Application Of Photogrammetry In The Study Of Deformation Characteristics Of Red Clay

Conventional triaxial test deformation measurement methods has limitations due to the end effect,and for the triaxial test method based on image measurement,and deformation of the pressure chamber and the light refraction affect the accuracy of the test measurement.In order to overcome these limitations and shortcomings,this article introduces the application of photogrammetry technology in triaxial test of Guilin remolded saturated red clay,and analyzes the radial,axial,local and total volume deformation characteristics of soil samples under different confining pressure and different experimental stages.the contents are as follows:(1)The pinhole camera model is used to calibrate the parameters of the single-lens camera(the Iphone6 mobile phone),and the results show that it meets the requirements of the new photogrammetry method for camera tools,making the test operation more flexible;Summarize the previous calculation process of the new photogrammetry method,using the programming software Matlab to write a series of programs to solve the problem of the method's intensive calculation,and it can be seen that it is necessary to develop a complete set of software packages for image processing and calculation.(2)Through the use of vernier calipers and photogrammetry technology to measure the distance on A4 paper with RAD marking points in the air,it is found that the measurement error between the two is very small,and the absolute error value is within 0.011mm;a hard cylindrical plastic bottle is used as the triaxial sample model,using the new photogrammetry method to measure the column height of the marked points in and outside the pressure chamber,and to take the vernier caliper measurement value of the column height of the model mark points in the air as the true value,the average measurement error of the model in the pressure chamber is 0.133 mm.The measurement error outside the pressure chamber is relatively smaller,indicating that the new photogrammetry method has higher accuracy,and it is completely feasible to use it for volume measurement in the triaxial test.(3)The unconsolidated and undrained triaxial test of Guilin reshaped saturated red clay was carried out,and the three-dimensional model of the soil sample was reconstructed by new photogrammetry,and the axial,radial,partial and total volume changes of soil samples were analyzed under different confining pressures and different test stages.Analyzing the axial deformation of the soil sample,it is found that the compression increment of the bulging part in the middle of the soil sample is obvious,while the constrained deformation of the soil at the end is uneven;the radial deformation characteristics of the soil sample are analyzed,and the deformation law and axial deformation are found Similarly,the expansion increment in the middle part is obvious but the end part deformation is not obvious;from the analysis of the local volume deformation of the soil sample under different confining pressures,the soil sample shows expansion and contraction during the test,and the end restraint has a great influence on the deformation of the soil sample;finally,the total volume deformation law of the soil sample is summarized,the soil sample is generally swelling,but the deformation law is inconsistent under different test stages,it is necessary to comprehensively analyze the characteristics of the soil sample's radial,axial and local volume deformation.In general,the deformation of the soil sample is greatly affected by the end constraint,which is manifested as uneven deformation,the deformation law of the soil sample is inconsistent throughout the test process,but the deformation analysis result is consistent with the deformation characteristics of the soil sample,the new photogrammetric method improves a good solution for the uneven deformation measurement of the local and total volume of the soil sample,but more experiments are needed to summarize the rules.(4)Through the error analysis of the mark point recognition,the more accurate the coordinates of the mark points are,the more close the three-dimensional model is to the real shape of the soil sample,some methods to reduce the errors and improve the accuracy are also proposed.