| Soil mechanics is a subject with great concern to practice, whose development is firmly relied on the improvement of soil testing technique. As one of the most important instrument for soil test, triaxial apparatus has been playing an essential role in the development of soil mechanics. However, there are many limitations and shortages in specimen deformation measurement in triaxial test. With application of digital image processing technique, some of these limitations and shortages can be overcome and lead to a new, more reasonable and more effective method in specimen deformation measurement.In the first part of the dissertation, the shortages of deformation measurement of soil specimen are discussed together with comparing and analyzing the traditional and improved methods. For eliminating these shortages, a digital imaging processing technique is developed to measure the deformation of triaxial specimen. The concrete work includes hardware preparation, software development and modification of some attachments of general triaxial apparatus. In order to gain a high accuracy, all types of error sources in digital image processing system and their influences are discussed in detail. Further more, a special auxiliary light, software means and the correction of the system errors are used to improve the accuracy of digital image processing system. At the end of this part, theoretical accuracy of digital image processing technique is presented with its real accuracy determined by measuring standard objects with known size.Compared with the traditional method, the digital image processing method has many advantages in measuring the deformation of soil specimen in triaxial test, such as higher accuracy, non-contact measuring process, and undisturbed specimen. It is valid to measure the deformation in large scale. It can select the section of specimen freely to measure the axial and radial deformation directly. It can also record the images of soil specimen in deformation which can be used to re-analysis after test.The second part of the dissertation concentrates on the applications of the digital image processing technique in measuring the specimen deformation in-triaxial test. It includes:(1) Discuss of some problems in triaxial test. It includes the influence of end contact and end restraint, the volume variety during the triaxial specimen being saturated, the characteristic of distributing of the gram at the surface of specimen, etc.Conclusions are made and some suggestions are presented.(2) Study of local deformation of triaxial specimen. The characteristic of local deformation and its effect factors are studied by quantificationally comparing the local deformation along the specimen height. All the results of axial and radial deformation measurement by digital image processing technique and those by traditional method are compared. The differences of the soil parameters on Duncan and Chang's nonlinear model made by these two methods are analyzed. Finally, a compress test results and FEM results are provided to show the reasonability and veracity of digital image processing technique to study the soil stress-strain characteristic in triaxial test.(3) Study of triaxial test of dry soil and the formation of shear band in triaxial specimen of fly ash. Because the digital image processing technique can directly measure the axial and radial deformation of soil specimen in any moisture, general triaxial apparatus can be used to do the triaxial test of dry soil. In the study of the triaxial test of dry soil, the stress-strain characteristic is compared with that of the saturate soil at the same condition. The shapes of shear band in triaxial specimens and the condition in which shear band forms are elucidated from the shear band study in triaxial test of fly ash. By digital image processing technique, the form and development of shear band in triaxial test are easily determined. Conclusions are agreeable with that of known research in plane strain test.
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