粒径对尾矿抗剪强度及坝体稳定性影响

为解决尾砂安全筑坝与井下充填之间的矛盾,开展了粒径对尾矿强度及坝体稳定性影响的研究。试验结果表明:尾砂加权平均粒径随干滩长度增大而下降的速率越来越缓,加权平均粒径与滩长之间关系满足幂函数沉积模型;尾矿内摩擦角随粒料加权平均粒径的减小而减小,当加权平均粒径小于0.05mm时,内摩擦角显著减小;尾矿坝稳定性随粒料加权平均粒径的减小而降低,当加权平均粒径小于0.05mm时坝体稳定性显著降低。研究结果为尾砂安全筑坝与井下粗料充填提供可借鉴的界限粒径,对于其它相同类型尾砂安全筑坝同样具有重要参考价值。     

粉粒含量对尾矿力学特性的影响

 尾矿的力学特性与粉粒含量有关,但目前对粉粒含量的影响机制研究较少。为了研究粉粒含量对尾矿力学性质的影响及其细观机制,通过显微观测、三轴试验和离散元模拟,研究砂粒和粉粒的显微特征,分析尾矿的临界粉粒含量,并讨论粉粒含量效应的细观力学机制。结果表明：砂粒和粉粒在粒径分布、棱角性和表面形貌方面存在差异,粒径小于30 µm的颗粒具有独特的显微特征;随着粉粒含量的增加,混合尾矿逐渐由砂性尾矿过渡到粉性尾矿,临界粉粒含量在30%～50%范围;理论推导证明,粉粒的粒径和弹性模量越小,相同力作用下的土体形变越大;从介观上看,粉粒含量的增加弱化了原有的强力链,是导致粉粒含量效应的重要原因。研究结果揭示了混合尾矿的细观力学行为机制,为宏细观关联性研究提供了参考。     

高速铁路级配碎石颗粒三维形态特征多尺度分析

高速铁路路基级配碎石颗粒形态对宏观力学性质具有显著影响,合理量化颗粒三维形态特征是粗颗粒填料细观机制研究的基础性工作。采用激光扫描仪获取2.36～31.5mm粒径范围7个粒组共计700个碎石颗粒的点云数据,重构形成三维网格模型;引入描述颗粒表面凹凸特征的主曲率均值平方根RMS,基于颗粒网格模型平滑处理及RMS曲率分布特征,分别定义以棱角区域点云数量占比表征的棱角参数、以平滑前后模型RMS差异描述的纹理参数。结合长、中、短轴相互关系所描述的形状参数,形成刻画碎石颗粒多尺度形态特征的指标体系;通过选取典型形态特征颗粒,验证所建立的指标体系具有良好形态甄别能力;根据所扫描碎石颗粒的统计分析,不同粒组碎石颗粒的形状、棱角、纹理指标基本呈正态分布特征,随粒径增大,块状颗粒占比提高,棱角和纹理特征愈加突出。研究成果可为从宏、中、细观3个尺度量化评价颗粒形态特征提供参考。     

细粒铁尾矿的沉积特性与基本物理力学性质试验研究

尾矿的沉积与固结过程是形成强度和确定变形量的重要依据。为探求尾矿沉积过程中应力和孔隙水压力演变规律,揭示尾矿料的强度形成机理和变形特征,结合现场溜槽试验,对细粒铁尾矿的沉积坡度、以及沉积过程中的应力、孔隙水压力和有效应力的演变规律进行了监测。同时,采用十字板剪切仪确定了沉积完成后尾矿的剪切强度。在此基础上,对不同沉积断面尾矿料的颗粒级配和渗透特性进行了试验研究,分析尾矿沉积速率的演变机理。试验结果表明:颗粒研磨极其均匀的尾矿料的堆积形式和渗透特性与尾矿料的水力特性存在差别;受尾矿颗粒相对密实度较大、颗粒分布均匀等因素影响,增加尾矿料的可透水边界较施加外荷载,更能提升尾矿料中有效应力的形成速率;尾矿料表层硬化和封闭微孔隙引发了上层滞水入渗困难,应采用必要的引水导流措施降低高势能流体对筑坝稳定性的影响。     

孔隙水运移特性及对尾矿细观结构作用机制试验研究

 利用自行研制的尾矿细微观力学与形变观测试验装置,研究尾矿充水过程、荷载作用和排水过程中孔隙水的运移特征及其对尾矿细观结构作用机制。结果显示：尾矿水位线实际达到高度大于计算获得的水位线高度;受荷载作用,充水条件下各层尾矿颗粒沉降位移显著大于未充水条件下相同位置颗粒的沉降位移;充水条件下尾矿颗粒沉降位移随荷载的增加可分为线性增长阶段、显著增长阶段和稳定阶段,显著增长阶段出现在200～400 kPa荷载下;受荷载与孔隙水的作用,尾矿细观结构会形成曲折复杂供水运移的通道,该通道的形成过程发生在尾矿颗粒沉降位移的显著增长阶段;孔隙水夹带尾矿小颗粒运移,对尾矿颗粒分布有一定的影响;尾矿颗粒沉降位移与细观结构受排水影响较小,其变化主要在排水初期。最后,提出水的毛细管作用下尾矿坝实际浸润线的概念与计算方法,研究孔隙水与荷载综合作用下尾矿细观结构变形破坏机制,为深入探索水引起的尾矿坝灾变机制及稳定性评价等具有重要的实际意义。     

堆石体粒径的概率分布特征

堆石体的物理力学性质与堆石体颗粒的几何特性密切相关,如颗粒形状、粒径和堆积方式等,对堆石体物理力学性质的研究建立在对颗粒几何形态研究的基础上,而颗粒的几何特性具有概率统计特征。针对目前对堆石体的研究主要以散体力学、细观力学和数理统计为基础的研究这一特点,分析了堆石体粒径的概率分布特征,给出了粒径的分布密度和分布函数,求出了统计特征值。其分析结果对进一步研究堆石体的物理力学特性及稳定性分析提供了理论基础。     

考虑颗粒形貌的干砂热传导特性研究

为揭示颗粒形貌对干砂热导率的影响规律,通过砂颗粒形貌测量和室内热探针试验,研究不同天然河砂的二维颗粒形貌统计分布特征以及颗粒形貌特征参数与热导率的相关关系,同时从细观尺度探讨砂颗粒接触传热的内在机制。结果表明：天然河砂颗粒圆度和球度值的统计分布具有正态分布特征,期望值可作为定量表征颗粒形貌的参数;干砂热导率随孔隙率增加而减小,在半对数坐标中两者具有良好的线性关系,直线斜率与“平均形貌因子”Am呈线性减小关系;相同孔隙率下,浑圆颗粒的干砂热导率值较大,不同干砂间热导率值的差异随孔隙率的增加而逐渐减小;提出的热导率计算新模型综合考虑了颗粒形貌和矿物组分的影响,相比于传统C?té和Konrad模型,具有更好的适用性和先进性;颗粒形貌对干燥状态下无黏性土热传导特性的作用受多因素综合影响,与应力环境、颗粒刚度等密切相关。     

透水性基床级配碎石填料宏细观压实特性试验研究

透水性级配碎石填料因其良好的渗透性而逐渐用于透(排)水性基床结构层,其压实质量直接影响路面结构工后变形和耐久性等关键服役性能。针对由颗粒堆积理论提出的石砂比(G/S)指标所设计的7种不同的透水性级配,分别开展室内重型击实和新型平板振动压实试验,研究级配、压实方式和能量水平等因素对碎石填料宏观压实特性和颗粒破碎的影响以及平板振动压实的最优激振参数组合,提出并初步验证对同种类型填料级配、压实方法和能量等的改变不敏感的干密度–饱和度归一化压实曲线;进一步采用高精度工业XCT扫描技术,从细观尺度对比研究了最优激振参数组合下不同级配的碎石填料试样内部颗粒运动、空隙分布和连通性特征等。结果表明：石砂比(G/S)指标级配设计方法可有效地区分透水性级配碎石填料不同的颗粒堆积结构类型,存在最优G/S值范围可使压实后的干密度最大、颗粒破碎程度最低和空隙结构最佳;平板振动压实下干密度随激振时间呈现3个不同的阶段,最优激振频率范围为25～27 Hz,且存在有效的激振时间和激振力组合,XCT扫描结果从细观层面分析不同阶段颗粒的运动规律验证宏观压实特性的变化规律,对比不同级配的空隙分布和连通性证实石砂比(G/S)...     

砂土渗透系数影响因素试验研究

砂土渗透系数的大小与土体的颗粒级配、土体干密度、土体孔隙比、土体颗粒粒径和土体矿物成分等因素相关。通过室内常水头渗透试验研究土颗粒粒径、土颗粒级配、土体干密度对砂土渗透系数的影响。采用控制变量法设计3大组试验,并对结果进行分析,确定了渗透系数随3种因素的变化关系。试验结果表明,砂土渗透系数随着颗粒粒径减小而减小,随级配增良而减小,随干密度增大而减小。     

颗粒介质剪胀、软化特性的直剪试验研究

颗粒介质的宏观力学行为特征与其微观组构演化密切相关,涉及孔隙比、颗粒形态、颗粒破碎以及各向异性等因素的交叠影响。采用DRS-I型超高压直剪试验系统对3种不同粒径的钢球进行0.4～12 MPa法向压力下的直剪试验,避免颗粒形态、颗粒破碎及各向异性的交叠影响,进而单独分析峰值强度、残余强度与孔隙比演化的关联性,以期为揭示颗粒介质的细观力学机制提供参考。结果表明:1)落雨法制得的圆球颗粒介质普遍呈现剪切软化特性,剪切过程中存在明显的峰值应力和残余应力;2)峰值强度随围压增大呈现出一定程度的减小趋势,与孔隙比变化斜率的极值相对应;3)残余强度基本不受颗粒粒径、围压的影响,对应着孔隙比的稳定值即临界状态;4)采用Rowe剪胀方程能够较好地描述颗粒介质的强度特性与体变特性的关联性。     

塌陷区全尾砂–废石混合处置体抗剪强度特性试验研究

 某矿将尾砂、废石制备成膏体对采矿引起的地表塌陷区进行回填处置,其强度特性直接影响到塌陷区处置效果及井下生产安全。废石含量及粒径是影响处置体抗剪强度的关键因素。采用改进的小型直剪装置对处置体试块进行试验,得到废石含量、粒径对处置体抗剪强度、黏聚力c、内摩擦角? 的影响规律,采用改进的黏着摩擦理论对其强度机制进行分析。试验结果表明：随废石含量增加c值总体呈下降趋势、?值总体呈上升趋势;根据废石含量及粒径不同,抗剪强度可分为黏聚力控制型、黏聚力–摩擦力共同作用型、摩擦力控制型;抗剪强度在含石量20%～30%时达到最低值;抗剪强度随废石粒径增大而增大;应力–应变曲线在低应力区呈应变软化、高应力区呈微应变硬化;摩擦强度对抗剪强度贡献率达到80%,颗粒间摩擦强度决定了宏观抗剪强度;废石粒径及含量的改变,实质是改变了处置体粒间的实际接触面积,引起粒间摩擦强度的改变,引起宏观抗剪强度的变化。     

基于SEM图片的钙质砂连通孔隙分析

钙质砂是一种以碳酸钙为主要成分的特殊砂土,由于在形成过程中保留了原生物的骨架,故钙质砂颗粒不仅形状各异而且富含孔隙。颗粒孔隙的存在对钙质砂的压缩、剪切、强度和破碎性等力学性质有很大影响。针对这一问题,取南海一处岛礁建设地基的钙质砂试样,根据粒径大小将其分为6个不同的粒组,在每个粒组中选出不同形状的代表性颗粒,对其进行电镜扫描试验。借助MATLAB图像处理程序,选取合适的阈值对扫描试验得到的图片进行二值化处理,对钙质砂的连通孔隙进行了分析,系统的研究了不同粒径和粒形钙质砂颗粒的表观孔隙率的分布规律。结果表明:对于粒径小于1 mm的颗粒,面孔隙度随着粒径的增大而增大,不同形状颗粒面孔隙度差别不大;粒径超过1 mm后,面孔隙度随着粒径的增大而减小;条状颗粒面孔隙度最大而片状颗粒的面孔隙度最小。     

Mechanical properties of rock materials with related to mineralogical characteristics and grain size through experimental investigation: a comprehensive review

Mechanical properties of rock materials are related to textural characteristics. The relationships between mechanical properties and textural characteristics have been extensively investigated for differently types of rocks through experimental tests. Based on the experimental test data, single- and multiple- variant regression analyses are conducted among mechanical properties and textural characteristics. Textural characteristics of rock materials are influenced by the following factors: mineral composition, size, shape, and spatial distribution of mineral grains, porosity, and inherent microcracks. This study focuses on the first two: mineral composition and grain size.This study comprehensively summarizes the regression equations between mechanical properties and mineral content and the regression equations between mechanical properties and grain size. Further research directions are suggested at the end of this study.     

Scale effect on the behavior of geocell-reinforced soil

Existing studies confirmed that the response of geocell-reinforced beds is directly affected by contributory factors, including soil's grains, geocell's characteristics, and surface loading geometries. In this paper, a series of plate load tests has been carried out for the further understanding of the behaviour of geocell-reinforced soil. Four different soil grains sizes, two different geocell's opening sizes and three different loading plate sizes were the considered variables. During the tests, the applied loading and soil surface settlements were recorded to evaluate the systems' response. As it was expected, the geocell-reinforced soil exhibited higher bearing capacity than the unreinforced status, up to 524%. The results further focused on the important role of scale effect on the response of reinforced foundations. The optimum nominal cells size of geocells was obtained about 15 times of medium grain size of soil. Also, it was found that in order to obtain the highest reinforcement benefits, the footing's width should be in the range 13–27 (20 in average) times of medium grain size of the backfill. Finally, to provide more stable and reliable geocell-reinforced backfill, it is recommended that the cells size of geocells should be selected smaller than 0.67 times of footing width.     

火场中铝合金导线熔痕的定量金相分析

借助计算机图像处理技术和金相分析技术对铝合金导线短路及火烧熔痕的晶粒与气孔的特点进行定性与定量分析,并依次与相同条件下铝导线熔痕金相组织特征对比。结果表明：铝合金导线一次、二次短路熔痕及火烧熔痕在晶粒、气孔的大小、形状等方面的几何参数有一定的差异,且与同条件铝导线熔痕在晶粒面积、气孔分布上也有差异。     

Surface features of uniaxial tensile fractures and their relation to rock anisotropy in Inada granite

Uniaxial tensile fractures parallel to the rift, grain and hardway planes were formed in Inada granite. Most of the fractures split the rock-forming mineral grains as transgranular paths under microscopic observations. The surface topography of the fractures was measured by the stereo-photogrammetric technique, and is different in different orientations. The rift-parallel uniaxial fracture has the smoothest surface, and the grain-parallel fractures are smoother than hardway-parallel fractures. The mineral compositions are also different on the failed surfaces of different directions. The rift-parallel fractures have almost the same constituent mineral ratio as the parent rock. However, the grain-parallel fractures pass preferentially through feldspar grains, and contain less quartz grains as compared to the bulk composition of the parent rock. In addition, it is remarkable on hardway-parallel fractures. It is considered that the differences of surface topography and mineral compositions are caused by preferred orientations and spatial distributions of pre-existing microcracks in Inada granite.     

梯级粉磨制备铁尾矿矿渣基胶凝材料

运用梯级粉磨技术制备铁尾矿矿渣基胶凝材料(TSBC）,研究了梯级粉磨时间组合、材料配比和助磨剂对TSBC粉料粒度分布与浆体强度的影响,通过压汞、X射线衍射(XRD）和扫描电镜(SEM）研究了TSBC浆体的亚微观结构及水化产物,探讨了利用TSBC和铁尾矿砂制备活性粉末混凝土的可行性.结果表明：合理的梯级粉磨时间组合有利于TSBC粉料的颗粒分布宽化和亚微米级铁尾矿颗粒含量的增加,可改善TSBC浆体的孔结构和提高强度;材料配比主要通过影响TSBC的水化活性而影响浆体早期强度;掺入适量助磨剂使TSBC粉料粒径细化,增强组分的胶凝活性和填充效应,利于改善TSBC浆体的孔结构和提高强度;TSBC和原状铁尾矿砂可用于制备活性粉末混凝土.     

用于岩石微焦CT扫描的三轴仪及其初步应用

 了观察和度量岩石空隙结构随应力的变化,研制了一种能和微焦X射线CT系统配套使用的三轴仪,该设备轻便,能够施加三轴压力,并在不卸载压力情况下对试样进行CT扫描和渗透系数的测量,且能够实时记录压力和变形等数据。利用研制的CT三轴仪得到了Berea砂岩在加载过程中的一系列CT图像,结合3DMA空隙结构计算方法,获得了Berea砂岩在不同应力状态下的有效孔隙半径分布、有效喉道半径分布以及弯曲度分布等定量细观几何特征。同时采用瞬态脉冲法测量了Berea砂岩不同方向的渗透率随有效围压的变化规律。结合围压对细观空隙结构参数的影响,认为细观空隙结构的变化是导致渗透发生改变的根本原因,当有效围压从零增至15 MPa时,半径40～100 μm的孔隙数量减少、孔喉半径减小以及Z方向的迂曲度增加,这是导致Berea砂岩渗透率随有效围压增大而降低的主要原因。     

Microscopic Particle Crushing of Sand Subjected to High Pressure One-Dimensional Compression

It is commonly accepted that the yield point during one-dimensional compression is related to the initiation of marked particle crushing. Different materials have clear to very amorphous yield points depending on the compression line curvature. In order to examine the relationship between the curvature and slope of the compression line and the statistics of individual particle crushing taking into account particle size and overall grading, high pressure one-dimensional compression tests on silica sand samples seeded with marked particles were carried out. Five levels of particle damage were obtained and defined from microscopic observations of the particles before and after testing. A statistical analysis was carried out on the data for the observed levels of damage to investigate the frequency variation with increasing applied stress. Additionally, one-dimensional compression tests were conducted to examine the effects of initial void ratio and grain size distribution on soil crushability and consequently the compression behaviour. It was found that even for the same material the yielding characteristics were dependent on the grading curve with much more marked yielding occurring for uniformly graded sands in comparison with well graded sands. This was related to the nature of the microscopic particle crushing during yielding. As the material changed from uniform to well graded, the nature of the particle crushing changed from the sudden catastrophic onset of splitting to the gradual splitting of smaller size particles, breaking of the smaller asperities and grinding of the surface.