Influence Of Excavation Method On The Bearing Behavior Of Asymmetric Gourd Shaped Underground Diaphragm Wall

In recent years,the use of underground diaphragm wall as supporting structure for foundation pit engineering is becoming more and more common.In order to adapt to the complex variability of the field environment and the limitation of the site conditions,the design of underground diaphragm wall has made a great breakthrough in the structure selection,from the conventional rectangular to circular to more complicated double circular or gourd-shaped.This linear-to-curve change trend makes the effect of the underground diaphragm wall structure on the spatial effect more and more significant,especially the gourd-shaped diaphragm wall,which is difficult to guarantee the uniformity and symmetry of the excavation during large and small circular excavation construction,resulting in the forces and deformation traits of gourd-shaped wall are different from rectangular,circular or double circular diaphragm wall.In this paper,the anchorage foundation pit of Dongting Lake Bridge is taken as the engineering background,and the gourd-shaped ground connection wall is taken as the research object,the key process of foundation pit construction control is studied.Through the calculation of two-dimensional elastic foundation beam and three-dimensional numerical simulation,the following work is mainly carried out:(1)For the current specification,only the calculation method of the circular ground wall is provided.This paper proposes a method to determine the equivalent elastic coefficient,which can simplify the double circular or gourd-shaped diaphragm wall into the circular diaphragm wall,and then calculate according to the current code.(2)Taking the cross section of the unit wall as the research object,and considering it as the elastic foundation beam for two-dimensional analysis and calculation,the curve of the displacement and bending moment of the wall along the depth direction is obtained,and compared with the measured results,it was found that the two were basically consistent,and the rationality of the calculation results was verified.(3)In combination with the practical situation of project,by using the finite element software Flac3D to anchorage foundation pit to establish three-dimensional model,several different excavation processes are simulated respectively,namely uniform excavation,large and small circle excavation,core soil excavation reserved and local excavation,it is concluded that different excavation methods will definitely affect the diaphragm wall enclosure system.Compared with the result calculated by detailed structure of the characteristics of stressed deformation of such as the horizontal displacement of the wall,the hoop stress and the surrounding soil vertical direction displacement etc,although there are some differences in the numerical values,the general trend of change and the related laws are the same.The horizontal displacement and circumferential stress along the wall depth were distributed parabolically,and the maximum value was approximately 28m away from the top of the wall;the settlement of the soil around the earth wall was concave along the direction away from the foundation pit,which confirms the feasibility of three-dimensional numerical simulation analysis.At the same time,it is found that only the excavation method of reserved core soil showed certain advantages in the specific numerical results,and the other asymmetrical asymmetric excavation would cause a little adverse effect on the underground diaphragm wall.