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1.
动剪切模量和阻尼比是工程场地地震安全性评价及地基动力反应分析的重要动力学参数。为评价某海域海洋土的动力学特性,对10.3～84.2 m深度范围内的海底淤泥质粉质黏土、粉砂及细砂开展共振柱试验。利用双对数模型建立了最大动剪切模量随上覆压力的递增关系。研究发现,现有规范的剪切模量比与阻尼比的推荐取值并不适用于海洋沉积土,即使考虑借鉴以往研究成果也必须将其限制在一定的应变范围,并应考虑土体的天然应力状态取值。利用马丁-达维登科夫（Martin- Davidenkov）模型及阻尼比与剪应变的经验关系建立了剪切模量比和阻尼比随剪应变的变化规律,并由此提出了适用于海洋沉积土的5×10-6～10-3应变范围内剪切模量比及阻尼比的推荐值。研究成果可为海洋工程场地的设计、施工及抗震分析提供技术参考依据。 相似文献
2.
黄河三角洲粉质土的动模量和阻尼比试验研究 总被引：9，自引：2，他引：7
结合室内共振柱和动三轴实验,对黄河三角洲饱和原状粉质土体(粉土、粉砂、粉质粘土)动模量和阻尼比的影响因素和发展规律进行了详细的研究。研究表明,在粉粒和粘粒含量对动模量的共同影响中,粉粒含量起着举足起重的作用;侧限压力对归一化剪模比和阻尼比的影响均较显著,相比粘粒含量的影响不大。通过与Seed建议的砂土及饱和粘土的G/Gmax~曲线和~曲线进行对比,结果显示研究区的粉质土相比一般的砂土和饱和粘土而言,其动力变形特性更接近于砂土,但是与砂土也存在着非常明显的差异;其发展规律与其他地区沉积粉质土也较为不同,具有明显的区域性。采用修正了的Hard in-D rnevich模型和对数模型分别对G/Gmax~曲线和~曲线进行拟合,给出了三类粉质土的归一化动力变形G/Gmax~/r关系曲线,对模型中有关参数的影响因素做了初步的探讨。 相似文献
3.
互层土的动参数试验研究及其地震反应分析 总被引：3，自引：0，他引：3
通过对两个工程场地的淤泥质粉质粘土、粉土、粘土、粉细砂及粉土与（粉质）粘土、粘土与粉砂互层土的自振柱试验结果进行分析,给出了部分土的 - 和 - 曲线,与Seed和Idriss建议的砂土和粘性土的 - 和 - 曲线变化范围进行了对比;同时分析了这两个场地的地震反应,结果表明：在强震时互层土对地震波有很强的滤波作用,且互层土的最大剪应变远大于一般土,在水平地震作用下很容易接近或达到破坏状态。初步分析结果表明：互层土具有软土的动力特性,这主要是由互层土的特殊物理构造造成的,即在互层土中存在很密的水平薄弱面。 相似文献
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《Geomechanics and Geoengineering》2013,8(2):135-140
Many geotechnical problems such as seismic resistant designs and machine vibrations require the installation of dampers or isolators to control the amplitude of vibrations. Engineered fills designed with increased capability of dissipating energy can provide a more economical approach to control excessive vibrations. This study presents a novel technique to increase the damping ratio of sand without affecting its stiffness and shear strength. The increase in damping ratio is evaluated by performing resonant column tests on the engineered sand. The damping ratio of the sand is increased by adding a controlled amount of viscoelastic material to the voids. The resonant column tests indicate that the damping ratio of the sand can be increased manifold without affecting the shear modulus. The micromechanical evaluation of the results shows a good correlation between the particle surface area in contact with the pore-mixture and the damping ratio of the sand. The suitability of engineered sand as foundation material is also evaluated by performing direct shear tests. The direct shear tests on mixtures indicate similar or better shear strength parameters compared to pure sand. 相似文献
6.
A series of tests were conducted to investigate the improvement of damping properties of clay samples with geosynthetic inclusions.
Flexible thermoplastic polymer synthetics improve damping properties of clay samples. Resonant column tests were conducted
to measure the low strain shear modulus and damping ratio of laboratory prepared synthetic inclusion clay specimens. The shear
modulus and damping ratio of the reinforced clay samples were investigated considering geosynthetic type (geotextile and geomembrane),
number of geosynthetic sheets, and confining pressure. The test results demonstrated that the geomembrane and the number of
geosynthetic sheets significantly improved the shear modulus and damping ratio of reinforced clay samples compared with those
of the unreinforced clay samples. 相似文献
7.
通过反复荷载三轴剪切试验研究了EPS颗粒混合轻质土在反复荷载下的变形和阻尼特性,分析了不同围压、不同水泥掺入比及不同土质条件下轴向累积应变、回弹模量及阻尼比随轴向总应变的变化规律。结果表明：轴向累积应变与轴向总应变呈线性关系,与轴向总应变的比值较大,且在不同条件下基本不变;回弹模量随围压和水泥掺入比的增大而增大。在一定的围压和水泥掺入比下,当应变小于8%时,砂土EPS颗粒混合轻质土的回弹模量大于淤泥质土EPS颗粒混合轻质土的回弹模量;当应变大于8%时,情况相反。回弹模量与轴向总应变的关系曲线可用递减的幂函数来拟合;EPS颗粒混合轻质土的阻尼比随轴向总应变的增大而增大,随围压和水泥掺入比的增大而减小,砂土EPS颗粒混合轻质土的阻尼比小于淤泥质土EPS颗粒混合轻质土的阻尼比,但以上变化和差别都非常小,阻尼比基本保持为一常数。 相似文献
8.
In the present study, a series of resonant column tests was performed to determine the influence of confining pressure, shear strain and relative density on the dynamic properties and Poisson's ratio of poorly graded clean sand. The tests were performed on the sand specimens of size 50 × 100 mm compacted at relative densities 30, 50 and 75 %. To achieve the corresponding relative density, sand was compacted in 5 equal layers with a specific number of blows. A fixed-free type resonant column apparatus was used to determine the dynamic soil properties at various confining pressures. It has been inferred from the data that the shear modulus (\(G\)) increases with an increase in confining pressure and relative density; and decreases with an increase in shear strain. In addition, damping ratio (\(D\)) decreases with an increase in confining pressure and relative density; and increases with an increase in shear strain. In addition, Poisson’s ratio (\(\nu\)) decreases with an increase in confining pressure and relative density and increases with an increase in the shear strain. The variation of shear modulus with Poisson’s ratio is also discussed. It has been found that there has been a decrease in shear modulus with an increase in Poisson’s ratio of the soil. It is noticed that the small strain shear modulus determined from the present study closely matches with the value determined using the correlations from the literature. 相似文献
9.
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
10.
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
11.
Small-Strain Shear Modulus and Damping Ratio of Sand-Rubber and Gravel-Rubber Mixtures 总被引：2，自引：0，他引：2
Anastasios Anastasiadis Kostas Senetakis Kyriazis Pitilakis 《Geotechnical and Geological Engineering》2012,30(2):363-382
This study examines the small-strain dynamic properties of mixtures composed of sandy and gravelly soils with granulated tire
rubber in terms of shear modulus (GO), and damping ratio in shear (Dmin). Torsional resonant column tests are performed on dry, dense specimens of soil-rubber mixtures in a range of soil to rubber
particles size 5:1–1:10 and rubber content from 0 to 35% by mixture weight. The experimental results indicate that the response
of the mixtures is significantly affected by the content of rubber and the relative size of rubber to soil particles. Concering
the small-strain shear modulus, an equivalent void ratio is introduced that considers the volume of rubber particles as part
of the total volume of voids. Based on a comprehensive set of test results a series of equations were developed that can be
used to evaluate the shear modulus and damping ratio at small shear strain levels if the confining pressure, the content of
rubber by mixture weight, the grain size of soil and rubber particles, and the dynamic and physical properties of the intact
soil are known. 相似文献
12.
动剪切模量Gd与阻尼比D是岩土体地震反应分析的两个主要参数,而初始状态是动力参数主要影响因素之一。通过大型动三轴试验,研究了应力比与含水状态对松散堆积体Gd与D的影响。试验结果表明,应力比Kc对松散堆积体最大动剪切模量Gdmax有重要影响,一定范围内（Kc=1～3）,Kc越大,最大动剪切模量Gdmax越大,在Hardin公式基础上发展了一个考虑Kc影响的经验公式。对比松散堆积体饱和与风干两种状态的Gd/Gdmax-?dn（归一化动剪应变）关系曲线,发现风干状态下松散堆积体的Gd/Gdmax-?dn关系表现出更明显的非线性,另外风干状态阻尼比略大于饱和状态。应用改进的Gdmax经验公式与Gd/Gdmax-?dn关系进行了松散堆积体地表的地震反应谱分析,计算结果表明,应力比与含水状态对地表加速度反应谱有重要影响。 相似文献
13.
以福州盆地广泛存在的3层结构性软土为研究对象,首先阐述了三者的沉积特征及常规物理力学性质,然后利用共振柱试验仪进行了一系列不同固结应力下动力试验,得到不同结构性软土在动荷载作用下的动阻尼比λ,通过数值分析给出其阻尼比λ与剪应变γ关系曲线,进而分析不同结构性软土试验结果的差异。试验结果表明:动阻尼比λ与剪应变γ关系与固结应力没有很强的相关性,在剪应变0.00001~0.01范围内三层结构性软土λ-γ曲线差异较大。试验成果为进一步了解福州盆地土层地震效应提供了可靠的数据,具有现实意义。 相似文献
14.
尾矿料的动力特性试验研究 总被引：10，自引：0，他引：10
通过对某铜矿的尾矿料进行动三轴和共振柱试验,研究了尾矿材料动力变形特性,提出了简单实用的孔隙水压力模型,给出了能更加准确地预测尾矿材料的动孔隙水压力的公式,并将其与Seed提出的预测公式进行了比较。在不同密度尾矿料的动三轴试验基础上,分析了相对密度对液化特性的影响,得出了相对密度小于70 %时抗液化强度随相对密度的增加而明显增加的结论。在不同围压下进行动三轴试验,结果表明：在相同的液化振次条件下,围压越高,动剪应力比越低。由共振柱试验可知,尾矿料的阻尼比随着动剪应变幅的增大而增大,而动剪模量随动剪应变幅的增大而减小,动剪模量和阻尼比与动剪应变幅的关系受围压影响不太敏感。 相似文献
15.
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
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材料状态对干砂小应变特性的影响 总被引：2，自引：0，他引：2
利用注能虚拟质量(EIVM)共振柱系统进行了干砂小应变特性试验,研究了有效平均正应力、土样密度、剪应变幅值以及荷载往复次数对剪切模量和阻尼比的影响。试验结果表明,剪切模量随有效平均正应力与土样密度的增加而增加,而阻尼比的变化规律则与之相反,并且有效平均正应力对干砂小应变特性的影响程度比土样密度的影响程度大得多;随着剪应变的增加,剪切模量越来越小,而阻尼比越来越大;荷载往复次数对剪切模量基本没有影响,而对阻尼比有较大影响。 相似文献
18.
Aliakbar Hajimohammadi Seyed Majdeddin Mir Mohammad Hosseini Akbar Cheshomi 《Environmental Earth Sciences》2010,61(4):813-820
Shear wave velocity is one of the important factors representing the dynamic characteristics of soil layers. Hence, many researchers
have focused their studies on determining shear wave velocity by direct field measurements or expressions developed by other
soil parameters. The shear module and damping ratio of the soil layers also play a similar role in the majority of dynamic
soil response analyses. Nevertheless, since they have to be measured in the laboratory by resonant column or cyclic triaxial
tests on undisturbed samples, the possibility of preparing such samples and the reliability of the obtained results are of
great concerns. In the present study, great effort has been made to determine the above dynamic factors by means of field
data obtained from a versatile instrument, namely the seismic piezocone (SPCTU), and to derive expressions correlating them with some parameters obtainable by much simpler instruments. The reliability
of laboratory measurements on undisturbed samples is also evaluated. The seismic piezocone test apparatus has been employed
to evaluate the soil properties at 1-m depth intervals by means of measuring tip resistance, sleeve resistance, pore pressure
and shear wave velocity. The shear module and the damping ratio are calculated using field data. Meanwhile, in order to assess
the laboratory measurements of these parameters, some resonant column tests and cyclic triaxial tests on undisturbed samples
of the same soil layers have been carried out. In order to compare the field results of shear modulus and damping ratios with
those obtained from laboratory tests, the influences of the soil nature and sample disturbance on the conventional laboratory
methods are evaluated and discussed. The shear wave velocity is correlated to overburden pressure and the corrected tip resistance
for two groups of fine soils, namely silty clays and carbonate clayey silts, which mainly cover the areas under study in this
project, are located in southern parts of Iran near the Persian Gulf. According to the results of the present study, there
are narrow limits of shear modulus regarding soils for which the laboratory tests and the field measurements yield approximately
the same shear modulus. This limit of shear modulus is about 30–50(MPa) for clay deposits and 70–100 (MPa) for sandy deposits.
Also the shear wave velocity can be calculated by a simple expression from total overburden pressure and the tip resistance
of simple cone penetration test results conventionally available in many soil explorations prior to engineering practices.
However, if the pore pressure inside the saturated soil deposits can be measured by a piezocone apparatus, the shear wave
velocity may be calculated using another suggested equation in terms of effective overburden pressure in the present study.
Regarding the shear module and the damping ratio, due to the disturbances of the stiff deposits in the sampling process and
great deviations of laboratory results from field results, the laboratory measurements of these parameters out of the above
limits are not recommended. 相似文献
19.
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