subsidence during shield crossing. Among these three, QGXJ1 settles at the fastest rate of 3.44 mm/d, surpassing the allowable value. During the grouting phase of tunneling, data from measuring points QGXJ2 and QGXJ3 signify an upheave, while QGXJ1 shows more settlement. There is a large settlement difference of 6.18 mm at both sides of the water pipeline, and it also ultimately slants vertically. Both communication pipelines and water pipeline are independent structures from the bridge and receive no reinforcements before tunnel construction. Therefore, vast vertical displacements of these pipelines occur during the tunneling process, even with some measurements exceeding allowable values. In view of
Fig. 6. Monitoring point layout (unit: cm).
in up-line, the variation rate of subsidence is greater than that in up-line at some monitoring points. QCJ16 and QCJ7 are both in the middle of the bridge deck and on the side of the down-line. In comparison to other measuring points, they show greater settlement during stage 2 of shield tunneling. However, after grouting at the shield tail, settlement at QCJ16 and QCJ7 greatly declines, and is then comparable to other measuring points. Subsidence variations at three stages of shield tunneling process exhibit obvious trends. However, these trends are vastly different for up-line and down-line construction. 3.2. Analysis of abutment settlement Relationship between abutment settlement and progressing rate of up-line shield tunnel construction is shown in Fig. 9. In Fig. 9(a), we 257
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Fig. 7. Deck measuring results during up-line shield tunneling.
our findings, in addition to reinforcing the bridge, independent pipelines should also be strengthened correspondingly to ensure the safety of shield tunneling (see Fig. 13).
Fig. 14(c) and (d) shows results from cross-sections 1 and 2, respectively, throughout the course of down-line construction around Fengqi Bridge. A positive horizontal displacement here signals movement of the abutment toward the river, as moving toward the ground is represented by a negative value (see Fig. 15). Horizontal abutment displacement associated with up-line and down-line tunneling is limited within 2 and 1 mm, respectively. Based on observed variations in horizontal as well as vertical abutment displacements, both east and west sides of the “U” structure tilt down toward the shield during up-line tunneling. By contrast, the two sides of
3.5. Analysis of abutment horizontal displacement Fig. 14 summarizes lateral abutment movement at various phases of shield tunneling. Observed horizontal displacement of the abutment from measuring points at cross-sections 1 and 2 during up-line tunneling are presented in Fig. 14(a) and (b), respectively. Likewise, 258
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Fig. 8. Deck measuring results during down-line shield tunneling.
the “U” structure both slant up in the direction of theabutment while down-line tunnel construction is underway. In short, up-line shield tunneling has a greater impact on horizontal abutment displacement.
Fig. 10. Abutment measuring results during down-line shield tunneling.
Subsidence data from surface monitoring point SD43 and bridge monitoring point QCJ1 during the up-line construction is shown in Fig. 16(a), where Fig. 16(b) reports settlement results of surface monitoring point SD69 and bridge monitoring point QCJ9. Correspondingly, Fig. 16(c) displays measured settlement from surface monitoring point XD43 and bridge monitoring point QCJ3 during down-line tunnel
3.6. Analysis of differential settlement at the bridgehead area Monitoring results regarding ground and bridgehead settlement in relations to advancement of tunneling process are presented in Fig. 16.
Fig. 9. Abutment measuring results during up-line shield tunneling. 259
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Fig. 11. River bank settlement measuring results during shield tunneling.
Fig. 12. Pipeline settlement measuring results during shield tunneling.
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Fig. 13. Pipeline behind The Bridge.
Fig. 14. View of abutment horizontal displacement measuring results during shield tunneling.
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Fig. 15. Deformation of original abutment and the added “U” structure.
Fig. 16. View Analysis of settlement difference of bridgehead in shield tunneling process.
emerges rapidly at measuring point SD43, and the largest one-day settlement surpasses the allowable value and reaches 3.66 mm. The accumulative subsidence of SD43 is 15.04 mm, while the bridgehead measuring point QCJ1 only settles by 0.04 mm cumulatively. Thus, there is an ultimate settlement difference of 15 mm, as shown in
construction, while subsidence data from surface monitoring point XD69 and bridge monitoring point QCJ11 are exhibited in Fig. 16(d). Even measuring points SD43 and QCJ1 are only 1 m apart and on the same vertical cross-section, they recorded vastly different settlement results. When shield cutter approaches the bridgehead, settlement
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bridge in up-line construction, but only 5 days for down-line tunneling. A longer construction time is more likely to cause bigger soil loss, and thus results in larger settlement of bridge structures and greater differential subsidence at the bridgehead. Second, average thrust of the shield crossing the bridge for up-line and down-line tunnels is 12,210 and 12,670 kN, respectively. Higher average speed of shield advancement and bigger average grout injection volume in down-line tunnel construction may also lead to uplift in the riverbank and abutments (see Tables 2 and 3). 4. Conclusion (1) This study investigates the effect of shield tunneling on pile underpinning and base reinforcement of a long-span bridge. Compared to the case presented by Xu et al. (2015), the strengthening in our study is more difficult. As the subway tunnels are planned to cross Fengqi Bridge, pile underpinning and foundation improvement become necessary. For the purpose of reducing overall settlement, the bridge modification scheme includes adding a new “U” shaped substructure and reinforcing of foundation of the “U” structure. Real-time field data demonstrate that overall deformation of the bridge is relatively small and distortion features are reasonable for the entire shield tunneling process. Therefore, the operation plan for pile underpinning and ground improvement is feasible and rational. (2) As indicated by results of various monitored aspects, change in measurements mainly occurs during the stage of shield body crossing and the stage of shield departure. Based on all the date collected, up-line shield tunneling has a bigger impact on bridge deformation than the down-line process. (3) Due to differences in settlement mechanism between the pile foundation and soil, differential settlement occurs in both sides of bridgehead. As a result, bridgehead bump arises and impedes normal traffic, which demands further investigations. (4) Even monitoring data signal the feasibility of the operation plan, some limitations are also exposed, as some measurements such as
Fig. 17. Abutment cracks.
Fig. 16(a). Concurrently, Fig. 16(b) shows surface measuring point SD69 settles by 6.72 mm cumulatively, while there is an aggregate subsidence of −3.18 mm recorded by bridgehead measuring point QCJ1 during the up-line construction. The ultimate differential settlement is found to be 10 mm. Similarly, the settlement difference shown in Fig. 16(c) and (d) are 7.65 and 8.90 mm, respectively. Despite the surface reinforcement, differential settlement still appears around bridgehead area. As cracks at the bridgehead grow because of differential settlement, bridgehead bump becomes increasingly prominent. However, there is no reported differential bridge settlement during shield crossing in the case reported by Li and Wei (2015). Therefore, pile grinding can greatly impact differential settlement of the bridge (see Fig. 17). 3.7. Contrast of measurements during up-line and down-line shield tunnel construction Comparison of monitoring data of the two lines clearly indicates that up-line shield tunneling has a greater effect on bridge deformation, and analysis of the results can offer some insights on the impact difference. First, it takes 8 days for the shield body to cross under the Table 2 Construction parameters in shield tunnel construction. Construction parameters comparison
Construction days/day
Average thrust/kN
Average speed of advance/mm/min
The average injection volume m3
up-line down-line
8 5
12,210 12,670
18 27
1.5 4.5
Table 3 Comparison of collected data during up-line and down-line shield tunneling. Monitored parameters
Up-line
Down-line
Deck settlement
−5.18 mm to 3.14 mm; Shield construction through the bridge after the tilt phenomenon −4.00 mm to 4.31 mm; Most of the test points show gradual settlement; U-shaped groove on both sides of the wall along the shield direction deformation and settlement −4.22 mm to 1.56 mm; Shield construction after the adoption of all the points after the gradual settlement
−4.50 mm to 1.00 mm; Relatively stable
Abutment settlement
River bank settlement
Abutment Horizontal Displacement Summary
−1.68 mm to 2.93 mm; Most of the test points after the first rise after a slight settlement phenomenon; U-shaped groove on both sides of the wall to the lateral direction of deformation and deformation −1.18 mm to 2.36 mm; After the construction of the shield through the river, most of the test points appear first after the ups and downs of the settlement phenomenon East end of bridgehead: 15 mm; The east end of the bridgehead: 7.65 mm; The west end of the bridge: 10 mm The west end of the bridge: 8.90 mm The effect of the up-line construction on the deformation of bridge is great
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pipeline monitoring exceeds the allowable values. Therefore, there is still much room for improvement of the reinforcement scheme of Fengqi Bridge.
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Acknowledgments The work presented in this paper is financially supported by the National Key R and D Program of China (No. 2016YFC0800203), and the National Natural Science Foundation of China (No. 51778585). Thanks for the help and support of LI Shi-da (China Railway 19th Bureau Group Co., ltd), SHI Chang-jiang (East China survey and design Co., ltd), and SHI Li (Associate Professor of Zhejiang University of Technology). Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.tust.2018.06.018. References Afifipour, M., Sharifzadeh, M., Shahriar, K., Jamshidi, H., 2011. Interaction of twin tunnels and shallow foundation at Zand underpass, Shiraz Metro, Iran. Tunn. Undergr. Space Technol. 26, 356–363. Basile, F., 2014. Effects of tunnelling on pile foundations. Soils Found. 54, 280–295. Chen, R.P., Zhu, J., Liu, W., Tang, X.W., 2011. Ground movement induced by parallel EPB tunnels in silty soils. Tunn. Undergr. Space Technol. 26, 163–171. Dias, T.G.S., Adam Bezuijen, P.D., 2015. Data analysis of pile tunnel interaction. J. Geotech. Geoenviron. Eng 141 (12), 04015051. Fang, Y., He, C., 2008. Study on the influence of metro shield tunneling on close- by pile foundation. Mod. Tunn. Technol. 01, 42–47. Hong, Y., Soomro, M.A., Ng, C.W.W., 2015a. Settlement and load transfer mechanism of pile group due to side-by-side twin tunnelling. Comput. Geotech. 64, 105–119. Hong, Y., Soomro, M.A., Ng, C.W.W., Wang, L.Z., Yan, J.J., Li, B., 2015b. Tunnelling under pile groups and rafts: numerical parametric study on tension effects. Comput. Geotech. 68, 54–65.
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Tunnelling and Underground Space Technology journal homepage: www.elsevier.com/locate/tust
Field measurement analysis of the influence of double shield tunnel construction on reinforced bridge
T
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Wang Zhea, Zhang Kai-weia,e, Wei Gangb, , Li Binc, Li Qiangd, Yao Wang-jinga a
Institute of Geotechnical Engineering, Zhejiang University of Technology, Hangzhou 310014, China Department of Civil Engineering, Zhejiang University City College, Hangzhou 310015, China c East China Survey and Design Co., Ltd, Hangzhou 430000, China d China Railway 19th Bureau Group Co., Ltd, Beijing 100176, China e Greentown Real Estate Construction & Management Group Co., Ltd, Hangzhou 43000, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Double shield tunnel Bridge pile foundation underpinning Foundation reinforcement Field measurement
Constructing subway systems by shield tunneling in urban area may require tunnels to cross through pile foundations of buildings and bridges, which will definitely affect existing structures. Therefore, it is of great importance to study the construction schemes and influence of shield tunneling on reinforcing and rebuilding bridges. Investigating the case of the double-line shield tunnel of Hangzhou Metro Line 2 crossing through Fengqi Bridge, this paper discusses the project of reinforcing Fengqi Bridge and analyses monitoring data before and after the shield body crosses the bridge. Modification of Fengqi Bridge involves expansion and reinforcement of the raft foundation and improvement of composite ground. Our research findings indicate that these enhancements can effectively decrease bridge settlement during tunneling and improve mechanical conditions of bridge structures. Meanwhile, shield tunnel construction cuts pile and causes pile foundation displacement, leading to settlements behind bridge abutment, deck surface, and pipelines. Settlement of pipelines even exceeds the allowable levels. In addition, due to differences in settling mechanism between pile foundation and soil, differential settlement occurs in both sides of the bridge head and consequently bridge bump arises.
1. Introduction Construction of intercity rail transit networks, such as subway systems, is flourishing around the world and has gradually become focus of urban infrastructure development. However, with no forethought to include metro lines in early city planning, a common challenge encountered is the crossing of new underground tunnels through pile foundation of existing structures like bridges. Crossing of this kind not only increases difficulty in tunnel construction, but may also endanger existing bridges in the ways of deformation of pile formation, settlement and cracking of bridge deck surface, or bridge collapse. Therefore, it is of great significance to study this burdensome situation in engineering practices. There are many investigations in the effect of tunnel construction on surrounding bridges around the world (Afifipour et al., 2011; Basile, 2014; Chen et al., 2011; Dias and Adam Bezuijen, 2015; Fang and He, 2008; Hong et al., 2015a; Hong et al., 2015b; Jongpradist et al., 2013; Li and Wei, 2015; Li et al., 2014; Liu et al., 2014; Liu and Zhang, 2014; Marshall and Haji, 2015; Ni, 2014; Park et al., 2015; Shen and Liu,
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2015; Soomro et al., 2015; Wei et al., 2013; Xiang et al., 2008; Xiao-jie et al., 2009; Xu et al., 2015; Yoo, 2013; Zhang and Chen, 2011; Zheng et al., 2015). Research approaches often employed are empirical equations, theoretical analysis, numerical analysis, model testing, and field observation. Li and Wei (2015) studied the settlement and deformation of piles and surrounding ground at different stages of the shield tunneling process of the new Changping Line (Beijing Metro). They collected and analyzed field monitoring results of measured bridge subsidence, soil pressure, and grouting quantity, and also settlement data of piles and ground. Some researchers carried out numerical analysis of tunnel–pile interaction (Dias and Adam Bezuijen, 2015; Fang and He, 2008; Hong et al., 2015b; Jongpradist et al., 2013; Li et al., 2014; Liu et al., 2014; Liu and Zhang, 2014; Marshall and Haji, 2015; Ni, 2014; Soomro et al., 2015; Xiao-jie et al., 2009; Xu et al., 2015; Yoo, 2013; Zhang and Chen, 2011; Zheng et al., 2015). Using theoretical analysis, Wei et al. (2013) found that erection of a double-O-tube (DOT) tunnel would result in additional load to the
Corresponding author. E-mail address: [email protected] (G. Wei).
https://doi.org/10.1016/j.tust.2018.06.018 Received 30 June 2017; Received in revised form 22 February 2018; Accepted 26 June 2018 0886-7798/ © 2018 Elsevier Ltd. All rights reserved.
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ground improvement, effects of shield tunneling on bridges merit further study. Our study centers on the case of shield tunneling of Hangzhou Metro Line 2 from Jianguo North Road Station to Zhonghe North Road Station, crossing through the northern side of Fengqi Bridge. With discussion of scheme of Fengqi Bridge modification, this paper focuses on analyzing field date to explore influence on bridge foundation piles by the shield tunneling process after pile underpinning and foundation/ ground reinforcement of that long-span bridge. Our analysis of actual measurements of bridge distortions during shield tunnel construction can indeed compensate many deficiencies of unilateral numerical simulation.
surrounding pile foundation. According to the plan of Shanghai Metro Line 10, interval tunnel from Liyang Road station to Quyang Road station has to cross through the group pile foundation of Shajinggang Bridge on Siping Road. Xu et al. (2015) conducted a series of theoretical analysis and numerical simulation on the entire construction process to explore the load transfer mechanism of bridge structure. Calculation results indicate that both bridge static and traffic live loads can be successfully transferred from pile foundation to raft after pile underpinning, and removal of obstructed piles during tunneling has very limited influence on bridge structure. Previous studies rarely focus on the technology for foundation reinforcement and pile underpinning of long-span bridges. There is also a lack of field monitoring data on actual deformation in bridges. Furthermore, with diversities in technologies for pile underpinning and
Fig. 1. Vrious views of tunnel crossing bridge foundation (unit: cm). 253
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Fig. 1. (continued) Table 1 Physico-mechanical parameters of soil layers. Layers number
Soil name
Water content (%)
Unit weight (kN/m3)
Compressive modulus (MPa)
Cohesion (kPa)
Friction angle (°)
②2 ③3 ③6 ③7 ④2 ④3 ⑥1 ⑦1 ⑦3 ⑧1 ⑨1 ⑩1 (12)1
Sandy silt Silt with sand silt Silt with sand silt Sandy silt Silty silty clay Clayey silt Silty silty clay Silty clay Silty clay Silty clay Silty clay Silty clay Fine sand
27.8 25.6 26.2 26.1 31.8 30.9 39.0 29.5 33.3 36.6 23.2 30.8 23.6
18.9 19.1 19.1 19.4 18.4 18.2 17.7 18.9 18.4 18.0 19.7 18.8 19.1
7.5 10.0 11.0 7.0 2.8 4.0 2.5 5.8 4.5 4.5 6.5 4.8 10.0
4.0 3.0 1.0 6.0 13.0 6.0 14.0 31.0 23.0 18.0 40.0 35.0 0.0
25.5 29.0 30.0 18.0 10.0 18.0 10.5 16.0 12.0 11.9 17.5 15.0 31.0
Fig. 2. The reinforcement plan view of A-A elevation 1:150 (unit: cm).
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Fig. 3. The reinforcement plan view of B-B elevation (unit: cm).
Fig. 4. Details of high pressure jet grouting pile (unit: cm).
2. Project overview
because of the location, complex surrounding environment, and large traffic flow. As a result, modifying and reinforcing the original bridge, with bridge deck widened to 36.4 m, emerges as the best choice to meet the requirements for shield tunneling. Shield construction across Fengqi Bridge requires covering the surface with soil of 6.1 m thick and grinding 4 rows of piles. Two rows are Φ100 cm bore-hole cast-in-situ piles, with the foundation concrete labeled C25 and Φ22 main reinforcements. The other two rows are Φ30 cm reinforced concrete piles, arranged in quincuncial shape, as shown in Fig. 1. There is a visible communication pipeline bridge, with a pipeline truss of 60 cm × 40 cm, on the north side of the bridge. In addition, a cast-iron water pipe of Φ50 cm is set up in the cantilever of the north side of the bridge, while a pipeline of 60 cm × 60 cm for electric power supply is located under the sidewalk on the south side.
2.1. Original Fengqi bridge With a total length of 43.3 km, Hangzhou Metro Line 2 is completely constructed underground with 33 stations connecting 6 districts, namely Yuhang, Gongshu, Xihu, Xiacheng, Jianggan and Xiaoshan. Its southern section is prearranged for the Linpu rail, while the northern portion is reserved for the Anji intercity rail. Based on the Metro Line 2 route plan, the subway tunnel between North Jianguo Road Station and North Zhonghe Road Station will cross through the Fengqi Bridge pile on Fengqi Road. Fengqi Bridge is 100 m away from the west side of the intersection of North Jianguo Road and Fengqi Road, and it is at a distance of 60 m from the well head at the western part of North Jianguo Road Station. The bridge is a single-span simply supported beam structure with two abutments, over a river of 20.54–23.62 m wide. Superstructure of the bridge consists of 20 m post-tensioned prestressing concrete hollow slab, and the beam is 95 cm high. Meanwhile, the substructure is light abutment with Φ100 cm bore-hole cast-in-situ pile foundation. Great difficulty in rebuilding Fengqi bridge exist
2.2. Engineering geological conditions The thickness of Quaternary stratum in the project area is about 50 m, and the surface layer at the site is miscellaneous backfilling ranging from 2.8 to 5.7 m in thickness. There are silt and sand layer of 255
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Fig. 5. Fengqi bridge site photo.
Observation of ground settlement is set up near the bridgehead, 1 m away from the closest bridge measuring point. Monitoring of abutment settlement and horizontal displacement are shown in Fig. 6(b). QC1 to QC8 are the measuring points of abutment settlement, while QS1 to QS8 are for tracking horizontal displacement of retaining wall. These observation points are laid out on both sides of the bridge abutment with an interval of 18 m, and the space among the points on each side is 8, 8, and 7 m, respectively. After the “U” structure is added and connected with the abutment, monitoring of abutment settlement and displacement is moved to the “U” structure. Lastly, Fig. 6(c) demonstrates configuration of measuring points for dike and pipeline settlement. QD1 to QD8 are the dike measuring points, installed on the north and south sides of the bridge. QD8 was faulty, and so no data were recorded during monitoring. QGX1 to QGX3 and QGXT1 to QGXT 3 track communication pipelines, while QGXJ1 to QGXJ3 surveil water pipelines. Pipelines are set up on both north and south sides of the bridge.
about 8.0–15.1 m thick in the alluvium in the subordinate Qiantang River. Most of the soil layers in the interval range are silt with sand, silt, and sandy silt, while some of which are silty clay, silty clay with silt, and silty clay, as shown in Table 1. 2.3. Scheme of Fengqi bridge modification 2.3.1. Design of bridge modification Since the interval shield tunneling crosses through the north side of Fengqi Bridge, alteration of the bridge involves moving bridge support in the superstructure 0.5 m toward the river channel so as to reduce the span of the existing bridge. A “U” structure is added to the lower part of the bridge as the expanding foundation, which is also connected with the original bridge abutment by planting bars, as presented in Figs. 2–4. Fig. 5 is a field photo of Fengqi Bridge. High-pressure rotary jet grouting piles with diameter of 800 mm and 15.5 m in length are used in underpinning. In area requiring strong reinforcement, jet grouting piles are arranged at the four corners of a square, with center spacing of 120 mm. On the other hand, piles in weak reinforcement area are configured in two ways, as 120 mm × 120 mm or 160 mm × 160 mm equilateral triangles. Layout of piles is presented in Fig. 4. Strong reinforcement is mainly arranged on both sides of the abutment, while other area only primarily involves weak reinforcement.
3. Results of field measurements and discussion 3.1. Analysis of deck subsidence Settlement data of bridge deck surface during construction of upline shield tunnel is presented in Fig. 7. Fig. 7(a) shows the relationship between bridge deck settlement and progress of the tunneling process with measurements from all deck observation points included, whereas Fig. 7(b), (c), and (d) shows, respectively, data from each of the three cross-sections of the deck settlement monitoring points. Fig. 7(e) demonstrates final settlement recorded at measuring points of the three cross-sections of bridge deck in relation to spatial arrangement of these points, as Fig. 7(f) displays the final spatial variation of the bridge surface. Similarly, Fig. 8 illustrates the relationship between bridge deck settlement and advancing rate of down-line tunneling. Here, a positive value of settlement signifies that the bridge surface is heaved, while a negative value denotes subsidence. Results presented in Figs. 7 and 8 indicate that measured settlement varies from −5.18 to 3.14 mm with crossing of the up-line tunnel, while the range of subsidence at deck surface is from −4.50 to 1.00 mm for the down-line tunneling process. Our field data also show that the bridge started to slant after construction of up-line tunnel, and the largest differential settlement reaches 6.74 mm. Differential subsidence grows with increasing distance of the measuring points from the tunnel, while bridge surface nearest to the tunnel has an uplift. Although the settlement variation during down-line construction is smaller than that
2.4. Measuring-point layout of Fengqi bridge With the purpose of investigating effects of shield tunneling on the bridge, we set up and conducted a series of monitoring, which mainly concern settlement of bridge deck surface, subsidence behind abutment, horizontal displacement of abutment, embankment subsidence, and bridgehead and pipeline settlement. According to Code for Monitoring Measurement of Urban Rail Transit Engineering GB50911-2013 (Chinese national standard), the allowable value of bridge deck surface and abutment subsidence is ± 2 mm/d and the cumulative value is ± 15 mm. Axis settlement must be no more than 3 mm/d, with the accumulated one less than 20 mm and allowable upheaval value of 7 mm. Maximum cumulative subsidence of pipeline is 30 mm, while the allowable settling rate is less than 2 mm/d with pressure, and 3 mm/d without pressure. Fig. 6(a) presents the layout of monitoring points for bridge and ground settlement. QCJ1 to QCJ12 are the measuring points of bridge settlement, arranged in three rows. Each row is 10 m from the other, while the distance between two points at each row is also 10 m. 256
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present measured results from all monitoring points tracking abutment settlement. Collected data on abutment subsidence from the first and second cross-section monitoring points are illustrated in Fig. 9(b) and (c), respectively, while Fig. 9(d) exhibits spatial variation of both crosssections of abutment. Likewise, relationship between abutment settlement and advancing down-line tunneling process is displayed in Fig. 10. According to Figs. 9 and 10, variation of observed abutment settlement ranges from −4.00 to 4.31 mm during up-line construction; when the range for down-line tunneling is from −1.68 to 2.93 mm. Settlement gradually emerges for abutment at most of the measuring points during up-line tunnel construction. On the other hand, nearly all measuring points record a heave at the beginning and then a subsidence in down-line tunneling. That is, in the case of down-line construction, the abutment is upheaved during the stage of shield crossing, and it then settles slightly, and eventually stabilizes after the passing of the shield body. Fluctuation in abutment settlement is more substantial in the tunneling process of up-line than down-line. As a whole, measuring points in up-line settle, while there is uplift at down-line observation points. The tunneling process affects abutment settlement in up-line and down-line differently. 3.3. Analysis of riverbank settlement monitoring results Fig. 11(a) and (b) depicts change in riverbank subsidence at various stages of tunneling of the up-line and down-line, respectively. Measured settlement at the riverbank ranges from −4.22 to 1.56 mm for up-line tunnel construction, while the variation is from −1.18 to 2.36 mm for down-line tunneling. Similar to variations in abutment settlement, all up-line observation points on the riverbank subside steadily, when most down-line measuring points show an initial upheave, followed by a settlement. Compared to the down-line process, our obtained data reveal a more sizable variation in riverbank settlement for the up-line tunneling. Overall, riverbank is noted to settle after crossing of the shield body in the up-line tunnel, while a heave is observed for most of the down-line measuring points. 3.4. Analysis of measured pipeline settlement Fig. 12 illustrates pipeline settlement during construction of shield tunnels. Subsidence data of all three pipelines at various stages of the tunneling process is presented in Fig. 9(a). Measurements form observations points at both bridge communication lines (QGX and QGXT) and water supply pipeline (QGXJ) are shown in Fig. 12(b)–(d) separately. Settlement of communication pipeline QGX varies from −2.77 to 1.6 mm during tunneling, while variation ranges from −7.92 to 0.68 mm and −7.17 to 0.92 mm for QGXT and QGXJ, respectively. Monitoring points QGX1 to QGX3 for tracking subsidence of communication line QGX are located right above the tunnel, and steady settlement is recorded during the stage of shield crossing. On the other hand, communication line QGXT exhibits more rapid subsiding, with QGXT1 settles at the fastest rate of 6.44 mm/d and QGXT2 at 5.18 mm/ d, both exceeding the allowable rate. Even after grouting, both sides of the pipeline still show vast differential settlement of 5.31 mm, and the pipeline eventually slants vertically. All measuring points of water pipeline QGXJ1 to QGXJ3 indicate subsidence during shield crossing. Among these three, QGXJ1 settles at the fastest rate of 3.44 mm/d, surpassing the allowable value. During the grouting phase of tunneling, data from measuring points QGXJ2 and QGXJ3 signify an upheave, while QGXJ1 shows more settlement. There is a large settlement difference of 6.18 mm at both sides of the water pipeline, and it also ultimately slants vertically. Both communication pipelines and water pipeline are independent structures from the bridge and receive no reinforcements before tunnel construction. Therefore, vast vertical displacements of these pipelines occur during the tunneling process, even with some measurements exceeding allowable values. In view of
Fig. 6. Monitoring point layout (unit: cm).
in up-line, the variation rate of subsidence is greater than that in up-line at some monitoring points. QCJ16 and QCJ7 are both in the middle of the bridge deck and on the side of the down-line. In comparison to other measuring points, they show greater settlement during stage 2 of shield tunneling. However, after grouting at the shield tail, settlement at QCJ16 and QCJ7 greatly declines, and is then comparable to other measuring points. Subsidence variations at three stages of shield tunneling process exhibit obvious trends. However, these trends are vastly different for up-line and down-line construction. 3.2. Analysis of abutment settlement Relationship between abutment settlement and progressing rate of up-line shield tunnel construction is shown in Fig. 9. In Fig. 9(a), we 257
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Fig. 7. Deck measuring results during up-line shield tunneling.
our findings, in addition to reinforcing the bridge, independent pipelines should also be strengthened correspondingly to ensure the safety of shield tunneling (see Fig. 13).
Fig. 14(c) and (d) shows results from cross-sections 1 and 2, respectively, throughout the course of down-line construction around Fengqi Bridge. A positive horizontal displacement here signals movement of the abutment toward the river, as moving toward the ground is represented by a negative value (see Fig. 15). Horizontal abutment displacement associated with up-line and down-line tunneling is limited within 2 and 1 mm, respectively. Based on observed variations in horizontal as well as vertical abutment displacements, both east and west sides of the “U” structure tilt down toward the shield during up-line tunneling. By contrast, the two sides of
3.5. Analysis of abutment horizontal displacement Fig. 14 summarizes lateral abutment movement at various phases of shield tunneling. Observed horizontal displacement of the abutment from measuring points at cross-sections 1 and 2 during up-line tunneling are presented in Fig. 14(a) and (b), respectively. Likewise, 258
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Fig. 8. Deck measuring results during down-line shield tunneling.
the “U” structure both slant up in the direction of theabutment while down-line tunnel construction is underway. In short, up-line shield tunneling has a greater impact on horizontal abutment displacement.
Fig. 10. Abutment measuring results during down-line shield tunneling.
Subsidence data from surface monitoring point SD43 and bridge monitoring point QCJ1 during the up-line construction is shown in Fig. 16(a), where Fig. 16(b) reports settlement results of surface monitoring point SD69 and bridge monitoring point QCJ9. Correspondingly, Fig. 16(c) displays measured settlement from surface monitoring point XD43 and bridge monitoring point QCJ3 during down-line tunnel
3.6. Analysis of differential settlement at the bridgehead area Monitoring results regarding ground and bridgehead settlement in relations to advancement of tunneling process are presented in Fig. 16.
Fig. 9. Abutment measuring results during up-line shield tunneling. 259
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Fig. 11. River bank settlement measuring results during shield tunneling.
Fig. 12. Pipeline settlement measuring results during shield tunneling.
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Fig. 13. Pipeline behind The Bridge.
Fig. 14. View of abutment horizontal displacement measuring results during shield tunneling.
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Fig. 15. Deformation of original abutment and the added “U” structure.
Fig. 16. View Analysis of settlement difference of bridgehead in shield tunneling process.
emerges rapidly at measuring point SD43, and the largest one-day settlement surpasses the allowable value and reaches 3.66 mm. The accumulative subsidence of SD43 is 15.04 mm, while the bridgehead measuring point QCJ1 only settles by 0.04 mm cumulatively. Thus, there is an ultimate settlement difference of 15 mm, as shown in
construction, while subsidence data from surface monitoring point XD69 and bridge monitoring point QCJ11 are exhibited in Fig. 16(d). Even measuring points SD43 and QCJ1 are only 1 m apart and on the same vertical cross-section, they recorded vastly different settlement results. When shield cutter approaches the bridgehead, settlement
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bridge in up-line construction, but only 5 days for down-line tunneling. A longer construction time is more likely to cause bigger soil loss, and thus results in larger settlement of bridge structures and greater differential subsidence at the bridgehead. Second, average thrust of the shield crossing the bridge for up-line and down-line tunnels is 12,210 and 12,670 kN, respectively. Higher average speed of shield advancement and bigger average grout injection volume in down-line tunnel construction may also lead to uplift in the riverbank and abutments (see Tables 2 and 3). 4. Conclusion (1) This study investigates the effect of shield tunneling on pile underpinning and base reinforcement of a long-span bridge. Compared to the case presented by Xu et al. (2015), the strengthening in our study is more difficult. As the subway tunnels are planned to cross Fengqi Bridge, pile underpinning and foundation improvement become necessary. For the purpose of reducing overall settlement, the bridge modification scheme includes adding a new “U” shaped substructure and reinforcing of foundation of the “U” structure. Real-time field data demonstrate that overall deformation of the bridge is relatively small and distortion features are reasonable for the entire shield tunneling process. Therefore, the operation plan for pile underpinning and ground improvement is feasible and rational. (2) As indicated by results of various monitored aspects, change in measurements mainly occurs during the stage of shield body crossing and the stage of shield departure. Based on all the date collected, up-line shield tunneling has a bigger impact on bridge deformation than the down-line process. (3) Due to differences in settlement mechanism between the pile foundation and soil, differential settlement occurs in both sides of bridgehead. As a result, bridgehead bump arises and impedes normal traffic, which demands further investigations. (4) Even monitoring data signal the feasibility of the operation plan, some limitations are also exposed, as some measurements such as
Fig. 17. Abutment cracks.
Fig. 16(a). Concurrently, Fig. 16(b) shows surface measuring point SD69 settles by 6.72 mm cumulatively, while there is an aggregate subsidence of −3.18 mm recorded by bridgehead measuring point QCJ1 during the up-line construction. The ultimate differential settlement is found to be 10 mm. Similarly, the settlement difference shown in Fig. 16(c) and (d) are 7.65 and 8.90 mm, respectively. Despite the surface reinforcement, differential settlement still appears around bridgehead area. As cracks at the bridgehead grow because of differential settlement, bridgehead bump becomes increasingly prominent. However, there is no reported differential bridge settlement during shield crossing in the case reported by Li and Wei (2015). Therefore, pile grinding can greatly impact differential settlement of the bridge (see Fig. 17). 3.7. Contrast of measurements during up-line and down-line shield tunnel construction Comparison of monitoring data of the two lines clearly indicates that up-line shield tunneling has a greater effect on bridge deformation, and analysis of the results can offer some insights on the impact difference. First, it takes 8 days for the shield body to cross under the Table 2 Construction parameters in shield tunnel construction. Construction parameters comparison
Construction days/day
Average thrust/kN
Average speed of advance/mm/min
The average injection volume m3
up-line down-line
8 5
12,210 12,670
18 27
1.5 4.5
Table 3 Comparison of collected data during up-line and down-line shield tunneling. Monitored parameters
Up-line
Down-line
Deck settlement
−5.18 mm to 3.14 mm; Shield construction through the bridge after the tilt phenomenon −4.00 mm to 4.31 mm; Most of the test points show gradual settlement; U-shaped groove on both sides of the wall along the shield direction deformation and settlement −4.22 mm to 1.56 mm; Shield construction after the adoption of all the points after the gradual settlement
−4.50 mm to 1.00 mm; Relatively stable
Abutment settlement
River bank settlement
Abutment Horizontal Displacement Summary
−1.68 mm to 2.93 mm; Most of the test points after the first rise after a slight settlement phenomenon; U-shaped groove on both sides of the wall to the lateral direction of deformation and deformation −1.18 mm to 2.36 mm; After the construction of the shield through the river, most of the test points appear first after the ups and downs of the settlement phenomenon East end of bridgehead: 15 mm; The east end of the bridgehead: 7.65 mm; The west end of the bridge: 10 mm The west end of the bridge: 8.90 mm The effect of the up-line construction on the deformation of bridge is great
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pipeline monitoring exceeds the allowable values. Therefore, there is still much room for improvement of the reinforcement scheme of Fengqi Bridge.
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Acknowledgments The work presented in this paper is financially supported by the National Key R and D Program of China (No. 2016YFC0800203), and the National Natural Science Foundation of China (No. 51778585). Thanks for the help and support of LI Shi-da (China Railway 19th Bureau Group Co., ltd), SHI Chang-jiang (East China survey and design Co., ltd), and SHI Li (Associate Professor of Zhejiang University of Technology). Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.tust.2018.06.018. References Afifipour, M., Sharifzadeh, M., Shahriar, K., Jamshidi, H., 2011. Interaction of twin tunnels and shallow foundation at Zand underpass, Shiraz Metro, Iran. Tunn. Undergr. Space Technol. 26, 356–363. Basile, F., 2014. Effects of tunnelling on pile foundations. Soils Found. 54, 280–295. Chen, R.P., Zhu, J., Liu, W., Tang, X.W., 2011. Ground movement induced by parallel EPB tunnels in silty soils. Tunn. Undergr. Space Technol. 26, 163–171. Dias, T.G.S., Adam Bezuijen, P.D., 2015. Data analysis of pile tunnel interaction. J. Geotech. Geoenviron. Eng 141 (12), 04015051. Fang, Y., He, C., 2008. Study on the influence of metro shield tunneling on close- by pile foundation. Mod. Tunn. Technol. 01, 42–47. Hong, Y., Soomro, M.A., Ng, C.W.W., 2015a. Settlement and load transfer mechanism of pile group due to side-by-side twin tunnelling. Comput. Geotech. 64, 105–119. Hong, Y., Soomro, M.A., Ng, C.W.W., Wang, L.Z., Yan, J.J., Li, B., 2015b. Tunnelling under pile groups and rafts: numerical parametric study on tension effects. Comput. Geotech. 68, 54–65.
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