Study On Volume Shrinkage Deformation Of Guilin Red Clay During Drying Based On Photogrammetry

Shrinkage curve is an important parameter to evaluate the mechanical characteristics of soil,which is closely related to the engineering properties.It is embodied in the functional relationship between moisture content and volume.In the stage of soil shrinkage,the change of moisture content of the sample was measured by drying method.However,due to the uneven deformation of soil and the generation of cracks,volume measurement has become a difficulty in drawing shrinkage curves.A fast and accurate volume measurement method is urgently needed in the drying shrinkage test of the sample.There are two main methods in conventional volume measurement: direct measurement and liquid volume replacement.Although these two kinds of methods are widely used,they all come into contact with interfering samples in the process of measurement,and their accuracy is affected by the accuracy of mechanical components of measuring tools and human operation and other factors.The wide application of cameras promotes the development of photogrammetry technology,and the photogrammetry technology based on ordinary digital cameras is constantly updated and improved.3D modeling of measured objects based on photogrammetry is very popular.Compared with the measuring digital camera,the ordinary digital camera wins because of its low price and flexible operation.In this paper,a method which is easy to operate with simple equipment is discussed to complete the volume measurement of soil samples in the process of drying and shrinkage.Using an ordinary digital camera,based on the multi-baseline image matching photogrammetry technology,the three-dimensional data of the sample surface and the three-dimensional model of the sample are obtained.This measuring method has no contact with the sample,and the sample can be reused.This method can recover the texture and three-dimensional data points of the sample at different shrinkage stages at any time.The functions of 3D reconstruction and measurement of soil samples are realized.The main research work is as follows: The main results are as follows:(1)Close-range photography is realized to monitor the volume deformation of soil samples in the process of drying,which proves the feasibility of the application of photogrammetry in soil sample volume monitoring.The software PhotoModeler Premium processes the image,identifies and matches the characteristic points of the soil sample surface,locates the image,obtains a large number of three-dimensional data of the point cloud on the sample surface,and imports the solved three-dimensional data points of the soil sample surface into Matlab,and uses the sphere function to draw the contour and calculate the volume.This method will be suitable for three-dimensional reconstruction and volume measurement of arbitrary shape.(2)Correction of non-metric digital camera based on two-dimensional linear transformation.The methods of camera calibration image matching and data acquisition are studied,and the factors affecting the accuracy in the process of measurement are analyzed.(3)Based on photogrammetry technology,PhotoModeler Premium photogrammetry software is used to process the image data under different shrinkage time nodes of the sample,and the three-dimensional point cloud data of the sample are obtained,and the global and local deformation characteristics are analyzed.(4)Compared with the RAD measurement method,the shrinkage test volume of soil samples with different dry density was measured by RAD method and point cloud method,and the complete shrinkage curve was drawn.The advantages and disadvantages of the above three methods are analyzed.The experimental study shows that it is feasible to use photogrammetry technology to realize the modeling and measurement of soil samples.There is no interference to the sample when measuring the volume of soil in the process of shrinkage,and the continuous measurement can be repeated.Get local and global deformation features.The surface texture information of the sample was recorded.It provides a method for modeling and measuring irregular objects.