Biaxial stress field is one of the classical forced states of surrounding rock in underground group caverns. So far, the data of biaxial compressive test of rock is still so less. In this note, macroscopic stress-strain curve is given in different loading path while free surfaces continuous deformation field of rock material is showed microscopically in the process of damage by technology of 3D Digital Image Correlation under biaxial stress state. Based on characteristics of macroscopic deformation and micro-mechanical damage, the failure format and regulation of Jinping marble in biaxial condition is revealed.
In water resources and hydropower engineering, during excavation of underground caverns, surrounding rock is partly in Plane stress state, that is σ 1 ≥σ 2, σ 3 =0. Under this condition, stress redistribution because of excavation usually leads to failure phenomena such as splitting of surrounding rocks, Rockburst, zonal disintegration and so on. Those phenomena seriously affect the stability and normal operation of underground caverns (2012).
At present, in the study of laboratory experiment, uniaxial and triaxial test accumulate more experience. But to biaxial compression test, experimental data is so less. According to failure mode and rheological properties of surrounding rock under excavation unloading, the characteristics of loading failure, creep effect and unloading mechanism were summarized and induced by Li et al. (2012). Based on the compression test results of limestone specimen in multiaxial conditions by Hou, Yun et al., it is found that the intermediate principal stress can obviously affect the strength of rock (2008, 2009). Considering different loading path, loading velocity and specimen size, biaxial test have been carried out by Yun, Mitri et al. and new failure criteria has also been established (2008, 2010). In addition, digital image correlation technique was used to analyze the failure process of marble precast en-echelon faults by Ma et al. (2006) in biaxial condition.
In this paper, biaxial compressive test of Jinping marble was carried out on css-283 universal testing machine. And 3D digital image correlation technique was used to measure the full-filed normal deformation of free surface of rock samples during the test process. It is shown that deformation characteristics of horizontal and vertical strain as well as normal deformation of free surfaces have a great impact on rock failure.
