Study on the regional characteristics of sandstone grotto deterioration in the Longdong area
There are a large number of sandstone grottoes in the Longdong area of Gansu.Affected by natural and human factors,the grottoes have various types of diseases.Through a systematic survey of samples from provincial and national heritage conservation units,the sandstone grottoes in Longdong area were divided into three regions,namely the Jing River Basin,the Pingding River area and the Liupan Mountain area,according to the topographic features.The instability of rock mass,water erosion and superficial weathering have all developed in the study areas.In the Jing River Basin,the instability of rock mass was mainly manifested by the development of unloading cracks and joints.There were also problems of slope instability,such as collapse and landslide,with the collapse scale being generally larger and there being roof collapse diseases in large caves.There were many types of water erosion,the main diseases being water seepage,wetting in the grotto and cliff erosion.With regard to superficial weathering,powdering exfoliation,efflorescence,crust and alveolization were widespread;the second cause was the biological disease,mainly reflected by microorganisms and lichen moss cover.In the Pingding River area,the instability of rock mass was mainly caused by the falling of small pieces of rock and the collapse of the roof.The water erosion was of many types and of small scale,such as water seepage,dampness and erosion at the foot of the slope.The superficial weathering was also prevalent,and powdering exfoliation and recess erosion were more serious.In the Liupan Mountain area,the instability of rock mass was not developed,although there was some collapse of the roof.Water erosion was relatively undeveloped,with erosion on the cliff and a small amount of water seepage.The superficial weathering was less developed,with surface crust spalling and uneven surface discoloration being the most prominent.The results of the study have important implications for guiding research and planning for grotto conservation.
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