Available online at www.sciencedirect.com ScienceDirect Procedia Engineering 189 (2017 ) 11 17 Transportation Geotechnics and Geoecology, TGG 2017, 17-19 May 2017, Saint Petersburg, Russia Structural response of existed metro tunnels to adjacent largesection pipe jacking construction Bo Liu a, *, Dingwen Zhang a, Lei Fang a a School of Transportation, Southeast University, 2 Sipailou, Nanjing 210096, P.R. China Abstract A rectangular pedestrian underpass of 94.5m long, 7m wide and 4.3m high was constructed across the existed metro tunnels using pipe jacking method. The minimum distance from underpass bottom to tunnel crown was 4.5m. In order to investigate the effects of pipe jacking on existed underlying tunnels, the instruments were installed in the tunnels and structural responses were extensively monitored. Based on the field observations, the vertical displacement, horizontal displacement and diameter convergence of the tunnel were analyzed. The results indicate that in the whole pipe jacking process, the tunnel vertical displacement mainly goes through three different stages, namely, initial settlement stage, quick heave stage and steady heave stage. The horizontal displacement of ballast bed is much smaller than that of tunnel crown and is almost negligible. The tunnel was horizontally compressed and vertically stretched after pipe jacking construction. Pipe jacking construction has a greater effect on the tunnel structures just below the underpass than that beyond the width scope of underpass, whether it is vertical displacement, horizontal displacement or diameter convergence of the tunnel. 2017 The Authors. Published by Elsevier Ltd. 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the scientific committee of the International conference on Transportation Geotechnics and (http://creativecommons.org/licenses/by-nc-nd/4.0/). Geoecology. Peer-review under responsibility of the scientific committee of the International conference on Transportation Geotechnics and Geoecology Keywords: Structural response; Metro tunnel, Pipe jacking, Field Monitoring 1. Introduction Pipe jacking is a trenchless method commonly used in the installation of sewers, oil pipelines, electricity cable ducts, etc. [1-2]. Many attentions have been paid on this method in recent years. Milligan [3], Meskele [4] and Barla * Corresponding author. Tel.: +86 15951812310. E-mail address: seuliubo@seu.edu.cn 1877-7058 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the International conference on Transportation Geotechnics and Geoecology doi:10.1016/j.proeng.2017.05.003
12 Bo Liu et al. / Procedia Engineering 189 ( 2017 ) 11 17 [5] investigated the pipe-soil interaction mechanisms of pipe jacking. Shou [6], Shimada [7] and Zhou [8] investigated the characteristics of different injected slurry (or lubricants) and their effects. Barla [9], Choo [10] and Yen [11] investigated the jacking force and its influencing factors. Sofianos [12], Liao[13], Shen [14] and Zhen [15] investigated the environmental responses to pipe jacking construction through several case histories. However, the pipe jacking projects in the above-mentioned literatures are mainly small to medium diameter circular pipelines or tunnels constructed in relatively simple environmental condition. There are few reports on the construction of large-section tunnel using pipe jacking method in complex conditions, such as jacking in soft clay with poor soil properties, jacking adjacent to existed metro tunnels or pipelines. This paper presents a rectangular pedestrian underpass, which was constructed across the existed metro tunnels using pipe jacking method in soft clay. In view of the scale and length of underpass, significant effects on the tunnels were expected. In order to investigate the effects of pipe jacking on existed underlying tunnels, the instruments were installed in the tunnels and structural responses were extensively monitored. Based on the field observations, the vertical displacement, horizontal displacement and diameter convergence of the tunnels were analysed. 2. Site condition Fig. 1 shows the cross section of this pipe jacking project. The pedestrian underpass was constructed across the existed tunnels (i.e., down track and up track) of Nanjing Metro Line 2 with intersection angle of 90, and the minimum distance from underpass bottom to tunnel crown was just 4.5 m. The full length of underpass (94.5 m) consists of 63 pipe segments labeled as 01 to 63. Each prefabricate reinforced concrete pipe segment is 1.5 m long, 7 m wide and 4.3 m high with thickness of 0.5 m. Starting shaft and receiving shaft were constructed at the two ends of underpass. Jiangdong Road Dates: month/ day Starting shaft 6/24 6/25 6/27 6/26 6/28 6/29 6/30 7/01 7/02 7/03 7/04 7/05 7/06 6 6 6 6 5 5 5 5 5 5 5 5 5 5 4 4 4 4 4 4 4 4 4 4 3 3 3 3 3 3 3 3 3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 4.5m 3m 33.0m 18.5m 7/07 7/08 7/09 7/10 7/11 7/12 7/13 7/14 7/16 7/15 7/21 Receiving shaft Down track Up track Fig. 1. Cross section of pipe jacking project Table 1 lists main physical and mechanical parameters of typical soil layers in the site. The pipe segments were jacked in muddy silty clay which has a natural water content of 37.3%, a high void ratio of 52 and a high liquidity index of 9. It indicates that the soil presents the plastic-flow state with low strength. The high sensitivity value of 5.42 indicates that the soil strength of this layer is liable to be decreased after being disturbed by construction. Table 1. Physical and mechanical parameters of typical soil layers in the site Soil types H (m) γ (kn/m 3 ) w (%) e I l Es (MPa) q u (kpa) s t Fill 4 18.0 40.9 1.119 0.96 3.45 / / Mucky silty clay 18 17.9 37.3 52 9 3.53 26 5.42 Silty clay 7 18.2 32.8 0.946 5 4.01 43 6.14 Silty fine sand - 1 14 18.1 28.4 85 / 14 / / Silty fine sand - 2 15 18.5 25.2 0.798 / 11.77 / / Note: H= soil thickness, γ = unite weight, w = water content, e = void ratio, I l = liquidity index, E s = compression modulus, q u = unconfined compressive strength, s t = sensitivity.
Bo Liu et al. / Procedia Engineering 189 ( 2017 ) 11 17 13 Fig. 1 also shows the progress of pipe jacking construction. The first pipe segment was jacked into the ground on June 24, 2015, and the whole underpass was completed on July 21, 2015, totalling 28 days. The pipe jacking machine passed the down track on July 3, 2015 and passed the up track on July 12, 2015. The pipe segments were not jacked from July 17 to July 20, 2015 due to the cutting of tunnel portal in receiving shaft, therefore the actual working time lasted only 24 days. 3. Monitoring program To ensure the safety of metro tunnels during pipe jacking construction, the deformation of tunnels was comprehensively monitored. Fig. 2 shows the plan layout of monitoring sections. Considering pipe jacking machine passed the down track ahead of up track, so the down track was firstly monitored from July 1 to July 8, 2015. 14 monitoring sections were instrumented in the down track, in which every reinforced concrete segment below the underpass set a monitoring section, while every two reinforced concrete segments beyond the width scope of underpass set a monitoring section. The monitoring sections distributed symmetrically on both sides of the centerline of underpass. The monitoring sections were named as DGX+1~DGX+11 in the north of centerline and named as DGX-1~DGX-11 in the south of centerline. In the same way, 14 monitoring sections were also instrumented in the up track and were monitored from July 9 to July 27, 2015. 4 monitoring points named as A, B, C and D were installed in each monitoring section. As shown in Fig. 3, point A was installed on tunnel crown, Point D was installed on ballast bed, and points B and C were installed on tunnel haunch. According to the coordinate of A and D, the vertical and horizontal displacement of tunnel crown and ballast bed can be obtained. And, diameter convergence can be obtained from coordinate of B and C. The automatic total station (with angle accuracy of 0.5 and distance accuracy of 2+2ppm) and prisms were used as instruments for monitoring, as shown in Fig. 4. The monitoring frequency was 1 time a day. Fig. 2. Plan layout of monitoring sections in tunnels
14 Bo Liu et al. / Procedia Engineering 189 ( 2017 ) 11 17 A Tunnel crown B Diameter convergence measure line C Prism D Ballast bed Automatic total station Fig. 3. Schematic diagram of monitoring section Fig. 4. The instruments used for monitoring 4. Analysis of monitoring results 4.1. Vertical displacement of tunnel Fig. 5 shows the variations of vertical displacement of tunnel crown with time. In the figure, positive value indicates the heave, and negative value indicates the settlement. The monitoring sections (DGS-3~DGS+3) directly below the underpass were denoted by hollow legends, and the other monitoring sections (DGS-5~, DGS+5~) beyond the width scope of underpass were denoted by solid legends. As shown in Fig. 5(a), the state of down track on June 29, 2015 was regarded as the initial state with no deformation. A little settlement of the down track was induced before July 2, 2015. On the contrary, obvious heave was observed from July 2 to July 3, 2015 when pipe jacking machine passes the tunnel. After July 3, 2015, the heave continued, but the growth speed began to slow down. The maximum heave reached 2.7 mm by July 8, 2015. As shown in Fig. 5(b), the vertical displacement evolution of up track is similar to that of down track. The maximum heave reached 3.0 mm by July 27, 2015. The locations of maximum heave were both on monitoring sections of DGX-1 and DGX+1 which were directly below the centreline of underpass. Vertical displacement (mm) 3.5 before passing passing 3.0 after passing 2.5 II +11 +01-01 -11 I 1.5 0.5-0.5-2015.6.29 2015.7.01 2015.7.02 2015.7.03 2015.7.04 2015.7.05 2015.7.06 2015.7.07 (a) DGX+11 DGX+09 DGX+07 DGX+05 DGX+03 DGX+02 DGX+01 DGX-01 DGX-02 DGX-03 DGX-05 DGX-07 DGX-09 DGX-11 3.5 before passing passing 3.0 II 2.5 +11 +01-01 -11 I Fig. 5. Variation of vertical displacement of tunnel crown with time (a) Down track (b) Up track Fig. 6 shows the variations of vertical displacement of ballast bed with time. It can be seen that the vertical displacement evolution of ballast bed was similar to that of tunnel crown. The heave of ballast bed in the down track Vertical Displacement (mm) 1.5 0.5-0.5 - after passing (b) DGX+11 DGX+09 DGX+07 DGX+05 DGX+03 DGX+02 DGX+01 DGX-01 DGX-02 DGX-03 DGX-05 DGX-07 DGX-09 DGX-11
Bo Liu et al. / Procedia Engineering 189 ( 2017 ) 11 17 15 reached 1.4 mm on July 8, 2015, and that reached mm on July 27, 2015 in the up track. The heave of ballast bed is about 1/2 and 2/3 of tunnel crown heave in the down track and up track, respectively. This is probably due to the distance between the ballast bed and underpass is longer than that between tunnel crown and underpass, and thus pipe jacking-induced vertical stress relief in the underpass has a smaller influence on the ballast bed than that of tunnel crown. Vertical Displacement (mm) 2.2 before passing passing after passing 1.8 II 1.6 +11 +01-01 -11 1.4 I - - 2015.6.29 2015.7.01 2015.7.02 2015.7.03 2015.7.04 2015.7.05 2015.7.06 2015.7.07 Fig. 6. Variation of vertical displacement of ballast bed with time (a) Down track (b) Up track From Fig. 5 and Fig. 6, the vertical displacement that tunnel went through can be divided into three different stages, namely, initial settlement stage (), quick heave stage (I) and steady heave stage (II). generally occurs before the pipe jacking machine passes the tunnel, in which a little initial settlement of the tunnel has a positive effect on reducing the ultimate deformation of the tunnel. I generally occurs during the time that pipe jacking machine passes the tunnel and a short time after passing, in which the tunnel heave accounts for the main part of the tunnel total deformation. II starts from the end of I, in which the heave reaches the stability for a long time as a result of soil creep. 4.2. Horizontal displacement of tunnel (a) DGX+11 DGX+09 DGX+07 DGX+05 DGX+03 DGX+02 DGX+01 DGX-01 DGX-02 DGX-03 DGX-05 DGX-07 DGX-09 DGX-11 2.2 before passing passing after passing The above analysis shows that the deformation evolution of down track is similar to that of up track except for the magnitude of deformation. Considering that the up track was monitored for a longer time and the monitoring data was more comprehensive than that of down track. Therefore, only up track was selected for further analysis in the following. Fig. 7 shows the variations of horizontal displacement of tunnel crown and ballast bed in the up track with time. In the figure, positive value indicates the movement towards the receiving shaft, and negative value indicates the movement towards the starting shaft. As shown in Fig. 7(a), the tunnel crown mainly moved towards the receiving shaft. The horizontal displacement of tunnel crown on DGS-3~DGS+3 sections increased more quickly with time than that on the other sections, e.g., DGS-9~ and DGS+9~. By July 27, 2015, the maximum horizontal displacement of tunnel crown, occurred on DGS-1 and DGS+1, reached mm which was 1/3 of tunnel crown heave and 1/2 of ballast bed heave. As shown in Fig. 8(b), the horizontal displacement of ballast bed fluctuated between - 0.1 mm and mm which was almost negligible. Vertical Displacement (mm) 1.8 1.6 1.4 - - +11 +01-01 -11 I II (b)
16 Bo Liu et al. / Procedia Engineering 189 ( 2017 ) 11 17 Horizontal Displacement (mm) - (a) Fig. 7. Variations of horizontal displacement in up track with time (a) Tunnel crown (b) Ballast bed Horizontal Displacement (mm) - (b) 4.3. Diameter convergence of tunnel Fig. 8 shows the variations of diameter convergence of up track with time. In the figure, positive value indicates tunnel is horizontally stretched, and negative value indicates tunnel is horizontally compressed. It was found that the diameter of tunnel was almost unchanged before July 11, 2015. After July 11, 2015, the horizontal diameter convergence increased with the time. The tunnel presented the state that compressed horizontally and stretched vertically, as shown in Fig. 9. Moreover, the diameter convergence of tunnel just below the underpass was larger than that beyond the width scope of underpass. Diametre Convergence (mm) - - - - - - -1.4-1.6-1.8 Fig. 8. Variations of horizontal diameter convergence with time 5. Conclusions before passing passing after passing Fig. 9. Schematic diagram of tunnel deformation Based on the above analyses, the following conclusions may be drawn: (1) The heave of ballast bed in the down track and up track induced by pipe jacking is 1/2 and 2/3 of tunnel crown heave, respectively. The horizontal displacement of ballast bed is much smaller than that of tunnel crown and is almost negligible. The tunnel is horizontally compressed and vertically stretched after pipe jacking construction. (2) In the whole pipe jacking process, the vertical displacement of existed tunnels mainly experiences the initial settlement stage, quick heave stage and steady heave stage successively. (3) Whether vertical displacement, horizontal displacement or diameter convergence, pipe jacking has a greater effect on the tunnel structures just below the underpass than that beyond the width scope of underpass. B A Final state Initial state C
Bo Liu et al. / Procedia Engineering 189 ( 2017 ) 11 17 17 Acknowledgements This study is supported by the Fundamental Research Founds for the Central Universities (No. 2242014R30020) and the Personnel Training Found for Outstanding Young Teacher of Qinglan Project of Higher Education in Jiangsu Province. References [1] D.N. Chapman, C.D.F. Rogers, H.J. Burd, et al., 2007. Research needs for new construction using trenchless technologies. Tunn. Undergr. Space Technol., 22(5): 491-502. [2] W. Bergeson, 2014. Review of long drive microtunneling technology for use on large scale projects. Tunn. Undergr. Space Technol., 39: 66-72. [3] G.E. Milligan, P. Norris, 1999. Pipe-soil interaction during pipe jacking. Proc. Inst. Civil Eng.-Geotech. Eng., 137(1): 27-44. [4] T. Meskele, A.W. Stuedlein, 2015. Static soil resistance to pipe ramming in granular soils. J. Geotech. Geoenviron. Eng., 141(3): 04014108. [5] M. Barla, M. Camusso, 2013. A method to design microtunnelling installations in randomly cemented Torino alluvial soil. Tunn. Undergr. Space Technol., 33(1): 73 81. [6] K. Shou, J. Yen, M. Liu, 2010. On the frictional property of lubricants and its impact on jacking force and soil pipe interaction of pipe-jacking. Tunn. Undergr. Space Technol., 25(4): 469 477. [7] H. Shimada, T. Sasaoka, S. Khazaei, et al., 2006. Performance of mortar and chemical grout injection into surrounding soil when slurry pipejacking method is used. Geotech. Geol. Eng., 24(1): 57 77. [8] S. Zhou, Y. Wang, X. Huang, 2009. Experimental study on the effect of injecting slurry inside a jacking pipe tunnel in silt stratum. Tunn. Undergr. Space Technol., 24(4): 466 471. [9] M. Barla, M. Camusso, S. Aiassa, 2006. Analysis of jacking forces during microtunnelling in limestone. Tunn. Undergr. Space Technol., 21(6): 668 683. [10] C.S. Choo, D.E.L. Ong, 2015. Evaluation of pipe-jacking forces based on direct shear testing of reconstituted tunneling rock spoils. J. Geotech. Geoenviron. Eng., 141(10): 04015044. [11] J. Yen, K. Shou, 2015. Numerical simulation for the estimation the jacking force of pipe jacking. Tunn. Undergr. Space Technol., 49: 218 229. [12] A.I. Sofianos, P. Loukas, C. Chantzakos, 2004. Pipe jacking a sewer under Athens. Tunn. Undergr. Space Technol., 19(2): 193-203. [13] H.J. Liao, M. Cheng, 1996. Construction of a piperoofed underpass below groundwater table. Proc. Inst. Civil Eng.-Geotech. Eng., 119(4): 202-210. [14] S.L. Shen, Q.L. Cui, C.E. Ho, et al., 2016. Ground response to multiple parallel microtunneling operations in cemented silty clay and sand. J. Geotech. Geoenviron. Eng., 142(5): 04016001. [15] L. Zhen, J.J. Chen, P. Qiao, et al., 2014. Analysis and remedial treatment of a steel pipe-jacking accident in complex underground environment. Eng. Struct., 59(2): 210-219.