Study On The Fundamental Mechanical Characteristics Of Calcareous Sand And The Influence Of Particle Breakage

Calcareous sand is a special marine geotechnical medium, which has unexpected physical and mechanical property due to its origin and fabric. And calcareous sand generally consists of the remains of marine organisms, which tend to crush relatively easily under load, compared to terrigenous materials. While the offshore constructing structures are often very large and the stress in the foundation is very high. In such case, the particle crushing of sand is very significant. It is demonstrated that the particle crushing is a main factor affecting the property of calcareous sand. So it is very important to study the particle crushing of calcareous sand under high stress levels. Currently, in our country the study on the calcareous sand has been concentrated on the basic static and dynamic characteristics at low pressure, while the research under high pressure and particle crushing is not so much. In this study, serials of compression and shear laboratory tests over a wide range of pressures were carried out on calcareous sand taken from the South China Sea, and the fundamental mechanical characteristics and the influence of particle crushing were also presented thoroughly. In fact, the low strength of particle is the reason of its tending to crush easily under load. According to this, the author proceeded a serials of strength tests on the calcareous sand particles with various sizes. It is very significant to develop and perfect the mechanical behavior investigation of calcareous soils, guide design, construction and assessing the stability of practical projects in marine condition and promote research level of particle crushing. The main work can be concluded as follows.Firstly, based on the overview of the research history of calcareous sand, the details of the testing procedures and the main physical property of testing material were presented. The testing device of individual particle strength was designed and individual calcareous sand particles with various sizes were tested. Using the Weibull distribution function,the author analyzed the testing data. The results indicate that the particle strength of calcareous sand,as measured by compression between flat platens, decreases as the particle size increases. It is demonstrated that particle strength of calcareous sand exhibits Weibullian behavior.Based on a serials of one-dimensional and isotropic compression tests with varies stress levels, the author then analyzed the compression behavior of calcareous sand in detailed. Through the combination of the particle strength and one-dimensional compression behavior with different particle size, the author tried to reveal the mechanism of special compression behavior of calcareous sand. The behavior of shear and strength of calcareous sand over a wide range of stress levels was also discussed in the thesis.The particle crushing is another research point in this thesis, so all the samples were sieved after test and the crushability of calcareous sand was quantified using Hardin model. The influence of particle crushing on the mechanical behavior was analyzed in the thesis. The relation of the relative breakage,plastic work and dilatancy was also discussed.Finally, the achievements of this thesis were summarized, and the research direction of the calcareous sand was also presented.