| Shallow buried Karst is often encountered in underground engineering construction in Karst development area.In the construction of underground tunnels,it is very easy to occur large-scale mud,water inrush,collapse and other geological disasters,especially in the multi-layer Karst areas,Karst induced geological disasters are more frequent.These disasters will seriously jeopardize the construction safety,delay the construction period,increase the investment of the project,and will affect the operation safety after the completion of the tunnel.It is an important research topic to identify Karst development rules and analyze the influence of Karst on tunnel stability by proper detection technology.In this paper,based on the Karst tunnel of Wuxi metro,combined with the topography,geomorphology,geological conditions,lithology and water circulation of the Wuxi metro engineering construction area,the development mechanism of Karst in the field area,especially the shallow buried bead like Karst,should be analyzed,and the cross hole CT detection technique should be used for the field formation.And the development characteristics of karst are computed by tomography to give out the rule of underground Karst space development.At the same time,the stability of tunnel surrounding rock in Karst area is analyzed by semi analytical solution and numerical simulation.This study provides a scientific basis for the design and construction of tunnels in this section.The main contents and results of this paper are as follows:(1)Through engineering geology survey and engineering investigation data analysis,the engineering geological conditions such as stratum lithology,geological structure and groundwater characteristics have been identified.Through the comprehensive analysis of the environmental and geological conditions in the field,the Karst development mechanism in the field area is systematically understood.The Karst is the basic condition for karst development.The field area adjacent to Huishan causes great relief,the groundwater is more active,and the Karst development is beneficial to the karst development,the fracture structure and the ground layer control the karst development.(2)The size,shape and distribution of karst development in the field area are detected by the cross hole CT detection technique.The results show that the Karst is mainly distributed within two buried depths of 20?24m and 27?30m below ground.The maximum diameter is 3M.The Karst morphology of the field area includes single cave,horizontal bead like cave and vertical bead like cave.(3)By using the complex function method and the Schwarz's alternation method,the semi analytical solution formula of the stress of the surrounding rock under the interaction of shallow buried Karst and loose tunnel surrounding rock was derived,and the variation law diagram of the vertical stress with the net distance was given.The calculation results showed that the maximum vertical stress appears in the arch of the tunnel.At the same time,the change of plastic zone of surrounding rock under 6 working conditions was analyzed,and the stability of surrounding rock of tunnel was evaluated.(4)The analysis model of Karst foundation was established by FLAC3D numerical calculation software,and the influence of Karst caves on the stability of tunnel surrounding rock under four conditions,such as single Karst cave,karst cave above tunnel,and Karst cave under tunnel and underneath tunnel,was studied.According to stress and displacement cloud map,the foundation is stable with the existence of single karst cave.When the net spacing between the tunnel and the Karst cave is less than 3m,the surrounding rock will lose stability and cause damage. |
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