Rock and Soil Mechanics ›› 2020, Vol. 41 ›› Issue (S1): 195-207.doi: 10.16285/j.rsm.2019.0904

• Geotechnical Engineering • Previous Articles     Next Articles

Deformation response of a tunnel under foundation pit unloading considering buried depth and shearing effect

XU Ri-qing1, 2, CHENG Kang1, 2, YING Hong-wei1, 2, 3, LIN Cun-gang4, 5, LIANG Rong-zhu6, FENG Su-yang1, 2   

  1. 1. Research Center of Coastal and Urban Geotechnical Engineering, Zhejiang University, Hangzhou, Zhejiang 310058, China; 2. Engineering Research Center of Urban Underground Development of Zhejiang Province, Hangzhou, Zhejiang 310058, China; 3. Institue of Geotechnical Engineering Science, Hohai University, Nanjing, Jiangsu 210098, China; 4. Norwegian Geotechnical Institute, Oslo 0806, Norway; 5. Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Tongji University, Shanghai 200092, China; 6. Faculty of Engineering, China University of Geosciences(Wuhan), Wuhan, Hubei 430074, China
  • Received:2019-05-19 Revised:2019-10-08 Online:2020-06-19 Published:2020-06-09
  • Supported by:
    This work was supported by the National Natural Science Foundation of China(41672264, 41702313, 41807262) and Key Research and Development Program of Zhejiang Province(2018C03G2010707).

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Abstract: Foundation pit unloading will create additional loads on the underlying existing tunnel. Based on the engineering practice, a semi-analytical solution considering the effect of foundation depth and tunnel shear effect is proposed to predict the longitudinal response of tunnel caused by the above excavation. A modified subgrade reaction coefficient considering different buried depth of tunnel is introduced, additional pressure induced by excavation is given based on the Mindin solution. By regarding the tunnel as a Timoshenko beam resting on the Pasternak foundation, the longitudinal deformations of the tunnel are analyzed. Compared with the three-dimensional finite element method and the measurements of the Jiusha river foundation pit crossing the No. 1 metro line in Hangzhou, the accuracy of the proposed method is verified. The effects of bending stiffness and shear stiffness on the response of the tunnel are systematically analyzed. The results suggest that the mechanical response of tunnels could be better analyzed with the Timoshenko beam model. Increasing bending stiffness can effectively reduce the displacement, moment and shear of the tunnel, but increase the distribution range of them. At the same time, the increase of bending stiffness will not affect the location of maximum positive bending moment and the location of maximum shear force but will make the location of the maximum negative bending moment move toward both ends of the tunnel. When the shear stiffness exceeds 20% of the bending stiffness, the displacement and the bending moment, as well as the shear force of the tunnel, is hardly affected by the shear stiffness. The conclusions can provide some theoretical support for similar projects.

Key words: depth effect, existing tunnel, unloading of foundation pit, Timoshenko beam, shearing effect

CLC Number: 

  • U452
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