Thermal-hydro-static Coupling Model And Mechanical Behavior Of Permafrost Considering Ice Structure

In recent years,with the vigorous development of the country in permafrost regions and the increase in permafrost temperature caused by climate warming,the requirements for foundation strength and deformation of cold region engineering have been further improved.The traditional frozen soil mechanics research methods can no longer meet the needs of cold region e ngineering.In the laboratory tests on frozen soil,mostly homogeneous remodeled samples are used,and there is no obvious ice structure.In practical engineering,frozen soil is not homogeneous.Frozen soil has a unique structure,and permafrost in different regions often has different structures.Therefore,the mechanical properties obtained by the laboratory test are different from those of the act ual undisturbed frozen soil.Undisturbed permafrost is difficult to sample and store.Moreover,the differences between the specimens are large,and there is no comparison.Aiming at the deficiencies in the research of frozen soil mechanics,this paper establishes the undisturbed frozen soil numerical specimen by means of the combination of laboratory test,X-ray CT scans,image processing and numerical simulation.The effects of temperature,confining pressure and icy soil structure on the mechanical properties of undisturbed frozen soil were studied by simulating laboratory experiments using finite element soft ware.The main research contents and results are as follows:Frozen soil specimens containing visible ice were pr epared by burying ice cubes in the specimens.Through the uniaxial compression test of the frozen soil at different temperatures,the stress-strain curve of the frozen soil is obtained.The effects of temperature,ice content and ice distribution on the mechanical properties of frozen soil were studied.It is found that the strength of frozen soil will be significantly reduced when there is obvio us visible ice structure,and both the ice content and the distribution of ice will affect the mechanical properties of frozen soil.X-ray CT scans were performed on artificial heterogeneous frozen s oil,and CT images of the interior of the frozen soil wer e obtained.Then,histogram homogenization,filtering noise reduction,threshold segmentation and morphological processing were performed on the frozen soil image,and the ice inside the frozen soil was successfully extracted.The geometric model of ice was imported into finite element software,the numerical model of heterogeneous frozen soil was established,and the uniaxial compre ssion test and the triaxial compression test were simulated.It is found that due to the uncoordinated deformation of ice and soil,there will be obvious stress concentration at the interface of ice and soil.The simulation results were compared with laboratory experiments to verify the accuracy of the model.The image processing of undisturbed frozen soil images was carried out,and three structural types of undisturbed frozen soil geometric models were established.On the basis of the Harlan model,the thermal-hydro coupled differential equation is derived according to the mass conservation differential equation and the energy conservation differential equation.Then through the research citation function,the thermal-hydro-static coupling model of undisturbed frozen soil is established.The model was used to simulate the uniaxial compression test and triaxial compression test of undisturbed frozen soil under different boundary conditions,and the effects of temperature,confining pressure and ice structure on the mechanical properties of undisturbed frozen soil were analyzed.