Study On Mesoscopic Damage Of Freeze-thaw Rocks Based On CT Image Processing Technology

With the proposal of the Belt and Road initiative and the development of the western regions in China,the infrastructure construction and energy and mineral exploitation in the western region have been paid more and more attention,and the requirements of geotechnical engineering in cold regions is also increased,among them,the freeze-thaw disaster is one of the key problems that need to be solved urgently.Damage identification and degradation mechanism analysis of rocks under freeze-thaw action are the basis to ensure the safety of projects in cold regions.This article is based on the geotechnical engineering in cold regions,through CT scanning test of freeze-thaw red sandstone and comprehensive use of image processing technology,to study the degradation mechanism and damage evolution law of red sandstone under different freeze-thaw cycles from the mesoscopic perspective.The red sandstone collected from the project site was prepared into(D50mm × 100mm samples that meet the recommended standards of the International Rock Mechanics Association,and its physical parameters were measured,after that the freeze-thaw cycles test under saturated water condition was carried out,different freeze-thaw degradation phenomena were observed and summarized,and CT scanning was applied to test the red sandstone samples after 0,5,10,20 and 40 freeze-thaw cycles.According to the original CT images of freeze-thaw red sandstone obtained by CT scanning,the gray distribution histogram was used to make a preliminary analysis firstly,and it was considered that the change of wave peak in the gray distribution histogram reflects the internal damage evolution of red sandstone under different freeze-thaw cycles.Then through the preprocessing operations such as image denoising and image enhancement,the image visibility was improved,and high-quality image files were obtained.The segmentation threshold of the CT image was determined by K-means clustering algorithm,and the CT image was segmented,Thus,the extraction and quantification of the pore structure of red sandstone on the 2D level were realized.By combining the finite element analysis method,ANSYS was used to analyze the temperature distribution and the generation law of ice swelling force of the red sandstone model considering the pore structure under the freezing environment.Considering the limitation of only analyzing 2D tomography images,3D reconstruction technology was used to reconstruct red sandstone samples under different freeze-thaw times based on CT scan images,and the reconstructed model was consistent with the real red sandstone samples.By extracting and quantifying the pore structure of the reconstructed model and defining the damage variable,the damage development law of red sandstone in freeze-thaw environment was studied.On this basis,the rock damage constitutive model under the coupling of freeze-thaw and load was established,and its rationality was verified by comparing with the experimental data.