共查询到20条相似文献，搜索用时 15 毫秒
1.
以广州地区花岗岩残积粘性土为研究对象,通过击样法制备特定含水量试样,在不同压力下进行固结加、卸荷试验,对比分析试验数据,初步研究加、卸荷状态下花岗岩残积粘性土的抗剪强度变化,探寻先期固结压力、含水量与抗剪强度间规律。重塑残积土抗剪强度随含水量增加而减小;在先期固结压力相同的条件下,卸荷相对加荷试验条件下的土体强度显著减小,且减少值随残积土含水量的增加而逐渐减小,故在基坑开挖等卸荷工程项目中,应充分考虑卸荷对土体抗剪强度的影响,在卸荷工程中采用土体卸荷抗剪强度指标更符合工程实际。 相似文献
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采用环剪仪对超固结黏土抗剪强度特性的研究 总被引：4，自引：1，他引：3
利用大型高速环剪仪,对不同超固结比、法向应力和剪切速率下的超固结饱和黏土的峰值强度和残余强度特性进行了研究,并对循环荷载作用前后残余强度的变化进行了初步探讨。试验结果表明,（1）超固结比对超固结黏土的峰值强度和残余强度有着明显的影响;（2）在剪切速率相同的条件下,土体达到残余强度时的位移取决于现存的应力状态,而与应力历史无关;（3）剪切速率越大,峰值强度随之增大,达到稳定残余强度时的剪切位移也随之增加,但剪切速率的变化对残余强度值几乎没有影响;（4）在循环荷载作用下残余强度不同程度的降低,最大降低幅度达12.2 %;当土体剪切面为不规则剪切带时,施加循环荷载后出现残余强度上升的现象。 相似文献
4.
碱渣是氨碱法制纯碱时排出的固体废弃物,经适当的加固处理后作为工程填垫土可以有效解决占地和污染问题。碱渣土的力学性质不稳定,在循环荷载作用下强度会发生明显弱化,导致承载力大幅降低。以天津港地区回填碱渣土为研究对象,开展了系列动三轴试验,以固结围压、动应力比和偏压固结比为试验变量,研究了不同应力组合下碱渣土中循环累积孔压发展规律以及循环后碱渣土不排水强度演化规律。基于等效超固结模型,引入强度弱化系数β,建立了考虑偏压固结比和动应力比影响的碱渣土循环强度弱化模型;引入强度提升系数α,建立了考虑偏压固结过程和循环加载过程耦合影响的碱渣土强度演化模型,并通过试验数据验证了模型的正确性。 相似文献
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Christopher L. Meehan Thomas L. Brandon J. Michael Duncan Binod Tiwari 《Landslides》2010,7(2):157-167
A series of ring shear and direct shear tests were performed to measure the drained residual strength of three clay soils.
For each of the soils, slickensided direct shear specimens were prepared by wire-cutting intact specimens, and polishing the
resulting shear plane on a variety of surfaces to align the clay particles in the direction of shear. Drained direct shear
tests were then conducted on each of the polished specimens. The resulting shear strengths were compared with the residual
strengths measured in the ring shear device to evaluate the effectiveness of the different polishing techniques for creating
slickensided surfaces. Test results indicated that the measurement of residual strengths along preformed slickensided surfaces
is extremely sensitive to both the soil type and the slickenside preparation technique that is used. Consequently, this approach
does not appear to be a viable alternative to conventional repeated direct shear or ring shear tests to measure residual shear
strengths. 相似文献
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M. K. Jafari F. Pellet M. Boulon K. Amini Hosseini 《Rock Mechanics and Rock Engineering》2004,37(1):3-23
Summary Evaluation of the effects of small repetitive earthquakes on the strength parameters of rock joints in active seismic zones is of interest of the designers of underground constructions. In order to evaluate these effects, it is necessary to study the behaviour of rock joints under dynamic and cyclic loadings. This paper presents the results of a systematic study on the behaviour of artificial rock joints subjected to cyclic shearing. More than 30 identical replicas have been tested using triaxial compression devices under different conditions of monotonic and cyclic loading. At the first stage a few samples have been tested in monotonic loading modes under various confining pressures and rate of displacement. In the second series of tests, small cyclic loads were applied on the samples for increasing number of cycles, frequency levels and stress amplitudes. These were then followed by monotonic loading again. The variations of maximum and residual shear strengths for each test have been studied. The results show increase of shear strength as a result of the increase in confining pressure and they display decrease of shear strength due to the increase of rate of loading, number of cycles, frequency levels and stress amplitudes. 相似文献
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冻融作用对兰州黄土力学性质的影响 总被引：7，自引：0，他引：7
以兰州黄土为研究对象,让土样在封闭系统下经历一个冻融循环,再考察土的强度参数（c,φ）和前期固结压力（Pc）在冻融作用下的变化规律。试验表明,冻融循环对不同干容重的土具有强化和弱化的双重作用,并由此导致其力学性质发生相应的变化。相同冻结温度梯度下,随着土样干容重的增大,冻融后Pc和c具有首先增大然后减小的规律,并存在一个临界干容重,在这个干容重下,土样经过冻融后Pc和c不发生变化;干容重较小时,冻融后φ变化不大,随着干容重的逐渐增大,φ有少许增大。同一干容重下,随着冻结温度梯度的增大,冻融后Pc变化量减小,c的变化量增大,而φ的变化不大（呈逐渐增大趋势）。冻结温度梯度对力学性质的影响,主要是孔隙水的不同冻结方式造成的。 相似文献
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Allison J. Quiroga Zachary M. Thompson Kanthasamy K. Muraleetharan Gerald A. Miller Amy B. Cerato 《Acta Geotechnica》2017,12(5):1003-1020
The results of a series of laboratory tests on unimproved and cement-improved specimens of two clays are presented, and the ability of a bounding surface elastoplastic constitutive model to predict the observed behavior is investigated. The results of the oedometer, triaxial compression, extension, and cyclic shear tests demonstrated that the unimproved soil behavior is similar to that of soft clays. Cement-improved specimens exhibited peak/residual behavior and dilation, as well as higher strength and stiffness over unimproved samples in triaxial compression. Two methods of accounting for the artificial overconsolidation effect created by cement improvement are detailed. The apparent preconsolidation pressure method is considerably easier to use, but the fitted OCR method gave better results over varied levels of confining stresses. While the bounding surface model predicted the monotonic behavior of unimproved soil very well, the predictions made for cyclic behavior and for improved soils were only of limited success. 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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本文借助于先进的多功能大型高速高压环剪试验机,通过进行不同应力历史、剪切速度和正应力等条件下的系列试验,对吉林长春地区广泛分布的超固结粉质黏土在快速大剪切位移条件下的力学响应特性进行了试验研究。试验结果显示,前期固结历史和剪切速度不仅对超固结粉质黏土的抗剪强度变化具有显著的影响作用,并且对于其峰后应变软化亦产生明显的影响。在相同剪切速率和正应力条件下,前期固结压力越大,其峰值强度和残余强度值越大。不同剪切速度下的试验结果表明,在具有相同应力历史的条件下,峰值强度和峰后应力降低随着剪切速度的增大而增大。剪切速度越快越有利于土应变软化的产生以及剪切面的形成。在快速大剪切条件下对长春地区超固结粉质黏土抗剪强度变化起主要作用的是剪切过程中土体结构的变化和剪切面的生成,而剪切过程中孔隙水的作用并不显著。 相似文献
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利用从现场取得的原状土样,通过室内动三轴试验对循环荷载作用下的变形、孔压和强度特性进行研究。试验研究主要考虑了周围固结压力、循环剪切应力比、荷载频率和循环次数等因素的影响。研究表明,在循环荷载作用下,孔隙水压力和轴向应变均是一个波动上升的过程。当循环应力比增大时,动孔隙水压力变化幅值显著增加,而残余孔压也较大。同时,孔隙水压力值也随着周围压力的增大而明显增大。当作用荷载频率比较大时,需要更多的循环次数才能达到小频率作用荷载能达到的孔隙水压力值。但是,随着循环荷载作用次数的增加,频率对孔隙水压力的影响有减小的趋势。 相似文献
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钙质砂抗剪强度特性的环剪试验 总被引：2，自引：0，他引：2
珊瑚礁沉积的钙质砂与石英砂的物理力学性质有较大差别。对取自南海岛礁的钙质砂进行了单次往返环剪试验以分析钙质砂的抗剪强度特性,试验中考虑了相对密实度和竖向应力对结果的影响,并与相同级配和试验条件下的石英砂进行对比分析。结果表明：钙质砂正向剪切时应力-位移曲线为软化型,具有明显的残余强度特性,而反向剪切时则表现为硬化型,正向和反向剪切强度基本一致;石英砂正向剪切和反向剪切均表现为软化型。钙质砂正向剪切和反向剪切残余强度与峰值强度的比值在0.75～0.93之间;石英砂正向剪切和反向剪切残余强度与对应峰值强度的比值在0.89～0.96之间。相同级配和试验条件下,钙质砂残余强度均大于石英砂,且强度比值基本保持在1.05～1.3之间。在100、200 kPa竖向荷载作用下,钙质砂0.5～2.0 mm的颗粒发生了破碎,破碎率分别为4%和6%。 相似文献
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Triaxial shear testing of polished slickensided surfaces 总被引：1，自引：1，他引：0
Christopher L. Meehan Binod Tiwari Thomas L. Brandon J. Michael Duncan 《Landslides》2011,8(4):449-458
A series of consolidated-drained triaxial tests were performed on precut and polished clay specimens to measure their drained
residual strength. Two soils were tested during this research program: Rancho Solano Clay and San Francisco Bay Mud. Specimens
were tested using a specially modified triaxial compression device which was developed to minimize the effects of end-platen
restraint on the measured strengths. Special attention was paid to the influence of changing specimen area and membrane effects
during the test. Triaxial test results were compared with baseline measurements of drained residual shear strength that were
made for each of the clay soils using Bromhead ring shear tests and polished-specimen direct shear tests. Residual strength
values measured in the triaxial device were higher than the drained residual strengths measured in the Bromhead ring shear
apparatus and the direct shear device, indicating that this test approach is more challenging than the use of direct shear
tests conducted on polished slickensided surfaces. Comparison of single stage and multistage triaxial test data indicates
that multistage triaxial testing may work well for specimens that fail along a well-defined plane, provided that careful attention
is given to the effects of end platen restraint, membrane restraint, and changes in specimen area during shear. 相似文献
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基于试验基础上建立的经典弹塑性模型--剑桥模型能够准确描述正常固结土的应力-应变关系。当土体的应力历史上经历过卸载或受到循环交变荷载作用即进入超固结状态,它作为土的应力历史的反映,相比正常固结土受力特性有着显著的差异。为研究超固结因素对土体加载特性的影响,在引入能考虑超固结状态影响的下负荷面剑桥模型后,通过三轴压缩和剪切试验对处于超固结状态下土体的受力特性进行了对比分析,并对循环剪切加载下的应力-应变关系以及超固结比的演化规律进行了研究。结果表明,下负荷面剑桥模型能准确反映超固结因素对土体力学特性的影响,相比原状土有着更高的屈服强度。而通过数值模拟自由场地基在地震作用下的动力响应可以看出,超固结因素对地基的动力响应起到了不可忽略的影响,尤其在强震下更需要考虑其影响。在自由场地基地震动力响应基础上,通过对桩柱结构桩-土耦合系统在地震作用下非线性动力响应的模拟对土体非线性以及超固结因素的影响进行了对比研究,研究表明：土体的非线性因素能显著降低结构振动响应中的高频成分,由于土体在交变加载下很快进入超固结状态,相对于剑桥模型,下负荷面剑桥模型在考虑超固结因素后土体的承载性能显著提高,尤其在强震作用下超固结因素带来的影响更加明显,因此,建议对桩基结构物地震响应研究考虑超固结因素影响,以提高桩基结构物地震响应模拟的精确度和可靠性。 相似文献
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通过室内三轴试验研究美国中部密西西比河流域低塑性粉土的液化重固结后剪切强度。研究成果表明,正常固结低塑性粉土液化后不排水剪切强度Su随重固结度的增加而提高,而且呈现类固结现象。类似于未受震动的情况,液化完全重固结后不排水剪切强度比Su,OC/Su, NC与固结比OCR呈幂指数关系,只是幂指数相对于未受震动情况稍大。随着OCR的增加,完全重固结引起的不排水剪切强度变化?Su, recon先提高后降低,当OCR =3.42时,?Su, recon达到最大值。液化完全重固结后不排水剪切行为不具有准稳态现象,随着轴应变增加,应力逐渐增加直至达到临界状态。另外,液化完全重固结后不排水剪切应力-应变曲线可被有效固结应力? ′c归一化。最终提出了计算液化完全重固结后低塑性粉土不排水剪切强度的计算公式。 相似文献
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We study the creep properties of clastic soil in residual state. The intact samples are taken from a reactivated slow-moving landslide in the Three Gorges Reservoir Region, China. Firstly, the patterns of the landslide movement are analysed based on recent monitoring data, which indicate that the soil within the shear zone is undergoing two deformation processes: a creep phase, characterised by different creep rates, and a dormant phase. We then study the creep behaviour of the soil samples through a series of ring shear creep tests under various shear stress conditions. The creep response depends strongly on the ratio of the shear stress to the residual strength, and the normal effective stress, whereas the creep rate decreases due to strength regain. The long-term strength of the clastic soil is close to the residual strength. Therefore, the residual strength obtained from conventional shear test, which is less time consuming than creep test, can be used in long-term stability analyses of creeping landslides. 相似文献
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冲击荷载作用对土体力学特性影响较大,为了研究此特性,基于天津滨海结构性软黏土,以空心圆柱扭剪仪模拟冲击荷载作用,并在冲击荷载作用前后对土体进行不固结不排水三轴试验,对比研究不同试验条件下结构性软黏土力学特性。试验结果表明:低围压常规三轴剪切试验状态下,土体表现出弱应变软化现象,且土体抗剪强度包线不能用直线表示,而是可由两条直线近似拟合而成;冲击荷载作用时,在一定应力范围内,冲击荷载越大,土体轴向应变、孔隙压力以及主应力差峰值也越大;冲击荷载作用后三轴剪切试验各围压下土体都呈应变硬化型,主应力差峰值均大幅减小,且土体抗剪强度包线均可用直线表示,c、φ值也远小于未受冲击荷载时三轴剪切试验相应数值。最后,总结分析冲击荷载作用对软黏土强度的影响,并拟合得到强度折减与围压、冲击荷载的关系,为实际工程中承受冲击荷载的结构性软黏土强度确定提供参考。 相似文献
19.
利用DTA-138型环剪仪对向家坝水电站库区某滑坡滑带土重塑样开展了大位移剪切条件下的环剪试验,探讨了剪切速
率（小于100 mm/min）、细粒（<0.075 mm）含量对残余强度的影响,对比分析了原状样滑面和重塑样剪切面的细粒含量变化以
及微观结构差异。研究结果表明：滑带土的原状样滑面细粒含量高于滑带,重塑样剪切面细粒含量高于剪切面上下区域;当剪
切速率由0.109 mm/min增大到98mm/min时,残余强度应力比的变化呈现先减后增的凹型,在1.09 mm/min时达到最小值（重塑
样Rr-1#,Rr-4#,Rr-5#残余强度应力比最小值分别为0.34,0.42,0.39）;残余强度随细粒含量的增加先增大后减小,呈二次多项
式关系,其临界值约为56%;随着细粒含量的增加,残余强度变化幅度随法向应力的增加而增大。 相似文献
20.
In this study the effect of cyclic loads on monotonic shear strength has been studied on torsional apparatus. Tests have been conducted on both reconstituted and undisturbed fine-grained hollow soil specimens. The plasticity index of soils is in the range from 2 to 33 for reconstituted specimens, prepared by dry pluviation, and from 5 to 13 for undisturbed soil specimens. The existence of a critical shear strain level, called yield shear strain, where softening starts, is determined from cyclic tests. The level of cyclic yield strain is ± 0.75% for the reconstituted soil specimens and ± 0.5% for the undisturbed soils. If soil undergoes a cyclic shear strain level below the cyclic yield strain, reduction of monotonic strength of reconstituted and undisturbed specimens is limited, but when cyclic shear strain level is larger than yield strain monotonic strength decreases down to 40% of its initial strength. 相似文献