饱和级配破碎泥岩压实与粒度分布分形特征试验研究

通过饱和级配破碎泥岩的压实试验,得到了不同级配下试样轴向位移和粒度分布分形维数随轴向应力变化曲线,分析了Talbol幂指数对饱和破碎泥岩压实变形与粒度分布的影响规律,建立了一种饱和破碎泥岩压缩模量与轴向应力的关系式。试验结果表明,饱和破碎泥岩的压实过程可分为2个阶段,即0~4 MPa的快速变形阶段和4 MPa后的缓慢变形阶段。其中,约80%的变形发生在快速变形阶段。轴向位移、压缩模量与粒度分布分形维数均可用轴向应力的指数函数拟合。相同轴向应力下,Talbol幂指数越大,试样轴向位移越大,粒度分布分形维数越小。轴向应力大于8 MPa后,各级配试样的粒度分布分形维数相差很小,且随着轴向应力的进一步增大,各级配试样的分形维数差异将继续减小,最终,分形维数将趋于一致。在加载初期,试样压实变形主要以岩石颗粒移位为主;而在加载后期,试样的压实变形则以颗粒破碎为主。     

郯庐断裂带肥东北部文集地区构造岩类型与构造变形分析

位于郯庐断裂带中南部的肥东地区是郯庐断裂带内韧性剪切带出露的主体区域之一。本文从肥东北部文集地区的构造岩组成及其变形入手,通过详细的野外观测、室内显微构造变形分析来确定该地区构造变形的几何学形态及其涡度、有限应变、分维度、差异应力、应变速率等参数。研究区主要出露角闪岩相肥东变质杂岩,构造岩以糜棱岩和糜棱岩化片麻岩为主,岩石变形强烈。根据极摩尔圆法得到的运动学涡度值为0.729~0.870,指示区域内的韧性剪切活动以简单剪切为主。几何学形态上,肥东北部文集地区构造整体呈一背形展出,其枢纽走向NE-SW,轴面倾向SE,物质及变形强度等方面均表现出一定的规律和对称性。研究区内动态重结晶石英颗粒边界具有统计学上的自相似性,其分维值D在1.143~1.208之间,且自背形核部向两翼,颗粒粒径增大,分维值减小。差异应力Δσ介于17.86~55.18MPa之间,应变速率ε值在1.960×10^-13~7.330×10^-12s^-1之间,且背形核部差异应力和应变速率较两翼大,呈近似对称性分布。通过对比以上构造参数可以发现,区内差异应力和应变速率表现出一定的正相关性,自核部向两翼二者均呈减小趋势;动态重结晶石英颗粒则与应变速率呈负相关性,即核部颗粒细小、两翼增大。本文从几何学、运动学以及显微构造变形分析等方面对该区构造变形展开精细化研究,借此来分析肥东北部地区郯庐断裂带的构造形态和运动学特征,这对进一步认识郯庐断裂带的演化过程及构造模型的建立有着重要的意义。     

Numerical simulation of the influence of small-scale defects on the true-triaxial strength of rock samples

A numerical model is used to investigate the influence of randomly located ‘defects’ on the strength of rock samples with a Mogi–Coulomb three-dimensional failure criterion that are subjected to polyaxial states of stress. A methodology is presented to compute ‘equivalent’ Mohr–Coulomb strength parameters as a function of the ‘instantaneous’ stress, and sensitivity analyses are employed to study the influence of the stress state, of the total percentage of defects, and of the type of spatial distribution of defects within the sample. Results indicate that increments of strength due to the intermediate principal stress are less relevant for samples with defects, hence suggesting that the influence of polyaxial stress states is less significant for rock masses (that incorporate ‘defects’ or ‘discontinuities’ into their structure) than for intact rock. Results also indicate that the strength of rock with defects can be modelled as a ‘homogeneous’ material with reduced strength properties. The reduction factors are a linear function of the percentage of defects, and they tend to be greater for “lumped” defects than for “isolated” defects.     

Thorium adsorption in the ocean: reversibility and distribution amongst particle sizes

Experiments have been carried out to determine whether the adsorption of Th by marine suspended particles is a reversible process. The results indicate reversibility on a time scale of hours. The distribution of Th between the ‘dissolved’ state (<0.22 μm particle size) and various particle size fractions has been compared with predictions based on a hyperbolic size distribution of marine particles assuming spherical geometry and surface adsorption. Thorium is present in small particles to a much smaller degree than such a model would predict, so that the use of 1 μm pore size filters to separate ‘dissolved’ and ‘particulate’ Th does not introduce serious errors. The implications of these results on the reversible exchange model of Bacon and Anderson (1982) and on the settling model of Tsunogai and Minagawa (1978) are discussed.     

The use of microstructures for discriminating turbiditic and hemipelagic muds and mudstones

The microstructures of turbiditic and hemipelagic muds and mudstones were investigated using a scanning electron microscope to determine whether there are microstructural features that can differentiate turbiditic from hemipelagic sedimentary processes. Both types of muddy deposits are, in general, characterized by randomly‐oriented clay particles. However, turbiditic muds and mudstones also characteristically contain aggregates of ‘edge‐to‐face’ contacts between clay particles with long‐axis lengths of up to 30 μm. Based on observations of the clay fabric of the experimentally‐formed muds settled from previously agitated muddy fluids, these types of aggregates, hereafter referred to as ‘aggregates of clay particles’, are interpreted as having been formed by the collision of component flocs in turbulent fluids. Furthermore, some aggregates of clay particles have ‘face‐to‐face’ contacts between clay particles; this is similar to face‐to‐face aggregates characteristically developed in fluid‐mud deposits that are commonly recognized only in turbiditic mudstones, indicating the possibility of a final stage of deposition under highly‐dense conditions, such as temporary fluid muds. In conjunction with earlier proposed lithofacies‐based and ichnofacies‐based criteria, aggregates of clay particles should be useful for the differentiation of turbiditic and hemipelagic muddy deposits, particularly with limited volumes of non‐oriented samples from deep‐water successions.     

三峡库区顺层灰岩岸坡劣化−溃屈灾变机制研究

三峡库区巫峡段发现多处顺层岸坡滑移−弯曲变形迹象,库水循环涨落加剧了岸坡前缘劣化损伤与失稳破坏。以巫峡段青石 6号坡为例构建室内概化模型,开展顺层灰岩岸坡在消落带岩体劣化下的灾变机制研究。研究结果表明：蓄水前岸坡整体长期处于稳定状态。随着劣化进行,蓄水后岸坡变形加剧直至溃屈破坏,岩体劣化缩短了劣化−溃屈失稳进程。运动学分析显示,溃屈破坏时同一岩层达到速度峰值近似。岩层“弯折点”后部运动特征较为一致,前部较为离散。溃屈破坏点是岸坡能量释放的转折点和顶点;随劣化演变位移、应力逐渐递增,呈现提前破坏征兆,溃屈破坏前后应力产生“集中−释放”。整体来看,应力变化提前于位移,表明应力监测更有效。应力监测的核心在于关键区段的确定,对于劣化−溃屈型岸坡来讲,前缘“挠曲段”处应力陡增可作为岸坡临界失稳的重要表征;“劣化−溃屈”演化进程中后缘推挤始终存在,它是岸坡灾变的前提。但岸坡失稳的主导因素却是消落带岩体持续不断的劣化。青石 6 号坡当前处于向强烈弯曲隆起演化进程中,由于消落带岩体持续劣化,可能由稳定/基本稳定逐渐演变为欠稳定状态。     

复杂滑坡三维离散建模方法及其在茂县滑坡中的应用

滑坡灾害调查发现,对于大型的高速远程滑坡,其堆积体中往往存在大粒径颗粒在上、小粒径颗粒在下的反粒序堆积现象。为了揭示大型滑坡反粒序堆积现象的机理和影响因素,借助离散元数值分析方法,研究分形维数、滑坡体积以及加速区长度对滑坡体内不同粒径颗粒移动过程的影响规律,并对鸡尾山滑坡进行模拟,分析其堆积体中反粒序堆积结构的形成原因。结果表明：滑坡体在滑动过程中因发生颗粒破碎而形成不同粒径大小的颗粒,在颗粒分选机制作用下,小粒径颗粒通过颗粒间的孔隙向滑坡体下方移动,大颗粒在剪切作用下越过小颗粒向滑坡体上方移动,最终在滑坡堆积体中形成反粒序堆积结构。颗粒分选过程主要通过动力筛分作用和剪切作用进行,其作用力大小与颗粒粒径大小和颗粒受到的上覆压力有关,分形维数越大、上覆压力越大,颗粒分选程度越小,反粒序堆积现象越不明显。     

A non-linear numerical model for soil mechanics

A new computer program (CONBAL-2) is developed for 2D numerical simulations of granular soil by random arrays of spheres. CONBAL-2 uses the discrete-element method and is based on 3D program TRUBAL, previously presented by Cundall. As in TRUBAL, the new program models a random array of elastic spheres in a periodic space. The main modification of TRUBAL is the implementation by the authors of a rigorous solution for the force–displacement relation at the interparticle contacts. This force-displacement relation is a function of the elastic constants, friction coefficient and sizes of the spheres, with the properties of quartz used to simulate sand. Other specific features of CONBAL-2 include its 2D character, the lack of particle rotation and its capability to simulate shear loading on any plane. Simulated laboratory test results are presented using CONBAL-2 and several random arrays of 531 spheres having two particle sizes. These simulations include monotonic loading drained and undrained (constant volume) ‘triaxial’ experiments, as well as a cyclic-loading, constant-volume ‘torsional shear’ test. The stress–strain curves, effective stress paths, volume changes, as well as the ‘pore water pressure’ build-up behaviour obtained in the simulations compare favourably—qualitatively and in some aspects quantitatively—with similar laboratory results on sands. However, the simulated soil is somewhat stiffer and stronger due to the perfectly rounded particles, limited range of grain sizes, lack of particle rotation and 2D character of the model.     

基于SEM图像的既有地基红黏土颗粒微观结构及分形特征研究

采用IPP（Image-Pro Plus）图像分析软件对贵州省贵阳市某工厂三种既有地基红黏土SEM图像的信息进行提取和处理,定性描述和定量分析土体的微观结构,并引入分形理论分析SEM图像,提出在IPP软件中获取颗粒三维分形维数的计算方法。结果表明:（1）抗剪强度参数随微观颗粒数、颗粒形态比的增大而增大,随颗粒平均面积的增大而减小;（2）颗粒分布及形态均具有明显的分形特征,分形维数介于2~3之间,抗剪强度参数均随颗粒分布及形态分维值的增大而增大;（3）与构建三维模型的方法相比,利用IPP软件计算土颗粒三维分形维数的方法具有可行性,简单易操作,结果可靠。      

土石料湿化变形计算方法探讨

土石料的湿化是一种普遍现象,虽然可以利用非饱和理论计算湿化变形,但人们更愿意采用常规的初应变法进行计算,湿化试验则常用单线法或双线法进行。对湿化试验和相关计算方法进行分析,提出考虑湿化变形及其影响的新思路,（1）在某一应力状态下的湿化变形是由两部分组成的,一部分是由于材料本身刚度变“软”引起的湿化变形,另一部分变形是湿化引起的附加变形;（2）在双线法试验中直接将相同应力状态下对应干土和湿土的应变相减计算是不合适的,应当采用相同应力状态下各自的切线模量计算;（3）基于广义位势理论,根据应力和应变的对偶特性,可以把湿化附加变形变换为一种湿化等效应力,虽然其是一种近似处理方法,但它比较简单,容易直观地量化湿化的作用。文中思路对于颗粒破碎、干湿循环引起的变形、流变变形等也具有借鉴意义。     

Assemblage of strike-slip faults and tectonic extension and compression analysis: A case study of a Lower Permian commercial coal reservoir in China

The Qinshui Basin was an active residual basin in the Mesozoic and Cenozoic periods and is located inside the North China Plate. The Upper Paleozoic strata in the basin have been strongly deformed and have developed a large number of strike-slip faults. The Qinshui Basin has been influenced by compressive stress from the northeast direction since the Himalayan period, and the faults have a dextral strike-slip property. Under the action of such a stress field, the right-slip, right-order faults indicate an extension region, and the right-slip, left-order faults indicate a compression region. Based on this principle, the extension and the compression areas were divided. From northwest to southeast direction in the study area, two types of regions have interactive distribution characteristics. For the Fanzhuang block in the eastern part of the study area, the fault distribution has an ‘S-type’ trend from north to south, and the middle extension region is the ‘elbow’ or the ‘hinge zone’ of the ‘S-type’ area, which can also be called the ‘stress transition zone’. The tectonic stress field of the stress transition zone is complex, and tensile fractures are usually extremely developed with extension tectonics. Gas wells with higher capacity are mainly distributed in the extension zone, while the capacity of the gas wells in the compression area is usually lower. The study showed that the distribution of the gas well capacity is consistent with the tectonic extension and compression analysis, indicating that the tectonic analysis method in this study is reliable. The Upper Paleozoic coal measure strata in the Qinshui Basin represent a whole gas-bearing and stress-bearing system, the tectonic analysis method in this study is also applicable to other types of tight reservoirs for this set of depositional systems.     

珊瑚砂高压力下一维蠕变分形破碎及颗粒形状分析

珊瑚砂是一种含钙极高的海洋生物成因材料,具有高棱角性、形状不规则、易破碎等特点。通过珊瑚砂的高压一维蠕变试验,研究颗粒破碎引起颗粒分布曲线和形状因子的演化规律。借助于高速动态图像的激光粒度粒形仪器,从统计学的角度分析试验前后颗粒形状随压力演化的关系,发现颗粒的形状因子,如长宽比、球形度和凹凸度等,随压力增加而逐渐增加。不同粒径的颗粒形状因子均向一个窄幅范围趋近,说明颗粒破碎具有无尺度性和自相似性的分形特性,分形维数随压力增加而逐渐增大,且趋近分形破碎极限。采用Hardin和Einav的方法计算相对破碎量,发现在两种计算方法下相对破碎量与压力呈幂函数关系,且幂指数相同。相对破碎量随时间增加的现象并不明显,说明在高压力下颗粒破碎主要为压缩破碎,且颗粒细化滑移填充孔隙引起的变形是造成蠕变的主要原因。     

Fractal-statistical analysis of grain-size distributions of debris-flow deposits and its geological implications

Breakage models and particle analyses have been widely used as tools for describing and interpreting various deposits and providing parameters for assessing the particle-size distribution of the deposits. Debris flows can be seen as a two-phase rheological fluid with a clay-fluid composition, and debris-flow deposits comprise mud, silt, sand, and boulders, with grain sizes ranging from less than one μm to more than several meters. As a consequence, according to fractal theory, the particles in debris-flow deposits have self-similarity in geometrical shape and scale invariance in size. In this paper, the fractal dimensions of particles in various debris-flow deposits are calculated and corresponding fractal features are determined based on fractal-statistical theory. The aims of the study are: to provide a quantitative grain parameter that reflects both the grain composition and grain-size distribution in debris-flow deposits; to compare the fractal dimensions of grains in different types of debris-flow deposits and the degree of self-organization of debris flows; as well as to discuss the geological implications of fractal dimensions and fractal features of particles in debris-flow deposits.     

A new fractal modification of ultrasonic attenuation model for measuring particle size in mineral slurries

Weight percentages of different size incremental particles in a mineral slurry is integrated into the ultrasonic attenuation model to derive a relation between ultrasonic attenuation and particle sizes. However, in the inertial and scattering regimes of frequency–radius space, irregularity and aggregation of particles can results in values of ultrasonic attenuation that are significantly different from those predicted by the derived model, which is based on the assumption of separated smooth spherical particles in mineral slurries. Experimental attenuation data obtained previously from mineral slurries of iron ores particles are compared with predicted values. It is shown that there is a negligible difference between predictions and experimental data. A new modification of theoretical model for ultrasonic attenuation is derived. The theory uses ωτ_v or κR as a fractal scale. It requires an empirical determination of the difference between the fractal dimension of the measured mineral slurry and that of a hypothetical slurry of spheres with the same particle size distribution. The new fractal modification of ultrasonic attenuation model is found to enable better agreement with measured attenuation as a function concentration for irregular particles than the theoretical model. Moreover, the fractal approach is found to discriminate between the effects of particle irregularity and aggregation.     

基于IPP图像处理的膨胀土微观结构定量研究

利用环境扫描电镜（ESEM）获取不同浸水时间下合肥膨胀土的微观结构扫描图像,基于专业图像处理软件Image-Pro Plus（IPP）对膨胀土的ESEM图像进行处理和分析,研究了不同浸水时间下合肥膨胀土的表观孔隙比、分形维数和大小组成情况。研究表明,膨胀土的表观孔隙比随着浸水时间的增大逐渐增大,其增长速率逐渐减小。运用小岛法对土样的颗粒和孔隙的分形维数进行研究,结果表明,膨胀土的颗粒和孔隙均具有明显的分形特征,分形维数在1.1～1.3之间。随着浸水时间的逐渐增大,颗粒的分形维数在减小,孔隙的分形维数在增大,二者呈现相反的变化趋势。对土样的颗粒和孔隙按照大（>5 μm）、中（2～5 μm）、小（1～2 μm）、微（<1 μm）4组进行分类,分析了不同浸水时间下各类颗粒和孔隙占比的演变趋势。     

Atmospheric aerosol characteristics retrieved using ground based solar extinction studies at Mohal in the Kullu valley of northwestern Himalayan region,India

Aerosol parameters are measured using a ground-based Multi-wavelength Radiometer (MWR) at Mohal (31.90°N, 77.11°E, 1154 m amsl) in the Kullu valley during clear sky days of a seasonal year. The study shows that the values of spectral aerosol optical depths (AODs) at 500 nm and the Ångstrom turbidity coefficient ‘β’ (a measure of columnar loading in atmosphere) are high (0.41 ± 0.03, 0.27 ± 0.01) in summer, moderate (0.30 ± 0.03, 0.15 ± 0.03) in monsoon, low (0.19 ± 0.02, 0.08 ± 0.01) in winter and lowest (0.18 ± 0.01, 0.07 ± 0.01) in autumn, respectively. The Ångstrom wavelength exponent ‘α’ (indicator of the fraction of accumulation-mode particles to coarse-mode particles) has an opposite trend having lowest value (0.64 ± 0.06) in summer, low (0.99 ± 0.10) in monsoon, moderate (1.20 ± 0.15) in winter and highest value (1.52 ± 0.03) in autumn. The annual mean value of AOD at 500 nm, ‘α’ and ‘β’ are 0.24 ± 0.01, 1.06 ± 0.09 and 0.14 ± 0.01, respectively. The fractional asymmetry factor is more negative in summer due to enhanced tourists’ arrival and also in autumn months due to the month-long International Kullu Dussehra fair. The AOD values given by MWR and satellite-based moderate resolution imaging spectro-radiometer have good correlation of 0.76, 0.92 and 0.97 on diurnal, monthly and seasonal basis, respectively. The AODs at 500 nm as well as ‘β’ are found to be highly correlated, while ‘α’ is found to be strongly anti-correlated with temperature and wind speed suggesting high AODs and turbidity but low concentration of fine particles during hot and windy days. With wind direction, the AOD and ‘β’ are found to be strongly anti-correlated, while ‘α’ is strongly correlated.     

固体颗粒破碎的分维演化规律

固体颗粒破碎后的粒径分布符合分形模型,颗粒破碎程度采用粒径分布的分维表示。本文采用垃圾炉渣的颗粒破碎试验,统计计算炉渣颗粒破碎的分维。收集总结了岩石颗粒破碎分维随破碎应力和破碎能量的变化规律,颗粒破碎的分维是变化的,随着破碎应力和破碎能量增加而增加,颗粒完全破碎后的粒径分布的分维趋于定值,为2.6左右。将颗粒破碎过程中变化的分维称为颗粒破碎的“似分维”,简称分维;分维的极限值称为“真分维”。结合颗粒破碎概率的Weibull统计理论,建立了颗粒破碎“似分维”与破碎应力和破碎能量的相关关系。     

应力路径试验前后不同黄土的孔隙分形特征

为了解不同黄土孔隙形状复杂程度的差异和应力路径对孔隙形状复杂程度的影响,对两种黄土应力路径前后孔隙分形特征进行了研究。首先比较了3种分维模型所得孔隙分形维数的可靠性,然后选用热力学关系模型,由进汞、退汞试验得到地裂缝区黄土、充填黄土初始样和三轴应力路径试验后的孔隙分布,据此分析了两种土体进汞孔隙和退汞孔隙分形维数的差异和受载后的分形维数变化,根据退汞过程仅管形孔内的汞流出及孔隙由管形孔和球形孔组成的假定,得到了应力路径试验前后孔隙形状的改变。结果表明,热力学关系模型得到的孔隙分形维数合理、可靠。初始状态,原状和重塑充填黄土的孔隙形状比原状和重塑黄土复杂;常规三轴试验后试样孔隙比减少,孔隙分形维数增加,球形孔向管形孔转变;相对于常规三轴压缩试验,减围压三轴压缩试验后试样的孔隙分形维数较小,管形孔占总孔隙的体积比例较少;总体上管形孔的分形维数比球形孔大,且基本不受应力路径的影响,其占总孔隙的体积比例随着试样宏观孔隙比的减少而增加。     

Stone column effectiveness in soils with creep: a numerical study

While it is well established that vibro stone columns reduce primary settlement and improve bearing capacity, their effect on creep compression has largely been overlooked to date. However, with increasing pressure to develop marginal sites underlain by soft organic soils, the effect of ground treatment on creep is an important emerging issue in geotechnical engineering. In this paper, a series of axisymmetric unit cell analyses have been carried out using the PLAXIS 2D finite element program in conjunction with the Soft Soil Creep (SSC) model. Examination of the evolution of settlement improvement factor with time has indicated that the presence of creep leads to a lower ‘total’ improvement factor than would be obtained for primary consolidation settlement alone. Separate ‘primary’ and ‘creep’ improvement factors have also been derived; the latter are much lower than the former, but are nevertheless greater than unity. Creep results in a stress transfer process; as the soil creeps, vertical stress is transferred from the soil to the stone column. The additional load carried by the column induces additional yielding and shear-plane formation in closely-spaced columns. The additional increment of stress transferred to the already yielded column reduces its efficacy.