Performance and environmental impacts of deep foundation excavation in soft soils: A field and modeling-based case study in Nanjing, China

Abstract

This paper focuses on the performance of a braced deep excavation in soft soil based on field monitoring and numerical modeling. Laboratory tests were conducted to determine the soil parameters used in the modified Cam-Clay (MCC) model. Intelligent field monitoring means were adopted and a three-dimensional model was established. Spatial and temporal effects induced by the excavation are investigated for the deep-large foundation pit in soft soil. Deformation characteristics of the enclosure structure and the surrounding environment throughout the excavation process are presented. The behaviors of diaphragm walls, columns, the maximum wall deflection rate, ground surface settlement, and utility pipelines were focused on and investigated during the whole excavation process. Besides, the axial forces of the internal supports are analyzed. Based on the measured and simulated data, the following main conclusions were obtained: the numerical simulation results are in good agreement with the measured values, which proves the accuracy of the model parameters; the wall and the ground surface showed the maximum displacement increment at stage 9, which was a coupled product of the “creep effect” of the soft soil in Nanjing, China and the “depth effect” of the excavation; as the excavation progressed, the ground settlement changed from a “rising” to a “spoon-shaped” trend, δ_vm was measured between δ_vm = 0.0686%H and δ_vm = 0.1488%H; the rebound deformation curve of the pit bottom was corrugated, and the depth of disturbance of the pit bottom after the completion of soil unloading was 2-3 times the excavation depth; the closer the pipeline is to the corner of the pit, the less the excavation process will affect the settlement of the pipeline and the less the obvious pit corner effect will occur; the support strength of the buttress and the longest corner brace should be strengthened during the actual construction process to ensure the stability of the foundation deformation.

Keywords

Deep excavation / Modified Cam-Clay / Deformation characteristics / Creep effect / Corner effect

CRediT authorship contribution statement

Chenhe Ge: Writing - original draft, Visualization, Validation, Software, Investigation, Formal analysis, Data curation, Conceptualization. Meng Yang: Project administration, Methodology, Funding acquisition. Pengfei Li: Writing - review & editing, Supervision. Mingju Zhang: Funding acquisition, Conceptualization. Zhonghao Zhang: Visualization, Project administration, Funding acquisition.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

The authors gratefully acknowledge the financial support provided by Beijing Natural Science Foundation (Grant No. 8222005), the National Natural Science Foundation of China (Grant No. 51978018), and Science and Technology Funding Scheme for Three Companies of China Construction Bureau II (No. CSCEC2b3c-2021-K-65).

References

[1] Ahmed, K. S., Sharmin, J., & Ansary, M. A. (2023). Numerical investigation of tunneling induced surface movement: A case study of MRT line 1, Dhaka. Underground Space, 12, 116-136.

[2] Bhatkar, T., Barman, D., Mandal, A., & Usmani, A. (2017). Prediction of behavior of a deep excavation in soft soil: A case study. International Journal of Geotechnical Engineering, 11(1), 10-19.

[3] Chen, B., Sun, D. A., & Lyu, H. B. (2013). Experimental study of compression behavior of marine soft clays. Rock and Soil Mechanics, 34(2), 381-388.

[4] Chen, H., Li, J., & Li, L. (2018). Performance of a zoned excavation by bottom-up technique in Shanghai soft soils. Journal of Geotechnical and Geoenvironmental Engineering, 144(11), 05018003.

[5] Chen, R. P., Meng, F. Y., Li, Z. C., Ye, Y. H., & Ye, J. N. (2016). Investigation of response of metro tunnels due to adjacent large excavation and protective measures in soft soils. Tunnelling and Underground Space Technology, 58, 224-235.

[6] Cheng, K., Xu, R. Q., Ying, H. W., Gan, X. L., Zhang, L. S., & Liu, S. J. (2021). Observed performance of a 30.2 m deep-large basement excavation in Hangzhou soft clay. Tunnelling and Underground Space Technology, 111, 103872.

[7] Clough, G. W., & O’Rourke, T. D. (1990). Construction induced movements of in situ walls. In Proceedings of the 1990 ASCE Geotechnical Specialty Conference on Design and Performance of Earth Retaining Structures (pp.439-470). New York: ASCE.

[8] Gao, Q., & Yu, W. L. (2014). Analysis on influence of excavation of foundation pit of municipal tunnel on existing underlying shield-bored metro tunnel. Tunnel Construction, 34(4), 311-317 (in Chinese).

[9] Goh, A., Zhang, F., Zhang, W. G., Zhang, Y. M., & Liu, H. L. (2017). A simple estimation model for 3D braced excavation wall deflection. Computers and Geotechnics, 83, 106-113.

[10] Goh, A., Zhang, W. G., & Wong, K. S. (2019). Deterministic and reliability analysis of basal heave stability for excavation in spatial variable soils. Computers and Geotechnics, 108, 152-160.

[11] Gu, Z. X., Lou, W. Z., Cheng, Y. B., Li, Y. W., Song, D. W., & Song, Y. (2021). Analysis on deformation behaviors of diaphragm walls of an extra-long special-shaped deep foundation pit in Nanjing soft soil area. Modern Tunnelling Technology, 58(1), 182-189 (in Chinese).

[12] Hashash, Y. M. A., & Whittle, A. J. (1996). Ground movement prediction for deep excavations in soft caly. Journal of Geotechnical Engineering, 122(6), 474-486.

[13] Hou, Y. J., Zhou, M. Z., Zhang, D. L., Fang, Q., Sun, Z. Y., & Tian, Y. H. (2022). Analysis of four shield-driven tunnels with complex spatial relations in a clay stratum. Tunnelling and Underground Space Technology, 124, 104478.

[14] Hou, Y. M., Wang, J. H., & Zhang, L. L. (2007). Three-dimensional numerical modeling of a deep excavation adjacent to shanghai metro tunnels. In Proceedings of the 7th International Conference on Computational Science - ICCS 2007 (pp. 1164-1171).

[15] Li, F. M., Chen, G. X., & Liu, X. Z. (2018). Deformation characteristics of suspended curtain deep foundation pit of metro lines. Chinese Journal of Geotechnical Engineering, 40(12), 2182-2190 (in Chinese).

[16] Liu, Y., Xiang, B. H., & Fu, M. F. (2019). Observed performance of a large-scale deep triangular excavation in Shanghai soft clays. Geotechnical and Geological Engineering, 37(4), 2791-2809.

[17] Long, M. (2001). Database for retaining wall and ground movements due to deep excavations. Journal of Geotechnical and Geoenvironmental Engineering, 127(3), 203-224.

[18] Luo, Z., & Das, B. M. (2016). System probabilistic serviceability assessment of braced excavations in clays. International Journal of Geotechnical Engineering, 10(2), 135-144.

[19] Luo, Z., Li, Y. X., Zhou, S. H., & Di, H. G. (2018). Effects of vertical spatial variability on supported excavations in sands considering multiple geotechnical and structural failure modes. Computers and Geotechnics, 95, 16-29.

[20] Mana, A. I., & Clough, G. W. (1981). Prediction of movements for braced cuts in clay. Journal of Geotechnical Engineering Division, 107(6), 759-777.

[21] Ministry of Housing and Urban-Rural Development of the People’s Republic of China, & State, Administration for Market Regulation (2019). GB/T 50123—2019: Standard for Geotechnical Testing Method. Beijing, China: China Planning Press (in Chinese).

[22] Ng, C. W. W., Lu, H., & Peng, S. Y. (2013). Three-dimensional centrifuge modelling of the effects of twin tunnelling on an existing pile. Tunnelling and Underground Space Technology, 35, 189-199.

[23] Ou, C. Y., Hsieh, P. G., & Chiou, D. C. (1993). Characteristics of ground surface settlement during excavation. Canadian Geotechnical Journal, 30(5), 758-767.

[24] Potts, D., Axelsson, K., Grande, L., Schweiger, H., & Long, M. (2002). Guidelines for the use of advanced numerical analysis. London: Thomas Telford.

[25] Randolph, M. F., & Wroth, C. P. (1981). Application of the failure state in undrained simple shear to the shaft capacity of driven piles. Géotechnique, 31(1), 143-157.

[26] Roscoe, K. H., & Burland, J. B. (1968). On the generalised stress-strain behaviour of wet clay. In Engineering Plasticity (pp. 535-609). New York: Cambridge University Press.

[27] Roscoe, K. H., Schofield, A. N., & Thurairajah, A. (1963). Yielding of clays in states wetter than critical. Géotechnique, 13(3), 211-240.

[28] Sun, D. A., Chen, B., & Zhou, K. (2010). Experimental study of compression and shear deformation characteristics of remolded Shanghai soft clay. Rock and Soil Mechanics, 31(5), 1389-1394 (in Chinese).

[29] Tan, Y., Jiang, W. Z., Luo, W. J., Lu, Y., & Xu, C. J. (2018a). Longitudinal sliding event during excavation of Feng-Qi Station of Hangzhou Metro Line 1: Postfailure investigation. Journal of Performance of Constructed Facilities, 32(4), 04018039.

[30] Tan, Y., & Li, M. W. (2011). Measured performance of a 26 m deep topdown excavation in downtown Shanghai. Canadian Geotechnical Journal, 48(5), 704-719.

[31] Tan, Y., Li, X., Kang, Z. J., Liu, J. X., & Zhu, Y. B. (2015). Zoned excavation of an oversized pit close to an existing metro line in stiff clay: Case study. Journal of Performance of Constructed Facilities, 29 (6), 04014158.

[32] Tan, Y., Lu, Y., Xu, C. J., & Wang, D. L. (2018b). Investigation on performance of a large circular pit-in-pit excavation in clay-gravelcobble mixed strata. Tunnelling and Underground Space Technology, 79, 356-374.

[33] Tan, Y., Lu, Y., & Wang, D. L. (2018c). Deep excavation of the Gate of the Orient in Suzhou stiff clay: Composite earth-retaining systems and dewatering plans. Journal of Geotechnical and Geoenvironmental Engineering, 144(3), 05017009.

[34] Tan, Y., & Wang, D. (2013a). Characteristics of a large-scale deep foundation pit excavated by the central-island technique in Shanghai soft clay. I: Bottom-up construction of the central cylindrical shaft. Journal of Geotechnical and Geoenvironmental Engineering, 139(11), 1875-1893.

[35] Tan, Y., & Wang, D. (2013b). Characteristics of a large-scale deep foundation pit excavated by the central-island technique in Shanghai soft clay. II: Top-down construction of the peripheral rectangular pit. Journal of Geotechnical and Geoenvironmental Engineering, 139(11), 1894-1910.

[36] Tan, Y., Zhu, H. H., Peng, F. L., Karlsrud, K., & Wei, B. (2017). Characterization of semi-top-down excavation for subway station in Shanghai soft ground. Tunnelling and Underground Space Technology, 68, 244-261.

[37] 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(7), 985-994.

[38] Wang, W. D., Xu, Z. H., & Wang, J. H. (2011). Statistical analysis of characteristics of ground surface settlement caused by deep excavations in Shanghai soft soils. Chinese Journal of Geotechnical Engineering, 33(11), 1659-1666 (in Chinese).

[39] Wang, C.B., Ding, W.Q., & Qiao, Y.F. (2014). Development and application of constitutive model of hardened soil in FLAC3D. Chinese Journal of Rock Mechanics and Engineering, 33(1), 199-208.

[40] Xu, Z. H., & Wang, W. D. (2010). Selection of soil constitutive models for numerical analysis of deep excavations in close proximity to sensitive properties. Rock and Soil Mechanics, 31(1), 258-264, 326.

[41] Ying, H. W., & Yang, Y. W. (2011). Characteristics of a large and deep soft clay excavation in Hangzhou. Chinese Journal of Geotechnical Engineering, 33(12), 1838-1846 (in Chinese).

[42] Yuan, K. K., Chen, W. Z., Yu, H. D., Tan, X. J., Zhao, W. S., & Li, X. L. (2012). Modified Cam-Clay model considering cohesion and S-D effect and its numerical implementation. Chinese Journal of Rock Mechanics and Engineering, 31(8), 1574-1579 (in Chinese).

[43] Zhang, M. J., Ge, C. H., Li, P. F., Wan, W. Z., & Yang, M. (2024). Bearing capacities and failure behaviors of bolt fasten wedge (BFW) active joints used in prestressed internal supports. Tunnelling and Underground Space Technology, 143, 105438.

[44] Zhang, M. J., Xie, Z. T., & Li, P. F. (2020). Experimental and numeric investigation on the bearing capacity of disconnectable coupling (DC) joints for prestressed internal bracing in subway excavations. Tunnelling and Underground Space Technology, 104, 103501.

[45] Zhang, M. J., Xie, Z. T., & Li, P. F. (2022). Bearing capacity and failure behavior of disconnectable coupling joint with double row wedges (DCJD) used in the prestressed internal bracing. Underground Space, 7, 498-513.

[46] Zhang, W. G., Goh, A. T. C., & Xuan, F. (2015). A simple prediction model for wall deflection caused by braced excavation in clays. Computers and Geotechnics, 63, 67-72.

[47] Zhang, W. G., Li, Y. Q., Goh, A. T. C., & Zhang, R. H. (2020). Numerical study of the performance of jet grout piles for braced excavations in soft clay. Computers and Geotechnics, 124, 103631.

[48] Zhang, W. G., Zhang, Y. M., & Goh, A. T. C. (2017). Multivariate adaptive regression splines for inverse analysis of soil and wall properties in braced excavation. Tunnelling and Underground Space Technology, 64, 24-33.

[49] Zhang, X. L., Lan, H., Zhao, X. H., Xu, C. S., & Jia, K. M. (2024). Study on different reinforcement methods of inclined liquefiable site. Soil Dynamics and Earthquake Engineering, 176, 108342.

[50] Zhao, C. G., & Liu, Y. (2021). Critical state soil mechanics. Beijing: Beijing Jiaotong University Press.

[51] Zheng, G., Yang, X. Y., Zhou, H. Z., Du, Y. M., Sun, J. Y., & Yu, X. X. (2018). A simplified prediction method for evaluating tunnel displacement induced by laterally adjacent excavations. Computers and Geotechnics, 95, 119-128.