Abstract: The Jinping Hydropower Station is a national important large-scale project. The tunnel of the project is very long and has a big diameter; and it is buried very deep. Its wall rocks are very complex in tectonic geology; and the faulted structure is very developed, especially this area is a high ground stress area. The process of excavation is the process of unloading for wall rocks. Through analyzing the confining pressure unloading experiments on marble with constant axial load, we discuss the relationships between elastic modulus, Poisson’s ratio, axial strain and confining pressure; and a conclusion that the axial strain of marble is nonlinear when confining pressure was unloading, is drawn.

Key words: marble, confining pressure unloading, elastic modulus, Poisson’s ratio, axial strain, linear elastic theory