云冈石窟砂岩特性与岩石风化试验

Characteristics of Yungang Grottoes Sandstone and Weathering Simulation Tests

侏罗纪期间河相沉积而成的巨大砂岩透镜体是云冈石窟遗产载体,在目前环境条件下,石窟砂岩风化破坏非常严重。通过现场调查表明,在不同细分层位,砂岩破坏特征与其沉积环境及沉积构造密切相关。进一步对不同风化程度样品进行测试,以此建立起风化评估依据,结果表明,该砂岩化学风化主要体现在胶结物流失、长石蚀变,而次生可溶盐结晶及冻融形成的物理破坏也不应该忽视。通过风化模拟试验可知:酸的溶蚀对石窟岩体表面造成直接破坏;同时,形成的可溶盐将导致砂岩出现由内而外劣化现象;由于岩石的孔隙率低、渗透性较差且胶结密实,岩石抵抗冻融作用相对较强。建议云冈石窟目前保护措施以治水为主,通过减少崖壁表面渗水、洞窟裂隙渗水及底部泥岩泛潮来减少上述劣化作用效应。

The relics carrier of Yungang Grottoes is a huge sandstone lens deposited by river in Jurassic period and the sandstones are weathering rapidly and seriously in present conditions. Based on the field investigation, there are close connections between the damages with the deposition surrounding and structure of every subdi- vide layer. Furthermore, a standard has been presented for evaluating the weathering degree depended on tests of rock samples to different deteriorated degrees. It has been shown from the tests of the sandstones that the ero- sion of the cements and alteration of feldspar are the main chemical weathering reasons and the mechanical weathering, crystallization of the secondary salts and cycle of freeze and thaws should be paid attention to. Con- clusions have been drawn from the weathering simulation tests that an inside to outside damage can be induced by the secondary soluble salts which come from the erosion of the acid on the grottoes rock surface directly and that the resistance for freeze-thaw cycle of the sandstone is good because of very low porosity, permeability and strong cementation. The suggestions has been presented for the relics protection that water controls such as the decrease of the surface flow on the cliff, the seepage from fracture inside caves and capillary water from the clay base of cliff are major ways to alleviate the weathering.