【作者】 赵斌；

【导师】 沈世伟；

【作者基本信息】 吉林大学 ， 土木工程， 2024， 硕士

【摘要】 近年来随着我国大型水利枢纽工程的建设,坝址区岩体开挖卸荷产生的破坏现象越来越受到学者们的关注。坝址区岩体在自然状态下,通常处于较为复杂的三向应力状态,对边坡岩体进行开挖后会引起显著的瞬时变形,并发生一定程度的破坏。同时,坝肩及拱肩槽开挖卸荷后的松弛效应会诱发岩体产生蠕变破坏现象,导致混凝土坝体产生复杂的应力重分布情况,使刚性坝体与坝肩岩体变形不一致,进而引起导致坝体产生附加应力,可能威胁大坝安全。因此,对高边坡岩体开挖卸荷松弛效应的研究显得尤为重要。由于岩体原位测试对试验条件和试验仪器要求过高而不易实现,对坝肩岩体开展室内卸荷蠕变试验,成为研究岩体开挖卸荷力学特性研究的首选方案。本文选用某水利枢纽坝肩灰岩为研究对象,通过对试样进行单轴、三轴压缩试验、三轴卸荷蠕变试验,研究其力学特性。分析卸荷蠕变破坏试样微观损伤与宏观力学性能的相关性,建立改进的三维Poynting-Thomson模型。取得主要研究成果如下:(1)分析灰岩基本物理力学性质,测定灰岩基本物理参数并基于单轴、三轴压缩试验测定灰岩压缩强度、变形模量、弹性模量等力学参数,根据相对压缩应变响应法和体应变规律得到起裂应力为峰值强度的50%-60%,扩容应力为峰值强度的70%-80%。试验结果表明,压缩强度随围压增大呈线性增大变化,变形模量、弹性模量等力学参数随围压增大呈非线性增长,试样破坏呈较为明显的斜剪特征。(2)研究灰岩卸荷蠕变力学特性演化规律,通过恒轴压、分级卸荷应力路径对灰岩进行三轴卸荷蠕变试验研究其轴向和径向应变、蠕变速率、强度特征随轴向应力、分级卸荷量的演化规律,并对比等时应力-应变曲线法、稳态黏塑性蠕变速率法得出不同轴向应力下的长期强度分别为127.128、153.179、176.257MPa。(3)揭示蠕变微观损伤与宏观力学性能的相关性,基于Matlab图像处理技术处理光学显微镜获得的微观损伤图片,选择直方图均匀化法进行图像增强、Qtus算法进行二值化处理。结合分形特征揭示微观分形维数与宏观力学性能的相关性,试样宏观力学性能劣化程度随微观分形维数下降而加剧。(4)构建了考虑非线性蠕变阶段、加速蠕变阶段变形的改进蠕变模型,在Poynting-Thomson模型基础上引入黏塑性元件和非线性黏壶,并借助张量表示法推导出三维改进模型。经L-M算法对模型进行参数辨识和拟合验证,结果表明黏塑性元件和非线性黏壶可以更好地描述非线性加速蠕变阶段,改进后的三维模型表征灰岩卸荷蠕变全过程曲线的契合度更高。更多还原

【Abstract】 In recent years,with the construction of large-scale water conservancy hub projects in China,the damage phenomenon generated by the excavation and unloading of the rock body in the dam site area has received more and more attention from scholars.The rock body in the dam site area in the natural state is usually in a more complex three-way stress state,the excavation of the slope rock body will cause significant transient deformation and a certain degree of damage.At the same time,the relaxation effect after excavation and unloading of the dam shoulder and arch shoulder groove will induce the rock body to produce creep damage phenomenon,resulting in complex stress redistribution of the concrete dam body,so that the rigid dam body and the shoulder of the rock body deformation is inconsistent,which in turn causes the dam body to produce additional stresses,which may threaten the safety of the dam.Therefore,the study of unloading relaxation effect of high slope rock body excavation is particularly important.Due to the rock body in situ test on the test conditions and test equipment requirements are too high not easy to realize,the dam shoulder rock body to carry out indoor unloading creep test,become the study of rock body excavation unloading mechanical properties of the preferred program.This research paper examines the mechanical properties of a water conservancy hub dam shoulder grey rock.Through conducting uniaxial and triaxial compression as well as triaxial unloading creep tests on the specimen,the study aims to analyze the correlation between microscopic damage on the rupture surface of the unloading creep damaged specimen,and its macroscopic mechanical properties.The study also establishes an improved three-dimensional Poynting-Thomson model to comprehensively understand the research object.The main research results are as follows:(1)Analyze the basic physical and mechanical properties of greywacke,determine the basic physical parameters of greywacke and determine the mechanical parameters of greywacke such as compressive strength,deformation modulus and elastic modulus based on uniaxial and triaxial compression tests,and obtain the cracking stress of 50%-60% of the peak strength and the expanding stress of70%-80% of the peak strength based on the relative compressive strain response method and the body strain law.The test results show that the compressive strength increases linearly with the increase of perimeter pressure,the deformation modulus,elastic modulus and other mechanical parameters increase nonlinearly with the increase of perimeter pressure,and the damage of the specimen is more obvious oblique shear characteristics.(2)The evolution law of unloading creep mechanical characteristics of limestone is studied.The triaxial unloading creep test is carried out on limestone with constant axial pressure and graded unloading stress path to study the evolution law of axial and radial strain,creep rate and strength characteristics with axial stress and graded unloading amount.Compared with isochronous stress-strain curve method and steady-state viscoplastic creep rate method,the long-term strengths under different coaxial stresses are 127.128,153.179 and 176.257 MPa,respectively.(3)Reveal the correlation between creep microscopic damage and macroscopic mechanical properties,based on Matlab image processing technology to deal with the microscopic damage pictures obtained by optical microscope,choose the histogram homogenization method for image enhancement,Qtus algorithm for binarization.Combined with fractal features to reveal the correlation between microscopic fractal dimension and macroscopic mechanical properties,the degradation of macroscopic mechanical properties of specimens increases with the decrease of microscopic fractal dimension.(4)An improved creep model considering nonlinear creep stage and accelerated creep stage deformation was constructed,and viscoplastic elements and nonlinear viscous pots were introduced on the basis of the Poynting-Thomson model,and a three-dimensional improved model was derived with the help of tensor representation.The L-M algorithm is used to identify the parameters of the model and validate the fitting,and the results show that the viscoplastic element and the nonlinear viscous pot can better describe the nonlinear accelerated creep stage,and the improved three-dimensional model characterizes the unloading creep curve of tuff with a higher degree of fit.更多还原