Surface weathering of the cliff at Bingling Temple Grottoes: A cultural relic on the Bank of Reservoir in NW China

The world cultural heritage Bingling Temple Grottoes (BTG) is a typical sandstone cultural relic on the bank of Liujiaxia Reservoir in the semi-arid region of northwest China. After the construction of the Liujiaxia Reservoir, the changes in the hydrogeological and climatic conditions in the small region have accelerated the weathering process of the cliff bottom. However, the influence of the water reservoir on rock surface weathering remains further understanding. In this study, we quantified the degree of surface weathering of a representative cliff in the BTG. Several typical in-situ tests were carried out, including peeling test, hardness test, and ultrasonic measurement, further supplemented by X-ray diffraction analysis. Despite good correlation among indices for the same lithology, the test results were insufficient for cross-lithology weathering evaluation. Consequently, the modified TOPSIS method was introduced to evaluate weathering across different strata. TOPSIS scores reveal altitude-related variations in weathering degree. Overall, the surface weathering degree of the cliff intensifies from top to bottom. The upper section (> 1743 m) of the cliff is primarily mechanically damaged, in contrast to the bottom layer (influenced by reservoir water level changes), which exhibits severe deterioration and intense chemical weathering related to water. Our study provides experience and methodological reference to the preservation of cultural relics and enhances the understanding of surface weathering of stone heritages on the bank of the reservoir in the semi-arid region of NW China.