This study proposed a new restricted zone of the existing tunnel in soft soil that considered the scale of adjacent excavation, the characteristics of tunnel movement, and the settlement influence zone. The rationale was that existing restricted zones did not follow the characteristics of tunnel movement due to an excavation because they only related to the position, diameter, and depth of the tunnel. The time-dependent deformation for a typical excavation in soft clay was evaluated using the finite element analysis. During excavation, deformations normally increase with time, both in the soil excavation time and the elapsed time between excavation stages. The increase may be due to consolidation and/or creep but the mechanism has never been studied comprehensively before. Compared to the measurement, the soft soil creep model could simulate the time-dependent wall deflection and maximum ground settlement properly. Creep had a significant contribution to increasing the wall deflection while consolidation had little effect. Creep also caused a significant increase in the ground settlement both in excavation stages and elapsed times while consolidation caused the ground settlement to rebound slightly during elapsed times. Soil movements in the undrained analysis and the time-dependent analysis had a similar influence zone pattern. Therefore, the characteristics of tunnel movement were examined using the finite element analysis only in the undrained analysis. The proposed restricted zone was within the primary influence zone and for the excavation depth larger than 0.4 times the tunnel depth. If necessary, it could be divided into two zones, namely zone I and II. The zones boundary was on 0.6 times the primary influence zone and for the excavation depth 0.6 times the tunnel depth. The new excavation in zone I or II could cause the tunnel subjected to a high or medium risk of damage, respectively. It was suggested both zones required a tunnel movement evaluation and appropriate improvement measures if necessary. The use of a relatively advanced analysis technique, such as three-dimensional finite element analysis, and more intensive field monitoring were also suggested for excavations in zone I.

This study proposed a new restricted zone of the existing tunnel in soft soil that considered the scale of adjacent excavation, the characteristics of tunnel movement, and the settlement influence zone. The rationale was that existing restricted zones did not follow the characteristics of tunnel movement due to an excavation because they only related to the position, diameter, and depth of the tunnel. The time-dependent deformation for a typical excavation in soft clay was evaluated using the finite element analysis. During excavation, deformations normally increase with time, both in the soil excavation time and the elapsed time between excavation stages. The increase may be due to consolidation and/or creep but the mechanism has never been studied comprehensively before. Compared to the measurement, the soft soil creep model could simulate the time-dependent wall deflection and maximum ground settlement properly. Creep had a significant contribution to increasing the wall deflection while consolidation had little effect. Creep also caused a significant increase in the ground settlement both in excavation stages and elapsed times while consolidation caused the ground settlement to rebound slightly during elapsed times. Soil movements in the undrained analysis and the time-dependent analysis had a similar influence zone pattern. Therefore, the characteristics of tunnel movement were examined using the finite element analysis only in the undrained analysis. The proposed restricted zone was within the primary influence zone and for the excavation depth larger than 0.4 times the tunnel depth. If necessary, it could be divided into two zones, namely zone I and II. The zones boundary was on 0.6 times the primary influence zone and for the excavation depth 0.6 times the tunnel depth. The new excavation in zone I or II could cause the tunnel subjected to a high or medium risk of damage, respectively. It was suggested both zones required a tunnel movement evaluation and appropriate improvement measures if necessary. The use of a relatively advanced analysis technique, such as three-dimensional finite element analysis, and more intensive field monitoring were also suggested for excavations in zone I.

Benz, T., 2007. Small-Strain Stiffness of Soils and Its Numerical Consequences. Ph.D. Thesis. Universitat Stuttgart. https://doi.org/10.1097/mpg.0000000000000537
Bertoldo, F., Callisto, L., 2016. Effect of consolidation on the behaviour of excavations in fine-grained soils. Procedia Engineering. 158, 344–349. https://doi.org/10.1016/j.proeng.2016.08.453
Brinkgreve, R.B.J., Bakker, J.K., Bonnier, P.G., 2006. The relevance of small-strain soil stiffness in numerical simulation of excavation and tunnelling projects, in: Schweiger, H. (Ed.), Numerical Methods in Geotechnical Engineering. Taylor & Francis, 133–139. https://doi.org/10.1201/9781439833766.ch19
Broere, W., Brinkgreve, R.B.J., 2002. Phased simulation of a tunnel boring process in soft soil. Numerical Methods in Geotechnical Engineering. Presses de l’ENPC/LCPC. 529–536.
Chang, C.T., Sun, C.W., Duann, S.W., Hwang, R.N., 2001. Response of a Taipei Rapid Transit System (TRTS) tunnel to adjacent excavation. Tunnelling and Underground Space Technology. 16, 151–158. https://doi.org/10.1016/S0886-7798(01)00049-9
Chen, R., Meng, F., Li, Z., Ye, Y., Ye, J., 2016. Investigation of response of metro tunnels due to adjacent large excavation and protective measures in soft soils. Tunnelling and Underground Space Technology. 58. https://doi.org/10.1016/j.tust.2016.06.002
Clough, G.W., O’Rourke, T.D., 1990. Construction induced movements of insitu walls. Design and Performance of Earth Retaining Structure. 439–470.
Degago, S.A., Grimstad, G., 2016. Evaluation of soil parameters for creep calculations of field cases, in: Proceedings of the 17th Nordic Geotechnical Meeting.
Devriendt, M., Doughty, L., Morrison, P., Pillai, A., 2010. Displacement of tunnels from a basement excavation in London. Proceedings of the Institution of Civil Engineers - Geotechnical Engineering. 163, 131–145. https://doi.org/10.1680/geng.2010.163.3.131
Finno, R.J., Harahap, I.S., 1992. Finite element analyses of HDR-4 excavation. Journal of Geotechnical Engineering. 117, 1590–1609.
Hsieh, P.G., Ou, C.Y., 2018. Mechanism of buttress walls in restraining the wall deflection caused by deep excavation. Tunnelling and Underground Space Technology. 82, 542–553. https://doi.org/10.1016/j.tust.2018.09.004
Hu, Z.F., Yue, Z.Q., Zhou, J., Tham, L.G., 2003. Design and construction of a deep excavation in soft soils adjacent to the Shanghai Metro tunnels. Cannadian Geotechnical Journal. 948, 933–948. https://doi.org/10.1139/T03-041
Huang, X., Schweiger, H.F., Huang, H., 2011. Influence of deep excavations on nearby existing tunnels. International Journal of Geomechanics. 13, 170–180. https://doi.org/10.1061/(asce)gm.1943-5622.0000188

Hwang, R., Duann, S.W., Cheng, K.H., Chen, C.H., 2011. Damages to metro tunnels due to adjacent excavations, in: Proceeding of TC302 Symposium Osaka 2011, International Symposium on Backwards Problem in Geotechnical Engineering and Monitoring of Geo-Construction. Osaka. 83–88.
Hwang, R.N., Moh, Z.C., Wang, C.H., 2007. Toe movements of diaphragm walls and correction of inclinometer readings. Journal of GeoEngineering. 2, 61–71. https://doi.org/10.6310/jog.2007.2(2).3
Ignat, R., Baker, S., Larsson, S., Liedberg, S., 2015. Two- and three-dimensional analyses of excavation support with rows of dry deep mixing columns. Compututers and Geotechnics. 66, 16–30. https://doi.org/10.1016/j.compgeo.2015.01.011
Jaky, J., 1944. The coefficient of earth pressure at rest. Journal of the Society of Hungarian Architecs and Engineers. (in Hungarian) 8, 355–358.
Johansson, E., Sandeman, E., 2014. Modelling of a Deep Excavation in Soft Clay, A Comparison of Different Calculation Methods to In-Situ Measurements. M.Sc. thesis. Chalmers University of Technology.
Juang, C.H., Schuster, M., Ou, C.-Y., Phoon, K.K., 2010. Fully probabilistic framework for evaluating excavation-induced damage potential of adjacent buildings. Journal of Geotechnical and Geoenvironmental Engineering. 137, 130–139. https://doi.org/10.1061/(asce)gt.1943-5606.0000413
Khoiri, M., Ou, C.Y., 2013. Evaluation of deformation parameter for deep excavation in sand through case histories. Compututers and Geotechnics. 47, 57–67. https://doi.org/10.1016/j.compgeo.2012.06.009
Kung, G.T.C., 2009. Comparison of excavation-induced wall deflection using top-down and bottom-up construction methods in Taipei silty clay. Compututers and Geotechnics. 36, 373–385. https://doi.org/10.1016/j.compgeo.2008.07.001
Lee, S.H., 1992. Analysis of the multicollinearity of regression equations of shear wave velocities. Japan Society of Soil Mechanics and Foundation Engineering. 32, 205–214.
Likitlersuang, S., Chheng, C., Keawsawasvong, S., 2019. Structural modelling in finite element analysis of deep excavation. Journal of GeoEngineering. 14, 121–128. https://doi.org/http://dx.doi.org/10.6310%2fjog.201909_14(3).1
Lim, A., Ou, C.Y., 2017. Stress paths in deep excavations under undrained conditions and its influence on deformation analysis. Tunnelling and Underground Space Technology. 63, 118–132. https://doi.org/10.1016/j.tust.2016.12.013
Lim, A., Ou, C.Y., Hsieh, P.G., 2010. Evaluation of clay constitutive models for analysis of deep excavation under undrained conditions. Journal of GeoEngineering. 5, 9–20. https://doi.org/10.6310/jog.2010.5(1).2
Liu, G.B., Huang, P., Shi, J.W., Ng, C.W.W., 2016. Performance of a deep excavation and its effect on adjacent tunnels in Shanghai soft clay. Journal of Performance of Constructed Facilities. 30, 04016041. https://doi.org/10.1061/(asce)cf.1943-5509.0000891
Mehli, M., 2015. Creep analysis of Onsøy test fill. Creep of Geomaterials. Trondheim.
Moh, Z.-C., Ou, C.D., 1979. Engineering characteristics of the Taipei silt, in: Sixth Asian Regional Conference on Soil Mechanics and Foundation Engineering, Singapore, Vol. 1. Singapore. 155–158.
Möller, S.C., Vermeer, P.A., 2008. On numerical simulation of tunnel installation. Tunnelling and Underground Space Technology. 23, 461–475. https://doi.org/10.1016/j.tust.2007.08.004
Mu, L., Huang, M., 2016. Small strain based method for predicting three-dimensional soil displacements induced by braced excavation. Tunnelling and Underground Space Technology. 52, 12–22. https://doi.org/10.1016/j.tust.2015.11.001
Neher, H.P., Wehnert, M., Bonnier, P.G., 2001. An evaluation of soft soil models based on trial embankments. Computer Methods and Advances in Geomechanics. 373–378.
Ou, C.Y., 2006. Deep Excavation Theory and Practice, Taylor & Francis. Taylor & Francis, Taipei.
Ou, C.Y., Hsieh, P.G., 2011. A simplified method for predicting ground settlement profiles induced by excavation in soft clay. Compututers and Geotechnics. 38, 987–997. https://doi.org/10.1016/j.compgeo.2011.06.008
Ou, C.Y., Lai, C.H., 1994. Finite-element analysis of deep excavation in layered sandy and clayey soil deposits. Cannadian Geotechnical Journal. 31, 204–214.
Ou, C.Y., Liao, J.T., Cheng, W.L., 2000. Building response and ground movements induced by a deep excavation. Cannadian Geotechnical Journal. https://doi.org/10.1680/geot.2000.50.3.209
Ou, C.Y., Liao, J.T., Lin, H.D., 1998. Performance of diaphragm wall constructed using top-down method. Journal of Geotechnical and Geoenvironmental Engineering. 124, 798–808.
Schanz, T., Vermeer, P.A., Bonnier, P.G., 1999. The hardening soil model: formulation and verification, in: Beyond 2000 in Computational Geotechnics – 10 Years of PLAXIS. 104–144.
Schuster, M., Kung, G.T.-C., Juang, C.H., Hashash, Y.M.A., 2009. Simplified model for evaluating damage potential of buildings adjacent to a braced excavation. Journal of Geotechnical and Geoenvironmental Engineering. 135, 1823–1835. https://doi.org/10.1061/(ASCE)GT.1943-5606.0000161
Shi, J., 2015. Investigation of Three-Dimensional Tunnel Responses due to Basement Excavation. Department of Civil and Environmental Engineering, Ph.D thesis. Hong Kong University of Science and Technology, Hong Kong.
Singapore Land Transport Authority, 2004. Code of Practice for Railway Protection, October. ed. Development and Building Control Department, Singapore.
Taipei Mass Rapid Transportation Authority, 2003. Regulations for Banning and Restricting Constructions along the Routes of Rapid Transit Systems.
Teng, F.C., Ou, C.Y., Hsieh, P.G., 2014. Measurements and numerical simulations of inherent stiffness anisotropy in soft Taipei clay. Journal of Geotechnical and Geoenvironmental Engineering. 140, 237–250. https://doi.org/10.1061/(asce)gt.1943-5606.0001010
Transport for New South Wales, 2015. Development Near Rail Tunnels, Version 1. ed. Transport for NSW.
Vermeer, P.A., Neher, H.P., 1999. A soft soil model that accounts for creep. Beyond 2000 in Computational Geotechnics – 10 Years of PLAXIS. 249–261. https://doi.org/10.1201/9781315138206-24
Wang, J.H., Xu, Z.H., Wang, W.D., 2010. Wall and ground movements due to deep excavations in Shanghai soft soils. Journal of Geotechnical and Geoenvironmental Engineering. 136, 985–994. https://doi.org/10.1061/_ASCE_GT.1943-5606.0000299
Washington Metropolitan Area Transit Authority, 2015. Adjacent Construction Project Manual, Revision 5. ed. Office of Joint Development & Adjacent Construction, Washington.
Waterman, D., 2009. CG1-7 Geometry and mesh selection in Plaxis 1–18.
Waterman, D., Broere, W., 2004. Plaxis tutorial, Practical application of the soft soil creep model. Plaxis Bulletin. 14–15.
Wheeler, S.J., Näätänen, A., Karstunen, M., Lojander, M., 2003. An anisotropic elastoplastic model for soft clays. Cannadian Geotechnical Journal. 40, 403–418. https://doi.org/10.1139/t02-119
Whittle, A.J., Corral, G., Jen, L.C., Rawnsley, R.P., 2014. Prediction and performance of deep excavations for Courthouse Station, Boston. Journal of Geotechnical and Geoenvironmental Engineering. 141, 04014123. https://doi.org/10.1061/(asce)gt.1943-5606.0001246
Woo, S.M., Moh, Z.C., 1990. Geotechnical characteristics of soils in the Taipei basin, in: 10th Southest Asian Geotechnical Conference. Taipei. 51–65.
Yao, A., Yang, X., Dong, L., 2012. Numerical analysis of the influence of isolation piles in metro tunnel construction of adjacent buildings. Procedia Earth and Planetary Science. 5, 150–154. https://doi.org/10.1016/j.proeps.2012.01.026
Zheng, G., Du, Y., Cheng, X., Diao, Y., Deng, X., Wang, F., 2017a. Characteristics and prediction methods for tunnel deformations induced by excavations. Geomechanics and Engineering. 12, 361–397. https://doi.org/10.12989/gae.2017.12.3.361
Zheng, G., Yang, X., Zhou, H., Du, Y., Sun, J., Yu, X., 2017b. A simplified prediction method for evaluating tunnel displacement induced by laterally adjacent excavations. Computers and Geotechnics. 95, 119–128. https://doi.org/10.1016/j.compgeo.2017.10.006