An experimental method for visualizing undrained shearing failure in a transparent soft clay surrogate

Transparent Soil;Soft Clay;Miniature Shear Vane;Penetrometers;Particle Tracking

Chini, Christopher Matthew

关键词: Transparent Soil;    Soft Clay;    Miniature Shear Vane;    Penetrometers;    Particle Tracking;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/78486/CHINI-THESIS-2015.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

This research investigated the use of non-invasive testing procedures to visualize the failure surface of four laboratory shear-testing techniques in a soft clay surrogate, Laponite RD, at shallow depths with minimal boundary effects. The thesis developed a procedure for tracking deformation in Laponite RD as a soft clay surrogate for the miniature shear vane and the T-bar, ball, and cone penetrometers and provided the first non-invasive in situ images of deformation patterns. Previous attempts to visualize the shear failure surfaces of a rotating vane or penetrometers included significant disturbance of the soil sample or methods of shearing along a transparent surface. Additional existing methods involved seeding of the soil with various markers creating a non-homogenous soil mixture, adding potential sources for error. None of the previous attempts to characterize the deformation patters surrounding the undrained shear strength testing devices provided an effective means of visualizing the deformations occurring in situ while minimizing potential boundary effects. The testing set-up utilized a helium-neon laser, a laser line-generator lens, a camera, and a computer to capture and analyze resulting displacement of the soil from the various testing devices. Within the transparent soil surrogate, the laser illuminated a plane with a camera all deformation for particle tracking purposes. A series of experimental tests used two sizes of rectangular lab vanes and three types of penetrometer tests (T-Bar, ball, and cone). Miniature shear vanes and the T-Bar penetrometer each had five planes of analysis with three tests taken at each plane, resulting in 45 tests in total. The symmetry of the ball and cone penetrometers required only one plane of analysis for each device with six different tests on the plane. In all, the research included 57 independent tests using open source particle tracking algorithms and additional processing to create a repeatable methodology for future studies.Contrary to previous studies that used particle image velocimetry (PIV) and digital image correlation (DIC), individual particle-tracking, algorithms were necessary and feasible due to the relatively sparse and random illuminated particle displays within the Laponite RD soft soil surrogate. The study provides a detailed description of the algorithms and the assumptions made in the process of tracking particles and plotting them for analysis. The results of the experiment yielded the first displacement plots of the failure surface without intrusively damaging the soil structure due to in situ shear strength measuring devices. Additionally, the similarities between tests at the same planes of analysis for each testing device supported the methodology as consistent and repeatable.