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为深入理解井水位同震响应机理,本文开展了向完整井-松散含水层系统输入由不同频率和振幅（加速度）组成的正弦波荷载的振动台实验。以实验模型为物理模型,建立了振动作用下松散承压含水层中孔隙水压力响应的流固耦合模型和含水层水流与井流的相互作用模型,并运用多物理场耦合模拟软件COMSOL Multiphysics对实验过程进行了数值模拟。实验中观测到的四种典型水位变化形态与野外场地同震井水位变化形态相似。数值模拟结果显示,本研究建立的数学模型能较好地反映松散承压含水层中孔隙水压力和水位的响应情况。本文研究对解释地下水同震响应机制、岩体渗流稳定性和安全问题具有重要意义。 相似文献
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To understand the post-liquefaction behavior of liquefied ground, it is important to get a better understanding and a more suitable characterization of the variation of excess pore pressure after liquefaction. In this paper, the soil permeability is considered as one of the key soil parameters for clarifying the mechanism of post-liquefaction behavior of liquefied ground. For this reason, a series of shaking table tests were conducted for a Toyoura sand deposit with different soil permeability values. Polymer fluid was used in model tests to vary the permeability of sand deposits. Excess pore pressures and settlements were measured in each test. A basic mechanism in post-liquefaction behavior and the solidification phenomenon after liquefaction were discussed based on these test results. Also, a new method for predicting the dissipation of excess pore pressure was developed. This study provides evidence of the important effect of soil permeability on the velocity with which the solidification front moves upward in liquefied ground. It is suggested that the value of coefficient of permeability of liquefied sand can increase to about 4.0 times the initial value. This variation of permeability after liquefaction should be taken into account in post-liquefaction analysis. 相似文献
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地震作用下,饱和砂土地层地铁车站的动力反应特征是城市轨道工程抗震的关键问题。以太原地铁新近沉积粉细砂地层地铁工程为对象,通过模拟地震运动输入的饱和砂土地基地下结构的振动台模型试验,分析了不同峰值加速度地震作用下饱和砂土与地下结构相互作用的动力反应性状。研究了地震波作用的放大效应与频率特征,动孔压比增长发展过程和液化区域分布,以及动土压力的变化规律。表明加速度放大系数为1.5~2.0;0.1~0.25g峰值加速度地震作用下饱和砂土均产生动孔隙水压力累计发展;0.3g峰值加速度地震作用下饱和砂土产生液化,抑制了土与地下结构的振动放大效应,地表面大量冒水,结构模型出现了明显上浮,地下结构两侧产生震陷。 相似文献
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黄河三角洲粉土液化的试验研究 总被引：2，自引：0，他引：2
在野外自然地理和地质调查的基础上，以黄河地区可液化场地粉土为研究对象，利用室内动三轴和振动柱试验进行测定，分析了动荷载作用下粉土的动应力应变关系并模拟了地震荷载作用下粉土的孔压响应及抗液化强度，得出了液化破坏标准，提出了原状粉土的振动孔压上升模型。对试验结果进行分析发现，随着粘粒含量的增加，粉砂、粉土、粉质粘土、粘土达到相同剪应变所需的动剪应力也依次增加；粉土孔压比0．68、粉砂土孔压比0．87作为液化破坏开始的标志；粉土发生液化所需的循环应力比大于砂土。这些研究为以后建立适合本地区的饱和地基土地震破坏判别方法提供了参数和依据。 相似文献
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Evolution of the shear wave velocity during shaking modeled in centrifuge shaking table tests 总被引：2，自引：1，他引：1
Chung-Jung Lee Chung-Ru Wang Yui-Chen Wei Wen-Yi Hung 《Bulletin of Earthquake Engineering》2012,10(2):401-420
Two in-flight shear wave velocity measurement systems were developed to perform the subsurface exploration of shear wave velocity
in a centrifuge model. The bender elements test and the pre-shaking test used in the study provided reliable and consistent
shear wave velocity profiles along the model depth before and after shaking in the centrifuge shaking table tests. In addition,
the use of the bender elements measurement system particularly developed here allowed continuous examination of the evolution
of shear wave velocity not only during and after the shaking periods in the small shaking events but also during the dissipation
period of excess pore water pressure after liquefaction in the large shaking events. The test results showed that the shear
wave velocity at different values of excess pore water pressure ratio varied as the effective mean stress to the power of
0.27, to a first approximation. Consequently, a relationship between the shear wave velocity evolution ratio and the excess
pore water pressure ratio is proposed to evaluate the changes in shear wave velocity due to excess pore water generation and
dissipation during shaking events. This relation will assist engineers in determining the shear stiffness reduction ratio
at various ru levels when a sand deposit is subjected to different levels of earthquake shaking. 相似文献
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In this study, cyclic hollow cylinder torsional tests were conducted on the reconstituted specimens of Toyoura sand in a practical range of initial density and stress states. The results were employed to evaluate the liquefaction resistance and residual pore water pressure of sand using the strain energy concept. A simple pore water pressure (PWP) model with two calibration parameters was developed for the prediction of residual pore pressure as a function of cumulative strain energy density and the capacity energy of sand. Capacity energy is defined as the cumulative strain energy that is required for liquefaction onset. Based on the results of the tests, an equation is then presented for the estimation of capacity energy in terms of relative density and initial effective confining pressure of sand. This equation is shown to work well as a state boundary curve, which can discriminate between the liquefied and non-liquefied field case histories. Several extra tests were also performed to investigate the effect of initial static shear stress on the proposed PWP model and capacity energy. The results show that initial shear stress has a minor effect on the trend of the proposed PWP model; however, it definitely affects the capacity energy. The final part of the paper aims to confirm reasonable performance of the proposed PWP model by the available observations of seismically induced pore water pressure in shaking table, centrifuge, and real site conditions. 相似文献
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将废弃橡胶轮胎内填充散体材料形成加筋土结构,已被应用于地基、挡土墙和边坡加固等工程,表现出较好的减震隔振效果,而轮胎加筋土的抗液化性能尚缺乏研究。开展3组小型振动台试验,通过改变轮胎垫层的排水条件,验证轮胎加筋砂垫层的抗液化效果。结果表明:轮胎加筋砂垫层具有良好的抗液化效果,与刚性垫层相比,超静孔压比峰值差值范围在0.01~0.19,残余超静孔压比差值范围在0.08~0.16,轮胎加筋砂垫层提供的排水通道具有抑制超静孔隙水压力发展和加速超静孔隙水消散的作用,孔隙水会沿着轮胎与下部土体的界面以及胎间的排水通道排出;采用量测侧向动土压力的方法,定义土体液化程度量化指标,进一步验证轮胎加筋砂垫层抗液化效果;振动过程中轮胎加筋垫层表面沉降范围为11.3~15.7 mm,表现出较好的变形协调性能。 相似文献
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为了研究在轨道交通荷载作用下桩板结构主动隔振措施的隔振效果,通过无限元边界与有限元边界相结合的有限元分析方法在路基中建立桩板结构模型,并在沙土地基中设置混凝土桩板结构进行模型试验,通过模型试验对有限元数值模拟结果加以验证,将桩长、埋深及置换率3个因素考虑在内,研究其对隔振效果的影响。结果表明:模型试验验证有限元计算方法的可靠性;随桩长增加振幅降低比减小,隔振效果明显,随着振源距离增加其振幅降低比减小明显;埋深为桩板结构主动隔振措施中的主要影响因素,随着埋深增加振幅降低比明显减小,隔振效果越明显;有限元计算过程中置换率对隔振效果的影响不明显,但是在模型试验中置换率对隔振效果影响较显著。 相似文献
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在混凝土空心砌块的空腔中填入橡胶砂形成的组合砌块（RSMCB）可作为简易隔震层应用于村镇建筑防震减灾。建立RSMCB的三维数值分析模型,进行循环剪切试验以及隔震分析,研究不同橡胶砂配比、竖向压应力、盖板尺寸和盖板埋深对隔震砌块动刚度和阻尼比的影响,分析不同的上部配重、输入地震波、橡胶砂配比、盖板尺寸和铺设方式对RSMCB垫层隔震效果的影响。结果表明:（1）橡胶砂芯组合砌块应变软化现象明显。（2）RSMCB的水平动刚度随橡胶砂配比增大而减小,随盖板埋深、盖板尺寸以及竖向压应力的增大而增大。（3）阻尼比随橡胶砂配比、竖向压应力、盖板尺寸和埋深的增大而减小,橡胶砂芯组合砌块隔震消能效果显著。在隔震数值模拟中,输入加速度在经过橡胶砂芯组合砌块垫层过滤后均有不同程度的降低,且被过滤掉大部分高频波。隔震效应随着盖板尺寸的增大而减小,上部结构配重越大,隔震效应越明显,橡胶砂配比为30%时RSMCB垫层隔震效应更好。橡胶砂芯组合砌块符合在村镇欠发达地区低成本隔震的要求,表现出广阔的应用前景。 相似文献
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分层液化土中桩基侧向动力反应机理的试验研究 总被引：2，自引：0，他引：2
饱和砂土中的桩基侧向动力响应研究一直是岩土工程界与地震工程领域关注的热点,尤其是群桩侧向动力响应机制是需要重点研究的课题之一。基于振动台试验,通过输入2种不同的波形,采用FBG光栅传感系统对饱和砂土中的单桩与群桩侧向动力响应特性和典型测试点的桩土动力p—y滞洄曲线进行研究。研究结果表明：振动初期,单桩和群桩试验孔压增长不大,随后单桩孔压迅速上升,振动后期逐渐下降至0.5,而群桩孔压则上升缓慢;单桩试验土表加速度在振动初期逐步升高后又迅速降低,且加速度放大值略大于台面加速度值,群桩试验土表加速度在振动初期逐渐升高时就达到了最大,且随着孔压比的升高,加速度没有继续放大,而是逐渐减小,直到后期与单桩试验土表加速度重合;饱和砂土液化对单桩承台加速度和位移的影响较大,群桩承台侧向动力响应对液化的敏感程度略低于单桩承台;在振动输入和承台输入相同的条件下,液化后的群桩基础比单桩基础能更好地抵抗侧向力的作用。 相似文献
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饱和砂土液化是由地震引起的一种最常见的工程地质现象,也是造成重大地震灾害的主要原因之一。由于成因的复杂性和所造成灾害的严重性,饱和砂土液化一直是土动力学和岩土地震工程研究领域的重要课题。针对饱和砂土液化问题,基于开源地震工程数值计算平台OpenSees,对材料库中的4种砂土本构模型进行数值计算。采用二维u-p单元模拟土颗粒位移和孔隙水压力,分析和对比4种模型在循环动力荷载作用下的加速度、超孔隙水压力、位移、剪应力-剪应变和平均有效应力路径方面的响应结果。研究结果表明:(1)砂土对输入加速度表现出一定的放大效应,对于不同的模型,该放大效应存在一些差异;(2) Stress Density模型在循环动力荷载作用下易产生永久变形;(3)在循环动力荷载作用下,PDMY模型和CycLiqCPSP模型的强度逐渐降低,直到完全消失;(4) Stress Density模型和Manzari Dafalias模型在循环动力荷载下表现出明显的剪胀效应。研究成果对砂土液化的数值模拟问题具有重要的理论价值,可为饱和砂土的液化模拟和砂土本构模型的选取提供参考。 相似文献
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Mitsutoshi Yoshimine Hiroto Nishizaki Kei Amano Yasuyo Hosono 《Soil Dynamics and Earthquake Engineering》2006,26(2-4):253-264
This paper intended to evaluate the behavior of saturated sand and sloped ground subjected to flow failure with seepage of pore water in the ground after earthquake and the resultant liquefaction. Triaxial compression tests of sand with constant deviator stress but changing of pore pressure and volume of the specimens were conducted in this study. It was revealed that the relation between the volume change and the amount of shear strain during deformation depended on the initial density of the sand but it did not much depend on shear stress and initial confining stress levels. Based on this test results and numerical analysis of the seepage of pore water in liquefied ground, a methodology was proposed to predict the deformation of inclined ground due to liquefaction. 相似文献
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Lateral spreads are complex dynamic phenomena that are challenging to represent numerically. In this paper numerical models are developed and calibrated using the displacement, acceleration, and pore water pressure time histories recorded in a free-field lateral spreading centrifuge test. The calibrated numerical model then is used to predict another free-field lateral spreading centrifuge test using the same soil profile but different input acceleration time history. The computed response shows good agreement with the centrifuge test measurements. This paper demonstrates that even in a large strain problem, such as lateral spreading, small strain damping plays an important role in numerical simulation results; it also shows the need to have pressure dependent dilation parameters in the employed soil constitutive model implemented in order to simultaneously reproduce measurements of pore water pressure, acceleration and lateral displacement. 相似文献
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江苏省连云港赣榆港区陆域采用航道和港池的疏浚土方吹填形成作业港区,吹填工艺以绞吸式疏浚为主,疏浚涉及土层为粘土和砂土,由此形成了粘土和砂土的混合土地基。为了提高地基承载力和均匀性,采用了强夯法对地基进行加固,但是目前对夹砂粘土地基强夯加固的理论和实践较少。为此,以砂夹粘土构成的混合土地基为对象,测试了多种能量单点夯击时的地基土夯沉量、孔压和夯坑周围土体强度等参数,探讨了强夯法加固该类地基的加固深度和水平影响范围。结果表明：对于该类地基而言,有效加固深度修正系数取0.35~0.5为宜;强夯过程中,孔压与强度的增长范围不对应,即孔压影响范围远大于强度影响范围。 相似文献
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为探究砂土液化的微观机理,根据室内试验中微生物反硝化反应气泡的生成速率,建立数值模拟的时效性关系,分别制取微生物处理0天、2天、3天和5天的高饱和砂土试样,采用CFD-DEM耦合方法模拟不同工况下砂土试样的循环三轴不排水剪切试验。依据砂土试样的力链分布、抗液化振次、孔压比、轴向应变和力学配位数在加载过程中的变化情况,从宏微观角度分析砂土试样的抗液化能力。模拟结果表明:含微生物气泡高饱和砂土的抗液化强度较饱和砂土有所提升;随着微生物处理时间的增加,砂土试样的饱和度降低,孔压比和轴向应变的累积变慢,抗液化能力增强。 相似文献
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液化地基自由场振动台模型试验研究 总被引：4，自引：0，他引：4
进行了液化场地自由场振动台试验,试验采用柔性容器以减小边界影响,采用上覆黏土层的饱和砂土作为模型土。试验中再现了液化场地土的震害现象。得出的主要规律有:随着振次的增加,地基的频率迅速降低,阻尼比迅速增大;砂土对地震动起滤波作用;土体的加速度峰值反应在高度上呈"K"形分布;当最初加速度峰值到达前,砂土层中的孔压比存在负值;震后土中振动孔隙水压力不一定随振动的停止而立即开始消散,在短期内可能继续增长。 相似文献
18.
Uplift mechanism for a shallow-buried structure in liquefiable sand subjected to seismic load: centrifuge model test and DEM modeling 总被引：2，自引：1，他引：1
Based on a centrifuge model test and distinct element method(DEM), this study provides new insights into the uplift response of a shallow-buried structure and the liquefaction mechanism for saturated sand around the structure under seismic action. In the centrifuge test, a high-speed microscopic camera was installed in the structure model, by which the movements of particles around the structure were monitored. Then, a two-dimensional digital image processing technology was used to analyze the microstructure of saturated sand during the shaking event. Herein, a numerical simulation of the centrifuge experiment was conducted using a two-phase(solid and fl uid) fully coupled distinct element code. This code incorporates a particle-fl uid coupling model by means of a "fi xed coarse-grid" fl uid scheme in PFC3D(Particle Flow Code in Three Dimensions), with the modeling parameters partially calibrated based on earlier studies. The physical and numerical models both indicate the uplifts of the shallow-buried structure and the sharp rise in excess pore pressure. The corresponding micro-scale responses and explanations are provided. Overall, the uplift response of an underground structure and the occurrence of liquefaction in saturated sand are predicted successfully by DEM modeling. However, the dynamic responses during the shaking cannot be modeled accurately due to the restricted computer power. 相似文献
19.
研究交通循环荷载作用下路基软黏土的长期沉降和动力力学性质对路基设计具有重要意义。本文通过GDS动三轴实验,研究(不排水条件下)振动波形、排水条件以及动应力比三因素对于软黏土动应变和动孔压的影响。试验结果显示:排水条件对饱和软黏土的动应变和动孔压影响最大,在部分排水条件下动孔压逐渐消散,动应变迅速发展。振动波形对软黏土动应变和动孔压影响较大,单向纯压半正弦波作用下软黏土的动应变和动孔压较容易达到最大值。在较少的振次内动应力比对孔压影响较大,但在归一化的孔压模型中,动应力比对孔压影响较小。通过以上分析,本文建立包含循环振次和纯压因素的孔压增长模型。 相似文献
20.
以天津汉沽地区某挡土墙地基粉土为研究对象,首先对不同颗粒组成的粉土做固结不排水动三轴剪切试验,采用各向等压固结,周围压力等于100kPa。固结完成后在不排水条件下施加轴向激振力,试验波形为正弦波,振动频率1.0Hz,试验中以试样在周期剪切时轴向周期应变达到5%作为破坏标准,得出粉土的动强度受颗粒组成的影响。细颗粒含量越大,其动强度越小,黏粒含量为7.2%的粉土循环剪应力比CSR约为20.3%黏粒含量粉土的2倍。粉土的动强度可以用循环剪应力比和破坏振次建立的幂函数关系式较好地拟合。在剪切过程中,粉土的孔隙水压力一直没有达到所施加的围压数值,最终稳定在75%~85%围压之间。同时,试验还得出孔隙水压力的增长模式不能用统一的Seed模型拟合,孔压增长规律的影响因素较多。 相似文献