Weathering Characteristics And Mechanism Study On The Carrier Of Rock Paintings In Helankou

The rock paintings in Helan Mountain are the fourth batch of key cultural relics protection units in China.They are mainly distributed on the mountain rock walls inside and outside the 29 mountain passes at the eastern foot of Helan Mountain,as well as on the lonely rocks in the flooded fan desert grasslands outside the passes,which have undergone severe weathering and erosion from long-term exposure to the external environment.In this paper,we investigate and classify the developmental diseases of the rock in the Helankou Rock Paintings Reserve,investigate and test the rock features,and sample the relevant indoor simulated accelerated deterioration test,and study and analyze the surface weathering characteristics and mechanisms of the Carrier of Rock Paintings in Helankou by combining the microscopic analysis of particle size distribution,XRD and SEM,and the macroscopic changes of surface morphology and quality.The main conclusions are as follows.(1)The main types of diseases are surface granular disintegration,surface flake exfoliation,cavernous weathering,surface salt crystal and water staining,superficial fissure,mechanical fissures,structural fissures,hollow drums,plant diseases,animal diseases,microbial diseases and cement repair,of which surface granular disintegration is most widely distributed.(2)According to the site survey and the rebound strength test of the rock surface,the rock fissure and the nodal structure development of the carrier of Rock Paintings in Helankou are gradually decreasing and increasing with the increase of trench depth and elevation,respectively;the degree of weathering of the rock body on the south bank is generally greater than that on the north bank;the thickness of the weathered shell is generally 6 to 10 mm.(3)Combined with thin schist phase identification and XRD analysis,the changes in the mineral composition of the rocks after weathering are mainly shown by the increase in the relative content of quartz and clay minerals,and the decrease in the relative content of feldspar and calcite;SEM image analysis shows that the microstructure of the rocks after weathering is loose,pore development,mineral particle erosion is obvious,and the loss of internal interparticle cemented material is serious.(4)Through the indoor dry freeze-thaw cycle test,the satiated freeze-thaw-salttolerant coupling cycle test at different pH values and the dry and wet cycle test at different pH values,it can be seen that the test surface appearance,microstructure characteristics,mineral composition,particle size distribution characteristics,quality,surface hardness and wave speed all have corresponding changes.The satiated freezethaw-salt-tolerant coupled cycle group is the most obvious change under acidic conditions.The acidic conditions had a significant effect on the etching of feldspar and calcite.The degree of damage to the specimens was greater in the full water freezethaw cycle than in the dry freeze-thaw cycle and in the freeze-thaw cycle than in the wet and dry cycle.(5)The weathering of the carrier of the Rock Paintings in Helankou is controlled by the internal composition and structural characteristics of the rocks themselves and by complex external environmental influences.