Particle-size distribution of interlayer shear zone material and its implications in geological processes—a case study in China

A case study was carried out at the Gaobazhou dam site on the Qingjiang River in Hubei Province, Central China, to investigate the particle-size distribution (PSD) of interlayer shear zone material and its implications in the geological processes. Forty-six disturbed samples were taken at various representative locations within the well-characterized interlayer shear zones at the Gaobazhou dam site. The particle-size distributions of these samples were analyzed, and the mass-based approach is used for fractal scaling of the particle-size distribution curves. It is shown that all curves on the log–log scale can be approximated by two intersecting lines. Thus, each curve can be quantified by α1, α2, Ps, and rs, which respectively correspond to the slopes of the two lines and the coordinates of the point of intersection. α1 and α2 can be replaced by fractal dimensions D1 and D2. The statistical analysis results reveal that Delta (=D2−D1) and Ps are closely related to D1. Therefore, only D1 and rs are used to characterize each curve. It is illustrated that 47 specimens are clustered into five groups with respect to rs and D1. Accordingly, five categories of particle-size distributions are identified. It is found that the D1 and rs values of a sample can reflect the geological processes of the interlayer shear zone. The larger the value of D1, the higher the degree of interlayer shear experienced. The value of rs implies the degree of subsequent secondary geological processes, but in a rather complex way due to the differences in intensity of interlayer shear undergone. Based on this, the geological evolution processes of the interlayer shear zones are postulated, and the current status can be defined through fractal scaling of the particle-size distribution of disturbed samples.