| Tunnel lining is a structure that maintains the space required for vehicle operation,prevents weathering of surrounding rocks and blocks groundwater erosion.The tunnel lining is also a permanent structure that supports and maintains the stability of the tunnel,it has sufficient strength,frost resistance and impermeability.When conducting research on existing tunnel lining diseases,it is necessary to ensure that the internal diseases of the structure are effectively detected,but also to ensure that the performance of the test object is not affected,and the internal structure of the test object is not damaged.Therefore,various non-destructive testing methods have emerged.At present,the commonly used non-destructive testing methods in tunnel structure testing mainly include rebound method,infrared thermal imaging method,ultrasonic echo method and ground penetrating radar method.As the most representative nondestructive testing method,the ground penetrating radar method is widely used in many fields such as geotechnical engineering survey,engineering quality inspection,mineral exploration,disaster geological survey,building structure inspection and archaeology.Its advantages are high efficiency,high precision,strong anti-interference ability and no damage to the structure.The thesis uses a combination of physical model test,COMSOL Multiphysics finite element forward simulation and mathematical morphology signal processing,carry out research on nondestructive testing of typical diseases of existing tunnel linings,and analyze the image characteristics of typical diseases of existing tunnel linings.The main research contents and results of this paper are as follows:(1)By consulting the related literature on typical diseases of existing tunnel lining,analyze the causes of the formation of typical diseases in existing tunnel linings.And according to the "Code for Design of Highway Tunnels"(JTG 3370.1-2018)and "Code for Design of Railway Tunnels"(TB10003-2016)(J 449-2016),physical test models for the two typical diseases of existing tunnel lining cavity and non-compact are established.Analyze the characteristics of two-dimensional ground penetrating radar images of two typical diseases in the physical model with different curing times,and study the three-dimensional image characteristics of different curing times and different slice depths.(2)Establish a finite element forward model in COMSOL Multiphysics.The finite element forward model is a cuboid with a size of length×width×height=1.2m×1.0m×0.6m,in the cuboid model,there are different relative positions of cavity,non-compact and cracks,there are four models of cavity disease above and below cracks and non-compact disease above and below cracks.The incident process and reflection results of the four models are analyzed,the research shows that the incident and reflection trajectories of electromagnetic waves in different disease models are basically the same as those of the physical model test.(3)The MATLAB signal processing program is written based on mathematical morphology theory.The basic operations of mathematical morphology image processing include erosion,expansion,opening and closing operations,etc,the principle of mathematical morphology image reconstruction is divided into two steps: selection and reconstruction,mathematical morphology top-hat operations are divided into top-hat opening operations and top-hat closing operations.In this paper,basic morphological operations and top-hat operations are performed on the two-dimensional images of two typical diseases of tunnel lining cavity and non-compact.In this paper,basic morphological operations and top-hat operations are performed on the two-dimensional images of the two typical diseases of tunnel lining cavity and uncompacted,the results show that the shape and area of the disease can be distinguished in the two-dimensional images after the top-hat operation. |
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