Study on the salt weathering and mechanism of the Banyueshan Giant Buddha in Ziyang City

Abstract The sandstones of the Banyueshan Giant Buddha in Ziyang has been suffered different degrees of weathering damage under the influence of external geological environment factors. Through field investigation and laboratory test, the weathering damage types and weathering mechanism of sandstones were defined and analyzed. The research shows that the main weathering damage types of sandstones include exfoliation, soiling, chapping, hollowing and encrustation. The lithotype of the sandstones is confirmed to be yellowish-gray medium-fine grained lithic feldspar sandstone by microscopy. Through XRF chemical composition analysis and field investigation, it was found that SO3 and CaO contents in the surface weathered samples increased significantly. Conventional XRD results show that clay minerals and calcite increased in weathered sandstone samples compared with unweathered core samples. Due to the high detection limit of XRD, soluble salt could not be detected in the samples. The sedimentation-separation can achieve the enrichment of trace soluble salts in the samples. XRD results after sedimentation-separation show that the weathered samples contain soluble salts such as gypsum (80.3%), thenardite (1.6%), etc, but little soluble salts are detected in the unweathered core samples. In addition, the soluble salt ion test further proves that the surface weathered samples are rich in soluble salts, indicating that the existence of soluble salts has an important effect on the weathering damage of sandstones. Based on the theoretical analysis of the crystallization process and pressure of soluble salts, combined with the above experimental results, it is believed that the water absorption, dehydration and crystallization of soluble salts and the accompanying volume expansion and contraction are the internal reasons for the weathering damage of the Banyueshan Giant Buddha in Ziyang.