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利用空心圆柱扭剪仪对含非塑性细粒的饱和砂土进行单调加载和循环扭剪试验,研究了不同细粒含量饱和砂土的液化特性。试验结果表明：（1）最大孔隙比与最小孔隙比均随着细粒含量的增加呈先减小后增大的趋势,分别在20%和40%时达到最小。（2）细粒含量从0%增加到20%,体积应变逐渐增加;细粒含量从20%增加到40%时,体积应变逐渐减小;之后随着细粒含量从40%增加到60%,体积应变再次增大;细粒含量超过60%以后,体积应变再次递减。（3）随着细粒含量的增加,土样的峰值强度随之降低,应力-应变关系从应变硬化特征发展为理想的弹塑性。相变角在细粒含量为30%时达到最小值。（4）细粒含量越大,达到液化所需的循环次数越小,液化时的应变越小。（5）抗液化强度曲线与抗液化应力比的变化趋势一致,在小于界限细粒含量（30%）时,随着细粒含量的增加而减小。在界限细粒含量附近（30%～50%）时,随着细粒含量的增加而增大。在细粒含量增加到60%时出现明显的骤减,之后再次随着细粒含量的增加而增大。界限细粒含量在40%左右。 相似文献
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在煤层气开发过程中，煤粉聚集及沉降会堵塞煤层气运移通道及导致卡泵、埋泵等事故。为了查明不同粒度煤粉的聚集及沉降特征，选取粒度>140目（<106 μm）、>70~140目（106~<212 μm）和>50~70目（212~<300 μm）3种粒度范围的煤粉，开展了在去离子水中煤粉的聚集及沉降实验，从煤粉聚集及沉降特征观察、悬浮液中煤粉含量及煤粉粒度分布探究不同粒度煤粉在去离子水悬浮液中的聚集及沉降特征。结果表明，随着静置时间的增加，各粒度煤粉悬浮液的颜色均不同程度地变浅，逐渐出现分层，其中，粒度>140目的煤粉悬浮液最先出现分层。煤粉粒度越小，煤粉悬浮液顶部漂浮的煤粉量越多；煤粉粒度越大，其下沉到煤粉悬浮液底部的煤粉量越多。不同粒度煤粉悬浮溶液中煤粉含量均随着静置时间的增加呈现不同程度的降低，在停止搅拌后3 min内，煤粉含量下降最快，粒度为>70~140目的煤粉悬浮液中煤粉含量最大。根据不同粒度煤粉悬浮液中煤粉粒度分布曲线，将煤粉聚集及沉降过程分为3个阶段:单峰变双峰阶段（煤粉快速上浮及沉降）、双峰变单峰阶段（煤粉快速聚集及沉降）和单峰阶段（煤粉缓慢沉降）。粒度>140目的煤粉在悬浮液中最先达到缓慢沉降阶段，粒度>70~140目的煤粉在悬浮液中最后到达缓慢沉降阶段。从煤粉的受力、扩展的DLVO理论及煤粉的有机分子结构方面探讨了煤粉聚集沉降的机理:煤样含有大量的脂肪烃和芳香烃等疏水性基团，疏水性强，润湿性低；随着煤粉粒度的减小，其比表面积显著增大，煤粉表面吸附大量空气，形成气膜；同时，煤粉颗粒间相互吸附聚集，内部形成很多微孔隙，导致粒度小的煤粉易聚集漂浮在悬浮液面上。实验得到的不同粒度煤粉的上浮、下沉及悬浮情况，为后期煤层气开发中煤粉管控措施提供依据。 相似文献
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利用GDS循环三轴试验系统,进行一系列不同细粒含量砂土的不排水动三轴试验,研究细粒含量对饱和砂土动弹性模量与阻尼比的影响。试验结果表明,砂土的动弹性模量随细粒含量的增加而减小,但当超过细粒含量的临界值30%后,变化趋势则相反;阻尼比随着细粒含量的增加呈现先增大后减小的趋势,其细粒含量的临界值也为30%。当细粒含量小于30%时,砂土的动力特性主要由粗粒决定,粗粒间形成的骨架孔隙比随细粒含量的增加而增大,相同应变水平下抵抗变形的能力随之减弱,从而使动弹性模量减小。同时,土颗粒间接触点的减少使应力波在土中传播速度变慢,使得土体对动荷载反应的滞后性增强,阻尼比随之增加;当细粒含量大于30%后,砂土的动力特性主要由细粒决定,细粒间孔隙比随着细粒含量的增加而减小,从而使砂土的动弹性模量与阻尼比呈现出相反的变化趋势 相似文献
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细粒含量对尾矿材料液化特性的影响 总被引：2，自引：0，他引：2
为了模拟沉积分选后颗粒组成的变化对尾矿材料的动力特性的影响,尾矿筛分后按不同的细粒（颗粒直径小于 0.074 mm）含量制备尾矿试样,并进行了大量的土动力学试验。分析了细颗粒含量对尾矿材料的动力液化特性的影响规律。研究表明,对于铜矿类尾矿坝的尾矿材料,当细颗粒含量占到总量的35 %时其抗液化性能最佳。根据尾矿材料动力特性试验的研究结果,并结合现场的标准贯入试验成果,提出了适用于尾矿材料的细粒含量对标准贯入击数的修正式。该式可以分析不同细粒含量的尾矿材料的抗液化强度,提高尾矿坝液化判别方法的判别准确程度。 相似文献
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大量低产低效井严重阻碍我国煤层气产业发展,其中,煤粉沉降导致的裂缝堵塞、管柱结块是气井稳产时间短、产气量降低甚至不产气的重要因素。系统梳理国内外煤层气井产出煤粉物质组成、生成机理、悬浮运移和产出控制等研究最新进展,总结煤粉凝聚–沉降及分散行为控制机理及关键问题,提出研究展望。煤粉问题伴随煤层气勘探开发全过程,涉及地质选区评价、工程压裂施工和排采管理控制的各个方面。煤粉包括因煤体结构破坏生成的原生煤粉和工程施工形成的次生煤粉,在气井产出中以有机碎屑和黏土矿物组成的混合物为主,部分样品黏土矿物含量高。煤粉悬浮运移受控于储层条件下煤岩结构和表面性质、nm~μm级煤粉颗粒的相互作用、有机质和黏土矿物的作用、通道内的气水流动等因素。煤粉能够适度稳定产出是排采管控的关键,涉及地层水环境对煤粉表面润湿性、表面电性和空间位阻效应的影响及作用机制,以及分散剂离子加入对煤层气的解吸和渗流能力影响等。围绕煤粉“黏附–润湿–凝聚–沉降全过程开展实验模拟”和“煤粉分散稳定性优化及流动实验”研究,以及煤粉理化性质精细表征、凝聚沉降机理分析和分散行为界定,提出适合煤粉稳定运移控制的流速,形成保持煤粉悬浮产出的基础性依据,为保障煤层气–水–煤粉稳定高效产出提供理论和技术支撑。 相似文献
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揭示煤层气排采储层非饱和流阶段煤粉与气体相互作用机理,对制定排采制度和提高产气量具有重要意义。通过气泡–煤粉微观作用实验装置,系统开展了不同直径大小的气泡对不同粒度和密度煤粉的作用实验,分析了气泡对煤粉运移轨迹和速度的影响及捕获煤粉特征。结果表明,气泡产出能够影响煤粉的运移轨迹,甚至能够捕获煤粉;煤粉通过气泡时会产生3种运动类型：沿着气泡表面运移到气泡底部最后被捕获、沿着气泡表面运移到气泡底部最后脱落及接近气泡时被排斥而轨迹发生偏转。煤粉若被气泡捕捉,则运动速度呈现出减小–增大–减小的变化特征;若未被气泡捕获,速度呈现出减小–增大–减小–增大的变化特征。不同条件下气泡对煤粉的捕获效率高达64.38%～86.64%;在气泡表面最高点附近发生碰撞煤粉被捕获的概率最大,并且随着偏离角度的增大,气泡捕获效率均呈现出逐渐减小的趋势;在相同的碰撞位置下,气泡对煤粉的捕获效率随着煤粉密度、煤粉粒径的增大而减小,随着气泡直径的增大而增大。煤层气产气初期应根据储层的实际导流能力合理控制降压速率,若储层导流能力较强,应加大排采速率,增大气体解吸对煤粉的扰动和捕获作用,促使大量煤粉随地下水或气泡产出;若储层... 相似文献
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《Engineering Geology》2007,89(1-2):1-8
Rock fines produced in rock blasting and crushing processes is a major problem for aggregate producers. Laboratory and full-scale studies were carried out to explore the possible relationship between fines production and water content of rock material. The Brazilian tensile test was selected for the laboratory study while a cone crusher machine was employed for the full-scale trials. Results of the laboratory work showed that the percentage of fines fraction produced was a function of the type of rock tested and the tensile strength of individual specimens. Different rocks produced various amounts of fines, but for the rocks investigated, a correlation between its strength and its fines generation could be attained. The influence of water content on production of fines was also examined and showed that increased water content reduces both tensile strength and fines generation in the laboratory. The impact of water content on aggregate production was also studied in full-scale but the results were not as clear as those of the laboratory tests. 相似文献
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The potential damage to man-made structures associated with earthquake-induced liquefaction has been demonstrated in catastrophic
fashion over the past 40–50 years. The phenomenon of liquefaction of relatively clean, poorly graded, sands is well understood.
However, the same cannot be said for cases when fine-grained materials are present within the sand matrix. A resolution of
what appears in some reported studies as conflicting observations related to the effect of fines on cyclic resistance is of
concern, particularly for land reclamation projects and sea fills where the material source is variable and may contain significant
levels of fines. The nature of the fines themselves may have a measurable effect on the matrix behavior. The work presented
herein explores the effect of silt and clay-size carbonaceous fines on the liquefaction susceptibility of sand. The choice
of fines was guided by the conditions associated with the Lebanon coastal reclamation projects, where limestone/marlstone
quarry source materials are dominant. The results obtained confirm the significant effect of fines on the cyclic resistance.
They also confirm the existence of a limit fines content and a plasticity index threshold and establish their effect on observed
behavior. 相似文献
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随着煤层气的开发，煤粉问题已逐渐成为制约煤层气开发的重要问题。由于近年来煤粉问题才开始被关注和重视，煤粉研究缺乏系统科学的研究思路和方法，从煤粉的危害、煤粉形成机制、煤粉产出规律及煤粉管控措施方面，总结了煤层气开发中产出煤粉的研究现状，指出了煤粉研究的不足，提出了一套由理论依据、研究内容、研究方法等核心环节构成的煤层气开发中煤粉问题的研究思路与方法:以煤层气地质与开发学、煤田地质学、岩石力学和流体力学等多学科理论为指导，以《煤层气勘探开发规范》《煤层气井监测方法》《测试分析技术方法》等相关技术标准和规范为依据，以历年煤层气地质资料和煤层气排采数据为基础，按资料收集→现场监测与采样→测试与数据处理→物理模拟与数值模拟→专题制图与综合分析→技术设备研发→现场工程应用的工作流程和方法，以煤粉产出的影响因素、煤粉产出机理、煤粉产出规律和煤粉管制措施等为主要研究内容，选择典型煤层气示范区，开展全面系统的煤粉研究工作，为实现煤层气高效开发提供保障。本研究思路与方法为科学研究煤粉问题提供方法学依据。 相似文献
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砂土渗透系数的细粒效应与其状态参数关联性 总被引：3，自引：0，他引：3
利用常规渗透仪进行了不同细粒含量砂土的渗透性能试验,通过引入粒间状态参量概念,探讨砂土渗透系数的细粒效应及其与表征砂土各种状态参数的相互关联性。发现砂土渗透系数总体上随细粒含量增加而减小,当细粒含量小于5%时影响较小;细粒含量在5%～10%时,渗透系数随细粒含量增加而急剧减小;而当细粒含量大于25%后,砂土的渗透系数则基本趋向相对稳定值。基于5种不同表征状态参数的拟合分析,表明采用现有常用的经验模型尚难以简便、有效地预测各种细粒含量砂土的渗透系数,而利用粉粒间孔隙比则能更好地反映细粒含量对渗透系数的影响,且其与渗透系数在半对数坐标内基本呈现线性关系,说明粒间状态参量适宜用来描述砂土渗透系数的细粒效应 相似文献
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Numerical investigation of rainfall-induced fines migration and its influences on slope stability 总被引：1，自引：1，他引：0
Xiaoqin Lei Zongji Yang Siming He Enlong Liu Henry Wong Xinpo Li 《Acta Geotechnica》2017,12(6):1431-1446
Rainfall-infiltration-induced fines migration within soil slopes may alter the local porosity and hydraulic properties of soils, and is known to be a possible cause of the failure of slopes. To investigate the intrinsic mechanisms, a mathematical formulation capable of capturing the main features of the coupled unsaturated seepage and fines migration process has been presented. Within the formulation, an unsaturated erodible soil is treated as a three-phase multi-species porous medium based on mixture theory; mass conservation equations with mass exchange terms together with the rate equations controlling fines erosion and deposition processes are formulated as the governing equations and are solved by the FEM method. The influences of both the fines detachment and deposition on the stability of slopes under rainfall infiltration have been investigated numerically. The results show that depending on whether the fines move out or get captured at pore constrictions, both desired and undesired consequences may arise out of the fines migration phenomenon. It is suggested that more attention should be paid to those slopes susceptible to internal erosion whose safety analysis cannot be predicted by traditional methods. 相似文献
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《Geomechanics and Geoengineering》2013,8(3):179-190
Void ratio has been used as a state variable for predicting the liquefaction behaviour of soils under the critical state, sometimes also referred to as the steady state, framework. Recent publications show that void ratio may not be a good parameter for characterising sand with fines because the steady state line (or curve) in the e-log(p′) space moves downward with increase in fines content until it reaches a threshold value referred to as the threshold fines content (TFC). Recently, an alternative state variable, referred to as the equivalent granular void ratio, has been proposed to resolve this problem. To calculate this alternative state variable, an additional parameter ‘b’ is needed. This parameter ‘b’ represents the fraction of fines that actively participate in the force structure of the solid skeleton. However, predicting the ‘b’ value is problematic. This paper examines the factors affecting the ‘b’ value based on published work on binary packing. This leads to a simple semi-empirical equation for predicting the ‘b’ value based on fines size and fines content. The proposed equations were evaluated with published data sets. Then, the concept of an equivalent granular steady state line is proposed. This concept was used to predict the location of SSLs for sand with different fines content from either the SSL of clean sand or the SSL of sand with a given fines content. The predictions agree well with experimental results. 相似文献
14.
Nima Akbari Paydar Mohammad Mehdi Ahmadi 《Geotechnical and Geological Engineering》2016,34(6):1857-1876
The use of shear wave velocity (V s) measurements as an in situ test for evaluation of liquefaction potential has increased substantially due to its advantages. Relatively large numbers of studies have been performed to establish the correlation between V s and liquefaction resistance (CRR) of clean sands. Usually, natural sands contain silt and/or clay, and previous studies have shown that both the amount of fines and their nature influence the values of CRR as well as V s. Therefore, the CRR–V s correlations may also be affected by fines content and type of sandy soils. However, effect of fines content and especially fines type of sandy soils on the correlation between V s and CRR is inadequately addressed in the literature. In this study, cyclic triaxial and bender element tests were conducted on samples of sand containing various amounts of different types of fines, and the effects of fines on the values of CRR and V s are investigated. The results show that G 0 and CRR reduce even when small amounts of fines are added to sand. Therefore, use of plasticity index (PI) of the fines fraction is better than the PI of the overall soil when trying to assess the effects of fines. Using obtained experimental data as well as the established semiempirical CRR–V s relationship, the CRR–V s correlation was developed for all the tested soils, and the effect of fines type on the correlation is also examined. Based on the results obtained in this study, CRR–V s correlation is affected by both the amount and the plasticity of the fines present in the sand, and this correlation is soil specific. 相似文献
15.
Clayey sand can be considered as a composite matrix of coarse and fine grains. The interaction between coarser and finer grain matrices affects the overall stress–strain behavior of these soils. Intergranular void ratio, es (which is the void ratio of the coarser grain matrix) can be utilized as an alternative parameter to express the compressive response of such soils. Oedometer tests conducted on reconstituted kaolinite–sand mixtures indicate that initial conditions, percentage of fines, and stress conditions influence the compression characteristics evidently. Tests showed that, up to a fraction of fines, which is named as transition fines content (FCt), compression behavior of the mixtures is mainly controlled by the sand grains. When concentration of fines exceeds FCt, kaolinite controls the compression. It was found that FCt varies between 19% and 34% depending on the above mentioned factors. This range of fines content is also consistent with various values reported in literature regarding the strength alteration. Performed direct shear tests revealed that there is also a close relationship between transition fines content and shear strength, which is harmonic with the oedometer test results. 相似文献
16.
Stress–strain modeling of sand–silt mixtures is important in the analysis and design of earth structures. In this paper, we develop a stress–strain model that can predict the behavior of sand–silt mixtures with any amount of fines content. This model is based on a micromechanics approach, which involves mean‐field assumptions. For the mixtures with low amount of fines, the mechanical behavior is dominated by sand grains network. On the other hand, for the mixtures with high amount of fines, the mechanical behavior is dominated by silt grains network. Using this concept of dominant grains network, the behavior of mixtures with any amount of fines can be predicted from knowing the behavior of sand and silt, alone. We also modeled the critical state friction angle, critical state void ratio, and elastic stiffness for the mixtures as a function of fines content. The applicability of this developed stress–strain model is shown by comparing the simulated and measured results for two different types of sand–silt mixtures with full range of fines content. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
17.
M.S. Guimaraes J.R. Valdes A.M. Palomino J.C. Santamarina 《International Journal of Mineral Processing》2007
The energy required to crush rocks is proportional to the amount of new surface area that is created; hence, a very important percentage of the energy consumed to produce construction aggregates is spent in producing non-commercial fines. Data gathered during visits to quarries, an extensive survey and laboratory experiments are used to explore the role of mineralogy and fracture mode in fines production during the crushing of single aggregates and aggregates within granular packs. Results show that particle-level loading conditions determine the failure mode, resulting particle shape and fines generation. Point loading (both single particles and grains in loose packings) produces clean fractures and a small percentage of fines. In choked operations, high inter-particle coordination controls particle-level loading conditions, causes micro-fractures on new aggregate faces and generates a large amount of fines. The generation of fines increases when shear is imposed during crushing. Aggregates produced in current crushing operations show the effects of multiple loading conditions and fracture modes. Results support the producers' empirical observations that the desired cubicity of aggregates is obtained at the expense of increased fines generation when standard equipment is used. 相似文献
18.
19.
细粒含量对粗粒土冻胀特性影响的试验研究 总被引：6，自引：0，他引：6
为了得到同时满足冻胀率和击实效果的最大细粒土含量,通过葡氏击实和冻胀试验,研究了不同细粒土含量、不同干密度条件下细圆砾土填料的冻胀特性。研究结果表明,9%细粒土含量下细圆砾土试样的压实效果最好;细圆砾土试样的冻结过程可以划分为快速冻结区、过渡区、似稳定区和稳定区;细粒土含量低于10%时,细圆砾土属于弱冻胀填料;同时满足冻胀率和压实效果的最大细粒土含量为9%;细粒土含量相同时,细圆砾土试样的冻胀率随干密度的增加,先增大而后减小,即存在一个最不利干密度;冻结48 h后,细圆砾土试样冻土段的含水率均大于初始含水率,其不同位置含水率分布曲线呈S型,且随着细粒土含量的增加逐渐呈现倒三角形分布;细圆砾土试样干密度的增大有效地阻断了水分迁移路径。 相似文献
20.
Granite fines are inorganic wastes produced in the elaboration of dimension stone. Because of the increasing development of that industry in NW Spain, some concerns related to their classification as type of waste and their environmental impact have been raised. We have performed a detailed physicochemical, mineralogical and geomechanical characterization of the fines and the results make up the basis of several modeling exercises addressed to give answers to particular topics: the impact of high pH waters on the environment and the mobility of some toxic metals. Based on our analyses, we conclude that granite fines do not constitute a significant hazard to the quality of natural waters. 相似文献