Triaxial creep tests of weak sandstone from fracture zone of high dam foundation

The lithology of fracture zone which was developed at the dam foundation of a hydropower station is weak sandstone with poor integrity and pore cementation contact. Its creep properties have a significant impact on the deformation and stability of the dam. Based on the characteristics of loose organizational structure, high moisture content and poor mechanical properties, the triaxial compression tests and creep tests were carried out, respectively. The results show significant non-linear, low strength and no obvious strength peaks. Both axial and lateral strains are achieved more than 3% when the tests are failed. The weak sandstone has a significant creep property, but only transient and steady state appear under low stress. Increased stress causes creep intensified and lateral strain gradually exceeds axial strain. In the failure stage, it has characteristics of large axial plastic deformation, obvious volumetric ductility dilation and large steady creep rate. The accelerated creep appears shortly after transient loading under confining of pressures 1.0 MPa and 1.5 MPa. Therefore, an improved Burgers creep model considering the non-linear characteristics of weak sandstone is built based on hyperbolic equation and the creep parameters are identified. This model can well describe the creep properties of weak sandstone.