单轴压缩条件下含双圆孔类岩石试样力学特性的细观研究

圆孔作为一种典型的岩石缺陷,对岩石的力学特性具有重要影响。采用室内试验及PFC2D程序,构建含双圆孔类岩石试样并对其进行单轴压缩试验,研究其不同圆孔间距、倾角组合条件下的强度、裂纹模式及破裂孕育演化特征。研究表明:(1)当间距不变时,随倾角的增大,试样单轴抗压强度呈先减小后增大的趋势,且在倾角为45°~60°时达到最低单轴抗压强度;当倾角为90°恒定时,随间距的增大,试样单轴抗压强度呈先增大后减小的趋势,且在间距为40 mm左右时达到最大单轴抗压强度。(2)试样产生的裂纹类型可分为I型(张拉型)裂纹、II型(剪切型)裂纹、III型(混合型)裂纹等三类。当孔距较近时,随倾角的增大,圆孔间裂纹类型逐渐由III型裂纹转变为II型裂纹,两圆孔靠近加载端部一侧的孔壁逐渐产生I型裂纹,靠近试样两侧边界处的孔壁始终会产生II型裂纹。当倾角为90°恒定时,随间距的增大,两孔间相互作用减弱,但两圆孔靠近加载端部一侧及靠近试样两侧边界处的孔壁,始终分别产生I型裂纹和II型裂纹。(3)两孔间岩桥连线上的II型裂纹首先产生,其次在圆孔靠近加载端部一侧的孔壁产生I型裂纹,最后在圆孔靠近试样两侧边界处的孔壁产生II型裂纹。通常构成II型裂纹的声发射事件破裂强度,高于构成I型裂纹的声发射事件破裂强度。     

Analysis of crack coalescence in rock-like materials containing three flaws—Part I: experimental approach

Fractures in the forms of joints and microcracks are commonly found in natural rocks, and their failure mechanism strongly depends on the crack coalescence pattern between pre-existing flaws. However, the crack coalescence pattern of rock specimens containing three or more flaws has not been studied comprehensively. In this paper, we investigate experimentally crack coalescence and peak strength of rock-like materials containing three parallel frictional flaws. Three flaws are arranged such that one pair of flaws lines collinearly and the third flaw forms either a non-overlapping pattern or an overlapping pattern with the first flaw. It is found that the mechanisms of crack coalescence depend on the flaw arrangement and the frictional coefficient μ on the flaw surface. Two “rules of failure” for the specimens containing three flaws are proposed. Rule No. 1: the pair of flaws with a lower value of coalescence stress will dominate the process of coalescence. Rule No. 2: mixed and tensile modes of coalescence are always the dominant modes if the coalescence stress of the two pairs of flaws is very close (say within 5%). In addition, it is found that the peak strength of the specimens does not depend on the initial crack density but on the actual number of pre-existing flaws involved in the coalescence. Comparisons of pattern of crack coalescence with the numerical approach are given in Part II of this study, and the two results agree well. The research reported here provides increased understanding of the fundamental nature of rock failure in uniaxial compression.     

Analysis of crack coalescence in rock-like materials containing three flaws—Part II: numerical approach

By using a Rock Failure Process Analysis code, RFPA^2D, numerical simulations on samples of rock-like material containing three flaws under uniaxial compressive loading are conducted to investigate the failure mechanism and crack coalescence modes. The pre-existing flaws are arranged in different systematic geometries. Friction in closed flaws is modelled by inserting ideal elasto-plastic materials into the flaws. As the uniaxial compression load is increased, new cracks propagate from the flaws and eventually coalesce. The simulations replicate most of the phenomena observed in actual experiments, such as initiation and growth of wing and secondary cracks, crack coalescence, and the macro-failure of the sample. For the samples containing three pre-existing flaws, four types of crack coalescence mode are obtained: the tensile mode (T); the compression mode (C); the shear mode (S); and the mixed tension/shear mode (TS). The C mode is mainly formed by coalescence of small tensile fractures in the form of a shear band, and is believed to correspond to the formation and growth of en-echelon cracks. The applied load required to initiate coalescence depends on which mode (tensile or shear) dominates the coalescence process. A higher load is required to cause coalescence in the shear mode (S) than that for coalescence in the tensile mode (T) and mixed mode (TS). A total of four types of samples containing three parallel inclined frictional flaws and nine samples containing two parallel inclined frictional flaws are numerically simulated. It is concluded that crack coalescence will occur following the weakest coalescence path among all possible paths between any two flaws. The results obtained in the simulations are qualitatively in good agreement with experiments presented in Part I of the accompanying paper and other reported experimental observations.     

Experimental study on crack propagation and the coalescence of rock-like materials with two preexisting fissures under biaxial compression

Bulletin of Engineering Geology and the Environment - Rock masses consist of rock and fissures, and fissures in rock masses play an important role in rock mass stability. In this paper, rock-like...     

Crack coalescence in specimens with open and closed flaws: A comparison

A comparison is presented between experimental observations made from gypsum specimens loaded in uniaxial compression, with open and closed flaws. Three types of cracks are observed: wing cracks, coplanar and oblique secondary cracks. Wing cracks are tensile cracks that initiate at or near the tip of the flaws, are stable, and propagate towards the direction of maximum compression. Secondary cracks are shear cracks; they are initially stable and may become unstable near coalescence. Coalescence is produced by the linkage of two flaws by a combination of wing and secondary cracks. When coalescence occurs through wing cracks or a combination of wing and secondary cracks, the process is stable. When coalescence occurs through secondary cracks only, the phenomenon is unstable. Eight types of coalescence have been identified, which apply to specimens with open and closed flaws. The types of coalescence are classified based on the types of cracks that produce linkage, and are closely related to the orientation, spacing, and continuity of the flaws. Interestingly, coalescence produced through the linkage of shear cracks only occurs at higher stress than coalescence produced by a combination of shear and wing cracks. The smallest coalescence stress occurs when produced only by wing cracks. The main difference between experimental results from open and closed flaws is that initiation stresses and coalescence are higher for closed than for open flaws. This is explained by the friction along the closed flaws, which needs to be overcome before a crack can initiate, and also by the capability of closed flaws to transmit normal stresses. Thus the differences are not fundamental, and so a unified conceptual framework and a common terminology are proposed for fracturing phenomena in brittle materials with open or with frictional pre-existing discontinuities.     

可用于水下混凝土结构裂缝修补的注浆材料

根据水下结构混凝土裂缝的饱水特征,设计一种高性能注浆修补材料。以流动性和水下抗分散性为首要设计指标,调整各组成材料之间的匹配关系,选择3组性能较好的注浆料进行对比试验,探讨其各方面的性能。各原材料之间的配合关系和水灰比的变化,都会对注浆料的流动性、凝结时间、黏度和强度等性能产生显著影响。所设计的注浆料性能良好,且对母体材料的裂缝基面有良好的粘结性能,可用于水下混凝土结构裂缝的修补。     

Thermal analysis of a building brick containing phase change material

This paper presents the thermal analysis of a building brick containing phase change material (PCM) to be used in hot climates. The objective of using the PCM is to utilize its high latent heat of fusion to reduce the heat gain by absorbing the heat in the bricks through the melting process before it reaches the indoor space. The considered model consists of bricks with cylindrical holes filled with PCM. The problem is solved in a two-dimensional space using the finite element method. The thermal effectiveness of the proposed brick-PCM system is evaluated by comparing the heat flux at the indoor surface to a wall without the PCM during typical working hours. A paramedic study is conducted to assess the effect of different design parameters, such as the PCM's quantity, type, and location in the brick. The results indicate that the heat gain is significantly reduced when the PCM is incorporated into the brick, and increasing the quantity of the PCM has a positive effect. PCM cylinders located at the centerline of the bricks shows the best performance.     

陶瓷材料在滑动接触中的裂纹扩展模拟

对刚性柱面和SIC陶瓷材料平面产生滑动接触进行了有限元数值分析,以有限元软件ABAQUS作为分析平台,以扩展有限元方法(XFEM)和最大主应力判定准则对整个滑动接触过程中裂纹扩展的行为进行了模拟,得出了裂纹尖端单元的最大主应力及裂纹扩展路径和裂纹张开角,为生产实际过程中的无损探伤提供理论的测量视角。     

混凝土裂缝用环氧树脂灌浆材料及其标准

介绍了用于修补混凝土的环氧树脂灌浆材料行业标准及其编制说明.为了保证环氧树脂灌浆材料使用后的防渗漏补强性能,标准中规定了浆液的密度、初始黏度与可操作时间,同时规定了浆液固化后的固化物性能,以及抗压、抗拉、拉伸剪切与粘结强度、抗渗压力与渗透压力比等指标及其相应的试验方法.     

浅析混凝土配合比和原材料对裂缝的影响

结合混凝土原材料的特性和配合比设计优化两方面简述了混凝土早期裂缝产生的原因，提出了避免混凝土早期裂缝产生的控制方法，以达到从源头上避免和减少裂缝产生的目的。     

Properties of cement mortars containing clinoptilolite as a supplementary cementitious material

This paper presents a study of the properties and behavior of cement mortar with clinoptilolite which is one of the most common zeolite minerals found in nature. Six mortar mixtures were prepared by replacing the Portland cement with 0%, 5%, 10%, 15%, 20% and 30% clinoptilolite by weight. Test results showed that water demand, soundness and setting times of the cement pastes increased with the increase of clinoptilolite content. Compressive and flexural strength of the mortars containing clinoptilolite were higher than the control mixture. Dry unit weight of the mortars with clinoptilolite was lower than the control mortar. Clinoptilolite replacement decreased water absorption and porosity of the mortars. The control mortar showed less durability to carbonation compared to the mortars made with clinoptilolite at the end of carbonation tests. Freeze–thaw resistance of the mortars containing 5% clinoptilolite was higher than control mortar. The effect of clinoptilolite incorporation on high-temperature resistance seemed to be dependent on amount of clinoptilolite, temperature level, and the cooling method.     

预裂纹混凝土拉压疲劳荷载下裂纹扩展速率

为研究C50混凝土预裂纹在拉压循环荷载下的扩展速率,进行了应力比为-1,应力幅值为020~130MPa的拉压疲劳试验.针对混凝土在拉压疲劳荷载下裂纹扩展时其长度不易确定的问题,提出潜行等效裂纹长度假说对试验结果进行分析.结果表明：混凝土裂纹第1阶段起始扩展区和第2阶段稳定扩展区比较明显,第3阶段加速扩展区不明显,在稳定扩展区后期,裂纹扩展曲线的斜率并不像金属那样快速增加,而是增幅趋缓,在稳定扩展阶段后期无征兆突然破坏,与混凝土脆性断裂的特性相一致.利用最小二乘法拟合得到裂纹扩展速率Pairs公式中的参数C,m,在考虑50%,90%,99%的存活率时,C可在031~045,076~099,122~198中取值,m取值范围对存活率大小的敏感性较低,可在30~48之间取值.     

冲击载荷作用下双裂纹材料断裂实验研究

采用透射式焦散线实验系统,进行了预置双裂纹有机玻璃试件在冲击载荷作用下的断裂实验,并与单裂纹材料进行比较,结果表明,应力强度因子与冲击能量、试件形状、裂纹的分布位置以及几何尺寸有关;应力强度因子在裂纹扩展前后呈现波动变化特征;Ⅰ型载荷为主要加载方式;与单裂纹试件相比,应力强度因子值有不同程度的降低。     

新型隧道衬砌施工缝粘结材料的应用研究

隧道施工缝处理得好坏往往影响工程的正常使用和行车安全.而施工缝的处理实质上就是新旧混凝土的界面粘结问题.通过隧道衬砌施工缝粘结材料的研究,提高隧道衬砌的粘结强度和抗渗性,改善界面处的使用性和耐久性.应用试验结果表明,研制的新型隧道衬砌施工缝粘结材料对施工缝的处理有明显的作用效果,新旧混凝土界面的力学性能和耐久性均得到不同程度的改善和提高,对隧道混凝土结构施工有较好的实用价值.     

压力注浆法修补混凝土裂缝材料试验研究

我国西北地区气候复杂多变,施工过程中混凝土裂缝等质量通病极易产生。本文针对西北地区气候干燥、低温、温差大、日照强、风沙大等自然环境特点,对混凝土裂缝修补材料进行试验研究,确定较能满足西北地区的裂缝修补材料。     

基于损伤力学的含裂缝混凝土评估研究

以混凝土损伤现象为研究对象,探讨了含裂缝混凝土的损伤机制,并通过相关实验及回归分析,得到混凝土密度与超声波量测纵向波速的关系式,建立了含不同裂缝损伤程度混凝土时,波速与损伤混凝土强度的关系式。     

两种常见的混凝土裂缝的分析与控制

阐述了裂缝在混凝土结构工程中的普遍性、危害性及其特有的规律性,讨论了结构中较为常见的温度和收缩两种类型的裂缝状况、成因,提出了在混凝土施工过程中有效防止和降低这两种裂缝的方法,从而为现场施工提供更好的控制手段和补救措施。     

基于商品混凝土组成材料引起的裂缝及控制

通过分析混凝土的组成材料及其配合比对混凝土裂缝的影响,提出通过合理选用混凝土原材料、严格检验原材料质量和控制配合比设计等措施,从而有效控制混凝土的裂缝,提高施工质量。