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1.
《岩土力学》2017,(1):33-40
针对天然强结构性湛江黏土,通过开展不同静偏应力影响下的不排水循环加载三轴试验,对循环荷载作用下的动变形、动强度和动孔隙水压力特性以及与土结构性间的内在联系进行系统性的试验研究。结果表明,结构性黏土在循环荷载作用下的突然破坏,具有脆性破坏特征,静偏应力越大,土体破坏应变越小。湛江黏土的临界动应力随静偏应力呈先增大、后减小的变化规律,在静偏应力较小时存在峰值。分析认为,静偏应力对结构性黏土动力特性的影响存在分界值,小于该值时静偏应力对土体的压密作用提高了土体的临界动应力和动强度,抑制了土的变形发展;当静偏应力继续增大,则土体结构损伤,动荷载下的临界动应力和动强度均呈下降趋势。结构性土的动孔隙水压力低于一般黏土,静偏应力的存在导致孔压在土体破坏后出现负增长,初始剪应力使结构性土体产生剪胀势。 相似文献
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黄土的冻胀特性与土体的含水率、 土体的密度以及外部荷载关系密切。在室内对不同含水率、 不同密度的黄土试样施加不同荷载, 进行了冻胀试验研究。结果表明： 黄土试样的冻胀率随着荷载增加呈指数形式递减; 冻胀率在土样含水率越大时随干密度的变化越大; 在自由冻胀状态下, 冻胀率随干密度的变化较大, 施加荷载后随干密度的变化较小。在荷载水平较高时, 冻胀率随着含水率增大而增大, 但增加幅度相较于自由冻胀显著降低。对于密度相同、 作用荷载相同的土样, 含水率增大时冻胀率线性增大。黄土地区的冻胀影响因素中, 荷载、 含水率、 干密度对冻胀影响是依次减小的。对不同含水率、 不同干密度以及不同作用荷载条件下的黄土冻胀试验结果进行拟合, 得到了可综合考虑含水率、 干密度和荷载的冻胀预报模型。 相似文献
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4.
分级循环荷载下低温冻结盐渍土动强度特性试验研究 总被引：4，自引：3，他引：1
为了探究寒区路基盐渍土在交通荷载作用下的强度破坏机理,采用室内GDS动三轴试验系统,对天然重塑盐渍土进行了不同冻结温度、围压及振动频率下一系列动荷载试验,从破坏动应力、动黏聚力和动内摩擦角方面分析各试验条件对盐渍土的影响机制。结果表明：冻结温度和围压对破坏动强度影响明显,动载频率对破坏动强度影响较弱;随着温度的降低,破坏动应力和动黏聚力明显增大,而动内摩擦角有先增大后减小趋势;随着动荷载频率的增大,破坏动应力和动黏聚力变化不明显,但内摩擦角有减小趋势;围压与破坏应力呈线性相关,温度分别与破坏动应力、动黏聚力呈良好指数关系。 相似文献
5.
循环荷载下饱和软黏土的动骨干曲线模型研究 总被引：2，自引：1，他引：1
通过饱和软黏土室内不排水动三轴试验,研究了循环周次和动应力幅值对土体动力特性的影响。结果表明,在循环荷载作用下,随着循环周次的增加,土体均存在不同程度的刚度软化现象。根据动应力幅值大小的不同,循环荷载作用下饱和软黏土的动应变发展形态可分为3种类型:稳定型、破坏型和临界型。根据动应力-应变关系曲线特点,提出了含动应力幅值、固结围压和循环周次等影响因素的动骨干曲线模型。该模型所得的拟合值与试验值比较吻合。与传统骨干曲线模型相比,该模型能够体现土体在循环荷载作用下的刚度软化特性,更加切合实际。 相似文献
6.
岩溶区老黏土在人类工程活动所引起的动荷载作用下,会产生动力变形特性的改变,强度参数也会发生相应的弱化,最终导致土洞上覆盖层结构性的破坏。以武汉市鹏湖湾地区的老黏土为研究对象,结合该岩溶塌陷场地的工程地质条件,开展相应的室内动三轴试验,研究老黏土在围压、动应力比和循环次数等因素变化时的动力响应特性和强度弱化规律,提出其在循环荷载作用下的强度弱化模型。结果表明,随着围压、动应力比及循环次数的增加,老黏土的孔隙水压力有所提高。当其它因素保持不变,且动应力比与循环次数不超过某一临界值时,土体的强度随着动应力比、循环次数的增加而降低,即超孔压的增长引起老黏土强度的衰减。而在围压增长的初期,土体的强度与围压成正比,当围压增大到某一临界值时,老黏土的抗剪强度显著降低。强度折减率随围压、动应力比、循环次数的增加均有不同程度的降低,提取出经验公式,得到的老黏土强度弱化模型具有较高的相关性,进一步得出老黏土的强度弱化机理。 相似文献
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水平液化场地地表往返位移的求解是基础和地下工程抗震设计的迫切需求。利用双层模型模拟实际水平场地,提出了可考虑液化层存在下的土表位移简化计算方法并给出频域理论解答,同时采用逐循环累计方法给出水平场地任意荷载下土表位移时域解答。采用适于水平场地孔压增量模型,并逐循环修正土层模量,模拟液化引起的土层的非线性过程。振动台试验结果和提出棋型的计算结果吻合,验证了所提方法能够反映土体液化对土表位移影响的基本过程。提出的方法和解答物理意义明确,可代表土体液化对土表位移影响的基本形态,并可用于频域及时域的无量纲分析。 相似文献
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为研究地震作用下饱和砂土液化判别及地震放大效应的影响因素,采用边界面塑性模型框架内开发的砂土本构模型,基于开源有限元平台OpenSees建立了一维剪切梁土柱模型。以循环应力比CSR和循环抗力比CRR为控制指标,对比了不同液化判别方法的差异,分析了地震荷载类型和砂土相对密度对液化判别和放大效应的影响。研究表明:与数值模拟结果相比,Seed简化法计算的CSR更大,判断饱和砂土场地发生液化的可能性更高;冲击型地震波较振动型地震波更容易使饱和砂土场地发生液化,砂土相对密度越小场地越容易发生液化;放大系数随埋深的减小而增大,振动型地震波引起的放大效应整体大于冲击型,埋深较大时放大系数随砂土相对密度的增大而减小。 相似文献
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以兰新铁路地基中的膨胀泥岩为试验材料,开展不同上覆荷载、不同干密度、不同初始含水率下的重塑土吸水变形试验。试验结果表明:当干密度和上覆荷载一定时,胀限膨胀率随初始含水率的增大而减小;当干密度和初始含水率一定时,胀限膨胀率随上覆荷载的增大而减小。上覆荷载的增大使得土颗粒间传递的平均法向应力增大,进而加大了土体的有效应力,土粒间应力的增大抑制了水分子与土体内黏土矿物的结合,削弱了结合水膜的厚度,从而使胀限膨胀率减小。通过对试验数据结果的分析,建立了初始含水率,干密度,上覆荷载耦合作用下的胀限膨胀率函数关系式。经过同等试验条件验证,试验得到膨胀率公式具有较好的可靠性。 相似文献
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城市污泥固化土用作路基填料,对于节约工程成本、保护环境等具有重要意义。本文以城市污泥固化土为研究对象,利用DDS动三轴仪,从干湿循环次数、初始静偏应力、动应力3个方面研究其对累积塑性应变及动强度特性的影响。试验结果表明:在干湿循环单独作用下,土体累积塑性应变随干湿循环次数的增加先增大后趋于稳定,但与初始静偏应力耦合作用下对土体累积塑性应变的影响不太显著。动应力对其影响较大,且存在临界值:当动应力小于临界值时,累积塑性应变呈现出先增大后逐渐稳定的趋势; 当动应力大于临界值时,累积塑性应变在达到某一振次后快速增大,土体迅速产生变形破坏。干湿循环与初始静偏应力都会降低土体的动强度,但干湿循环在达到10次后,动强度将趋于平稳,不再受其影响。通过回归分析,建立了考虑干湿循环次数、初始静偏应力及动应力等因素影响的城市污泥固化土稳定型累积塑性应变模型,并验证了其可行性。 相似文献
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Hanifi Missoum Mostefa Belkhatir Karim Bendani Mustapha Maliki 《Geotechnical and Geological Engineering》2013,31(1):279-296
In a number of recent case studies, the liquefaction of silty sands has been reported. To investigate the undrained shear and deformation behaviour of Chlef sand–silt mixtures, a series of monotonic and stress-controlled cyclic triaxial tests were conducted on sand encountered at the site. The aim of this laboratory investigation is to study the influence of silt contents, expressed by means of the equivalent void ratio on undrained residual shear strength of loose, medium dense and dense sand–silt mixtures under monotonic loading and liquefaction potential under cyclic loading. After an earthquake event, the prediction of the post-liquefaction strength is becoming a challenging task in order to ensure the stability of different types of earth structures. Thus, the choice of the appropriate undrained residual shear strength of silty sandy soils that are prone to liquefaction to be used in engineering practice design should be established. To achieve this, a series of undrained triaxial tests were conducted on reconstituted saturated silty sand samples with different fines contents ranging from 0 to 40 %. In all tests, the confining pressure was held constant at 100 kPa. From the experimental results obtained, it is clear that the global void ratio cannot be used as a state parameter and may not characterize the actual behaviour of the soil as well. The equivalent void ratio expressing the fine particles participation in soil strength is then introduced. A linear relationship between the undrained shear residual shear strength and the equivalent void ratio has been obtained for the studied range of the fines contents. Cyclic test results confirm that the increase in the equivalent void ratio and the fines content accelerates the liquefaction phenomenon for the studied stress ratio and the liquefaction resistance decreases with the increase in either the equivalent void ratio or the loading amplitude level. These cyclic tests results confirm the obtained monotonic tests results. 相似文献
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轨道交通振动下南京片状细砂的有效应力路径及破坏模式 总被引：2，自引：1，他引：1
以南京片状结构细砂为研究对象,采用英国WFI动静多功能三轴仪,研究了饱和南京片状结构细砂在列车振动荷载作用下静偏应力水平、循环应力比对其动力特性的影响;把振动孔压的发展与应力路径相联系,分析了循环荷载作用下不同阶段南京片状结构细砂所处的初始压密状态、压缩状态和膨胀状态的发生和发展过程;同时,根据静偏应力与循环偏应力的大小,视有无偏应力反向,南京片状结构细砂的破坏模式可分为循环活动性和塑性应变累积破坏,并对其循环活动性的机制进行了初步探讨。 相似文献
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饱和层状砂土液化特性的动三轴试验研究 总被引：2，自引：0，他引：2
利用GDS动三轴试验系统采用等幅循环应变加载方式对含有不同厚度粉土的饱和层状砂土进行了液化强度试验。分析了均匀砂和含有不同粉粒层厚度的层状砂土在循环荷载作用下的变形和力学特性。试验分析表明：由于含粉粒夹层的层状土特殊的土体结构,其孔隙水压力发展规律与一般的无黏性砂土不同;饱和层状砂土的抗液化强度并不是随着粉粒层厚度的增加而单调增加的,而是存在一个临界点;液化临界剪应变的大小与液化判别标准和循环次数有很大关系。试验结果表明,粉粒夹层对层状砂土的液化特性有很大的影响,且更能模拟自然环境条件下的层状砂土地基液化特性。 相似文献
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Wen-Jong Chang Sheng-Huoo Ni An-Bin Huang Yan-Hong Huang Yu-Zhang Yang 《Engineering Geology》2011,(3):235
Geotechnical reconnaissance of a recurrent liquefaction site at a Quaternary alluvial deposit in southern Taiwan was conducted to establish a comprehensive case history for liquefaction on silty fine sand with high fines content. The liquefaction occurred at a silty fine sand layer with D50 = 0.09 mm and fines content greater than 35% and was triggered by a Mw = 6.4 earthquake on March 4, 2010, which induced maximum horizontal acceleration up to 0.189 g at the site. In situ subsurface characterizations, including standard penetration test, cone penetration test, and shear wave velocity measurement, were performed as well as cyclic simple shear tests on undisturbed specimens retrieved by a modified hydraulic piston sampler. Comparisons of cyclic resistance ratios (CRRs) indicate that CPT sounding with standard penetration rate could overestimate the resistance ratio and drainage conditions during penetration should be considered for high fines content soil in the liquefaction analysis. Additionally, variations of CRRs from different in situ tests indicate that correlations among in situ tests and CRR could be soil specific and precautions should be taken when using these curves on silty fine sands. 相似文献
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液化型路堤边坡动力稳定性问题涉及岩土工程与工程地震两个学科领域,是边坡工程与砂土液化的交叉课题。采用天然地震记录为输入条件,应用Finn本构关系模型,运用有限差分法,对填土+砂土+卵砾土地层组合的路堤边坡进行了全时程动力分析,探讨了地震作用下路堤边坡的液化初步规律和稳定性。数值模拟结果表明:地震作用引起了路基饱和砂土有效应力急剧减小,并导致路基砂土液化,引起路堤变形破坏。孔隙水压力的积累与消散不仅与地震记录序列存在对应关系,也与砂土所处的位置和深度有密切关系。地表变形破坏主要表现为路堤顶面发生震陷和拉裂破坏,坡底面产生挤压隆起变形。地面以下的变形破坏主要包括土体剪切破坏和深部砂土液化引起的侧向流动破坏。 相似文献
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饱和粉土振动液化分析 总被引：9，自引：0，他引：9
液化是造成场地地震破坏的首要原因之一。自Casagrande的经典工作以来,对地震液化的研究已经取得了很大的进展。然而这些研究大多是针对于砂土而进行的,对于粉土液化研究的相对较少,且粉土的液化特性也有别于砂土。因此,在已有研究的基础之上利用粉土液化试验得出的结果,分析了粉土液化的机理、影响因素以及在振动过程中粉土中孔隙水压力的增长规律,认为粉土中的粘粒含量、密实度以及土的结构性对其抗液化能力有较大的影响。考虑到试验中振动次数的离散性,引入了时间参数的概念,根据动三轴试验结果提出了孔隙水压力增长的经验公式,可以比较方便地应用于计算液化的有限元程序中去。 相似文献
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以京津高铁和杭州地铁沿线的两种典型粉质黏土为研究对象,并采用英国GDS多功能三轴仪完成了静、动力强度测试,研究了两种土的静力不排水抗剪强度和在交通荷载高振次循环下的动强度、临界动应力比、应变发展模式以及振后抗剪强度等方面的差异。对比发现,长期循环荷载作用下两种土的应变发展和振后强度均有很大不同。与京津地区粉质黏土相比,杭州地铁沿线土含水率高、孔隙比大、密度低、灵敏度高、强度低。两种原状土在小幅振动后土体强度略有增大,而随振幅增大,振后强度将低于未经历振动时的不排水强度值;而重塑土振后强度均低于静剪强度。 相似文献
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循环加载方式与应力路径对砂土的抗液化强度有很大的影响。利用GDS空心圆柱扭剪仪对南海珊瑚砂进行了一系列复杂加载条件下均等固结不排水循环试验,探讨了90°突变应力路径下主应力方向角对珊瑚砂抗液化强度的影响。试验结果发现：以循环应力比（CSR）作为应力水平指标,当不控制中主应力系数b的变化时,主应力方向角 对珊瑚砂的抗液化强度并无显著影响;当控制b始终保持0.5时,珊瑚砂的抗液化强度随着 的增加呈现出先减小后增大的趋势,且在 45°时的抗液化强度最低。基于分析循环荷载引起的土单元大、小循环主应力 、 变化,定义了单元体循环应力比（USR）作为一个新的物理指标,发现不同循环加载方式与应力路径条件下施加于珊瑚砂试样的USR与引起液化所需的循环次数NL存在事实上的唯一性关系。通过引自文献的4种无黏性土原始试验数据的再处理,独立地验证了以USR表征砂类土液化强度的适用性。 相似文献
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For numerical studies of geotechnical structures under earthquake loading, aiming to examine a possible failure due to liquefaction, using a sophisticated constitutive model for the soil is indispensable. Such a model must adequately describe the material response to a cyclic loading under constant volume (undrained) conditions, amongst others the relaxation of effective stress (pore pressure accumulation) or the effective stress loops repeatedly passed through after a sufficiently large number of cycles (cyclic mobility, stress attractors). The soil behaviour under undrained cyclic loading is manifold, depending on the initial conditions (e.g. density, fabric, effective mean pressure, stress ratio) and the load characteristics (e.g. amplitude of the cycles, application of stress or strain cycles). In order to develop, calibrate and verify a constitutive model with focus to undrained cyclic loading, the data from high-quality laboratory tests comprising a variety of initial conditions and load characteristics are necessary. The purpose of these two companion papers was to provide such database collected for a fine sand. The database consists of numerous undrained cyclic triaxial tests with stress or strain cycles applied to samples consolidated isotropically or anisotropically. Monotonic triaxial tests with drained or undrained conditions have also been performed. Furthermore, drained triaxial, oedometric or isotropic compression tests with several un- and reloading cycles are presented. Part I concentrates on the triaxial tests with monotonic loading or stress cycles. All test data presented herein will be available from the homepage of the first author. As an example of the examination of an existing constitutive model, the experimental data are compared to element test simulations using hypoplasticity with intergranular strain. 相似文献
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For numerical studies of geotechnical structures under earthquake loading, aiming to examine a possible failure due to liquefaction, using a sophisticated constitutive model for the soil is indispensable. Such model must adequately describe the material response to a cyclic loading under constant volume (undrained) conditions, amongst others the relaxation of effective stress (pore pressure accumulation) or the effective stress loops repeatedly passed through after a sufficiently large number of cycles (cyclic mobility, stress attractors). The soil behaviour under undrained cyclic loading is manifold, depending on the initial conditions (e.g. density, fabric, effective mean pressure, stress ratio) and the load characteristics (e.g. amplitude of the cycles, application of stress or strain cycles). In order to develop, calibrate and verify a constitutive model with focus to undrained cyclic loading, the data from high-quality laboratory tests comprising a variety of initial conditions and load characteristics are necessary. It is the purpose of these two companion papers to provide such database collected for a fine sand. Part II concentrates on the undrained triaxial tests with strain cycles, where a large range of strain amplitudes has been studied. Furthermore, oedometric and isotropic compression tests as well as drained triaxial tests with un- and reloading cycles are discussed. A combined monotonic and cyclic loading has been also studied in undrained triaxial tests. All test data presented herein will be available from the homepage of the first author. As an example of the examination of an existing constitutive model, the experimental data are compared to element test simulations using hypoplasticity with intergranular strain. 相似文献