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Study on Deformation Mechanism of the Underlying Tunnel Caused by Excavation of the Deep Foundation Pit in Sandy Stratum
(1 Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering, Hohai University, Nanjing 210098;2 Geotechnical Research Institute, Hohai University, Nanjing 210098; 3 Construction Engineering Quality Center Laboratory of Zhenjiang New District, Zhenjiang 212132)
Abstract he stress release caused by excavation of a deep foundation pit may inevitably cause additional stress and deformation of the adjacent tunnel. In this paper, a three-dimensional finite element numerical analysis is performed to study the influence of the excavation size of the deep foundation pit and the stiffness of segment joint on three-dimensional deformation of the underlying tunnel. Then, the geotechnical centrifugal model test is used to verify the rationality of the finite element calculation model and relevant results. Below the centerline of the foundation pit, the uplift and lateral bending strain of the tunnel increase along with the increase of the excavation length of the foundation pit. When the excavation length of the foundation pit is 9 times of its excavation depth, the uplift and transverse bending strain of the tunnel reach the peak value while the longitudinal bending strain of the tunnel is almost close to zero. When the excavation length of the foundation pit is more than 9 times of the excavation depth, the foundation pit-soil-tunnel interaction could be simplified as a plane strain issue. If the three-dimensional effect of the short foundation pit is not considered, the plane strain simplification of the foundation pit-soil-tunnel would seriously lead to overestimate of the tunnel uplift and lateral bending strain. Along with the increase of the joint stiffness, the tunnel uplift gradually decreases, while the transverse and longitudinal bending strains of the tunnel increase. Therefore, if a discontinuous tunnel with joints is assumed as a continuous structure, the tunnel uplift might be greatly underestimated, while the bending strain might be largely overestimated.
Abstract：
he stress release caused by excavation of a deep foundation pit may inevitably cause additional stress and deformation of the adjacent tunnel. In this paper, a three-dimensional finite element numerical analysis is performed to study the influence of the excavation size of the deep foundation pit and the stiffness of segment joint on three-dimensional deformation of the underlying tunnel. Then, the geotechnical centrifugal model test is used to verify the rationality of the finite element calculation model and relevant results. Below the centerline of the foundation pit, the uplift and lateral bending strain of the tunnel increase along with the increase of the excavation length of the foundation pit. When the excavation length of the foundation pit is 9 times of its excavation depth, the uplift and transverse bending strain of the tunnel reach the peak value while the longitudinal bending strain of the tunnel is almost close to zero. When the excavation length of the foundation pit is more than 9 times of the excavation depth, the foundation pit-soil-tunnel interaction could be simplified as a plane strain issue. If the three-dimensional effect of the short foundation pit is not considered, the plane strain simplification of the foundation pit-soil-tunnel would seriously lead to overestimate of the tunnel uplift and lateral bending strain. Along with the increase of the joint stiffness, the tunnel uplift gradually decreases, while the transverse and longitudinal bending strains of the tunnel increase. Therefore, if a discontinuous tunnel with joints is assumed as a continuous structure, the tunnel uplift might be greatly underestimated, while the bending strain might be largely overestimated.
FAN Yanbo1,
2 CHEN Li3 SHI Jiangwei1,
2 DING Chu1 etc
.Study on Deformation Mechanism of the Underlying Tunnel Caused by Excavation of the Deep Foundation Pit in Sandy Stratum[J] MODERN TUNNELLING TECHNOLOGY, 2021,V58(2): 103-110
2021, Vol. 58 