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1.
In the first part of this study, a series of stress-controlled hollow cylinder cyclic torsional triaxial shear tests were conducted on loose to medium dense saturated samples of clean Toyoura sand to investigate its liquefaction behavior. A uniform cyclic sinusoidal loading at a 0.1 Hz frequency was applied to air-pluviated samples where confining pressure and relative density was varied. Cyclic shear stress–strain changes, the number of cycles to reach liquefaction and pore pressure variations were recorded. Results indicate that the liquefaction resistances of uniform sands are significantly affected by the method of sample preparation and initial conditions. 相似文献
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Pre-shear history has been shown to be a critical factor in the liquefaction resistance of sand. By contrast to prior experimental studies in which triaxial shear tests were used to examine the effects of pre-shear on the liquefaction resistance of sand, hollow cylinder torsional shear tests were used in this study to avoid the influence of the inherent anisotropy that is inevitably produced during the sample preparation process because of gravitational deposition. A series of cyclic undrained shear tests were performed on sand samples that had experienced medium to large pre-shear loading. The test results showed that the liquefaction resistance of sand can be greatly reduced by its pre-shear history, and a pre-shear strain within the range from 0.1% to 5% can cause sand to be more prone to liquefaction. During the cyclic shear tests, the samples that had experienced pre-shear loading exhibited different behaviors when cyclic shear loading started in different directions, i.e., the clockwise direction and the counterclockwise direction. If the cyclic loading started in the identical direction as the pre-shear loading, then the mean effective stress of the sand was almost unchanged during the first half of the loading cycle; if the cyclic loading started in the direction opposite to that of the pre-shear loading, then the mean effective stress decreased significantly during the first half of the loading cycle. However, this anisotropic behavior was only remarkable during the first loading cycle. From the second cycle onward, the speeds of the decrease in the mean effective stresses in the two types of shear tests became similar. 相似文献
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Laboratory resonant column and cyclic triaxial tests are performed to determine the dynamic response (i.e. shear modulus and damping) of chemically grouted sand. The effect of chemical grouting is evaluated as a function of shearing-strain amplitude, confining stress, cycling prestrain, number of cycles, grout type, concentration, and curing time. The test results show that the shearing-strain amplitude, grout type and grout concentration have significant effects on the shear modulus and damping ratio of the test specimens. The increased addition of sodium silicate grout, which produces stiff gels, improved the shear modulus of the test sand. The acrylate (AC-400) and polyurethane (CG5610) grout, which produces flexible (rubber-like) gels, improved the damping capacity of the sand with increasing grout concentration. The addition of chemical grout greatly reduces the effect of cyclic prestraining over untreated sands. In the case of dense sands, the reduction of cyclic prestraining is less pronounced than in loose sands, which have a higher potential for particle movement and reorientation. 相似文献
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Shear modulus and damping ratio of grouted sand 总被引：2，自引：0，他引：2
Estelle Delfosse-Ribay Irini Djeran-Maigre Richard Cabrillac Daniel Gouvenot 《Soil Dynamics and Earthquake Engineering》2004,24(6):461-471
An experimental comparative study of three different grouted sands in terms of their effects on the values of two dynamic properties is presented. The dynamic properties studied are the shear modulus and the damping ratio which are determined with resonant column tests and cyclic triaxial tests. The behaviour of a pure Fontainebleau sand is compared with the behaviour of a Fontainebleau sand grouted with a silicate grout, a micro-fine cement grout and a mineral grout. The effects of the grouting treatment, the type of grout, the confining pressure, and the strains, on the shear modulus and the damping ratio are studied. The test results have shown that grouting improves the stiffness of the sand especially for small strains. Whatever the type of material, confining stress improves the shear modulus whereas it has a negligible effect on the damping ratio. When strain increases, the shear modulus decreases and the damping ratio increases. 相似文献
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辽宁台安砂土属于易液化砂,提升其抗液化性能具有重要的工程意义。文章针对纳米硅溶胶(CS)对辽宁台安砂土抗液化性能的改良效果进行探究,通过不排水动三轴试验,对纯砂样和改良砂样的液化特性进行对比研究,分析CS浓度和固化时间两个参量对改良砂样动力特性的影响。研究结果表明：(1)CS能够显著提升台安砂土的抗液化性能,在动载作用下改良砂样均未发生液化破坏。(2)随CS浓度和固化时间的增加,试样动孔压ud、动应变εd呈现先迅速下降后趋于平缓的发展规律;当CS浓度增至4%、固化时间达到3周后,试样抗液化性能的提升效果不再明显。(3)改良砂样的滞回曲线变得更加稳定。随CS浓度增加,阻尼先降低后趋于稳定,动弹性模量逐渐增大并趋于平缓,但伴随有一定的波动;随固化时间增大,阻尼呈减小趋势,动弹性模量呈增大趋势。研究成果可为辽宁台安地区砂土液化治理提供参考依据。 相似文献
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Masayuki Hyodo Noritaka Aramaki Masayuki Itoh Adrian F.L. Hyde 《Soil Dynamics and Earthquake Engineering》1996,15(5):331-336
Cyclic triaxial tests have been carried out on a skeletal carbonate sand from the west coast of Eire. Results are presented for undrained cyclic shear tests on samples with 80% of relative density consolidated under both isotropic and anisotropic conditions. Failure was defined as a 5% double amplitude cyclic strain and a 5% peak axial strain for stress-reversal and non-reversal stress conditions, respectively. Using this definition the cyclic strength for isotropically consolidated samples was affected by the confining pressure although the angular platey nature of the sand resulted in higher cyclic strengths than for a comparable silica sand. For anisotropically consolidated samples the cyclic strength increased with increasing initial static shear stress while on the other hand the cyclic strength normalised in the usual way with respect to the initial confining pressure decreased as this pressure increased. 相似文献
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振动频率对饱和砂土液化强度的影响 总被引：4，自引：0，他引：4
采用“土工静力-动力液压三轴-扭转多功能剪切仪”对饱和砂土进行了一系列动三轴实验,探讨了振动频率对液化强度数值的影响程度。在1．0、1．5固结比和0．05、0．10、1．00Hz振动频率条件下,针对相对密实度分别为70％、28％的密砂和松砂进行了100、200、300kPa围压和100kPa围压条件下的液化强度实验。实验结果表明,饱和密砂和松砂在各种固结条件下,液化强度随着振动频率的增大而增大,相同破坏振次时,各种实验条件下的液化强度与振动频率的关系在双对数坐标上均符合线性关系;振动频率由0．05Hz变化到1．00Hz时,液化强度相差达25％以上;动强度指标翰值随振动频率的增大而增大,最大相差12．2％;随着振动频率的增大,砂土达到液化破坏所需的时间明显缩短;振动频率对松砂液化强度的影响比对密砂的影响更为显著。 相似文献
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The availability of efficient numerical techniques and high speed computation facilities for carrying out the nonlinear dynamic analysis of soil-structure interaction problems and the analysis of ground response due to earthquake loading increase the demand for proper estimation of dynamic properties of soil at small strain as well as at large strain levels. Accurate evaluation of strain dependent dynamic properties of soil such as shear modulus and damping characteristics along with the liquefaction potential are the most important criteria for the assessments of geotechnical problems involving dynamic loading. In this paper the results of resonant column tests and undrained cyclic triaxial tests are presented for Kasai River sand. A new correlation for dynamic shear damping (Ds) and maximum dynamic shear modulus (Gmax) are proposed for the sand at small strain. The proposed relationships and the observed experimental data match quite well. The proposed relationships are also compared with the published relationships for other sands. The liquefaction potential of the sand is estimated at different relative densities and the damping characteristics at large strain level is also reported. An attempt has been made to correlate the Gmax with the cyclic strength of the soil and also with the deviator stress (at 1% strain) from static triaxial tests. 相似文献
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Y. Jafarian A. Sadeghi Abdollahi R. Vakili M.H. Baziar 《Soil Dynamics and Earthquake Engineering》2010
Cyclic triaxial tests on reconstituted sand samples are broadly employed in practice while they ignore the inherent characteristics of soil in field condition such as aging, fabric, and prior strain history. Relative state parameter index, ξR, is utilized in a probabilistic framework to adjust the cyclic triaxial resistance ratio of sands at 15 uniform cycles (CRRtx,15) to field condition. A wide-ranging database containing the results of cyclic triaxial tests conducted on reconstituted samples has been compiled to derive a correlation between relative state parameter index (ξR) and triaxial cyclic resistance ratio. The adjustment coefficients proposed by researchers are employed to correct CRRtx,15−ξR relationship for actual field condition. The adjusted CRRtx,15−ξR relationships are applied to a database of field liquefaction case histories composed of both SPT and CPT based data and their performances in field condition are evaluated. It is demonstrated that constant triaxial-to-field adjusting coefficients cannot ever predict conservative results. Logistic regression method is employed to derive a field probabilistic criterion that obtains the likelihood of liquefaction initiation in terms of ξR. The ξR-based boundary curve standing for 20% likelihood of liquefaction initiation is found to be the most conservative limit state boundary to be used in field conditions. Finally, the triaxial and field CRR−ξR relationships are composed and a probabilistic triaxial-to-field adjustment coefficient is proposed in terms of ξR and a given liquefaction probability. It is anticipated that the proposed relationship could reasonably correct the results of cyclic triaxial testing on freshly reconstituted sand samples. 相似文献
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The August 17, 1999 Kocaeli earthquake affected the city of Adapazari, which is located in the northwest of Turkey, with severe liquefaction and bearing capacity failures causing tilting of buildings, excessive settlements and lateral displacements. To understand the stress–strain behavior and pore pressure behavior of undisturbed soils during the earthquake, the cyclic and post-cyclic shear strength tests have been conducted on soil samples obtained from Adapazari in a cyclic triaxial test system within the scope of this research. Cyclic tests have been conducted under stress controlled and undrained conditions. Post-cyclic monotonic tests have been conducted following cyclic tests. The strength curves obtained in the experiments showed that the dynamic resistance of silty sand was found to be 45% lower than those of high plasticity soils (MH). The strength of clayey soils with the plasticity index of PI=15–16% was lower compared to the strength of high plasticity soils. Also, it was observed that silty sand soils had the lowest strength. The dynamic strength of the soils increased with the increase in plasticity. 相似文献
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复杂应力条件下饱和松砂单调与循环剪切特性的比较研究 总被引：4，自引：0，他引：4
本文利用大连理工大学新引进与开发的“土工静力-动力液压-三轴扭转多功能剪切仪”,针对福建标准砂,在不排水条件下同时进行了单调剪切试验与循环剪切试验,进而对其进行了对比分析。通过比较表明,应力-应变关系的应变软化和硬化特性与流滑变形和循环流动特性密切相关,当循环剪切应力水平高于单调剪切过程中应变软化阶段最小强度时将会发生流滑变形。无论在单调剪切中,还是在循环剪切中,稳定状态时的有效偏应力比随着大主应力方向与竖向之间夹角的增大而减小,在中主应力系数相同的条件下,循环剪切中呈现显著剪胀时的有效偏应力比和最终稳定状态时的有效偏应力比峰值分别与单调剪切中达到相变状态时的有效偏应力比和最终稳定有效偏应力比基本上一致。然而不排水条件下单调与循环剪切过程中孔隙水压力的增长特性却并不相同,循环剪切中的最大孔隙水压力随着初始主应力方向角的增大而减小,单调剪切中的最大孔隙水压力却随着主应力方向角的增大而增大。 相似文献
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In this paper a study on the improvement of liquefaction strength of fly ash by reinforcing with randomly distributed geosynthetic fiber/mesh elements is reported. A series of stress controlled cyclic triaxial tests were carried out on fly ash samples reinforced with randomly distributed fiber and mesh elements. The liquefaction resistance of reinforced fly ash is defined in-terms of pore pressure ratio. The effects of parameters such as fiber content, fiber aspect ratio, confining pressure, cyclic stress ratio, on liquefaction resistance of fly ash have been studied. Test results indicate that the addition of fiber/mesh elements increases the liquefaction strength of fly ash significantly and arrests the initiation of liquefaction even in samples of loose initial condition and consolidated with the low confining pressure. 相似文献
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A laboratory study on the undrained strength of a silty sand from Central Western Taiwan 总被引：2，自引：0，他引：2
Yao-Tao Huang An-Bin Huang Yu-Chen Kuo Ming-Dou Tsai 《Soil Dynamics and Earthquake Engineering》2004,24(9-10):733
The sand deposit in Central Western Taiwan typically contained significant amounts of fines. The assessment of liquefaction potential using the simplified procedure often involved adjustment in field test results to account for the effects of fines. The available fines content (FC) adjustment methods are highly empirical and may lead to very different conclusions. The need and/or level of FC adjustment should be justified based on cyclic behavior of sand and its relationship with fines. This study made an attempt to provide that reference information for a silty sand commonly found in Central Western Taiwan. A series of isotropic consolidation, undrained monotonic and cyclic triaxial tests were conducted on reconstituted Mai Liao Sand (MLS) with various FCs and densities. Concurrent shear wave velocities were measured using bender elements in some of the cyclic triaxial tests. This paper describes the geological background, the laboratory tests and their implications in the assessment of liquefaction potential for MLS. 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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为探讨台安砂土液化相关特性及发展规律,针对辽宁台安砂土进行一系列不排水动三轴试验,研究台安砂土在动荷载作用下动孔压及动应变变化规律,分析影响台安砂土发生液化的主控因素,揭示动载作用次数下台安砂土动力响应特征。结果表明：动应力水平不同的各相对密度试样ud曲线可分为后期陡增和匀速增长两种类型,动应力幅值较大时,ud始终以较快速度增长,呈现匀速增长特征,动应力幅值较小时,ud曲线则呈现初期缓增后期陡增的特点;相对密度Dr和动应力幅值CSR是决定砂土液化的主控因素,在同一里氏震级等效动载作用次数下,随着Dr持续发展,液化所需CSR增长逐渐加快,当Dr足够大时,砂土基本处于密实状态,此时难以发生液化;循环荷载作用下,台安砂土呈现出初期整体受压、中期拉压平衡、后期受拉凸显的动力响应特征,到后期试样拉应变迅速增大,试样易发生受拉破坏。研究成果可为辽宁台安地区建筑物抗震设计提供参考依据。 相似文献
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采用多工况振动台实验研究液化对土层水平往返变形的影响.以干砂实验为参照,分析孔压增长与土层加速度和土层往返变形之间的关系.结果表明:液化将引起土表加速度显著降低,减小惯性力传递,但同时会引起土层往返剪应变明显增大.对往返变形而言,液化土层往返剪应变就可达到1%～5%的大变形状态,且液化土层往返剪应变沿深度呈下大上小分布.土层中孔压比0.4～0.8是往返变形出现放大的敏感段,在孔压比0.8左右而不是在1.0达到最大.作为其结果,土层液化将对刚性上部结构振动起减震作用,但同时增大的往返剪应变也易导致基础和地下结构破坏,特别是对液化层与下部非液化层交界处的构件更敏感. 相似文献
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Study of the liquefaction resistance of a saturated sand reinforced with Geosynthetics 总被引：1，自引：0，他引：1
This article presents various tests using a cyclic triaxial instrument, on samples of saturated Hostun RF sand, reinforced with circular sheets of geosynthetic material. Tests performed with different types of geosynthetics of different compressibility, rigidity and roughness characteristics indicate a significant increase in liquefaction resistance for samples reinforced with compressible, non-woven geotextiles. The undrained behaviour of saturated Hostun RF sand reinforced with non-woven geotextiles is analysed on the basis of different test series. This analysis highlights the influence of reinforcement compressibility on interstitial pressure distribution in the sample, thus showing the role of this type of inclusion in the increase in liquefaction resistance. 相似文献