Study on Strain Localization in Triaxial Specimen Using Image Processing

نوع: Type: thesis

مقطع: Segment: masters

عنوان: Title: Study on Strain Localization in Triaxial Specimen Using Image Processing

ارائه دهنده: Provider: Kiavash Karami

اساتید راهنما: Supervisors: Mohammad Maleki (Ph.D.)

اساتید مشاور: Advisory Professors: Morteza Heidari Mozaffar

اساتید ممتحن یا داور: Examining professors or referees:

زمان و تاریخ ارائه: Time and date of presentation: April, 09, 2021

مکان ارائه: Place of presentation:

چکیده: Abstract: Triaxial Test is one of the most important experiments in soil and rock mechanics. The data obtained from the triaxial test is used to determine soil properties such as shear strength, apparent cohesion, expansion angle, and volume change of different materials. Measuring the change in volume and local strain of the soil specimen during the triaxial test is essential when analyzing the mechanic behavior of the soil. In the saturated triaxial test, the volume change of the soil specimen is measured directly by measuring the inflow and outflow of pore water, by calibrated burette of the device panel or the pressure volume control device. This method cannot be used in unsaturated soils, because in addition to the water between the cavities, there is also air pressure inside the specimen that may change. Also, the types of shear bands of the soil specimens are different and the distribution of strains within the specimen is still unknown. In this research, a new method for measuring volumetric strain and local strain based on image processing and photogrammetry is introduced. This method includes imaging the specimen during the experiment, sizing the specimen, and analyzing it to obtain the soil specimen profile. The main purpose of this study is to investigate the non-uniform strain distribution within the triaxial specimen and also to predict the strain distribution within the specimen by monitoring and detecting the coordinates of points in the specimen. In this study, the soil composition of 161 Firouzkooh sand with 40% silt has been used. The soil specimen with two different relative density of 90% and 30% in the form of a triaxial test apparatus is subjected to confining stresses of 100, 200, and 300 kPa. The soil specimen is then imaged using a calibrated camera while loading. Images are scaled in different steps and created by specimen 3D model software. It is now possible to examine the direction and magnitude of local strains and deformations within the specimen. After modeling the soil sample using photogrammetry softwares such as Photomodeler and Agisoft Metashape and obtaining brief locations, the strain localization of each point on the sample surface were obtained. The result obtained from this study shows that the method presented in this study can measure the volumetric and local strain of the specimen with great accuracy. These results indicate that the increase in confining stress reduced the amplitude of volume strain change within the specimen so that for specimens with a relative density of 90%, in confining stress of 100 kPa, the maximum volume strain is 3.55% and in confining stress of 300 kPa, 1.63% was obtained. Also, in soil specimens made with a relative density of 30%, the increase in confining stress continues to cause the soil to resist deformation and reduce the volumetric strain. Meanwhile, the volumetric strain was recorded in the specimen with confining stress of 100 kPa, which is 1.15%, and in the confining stress of 300 kPa, which is 0.78%. Examining the three-dimensional models obtained from the proposed method, in the triaxial test, it was observed that changes in relative density of soil specimens and confining stress did not affected on the distribution, and direction of local strains in the soil and these parameters are affected by soil texture and texture. Key Words: Triaxial unsaturated test, Image Processing, Strain localization, Unsaturated volume change, Photogrammetry, Sandy soil.

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