【作者】 刘刚；

【导师】 姜清辉；

【作者基本信息】 武汉大学 ， 防灾减灾工程及防护工程， 2016， 博士

【摘要】 非贯通节理岩体为边坡和地下洞室工程中经常遭遇的一类复杂的工程介质,节理的存在及其相互影响对岩体的破坏和力学特性起着决定性的作用。本文采用水泥砂浆作为相似材料模拟砂岩,制作包含多条非贯通节理的岩体试件,开展了一系列的单轴、双轴及三轴压缩试验。同时,在试验过程中采用多通道声发射检测仪对试件的破坏过程进行了动态监测。通过物理试验、理论分析及数值模拟试验对包含多条节理岩体试件的变形和力学特性、破坏模式、分支裂纹的扩展和贯通机制以及声发射特性进行了分析研究,主要成果及创新点如下：(1)多节理岩体试件的破坏模式主要取决于裂纹的类型(翼裂纹和次生共面裂纹)和扩展路径。单轴压缩下随节理几何参数的变化主要衍生出的破坏模式有：平面破坏、台阶式破坏、块体转动破坏及混合破坏;双轴压缩下随着侧压σ2水平的提高,试件的破坏模式由节理面间的贯通破坏转变为岩体材料的压剪破坏；三轴压缩下随着围压的变化,45°试件的破坏模式均为沿试件对角线上节理面的平面破坏。(2)应力-应变关系曲线的线形特征受岩体试件上位置变化的节理的影响显著。单轴压缩下,根据节理岩体试件应力-应变曲线在峰后破坏阶段的线形特征,可以将其归纳为四种类型：单峰跌落式曲线、屈服后应变硬化式曲线、锯齿状应变软化曲线及渐进式应变软化式曲线；双轴压缩下,应力-应变曲线在峰前阶段存在先屈服后应力强化的现象；三轴压缩下,应力-应变曲线较为光滑,峰后残余强度水平较高。(3)试件峰值强度σma和弹性模量E的各向异性特征受节理倾角β及侧压σ2的影响非常明显。单轴压缩下,试件的峰值强度σmax随节理倾角β增加呈先减小后增加的变化规律,峰值强度σmax-节理倾角β关系曲线呈“U”形分布。当节理倾角β≤60°时试件的弹性模量E在5-10GPa间小幅波动,当节理倾角β≧75°时试件的弹性模量E超过19GPa。在双轴压缩条件下,随着σ2的增加,“U”形曲线中间部位逐渐抬高,曲线的分布特征逐渐趋于平坦,即随着σ2的增加,峰值强度受节理倾角的影响变小。同时,侧压σ2对试件的弹性模量E没有明显的影响,其随节理倾角的变化规律没有变化。(4)多节理岩体试件在单轴压缩下的声发射时序特征能够较好的反映试件内部裂纹的萌生和扩展状态。试件的声发射时序分布特征具有明显的阶段性特点。根据事件率反映的声发射活跃程度及事件累积计数的特征变化,可以将节理试件在整个加载过程中的声发射时序特征过程大致分为四个阶段。(5)声发射b值反映了声发射幅值分布的比例,也代表着岩体在荷载作用下声发射大小的相对尺度。在本研究中,在裂纹处于稳定扩展阶段时,b值在2-3之间波动；当裂纹开始发生不稳定扩展时b值减小；具有不同倾角节理岩体试件的b值在应力到达峰值强度时趋于一个定值,约为1.66。(6)将时间作为中间变量,声发射与力学特征参数间即可建立一一对应的关系,利用岩石微元强度weibull分布概率密度函数,推导出基于声发射事件累积计数的节理岩体损伤模型及本构关系,该损伤模型较好的反映了试件的损伤随加载进程的变化关系。(7)采用改进刚体弹簧法程序,模拟了多节理岩体试件在单轴和双轴压缩条件下的破坏过程,重现了多节理岩体试件在物理试验中的破坏模式,并进一步从微细观的角度揭示了裂纹的萌生和扩展机制。更多还原

【Abstract】 It is common that numerous rock engineering such as rock slope and underground cavern to be excavated in or on non-persistent jointed rock mass which is a kind of complex engineering medium. The existence and interaction of joints plays a decisive role in damage and mechanical characteristics of rock mass. To carry out a series of tests of uniaxial compression, biaxial compression and true triaxial compression on the jointed specimens, cement mortar was selected as the material to physically model the sandstone, and a set of specimens with non-persistent joints were made using the model materials. During the test, Multi-channel acoustic emission detector was used to dynamically monitor the destruction process of specimens. Through physical testing, theoretical analysis and numerical simulation test, the deformation, the mechanical properties and failure modes of the non-persistent jointed rock mass, mechanism of propagation and coalescence of branch crack and acoustic emission characteristics were analyzed. Through aforementioned analysis, the results and conclusions can be obtained as follows:(1) The failure modes of jointed specimens with multi non-persistent joints mainly depend on the crack type (e.g. wing crack and secondary-coplanar cracks) and the crack propagation path. As have been observed from tests, there are four failure modes, i.e., planar failure, stepped failure, rotation of new blocks, and mixed failure that influenced by the configuration of joints under uniaxial compression. With increasing the lateral pressure, the failure modes of jointed specimens change from breaking through joint plane to the compression-shear damage of rock mass. The failure will through the cater-corner plane for jointed specimens containing non-persistent joints with inclination of 45°under triaxial compression.(2) The configuration of non-persistent joints has significant influence on the characteristic of the stress-strain relationship curves. With respect to the uniaxial compression, according to the post-peak characteristic, the relationship curves of stress-strain of jointed rock specimens were divided into four types:falling with a single peak, strain hardening after yield, strain softening with zigzag fluctuation, and progressive strain softening. In terms of biaxial compression, the effect of lateral pressure eliminates the difference between stress-strain relationship curves in the post-peak phase. In the pre-peak phase, however, there is a stress hardening stage after yield. Under triaxial compression, stress-strain relationship curves turn to be relatively smooth with high residual strength in post-peak.(3) The anisotropic characteristics of uniaxial compression strength (UCS) σmax and elastic modulus E of jointed specimens are greatly influenced by the joint inclination βand lateral pressure σ2-Under uniaxial compression, the amax decreases with the increasing of β at beginning, then σmax increases as β increases, which show a U-shaped in the relationship curve between σmax and β. When β≤60°, the value of E fluctuates in the range of 5-10 GPa. When β≥75°, the value of E turns to be bigger than 19 GPa. Under biaxial compression, with the increase of σ2, the bottom of U-shaped curve of relationship between σmax andβ gradually rises, which means that the influence of β on σmax becomes non-significant as increasing the σ2.In addition, the lateral pressure σ2 shows no obvious effect on the elastic module E.(4) Due to the obvious periodic characteristic of the time series, the time series characteristic on acoustic emission of multi-joint rock specimens under uniaxial compression can appropriately reflect the initiation and propagation of crack in the jointed specimens. According to the active level and the characteristics of the cumulative count change events reflected by the acoustic emission event rates, the time series characteristic on acoustic emission can be divided into four stages during the whole loading process of jointed specimens.(5) The value of acoustic emission parameter b reflects the amplitude distribution ratio, and it also represents the relative scale of acoustic emission as the jointed rock mass under loading effect. In the present study, the value of b fluctuates between 2-3 in a stage of stable propagation of crack. The value of b will decreases as the crack starts unstable propagation. Significantly, the values of b of all the tested specimens with different joint inclinations will approach to a stable level that approximately is 1.66 as the stress reach its peak.(6) Taking the time as intermediate variable, a one-to-one relationship between the acoustic emission and the mechanical parameters of jointed rock specimens can be established. The damage model and constitutive equation were deduced using weibull probability density function of rock infinitesimal strength. The proposed damage model perfectly reflects the changes of damage with the loading process of the jointed specimens.(7) The failure process of jointed specimens under uniaxial and biaxial compression was numerically simulated by the improved rigid body spring method. The simulations can reproduce all the failure modes that observed in physical model tests, which deeply reveal the mechanism of the initiation and propagation of crack from a mesoscopic perspective.更多还原