Junxing Zheng

Roundness and Sphericity of Soil Particles in Assemblies by Computational Geometry

AbstractThe use of computational geometry methods for determining soil roundness (R) and sphericity (S) were evaluated and extended to particles segmented from images of three-dimensional particle assemblies. Two Adobe Photoshop lasso tools were used to delineate particles with full projections from the assemblies. Results were in excellent agreement with values published in traditional roundness and sphericity charts, thus confirming that the computational method can replace the much slower and less objective chart methods. Complete volume-based distributions of particle roundness and sphericity were presented for three soils with vastly different particle shapes. Values of R and S obtained from images of three-dimensional assemblies were almost indistinguishable from values obtained using images of detached particles showing their largest projected areas. Mean R values were also computed for 10 different soils of various geologic origins. As expected, crushed sands exhibited the smallest mean values of ...

Particle roundness and sphericity from images of assemblies by chart estimates and computer methods

AbstractSoil particle roundness (R) and sphericity (S) are two important intrinsic properties that govern a soil’s mechanical behavior. Although R and S have well-established mathematical definitions dating back to the 1930s, the values are much more typically estimated using charts developed in the 1940s and 1950s. The charts, are based on the earlier mathematical definitions. Using these charts, a class of undergraduate civil engineering students at the University of Michigan were asked to estimate (Rc and Sc) from images of twenty geologically and geographically diverse sands spanning a range of actual R and S values. The images were of three-dimensional (3D) assemblies of the sands as they would be found in images taken remotely or in situ. The students’ estimates were statistically analyzed and compared with rigorously determined R and S using a recently developed computational geometry algorithm. Overall, the students’ estimates were scattered, particularly for natural sands exhibiting intermediate ...

Soil Particle Size and Shape Distributions by Stereophotography and Image Analysis

Image-based soil particle size and shape characterization methods have witnessed great progress in duplicating traditional sieving and manual methods for shape measurement. Nevertheless, some discrepancies between results still existed since the third (vertical) dimension of particles are not attainable from single images. This paper described a simple, effective, and inexpensive stereophotography system to obtain precise 3D surfaces and thus, all three principal dimensions of many sand to gravel particles simultaneously. Advanced image analysis techniques, including improved watershed segmentation, dynamic programing, pyramidal matching, and sub-pixel estimation were used to obtain greater precision and higher computational speeds. Six hundred randomly selected soil particles covering a range of sizes, colors, shapes, and surface roughnesses were tested by the stereophotography system. Excellent agreement was found between the stereo image results when compared to sieving analysis and manual measurement of shapes using calipers.

Optical Flow Analysis of Internal Erosion and Soil Piping in Images Captured by the VisCPT

Internal erosion and soil piping are caused by the migration of fine soil particles through a skeleton of coarse grains or by progressive mass movement of soil grains under the tractive forces produced by concentrated subsurface flow, which may lead to the failure of dams and levees. The ability of the Vision Cone Penetrometer (VisCPT) to record internal erosion and soil piping in the laboratory and in-situ has previously been reported. The present paper focuses on developing a video-processing algorithm to quantify the soil particle motions. An optical flow technique is adopted to compute particle migration velocity fields. This makes it feasible to detect, track and quantify the movement of soil particles by the VisCPT. The research defines the eroded area percentage (EAP) and the sum of the absolute velocities of mobilized fine soil particles (SAV) which may eventually be used to quantify soil erosion and piping susceptibility.

Compressibility of Sands of Various Geologic Origins at Pre-crushing Stress Levels

This study quantifies the influence of various intrinsic soil properties including particle roundness, R, sphericity, S, 50% size by weight, D50, coefficient of uniformity, Cu, and the state property of relative density, Dr, on the compression and recompression indices, Cc and Cr, of sands of various geologic origins at pre-crushing stress levels. Twenty-four sands exhibiting a wide range of particle shapes, gradations, and geologic origins were collected for the study. The particle shapes were determined using a computational geometry algorithm which allows characterization of a statistically large number of particles in specimens. One dimensional oedometer tests were performed on the soils. The new data was augmented with many previously published results. Through statistical analyses, simple functional relationships are developed for Cc and Cr. In both cases, the models utilized only R and Dr since other intrinsic properties proved to have lesser direct influence on the compression indices. However, previous studies showed that the contributions of S and Cu are felt through their effects on index packing void ratios and thus on Dr. The accuracy of the models was confirmed by comparison of predicted and observed Cc and Cr values.