基于电阻率成像法的莫高108窟墙体内水盐运移过程分析

非均质的砂砾石层是莫高窟壁画的主要墙体,但砂砾石层的非均质性如何在水盐运移过程中发挥作用却还不清楚。为此,通过在108窟西壁面上1 m×1 m和2 m×2 m范围的三维高密度电阻率成像监测,发现在这些区域上,墙体电阻率的空间分布都是非均匀的,低阻值区域在空间位置、大小和形状上都会随时间而变化。这明确说明在构成墙体的非均质砂砾石层内存在着重要的水分饱和与非饱和过程(再分配过程),正是这一不断重复的饱和与非饱和过程促进了墙体内水分的运移和盐分在一些特定区域的聚集。研究成果对全面认识莫高窟墙体内的水盐运移机理,减轻和防治壁画盐害都具有重要意义。

Analysis of water and salt transport processes in the wall of Cave 108 of Mogao Grottoes by electrical resistivity tomography

A heterogeneous gravel bed is the main stratum for wall paintings of Mogao Grottoes, but it is still not clear how the heterogeneity of the stratum plays in the transport of water and salt in it. By three-dimensional high-density electrical resistivity tomographic monitoring, conducted in 1 m×1 m and 2 m×2 m regions at the surface of the west side wall of Cave 108, we found the spatial distributions of wall resistivity were heterogeneous in both regions. The spatial position, size and shape of the low-resistivity regions all changed with the time. This clearly indicates that there exists important water saturation and desaturation process (i.e. water redistribution process) in the heterogeneous gravel strata forming the painting wall. It is this repeated water saturation and desaturation process that drives the water to flow in the wall and causes the salt to accumulate in specific regions. The results of the study have a wider significance for fully understanding the water and salt transport mechanism in the walls of Mogao Grottoes, as well as reducing and preventing the salt-related damage to the wall paintings.