Space-time evolution law of progressive failure area and mechanical behaviour of rock under different seepage conditions

In engineering geological disasters, the presence of water can accelerate rock mass fracture, and the state of the seepage field has a varying influence on the elastic behaviour of rock mass. A three-dimensional digital image correlation (3D-DIC) system is used to conduct triaxial compression tests on sandstone under different seepage conditions. The variation law of rock mechanical behaviour and the space-time evolution law of the surface radial strain field in the progressive failure process are analysed. The results show that, as the seepage pressure increases, the rock peak stress decreases and the Young's modulus increases, and the mechanical properties of the rock are easily affected by the varying seepage conditions. Meanwhile, a constitutive equation based on the Gumbel distribution, which can accurately reflect the axial stress-strain relationship in the rock failure process is established. By analysing the spatial distribution of virtual data points with large radial strain values at different times on the sample surface, a patent strain localisation phenomenon is identified in the progressive failure process of the rock. The localisation degree and extent of the failure area can be quantified using the average nearest-neighbour analysis (ANNA) and user-defined parameter S, which is used to normalise the average distance from the virtual data points to the fitted fracture surface. The results show that, with the continuous compression of samples under different seepage conditions, ANN decreases as S increases, and the large strain regional distribution is increasingly concentrated. The research results can be applied to predict surrounding rock failure areas in underground spaces and provide monitoring references with respect to engineering geological disasters under different seepage conditions.