典型石窟砂岩的毛细吸水与变形响应特征

针对云冈石窟、乐山大佛和大足石刻,选择当地新鲜砂岩开展蒸馏水一维毛细上升试验,获取吸水质量和浸润前锋演变趋势,同时利用三向应变花测定试样不同高度处表面局部微应变的发展规律,并结合微观结构特征对宏观性质进行分析。研究结果表明:整个毛细吸水过程可划分为3个阶段,吸水率以及毛细高度随时间变化最快和最慢的分别是乐山砂岩和大足砂岩；云冈、大足和乐山砂岩局部微应变的最终值依次增加,且存在数量级上的差异,其变化趋势与浸润前锋运移密切相关,竖直和斜45°应变表现为先收缩后膨胀；砂岩毛细吸水和水化变形能力的关键影响因素分别是孔径分布和黏土矿物成分,其与文物真实产生的粉化、崩解、开裂和片状剥落等表面风化病害的形成密切相关。研究成果可为毛细水相关的劣化机理揭示提供丰富的参考数据,并向类似文物的病害评估与科学保护提供可靠的理论依据。

Characteristics of capillary water absorption and deformation response of sandstones in typical grottoes

Local fresh sandstone samples from Yungang Grottoes, Leshan Giant Buddha and Dazu Rock Carvings were used to conduct one-dimensional capillary rise tests for distilled water. Evolutions of absorption mass and wetting front were obtained while local microstrain was measured by strain gauge rosettes in three directions on the surface of specimen at different heights. Macroscopic properties were analyzed in combination with microstructural characteristics. The results show that the whole process of capillary water absorption can be divided into three stages. The fastest and the slowest changes of capillary water absorption and capillary height with time are in Leshan sandstone and Dazu sandstone, respectively. The final values of local microstrain gradually increase for Yungang sandstone, Dazu sandstone and Leshan sandstone, which have differences in order of magnitudes. The variation trend of local microstrain is closely related to the movement of wetting front in that both the vertical and tilted (45°) strains show a contraction first, followed by an expansion. Pore size distribution and clay minerals are critical in influencing the capacity of capillary water absorption and hydric deformation. Such ability is very closely correlated with the formation of surface weathering diseases such as powdering, disintegration, cracking and flaking.