四川乐山大佛风化的初步探讨

四川乐山大佛石刻是我国重要的“世界文化与自然遗产”之一,石刻表面毁损非常严重。本文通过（1）检测石刻所在地区粉砂岩的样品成分（XRFS）获悉,SiO₂含量高达84%;（2）安装微侵蚀测量装置（MEM）直接测得粉砂岩的表面侵蚀速率大约为0.216～0.305mm/a;结合（3）粉砂岩表面的相对硬度测试比较等途径,对石刻毁损的表面过程机制进行了初步的综合分析。结果表明,由于粉砂岩结构松散,经水浸后表面硬度急剧下降,而且当地的水、气等条件适宜于生物繁衍等特点,石刻风化毁损的原因主要在于水、生物等环境因素对粉砂岩胶结物有强烈的破坏作用。

A study on weathering processes of Leshan Grand Buddha,Sichuan,China

Leshan Grand Buddha is one of the most important heritage resources of the World Heritage of Culture and Nature in China,which is located in Lingyun Mountains at Leshan,Sichuan province,China.The surface weathering problem of the carved stone is very serious,and how to protect it from the bad weathering is a difficult task.Therefore,this paper studies on the surface weathering problems of the siltstone in Lingyun Mountains,where Leshan Grand Buddha is located,in order to get more deterioration information about the carved stones. The test results of the siltstone samples with the X-ray Fluorescence Spectrometry(XRFS) indicated that the SiO_2 is the main component and its quality percentage is up to 84%,the next parts are Al_2O_3 of 7.5% and Fe_2O_3 of 1.7%,etc.In addition,the siltstone includes a great deal of quartz powder,most of its diameter is around 0.250mm,and the other is the mauve cementation. In order to measure the erosion rates of the siltstone,we installed four suits of micro-erosion meter(MEM) instruments based on the principle of screwing measurement.The results indicated that the erosion thickness is mostly close 0.216-0.303mm of the year.We also investigated the environmental factors besides the experiment and found that water and biological intrusions are two important factors affecting the erosion rates. At the locale,we also tested the rigidity of the siltstone surfaces too with grout rebound instrument(ZC5 Model),which proved that siltstone weathering is faster than that of limestone because of the very low rigidity.The surface rigidity of siltstone will reduce quickly and become soft once it touches water,so the siltstone surface is easy to be destroyed by environmental factors. Therefore we can conclude that the Leshan Grand Buddha will go on weathering because the siltstone rocks has loose structure,and siltstone surface can be ruined easily.The good natural environment such as water vapor from the river,complex components of the siltstone cementation conditions is favorable for the microorganism and plants to grow.Therefore,water and bio-environment are important external factors accelerating the heritage surface deterioration and the fundamental internal factor is the unstable structure of the quartz grain and cementation system.