In this paper, we propose a methodology for validating landslide susceptibility results in the Pinggu district (Beijing, China). A landslide inventory including 169 landslides was prepared, and eight factors correlated to landslides (lithology, tectonic faults, topographic elevation, slope gradient, aspect, slope curvature, land use, and road network) were processed, integrating two techniques, namely the frequency ratio (FR) and the certainty factor (CF), in a geographic information system (GIS) environment. The area under the curve (success rate curve and prediction curve) analysis was used to evaluate model compatibility and predictability. Validation results indicated that the values of the area under the curve for the FR model and the CF model were 0.769 and 0.768, respectively. Considering spatial correlation, an alternative complementary method for validating landslide susceptibility maps was introduced. The spatially approximate maps could be discriminated from their matrices which carry structural information, and the structural similarity index (SSI) was then proposed to quantify the similarity. As a specific example, the SSI value of the FR (74.15%) scored higher than that of the CF model (69.36%), demonstrating its promise in validating different landslide susceptibility maps. These results show that the FR model outperforms the CF model in producing a landslide susceptibility map in the study area.

The mineralogy and chemistry of tuff rocks are variable and heterogeneous due to volcanic activity and hydrothermal alteration, in addition to weathering, which makes it difficult to explain the deterioration mechanisms of the weathered rocks based merely on mineralogical and chemical parameters. Studies of tuff weathering indicate that subtle weathering can modify pore structure and subsequently affect the rock mechanical behavior, suggesting that quantitative pore structure parameters are important indicators of the tuff deterioration mechanism. We identified the pore size distribution of pore bodies and pore throats of both slightly weathered tuffs and fresh tuffs using nuclear magnetic resonance technique and mercury intrusion porosimetry. Meso-level uniaxial compression tests were conducted on the tuff samples under a stereomicroscope using MTI-LMs (miniature tensile instrument-light microscopes) to obtain information regarding crack propagation and the deformation process. A comparison of pore properties of slightly weathered tuffs and fresh tuffs indicates that the introduction of additional mesopores (10–50 nm) and pore throat expansion occurs during weathering. The result of mechanical experiments reveal that alteration of the pore structure influences the tuff failure mode. Slightly weathered tuffs show shear failure as cracks initiate in the altered minerals or matrix, while the fresh tuffs exhibit tensile failure as cracks initiate in the intact and fresh minerals and matrix. Based on the results presented here, it is considerable to regard tuff pore properties as potential indicators of the micro-mechanism of substantial macro-deterioration due to weathering.