【作者】 张利洁；

【导师】 唐辉明； 黄书岭；

【作者基本信息】 中国地质大学 ， 岩土工程， 2016， 博士

【摘要】 近些年来,随着我国国民经济和科学技术的发展,深部岩体工程越来越多,深部岩石力学与工程研究中面临高地应力、高外水压力引起的结构安全、岩爆和长隧洞的快速施工等一系列挑战性的岩石力学与工程课题,通过试验研究深部岩体的力学性质成为一个紧迫的课题。深部高应力脆性岩体的微破裂机制及其强度随时间劣化的效应等关键问题是目前深埋岩石力学理论研究的国际前沿课题。西部水电工程地下洞室大都具有大埋深、超高地应力的特点,洞室围岩体的力学响应明显有别于浅部岩体,由此造成工程灾害的成灾机理、工程稳定控制及其设计理论等方面也有着显著的差异,研究高应力条件下围岩力学特性规律,明确其变形破裂机理是迫切需要解决的科学问题。本文以典型的脆性岩石大理岩和灰岩为研究对象,通过系统的试验研究、理论分析和数值仿真手段,研究了高应力脆性岩石的滞后破坏效应、高应力脆性岩石的破坏驱动应力水平随损伤时间演化的规律以及高应力脆性岩石的强度参数随损伤时间劣化的规律。考虑高应力和损伤时间的影响,选取合理的力学模型,对某水电站地下厂房洞室群围岩进行数值仿真开挖和支护分析,研究开挖过程中围岩的位移场、应力场、塑性区等的分布特征和演化规律,掌握地下厂房洞室群开挖过程中围岩的变形规律、变形量、可能的围岩失稳破坏模式及部位等围岩力学行为,为地下厂房的开挖支护设计改进、监测布置等提供依据。本论文的主要研究内容包括：(1)通过基于RMT系统的高应力脆性岩石常规单轴压缩试验和时滞性单轴压缩试验研究,分析了强度特征、应力应变特征及其破坏模式,获得高应力岩石的应力强度、破坏驱动应力水平随损伤时间的变化关系,并对关系曲线进行拟合得知,应力强度和破坏驱动应力水平随损伤时间的变化关系均可以用指数函数进行拟合。并且分析比较了高应力岩石常规单轴压缩的破坏模式和时滞性单轴压缩的异同点。(2)针对高地应力条件下地下洞室典型围岩大理岩与灰岩等脆性岩石,开展了基于MTS系统的不同应力状态(低围压、中围压、高围压)下的岩石三轴压缩加、卸载破坏试验,分析了不同围压范围与不同应力路径条件下岩石的强度特征,探讨了常规应力水平和高应力水平下岩石强度与变形特性的差异性。结果表明：大理岩与灰岩在低围压加载路径下均表现出较为明显的脆性,但随着围压的逐渐增大表现出一定的延性特征；相对于加载路径,岩石在卸载应力路径下峰后脆性更为显著,与三轴加载强度参数相比,两种岩石的三轴卸载强度参数均表现为内摩擦角增加及粘聚力降低的一致性规律。同时分析研究了大理岩和灰岩在不同应力状态下的岩石三轴压缩加、卸载试验后的破坏模式。(3)基于摩尔-库伦强度准则对岩石在低、中、高围压段下的强度特征进行拟合分析,得到不同围压范围段的强度参数相互间的差异性较大,表明高应力条件下随着围压的变化,强度参数并非一个恒定的常量,故线性关系无法很好地反映岩石试样围压与强度的变化规律,而Hoek-Brown准则、幂函数型准则等非线性强度准则,对描述高应力条件下岩石强度的非线性特征具有优势,能够较好地反映从低围压到高围压岩石的强度特性变化规律。针对高应力条件下岩体变形、强度特性呈现出的非线性,研究了高应力下岩石的本构关系及强度准则。(4)选择大理岩作为研究对象,研究了高应力下时滞性三轴压缩试验,试验结果表明：脆性岩石在有围压的时滞性破坏试验中均为小变形的脆性破坏,且表现明显的时滞性破坏特征,试验中岩样破坏的滞后时间甚至达到数小时甚至数天,围压使得岩石破坏的滞后时间大大增加。随损伤时间的延长,岩石内摩角和粘聚力等强度参数发生如下变化规律：粘聚力随着损伤的发展从峰值迅速下降,并很快到达残余极限值；而内摩擦角随着损伤的发展经历了先上升再降低两个过程,其中上升段是在大部分粘聚力损失后逐渐升高至峰值。时滞性三轴压缩试验中岩样产生的裂纹大都沿轴向扩展,并不呈现出大块的破坏,而是碎裂成许多相对较薄的片状和大量的片状碎屑,由于围压的存在,岩石时滞性破坏有增强的趋势,即滞后破坏时间延长。通过分析岩石破坏所需时间与破坏应力驱动水平(偏应力值／强度比值)的关系,可以对较低破坏驱动应力水平下岩石破坏所需滞后的时间进行预测。(5)通过脆性岩石在高应力下加、卸载应力路径下破坏机理的微细观试验研究,分析了不同应力路径下岩石破裂断口形貌、微裂纹扩展及断面CT扫描数规律,从微细观角度探讨了岩石在高应力下的宏观破裂模式。结果表明：大理岩加载破坏时,其宏观裂纹主要由于内部的矿物晶粒滑移运动和矿物晶体的解理位移所导致的；大理岩卸载破坏时,破裂断口出现了较多的扩展裂纹,表现更多的是裂隙面之间的摩擦滑移,卸荷条件下大理岩试样易产生拉剪破坏。灰岩加载破坏时,破裂面呈压剪状态下微孔裂纹聚集型断裂形式,可见较为明显的擦痕及粘土类矿物的定向排列,沿剪切面伴有磨损的断晶集合体；灰岩卸载破坏时,主要表现为拉剪状态下隐性层理面间的解理断裂和沿晶断裂以及它们的相互耦合形式,微裂纹部分为沿长石或石英解理拉断裂,且呈现随机性分布,多沿岩样初始缺陷发育。通过多种微细观测试手段包括电镜扫描、CT扫描试验及AE声发射等,分析相应路径下的AE声发射活动变化特征,研究脆性岩石在高应力下微裂隙扩张的特征及机制识别。(6)根据时滞性单轴压缩试验和时滞性三轴压缩强度试验的成果以及现有的理论的基础建立了应力强度随损伤时间变化的关系和破坏驱动应力水平随损伤时间变化的关系,并拟合出强度参数c,φ随时间变化的函数,在此基础上建立了岩石强度参数随时间劣化的模型,该模型能合理地描述持续加载对岩石强度的劣化过程,获得岩石强度随时间的演化规律,从理论机制上解释了岩石的滞后破坏效应。(7)深埋隧洞开挖以后围岩会出现损伤和应力重分布现象,这种应力变化在不同性质围岩中产生不同的现场现象,且损伤区内的岩体力学参数(弹性模量E、黏聚力c、内摩擦角φ)会随着损伤时间的延长不断降低,为反映围岩损伤区内脆性岩体力学参数劣化特性,故拟合出强度参数c,φ随时间变化的函数。同时考虑时间和高地应力的影响,选取合理的力学模型,将c,φ随时间变化的函数用在数值仿真分析中,岩体力学参数随着单元动态更新,这样可以反映现场围岩在洞室开挖扰动后不断发生劣化的过程,通过分析劣化过程中的应力场和位移场,从而评价和预测围岩破损区(松动圈)的范围和深度。(8)高应力大理岩和灰岩具有脆塑延转换特性,即靠近低围压条件下表现出脆性,高应力作用下的脆性岩体会很普遍地出现破裂损伤现象,由于损伤往往开始出现在应力水平相对不高(如60%的应力峰值)的条件下,这种损伤尽管现在还不能引起岩体强度和力学特性的急剧变化,但随着工程的进展损伤向着破裂的方向扩展,可能给深埋隧洞工程运行期间的安全留下了隐患。通过本文的研究,可以对围岩的滞后破坏进行预测、预报,并对其防治提供理论依据。更多还原

【Abstract】 In recent years, with the development of our national economy and science and technology, we will face more and more deeply rock engineering. A series of challenging rock mechanics and engineering issues such as high stress, high external water pressure due to structural safety, rock burst and long tunnel rapid construction will be faced. Study the mechanical properties of deep rock through experimental has become an urgent task. Key issues such as micro-fracture mechanism and strength deterioration with time of brittle deep rock under high stress is the deep rock mechanics theoretical study of international topics at the forefront currently. Most of the western hydropower project has a large underground cavern depth and high stress. The mechanical response of caverns is significantly different from the shallow rock mass. It has significant difference in aspects of disaster mechanism, engineering stability control and design theory. Study mechanical characteristics of surrounding rock under high stress conditions and clarify its deformation and fracture mechanisms is an urgent scientific issue need to solve.In this paper, typical brittle rock such as marble and limestone are chosen for the study. The effects of time-logged fracture, the law of destruction driving stress level evolution with damage-time and the law of strength parameters deterioration with damage-time of high stress brittle rock are studied by experiment, theoretical analysis and numerical simulation. Consider the impact of high stress and damage-time, selecting appropriate constitutive model, numerical simulation of excavation and maintenance analysis are studied on a hydropower station on the underground caverns. Distribution characteristic and evolution law of the displacement field, stress field, plastic zone, etc. of surrounding rock during excavation are researched. The regular pattern and the amount of deformation, potential failure mode and key location of the mechanical behavior of surrounding rock during the excavation of underground powerhouse is grasped. It can provide evidence for the underground plant support design improvements, monitoring arrangements, etc..The research wok mainly concentrated in the following aspects in this paper.(1) Based on conventional uniaxial testing and time-lagged fracture uniaxial compression testing of high stress brittle rock are carried out. This paper analyzes the strength characteristics, stress-strain characteristics and failure mode to obtain the relationship curve between stress intensity and destruction driving stress level with the damage-time. This paper gets a conclusion that the relationship curve between stress intensity and destruction driving stress level with the damage-time are exponential relationship by curve fitting. This paper alse compare and analyze the similarities and differences of high stress rock failure mode between conventional uniaxial testing and time-lagged fracture uniaxial compression testing.(2) Typical brittle surrounding rocks like marble and limestone which under high stress conditions of underground caverns are chosen as testing sampling. Based on MTS, different stress state (low pressure, medium pressure, high pressure) under triaxial compression plus, uninstall destruction tests are carried out. This paper analyzes the strength characteristics of different pressure and different stress paths. The differences of rock strength and deformation characteristics under normal stress levels and high levels are discussed. The results show that marble and limestone at low pressure loading path exhibite obvious brittle. But with the pressure increasing it shows some ductility characteristics. The peak brittleness under unloading stress paths is more significant than that under loading stress paths. The triaxial unloading strength parameters of two types of rocks show that the internal friction angle is increase and the cohesion is drop.(3) Based on Mohr-Coulomb strength criterion, the rock strength characteristics under low, medium and high pressure are analyzed. The strength parameters under different pressure are so different between each other. It indicates that strength parameters under high stress conditions are not constant with the pressure change. So that a linear relationship can’t be a good reflection of the rock sample pressure and variation of strength. And nonlinear strength criterion like Hoek-Brown criterion and power function criterion has advantages to describe nonlinear characteristics for the rock under high stress conditions.It can reflect the strength variation characteristics change from low pressure to high pressure of surrounding rock. Deformation and strength characteristics of rockmass are nonlinear under high stress conditions. Constitutive relation and strength criterion of rock under high stress is analyzed in this paper. Failure mode of the marble and limestone in different stress states (low pressure, medium pressure, high pressure) under triaxial compression loading and unloading test is analyzed.(4) In this paper, marble is chosen as the research object. The time-lagged triaxial compression test under high stress is analyzed. The test results show as follow:It is brittle fracture of small deformation in the confining pressure time-lagged fracture trials of brittle rock. It shows significant time-lagged fracture characteristic. The lag time of rock sample failure is up to few hours or even days. The lag time of rock destruction is greatly increased because the confining pressure. With extending damage-time the strength parameters like friction angle and cohesive of rock variation occurs in the following:The cohesion with the development of damage declines quickly from peak and soon reach the residue limits. The friction angle with the development of damage increases first and then reduces. Where in the increased phase is gradually increased to a peak when the most cohesive force losses. The crack of time-lagged triaxial compression test of rock samples are mostly along the axial extension which is not showing chunks of damage, but fragmented into a number of relatively thin sheet and a lot of flaky debris.In this paper, the relationship of damage-time with destruction driving stress level (partial stress/strength ratio) of high stress brittle rock are acquired. It can predict rock failure time under a relatively low level of destruction driving stress level.(5) In this paper failure mechanism through mesoscopic experiment of brittle rock under high stress loading and unloading stress paths is studied. The law of rock fracture morphology, micro-crack growth and the number of cross-sectional CT scan under different stress paths is analyzed. From Microscopic view, macro fracture mode of the rocks under high stress is discussed. The results show as follow. Fracture of marble under loading condition its macroscopic crack mainly due to mineral grains sliding movement and mineral crystal cleavage displacement. When fracture of marble under unloading condition, there are more burst fracture propagating crack. It is mainly the friction sliding between the crack surfaces. Under the condition of unloading marble sample is easy to led tensile shear failure. When fracture of Limestone under loading condition, microporous crack fracture aggregate in crack surface under compression-shear fracture state. It is obvious that scratches and clay minerals are alignment and worn-off crystal aggregates along the shear plane. When fracture of Limestone under unloading condition, mainly shows the state of tension and shear fracture cleavage plane between the hidden bedding and intergranular fracture as well as their mutual coupling form. Micro-cracks are along quartz or feldspar cleavage fracture randomness distributed and develop along the initial defects. Mesoscopic testing through a variety of means, including the fine scanning electron microscope, CT scans and other tests and acoustic emission AE. Characteristic and mechanism of micro-crack of brittle rock under high stress is studied.(6) Deep buried brittle rock will be influenced by the time and surrounding high stress. In the long process of loading, rock strength can be reduced to approximately 60% of the instantaneous strength. According to time-logged uniaxial compression test and time-logged triaxial compression test as well as the existing basic theory, the relationship between stress intensity and damage-time and the relationship between driving stress level and damage-time is established. The function of strength parameters c,φ over time is fitted. On this basis, a rock strength parameters over time weaken model is established. This model can reasonably describes the rock strength weakening process with continuous loading. It can obtain the law of rock strength with time weakening. It can explain the effect of time-lagged fracture of rock from the theoretical mechanism.(7) Surrounding rock of deep tunnel will be damaged and stress will be redistributed after the excavation. This stress change produces a different in-site phenomenon in the different kind of surrounding rock. The rock mechanics parameters (elastic modulus E, cohesion c, internal friction angle cp) will continue to decrease with the extension of damage time. The characteristic of surrounding rock within a certain region will be deteriorated after excavation. A reasonable constitutive model is selected which consider not only the high stress but also damage-time to reflect the deterioration characteristic of brittle rock damage zone. With the numerical simulation analysis, rock mechanics parameters is dynamically updated following the unit to reflect the continued deterioration of the surrounding rock during the cavern excavation. It can evaluate and predict the scope and depth of surrounding rock damaged area (loose circle) by analyzing the stress and displacement field after fractured.(8) Marble and limestone under high stress have the characteristic that brittleness can change to plastic. It can exhibit brittleness when close to the low confining pressure condition. It is a very widespread phenomenon when damage occurs in brittle rock under high stress. Fracture began to appear in the stress level under relatively high (such as 60% of peak stress) conditions. Although this damage is not yet cause a sharp change in rock strength and mechanical properties, but with the progress of the project develop, the damage expand in a direction of fracture that may give a hidden danger during tunnel project operation. Through this study, time-lagged fracture of the surrounding rock can be predicted and forecasted. It can provide a theoretical basis for its prevention.更多还原