真三轴压缩下砂岩的能量和损伤分析

为了探究真三轴压缩下砂岩的能量和损伤演化规律，利用自主研发的真三轴扰动卸荷岩石测试系统进行真三轴一次加卸载试验和真三轴压缩试验，对真三轴压缩应力–应变演化规律进行研究，探讨三向主应力加、卸载的对岩体的影响，利用图形面积积分法分别计算了真三轴压缩的弹性能密度、耗散能密度与输入能密度，分析三者随最大主应力卸载水平增加的规律及其相互之间的关系，进一步研究真三轴压缩过程中损伤演化规律，并对冲击地压倾向性判定条件弹性能量指数进行讨论。研究结果表明：真三轴压缩下最大主应力增大，使砂岩内部应力调整，从而引起中、小主应力方向应变变化，从能量角度定义该现象为能量“诱增”；划分了三个方向主应力加、卸载的种类，将加载分为损伤加载(最大主应力加载)与保护加载(中、小主应力加载)；将卸载分为常规卸载(最大主应力卸载)与损伤卸载(中、小主应力卸载)；真三轴压缩下中间主应力方向约束应力较大，使得该方向“诱增”弹性能密度比例高于最小主应力方向“诱增”弹性能比例；真三轴压缩下最大主应力方向应力提升，砂岩的弹性能密度、耗散能密度均与输入能密度之间存在线性函数关系，提出了真三轴压缩的能量分析方法，进一步得到了砂岩的储能极限...     

高地应力下岩石的真三轴试验研究

通过真三轴试验模拟高地应力条件下地下工程开挖引起的复杂的应力路径的演化。在设定的加载方式下，针对拉西瓦新鲜花岗岩的试验结果表明：当卸载最小主应力时，岩石发生回弹变形，声发射计数率比卸载前显著增加，增加的幅度随中间主应力的增加而逐渐提高。岩石的应力一应变关系为弹脆性，峰值强度随中间主应力的增加有所提高，峰值强度的提高值与中间主应力的比值随中间主应力的提高逐渐减小。声发射计数率峰值与应力水平有关，峰值的次数与破坏后主裂缝的条数相对应。最后，分析了岩石的破坏机制。     

考虑空隙压密特征的岩石弹塑性损伤增量本构模型

岩石的变形破坏全过程包括压密–弹性–塑性–损伤多个阶段,现有的基于经典弹塑性理论与损伤力学同时考虑岩石压密变形机制的本构模型研究较少。将岩石抽象为岩石骨架与岩石空隙2部分,依据空隙变形机制计算非线性压密变形,基于Drucker-Prager准则分析塑性变形特性,采用体积变形描述损伤演化规律,在经典弹塑性损伤理论框架下建立岩石压密–弹塑性损伤增量型本构模型及其积分算法。将岩石总变形视为压密、弹性与塑性3个部分,考虑空隙部分无法承受剪力且各方向变形无相互影响的特征,通过应力、应变张量谱分解在主应力方向上计算总应变。数值积分方法为基于Drucker-Prager准则的主应力方向回映算法,采用压密弹性预测方法计算预测应力,以分析迭代步中压密应变增量对总应变增量的影响。压密–弹塑性损伤本构模型与算法充分考虑空隙非线性变形机制与压密变形特性,共涉及压密、弹性、塑性、损伤4类10个参数,适用于长期服役过程中外部环境作用下空隙占比逐渐增加,骨架强度逐渐减小的工程岩体。应用模型研究干湿、冻融循环2种典型外部环境对岩石特性的影响,结果表明模型能够很好地模拟外部作用后工程岩体变形破坏的全过程,具有一定的理论...     

中间主应力对塑性混凝土变形性能的影响研究

为研究中间主应力对塑性混凝土变形性能的影响,设计2种不同配合比的塑性混凝土开展不同中间主应力的真三轴试验。试验过程中,最小主应力设计为0.4MPa和0.8MPa这2种情况,每种情况下中间主应力设置为3～4个等级,保持最小主应力和中间主应力不变,施加最大主应力,直至试件破坏。试样结果表明,中间主应力对塑性混凝土的变形性能有较明显的影响。在保持最小主应力不变的情况下,随着中间主应力的增加,塑性混凝土轴向峰值强度、峰值应变均随之增大,峰后近似水平段长度也随之增加,提高了试件的延性变形能力和抗裂性能,但对峰值前的变形模量和体积变形模量影响较小。试件破坏的特征受中间主应力与最小主应力差值影响,差值越大越偏向小主应力方向。     

最大主应力增加和最小主应力同时等量减小时岩石的声发射特征

使用真三轴压力机研究了E型、Am型应力途径下大理岩的声发射特征。其中E型实验,是从一定的应力状态开始,最大主应力增加,最小主应力同时等量减小使岩石破坏。这一过程中,声发射率的显著增加发生在极限应力状态处或其后的前兆应力降阶段。而在单独增加最大主应力使岩石产生破坏的Am型实验中,达到峰值差应力的90％左右时,声发射率就开始显著增加。结合前人的有关研究成果,我们认为:在复杂应力途径下,声发射率显著增加这一前兆的滞后出现是侧压减小的效应。     

岩石破裂声发射过程的围压效应

针对由于地下开挖引起的岩石声发射率突增及最小主应力减小可能引起地震等地质现象，利用统计损伤理论对岩石破裂过程中声发射率的时间序列特征，特别是三维应力下岩石的快速加卸围压对声发射的影响进行了理论探讨。结果表明：三维应力下岩石快速卸围压，促使声发射率突增，而在一定范围内快速增加围压，声发射并不发生，只有增加一定轴压，才会有声发射的产生，这些结果在计算机上得到了很好的模拟，并与实验结果相吻合     

损伤岩石受拉变形模量的理论计算方法

岩石受拉破坏过程本质是微裂纹扩展过程,假设均匀损伤的岩样由很多单裂纹岩石单元组成,受拉条件下含裂纹岩石单元的应变包括裂纹张开引起的岩石弹性应变,非弹性应变,岩石基质的弹性应变。采用COD理论计算裂纹尖端的最大张开位移,根据裂纹张开位移计算单裂纹单元的应变增量,计算出岩样受拉破坏时的应变与初始裂纹密度和裂纹最小间距的关系,最后建立了受拉条件下损伤岩样的体积变形模量计算方法。本方法能同时有效描述初始裂纹数量和裂纹长度对岩石变形的影响,更符合实际情况。结合算例分析显示:岩石裂纹张开引起的应变(包括弹性部分和塑性部分)是损伤岩石变形的重要组成部分,与初始损伤系数和内在抗拉强度成正比,与岩石基质弹性模量成反比。岩石的变形模量随着岩石的初始损伤增加而减小,随着裂纹长度损伤因子的增大而减小。并且初始损伤系数与初始裂纹密度以及裂纹最大半长的平方均成正比。     

水压致裂过程的三维数值模拟研究

基于RFPA数值分析方法和并行计算技术,建立了反映岩石细观损伤演化过程的三维渗流–应力–损伤耦合模型。对具有120万单元的方形岩石材料模型,进行了4组不同应力状态下水压致裂过程的三维大规模科学计算分析。计算结果分析表明：起裂压力与失稳压力并不重合,起始裂纹均为张性,裂纹扩展形式、表面平整度、走向、扩展失稳过程以及裂纹的空间分布形态受应力状态影响。当竖直方向为最大主应力方向时裂纹呈空间竖片分布,当水平应力差较大时裂纹表面形态平整,失稳到来较快;当竖直方向为最小主应力方向时裂纹的空间分布呈水平片状;不等的主应力情况下裂纹总是分布在最小主应力面内;当三向主应力相等时,裂纹起裂位置和扩展方向具有竞争趋势,空间分布不具规律,裂缝分支较多。数值模拟结果与物理实验结果有着较好的吻合,该研究对水压致裂工程设计有一定参考价值。     

用单轴抗压强度试验分析瑞典Äspö 废物 罐回取试验中的岩石损伤

 废物回取试验是一个在瑞典Äspö 地下实验室完成的,历时近5 a,为全尺寸处置库模拟加热试验。试验在一个直径f 1.75 m、深度8.5 m的钻孔中进行。开挖和加热后周边岩石中的温度升高、应力改变,因此,试验中岩石中可能产生的损伤是工程设计中关心的课题之一。为此,试验结束后,在试验孔3个不同深度处沿垂直和平行于最大主应力方向施打6个深度约1.5 m的近水平取样孔,并采集了12组岩样。对这12组岩样用MTS 815 岩石力学试验系统进行了单轴抗压强度试验。从单轴抗压强度、裂隙起始应力、裂隙损伤应力、最大裂隙体积应变和最大总体变进行了对比和分析,试验结果分析表明：从最大裂隙体积应变分析,在垂直于最大主应力方向的处置孔孔壁的岩石上可能存在一些轻微的微破裂为特征的损伤。从宏观力学特性来说,岩石没有任何可测的损伤。     

用单轴抗压强度试验分析瑞典Aspo废物罐回取试验中的岩石损伤

废物回取试验是一个在瑞典(A)sp(o) 地下实验室完成的,历时近5 a,为全尺寸处置库模拟加热试验.试验在一个直径Φ1.75 m、深度8.5 m的钻孔中进行.开挖和加热后周边岩石中的温度升高、应力改变,因此,试验中岩石中可能产生的损伤是工程设计中关心的课题之一.为此,试验结束后,在试验孔3个不同深度处沿垂直和平行于最大主应力方向施打6个深度约1.5 m的近水平取样孔,并采集了12组岩样.对这12组岩样用MTS 815 岩石力学试验系统进行了单轴抗压强度试验.从单轴抗压强度、裂隙起始应力、裂隙损伤应力、最大裂隙体积应变和最大总体变进行了对比和分析,试验结果分析表明:从最大裂隙体积应变分析,在垂直于最大主应力方向的处置孔孔壁的岩石上可能存在一些轻微的微破裂为特征的损伤.从宏观力学特性来说,岩石没有任何可测的损伤.     

中间主应力与层理方向对页岩力学和渗透特性影响的试验研究

 为探讨中间主应力与层理方向对页岩力学和渗透特性的影响,运用自主研制的多功能真三轴流固耦合试验系统,以含气页岩为研究对象,进行真三轴应力条件下不同中间主应力加卸载试验。研究结果表明：中间主应力对页岩渗透率的影响在中间主应力垂直于层理面时最大,最小主应力垂直于层理面时次之,最大主应力垂直于层理面时最小;当中间主应力垂直于层理面或平行于层理面时,中间主应力与渗透率呈负相关。中间主应力垂直于层理面时渗透率对中间主应力的敏感性明显大于中间主应力平行于层理面时的敏感性,二者相差1～2个数量级;此外,定义损伤变量D表达式,发现加载过程中损伤变量–中间主应力曲线斜率变化不大,而在卸载过程中斜率变化明显,中间主应力垂直于层理面时损伤变量全程大于中间主应力平行于层理面时的损伤变量。     

Damage in a rock core caused by induced tensile stress and its relation to differential strain curve analysis

A finite element analysis was carried out to analyze the distribution of tensile stress within and below a long HQ core stub for 77 in situ stress conditions. The maximum tensile stress experienced by the core along the axis during boring under in situ stress was accumulated in an equal-area stereonet for a central part of the cross-section. The maximum tensile stress accumulated for a central area of less than about 60% of the total cross-sectional area was concentrated in a certain direction, which was nearly the same direction as the minimum principal stress for all of the stress conditions, except those in which the minimum principal stress (σ₃) was equal to the intermediate principal stress (σ₂). When σ₂=σ₃, the direction of the cumulative maximum tensile stress lay approximately in the plane of σ₂=σ₃, which is perpendicular to the maximum principal stress. Based on the assumption that a penny-shaped crack is produced normal to the maximum tensile stress in proportion to the magnitude of such stress, the crack density in the core was analyzed by calculating strain under hydrostatic pressure as in differential strain curve analysis (DSCA). The maximum principal crack density in the central part of the core was much greater than the intermediate and minimum principal crack densities, excluding special cases in which σ₂=σ₃. The direction of the maximum crack density was similar to that of the accumulated maximum tensile stress. Thus, the direction of the maximum crack density obtained by DSCA predicts the direction of the minimum principal stress rather than that of the maximum principal stress, if the distribution of pre-existing microcracks before stress relief is isotropic and if additional microcracks are produced only by tensile stress during boring under in situ stress. To verify this, crack parameters were measured by DSCA for two cores of quartz-diorite, which were taken by overcoring when the hemispherical-ended borehole technique was used to measure in situ stress. The directions of the maximum crack parameters measured by DSCA were nearly the same as that of the minimum principal stress for one of the cores. For the other core, for which the magnitudes of the intermediate and minimum principal stresses were close to each other and, accordingly, the direction of the minimum principal stress was uncertain, the direction of the maximum crack density estimated by damage analysis under the assumption that σ₂=σ₃ coincided with the directions of the maximum crack parameters measured by DSCA.     

定轴剪切条件下砂土强度与非共轴性试验研究

针对现有定轴剪切试验大多忽略中主应力系数b值变化这一问题,基于不同力系之间的映射关系,严格推导了空心圆柱扭剪仪4个外荷载的加载参数。采用重塑福建标准砂试样,分别在2组围压下开展主应力方向固定的剪切试验,研究主应力方向角α不同时,砂土变形、强度、非共轴性等力学特性的差异。结果表明:砂土的强度、应力-应变关系等力学特性均具有显著的应力方向依赖性;随着应力方向从0°到90°变化,应力路径表现为2个变化阶段,峰值强度先减小后增大,在α为67.5°附近取极小值;对比大主应变增量方向与大主应力方向之间的关系,发现当偏应力比较小时,试样存在明显的非共轴现象,随着偏应力比的增大,应变增量方向逐渐趋近于应力方向。     

主应力对洞室围岩失稳破坏行为的影响研究

 针对复杂应力环境三向应力状态下地下洞室围岩破坏条件和破裂机制,采用统计损伤理论和数值模拟方法,建立三维非均匀性地质模型,考虑应力的三维效应,引入强度折减法,一方面在保持模型边界条件的同时实现洞室围岩的逐步破坏,另一方面以此定量评价不同应力场中洞室安全稳定状况,探讨不同侧压力系数和轴向应力条件下洞室围岩破坏模式,探究中间主应力对洞室稳定性的影响以及深部岩体分区破裂化现象产生条件和破裂规律等。结果表明,侧压力系数影响洞室围岩初始破裂形成部位和发展趋势;不同的轴向应力使得洞室围岩破裂区域和范围显著不同,在不同的侧压力系数条件下,轴向应力影响洞室稳定的规律存在差异;不同方向中间主应力对洞室围岩安全稳定状况的影响是不同的;当洞室轴线方向与最大水平应力方向平行时,较大的轴向应力会使洞室围岩产生分区破裂化现象,围岩破坏的区域也是拉应变集中的区域等。这些结果对进一步揭示地下洞室围岩非线性变形破坏行为,评价岩土工程安全稳定性,采取合理的支护措施等均具有重要意义。     

Comparative analysis of deformation and failure mechanisms of underground powerhouses on the left and right banks of Baihetan hydropower station

The stability of the surrounding rocks of large underground powerhouses is always emphasized during the construction process, especially in large-scale underground projects under construction, such as the Baihetan hydropower station in China. According to field investigations, numerical simulations and monitoring data analysis, we present a comparative analysis of the deformation and failure characteristics of the surrounding rocks of underground powerhouses on the left and right banks of the Baihetan hydropower station. The failure characteristics and deformation magnitude of the underground powerhouses on the left and right banks are quite different. Under the disadvantageous condition where the maximum principal stress intersects the axis of the powerhouse at a large angle, the left bank underground powerhouse shows prominent stress-controlled failure characteristics such as spalling, slack collapse and concrete cracking. Although the maximum principal stress is in the favorable condition which intersects the right bank powerhouse at a small angle, the relatively high intermediate principal stress with an angle subvertical to the right bank powerhouse plays an essential role in its deformation and failure, indicating that the influence of high intermediate principal stress cannot be ignored. In addition, structural plane-controlled failure and large deformation are also more evident on the right bank due to the extensive distribution of weak structural planes and complex surrounding rock properties.     

Rock failure with weak planes by self-locking concept

In order to investigate failure of a rock mass having planes of weaknesses, a three-dimensional model is proposed based on the self-locking concept in friction analysis. In the case of two-dimensional problems, the model gives the same results as that of the Mohr–Coulomb criterion. The three-dimensional model can be reduced to the two-dimensional model, if the weak plane is parallel to the intermediate principal stress and/or the intermediate stress is equal to the minimum principal stress. The results indicate that the influences of three principal stresses and mechanical parameters of the weak plane on spatial failure region are remarkable, in terms of shape and range, that the spatial failure region becomes smaller as the mechanical parameters increases, and the weak plane will never fail when some threshold of mechanical parameters is reached, no matter what values of weak plane strike and dip will be. The spatial failure region becomes smaller with increased values of the intermediate and minimum principal stresses, conversely it becomes larger with the maximum principal stress increased. Additionally, the influence of bottom hole pressure on the failure range of weak plane is analyzed, for bore holes in naturally fractured formations, with the help of a local coordinate system.     

基于Mogi-Coulomb强度准则的隧道围岩理想弹塑性解答

合理选择岩石强度准则对隧道应力及位移预测和支护设计都具有重要意义,基于MogiCoulomb强度准则和理想弹塑性模型,通过中间主应力系数反映中间主应力的影响,推导了圆形隧道围岩应力和位移的解析解,并对所得结果进行比较与验证,得到了中间主应力和围岩抗剪强度参数的影响特性。研究表明:具有广泛的适用性和较好的可比性,Mohr-Coulomb强度准则解答和Matsuoka-Nakai准则解答均为其特例;结果关于中间主应力系数b=0.5对称,较好地反映了岩石强度的中间主应力效应及其区间性;粘聚力及内摩擦角对围岩塑性区半径和隧道洞壁位移的影响显著,应充分考虑中间主应力影响及围岩抗剪强度参数变化对隧道设计与施工的影响。     

Influence of intermediate principal stress on rock fracturing and strength near excavation boundaries—Insight from numerical modeling

The influence of the intermediate principal stress on rock fracturing and strength near excavation boundaries is studied using a FEM/DEM combined numerical tool. A loading condition of σ₃=0 and σ₁≠0, and σ₂≠0 exists at the tunnel boundary, where σ₁, σ₂, and σ₃, are the maximum, intermediate, and minimum principal stress components, respectively. The numerical study is based on sample loading testing that follows this type of boundary stress condition. It is seen from the simulation results that the generation of tunnel surface parallel fractures and microcracks is attributed to material heterogeneity and the existence of relatively high intermediate principal stress (σ₂), as well as zero to low minimum principal stress (σ₃) confinement. A high intermediate principal stress confines the rock in such a way that microcracks and fractures can only be developed in the direction parallel to σ₁ and σ₂. Stress-induced fracturing and microcracking in this fashion can lead to onion-skin fractures, spalling, and slabbing in shallow ground near the opening and surface parallel microcracks further away from the opening, leading to anisotropic behavior of the rock. Hence, consideration of the effect of the intermediate principal stress on rock behavior should focus on the stress-induced anisotropic strength and deformation behavior of the rocks. It is also found that the intermediate principal stress has limited influence on the peak strength of the rock near the excavation boundary.     

Mine-by试验洞开挖过程中围岩应力路径与破坏模式分析

 地下洞室开挖过程中,围岩经历了复杂的应力路径,正确刻画围岩的应力路径及其影响是岩石地下工程中亟待解决的关键科学问题。基于起裂判据(CIC)、扰动应力比( )和Lode参数等力学表征指标,采用FLAC3D对Mine-by试验洞掌子面掘进过程中围岩的复杂应力路径和破坏模式进行探讨。研究表明：围岩应力场的扰动主要集中在掌子面前后一倍洞径范围内,围岩损伤受掌子面附近高度集中的偏应力和应力主轴旋转支配;随掌子面掘进,围岩顶部和底部偏应力集中程度加大,应力比n逐渐降低,逐步形成V型剥落,而隧洞边墙部位逐渐卸荷,损伤破裂转变为拉应力控制;原位岩体的应力路径涉及应力主轴旋转效应,远比实验室的单调加载路径复杂,Mine-by试验洞开挖过程中,在掌子面的顶部和底部,围岩大主应力方向几乎没有转动,而中主应力和小主应力旋转一定角度(35.2°)后回到初始方向,由于中主应力超过了岩体起裂强度(CIC＞1),其方向的旋转加剧了围岩的损伤程度。相关认识和结论具有一定的理论和工程意义。     

新型引水式电站中水压致裂地应力测量技术应用研究

在中国西南某新型引水式水电站工程中使用水压致裂技术开展了原地应力及相关岩体力学参数测试。结果表明,工程区现今应力场状态以NNW向挤压为主,最大主应力值为7.35～8.16 MPa,方向约为N33～52°W,倾角约26～39°。气垫调压室三维原地应力状态的最大主应力值为10.63 MPa,最小主应力为4.98 MPa;围岩岩体抗劈裂强度高值区在5.50 MPa以上,低值区为3.00～3.50 MPa。根据围岩应力分布非均匀性遵循的一般性规律,结合原地应力测量与裂隙围岩原地承载能力测试结果的各自特点,提出了利用地应力测量数据、原地承载力测试结果、弹性模量数据综合评估承压洞室围岩最小主应力的方法,给出气垫式调压室部位最小主应力综合评估值2.86 MPa。并分析了地应力状态对地下厂房、引水隧洞、气垫调压室稳定性的影响。