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1.
固结比对黏性土动剪切模量影响的研究 总被引：1，自引：0，他引：1
采用共振柱试验方法,对固结比对黏性土最大动剪切模量和对动剪切模量比与剪应变非线性关系的影响进行了研究,并通过土层地震反应计算,初步给出了这种影响对地表反应谱作用的估计。通过对粉质黏土和粉土的系统试验,提出了计算不同固结比粉质黏土和粉土最大动剪切模量的建议公式,并与Hardin公式进行了对比。结果显示,固结比kc >1.0时的最大动剪切模量较kc=1.0时的增长程度明显比Hardin公式要大。与砂土试验结果相比,固结比对黏性土最大动剪切模量影响程度更大。同时,分析了固结比对动剪切模量比与剪应变非线性关系及对地表反应谱的影响。结果表明,固结比对黏性土动剪切模量比与剪应变非线性关系有一定影响,随固结比增加,动剪切模量比非线性关系曲线有一定提高,动剪切模量比值增大,在强地震动作用下的土层反应分析中应考虑实际固结比的影响。 相似文献
2.
昆明泥炭质土动剪切模量与阻尼比的试验研究 总被引：1，自引：0，他引：1
《岩土力学》2017,(12):3627-3634
利用DDS-70型动三轴仪开展了昆明盆地泥炭质土的动力学参数试验研究,分析了不同围压、固结比、振动频率对泥炭质土的最大剪切模量G_(max)、动剪切模量G_d、剪切模量比G_d/G_(max)及阻尼比λ的影响规律。试验结果表明:泥炭质土的G_(max)随围压和固结比呈线性增大。随着剪应变dg的增大,泥炭质土的G_d减小,λ增大,当剪应变较小时,变化幅度较小,剪应变增大到一定程度后,变化速率加快。相同剪应变下,G_d随着围压和固结比的增大而提高。不同围压、固结比及振动频率下的G_d/G_(max)变化较小。围压、振动频率对λ的影响较为明显,而固结比对λ的影响没有明显的倾向性。根据试验结果,建立了考虑围压和固结比影响的G_(max)回归方程,采用Davidenkov模型及依据阻尼比与剪应变的经验关系,得到了泥炭质土的动剪切模量比及阻尼比模型,拟合结果显示,建立的模型能较好地描述泥炭质土的模量阻尼比随剪应变的变化规律。进一步对比分析了不同地区泥炭质土以及不同土类的模量阻尼比特性的差异性。 相似文献
3.
利用GDS共振柱试验系统对不同干密度、不同含水率的断层泥试样进行了动剪切模量和阻尼比试验研究。结果表明,使用Hardin-Drnevich双曲线模型能够较好地描述断层泥的动剪切模量随剪应变的变化趋势;随干密度增加,动剪切模量和阻尼比均增大;而随含水率增加,动剪切模量和阻尼比均减小;归一化动剪切模量试验点主要位于Seed和Idriss提出的砂土G/Gmax～γ曲线变动范围内,且与Sun和Seed推荐黏性土曲线变化趋势一致;在半对数坐标系中,阻尼比与动剪应变呈良好的线性关系,并给出了拟合关系式。 相似文献
4.
开展对水泥土搅拌桩软土地基土体试样的GDS（Global Distribution System）共振柱试验,研究不同剪应变、围压、水泥土置换率对土体动力特性的影响。结果表明,水泥土搅拌桩软土地基土体的动剪切模量G和阻尼比D随剪应变? 变化趋势与软黏土一致,在小应变范围内围压和置换率对土体的动剪切模量G和阻尼比D的影响显著,随着剪应变? 增大,围压和置换率的影响减弱;水泥土搅拌桩软土地基土体的最大动剪切模量Gmax与围压表现出良好的线性关系,围压越大,提高水泥土的置换率对土体最大动剪切模量Gmax增强效果越明显。研究结果可为地区水泥土搅拌桩软土地基土体动力参数的取值提供一定的参考。 相似文献
5.
开展对水泥土搅拌桩软土地基土体试样的GDS(Global Distribution System)共振柱试验,研究不同剪应变、围压、水泥土置换率对土体动力特性的影响。结果表明,水泥土搅拌桩软土地基土体的动剪切模量G和阻尼比D随剪应变γ变化趋势与软黏土一致,在小应变范围内围压和置换率对土体的动剪切模量G和阻尼比D的影响显著,随着剪应变γ增大,围压和置换率的影响减弱;水泥土搅拌桩软土地基土体的最大动剪切模量G_(max)与围压表现出良好的线性关系,围压越大,提高水泥土的置换率对土体最大动剪切模量G_(max)增强效果越明显。研究结果可为地区水泥土搅拌桩软土地基土体动力参数的取值提供一定的参考。 相似文献
6.
CAS-1模拟月壤动剪切模量与阻尼比的试验研究 总被引：2，自引：0，他引：2
针对中国科学院地球化学研究所与国家天文台合作研制成功的CAS-1模拟月壤（国家标准试样）,利用GDS共振柱试验仪对模拟月壤开展动力学参数的试验研究,分析了不同孔隙比、不同围压对动剪切模量G及剪应变 的影响规律。试验结果表明,在应力水平很低、孔隙比较大的真实月面环境条件下,动剪切模量G较小,阻尼比 较大,且随着动剪应变 的增大,动剪切模量快速减小,阻尼比急剧增大。采用Hardin-Drnevich模型,得到了不同孔隙比、不同围压下归一化动剪模量G/Gmax与归一化阻尼比 / 随 变化的平均拟合曲线,探讨了最大动剪切模量Gmax、最大阻尼比 和参考剪应变 等动参数与应力水平 的相关关系式,并据此给出了月壤钻取采样深度（0～3 m）内Gmax、 和 的值域区间以及各剪应变对应的G/Gmax和 的推荐值。 相似文献
7.
强风化花岗岩动力学参数的试验研究 总被引：1，自引：0，他引：1
地震反应分析通常采用等效非线性模型,动剪切模量G和阻尼比λ是该模型的两个重要参数。为研究目前在大型工程建设中遇到越来越多的强风化花岗岩的动力特性,利用固定-自由型共振柱（GDS RCA）对强风化花岗岩的剪切模量和阻尼比进行试验研究。GDS RCA为一种国际上广泛应用的共振柱,具有良好的性能,利用其控制试样的固结围压和孔隙水压力,可以测得试样在不同有效应力状况下的动剪切模量和阻尼比。对比研究不同有效应力下共振频率、动剪切模量和阻尼比随剪应变的变化情况,给出其变化曲线。按照Hadin-Drnevich[1]所提出的双曲线模型,拟合动剪切模量比和阻尼比随剪应变的变化曲线。利用摩擦理论,对试样阻尼的产生机制进行探讨。试验结果表明,随着剪应变的增加,试样系统的共振频率随之减小,试样阻尼比随之增大;试样的动剪切模量和阻尼比皆与试样固结时的有效应力有关,而试样阻尼比也受孔隙水压力的影响。 相似文献
8.
随着沙漠-黄土高原过渡地带各类资源的不断勘探和开发,对风积砂-黄土过渡型砂性黄土的动力特性缺乏了解这一问题愈来愈成为此类地区地震与人工动力相关工程建设发展的制约因素。本文在等压固结条件下,通过进行室内固结不排水动三轴试验,获得了风积砂-黄土过渡型砂性黄土的动力学参数,并以此为基础绘制了风积砂-黄土过渡型砂性黄土的动应力-应变关系曲线,探讨了风积砂-黄土过渡型砂性黄土动模量的变化特征、阻尼比随动剪应变变化的曲线关系及适合的拟合模型,进一步建立了适用于风积砂-黄土过渡型砂性黄土的等效动黏弹性本构模型。结果表明:Hardin双曲线模型对风积砂-黄土过渡型砂性黄土动剪切模量与动剪应变关系曲线的拟合较好,而幂函数经验公式对阻尼比与动剪应变关系曲线的拟合较好。本文研究结果为风积砂-黄土过渡型砂性黄土动力特性的研究提供了基础。 相似文献
9.
固结比对砂土动剪切模量及地表反应谱的影响 总被引：1，自引：0，他引：1
采用共振柱试验方法,研究了固结比对砂土最大动剪切模量以及对动剪切模量比与剪应变非线性关系的影响。通过土层地震反应计算,初步给出了这种影响对地表反应谱作用的估计。对福建标准砂和哈尔滨砂进行了系统试验,提出了计算不同固结比砂土最大动剪切模量的建议公式,公式显示固结比kc>1、最大动剪切模量较kc=1时的增长程度明显比Hardin公式要大。同时,给出了固结比对动剪切模量比与剪应变非线性关系及其对地表反应谱的影响。结果表明,固结比对砂土动剪切模量比与剪应变非线性关系有一定影响。随着固结比增加,模量比非线性关系曲线有一定提高,在强地震动作用下的土层反应分析中应考虑实际固结比的影响。 相似文献
10.
珊瑚砂的物理力学性质与陆相沉积物有显著的差异。对南沙岛礁饱和珊瑚砂进行了不排水应变控制分级循环加载动三轴试验,研究了有效围压 和相对密实度Dr对饱和珊瑚砂动剪切模量和阻尼比特性的影响。通过与陆源砂砾土试验结果的对比发现：珊瑚砂与陆源砂砾土在最大动剪切模量Gmax、动剪切模量比G/Gmax曲线及其上下界、参考剪应变 、阻尼比? 曲线及其上下界等均存在显著的差异;珊瑚砂的Gmax比陆源砂的大,采用陆源砂Gmax的经验模型,珊瑚砂的Gmax将被低估约30%;珊瑚砂的非线性稍弱于陆源砂砾土,陆源砂砾土G/Gmax和? 的经验公式不适用于珊瑚砂。给出了珊瑚砂G/Gmax和? 的经验公式及相关参数。 相似文献
11.
Appropriate evaluation of shear modulus and damping characteristics of soils subjected to dynamic loading is key to accurate
seismic response analysis and soil modeling programs. Dynamic centrifuge experiments were conducted at C-CORE (Memorial University
of Newfoundland) centrifuge center to investigate the dynamic properties and seismic response of soft clay and dry loose sand
strata. Soft clay with shear strength of about 30 kPa and well graded silica sand at about 35% relative density were employed
in a rigid container to simulate local site effects. Several earthquake-like shaking events were applied to the model to evaluate
variation of shear modulus and damping ratio with shear strain amplitude and confining pressure, and to assess their effects
on site response. The estimated modulus reduction and damping ratio were compared to the predictions of empirical formulae
and resonant column tests for both soft clay and loose sand. The evaluated shear modulus and damping ratio were found to be
dependent on confining pressure in both soil types. Modulus variation in both soils agreed well with the empirical curves
and resonant column test results. However, the sand modulus values were slightly higher than the empirical relations and resonant
column tests. This discrepancy is attributed to higher stress and densification of sand during large amplitude shaking applied
to the model. The damping ratio at shear strains lower than 0.5% was in reasonable agreement with the empirical curves and
the resonant column tests in both clay and sand models, but was generally higher at shear strain larger than 0.5%. 相似文献
12.
Abbas Abbaszadeh Shahri Katayoun Behzadafshar Roshanak Rajablou 《Arabian Journal of Geosciences》2013,6(3):881-892
The seismic response of existing earth dams in Iran is important after an earthquake both to provide emergency supplies and to society as well as to ensure structural safety in engineering terms. Better seismic capacity of earth dam results in less structural damage and reduced impacts following an earthquake disaster. Indirect as well as direct costs following earthquakes have gained much attention from both the engineering and socioec onomic research communities in the last few decades. This study is a valuable tool used to study the response of geotechnical structures to infrequent or extreme events such as earthquakes. The Avaj earthquake (2002, Iran) was applied to a series of model tests which was conducted to study the response of soil profiles under seismic loading. The acceleration records at different locations within the soil bed and at its surface along with the settlement records at the surface were used to analyze the soil seismic response. A combination of several software packages with a generated visual user interface computer code by authors named as “Abbas Converter” were employed to evaluate the variation of shear modulus and damping ratio with shear strain amplitude to assess their effects on site response. The proposed method was applied to the Korzan earth dam of Hamedan province in Iran. Site response analysis using the measured shear wave velocity, estimated modulus reduction, and damping ratio as input parameters produced good agreement with the computed site response in this study. 相似文献
13.
确定土体动剪切模量的常用方法有规范法、Kumar法和自相关函数法,确定相应阻尼比的方法有规范法、Das and Luo法、Kokusho法、Kumar法和互相关函数法,为了分析不同方法所产生差异,实现定量化对比分析,笔者以福建标准砂（粒径为0.5~1.0 mm）为研究对象,采用不排水的应力控制动三轴试验,探讨不同的确定土体动剪切模量和阻尼比方法的差异性,并给出了不同土体条件建议选用的方法。结果表明：1）3种方法确定动剪切模量的结果有一定的差异,随剪应变的增大结果的差异逐渐增大,有效围压对结果的差异性有所影响,当剪应变为4×10-3,有效围压为100 kPa时,3种方法差异显著,相对误差最大接近20%;2）而5种方法确定阻尼比的结果差异显著,随着剪应变的增大,5种方法确定的阻尼比相对误差大体上均在迅速减小,只有规范法在有效围压为100 kPa时,其相对误差有较小的增大趋势;5种方法中,Kumar法确定的阻尼比最接近平均阻尼比,互相关函数法远高于平均阻尼比,Das and Luo法和Kokusho法确定的阻尼比基本一致但低于平均阻尼比。建议以后的工程应用中,加载方式为应力控制时,可采用自相关函数法确定动剪切模量,采用Kumar法确定阻尼比,二者确定的动剪切模量和阻尼比均最接近平均值。 相似文献
14.
借助GDS动三轴试验研究了不同负温下经历多次冻融循环后粉砂土的动应力、动模量、动模量比和阻尼比等动力参数的变化规律。试验发现，相同动应变下，冻融循环与动应力和动模量呈负相关性，而与动模量比和阻尼比呈正相关性，随着冻融次数增加，动应力和动模量都减小，动模量比和阻尼比都增大，通过回归分析分别给出了动模量比与动应变关系曲线和阻尼比与动应变关系曲线的归一化拟合模型。冻融循环对初始动模量和最大阻尼比影响显著。随着冻融次数增加，初始动模量减小，而最大阻尼比增大。分别对不同负温下冻融次数对初始动模量和最大阻尼比的影响进行了回归分析，提出了冻融次数修正系数的计算公式。结果表明，温度越低冻融循环对粉砂土动力特性影响越明显，经历5次冻融循环后的动力参数相对稳定，建议将5次冻融循环后的动力参数作为基本参数进行动力反应分析计算。 相似文献
15.
随着高速铁路建设的兴起,轨道以及沿线附近建筑物承受低幅值小应变振动荷载的作用。对于小应变振动下土体的有限元计算,如何确定连接应力和应变之间纽带的刚度张量E,对于建立合理的预测模型来分析高速铁路轨道以及沿线建筑物的沉降变形至关重要。低幅值小应变振动下剪切模量G和阻尼比D随剪应变幅值的变化是反映土体刚度及阻尼特征最重要的两个参数。通过共振柱试验发现,振动荷载作用下土体的剪切模量G必须通过振动应变幅值和固结围压共同来确定,即使在小应变（剪应变幅值10-6相似文献
16.
Magdi M. El-Emam 《Geomechanics and Geoengineering》2014,9(4):279-293
The paper presents rational procedures to estimate normalised shear modulus and damping ratio from measured responses of reinforced soil model walls tested in a 1-g shaking table. Displacement measured at the top of the model walls and input base acceleration time histories are used to produce equivalent hysteretic responses of the model walls. Equivalent hysteretic loops at different strain amplitudes are developed and used to calculate normalised modulus degradation curves and damping ratio for the tested model walls. Model wall responses are also analysed using the single degree of freedom (SDOF) model to determine damping ratio and phase difference, and to verify the validity of SDOF model for application with reinforced soil walls.
Results indicate that the normalised shear modulus significantly decreased at the early stage of the base shaking (i.e. γs < 0.03%). For example, about 68% and 80% reductions in shear modulus occurred at γs = 0.005% and 0.01% respectively. In addition, a 90% reduction in the normalised shear modulus realised at relatively strong input base acceleration (i.e. for γs > 0.03%). Minimum damping ratio of 5% to 10% for both model walls was obtained, increased to 15% to 20% at strain amplitude γs = 0.3%, and reached higher values thereafter. Finally, dynamic properties determined from the proposed method are compared with experimental and empirical relationships proposed in literature as well as resonant column test results. 相似文献
17.
Evaluation of Shear Modulus and Damping Ratio of Granular Materials Using Discrete Element Approach 总被引：1，自引：0，他引：1
In this paper, an attempt has been made to highlight the influence of different parameters such as number of cycles, confining pressure, void ratio, gradation, initial anisotropy and stress path on the dynamic properties of granular materials using Discrete Element Method (DEM). A series of strain controlled cyclic triaxial numerical simulations using three dimensional DEM have been carried out on an assembly of spheres. Dynamic properties such shear modulus (G) and damping ratio (D) were determined from the typical hysteresis loop obtained during cyclic triaxial test simulation. It has been observed from the test results that the numerical simulation using DEM has captured the variation of dynamic properties over a wide range of shear strain values for different parameters considered for the current investigation. Maximum shear modulus (G max) was found to be influenced by initial confining pressure, void ratio, gradation and initial anisotropy. Whereas, the damping ratio (D) was found to be influenced by number of cycles, initial confining pressure, gradation and stress path. Further it has been shown that the variation of shear modulus with shear strain can be divided into three distinct zones such as Isotropic Zone (IZ), Anisotropic Zone (AZ) and Stable Anisotropic Zone (SAZ). A drastic reduction of shear modulus with shear strain has been observed in the Anisotropic Zone (AZ). In addition, the results obtained using numerical simulations have been compared with the laboratory experimental values. 相似文献