冻融作用对条带状磁铁石英岩物理力学性能影响试验研究

为研究冻融作用对条带状磁铁石英岩物理力学特性的影响,对条带状磁铁石英岩进行了矿物成分与结构分析,在对该岩石进行了最高280次的冻融循环试验后,展开了基于应变监测的单轴压缩试验。试验结果表明:条带状磁铁石英岩主要成分为石英和磁铁矿物,其结构致密,原生裂隙主要为贯穿条带分布;随冻融循环周期增加,岩样饱水质量、开口孔隙率和纵波波速呈阶段式变化;自干燥至冻融280次,岩样的单轴抗压强度、弹性模量分别下降了46.93%、61.98%,在冻融前、中期岩样单轴抗压强度、弹性模量下降最为显著;根据岩石变形特征获得不同冻融循环周期下岩样的应力特征值,岩样压密应力、起裂应力随冻融循环周期的变化幅度最为显著,并结合其与峰值应力的占比变化情况,发现岩样在低、中荷载下其内部裂隙活跃程度与冻融循环周期存在较高的相关性。

岩石单轴压缩下损伤表征及演化规律对比研究

采用声波、声发射一体化装置同步测试单轴压缩下花岗岩应力应变、超声波及声发射(AE)特征演化规律,分析岩石特征应力对应的宏–细观表征,通过裂纹体积应变、声发射及声波特征等共同量化岩石损伤演化过程。结果表明:裂纹体积应变和波速对应的损伤起始应力吻合较好,AE事件、幅值分布、b值对应的应力特征值基本一致,但AE事件表征的损伤累积开始早于宏观变形和声波;初始加载阶段波速及各项异性系数K均逐渐增加,之后变化趋缓,起裂应力后侧向波速开始减小,而K逐渐增大;峰值应力前裂纹的快速聚结引起AE信号幅值大幅增加,伴随的是b值的快速下降和AE累积能量的陡增;基于起裂应力后损伤才开始累积的假定,量化并对比了裂纹体应变、AE事件等多参量表征的损伤演化规律,发现花岗岩损伤累积绝大部分发生在损伤应力之后。裂纹体应变表征的损伤具有明确物理意义,但裂纹体应变计算中泊松比选取存在一定主观性,裂纹体应变、AE能量、模量等参数表征的损伤在接近峰值应力前均出现大幅增加,与b值的快速下降对应。综合对比分析,AE能量表征的损伤具有更好的可靠性,反映了岩石损伤破裂的本质特征。

高碾压混凝土重力坝分区材料-结构界面特性与变形协调仿真分析

高碾压混凝土重力坝不同功能部位“结构特性”与“材料性能”的差异产生的变形协调问题直接关系到工程结构的安全运行,现阶段变形协调分析多是对结构变形和受力进行分析,对异种材料变形协调机理认识不足,缺乏理论基础研究。本文基于界面力学理论,考虑混凝土坝分区中常见的两种双材料界面形式与理想界面的连续边界条件,基于奇异性特征值的特征方程,提出了以应力奇异性特征值作为异种材料变形协调的评价指标,并通过有限元分析验证了理论计算的正确性与有效性;进而分析了界面结合角度和异种材料组合对单侧自由界面端与埋入界面折点处应力奇异性的影响,通过非均质有限元数值仿真分析了复合试件破坏模式,研究了抗压强度与应力奇异性特征值的关系;最后通过统计实际混凝土坝工程中不同坝段内的双材料界面的材料参数(弹性模量)与结构参数(界面形式与结合角度),计算奇异性特征值,评价了该工程中界面的变形协调特性,为高混凝土坝分区材料-结构设计与材料选取提供新的思路。

Mechanical response features and failure process of soft surrounding rock around deeply buried three-centered arch tunnel

Due to the extreme complexity of mechanical response of soft surrounding rock(SR) around a tunnel under high geostatic stress conditions, the integration of physical and numerical modeling techniques was adopted. Based on the similarity theory, new composite-similar material was developed, which showed good agreement with the similarity relation and successfully simulated physico-mechanical properties(PMP) of deep buried soft rock. And the 800 mm×800 mm×200 mm physical model(PM) was conducted, in which the endoscopic camera technique was adopted to track the entire process of failure of the model all the time. The experimental results indicate that the deformation of SR around a underground cavern possessed the characteristics of development by stages and in delay, and the initial damage of SR could induce rapid failure in the later stage, and the whole process could be divided into three stages, including the localized extension of crack(the horizontal load(HL) was in the range of 130 k N to 170 k N, the vertical load(VL) was in the range of 119 k N to 153.8 k N), rapid crack coalescence(the HL was in the range of 170 k N to 210 k N, the VL was in the range of 153.8 k N to 182.5 k N) and residual strength(the HL was greater than 210 k N, the VL was greater than 182.5 k N). Under the high stress conditions, the phenomenon of deformation localization in the SR became serious and different space positions show different deformation characteristics. In order to further explore the deformation localization and progressive failure phenomenon of soft SR around the deeply buried tunnel, applying the analysis software of FLAC3 D three-dimensional explicit finite-difference method, based on the composite strain-softening model of Mohr-Coulomb shear failure and tensile failure, the calculation method of large deformation was adopted. Then, the comparative analysis between the PM experiment and numerical simulation of the three centered arch tunnels was implemented and the relationship of deformation localization and progressive failure of SR around a tunnel under high stress conditions was discussed.

Study on Improvement of Seismic Performance of Transmission Tower Using Viscous Damper

The earthquake resistance of transmission tower has been often discussed from the viewpoint of reinforcing the foundation of steel tower, but there are also few studies considering the damping characteristics of the tower. This paper focuses on the viscous damper which has been adopted for seismic reinforcement of bridges in recent years. The purpose of this study is to improve the seismic performance of steel tower by giving the high damping to the tower. We construct a single tower model considering the influence of transmission line, and then simulate the vibration characteristics and seismic behavior of the tower by the eigenvalue analysis and the dynamic response analysis. The results show that the transmission tower with viscous damper can reduce its own response effectively and drastically. This research concludes that it is necessary to consider the extreme increase of steel tower＇s response depending on the seismic wave and the collapse of steel tower can be avoided by using the optimum damper in the design of the transmission tower.

基于强度理论的岩石脆延转化统计损伤本构模型

岩石脆延特性转化过程模拟是现有统计损伤本构模型理论研究的重要内容之一。首先,基于三轴压缩试验资料,分析了围压水平变化对岩石应力特征值及其脆性指标的影响规律,针对M-C强度准则仅能够预测低围压水平岩石应力特征值,提出能够适用于预测围压水平大区间变化条件下新型岩石强度准则;然后,结合统计损伤理论,建立基于强度理论的岩石统计损伤演化模型,进而在考虑残余强度特征的损伤模型基础上,建立岩石脆延转化统计损伤本构模型,并给出参数的确定方法;最后,通过大理岩试验资料分析表明,本文强度准则能够很好地预测大理岩应力特征值的变化规律,本文模型能够很好地模拟大理岩脆延特性转化过程,揭示出现有统计损伤模型无法模拟脆延特性转化的关键因素在于它缺乏适用于围压水平大区间变化条件下岩石强度准则并忽视了应力特征值的预测值偏离程度对模型曲线产生的影响,拓宽了现有统计损伤本构模型理论的应力水平适用性范围。

稀硫酸浸矿过程氧化铜矿岩力学特性演化规律

为了研究稀硫酸浸矿过程中氧化铜矿岩力学特性演化规律,通过不同浸矿时间下氧化铜矿岩单轴压缩试验,对矿岩单轴压缩破坏下应力-应变曲线、应力特征值和弹性模量等参数的变化规律进行了分析。研究结果表明:随浸矿时间逐渐增加,矿样孔隙闭合点的应力逐渐减小,应变逐渐增大,并且弹性变形阶段应变量显著减小,屈服变形阶段应变量增加,岩石达到峰值强度所需应变量增加;在化学浸矿初期即浸矿时间0~20h,矿样单轴抗压强度降低趋势最为显著,在浸矿80h后单轴抗压强度降低速率逐渐减小;矿岩单轴抗压强度和弹性模量均与浸矿时间呈多项式相关。