Experimental Study On Deformation Characteristics Of Sand

As the development of the Basic Construction Engineering, Earthquake Engineering, Offshore Engineering, researching on the soil behavior is more and more important. Tri-axial test is a most common method to determine the soil mechanical parameters, to study the deformation mechanism and constitute model. But the method of deformation measurement in traditional Tri-axial test has some flaws. The application of digital image processing technique for local deformation measurement in tri-axial test leads to many advantages comparing to traditional measuring method. It improves the accuracy of deformation measurement, and provides a new method with more reasonable and effective in specimen deformation measurement, besides, the experimental result of the fine sand is the most representative one among the all selected sands. By taking the advantage of digital image processing technique, the deformation characteristics of fine sand are studied in this text.Firstly, in order to study the deformation characteristics of fine sand under monotonic loading, laboratory tri-axial tests are carried out. Based on experimental data the effect of cell-pressure, density and void water to the specimen deformation were analyzed especially. The result shows that the deformation process can be divided into three stages as the specimen-structure building, compacting and failure; the density mainly influences radial-strain as cell-pressure influences peak load, but the density and cell pressure both have a great influence on the initial elastic modulus of the specimen; in the CD test, the void water affects the deformation by sharing the axial-load and humidifying the sand grain; the primary radial-strain section located at the 35-65mm below the specimen cap, with the test data of this section, the sensitivity of the Duncan-Chang model parameters to deformation was analyzed.The deformation mechanism of sand can be further disclosed by its deformation behavior under cyclic loading. Studied on the cyclic-loading deformation process of fine sand and silty soil leads to the conclusions that there has much irreversible deformation in its initial strain; cell-pressure has a significant effect on the grain state while little on radial-strain, and its coupling with axial-load makes the volume of specimen contract in the unloading stage; density makes a good contribution to void ratio and structural stability of the specimen, so it impacts on the unloading recovery strain; The size of the grain influences the deformation by its effect on the grain slippage and potential energy.