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不同胶结宽度粒间胶结特性试验研究 总被引：2，自引：0，他引：2
胶结砂土中水泥含量、能源土中水合物的含量会导致其宏观力学特性的差异,从微观层面可以解释为颗粒之间胶结物含量的不同所导致的粒间力学性质的差异所致。为研究不同胶结物含量的胶结颗粒的力学特性,进行了不同胶结宽度的粒间胶结试验,试验结果表明：（1）峰值压缩荷载随胶结宽度的减小呈非线性变化,宽高比对峰值荷载有明显影响;（2）峰值拉伸荷载随胶结宽度减小而线性减小,宽高比对其影响不大;（3）峰值剪切荷载和峰值扭矩由两部分组成,即胶结部分和摩擦部分。且其变化趋势相似,随着法向荷载的增大,峰值荷载先随之增大,在达到临界应力比后,峰值荷载开始减小,当应力比达到1,即胶结破坏时,胶结部分不再发挥作用,此时粒间荷载由摩擦部分提供;（4）在压-剪-扭试验中,不同初始偏心距情况下得到的峰值荷载在剪力-扭矩平面内呈椭圆状。 相似文献
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土体粒间胶结是建立天然结构性土本构模型的决定性因素之一,将胶结颗粒理想化为两铝棒,在指定位置处形成胶结。采用水泥作为胶结材料,对胶结颗粒进行了一系列简单加载试验（包括拉伸、压缩、压剪、压扭）和复杂应力路径试验,并与蒋明镜等所做的环氧树脂胶结试验进行对比。结果表明：胶结材料对胶结颗粒的力学性能存在一定影响,但基本规律符合蒋明镜等所提出的理想颗粒间胶结模型。水泥胶结抗拉强度低于环氧树脂胶结抗拉强度,但延性相对较好,抗压特性均呈塑性软化现象;二者的抗剪强度初始均随法向压力的增加而增大,当法向压力超过一定值时,又随法向压力的增加而减小（该压力称为界限法向压力）,但水泥胶结的界限法向压力明显高于环氧树脂胶结,扭转试验规律与剪切试验规律类似。在三维应力空间中（法向压力-扭矩-剪力）水泥胶结的强度包线呈橄榄球状,环氧树脂胶结强度包线呈水滴状。 相似文献
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胶结颗粒接触力学特性测试装置研制 总被引：5，自引：2，他引：3
为验证天然结构性砂土离散元模拟中接触模型及其参数的合理性,设计了一套用于理想胶结颗粒成型及实现不同加载条件下接触力学特性测试装置。通过胶结颗粒成型装置在两大小相同的铝棒间形成具有特定几何尺寸的胶结物,随后,采用一系列辅助加载装置实现简单及复杂加载条件下胶结颗粒接触力学特性的测试。试验结果表明：该装置可用于胶结颗粒在不同加载条件下接触力学特性的测试,实测胶结颗粒接触力学响应与天然砂土离散元中接触模型基本相符,且其抗剪和抗扭强度均随着法向压力的增大而增大,在三维应力空间中胶结颗粒强度包线呈椭圆抛物面状。 相似文献
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基于微观胶结厚度模型的深海能源土宏观力学特性离散元分析 总被引：1，自引：0，他引：1
首先,引入蒋明镜等提出的考虑水合物胶结厚度的深海能源土粒间微观胶结模型,用以反映能源土颗粒之间水合物微观胶结接触力学特性;其次,采用C++语言将模型程序化,并将其引入离散单元法中;然后,对选定的水合物饱和度经过实际二维离散元模拟调算,得出相应的水合物胶结尺寸,以修正水合物临界胶结厚度、最小胶结厚度及胶结宽度,进而确定水合物微观胶结参数;最后,根据所确定的胶结参数,针对不同水合物饱和度试样进行能源土宏观力学特性离散元双轴试验模拟,并从应力-应变、体变、剪胀角等方面与Masui等所进行的能源土室内三轴试验进行对比分析。结果表明：采用考虑粒间胶结厚度的水合物微观胶结模型,能够定性反映深海能源土的宏观力学特性,能源土试样的峰值强度、黏聚力和剪胀角均随水合物饱和度的增加而增加,但水合物饱和度对内摩擦角的影响规律不明朗;能源土试样的峰值强度、残余强度及体积剪缩量随着有效围压的增大而增大;剪胀角随有效围压的增大而减小。 相似文献
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为实现结构性砂土离散元接触模型合理性的三维试验验证,设计了一套可用于三维半球形理想胶结颗粒成型及实现不同加载条件下的接触力学特性测试装置,制备了一定胶结尺寸的环氧树脂半球形颗粒胶结试样,在一系列辅助加载装置中初步开展了不同加载条件（拉伸、压缩、剪切、弯转、扭转）下的力学性能测试。结果表明,该装置可用于实现三维情况下胶结颗粒接触力学特性测试;不同加载条件下的实测试验结果与二维试验成果基本一致;峰值剪切、弯矩、扭矩随着法向荷载的增大呈现先增大后减小的趋势,存在一个相同的临界法向荷载。 相似文献
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利用二维颗粒流程序生成5种不同粗糙程度的节理模型,并对5种节理模型进行了5种不同法向恒定荷载作用下的直剪试验,从细观角度分析了不同粗糙程度的节理模型在法向荷载下的形貌损伤情况和裂纹演化机制。与此同时,分析了节理JRC值和节理面颗粒摩擦系数对节理抗剪强度影响,并反推出了节理面抗剪强度参数Cj与?j与JRC值的关系。结果为：法向恒定荷载越大时,节理峰值抗剪应力越大,剪胀现象越小,节理形貌损伤范围越大。随着剪切的进行,上下节理面接触范围减小,微裂纹开始主要沿节理面产生,随着剪切位移的继续增加微裂纹数量显著增加,并且不局限于节理面附近而深入到模型内部。随着节理粗糙程度（JRC值）和节理面颗粒摩擦系数的增加节理峰值抗剪应力也增大。节理抗剪强度参数Cj与?j随着JRC值的增大而增大。所得结果可以为室内试验和工程应用提供参考和依据。 相似文献
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工程开挖扰动、卸荷和水力破岩产生的工程裂缝与先存裂隙的相互作用在岩石工程中十分普遍,建立适用于工程裂缝遇先存裂隙的扩展准则是解释工程裂缝扩展机制和研究岩体弱面剪切滑移的关键。采用两种不同强度的混凝土充填材料模拟强、弱胶结的先存裂隙,在只考虑准静态张拉应力作用下,依据半圆三点弯法测定了充填胶结型岩石的Ⅰ型静态断裂韧度;通过分析工程裂缝扩展轨迹,获得了临界启裂角与应力逼近角的关系;进一步探讨了工程裂缝与先存裂隙的相互作用扩展模式与判别准则。结果表明：张拉应力作用下工程裂缝与先存裂隙的相互作用受应力逼近角、启裂逼近距离和充填物胶结强度的共同影响;充填胶结砂岩的静态断裂韧度随应力逼近角增大先增大后减小;启裂逼近距离较大时,断裂韧度随应力逼近角变化不大,而启裂逼近距离较小时,断裂韧度随应力逼近角增大呈现先增大后减小的规律;应力逼近角影响充填胶结岩石的断裂韧度,但影响程度不如启裂逼近距离和充填物胶结强度,且存在一个极限影响距离。即使在张拉应力作用下,岩石材料的裂隙前端同样存在剪切局部化,因此,工程裂缝是否穿过先存裂隙取决于应力逼近角、启裂逼近距离和充填物胶结强度共同作用下裂隙面的抗剪强度和先存裂隙... 相似文献
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人工胶结砂土力学特性的离散元模拟 总被引：1，自引：1，他引：0
采用离散单元法（DEM）对胶结砂土力学特性进行模拟。将基于室内试验测得的理想胶结颗粒接触力学响应引入到开发的二维离散元程序（NS2D）中,模拟胶结砂土颗粒间的胶结作用。对不同胶结强度和围压的胶结砂土进行平面应变双轴压缩试验模拟,并将模拟结果与Wang和Leung[1]提供的人工胶结砂土的试验结果进行比较。最后对数值模拟中胶结试样的微观力学响应（接触力链、胶结点破坏率和位移场）进行分析。结果表明,离散元数值模拟能够有效地反映胶结砂土的主要力学特性,相比同一初始孔隙比的无胶结松散砂土,胶结砂土将具有更高的强度,应力-应变关系呈应变软化,体变为先剪缩后剪胀,且两者的差异随胶结强度的增大和围压的减小而越趋显著。此外,胶结砂土宏观力学响应（应力-应变关系和剪胀性）与其微观力学响应密切相关。 相似文献
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开展岩石模型结构面抗剪强度特征的多尺度（尤其大尺寸）直剪试验研究对于理解岩石结构面力学特性具有重要的理论价值和实践意义。首先,基于多尺度直剪试验仪(MSJ-DST),对20 cm×20 cm、40 cm×40 cm、60 cm×60 cm、80 cm×80 cm和100 cm×100 cm的岩石模型结构面试样采用法向应力分别为200～1 000 kPa进行直接剪切试验;然后,研究不同尺寸岩石模型结构面抗剪强度的特征。结果表明：不同法向荷载作用下模型的受力变形特点相近,峰值剪切位移总体上随着某一数值附近上下浮动;在同一法向应力作用下,不同尺寸结构面试样的峰值抗剪强度表现出在某一数值附近上下浮动的特征,残余抗剪强度则表现出随尺寸的增加有小幅度增加;5级法向应力作用下,不同尺寸的峰值抗剪强度和残余抗剪强度随着法向应力的变化规律均近似相同,抗剪强度残余值与峰值的比值随着法向应力的增大逐渐增大并趋于稳定。 相似文献
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A bond failure criterion for DEM simulations of cemented geomaterials considering variable bond thickness 总被引：1，自引：0，他引：1
A series of micromechanical tests were conducted to investigate the bond failure criterion of bonded granules considering the effect of bond thickness, with the aim of enhancing the bond contact model used in the distinct element simulations of cemented geomaterials. The granules were idealized in a two‐dimensional context as one pair of aluminum rods bonded by resin epoxy or cement. The mechanical responses of nearly 500 rod pairs were tested under different loading paths to attain the yield loads of bonded granules at variable bond thickness. This study leads to a generic bond failure criterion incorporating the effect of the bond thickness. The results show that the bond compressive resistance largely decreases with increasing bond thickness owing to the presence of the confinement at the bond‐particle interface. The strength envelopes obtained from the combined shear compression tests and combined torsion compression tests have identical functional form, and they decrease in size with increasing bond thickness but remain unchanged in shape. Given the same cementation material, the generic bond strength envelope in a three‐dimensional contact force space under different loading paths remains the same in shape but shrinks with the increase of bond thickness. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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The cohesive‐frictional nature of cementitious geomaterials raises great interest in the discrete element method (DEM) simulation of their mechanical behavior, where a proper bond failure criterion is usually required. In this paper, the failure of bond material between two spheres was investigated numerically using DEM that can easily reproduce the failure process of brittle material. In the DEM simulations, a bonded‐grain system (composed of two particles and bond material in between) was discretized as a cylindrical assembly of very fine particles connecting two large end spheres. Then, the bonded‐grain system was subjected to compression/tension, shear, rolling and torsion loadings and their combinations until overall failure (peak state) was reached. Bonded‐grain systems with various sizes were employed to investigate bond geometry effects. The numerical results show that the compression strength is highly affected by bond geometry, with the tensile strength being dependent to a lesser degree. The shear, rolling and torsion strengths are all normal force dependent; i.e., with an increase in the normal force, these strengths first increase at a declining rate and then start to decrease upon the normal force exceeding a critical value. The combined actions of shear force, rolling moment and torque lead to a spherical failure envelope in a normalized loading space. The fitted bond geometry factors and bond failure envelopes obtained numerically in this three‐dimensional study are qualitatively consistent with those in previous two‐dimensional experiments. The obtained bond failure criterion can be incorporated into a future bond contact model. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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A discrete element modelling of bonded granulates and investigation on the bond effect on their behaviour are very important to geomechanics. This paper presents a two‐dimensional (2‐D) discrete element theory for bonded granulates with bond rolling resistance and provides a numerical investigation into the effect of bond rolling resistance on the yielding of bonded granulates. The model consists of mechanical contact models and equations governing the motion of bonded particles. The key point of the theory is that the assumption in the original bond contact model previously proposed by the authors (55th CSCE‐ASCE Conference, Hamilton, Ont., Canada, 2002; 313–320; J. Eng. Mech. (ASCE) 2005; 131 (11):1209–1213) that bonded particles are in contact at discrete points, is here replaced by a more reliable assumption that bonded particles are in contact over a width. By making the idealization that the bond contact width is continuously distributed with the normal/tangential basic elements (BE) (each BE is composed of spring, dashpot, bond, slider or divider), we establish a bond rolling contact model together with bond normal/tangential contact models, and also relate the governing equations to local equilibrium. Only one physical parameter β needs to be introduced in the theory in comparison to the original bond discrete element model. The model has been implemented into a 2‐D distinct element method code, NS2D. Using the NS2D, a total of 86 1‐D, constant stress ratio, and biaxial compressions tests have been carried out on the bonded granular samples of different densities, bonding strengths and rolling resistances. The numerical results show that: (i) the new theory predicts a larger internal friction angle, a larger yielding stress, more brittle behaviour and larger final broken contact ratio than the original bond model; (ii) the yielding stress increases nonlinearly with the increasing value of β, and (iii) the first‐yield curve (initiation of bond breakage), which define a zone of none bond breakage and which shape and size are affected by the material density, is amplified by the bond rolling resistance in analogous to that predicted by the original bond model. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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A simple three‐dimensional distinct element modeling of the mechanical behavior of bonded sands 
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下载免费PDF全文 This paper presents a simple three‐dimensional (3D) Distinct Element Method (DEM) for numerical simulation of the mechanical behavior of bonded sands. First, a series of micro‐mechanical tests on a pair of aluminum rods glued together by cement with different bond sizes were performed to obtain the contact mechanical responses of ideally bonded granular material. Second, a 3D bond contact model, which takes into account the influences of bond sizes, was established by extending the obtained 2D experimental results to 3D case. Then, a DEM incorporating the new contact model was employed to perform a set of drained triaxial compression tests on the DEM bonded specimens with different cement contents under different confining pressures. Finally, the mechanical behavior of the bonded specimens was compared with the available experimental results. The results show that the DEM incorporating the simple 3D bond contact model is able to capture the main mechanical behavior of bonded sands. The bonded specimen with higher cement content under lower confining pressure exhibits more pronounced strain softening and shear dilatancy. The peak and residual strengths, the apparent cohesion and peak/residual friction angles, and the position and slope of the critical state line increase with increase in cement content. Microscopically, bond breakage starts when the system starts to dilate and the maximum rate of bond breakage coincides with the maximum rate of dilation. Bond breakage is primarily due to tension‐shear failure and the percentage of such failures is independent of both confining pressure and cement content. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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天然气水合物被公认是解决当前能源危机的潜在新型能源而备受关注。含水合物的海底土体称为深海能源土。水合物在能源土中有不同的赋存形式（如填充型水合物和胶结型水合物等）,由于胶结型水合物对整体强度的贡献比其他存在形式更大,尤其是饱和度较低的情况。针对于胶结型水合物的赋存形式进行研究,水合物作为胶结物质存在于土颗粒之间,胶结厚度会在一定范围内变化。为真实地反映此现象,通过对能源土试样的电镜扫描图片整理分析,获得水合物饱和度与粒间胶结厚度的函数关系。基于前期已经完成的不同粒间胶结厚度下胶结力学特性的试验研究成果,为探究胶结厚度变化对能源土体宏观力学特性的影响,建立了考虑水合物胶结厚度的能源土粒间胶结模型,并介绍此模型中相关胶结参数及其确定方法。 相似文献