广元千佛崖摩崖石质文物保护的环境地质问题研究

【作者】 宗静婷；

【导师】 岳乐平；

【作者基本信息】 西北大学 ， 地球环境科学， 2011， 博士

【摘要】 按照石质文物病害的不同表现,大体可分为两大类型：石窟岩体的失稳问题和风化问题。失稳问题是指石质文物所依托的岩(山)体出现岩体结构不稳定和局部危石等问题。风化问题是指在文物表面毫米到厘米级的范围内,文物外观的破坏。稳定性问题与地质结构条件有关系。岩石材料是地质作用的产物,岩石的变形和破坏性质不但与岩石的复杂成因和结构密切相关,而且还受温度、围压、孔隙水等环境因素的影响。因此,对病害机理的分析首先应当对地质环境进行勘察,了解它所依存的地质环境以及当地的气候环境条件与石质文物病害的关系。四川广元千佛崖窟区属亚热带湿润季风气候区,在大地构造上位于扬子地台西缘北段,龙门山造山带和前陆盆地区,东侧与大巴山造山带及其前陆盆地相邻,属于地震多发区。广元千佛崖摩崖造像分布区域地层出露单一,岩层为中厚层夹薄层侏罗系千佛崖统泥质砂岩。主要矿物为长石、石英,也含有绿泥石、蒙脱石等粘土矿物和硬石膏等成分。岩层产状210-240°<23-29°。千佛崖摩崖造像的泥质石英砂岩,结构疏松、干抗压强度范围值在29.9-4.763MPa之间,湿抗压强度范围值在10.467-11.079MPa之间,抗压强度值低、软化系数仅为0.33。千佛崖窟区岩体深部构造完整,但在岩质边坡上纵横交错分布有多次构造运动形成的区域性构造节理,其中较为发育节理有三组,其产状分别为：26°-76°<62°-82°、100°-122°<63-77°、315°-336°<65-78°。区域性构造节理具有发育广泛,产状稳定,规模较大,延长较远,间距较宽,节理面平滑,多见羽列状和共轭“X”型节理系等特征。大量节理切割使千佛崖岩体具有多裂性,不仅为加速风化和风化向深部发展提供了界面条件,而且将岩体切割成菱形块状体或楔形体易产生拉裂式和滑移式崩塌进而坠落破坏。尤其是其中一组顺坡向的节理破坏性大。采用DT8380红外线温度测试仪先后对岩石不同部位和大小不同文物表面进行温度测试、岩石渗水的原位实验和日本NEC TH7700SP红外热像仪对部分窟龛佛像进行了含水率的全面热成像检测,揭示窟区岩石风化的机理。千佛崖窟龛造像表面的风化机理表现为三个方面,温差冻胀作用物理风化和水-岩相互作用的化学风化和微生物的生物风化作用：温差冻胀作用的破坏表现为：窟龛岩石的韵律层的层裂破坏；矿物膨胀系数不同造成矿物颗粒连接的破坏；暴雨浇淋的涨缩作用和吸水矿物的结晶压力对矿物晶体结构的破坏及冰劈作用等。水-岩相互作用：水-岩相互作用是水溶液与石雕中的矿物进行化学反应,不仅导致化学元素在岩石与水之间重新分配,而且导致岩石细微结构的改变。其作用的机理表现在四个方面：一是减小岩体内部粘结力,增加岩体孔隙度,促使长石、石膏和岩盐等溶解,使岩体内孔隙度增大；二是粘土矿物如蒙脱石等遇水即膨胀的特性,会给岩体内部增大压力而破坏岩石结构；三是裂隙水分迅速蒸发时,水中盐类结晶体积的膨胀将对岩壁产生强大压力,引起石雕的碎裂等；四是发生化学溶蚀,长石等矿物易于风化成高岭石、蒙脱石等在地表条件下稳定的新矿物,扩大岩体中的裂隙；同时可溶盐成分逐渐从岩体内部迁移到表层析出,形成表层粉化、彩绘起甲、空鼓、脱落等灾害现象。千佛崖石窟岩壁表层生长有大量的微生物,包括细菌、真菌、藻类、地衣、苔藓等。植物和细菌在新陈代谢中常常析出有机酸、硝酸、亚硝酸、碳酸和氢氧化铵等溶液,腐蚀石刻岩体并在石刻表面形成淀积物；表生风化环境中,微生物主要通过质子交换、配体络合、氧化还原生物膜等方式促进硅酸盐矿物(长石、粘土矿物等)溶解破坏。四川广元千佛崖紧邻公路,采用英国GURALP公司生产CMG-40T-1短周期速度型三分向地震计,对过往汽车产生的震动程度进行了现场测试。汽车单次在四川广元千佛崖石窟附近通过不会对完整石窟造成破坏性影响,但可能诱发处在临界稳定状态的文物或岩块失稳而破坏。虽然汽车单次行驶对不会对完整石窟造成破坏性影响,但汽车长期行驶产生的震动会对千佛崖石窟造成疲劳性损伤。提出的川陕公里改道对策已被有关部门采纳。对千佛崖石窟岩体的稳定性的评价,采用了根据地质特征的结构面、风化程度以及边坡岩体结构等对危岩体的地质稳态等级做出判断,以区划图的形式来标示千佛崖石窟危岩的危险性等级。提出在广元千佛崖窟区应该进行系统的全面的加固治理,对不稳定的岩体采用不锈钢全长胶结锚杆加固,窟室间岩体张裂缝和起壳病害采用微型碳纤维锚杆加固,设置边坡岩体应力应变监测系统,准确掌握其本构关系。锚杆加固的工程措施已被有关部门采纳。作好防水措施,提出的在山顶和山梁开挖排水沟槽,在降雨时迅速疏排水,对缝宽>1.5mm裂缝进行灌浆加固和嵌补,建议已被采纳。并且全面评价了千佛崖摩崖石窟的风化程度,通过调查、测量、照相、采样等,了解并记录各龛窟的主要病害特征,分析评估这些龛窟的风化程度,风化程度的指标选取不同种类病害的面积来表征。绘制了重点龛窟的病害图。风化病害的治理措施上鉴于目前无机和有机表面处理剂均存在不同程度的文物原貌改变,提出研制岩石文物表面防风化的生物膜,降低和减缓石质文物表面的风化速度。同时通过大环境的治理,降低人为因素的影响。更多还原

【Abstract】 The disease of stone artifacts can be divided into two types:instability problem and weathering problem. The instability problem is the unstable of rock structure and stone local crisis of relying on the rock (hill) body of stone artifacts. The weathering problem is destruction of cultural appearance in millimeter and centimeter range of artifacts surface-Rock material is the product of geological rock that deformation and failure of rock is the closely related of not only the complex nature of the causes and structure, but also temperature,onfining pressure, pore water and other environmental factors. Therefore, the mechanism of disease should first survey the geological environment, and understand relationship between diseases of stone artifacts in dependencies of the geological environment and local climate conditions.The cave area of The thousand buddha cliff belonged to the subtropical humid monsoon climate zon, located in the tectonic western margin of the northern section of the yangze, the longmenshan orogenic belt and foreland basin area. adjacent the daba mountains orogenic belt and foreland basin in the east.The Single rock type expose in cave area of Qianfo Ya what is the thick layer and laminar shale argillaceous sandstone of The thousand buddha cliff system of Jurassic,t is J2-Q3. The major minerals are the feldspar, the quartz, and anhydrite and clay minerals, such as chlorite, montmorillonite. The stratigraphic occurrence is 210-240°<23-29°. The grains of argillaceous quartz sandstone of The thousand buddha cliff cliff are loose, the dry compressive strength range of values is in the 29.9-4.763 MPa, the wet compressive strength range is between 10.467-11.079MPa, the compressive strength value is low, softening coefficient is only 0.33.The deep structural is integrity in cave area of The thousand buddha cliff rock, however,the rock slope crisscross distribute regional structural joints with the formation of several tectonic movement. There are three groups of joints of more development, their occurrence are:26-76°<62-82°,100-122°<63-77°,315-336°<65-78°. The features of regional structural joints has wide range of occurrence, stability, the larger, extended farther, wider spacing, joint surface smooth, more feather-like and the conjugate "x"-type section of the faculty. The rock was cut into multiple cracking by large number of joints that not only provides the interface conditions to speed up the deep weathering and further weathering,but also easy to produce crack- sliding and falling damage collapse owing to diamond or wedge block in The thousand buddha cliff, the most serious along the slope direction of the joint.The mechanism of weathering of rocks was reveal by the temperature test in different parts of the surface of different cultural by using infrared temperature dt8380, and seepage of rock by situ experiments, and moisture detection by infrared imaging system in japan nec th7700sp.the mechanism of surface weathering of grotto express in two ways:temperature and frost weathering, water-rock interaction.The temperature and frost weathering shows in what way:rhythmic layer spallation of cave rock; mineral grains connected damaged by the different of mineral expansion coefficient; the expanding role by heavy rain poured over; crystal structure of the damaged by absorbent mineral crystallization pressure and splitting by the role of ice.The water-rock interaction is chemical reaction between solution and mineral in statue. The chemical reaction results not only redistribution between rocks and water re-allocation of chemical elements, but also diversification of rock microstructure.The mechanism of its role in four way:the first, its reduces the internal cohesive force, increases rock porosity, promotes feldspar, gypsum and rock salt dissolved, so that orosity increased in rock; the second, water swelling properties of clay minerals would increase pressure and damage the internal structure, such as montmorillonite, etc. The third, fissure water quickly evaporates, the expansion of salt crystals from water volume will generate strong pressure to the rock, causing stone fragmentation, etc. The chemical dissolution would expand the crack rock from feldspar and other minerals into kaolinite, montmorillonite, etc. At the same time, the soluble salts composition is gradually migrated to the surface from the joints,lead to disaster, such as powder of surface, painted crust, painted hollowing, and painting shed.There grow a large number of microorganisms surface of caves of Qian foya, including bacteria, fungi, algae, lichen, moss and so on. The metabolism of plants and bacteria often precipitates solution that have organic acid, nitric acid, nitrous acid, arbonic acid and ammonium hydroxide will corrode and deposit on surface of carves. The mechanism of microbial destruction is solution of silicate minerals (feldspar, clay minerals, etc.) by proton swap, ligand complexation, oxidation-reduction biofilm in supergene weathering environment.The vibration level of passing vehicles was field tested by one-third of the short period seismometer of speed-type cmg-40t-1. the results show that single vehicle through the caves in the vicinity not effect to integrity grotto, but may induce instability and destruction of artifacts or rock of the critical steady-state. While the single vehicle vibration is not a devastating effect on the integrity of caves, long-running vibration would cause fatigue damage on The thousand buddha cliff cave.The steady-state level of geological of rock caves of the The thousand buddha cliff was judged by the structure surface, weathering and other geological characteristics of rock slope, and marked form of the zoning map. Strengthening governance systems and comprehensive should be implemented in Guangyuan The thousand buddha cliff cave area, especially in dangerous areas as soon as possible. The degree of weathering was comprehensive evaluated by the diseases characterized of the size of different types, through surveys, surveying, photographic, sampling, etc. And a disease map of focus cave was drawn. The precaution measures of weathering disease should be developed wind of the biofilm of the surface, reduce and slow down the speed of weathering on stone artifacts, because inorganic and organic surface treatment agents are varying degrees of change of original cultural. The influence of human factors should be reduce through the governance environment.更多还原