<<
[an error occurred while processing this directive] | [an error occurred while processing this directive] >>
Measurement and Numerical Simulation of Deformation of the Cofferdam with Geotextile Sand-Bags in the Zhoutouzui Immersed Tunnel Project
(1 Guangzhou Municipal Engineering Design & Research Institute, Guangzhou 510060; 2 School of Civil Engineering and Transportation, South China University of Technology, Guangzhou 510641)
Abstract The deformation development law of cofferdam with geotextile sand bags is explored by field measure? ment based on the construction process of the Zhoutouzui immersed tunnel in Guangzhou. Based on the existing research results, the deformation saltation mechanism is determined, the main control indexes for design and construction of the cofferdam are proposed and the rationality is verified by a refined FEM calculation. The results show that:1) the response law and degree of deformation are different at different positions during the construction of the geotextile sand bag cofferdam, with saltation of the local displacement and a larger influence in the vertical direction than in the horizontal direction; 2) the main reason for deformation saltation of the cofferdam is that the buoyant unit weight turns into a dry unit weight due to the dewatering of the geotextile sand bag, which increases the overlying pressure of the upper geotextile bag to the lower ones and flattens them and causes large deformation; and 3) the foundation soil experiences three phases of vertical pressure consolidation, lateral extrusion and local sliding, which cause the maximum vertical and horizontal displacements to occur at the top and foot of the cofferdam. The numerical calculation results show that: 1) it is stable since no sliding failure occurs at the cofferdam and no cut-through plastic zone is formed, which is consistent with the results deduced by theoretical analysis; 2) the stack height of cofferdam should be taken as the control index; and 3) there are some weak points in using the displacement limit value for traditional foundation pit support structure to judge the mechanical state of the cofferdam with geotextile sand bags, and the design for the slope ratio of the cofferdam should fully consider the reinforcement effect of the geotextile sand bags.
Abstract：
The deformation development law of cofferdam with geotextile sand bags is explored by field measure? ment based on the construction process of the Zhoutouzui immersed tunnel in Guangzhou. Based on the existing research results, the deformation saltation mechanism is determined, the main control indexes for design and construction of the cofferdam are proposed and the rationality is verified by a refined FEM calculation. The results show that:1) the response law and degree of deformation are different at different positions during the construction of the geotextile sand bag cofferdam, with saltation of the local displacement and a larger influence in the vertical direction than in the horizontal direction; 2) the main reason for deformation saltation of the cofferdam is that the buoyant unit weight turns into a dry unit weight due to the dewatering of the geotextile sand bag, which increases the overlying pressure of the upper geotextile bag to the lower ones and flattens them and causes large deformation; and 3) the foundation soil experiences three phases of vertical pressure consolidation, lateral extrusion and local sliding, which cause the maximum vertical and horizontal displacements to occur at the top and foot of the cofferdam. The numerical calculation results show that: 1) it is stable since no sliding failure occurs at the cofferdam and no cut-through plastic zone is formed, which is consistent with the results deduced by theoretical analysis; 2) the stack height of cofferdam should be taken as the control index; and 3) there are some weak points in using the displacement limit value for traditional foundation pit support structure to judge the mechanical state of the cofferdam with geotextile sand bags, and the design for the slope ratio of the cofferdam should fully consider the reinforcement effect of the geotextile sand bags.
.Measurement and Numerical Simulation of Deformation of the Cofferdam with Geotextile Sand-Bags in the Zhoutouzui Immersed Tunnel Project[J] MODERN TUNNELLING TECHNOLOGY, 2017,V54(6): 180-186
2017, Vol. 54 