Research On Sand Shear Wave Velocity Based On Particle Contact Model

Shear wave velocity of sand, which represents the structure of sand skeleton, is an important parameter in soil dynamic mechanics. Research on shear wave velocity of sand has been always one of primary problems in soil dynamic mechanics and geotechnical engineering. A lot of meaningful researches have been obtained in the past several decades, which mostly focus on macro-scope. Recently, researches on micro structures of sand turn to be more and more important in soil dynamics. In this dissertation, the contact of sand particles is taken to be the breakthrough point, and the shear wave velocity of sand is studied based on particle contact theory.Firstly, the surface characteristic of sand particles is analyzed. Several sand samples are made through filtration and screening of Fujian standard sand, Hangzhou sand and man-made quartz sand. Afterwards a few sand particles which are picked up randomly from every sample are scanned by electron microscope.2-D photos of sand particles obtained by scan are analyzed to calculate the average values of surface characteristic parameters of every sand sample. Diameters of sand particles are mostly ranged in 2-0.75mm, which means people can't observe sand particles with naked eyes. By using scanning electron microscope, the images of sand particles can be magnified hundreds or thousands times. Then some graphical and mathematical treatments are taken based on these images to describe the surface characteristic of sand particles, which provides some essential parameters for the deriving of sand particles contact model.For sands in different depths, contact forces between sand particles vary with gravity stress, additional stresses and porosity (compactness), and the distribution of contact stress is greatly influenced by surface characteristic of sand particles. According to previous researches on metal particle contacting, the contact model of sand particles is discussed. Subsequently, on the basis of research on sand particles surface characteristic, the formulas of real contact area and distribution of contact stress under different contact force and roughness are derived using theoretical analysis and numerical simulation. At the same time, the calculation method and formulas of normal deformation and shear deformation are obtained. Then, normal contact stiffness and shear contact stiffness of sand particles are derived according to researches above.Equivalent shear modulus and shear wave velocity are derived by considerirg sand as continuous media macroscopically. With average treatment on contact forces, contact points and particle radius, the relationships between macro parameters and contact model of sand are established according to fabric and constitutive research of granular media.Formulas and relationships established in this dissertation are verified by experiment and measured data, and the effect of application is also evaluated. An experimental research concerning the influence of particle surface characteristic on shear wave velocity is taken by using bender element testing equipment, which provides addition and correction to theoretical formulas above. A simplized calculation method for shear wave velocity is established which can be used to predict shear wave velocity of sand in projects. The application feasiblity and effect of this method is analyzed by comparing calculated results of simplized method with measured data.