【作者】 王宇；

【导师】 李建林；

【作者基本信息】 武汉大学 ， 水工结构工程， 2012， 博士

【摘要】 随着我国国民经济的快速发展,交通、矿山、水利水电等工程领域出现了大量的边坡、地下洞室、坝基等岩土工程,这些岩土工程中存在的岩体的稳定性问题通常是工程建设进程与安全的重要制约因素。影响岩体稳定性的因素众多,诸如岩体所处的应力状态、各向异性、尺寸效应、节理倾角以及随时间推移产生的流变效应等。地下工程的施工经常遇到软弱岩体,大规模的地下开挖及回填使得地下工程周围地基的稳定性和软岩地基的力学特性研究显得十分重要和迫切。本文以典型软岩-泥质粉砂岩和软弱夹层为主要研究对象,研究了考虑应力路径、节理倾角及卸荷速率等因素影响下的软岩瞬时力学特性及其在恒定外荷载长期作用下的流变力学特性,主要研究工作如下：(1)对完整软岩进行了瞬时三轴压缩试验,研究了不同围压下的软岩强度、变形及破坏特征。试样结果表明,软岩瞬时三轴压缩过程中表现出典型的延性破坏特征,随围压增高未出现明显的脆-延转化点。(2)对含三种不同倾角的断续节理软岩进行了瞬时三轴压缩试验,结果表明,节理软岩瞬时三轴压缩强度明显低于完整软岩,且节理倾角40°的试样强度最高,0°的其次,60°的最低,且随着围压的增高,节理对试样的应力应变特性影响程度降低。节理倾角60°的试样破坏时沿预制节理面端部扩展形成贯通破裂面,节理倾角分别为0°和40°的试样则从左右节理面端部开始沿近轴向应力方向扩展直至形成一组至两组贯通剪切破裂面,预制断续节理间并未贯通形成破坏面。(3)对完整软岩进行了不同卸围压速率下的恒轴压卸围压试验,试验结果表明,试样达到破坏所需的围压卸荷量随卸荷速率加快呈对数形态增大,且应力应变特性及破坏特征均受卸荷速率影响显著。根据试验结果,提出反映试样卸荷过程中的变形模量随围压卸荷量变化规律的公式E(σU)=a*e(b/σuc+d)并在其中引入参数c表征不同的卸荷速率。(4)对含不同倾角断续节理软岩进行恒轴压卸围压试验,试验结果表明,预制节理对试样强度影响显著,含节理试样破坏所需的围压卸荷量约为完整试样的58%-84%,且节理倾角为60°的试样强度降低最显著。节理试样卸荷破坏时,变形模量降低幅度较大,其降低程度为同条件下完整试样的2-3倍。与完整试样相比,节理倾角0°和40°的试样的峰值变形及残余变形和完整试样接近,而节理倾角60°的试样峰值及残余变形明显小于完整试样。节理倾角对试样破坏形态影响显著,节理倾角与试样剪切破坏角之间关系较为复杂,无明显规律可循。(5)根据亭子口水利枢纽坝基实际工程应力状态,进行了一组四级正应力水平下的软弱夹层剪切流变试验,试验结果表明,软弱夹层剪切流变变形特性显著,在各级剪应力水平下有较大的流变变形量。根据试验结果分析,提出用u=m×enτ的指数函数关系可以较好的表征试样的平均及稳态流变速率变化规律,并基于等时簇曲线法,提出利用u-△τ／△u曲线确定流变屈服拐点的新方法,结果证明该方法便捷直观,能准确的确定软弱夹层的长期抗剪强度,对工程实际具有一定的参考价值。(6)根据亭子口水利枢纽坝基实际工程应力状态,进行了一组四级正应力水平下的软岩剪切流变试验,试验结果表明软岩流变特性与软弱夹层基本相似,但软岩流变变形量远小于软弱夹层。根据软岩流变曲线特征提出了软岩剪切流变经验方程u=u0+A(1-exp(-Bt))+Ctn,拟合结果表明该经验方程能较好的反映软岩各阶段的流变变形特征。(7)通过瞬时三轴压缩试验确定了完整软岩在不同围压下的抗压强度,据此确定出软岩试样在不同围压下的三轴压缩流变试样的轴向应力水平分级方案。采用RLW-2000岩石三轴流变试验机对完整软岩进行了不同围压下的三轴流变力学试验,分析了不同围压条件下软岩试样的轴向及侧向变形随时间的变化规律；探讨了加速流变阶段软岩试样流变变形及速率的发展趋势和特征；分析了不同围压条件下的软岩试样三轴流变破裂形式与机制。(8)基于软岩三轴压缩流变试验结果,采用RLW-2000岩石三轴流变试验机对完整及节理软岩进行了不同应力水平及不同围压下的三轴卸荷流变力学试验,分析了不同应力水平及围压条件下完整及节理软岩试样的轴向及侧向变形随时间的变化规律；探讨了加速流变阶段完整及节理软岩试样流变变形及速率的发展趋势和特征。(9)基于软岩试样三轴流变全过程曲线,参考流变本构模型的选取及参数辨识流程,利用线性Burgers流变本构模型,通过Levenberg-Marquardt非线性优化最小二乘法对软岩试样流变模型参数进行了辨识,并分析了辨识所得的试样轴向及侧向流变参数随应力水平及围压的变化规律。(10)以线性Burgers流变模型为基础,将一个新的黏性元件与Burgers模型串联起来,并在该元件的黏滞系数ηD中引入损伤因子D,建立了一个新的非线性损伤流变模型,以便更好的描述流变全过程曲线中的非线性加速流变变形阶段。验证结果表明该模型能与流变试验曲线很好的吻合,反映了该模型的正确性与合理性。(11)采用提出的非线性损伤流变模型对亭子口水利枢纽坝基工程进行了数值模拟计算,研究了坝基岩体的流变力学特性及其长期稳定性,研究成果对亭子口水利枢纽坝基岩体的长期稳定与安全具有一定的参考价值和指导意义。更多还原

【Abstract】 With rapid economic development, a great number of geotechnical engineering such as slope, underground cavern and dam foundation had appeared in engineering fields such as transportation, mine, water conservancy and hydropower engineering. It is noteworthy that the rock stability in these geotechnical engineering is usually the important restrictive factors of the construction process and safety. As we all know there are many factors which can affect the rock stability, such as stress state, anisotropy, size effect, joint inclination, the rheological effects appeared with time, and so on.In the construction of the underground works the weak rock are frequently encountered, the large-scale underground excavation and backfill make the research on the stability of surrounding rock foundation and mechanical properties of soft rock foundation become quite important and urgent. In this paper, the typical soft rock-muddy siltstone and soft interlayer were took as the main study objects to study the instantaneous mechanical properties of soft rock and the rheological mechanical properties under the long-term effect of constant external load, considering the influence of stress path, joint inclination, unloading rate and some other factors. The main research work is as follows:(1) The instantaneous triaxial compression test was carried out on the intact soft rock mass to study the strength, deformation and damage characteristics of soft rock mass under different confining pressures. Test results show that in the process of instantaneous triaxial compression the typical ductile failure features is obvious, however with increase of the confining pressures the obvious brittle-ductile transition points didn’t appeared.(2) The instantaneous triaxial compression test has also been carried out on the soft rock masses with three different inclinational intermittent joints; the test results show that the instantaneous triaxial compression strength of the jointed soft rock is significantly lower than that of the intact soft rock. What’s more the strength of rock mass with40°joint inclination is the highest, the strength of rock mass with0°joint inclination is the second, and the strength with60°joint inclination is the lowest. Moreover the influence of joints on rock stress-strain feature reduces with the increase of confining pressures. In the destruction process for rock mass with60° joint inclination, the penetrating failure surface was extended from the precast joint surface, for rock mass with0°and40°joint inclinations one or two set penetrating shear failure surfaces was finally formed from the end of the left and right precast joint surfaces along the direction of the axial stress, however the precast joint surface didn’t run-through, and didn’t form the failure surface.(3) The confining pressure unloading test with constant axial compression pressure was carried out on the intact soft rock which considered the different unloading rates, the test results show that the unloading confining pressure amount required in destruction increases in logarithmic form with the increase of the unloading rate, what’s more both the stress-strain behavior and damage characteristics are influenced by the unloading rate significantly. According to the test results, the formula which can reflect the variation law formula E(σU)=a*e(b/σuc+d) of deformation modulus with the confining pressure unloading amount during unloading was proposed. In the formula, the parameter C represents the unloading rate.(4) The confining pressure unloading test with constant axial compression pressure was also carried out on the soft rock masses with three different inclinational intermittent joints; the test results show that the sample strength were significantly affected by the precast joint. For rock samples with joints, the confining pressure unloading amount required in destruction is about58%-84%the amount of the intact rock mass, what’s more for rock samples with60°joint inclination the strength decrease is the most significant. For joint rock samples, the deformation modulus dropped with large amplitude in destruction, and the decrease extent is2-3times of the intact rock samples in same condition. CoMPared with the intact rock samples, the peak deformation and residual deformation of rock samples with0°or40°joint inclination is close to that of the intact rock mass, while the value of rock samples with60°joint inclination is significantly less than that of the intact rock mass. All in all, the influence of the joint inclination on failure mode is remarkable; however the relationship between the joint inclination and the shear failure angle is quite complex without obvious pattern.(5) According to the actual engineering stress state of the dam foundation in Tingzikou project, a group of shear rheological tests on the weak intercalation under four normal stress levels was carried out, the test results show that the shear rheological deformation properties of the weak intercalation is significant, and the rheological deformation amount at all shear stress levels is large. According to the test results analysis, the exponential function u=m×enτ was proposed to express the change law of the average and state rheological rate, and on base of the isochronous curve method a new method which use the curves u-Δ τ/Δ u to certify the yield inflection point was proposed. Finally the calculation results show that the method is quite convenient and intuitive, and can calculate the long-term shear strength of the weak intercalation accurately, what’s more the method has a certain reference value for the actual engineering.(6) According to the actual engineering stress state of the dam foundation in Tingzikou project, a group of shear rheological tests on the soft rock mass under four normal stress levels was also carried out, the test results show that the rheological deformation properties of the soft rock is similar to that of the weak intercalation, but the rheological deformation of the soft rock is far less than that of the weak intercalation. According to the rheological curve of the soft rock, the shear rheological empirical equation u=u0+A (1-exp (-Bt))+Ctπ was proposed, and the fitting results show that the empirical equation can reflect the rheological deformation characteristic of soft rock in various stages better.(7) According to the compressive strength of the intact soft rock at different confining pressures which were got in the instantaneous triaxial compression test, the axial stress level classification scheme of triaxial compression rheological samples under different confining pressures was set up. The triaxial compression rheological test of the intact soft rock under different confining pressures was conducted with RLW-2000, the change law of the axial and lateral deformation with time under different confining pressures was analyzed, the develop trend and characteristics of the rheological deformation and rate in rheological deformation accelerated phase was researched, and the triaxial rheological rupture form and mechanism under different confining pressures was analyzed.(8) Based on the triaxial compression rheological experimental results of soft rock, the triaxial unloading rheological test of the intact and joint soft rock under different confining pressures was conducted with RLW-2000, the change law of the axial and lateral deformation with time under different confining pressures was analyzed, the develop trend and characteristics of the rheological deformation and rate in rheological deformation accelerated phase was researched.(9) On base of the triaxial rheological complete curve of the soft rock samples, and refer to the selection and the parameter identification process of the rheological constitutive model, the linear rheological constitutive model Burgers was used to identify the soft rock parameters by the nonlinear optimize least squares Levenberg-Marquardt, what’s more the change law of the identified axial and lateral rheological parameters with the variation of stress level and confining pressure was also been analyzed.(10) On base of the linear rheological model Burgers, A new viscous element was cascaded with Burgers model, and a damage factor D was introduced to the element viscosity coefficient ηD, and then a new non-linear rheological damage model was established, which can better describe the nonlinear accelerated rheological deformation stage in the rheological complete curves. The verification results show that the model can close fit to the rheological test curves, reflecting the accuracy and reasonableness of the model.(11) The nonlinear damage rheological model was used to simulate the dam foundation of Tingzikou project, and the rheological mechanical characteristics and long-term stability of the rock mass in dam foundation were analyzed, the research results have an a certain reference value and guiding significance to the long-term stability and security of the rock mass in Tingzikou project.更多还原