Applying ultrasonic waves to evaluate the volumetric block proportion of bimrocks

As a result of civilization, a lot of underground and surface structures have been constructed on or within complex rocks such as mélange and lahars. There are many engineering problems related to this group of rocks called block-in-matrix rocks (bimrock). In the literature, the more important parameter controlling the geomechanical characteristics of bimrocks is volumetric block proportion (VBP), and there is much uncertainty related to estimated VBP applying sieve or image analysis. So, in this research, to develop a relation between the VBP and ultrasonic wave velocities and find how the fractal dimension and maximum block size affect the P and S wave velocities, 90 large-scale cubic samples were fabricated and the P and S wave velocities were measured in three perpendicular directions inside the physical samples. The fabricated samples were almost isotropic, and there was a direct relation between ultrasonic wave velocities and VBP. The difference between the evaluated VBP and the real one was in the range of ?10 to +15% when the real VBP was equal or less than 60% and up to +25% when the real VBP was equal to 75%. In general, the fractal dimension had an indirect relation with ultrasonic velocities and there was no dominant trend for ultrasonic wave velocity variation versus the maximum block size.     

动态冲击下锦屏大理岩力学响应与能量特性

为了分析锦屏水电站大理岩的动力学响应和能量特性,采用分离式霍普金森压杆对岩样开展了动态压缩试验,并引入分形维数定量表征试样的破碎形态、能耗特性及其与应变率的内在关系。结果表明：动态载荷下大理岩应力-应变曲线初始压密段不明显,当应变率较低时,应力-应变曲线呈现出回弹现象;试样峰值应力随应变率的增大而增加,且动态抗压强度与...     

不同岩石破裂全过程的声发射序列分形特征试验研究

通过对不同岩性的岩石进行单轴压缩声发射试验,获取岩石破裂全过程中的载荷-轴向变形曲线及声发射参数,观察试件破裂失稳时的破坏情况,分析破坏过程的载荷变化关系。着重对比了不同岩石的不同力学性质、岩石声发射序列的时域特征和声发射序列的分形特征。研究结果表明,采用声发射率、能率可以很好地描述岩石破裂损伤的整个阶段;计算岩石声发射率、声发射能率的关联维数,可得出岩石破裂过程的声发射序列具有分形特征;岩石破裂过程的声发射分维值D反映了岩石内部微裂隙的统计演化规律;不同岩性的岩石破裂过程的声发射参数序列的分形特征具有一定的共性;归纳总结出岩体声发射序列分维曲线的演化模式,即波动→持续下降演化模式,提出可以将分维值的持续下降作为岩体破裂失稳的前兆。     

土石混合体分形几何特征与强度演化特征

针对土石混合体的结构性特点,以含石量为20%、30%、40%、50%、60%的土石混合体为研究对象,基于多重分形原理研究多重分形特征,研究分形维数与强度之间的关系。研究表明,土石混合体具有双重分形特征,不同尺度条件下具有不同分形指标,包括块石粒度、土体粒度以及平均粒度等分形维数,与含石量相关。单轴压缩试验表明,抗压强度随含石量增加呈现先增大后减小的趋势,根据单维分形特征,确定最优含石量约为40%。建立了含石量、不同分形维数指标与抗压强度之间的关系,分析了双重因素综合影响下抗压强度的变化特征,确定了含石量与分形维数之间存在最优区域。     

Mechanical Behaviour of Reservoir Rock Under Brine Saturation

Acoustic emissions (AE) and stress–strain curve analysis are well accepted ways of analysing crack propagation and monitoring the various failure stages (such as crack closure, crack initiation level during rock failure under compression) of rocks and rock-like materials. This paper presents details and results of experimental investigations conducted for characterizing the brittle failure processes induced in a rock due to monocyclic uniaxial compression on loading of two types of sandstone core samples saturated in NaCl brines of varying concentration (0, 2, 5, 10 and 15 % NaCl by weight). The two types of sandstone samples were saturated under vacuum for more than 45 days with the respective pore fluid to allow them to interact with the rocks. It was observed that the uniaxial compressive strength and stress–strain behaviour of the rock specimens changed with increasing NaCl concentration in the saturating fluid. The acoustic emission patterns also varied considerably for increasing ionic strength of the saturating brines. These observations can be attributed to the deposition of NaCl crystals in the rock’s pore spaces as well some minor geo-chemical interactions between the rock minerals and the brine. The AE pattern variations could also be partly related to the higher conductivity of the ionic strength of the high-NaCl concentration brine as it is able to transfer more acoustic energy from the cracks to the AE sensors.     

人工冻土破碎块度分布的分形性质

从分形几何的观点出发，通过对冻土模型的爆破试验，着重对试样爆后破块块度分析进行了统计分析。结果表明，冻土爆后块度分布是个分形，分形维数不仅是反映冻土破碎程度恰当的统计特征量，而且与试样冻结温度密切相关，还探讨了分维值与冻土抗压强度的关系。     

Strain rate, temperature, and sample size effects on compression and tensile properties of frozen sand

Selection of material properties for use in design of frozen earth structures has been a limiting factor for some field applications. In particular, the mechanical properties governing the behavior of a frozen soil structure subjected to bending stresses are of interest. The effects of strain rate, temperature, and sample size on the compressive and tensile properties of frozen silica sand have been determined experimentally using uniaxial compression and split cylinder tests. Data included on the initial tangent modulus, compressive strength, failure strains, and tensile strength help delineate some limitations of available test procedures. Failure modes for various test conditions are described.

Data analysis shows that the initial yield stress, the compressive peak strength, and the initial tangent modulus increase with decreasing temperatures and increasing strain rates. Tensile strengths from split cylinder tests appear to be independent of deformation rates. Uniaxial compressive strengths decreased slightly and the initial tangent modulus increased with increasing sample diameter (constant length to diameter ratio). Deformation and failure modes changed from a plastic to a brittle behavior when strain rates were increased from low to high values. Larger failure strains at slower strain rates (more time available) appear to be a result of pressure melting, water migration and refreezing, permitting more particle readjustments before development of the peak strength. Observations on failure strains suggest limiting values for design situations.     

基于离散元法的砂石混合体直剪试验结果分析

砂石混合体由力学性质以及结构相差极大的材料组成,其组成的重塑地层易发生塌陷等问题,因此对砂石混合体力学特性的研究具有重要的工程意义。砾石形状是砂砾石力学特性研究的重要属性参数,但采用规则图形对砾石进行描述不能反映出其真实的力学性质,采用数字图像处理技术构建的砾石数据库能反映砾石真实形状并可对特定形状参数进行具体分析。由于砂石混合体的粒径分布较广,采用特征粒径等无法描述整体粒度分布,故本文结合分形理论构建砂石混合体的二重分形结构模型,通过粒度分维值反演出完整的级配分布曲线。考虑到砂石混合体离散型的特点,采用离散元软件进行直剪试验数值模拟并对细观结构进行分析,研究结果表明,砂石混合体一般具有2个粒度分维值:砂粒度分维值和砾石粒度分维值,砂、砾石粒度分维值越接近,抗剪强度和内摩擦角越大;当两者相等时,砂石混合体具有一重分维,此时均一性最好,抗剪强度和内摩擦角最大;轴向系数是形容砾石形状的一个重要参数,随着轴向系数的增加,砾石显示出明显的条状性,在直剪试验中抗转动能力增强、周围接触数量增加,导致抗剪强度和内摩擦角不断增加。     

岩石破裂过程中的声发射b值及分形特征研究

应用声发射及其定位技术,通过单轴受压岩石破坏声发射试验,对岩石破裂过程中的声发射b值和空间分布分形维值随不同应力水平的变化趋势进行了研究。研究结果表明：声发射分形维值D和b值反映了岩石破坏过程中微裂纹的初始和扩展;在小尺度微裂纹所占比例较高的加载初期,分形维值和b值在较高的水平波动变化,部分岩石试件分形维值和b值呈现升高现象;随着载荷的增加,岩石内部微裂纹的空间分布由无序向有序转变,大尺度裂纹所占比例增加,声发射定位事件出现群集现象,分形维值和b值开始较快速下降并在岩石失稳破坏时达到最低值。在岩石破坏过程中,声发射分形维值和b值的变化趋势相近。由于实际应用时,分形维值和b值的最小值（临界点）难以确定,故可将2个参数相结合,以分形维值D和b值较快速下降作为前兆特征,以提高现场岩体稳定性监测的准确性。     

Texture, mineralogy, and rock strength in horizontal stress-related coal mine roof falls

Geologic structures can represent planes of preferential weakness that, by dismembering the roof beam, may contribute to the failure of roof spans. However, beam deflection and roof failure also occur in rocks where no visible geologic discontinuities are present. This suggests that roof failure may depend on rock strength, which in turn depends on intrinsic textural properties inherent to the rock. In this study, rock samples were collected from horizontal stress-related roof fall material in coal mines for petrographic characterization and compressive strength testing. Brittle, stress failure-prone rock types include thinly interlaminated siltstone and shale, and black shale that had been lightly recrystallized. Samples exhibit a narrow range of density values between approximately 2.5–3.0 g/cm³ but exhibit a wide range of unconfined compressive strength values, between approximately 20–70 MPa. Results of laboratory observations suggest that for samples of coal mine immediate roof shale, compressive strength is not well correlated with density, grain size, sutured grain boundaries, or quartz content. These results for shale are generally at odds with the results of similar studies for sandstone. The great variability of strength, texture, and mineralogy documented in these samples may be an indication of their complexity and the need for specialized methodology in the study of shale strength.     

排土场散体岩石粒度分布与剪切强度的分形特征

应用分形理论研究了矿山排土场散体岩石粒度分布的分维规律,建立了分维数与排土场散体物料剪切强度参数的定量关系式。研究表明,排土场岩石块度分布具有良好的分形结构,分维数值大小随着排土场高度的增加而增加,但不超过3。当采样尺度范围一定时,分维数越大,散体中细颗粒含量越多,平均粒径也越小。分维数与散体岩石的剪切强度参数摩擦角?呈负指数关系。分维数值可用于排土场粒度资料的统计分析与剪切力学强度参数的预测。     

Investigation of the effect of aggregate shape and surface roughness on the slake durability index using the fractal dimension approach

Argillaceous rocks cover about one thirds of the earth's surface. The major engineering problems encountered with weak- to medium-strength argillaceous rocks could be slaking, erosion, slope stability, settlement, and reduction in strength. One of the key properties for classifying and determining the behavior of such rocks is the slake durability. The concept of slake durability index (SDI) has been the subject of numerous researches in which a number of factors affecting the numerical value of SDI were investigated. In this regard, this paper approaches the matter by evaluating the effects of overall shape and surface roughness of the testing material on the outcome of slake durability indices.

For the purpose, different types of rocks (marl, clayey limestone, tuff, sandstone, weathered granite) were broken into chunks and were intentionally shaped as angular, subangular, and rounded and tested for slake durability. Before testing the aggregate pieces of each rock type, their surface roughness was determined by using the fractal dimension. Despite the variation of final values of SDI test results (values of I_d), the rounded aggregate groups plot relatively in a narrow range, but a greater scatter was obtained for the angular and subangular aggregate groups. The best results can be obtained when using the well rounded samples having the lowest fractal values. An attempt was made to analytically link the surface roughness with the I_d parameter and an empirical relationship was proposed. A chart for various fractal values of surface roughness to use as a guide for slake durability tests is also proposed. The method proposed herein becomes efficient when well rounded aggregates are not available. In such condition, the approximate fractal value for the surface roughness profile of the testing aggregates could be obtained from the proposed chart and be plugged into the empirical relation to obtain the corrected I_d value. The results presented herein represent the particular rock types used in this study and care should be taken when applying these methods to different type of rocks.     

基于细观力学脆性岩石剪切特性演化模型研究

压缩作用下岩石内部细观裂纹扩展导致岩石产生损伤,其对岩石变形、强度等力学特性有着重要影响;然而,岩石内部裂纹扩展与剪切特性（黏聚力、内摩擦角及剪切应力）动态演化关系很少被研究。基于裂纹扩展机制推出的岩石应力-应变本构模型,并结合摩尔-库仑失效准则,推出了在岩石应力-应变关系峰值应力（对应岩石压缩强度）状态时,本构模型细观力学参数与岩石黏聚力、内摩擦角及剪切强度之间的状态关系。然后,引入岩石应力-应变本构关系塑性变形阶段服从摩尔-库仑屈服准则的力学流动规律,进而将已推出的应力-应变关系峰值状态点所满足的细观力学参数与黏聚力、内摩擦角关系,推广到岩石进入塑性变形后,岩石内部裂纹扩展（或应变）与黏聚力、内摩擦角及剪切应力动态演化的理论关系。随着裂纹扩展或应变增加,黏聚力、内摩擦角及剪切应力先增大,达到一个峰值点后减小,该结果与应力-应变本构曲线变化趋势相对应。通过试验结果验证了所提出理论结果的合理性。并讨论了初始裂纹之间摩擦系数对黏聚力、内摩擦角及剪切应力随裂纹扩展或应变演化规律的影响。     

珊瑚砂大剪切应变下的剪切特性和分形维数

利用Wille Geotechnik环向剪切仪对3种不同粒径的珊瑚砂进行了大剪切位移的环向剪切试验,探讨了颗粒破碎对珊瑚砂强度和残余应变发展的影响。试验结果表明：颗粒破碎随着剪切位移的增加逐渐增加,且初始粒径较大的均匀级配珊瑚砂粒径越大颗粒破碎越多。颗粒破碎对峰值强度和残余强度无影响,但对珊瑚砂的体积应变有显著影响,颗粒破碎较多的试样其体积应变也较大。建立了考虑长宽比、球形度和凹凸度的分形维数计算公式。由于颗粒破碎后颗粒形状在全粒径范围内的自相似性和无尺度性,考虑颗粒形状与不考虑颗粒形状的公式计算得到的珊瑚砂分形维数基本一致。     

Study on the Fractal Model of Erosion of Soft Rock by Water Immersed: Case Study Erosion of Metamorphic Slate

One of the characteristics of soft rock that contains clay and engineering geology is water swelling and.disintegration. The fractal model of slate disintegration is established by Gate Gaudin Sehuhmann distribution function, representative slate samples are chosen to perform laboratory tests of slaking, and the fractal dimension value of slate disintegration change law with time is obtained. The results show that absorbing water and disintegrating progress of slate is also a progress that fractal dimension of slate scrap change successively, when disintegrating of slate arrived to some extent, grade of scrap of slate disintegrated is no more change, fractal dimension of scrap of slate disintegrated incline to a critical value. The disintegration of slate has lag phenomenon in time. The initial disintegration time and the maximum disintegration fractal dimension of rocks are different because of the different microstructure and material composition.

     

不同围压下岩石抗压强度与变形参数尺寸效应的数值模拟

岩石抗压强度和变形参数是岩石工程设计的重要指标。由于岩石是典型的非均质材料,其强度和变形特性随样品尺 寸的变化而不同。本文采用PFC2D程序模拟了不同围压下不同尺寸岩样的压缩试验。结果表明（1） 岩样具有明显的尺寸效 应。同一围压下,尺寸越大,岩石强度、峰值应变和压缩模量越小,尺寸的变化对岩样的破坏模式影响较小;（2） 岩样具 有明显的围压效应。同一尺寸的岩样,随着围压的增大,岩石强度、峰值应变和压缩模量均增加,其中强度和峰值应变随 围压的增加呈线性增加。同时,随着围压的增大,岩石破裂模式由轴向劈裂破坏向剪切破坏变化;（3） 围压的存在会影响 岩样的尺寸效应。不同尺寸岩样的强度和峰值应变在相同围压区间内的增量基本相同,同时随着围压的增大,其强度和峰 值应变增加,进而使岩石强度和峰值应变的尺寸效应弱化;而不同尺寸岩样的压缩模量在相同围压区间内的增长率大致相 同,因而造成围压对压缩模量尺寸效应的影响较小     

孔隙分布分形维对多孔材料抗压强度的影响研究

建立了4组不同孔隙分布形式的多孔材料模型,在考虑孔隙分布范围和密度的基础上计算其孔隙分布分形维数,并利用假三维数值试验的方法获得了相同初始强度、不同孔隙度和孔隙分布形式试样的抗压强度。数值试验结果表明,除了孔隙度较小和孔隙分布分维数较大的试样破坏形式基本满足45° 破裂角的规律以外,该分维数较小的试样均呈现出不对称的斜截面破坏;在孔隙度相同的情况下,该分维数越大,样品的抗压强度越高;通过推导假三维情况下材料孔隙度与抗压强度的理论关系发现,该分维数越大,样组的抗压强度随孔隙度增大而衰减的速率越慢;根据损伤力学模型对试样的抗压强度进行预测分析发现,当样组的该分维数较大时,该模型能够较准确地预测多孔材料的抗压强度,而当样组的该分维数逐渐减小时,损伤力学模型的精度也逐渐降低。上述规律是由孔隙分布分维数越小、孔隙分布越不均匀、试样中应力集中的累积效应越显著的原因而造成的。     

Particle shape evolution in natural carbonate granular wear material

A fundamental yet still unresolved puzzle provided by cataclasis is whether particle size reduction mostly progresses through time by the same fragmentation mechanism or not. Available field, laboratory and numerical modelling results on the evolution of cataclastic rocks are still controversial. The evidence that cataclastic rocks exert a primary control on the frictional strength, stability, seismic velocity and permeability properties of fault zones encourages further research on cataclasis. Here, we report data on particle shape from natural cataclastic rocks in poorly layered carbonates in the Apulian foreland of the Southern Apennines of Italy. Particle shape analyses show that particle angularity decreases with increasing size and, for a given size class, it decreases with increasing fractal dimension of the particle size distribution. These results offer support to the temporally and spatially variable nature of rock comminution.     

断裂岩石蠕剪中的细观接触损伤试验研究

为深刻理解构成断裂岩体长期抗剪强度的细观机制,对岩石断裂面的细观接触和损伤演化进行了试验研究。采用压剪方式和巴西劈裂方式制作出两类断裂岩石,在恒定法向力作用下对破坏岩石试件进行分级施加剪切力的蠕变试验。在加载前、中、后对断裂岩石分别进行CT和激光扫描,观察到不同蠕变阶段断裂岩石的细观接触和损伤状态,获得不同性质的断裂岩石抗剪强度特征。试验研究表明：构成断裂岩石长期抗剪强度的机制主要有两个：一是细观凹凸啮合体的抗剪断能力;二是表观凹凸接触体的抗摩擦能力。拉破裂岩石表面局部粗糙度相对较大,抗剪强度以第1种破坏机制为主,剪切破坏岩石表面宏观起伏度较大,抗剪强度是以第2种破坏机制为主。在蠕变剪切过程中,两种机制交织在一起,并随时间或剪位移的增加而相互转换。     

基于软硬石模板库的土石混合体细观损伤与力学特性分析

为了探究含软、硬两种岩性碎块石土石混合体的变形破坏过程与力学性质,发展了一种基于软硬石模板库的土石混合体建模方法。通过在PFC2D中建立符合原位结构特征的软硬石模板库,利用此模板库生成了不同含石量土石混合体颗粒流模型,对土石混合体进行了单轴压缩颗粒流模拟。结果表明：土石混合体破坏始于土-石接触面,土石介质分离大多因剪切破坏导致,加载前期微裂纹迅速增长,中、后期微裂纹增长速率减缓,但宏观变形渐趋显著;随着含石量的增加,土石混合体单轴抗压强度逐渐降低,块石的转动与侧向移动会加剧土石混合体的整体破坏;相同含石量下,随着软石比例的增加,单轴抗压强度呈下降趋势,试验后试样破裂率与单个软石颗粒的破裂程度均保持在较高水平,软石颗粒破裂是引起土石混合体单轴抗压强度降低的重要原因。