云冈石窟砂岩表层温度效应及劣化机理研究

发布时间：2018-05-19 14:42

本文选题：砂岩表层 + 温度效应　；参考：《中国地质大学》2012年硕士论文

【摘要】：云冈石窟是依据自然崖壁山体开凿营建而成,既是建筑体(或构筑物),又是地质体。石窟赋存于地质环境之中,在漫长的历史时期受地质构造和各种地质营力的影响,产生了各种环境地质病害,导致石窟岩体发生破坏,严重威胁了石窟的保存。现场调查发现,石窟立壁岩体表层片状开裂是云冈石窟的主要病害之一。石窟岩体表层是雕刻艺术品的载体,表层的开裂剥落既破坏了石窟的雕刻艺术,同时又会弱化岩体的物理力学性质,导致洞窟失稳,如窟前立柱表层的不断剥落最终会导致洞窟失稳破坏。云冈石窟砂岩表层温度效应劣化研究,是国家科技支撑计划项目“石质文物保护关键技术”之“石窟岩体稳定性分析研究”课题(编号：2009BAK53B03)的重要内容。本文的主要研究成果如下： (1)温差变化在云冈石窟岩体风化中的物理作用机制,分为岩体的热胀冷缩和含水岩体的冰劈作用。现场调查发现,在岩体总体稳定性完好的石窟区,岩体表层的失稳破坏形式主要表现为崖壁岩体表层的片状开裂以及剥落。此类开裂体通常是温差应力下岩体表层沿原生微结构面拉裂扩展而成。因此,有必要研究环境气温变化对云冈石窟岩体的影响深度及岩体表层温度场随季节的变化规律。由岩体热物理参数测试可知,云冈砂岩的主要热物理参数：λ=3.516[W/(m·k)],0℃-35℃内,云冈石窟砂岩比热为0.63[J/(m3·℃],35℃-60℃内,比热为0.85[J/(m3.℃]；线膨胀系数α为11.7×10-6(1/K)。由温度的现场监测结果可知,云冈石窟砂岩表面温度与环境温度成正相关,呈现周期性变化。岩体内部各处温度随深度的变化也具有一定的周期性,同时反映了岩体在日夜交替环境下存在一定深度的热量交换,得出云冈砂岩日变温带范围为0-50cm。监测表明在0-5cm范围内温度梯度最大,是温度应力较明显部位。采用热传导微分方程解算温度场时需要进行适当假定。采用Maple软件能解决偏微分方程计算工作量大的问题。 (2)云冈石窟地区属于寒区,由现场温度监测结果可知,冬季石窟岩体温度长期低于0℃。岩体裂隙中水分在低温下发生相变,水结冰的过程中对岩体形成冻胀力。试验冻融前后在形态上出现颗粒脱落甚至断裂破坏,体积普遍膨胀,质量下降,纵波波速下降。且随着冻融循环次数的增加,上述物理指标也随之降低。试验冻融岩样的单轴抗压强度降低,随着冻融循环次数增加,强度衰减加剧。依据岩样的波速与单轴抗压强度建立了二者关系曲线。试验中对岩样S-6-1/S-6-2/S-2-3分别进行实时变形监测。通过监测结果发现原生缺陷(纵向裂隙或水平裂隙)对岩样的轴向应变和径向应变影响较大。试验冻融前后岩样的微观结构发生明显变化。随着冻融循次数的增加,岩样内部结构愈疏松,微裂纹不断扩展。通过对试验结果的分析,得出云冈石窟砂岩的冻融循环破坏机理。砂岩的冻融破坏主要是由岩体所含水分的相变引起。根据现场破坏情况及室内试验损伤情况总结出云冈石窟砂岩冻融循环破坏呈现片状剥落和裂纹扩展两种劣化模式。 (3)对于温度场对岩体的影响要分为低温和高温进行处理分析。高温时主要考虑岩体自身的热应力,低温时要同时考虑岩体中水分相变产生的冻胀力。边界条件的设置与荷载的施加准确的前提下,采用ANSYS进行温度场分布的数值模拟是较切合现场监测试验结果的。在高温条件下,进行岩体的热力耦合时,岩体的应力、应变均出现增大趋势。在升温和降温循环反复作用下,岩体出现应力反复变化,导致岩体出现一定的损伤。在云冈石窟地区的窟檐立柱长期处于应力调整中,不仅对立柱本身产生损伤,对其上的砂岩窟檐也会出现拉压破坏。在低温条件下,进行岩体的热力耦合时,岩体的应力、应变均出现增大趋势。尤其在低温下含水裂隙处出现相变,导致该部位出现相对的应力集中、应变增大。本文的创新点主要表现在： (1)采用自主研制的温度现场监测设备,获取了云冈石窟砂岩浅层温度一个气象年的完整数据,为今后该地区岩体浅层温度场的研究工作奠定了数据基础。首次对云冈石窟大气及浅层岩体的温度变化规律进行分析。结合云冈砂岩热物理参数,建立了该地区浅层岩体的温度分布统计学公式。 (2)课题组自主研制变形监测设备,在常规冻融试验的基础上增加冻结过程的径向、轴向的位移监测,揭示云冈砂岩的冻结劣化过程。 (3)采用ANSYS软件对高温下石窟立柱进行热力耦合分析,揭示该立柱风化的热力学本质。在岩体裂隙水低温相变的条件下,对石窟区某边坡进行热力耦合分析,得出冻结条件下岩体局部稳定性降低的结论。
[Abstract]:Yungang Grottoes is built on the basis of the excavation of the natural cliff mountain, which is both the building body (or structure) and the geological body. The grottoes are located in the geological environment. In the long historical period, the geological structures and various geological camping forces have caused various environmental geological diseases, resulting in the destruction of the grotto rock mass and the serious threat to the grottoes. It is found that the crack in the surface layer of the Grottoes is one of the main diseases of the Yungang Grottoes. The surface of the grotto rock mass is the carrier of the sculptured art. The cracking and peeling of the surface not only destroys the carving art of the grottoes, but also weakens the physical and mechanical properties of the rock mass, which leads to the instability of the grottoes, such as the continuous stripping of the surface of the front column of the grottoes. The collapse of the cave eventually leads to the failure of the caves.
The study on the surface temperature effect deterioration of the Yungang Grottoes sandstone is the important content of the "rock mass stability analysis study" (number: 2009BAK53B03) of the national science and technology support project "key technology of stone cultural relic protection" (number: 2009BAK53B03). The main achievements of this paper are as follows:
(1) the physical mechanism of the variation of the temperature difference in the weathering of the rock mass of the Yungang Grottoes is divided into the thermal expansion and contraction of the rock mass and the ice splitting of the hydrous rock mass. So it is necessary to study the influence depth of the environmental temperature change on the rock mass of the Yungang Grottoes and the change law of the surface temperature field of the rock mass with the season. It is known that the main thermal physical parameters of Yungang sandstone are lambda =3.516[W/ (M. K)], 0 C -3. Within 5 C, the specific heat of the Yungang Grottoes sandstone is 0.63[J/ (M3. C), the specific heat is 0.85[J/ (m3. C) and the coefficient of linear expansion is 11.7 * 10-6 (1/K) within 35 C -60 C. It is known that the temperature of the sandstone surface has a positive correlation with the environmental temperature, and shows a periodic change. At the same time, it reflects a certain depth of heat exchange in the rock mass in the environment of day and night. It is concluded that the range of 0-50cm. monitoring shows that the temperature gradient of the diurnal temperature zone of Yungang sandstone is the largest in the range of 0-5cm, and the temperature stress is more obvious. Maple software can solve the problem of heavy computation of PDE.
(2) the Yungang Grottoes area belongs to the cold region. It is known from the field temperature monitoring results that the temperature of rock mass in the winter Grottoes is lower than 0 C. the moisture of the rock mass in the rock fracture occurs at low temperature, and the frost heave force is formed in the process of water freezing. With the increase of the freezing thawing cycle times, the above physical indexes also decrease. The uniaxial compression strength of the test freeze-thaw rock decreases. With the increase of the freezing thawing cycle times, the intensity attenuation increases. According to the wave velocity and the uniaxial compressive strength of the rock samples, the two relation curves are set up. In the test, the rock sample S-6-1/S-6-2/S-2-3 is respectively in the test. Real time deformation monitoring is carried out. Through monitoring results, it is found that primary defects (longitudinal fissures or horizontal fractures) have great influence on the axial and radial strain of rock samples. The microstructure of rock samples changes obviously before and after freezing and thawing. With the increase of freezing thawing times, the internal structure of rock samples is looser and the micro cracks continue to expand. The failure mechanism of the freeze-thaw cycle of the Yungang Grottoes sandstone is analyzed. The frost thawing failure of the sandstone is mainly caused by the phase change of the water content in the rock mass. According to the damage of the site and the damage of the indoor test, it is concluded that the damage of the freeze-thaw cycle of the Yungang Grottoes is two deterioration patterns of flake flake and crack growth.
(3) the influence of temperature field on rock mass should be divided into low temperature and high temperature. The thermal stress of rock mass is mainly considered at high temperature. At low temperature, the frost heaving force produced by water phase change in rock mass should be considered at the same time. Under the premise of setting the boundary condition and applying the load accurately, the numerical simulation of the distribution of temperature field is carried out by ANSYS. Under the thermal coupling of rock mass, the stress and strain of rock mass appear to be increased under the thermal coupling of rock mass under the condition of high temperature. Under the repeated action of heating and cooling cycle, the rock mass appears repeated changes, which leads to a certain damage in the rock mass. The grotto column in the Yungang Grottoes area is in the stress adjustment for a long time. At low temperature, the stress and strain of rock mass appear to increase, especially in the water cut cracks at low temperature, which leads to the relative stress concentration and strain increase.
The main innovation points of this paper are as follows:
(1) to obtain the complete data of a meteorological year of the shallow temperature of the sandstone in the Yungang Grottoes by using the self developed temperature field monitoring equipment, which has laid the data foundation for the study of the shallow temperature field of the rock mass in the area in the future. The temperature change law of the atmosphere and shallow rock in the Yungang Grottoes is analyzed for the first time. The statistical formula for the temperature distribution of shallow rock mass in this area is established.
(2) the project group independently developed the deformation monitoring equipment. On the basis of the conventional freezing and thawing test, the radial and axial displacement monitoring of the freezing process was added to reveal the freezing and deterioration process of the Yungang sandstone.
(3) ANSYS software is used to analyze the thermomechanical coupling of the grottoes at high temperature to reveal the thermodynamic essence of the column weathering. Under the condition of the low temperature phase change of the fractured water in the rock mass, the thermodynamic coupling analysis of a slope in the Grottoes is carried out, and the conclusion that the local stability of the rock mass is reduced under the freezing condition is obtained.
【学位授予单位】：中国地质大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：K879.22;P642

【参考文献】