共查询到19条相似文献，搜索用时 125 毫秒
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饱和粉土液化和应变特性试验研究 总被引：3，自引：0，他引：3
对取自徐州市棠张镇拟建京沪高速铁路路基的粉土,在试验室内按不同的干密度和细粒含量进行重塑,完成了三组不同干密度和四组不同细粒含量的振动三轴液化试验。分析了粉土干密度和细粒含量对饱和粉土抗液化强度的影响;通过曲线拟合方法建议了粉土振动液化过程中的孔压增长模型和永久应变势模型,给出了模型参数。 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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徐州市棠张镇饱和粉土液化性能试验研究 总被引：8，自引：2，他引：6
徐州市棠张镇高速铁路路基的粉土粘粒含量少于1．5％、粉粒含量约为80％,在强烈地震作用下存在着液化可能性,为了分析该路基粉土的液化特性,进行了多组振动三轴液化试验。对试验结果进行分析发现,该地区的粉土振动孔压发展模式与Seed提出的用反正弦三角函数拟合的砂十振动孔压发展模式不同,可以用双曲线进行拟合。采用最大往返剪切作用面上的应力条件确定了该地区的孔压发展模式的拟合参数,为该地区粉土地震液化动力计算分析提供了所需的地震孔隙水压力增长模型。同时,本文指出粉土的密度和结构是振动孔压发展的重要影响因素。 相似文献
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除饱和砂土液化外,饱和粉土地震液化问题也是岩土地震工程中一个重要的研究课题。饱和粉土地基的地震液化及变形可以采用多种地基加固方法防治,碎石桩技术是常用方法之一。碎石桩复合地基的抗液化效应,主要是增加桩周土体的密度、利于桩体的排水以及由桩体分担地震水平剪应力（桩体减震作用）。但由于粉土的土质特性,粉土-碎石桩复合地基的抗液化特性与砂土有着明显的差异。本文结合目前国内外碎石桩复合地基抗液化研究的最新进展,对粉土-碎石桩的密实、排水减压和减震作用做了较详细的评述,最后提出了关于碎石柱复合地基抗液化特性需要进一步研究的问题。 相似文献
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《国际地震动态》2017,(5)
黄土液化的判别是工程界长期存疑的问题,现场黄土含水量较低,剪切波速较高,而实验室对其饱和,饱和过程对其土体结构影响还不确定,又由于固结比对土体刚度的影响仍然没有定论,这就导致室内黄土动三轴液化试验结果与现场力学指标一直无法建立联系。另一方面,黄土从颗粒组成来说,属于细粒土范畴,细粒土液化判别方法应可为黄土液化判别提供参照,但由于实验室配制试样相对密度、土体骨架强度及细颗粒赋存形式很难控制,导致细颗粒对土体液化势影响研究饱含争议与矛盾。本文紧密结合工程和科研工作需求,设计了一系列原状黄土在均等固结与偏压固结下的动三轴弯曲元试验,以及原状黄土在动三轴内饱和过程及饱和后的剪切波速试验,并且对一个饱和黄土场地进行了现场原位测试,回顾了现有标贯液化判别方法,对含细粒土体液化判别指标进行了系统研究,改进了细粒土液化初判准则以及含细粒砂性土液化判别式,最后对CPT液化判别方法的可靠性进行了数据检验。具体工作和成果包括:(1)采用动三轴弯曲元试验系统,对兰州市多个场地原状黄土进行了均等固结与偏压固结下剪切波速测试,证实了相关固结比对土体刚度影响的试验研究结果,进一步对比均等固结与偏压固结下试样轴向变形,分析了固结比对土体刚度影响的机理。(2)采用动三轴弯曲元试验系统,首先对原状黄土饱和过程进行了剪切波速跟踪测试,并进一步对比饱和黄土与原状黄土在同一逐级加压的过程中剪切波速与轴向变形测试值,最后通过与现场饱和黄土场地水位上下黄土层实测标贯击数、剪切波速对比,分析了原状黄土遇水及饱和后的软化特征。(3)通过对比唐山、海城地震两个液化地区粉土与砂土的剪切波速与标贯击数统计关系,发现对于剪切波速相同的饱和粉土和砂土,由于粉土的触变性,粉土标贯击数显著小于砂土。结合NCEER推荐的基于SPT与VS的液化判别方法,建立了3个细粒含量下临界剪切波速与临界标贯击数的相关关系,证实了含细粒土体的触变性。(4)回顾了目前国内外有关含细粒土液化研究现状,结合1975年海城地震,1976年唐山地震,1999年土耳其Kocaeli地震和台湾集集地震液化与非液化土数据分析,详细对比了现有液化判别式和初判条件的优劣,改进了细粒土液化初判准则以及含细粒砂性土标贯液化判别式。(5)回顾了NCEER推荐的Robertson的CPT液化判别方法和Olsen的CPT液化判别方法,通过对1999年台湾集集地震液化与非液化土数据分析,并将判别结果与SPT方法判别结果进行比较,指出了CPT液化判别方法还没有达到SPT方法的准确性,但是CPT的土分类图却是其最大的优势所在。 相似文献
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Shake table test of soil-pile groups-bridge structure interaction in liquefiable ground 总被引：2，自引：1，他引：1
<正>This paper describes a shake table test study on the seismic response of low-cap pile groups and a bridge structure in liquefiable ground.The soil profile,contained in a large-scale laminar shear box,consisted of a horizontally saturated sand layer overlaid with a silty clay layer,with the simulated low-cap pile groups embedded.The container was excited in three E1 Centra earthquake events of different levels.Test results indicate that excessive pore pressure(EPP) during slight shaking only slightly accumulated,and the accumulation mainly occurred during strong shaking.The EPP was gradually enhanced as the amplitude and duration of the input acceleration increased.The acceleration response of the sand was remarkably influenced by soil liquefaction.As soil liquefaction occurred,the peak sand displacement gradually lagged behind the input acceleration;meanwhile,the sand displacement exhibited an increasing effect on the bending moment of the pile,and acceleration responses of the pile and the sand layer gradually changed from decreasing to increasing in the vertical direction from the bottom to the top.A jump variation of the bending moment on the pile was observed near the soil interface in all three input earthquake events.It is thought that the shake table tests could provide the groundwork for further seismic performance studies of low-cap pile groups used in bridges located on liquefiable groun. 相似文献
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Cement-mixed piles, as countermeasure against liquefaction of silt and sand ground, can improve the shear strength and bearing capacity of foundation soil, meaning cement-mixed piles are capable of resisting displacement when an earthquake happens. However, investigations of cement-mixed piles by experimental methods such as the shaking table test is few and far between. It is especially true for the seismic performance of cement-mixed piles in liquefiable railway foundations in high seismic intensity regions. To this end, a cross-section of the Yuxi-Mengzi railway was selected as the prototype and studied by the shaking table test in this study. The results showed that composite foundation of cement-mixed piles was not liquefied when the seismic acceleration was lower than 0.30g. In the process of acceleration increasing from 0.30g at 2Hz to 0.60g at 3Hz, the upper middle silt outside slope toe was partly liquefied. The foundation soil under the shoulders and center of subgrade was far from the initial liquefaction criterion during the test. Cement-mixed piles can effectively reduce the embankment settlement and differential settlement. It can be concluded that, the design of cement-mixed piles can ensure the seismic performance of the subgrade, and satisfy the seismic design requirements of the Yuxi-Mengzi railway in areas of VⅢ degrees seismic fortification intensity. 相似文献
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黄土液化演化过程的微观机理分析是液化防御的科学问题之一。通过微细观及动力学试验探索黄土液化的本质和影响因素。首先用CT细观扫描实验探索黄土渗透液化的细观变化,研究表明土体液面上升的根本原因是弱碱性盐类胶结物的吸水作用导致土样含水面整体上升;试样达到高饱和度,大孔隙周围颗粒间胶结物质破坏后有效应力为零,土层液化。粉土的孔隙尺寸和特殊的胶结物质导致高饱和度。土样微观结构的差异也会影响土的液面上升和破坏强度。针对低黏性粉土、粉质砂土及粉质黏土的三类黄土液化实验分析表明,低黏性粉土动荷加载时间更短,更易于液化,即低粘性粉土液化最为严重,粉质砂土为中等液化,粉质黏土相比其他黄土类别不易液化。电镜扫描土样微观结构参数分析表明,土颗粒周围胶结物质的化学元素比值(Ca/Fe),以及土颗粒粒径分布和孔隙尺寸(孔隙与颗粒比)均影响液化等级,可初步判断液化的强弱。 相似文献
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为研究倾斜场地中桩基的动力响应,以2011年新西兰地震中受损的Dallington桥为原型,设计并完成可液化倾斜场地桥梁桩-土相互作用的振动台模型试验。试验再现了喷砂、冒水、地裂缝、场地流滑等宏观现象。试验结果表明,土层足够的液化势及惯性是造成倾斜场地侧向流滑的必要条件;浅层土相比深层土更易液化,液化层中的加速度由下至上呈现逐渐衰减的趋势,而未液化砂土层却表现为逐渐增大的特征;深部测点的桩侧土压力明显大于浅部测点,且土体的液化会弱化土对结构的压力;结构应变最大值位于上部桥台,而结构弯矩在桩身中部及土层分界面附近出现两个较大值,桩端嵌固及倾斜场地流滑是造成出现两个弯矩较大值的主要原因。 相似文献
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液化土中桩基础动力响应规律一直是工程抗震领域关注的热点问题。本文基于非液化砂土和不同厚度饱和砂土中的2×2群桩结构模型振动台试验,通过输入一定峰值加速度和频率的正弦波,对群桩在非液化土层和两种不同厚度饱和砂土层中的横向动力响应特性进行振动台试验研究。研究结果表明:在正弦波输入情况下,非液化砂土中群桩承台加速度和位移时程与台面输入时程相比,波形变化规律与峰值大小均相差不大;而对两种不同厚度饱和砂土中承台加速度和位移峰值放大较多,在相对较薄的饱和砂土中群桩承台加速度峰值较台面输入放大了1.83倍,较台面输出位移峰值放大了1.58倍;在相对较厚的饱和砂土中承台加速度和位移峰值则分别放大了2.18倍和1.91倍,说明在相同输入条件下,较厚的饱和砂土在发生液化后群桩承台的动力响应更加显著。 相似文献
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Softening and strength loss of sands with increasing excess pore water pressure under repeated loads is well-known. However, extensive damage to the built environment also occurs at the sites underlain by fine grained soils during seismic shaking. The primary objective of this study is to investigate the factors affecting cyclic behavior of saturated low-plastic silt through laboratory testing. For this purpose, an extensive laboratory testing program including conventional monotonic and cyclic triaxial tests was carried out over reconstituted silt samples. The effects of the inherent soil properties and the effects of loading characteristics on the cyclic response of saturated low-plastic reconstituted silt samples were examined separately. Based on the test results, a model was introduced to estimate the effect of initial shear stress on the cyclic response. Besides, liquefaction susceptibility of the samples was examined via current liquefaction susceptibility criteria. 相似文献
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Shaking table tests were conducted on saturated clean Vietnam sand in the large biaxial laminar shear box (1880 mm×1880 mm×1520 mm) at the National Center for Research on Earthquake Engineering (NCREE), Taiwan. The settlement of sand specimens was measured and evaluated during and after each shaking test. Without liquefaction, the settlement of sand caused by shaking is very small. Significant volume changes occur only when there is liquefaction of sand. The volumetric strain of liquefied sand was calculated according to the measured settlement and the thickness of liquefied sand in the specimen. Relations between volumetric strain after liquefaction and the relative density of saturated clean sand were developed for various shaking durations and earthquake magnitudes. They are not affected by the shaking amplitude, frequency, and direction (one- or multidirectional shaking). 相似文献
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It is well known that the generation of excess pore water pressure and/or liquefaction in foundation soils during an earthquake often cause structural failures.This paper describes the behavior of a small-scale braced wall embedded in saturated liquefiable sand under dynamic condition.Shake table tests are performed in the laboratory on embedded retaining walls with single bracing.The tests are conducted for different excavation depths and base motions.The influences of the peak magnitude of the ground motions and the excavation depth on the axial forces in the bracing,the lateral displacement and the bending moments in the braced walls are studied.The shake table tests are simulated numerically using FLAC 2D and the results are compared with the corresponding experimental results.The pore water pressures developed in the soil are found to influence the behavior of the braced wall structures during a dynamic event.It is found that the excess pore water pressure development in the soil below the excavation is higher compared to the soil beside the walls.Thus,the soil below the excavation level is more susceptible to the liquefaction compared to the soil beside the walls. 相似文献
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通过成都平原砾性土场地勘察测试,研究汶川地震中大量砾性土液化场地的基本特性,找出一般规律,对砾性土场地液化发生主客观原因提出解释,并修正以往若干认识偏差.分析表明:汶川地震液化砾性土层粒径范围宽,含砾量5%~85%甚至更大,同时其实测剪切波速140~270 m·s~(-1),修正剪切波速160~314 m·s~(-1),都远超历史记录;液化砾性土场地1/2集中在Ⅷ度区内,表明如砂土层液化一样,砾性土场地大规模液化需要较强地震动触发,但超过触发强度后液化规模增长均有限;成都平原浅表地层二元基本结构是汶川地震中出现大量砾性土场地的客观条件之一,该结构可使饱和砾性土层处于封闭状态,构成了砾性土液化的基本条件;虽然液化砾性土层剪切波速很高,但实际上大多松散状态,是此次地震大量砾性土场地发生液化的客观条件之二;地震中地表(井中)喷出物与地下实际液化土类大相径庭,且液化层埋深大多小于6.0 m,以往以地表喷出物反推地下液化层土性类型的做法不再成立;认为砾性土层波速大、透水性好而不会液化的传统认识也不再成立,但砾性土层液化条件与砂土层液化条件不同,前者要求更高. 相似文献