平遥古城墙基外侧砂岩的风化速度研究

Weathering rates of sandstone in lower walls of Ancient City of Pingyao

岩石风化的研究一直受到地貌学家、地质学家和岩土工程学家的关注。暴露于自然环境下的石质文物(特别是不可移动文物)可认为是在当地环境下经历了一段较长时间的风化试验。作者利用自行研制的、具有较高精度的仪器,量测了平遥古城墙基底部的砂岩经过638 a自然风化后的风化丧失深度,得其风化丧失深度和最大风化丧失深度分别为8.03～32.30 mm和11.80～46.97 mm,并以此计算出相应风化速度分别为0.0125～0.0506 mm.a-1和0.0185～0.0737 mm.a-1。比较砂岩的风化速度,发现其受朝向控制:朝南、朝西、朝东和朝北的砂岩的平均风化速度值分别为0.0481,0.0377,0.0286和0.0220 mm.a-1。笔者认为上述风化速度的差异是由不同朝向的砂岩受到的太阳辐射不同造成的。

The study on rock weathering attracts attention of geomorphologists,geologists and geotechnical engineers.Historic structures can be viewed as the exposure trials of the stone of which they are constructed.And,they represent a weathering experiment.Long-term weathering rates of sandstones are obtained for well-dated historic structures,that is,the bottom walls of the Ancient City of Pingyao（with 638 a exposure time） by using an especially designed movable instrument with high precision.The weathering depth and maximum weathering depth of the sandstone are 8.03~32.30 mm and 11.80~46.97 mm respectively.The difference of sandstone weathering rates in sample areas is exhibited between four aspects,which are higher in the south facing sandstone wall areas（0.0481 mm.a-1） than those in the west（0.0377 mm.a-1） and east faces（0.0286 mm.a-1）,and the north facing sandstone wall areas have the lowest weathering rate（0.0220 mm.a-1）.The reasons for the difference of weathering rate probably are the difference of insolations with four aspects.