A Sub-pixel Edge Detection Algorithm to Measure the Volume of Unsaturated Soil Sample in the Triaxial Test

The volume measurement of the unsaturated soil sample in the triaxial test is very important for studying the properties of unsaturated soil. Based on the previous studies, a subpixel high-precision edge detection algorithm is proposed to measure the volume of soil samples. This method combines Sobel operator, interpolation method and fitting method to calculate the position of sub-pixel edge points by the least square method. Compared with other algorithms, the edge of the soil sample can be detected quickly and accurately. Finally, the algorithm is applied to the volume measurement of unsaturated soil samples. The relative error between the volume obtained by this method and the standard sample volume is less than 2.5%.