敦煌莫高窟底层洞窟岩体内水汽与盐分空间分布及其关系研究

RESEARCH ON SPATIAL DISTRIBUTION AND RELATIONS OF SALINITY AND MOISTURE CONTENT INSIDE ROCK MASS OF LOW-LAYER CAVES IN DUNHUANG MOGAO GROTTOES

著名的世界文化遗产——敦煌莫高窟开凿于第四纪砂砾岩组成的崖壁上,受自然环境及人为因素影响,洞窟内壁画产生起甲、空鼓和酥碱等多种病害,尤其以底层洞窟最为严重。以病害最具代表性的底层洞窟之一莫高窟第98窟为例,通过在98窟西壁下部无壁画部位钻孔取样测定可溶盐,并在钻孔内布设高精度温湿度监测探头,西壁下部由南向北电阻率测定等研究,得出如下结论:98窟西壁表面到岩体内的可溶性盐主要以硫酸盐和氯盐为主,主要富集在表面至35cm深的岩体内;岩体内的温湿度和盐分有很好的关联性,盐分随着岩体内水汽含量的上升而下降;在岩体深125cm有凝结水产生;在高湿度和崖体源源不断的盐分来源的作用下,导致背靠崖体的西壁壁画内的含盐量要高于其他各壁,对洞窟环境的变化也更为敏感,病害也要远远严重于其他各壁等,这些结论可为壁画病害产生机制研究和防治提供科学依据。

Dunhuang Mogao Grottoes,the very famous world culture heritage,was chiseled in the cliff face of alluvial grit etching by the Daquan River in the Quaternary Period.Undergone natural and human factors,caves of Mogao Grottoes have many diseases and deteriorations including flaking,detachment and disruption;especially the caves of low-layer are most serious.Cave 98,one of the most valuable and representative diseases of low-layer caves in the Five Dynasties（AD914—AD935）,is selected as an example.Like all other caves in Mogao Grottoes,it has been affected by the natural environment.From the hole drilled at the lower portion of the western wall without painting,samples obtained for salinity analysis.The temperature and humidity are measured inside the hole.The analysis of electrical resistivity data from south to north of the lower portion of the western wall indicates that the soluble salt contents of the rock mass are mainly vitriolic and chloride,mainly concentrated between the surface and the depth of 35 cm.Water condensation occurs in the rock mass at depth of 125 cm.Inside the rock mass,there is close correlation between relative humidity and salinity.When moisture content rises,salinity drops.Due to the high humidity and abundant supply of salt,the salinity of the western wall,which is backed by the main cliff structure,is higher than the other walls,and it is more sensitive to changes in the environment.These achievements have provided a scientific basis for conservation wall paintings.