组构对自然休止角影响的试验研究

利用自制的模型试验装置,通过在不同方位沉积散体颗粒生成堆积体,研究不同沉积组构特征对自然休止角的影响,以及通过在母堆积体底部设置漏孔以生成子堆积体,研究堆积体内部结构对自然休止角的影响。研究发现,母堆积体休止角? 和子堆积体休止角? 随着沉积面倾角? 的增大（0° → 90°）呈现先减小后增大的趋势,子堆积体休止角? 则先增大后减小,且最小和最大值的分布区间正好互余,分别为? = 30°～45°和? = 45°～60°。当漏孔位置从左至右靠近母堆坡脚时,? 先增大后减小,? 则单调增大。基于模型的分析和推导,发现当沉积面与潜在滑动面越接近平行,休止角越小,越偏离,休止角则越大,并从细观上合理解释了?、? 和? 在特殊角度区间出现最大或最小值的原因。最后,提出了散粒堆积体的扰动分区模型,并以此为基础阐释了漏孔位置（堆积体内部结构）对休止角? 和? 的影响机制。     

粗粒土的破碎耗能计算及影响因素

粗粒土的颗粒破碎直接改变了土体本身结构,对粗粒土的剪胀和内摩擦角都会产生影响。在土体剪切过程中,体积应力和剪切应力在体积应变和剪切应变上做功,这部分能量在剪切过程中转化为颗粒的弹性储能、颗粒间的摩擦耗能、颗粒剪胀时对外做功和颗粒破碎耗能4部分。准确计算剪切过程中粗粒土破碎耗能的目的是：从能量角度分析颗粒破碎对土体本构关系的影响,为建立考虑颗粒破碎的粗粒土本构关系创造条件。通过分析粗粒土的常规三轴试验数据,计算得到了剪切过程中的粗粒土破碎耗能。计算结果表明,常规三轴试验条件下粗粒土破碎耗能主要受固结应力、土体摩擦系数M等因素的影响。     

An analytical and experimental study of zoning in plagioclase

A detailed electron microprobe study has been conducted on natural and experimentally grown zoned plagioclase feldspars. Discontinuous, sector, and oscillatory chemical zoning are observed superimposed on continuous normal or reverse zoning trends. The relative accuracy of 3 element (Na, Ca, K) microprobe traverses was found statistically to be 2 mole percent. Comparison of microprobe data on natural zoned plagioclase with zoned plagioclase grown in controlled experiments has shown that it may be possible to distinguish zonal development resulting from physio-chemical changes to the bulk magma from zoning related to local kinetic control on the growth of individual crystals.     

Work-softening and hardening behaviour of granular rocks

SummaryWork-Softening and Hardening Behaviour of Granular Rocks Experimental results from granular and dense rocks indicated that the plastic strain increment vector was inclined at a constant angle (approximately 70°) to the tangent of a curve fitted either to peak strength data or to strength data associated with a given value of axial or volumetric strain. The angle of inclination was independent of the direction of stress increment. When a small axial strain was exceeded changes of volumetric strain were found to be non-zero and had a linear relationship with the corresponding changes of axial strain. This applied for both work-softening and work-hardening behaviour. Close links between volumetric strain and microfacturing and between the ratios of stress and of strain increments were revealed. The role of confining pressure was predominant and the mode of deformation was cataclastic for granulated and intact marbles.With 11 Figures     

Micromechanical investigation of the particle size effect on the shear strength of uncrushable granular materials

Particle size strongly influences the shear strength of granular materials. However, previous studies of the particle size effect have focused mainly on the macroscopic behavior of granular materials, neglecting the associated micro-mechanism. In this study, the effect of particle size on the shear strength of uncrushable granular materials in biaxial testing is investigated using the discrete element method (DEM). First, a comprehensive calibration against experimental results is conducted to obtain the DEM parameters for two types of quartz sand. Then, a series of biaxial tests are simulated on sands with parallel particle size distributions to investigate the effect of particle size on macro- and microscopic behaviors. Finally, by adopting the rolling resistance method and the clump method, irregular-shaped particles are simulated to investigate how the particle size effect will be influenced by the particle shape. Simulation results demonstrate that (1) the peak shear strength increases with particle size, whereas the residual shear strength is independent of particle size; (2) the thickness of the shear band increases with the particle size, but its ratio decreases with particle size; (3) the particle size effect can be explained by the increase of friction utilization ratio with particle size; and (4) the particle size effect is more significant in granular materials that consist of particles with higher angularity.

     

An investigation on the kerf width in abrasive waterjet cutting of granitic rocks

This paper presents an experimental and statistical study on the kerf width, used instead of the width of the cut in abrasive waterjet (AWJ) cutting. Pre-dimensioned granitic rocks were sampled for the experimentations designed by using Taguchi orthogonal arrays. The effects of the AWJ operating variables on the kerf width were studied and the rock properties were correlated with the kerf widths. Additionally, predictive models for the kerf widths were developed using multi-variable regression analysis and the developed models were verified through some statistical tests. The results demonstrated that the standoff distance and the traverse speed have significant effects on the kerf widths. The results also showed that water absorption, unit weight, microhardness, the maximum grain size of rock-forming minerals, and mean grain size of the rock have significant correlations with the kerf widths of the tested rocks. Furthermore, the modeling results revealed that the predictive models derived from rock properties, can be successfully used as a practical guideline.     

An experimental investigation of olivine morphology

Olivine crystals can adopt ten types of shape. Experimental crystallization of eight rock melts shows that there is a systematic change from polyhedral or granular olivines hopper olivines branching olivines randomly oriented chain olivines parallel-growth chain olivines chain+lattice olivines plate or feather olivines, with increase in cooling rate and with increase in degree of supercooling. This sequence involves changes from complete to progressively less complete crystals and from equant habit to elongate bladed habit (c>ab) to tabular habit (ac b). The sequence is not affected by the phase relations of the melt. The larger the olivine content of a melt the slower the cooling rate at which a particular olivine shape grows, whereas the lower the melt viscosity, the greater the cooling rate. Irrespective of the melt composition, comparable crystal shapes grow at the same degrees of supercooling. By comparison of the shapes of olivine crystals in experiments with those in rocks of similar composition, it is possible to deduce the cooling rate through the olivine crystallization interval and the approximate degree of supercooling at which the olivine crystals nucleated and grew in the rocks. The various shapes of skeletal olivines in many picrites, olivine-rich basalts and the Archaean spinifex rocks are not due to rapid cooling, but to rapid olivine growth caused by the high normative olivine content of the magma.     

施用农肥对岩溶溶蚀作用的影响及其生态环境意义

土壤下伏碳酸盐岩溶蚀作用研究对岩溶区成土作用及大气中CO_2影响意义重大.施肥改变了土壤的生物地球化学场,进而会影响岩溶区的岩溶动力学过程及碳循环.本文在贵州贵阳碳酸盐岩土壤剖面不同深度,埋设白云石、石灰石试片,进行了野外溶蚀试验,观测了试片溶蚀量、土壤CO_2、土壤pH及其他如土壤含水量、土壤矿物与化学成分、土壤水化学成分等影响凶素.结果表明:(1)施用农家肥降低了碳酸盐岩的溶蚀速率:石灰石的溶蚀速率降低了10.48%～53.90%.平均25.51%;白云石的溶蚀速率降低了25.0%～65.69%,平均39.45%.同样条件下土壤中石灰石溶蚀量比白云石大.(2)施用农家肥降低了当地的碳酸盐岩成土速度,降低了35.77%～37.27%.(3)施肥土壤更利于CO_2的产生:施肥剖面土壤中CO_2浓度比空白剖面CO_2浓度高22.52%～198.87%,平均高93.94%;施肥剖面地面CO_2通量比空白剖面地面CO_通量高67.64%.(4)施用农家肥减少了土壤对大气CO_2的沉降量,在贵州贵阳地区,减少的大气CO_2沉降量为25.50%～39.45%;间接地对岩溶水CO_2汇的作用产生了抵消作用,在贵州贵阳地区,抵消作用为59.41%～62.73%.     

DEM investigation of the effect of intermediate principle stress on particle breakage of granular materials

This study investigates the influence of the intermediate principle stress on the particle breakage of granular materials. The crushable agglomerate method is applied to model soil particles and numerical true triaxial tests were carried out. The results show that particle breakage increases with increasing b value, the relationship of which follows an exponential function and agrees well with previous experimental results. More importantly, the study found that the relationship between particle breakage and total energy input is independent of the intermediate principle stress, which provides a good basis for the constitutive modeling of granular materials.     

颗粒大小对颗粒材料力学行为影响初探

利用一种特殊颗粒材料-玻璃珠进行了一系列室内直剪试验,研究颗粒大小对颗粒材料力学行为的影响。试验一共考虑了3条近乎平行的级配曲线和4种颗粒摩擦情况：干燥状态、水浸润状态、水淹没状态和油浸润状态。试验结果表明,颗粒大小对颗粒材料的力学行为有显著影响,剪胀性随着粒径的增大而增强。为考虑颗粒大小对剪胀性的影响,提出了一种新的剪胀关系式。在该剪胀关系式中,剪胀系数为依赖于颗粒大小和颗粒摩擦等颗粒基本性质的变量。试验研究同时表明临界状态摩擦角随着颗粒大小的增加而增加。此外,从颗粒细观运动的角度提出了颗粒滑动的功能模型,推导出了功能方程,并以此揭示了颗粒大小对临界状态摩擦角影响的细观机制。     

An experimental study on the time-dependent behavior of crushable granular materials using 3D-printed particles

Acta Geotechnica - This paper aimed to investigate the potential capability of using 3D-printed particles to study the time-dependent behavior of a typical crushable granular material, i.e.,...     

Analysis of mobilized stress ratio of gap-graded granular materials in direct shear state considering coarse fraction effect

Weathered rockfill materials, characterized by a mixture of soil matrix and rock aggregates, are widely distributed in mountainous areas. These soils are frequently used for subgrade or riprap in engineering practice, and the mobilized shear strength is crucial for analyzing the displacement and stability of these geo-structures. A series of direct shear tests are performed on a gap-graded soil with a full range of coarse fraction. The behavior of gap-graded soils is analyzed, and a simple model is proposed for the evolution of mobilized stress ratio during direct shearing process based on mixture theory. The change of inter-aggregate configuration is incorporated by introducing a structure variable which increases with coarse fraction and decreases approximately linearly with the overall horizontal shear strain in double logarithmic plot. It reasonably reflects a gradually transformation from a matrix-sustained structure into an aggregate-sustained one with the increase of coarse fraction. The model has four parameters, and at least two direct shear tests need to be done for the calibration. Validation of the model is done by using the test data in this work and those from the literature.

     

Strength and dilatancy of jointed rocks with granular fill

It is well recognised that the strength of rock masses depends upon the strain history, extent of discontinuities, orientation of plane of weakness, condition of joints, fill material in closely packed joints and extent of confinement. Several solutions are available for strength of jointed rock mass with a set of discontinuities. There is a great multiplicity in the proposed relationships for the strength of jointed rocks. In the present study, the author conceives the effect of increasing stresses to induce permanent strains. This permanent strain appears as micro crack, macro crack and fracture. A fully developed network of permanent deformations forms joint. The joint may contain deposits of hydraulic and hydrothermal origin commonly known as gouge. The joint factor numerically captures varied engineering possibilities of joints in a rock mass. The joints grow as an effect of loading. The growth of the joints is progressive in nature. It increases the joint factor, which modifies the failure stresses. The dilatancy explains the progressive failure of granular media. Hence, a mutual relationship conjoins effectively the strength of jointed rock and a dilatancy-dependent parameter known as relative dilatancy. This study provides a simple and integral solution for strength of jointed rocks, interpreted in relation to the commonly used soil, and rock parameters, used for a realistic design of structure on rock masses. It has scope for prediction of an equivalent strength for tri-axial and plane strain conditions for unconfined and confined rock masses using a simple technique.     

An analytical assessment on the impact of covers on the onset of air convection in mine wastes

If a mine waste pile is left open, an active chemical reaction of oxidation is often found due to the commonly high content of pyritic materials. The oxidation of pyrites is an exothermic process and the released heat will promote the flow of fresh oxygen from the surrounding atmosphere into the waste dump. As a result, oxidation reaction will accelerate and temperature within the dump can increase to as high as 60°C above the ambient temperature. The oxidation process also releases sulphuric acid and hydrogen ions into ground water to cause water contamination. Low‐permeability covers such as clay liners have been recently proposed to abate the oxidation process in mine wastes. The effectiveness of using low‐permeability materials to cover mine wastes in order to suppress the pyrite oxidation is examined. By conducting the theoretical analysis of the onset of convective air flow within waste rocks, the conditions under which soil gas flow is significant are identified. By comparing the results with previous field measurements and theoretical analysis for the uncovered conditions, it is shown that low‐permeability covers can effectively suppress soil gas flow and slow down the pyrite oxidation process in mine wastes. Copyright © 2001 John Wiley & Sons, Ltd.     

An experimental investigation on diffusion of water in haplogranitic melts

  The diffusivity of water has been investigated for a haplogranitic melt of anhydrous composition Qz₂₈Ab₃₈Or₃₄ (in wt %) at temperatures of 800–1200°C and at pressures of 0.5–5.0 kbar using the diffusion couple technique. Water contents of the starting glass pairs varied between 0 and 9 wt %. Concentration-distance profiles for the different water species (molecular water and hydroxyl groups) were determined by near-infrared microspectroscopy. Because the water speciation of the melt is not quenchable (Nowak 1995; Nowak and Behrens 1995; Shen and Keppler 1995), the diffusivities of the individual species can not be evaluated directly from these profiles. Therefore, apparent chemical diffusion coefficients of water (D _water) were determined from the total water profiles using a modified Boltzmann-Matano analysis. The diffusivity of water increases linearly with water content <3 wt % but exponentially at higher water contents. The activation energy decreases from 64 ± 10 kJ/mole for 0.5 wt % water to 46 ± 5 kJ/mole for 4 wt % water but remains constant at higher water contents. A small but systematic decrease of D _water with pressure indicates an average activation volume of about 9 cm³/mole. The diffusivity (in cm²/s) can be calculated for given water content (in wt %), T (in K) and P (in kbar) by

An investigation of Malaysian granitic rocks as suitable sources of feldspar

Medium- to coarse-grained leucocratic granitic bodies containing more than 60% feldspar and less than 10% mafic minerals are found to be appropriate and potential source materials of local feldspar. Out of the 72 granite quarries/outcrops studied in Peninsular Malaysia, 31 have been identified as “ideal” sources of feldspar conforming to the “preferred” feldspar specification of >18% Al₂O₃, >11% (Na₂O+K₂O) and <0.3% Fe₂O₃. A feldspar recovery efficiency exceeding 60% was achieved in this study. Despite the positive and encouraging indication that the extracted feldspar samples of different chemical composition are found to be suitable for the general purpose of making ceramic bodies and glaze, the chemical content of the feldspar, nevertheless, could be critical for the manufacture of specific end products. At 1250°C all extracted feldspar samples were fused; however, at the lower temperature of 1170°C feldspar samples extracted from some “Central Belt granites” remained unfused. The Eastern Province granites generally yielded feldspars which show better fusion characteristics i.e. (unblemished) than those extracted from the Main Range Province. A valuable by-product of the feldspar extraction process is silica sand.     

岩石疲劳强度试验和弹性理论分析初步研究

通过单轴压缩试验研究了岩石强度,并用空间弹性力学理论进行分析比较,采用高频振动疲劳试验研究了岩石的疲劳强度,得出了试验中所用材料603号花岗岩的纵向应力-应变曲线以及疲劳强度区间,并对其疲劳现象进行了分析。     

An experimental investigation of density-stratified inertial gravity currents

Turbidity currents and pyroclastic density currents may originate as stratified flows or develop stratification during propagation. Analogue, density‐stratified laboratory currents are described, using layers of salt solutions with different concentrations and depths to create the initial vertical stratification. The evolving structure of the flow depends on the distribution of the driving buoyancy between the layers, B* (proportional to the layer volumes and densities), and their density ratio, ρ*. When the lower layer contains more salt than the upper layer, and so has a greater proportion of the driving buoyancy (B* < 0·5), this layer can run ahead leading to streamwise or longitudinal stratification (ρ*→0), or the layers can mix to produce a homogeneous current (ρ*→1). If the upper layer contains more salt and thus buoyancy (B* > 0·5), this layer travels to the nose of the current by mixing into the back of the head along the body/wake density interface to produce a homogeneous flow (ρ*→1) or overtaking, leading to streamwise stratification (ρ*→0). Timescales describing the mixing between the layers and the streamwise separation of the layers are used to understand these flow behaviours and are in accordance with the experimental observations. Distance–time measurements of the flow front show that strongly stratified flows initially travel faster than weakly stratified flows but, during their later stages, they travel more slowly. In natural flows that are stratified in concentration and grain size, internal features, such as stepwise grading, gradual upward fining and reverse grading, could be produced depending on B* and ρ*. Stratification may also be expected to affect interactions with topography and overall fan architecture.     

An experimental investigation of barite formation in seawater

We report results from time-series decay and sequential leaching experiments of laboratory cultured and coastal plankton to elucidate the mechanisms controlling barite formation in seawater. Batch-cultured diatoms (Stephanopyxis palmerina) and coccolithophorids (Emiliania huxleyi) were let to decay in the dark for 8-10 weeks, suspended in aerated seawater. The development of barite crystals was monitored by Scanning Electron Microscopy (SEM). A similar experiment was conducted with plankton collected during the spring-bloom in Vineyard Sound (MA). In addition to SEM, suspended particles were sequentially leached for Ba (distilled water rinse; 10% (v/v) HNO₃ rinse at room temperature; 30% (v/v) HCl at 80°C overnight; 50% (v/v) HNO₃ at 80°C overnight) immediately after collection, and after 10-week decay in seawater, in seawater poisoned with HgCl₂, and in seawater spiked with ¹³⁵Ba.Both experiments showed an increase in the number of barite crystals during decay. The spring-bloom plankton had initially a large pool of labile Ba, soluble in distilled water and cold dilute HNO₃ that was lost from the plankton after 10-week decay in both axenic and nonaxenic conditions. In contrast, Ba in the decayed plankton samples was predominantly in forms extracted by hot HCl and hot HNO₃ acids, which were attributed to presence of barite Ba and refractory organic Ba respectively. The increase in barite crystal counts under a Scanning Electron Microscope (SEM), the increase in HCl extractable Ba relative to organic carbon, and the loss of a large fraction of Ba during plankton decay suggest that living plankton consists of a relatively large pool of labile Ba, which is rapidly released during plankton decomposition and acts as the main source of Ba for barite formation in supersaturated microenvironments. Since mass balance indicates that only a small proportion (2 to 4%) of the labile-Ba pool is converted to barite, the availability of microenvironments that could locally concentrate Ba released by plankton decay seems to be the main limiting factor in barite precipitation.     

An experimental,analytical and numerical study on the thermal efficiency of energy piles in unsaturated soils

Energy piles are bi-functional foundation elements used as structural support as well as ground heat exchangers for shallow geothermal energy systems. Because they are relatively short, energy piles may be partially embedded in unsaturated soils. Saturation conditions influence the thermal properties of the ground and therefore the heat exchange rate, which in turn affects the efficiency of energy piles. This paper combines analytical, experimental and numerical investigations to evaluate the heat exchange rate of energy piles partially or fully embedded in unsaturated soils. The proposed analytical solution is based on the cylindrical heat source theory that treats the soil as a semi-infinite, homogeneous, and isotropic medium. The solution from this theory is multiplied by a function developed analytically in this paper and the outcome is the heat exchange rate for energy piles in unsaturated soils. The proposed function depends on soil saturation, soil and pile thermal properties, and pile geometry. The analytical solution was compared against a finite element solution; which was in turn validated against results from laboratory experiments. Very satisfactory agreements between the analytical, numerical and experimental outputs were observed. The proposed method can be used for a quick and simple evaluation of the efficiency of energy piles in unsaturated conditions. The proposed analytical solution can also be a useful tool for the verification of numerical codes developed for the design of energy piles in unsaturated soils.