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基于一维和三维固结挤土桩沉降时效计算分析 总被引:1,自引:0,他引:1
饱和软黏土地基中的挤土桩,施工引起的桩侧土体超孔隙水压力消散和竖向荷载引起的桩底土体固结是导致其沉降的主要因素。基于三维固结理论,研究了桩侧地基土再固结沉降的变化规律,并从桩-土相互作用的原理出发,结合边界条件,推导出了在桩侧地基土再固结沉降的作用下挤土桩沉降的计算公式。运用太沙基一维固结理论并采用分层总和法计算竖向荷载作用下桩底土体的沉降。提出了饱和软土中挤土桩沉降时效的计算方法。并对工程实例进行了计算分析,其结果符合工程实际沉降规律。 相似文献
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为了研究超载预压软土的次固结特征,分析超载预压处理软土地基的工后沉降,文章考虑应力历史对软土结构性的影响,模拟现场工况,对重塑洞庭湖软土试样进行超载预压后再压缩的一维固结蠕变试验。研究结果表明:经过超载预压的软土卸荷后再进行加载,压缩变形过程中主固结时间明显缩短,约为未经超载预压处理软土主固结时间的1/3,打设排水竖井对软土主固结时间几乎没影响;预压荷载越大,次固结系数越小,超载预压有利于消除软土的次固结沉降;随着建(构)筑物荷载的增加,次固结系数增大;打设排水竖井,未经预压处理软土的次固结系数略有增加,经过超载预压处理软土的次固结系数略有减小,但影响效果不是很明显。考虑应力历史,引入超载增量比,发现次固结系数与超载增量比呈线性递减关系,建立了相应的计算模型,提出了次固结沉降计算公式。试验及分析结果对预压处理地基的设计和施工具有一定的指导意义。 相似文献
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Vertical drains are widely used in soft ground improvements to accelerate the consolidation process. This paper develops a new simplified Hypothesis B method for calculating the consolidation settlement of a soil layer improved by vertical drains under the instant and ramp loadings. As a comparison, the traditional Hypothesis A method is also used to calculate the settlement. Then, a fully coupled finite element consolidation analysis is utilized to examine and verify this simplified method and Hypothesis A method. For the instant loading, Carrillo‐Barron method and Zhu‐Yin method are used to obtain the average degree of consolidation for vertical drain system. Typical parameters, such as over‐consolidation ratio (OCR), smear zone, and space ratio of vertical drains, are considered. It is found that the calculation results from the new simplified method in this study agree well with finite element simulations, and relative errors are in the range of 0.1% to 12.3%. Comparatively, there are obvious differences between the calculated results from Hypothesis A method and finite element results. Carrillo‐Olson method and Zhu‐Yin method are utilized to obtain the average degree of consolidation for the vertical drain system to consider the ramp loading. Equivalent time is determined from half of the construction period to calculate the creep compression under the ramp loading. The accuracy of this simplified Hypothesis B method using both Carrillo‐Olson method and Zhu‐Yin method is acceptable with the relative errors less than 9.4%. 相似文献
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In 1986, the Malaysian Highway Authority constructed a series of trial embankments on the Muar Plain (soft marine clay) with the aim of evaluating the effectiveness of various ground improvement techniques. This study investigates the effect of two such ground improvement schemes: (a) preloading of foundation with surface geogrids and synthetic vertical drains and (b) sand compaction piles. The paper is focused on the finite element analysis of settlements and lateral displacements of the soft foundation. In scheme (a), the numerical predictions are compared with the field measurements. In scheme (b), only the numerical analysis is presented and discussed in the absence of reliable measurements due to the malfunctioning of the electronic extensometer and inclinometer system during embankment construction. The current analysis employs critical state soil mechanics, and the deformations are predicted on the basis of the fully coupled (Biot) consolidation model. The vertical drain pattern is converted to equivalent drain walls to enable plane strain modelling, and the geogrids are simulated by linear interface slip elements. The effect of sand compaction piles is investigated considering both ideal drains and non-ideal drains, as well as varying the pile stiffness. © 1997 by John Wiley & Sons, Ltd. 相似文献
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软土一般具有结构性,试验表明,加荷比会对结构性软土压缩特性有很大的影响,加荷比增加土体剪切趋势,降低土体结构强度,使土体的结构屈服应力值和压缩指数降低。在试验的基础上,给出了考虑加荷比影响的结构性软土地基的沉降计算方法。工程算例表明,在加载终值相同的情况下,如果加荷比过大,就会增大结构性软土地基沉降产生附加沉降,为了减小对软土结构性的破坏而影响土体压缩特性,建议对结构性软土的加荷比不宜采用为1:1以上,宜采用1:0.25或1:0.5。 相似文献
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山区机场高填方地基工后沉降变形简化算法 总被引:3,自引:0,他引:3
我国西部山区机场建设的迅猛发展导致高填方地基日益增多。填方体量大、高度高,且存在软弱原地基是此类填方地基的主要特点,这也增加了预测其工后沉降变形的难度。针对山区机场高填方地基的构成特点,将其工后沉降变形的计算分为软弱原地基和上部粗粒填料填方体两部分进行考虑。在分析比较已有简化算法的基础上,对软弱原地基的沉降变形提出了可以考虑施工加载过程的简化计算方法,并应用此法对实际工程进行了计算,所得结果与现场实测值吻合相对较好;通过对室内试验数据进行分析,发现双曲线模型亦能较好的预测粗粒料的蠕变变形,进而在此基础上提出了计算粗粒料填方体长期蠕变变形的简化算法。 相似文献
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水库蓄水对库底沉降影响的数值分析 总被引:1,自引:0,他引:1
抽水蓄能电站常采用沥青混凝土进行库底防渗护面处理,过快的蓄水速率和过大的蓄水水头可能导致库底护面开裂。以某抽水蓄能电站的上水库为例,用考虑Biot固结理论的平面有限元法,在依据沉降观测点实测资料优化确定地基土模型参数的基础上,分析了水库蓄水速率和蓄水水头对库底沉降量、沉降率及库底沥青混凝土应变率的影响。结果表明,蓄水速率对地基的最终沉降值影响不明显,而在蓄高水位历时内,地基的沉降增量和最大沉降率均与蓄水速率和蓄水水头有很好的相关性,沥青混凝土的最大应变率仅与蓄水速率相关。 相似文献
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