Quantitative Assessment Of Weathering Degree Of Sandstone Material In Dazu Rock Carvings

Dazu Rock Carvings,located in Dazu District,Chongqing,is the religious inscriptions on precipice during the end of Tang Dynasty and the begin of Song Dynasty.It bases on the Buddhism,with statues of Confucianism and Taoism.The carved cultural heritage experiences hundreds of historical period,which results in different kinds and degrees weathering diseases.However,there is a lack of clear qualitative and quantitative understanding and assessment for weathering damage of surface rock,the core problem of sandstone caved temple and stone caving preservation.In this paper,the sandstone material of Dazu rock carvings is taken as the research object.The samples of 48 different weathered sandstone are selected.Richter hardness,the measured velocity,flat velocity measurements,compressive strength,the drilling resistance,the coefficient of capillary suction,the mineral composition,the chemical composition,microstructure,dry density and porosity are tested for each sample.In order to fully grasp the changes in the physical and mechanical properties,chemical composition,mineral microstructure of Dazu Rock Carvings sandstone material weathering process,establish a quantitative evaluation system of sandstone weathering degree,the correlation of the test results and the degree of weathering is analysised,Compare the advantages and disadvantages of the techniques,various of test technology are comprehensive applied to explain the results.The main conclusions of this paper are as follows:(1)The Dazu carved sandstone material has smaller dry density,larger porosity and water absorption rate.It also has little difference between the open porosity and the total porosity,the corresponding is the little difference between free water absorption and saturated water absorption(a larger water saturation coefficient),which caused the sandstone easily affected by water and salt water and has weaker weathering resistance.(2)The quantitative evaluation system for the weathering degree of Dazu Rock Carvings is got by testing the compressive strength of fresh sandstone cores,referencing to the "Geological Engineering Manual" in the fourth edition of the degree of quantitative criteria for weathering and the fitting relationship among the indexes.Each index has its own advantages and disadvantages.Comprehensive use of a variety of indicators for the comprehensive evaluation of the research object can avoid the limitation of single index effectively.(3)Dazu Rock Carvings sandstone weathering is accompanied by changes in mineral composition and chemical composition.The specific performance is the decomposition of calcite and dolomite and the loss reduction of Sodium,Magnesium,Calcium and Potassium oxide.The selected weathering index Wck and four chemical weathering indices all have a good indication for the degree of weathered sandstone of Dazu Rock Carvings and can be used to quantify the sandstone material weathering degree.There is a certain amount of clay minerals in the sandstone of Dazu Rock Carvings(mainly illite,illite mixed layer mineral,chlorite and green smectite mixed layer mineral).The clay minerals have the characteristics of water swelling and shrinkage,which result in weathering sandstone.