Experimental Studies On Fault Propagation Based On Digital Image Correlation Method

Active fault is not only the main cause of tectonic earthquake, but also the intensified cause of geological and earthquake disasters. Active fault covered by the quaternary loose sediment is more covert and dangerous compared to active fault exposed on the ground surface, so the study of active fault propagation in sedimentary layer is a very important topic in the study of seismic geology and earthquake disaster reduction engineering. In order to reveal the active fault propagation characteristics and mechanism, the rock fracture experiments and the fault propagation experiments were carried out based on the digital image correlation method.In order to reveal the rules of typical active fault rupture in sediments and the distribution characteristics of ground surface rupture zone, we developed the modeling test systems and analogue materials to simulate the strike slip fault and thrust fault rupture propagation process in sedimentary layer. The modeling frame of experimental system can easily adjust the geometry parameters of the fault, and the loading system can precisely control the displacement value and model of the fault by servo motor. The analogue material made of quartz sand and plaster has the advantages of low cost, easy-to-use and wide adjustable range of strength. It can effectively simulate the physical and mechanical characters of rock and sediment. So, the analogue material is suitable for large-scale and repeatability modeling test research of active fault rupture propagation process in sedimentary layer. In order to measure the rupture propagation process of active fault, we reviewed the technique of measuring discontinuous deformation field by digital image correlation method (DICM), and developed3D-DICM measuring system. The improved DICM and measurement systems can effectively measure the evolutionary process of the ground surface deformation field and rupture zone. In order to reveal the crack propagation mechanism in bedrock, we developed a new method based on DICM to measure stress intensity factors, crack tip position and crack length during the crack extension process. It shows that the fracture parameters measured by the above method can be used in rock fracture mechanics to analyse the problem of rock fracture.The mode I and mixed-mode Ⅰ-Ⅱ crack propagation characteristics of rock are studied utilizing DICM, and the rock interface layer’s influence on the crack propagation in stratified rock is studied at the same time. The experimental result shows that there is a subcritical crack growth stage in rock fracture process, and the stage can be identified by stress intensity factor and crack extension speed. The study of subcritical crack growth stage has important geological significance in the research of bedrock rupture propagation and earthquake precursor. The experiment of crack propagation in stratified rock was carried out, which shows that the rock interface, interface slip and rock property have influence on the crack propagation.The analogue material and equipment system of geological mechanics modeling test were used to study the strike slip fault propagation process in sedimentary layer, then influence of bedrock displacement and sedimentary thickness on sedimentary fracture are mainly studied. The experimental results indicate that the ground surface deformation and fracture band width are mainly controlled by bedrock movement, the surface deformation band width increases with fault displacement are nearly quadratic curve, which finally tends to be stable width; ground surface rupture zone increases with sedimentary thickness, the crack in rupture zone is formed after the initial crack in bedrock penetrated the sedimentary layer, and the rupture plane in sedimentary is a spiral curved surface, the cracks distributed in spacing mode, sedimentary thickness is proportional to the fracture spacing.The influence rule of bedrock slide displacement, fault dip angle and sedimentary thickness on the fracture propagation process and ground surface deformation is studied in the modeling test of thrust fault propagation. The experiment results indicate that the deformation band width increases with bedrock slide displacement and sedimentary thickness, tends to be a constant value after the rupture appeared on ground surface; the width of deformation band dereases with the fault dip angle, but the fracture degree on ground surface increases with the fault dip angle...