Research On Triaxial Test Soil Sample Deformation Based On Computer Vision Measurement System

Geotechnical triaxial test,as an important way to study soil performance parameters,plays an important role in the study of soil constitutive characteristics,soil mechanical properties,stress and strain properties,including soil strength characteristics.Therefore,the precision and data accuracy of geotechnical triaxial test affect the judgment of mechanical properties and strength of soil,and then affect the application of soil in practical engineering.When the soil is shear deformed in the conventional triaxial test,the volume change of saturated soil is usually measured by the displacement of the volume variable tube of the triaxial instrument.In addition,the mean volumetric strain in the whole shearing process of soil samples wh en the displacement obtained from the volumetric variable pipe is obtained makes the study of soil properties have great limitations,and it is impossible to measure the radial deformation of soil.It is difficult for the soil sample to reach the saturation state completely when the displacement is collected by the volume variable tube.In this paper,a monocular measurement system with digital camera as the acquisition element is proposed to conduct non-contact measurement of triaxial test,and an image processing software is developed by using MATLAB.The key camera parameter calibration problem is solved by the multi-angle checkerboard calibration method and the testing accuracy is improved.Making full use of MATLAB image processing function simplifies the programming difficulty and improves the recognition efficiency.The edge recognition algorithm was used to test the deformation of soil samples,and the axial and radial deformation of soil samples were obtained.The non-contact method of measurement is more direct,more rapid won't produce disturbance in the process of test,and can be intuitive measuring soil samples at any time during the process of deformation of the radial deformation,good make up for the conventional triaxial instrument on the measuring volume strain and radial strain,provide geotechnical triaxial test with a new kind of t ools and methods.Compared to other to apply digital image measurement method to the conventional triaxial test,in this paper,using the common CMOS camera,no pixel equivalent simple calibration is obtained by using the direct way,through the checkerboard calibration method to get the camera parameter matrix,through the Pn P DLT solutions of problems in the launch of camera parameter matrix acceded to the outsi de appearance transformation matrix,the calibration precision is improved greatly,the conventional triaxial test instrument under the premise of not do any modification,still on measuring results have higher accuracy.The monocular measurement system is used to measure the whole process of soil deformation in the conventional triaxial test,and the data measured by the triaxial instrument are compared,and the test results are analyzed to prove the feasibility of the monocular measurement system to the soil deformation measurement method,and the advantages of the monocular measurement method are compared with the conventional triaxial test.Finally,the influence factors of the errors are analyzed.The test results show that the new method can avoid the disturbance caused by the traditional triaxial test,although some influencing factors may cause some errors.Moreover,the new method has a high precision,and the digital image measurement technology still has a broad research prospect and great research value.