Through the field inspection, this study investigated the performance of a deep foundation pit supported by suspended piles in soil and rock strata for a subway station in Qingdao Metro Line 3 in China. A large number of site-measured data are analyzed to investigate the settlement of ground surface and pile top, the horizontal displacement of pile and soil at different depths, and the relations between pile displacement and surface settlement under different construction stages. The deformation mechanism and the various influencing factors are discussed. Results showed that the blasting excavation of rock stratum has a great disturbance on the surface settlement outside the pit. The construction of the upper steel pipe support can effectively reduce the influence of disturbance, and the application of lock bolt support with shotcrete below the soil-rock interface can enable the surface settlement rate to be stable. When the foundation bottom reinforced concrete is completed, the ground surface settlement at different measuring points stabilizes in the range of 7~9mm. At the blasting excavation site, the maximum ground surface settlement accounts for 0.051% of the excavation depth. The ratio of maximum pile final lateral displacement to the final ground surface settlement is 1.43. The maximum ground surface settlement accounts for 0.058% of the excavation depth. The ratio of maximum horizontal displacement of soil to the final ground surface settlement is 0.7. Besides, the excavation of the upper soil layers of the foundation pit will result in the soil unloading and sublayer rebound, thus driving the uplift of the pile. The excavation of the lower rock layer influences the overall stability of the bored pile, and the construction of the steel pipe support and the anchor cable can effectively offset this effect. Although the horizontal displacement value is about 6 mm, it still cannot be ignored when compared with the overall lateral shift. When the bottom concrete slab is built, the maximum lateral displacement of the pile is located near the soil-rock interface.
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The authors gratefully acknowledge the financial supports from the National Natural Science Foundation of China (Grant Nos. 51978315 and 41402251) and the Natural Science Foundation of Jiangsu Province (Grant No. BK20180934). The opinions, findings, conclusions, or recommendations expressed herein are those of the authors and do not necessarily represent the views of the sponsors.
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The authors declare that they have no competing interests.
Responsible Editor: Zeynal Abiddin Erguler
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Shen, Ys., Yin, J., Zhu, DS. et al. Performance of a deep foundation pit supported by suspended piles in soil and rock strata: a case study. Arab J Geosci 14, 2211 (2021). https://doi.org/10.1007/s12517-021-08606-x
- Suspended pile
- Soil and rock strata
- Foundation pit