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针对砂土地震液化预测问题,基于Fisher判别分析原理(FDA),选用平均粒径、不均匀系数、标贯击数、地下水水位、砂层埋深、剪应力与有效上覆应力比、地震烈度.震中距等8个实测指标为判别因子,建立Fisher线性判别函数模型,对砂土液化进行预测.研究结果表明,Fisher判别分析结果与神经网络输出结果一致,优于规范法和Seed法判别结果,验证了该模型的合理性和可靠性.运用该模型进行判别分析,简易方便,分类效率高,对砂土液化判别快速、有效,模型适用性强,具有一定的工程应用前景. 相似文献
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对于饱和砂土液化判别,目前规范要求以标准贯入试验为主,以静力触探为辅,有经验地区可采用剪切波速测试,但就目前的每种判别方法都有一定的局限性。在实际工作中采用综合评价的方法,就能减少单一评价方法的局限性。综合应用标准贯入试验法、静力触探试验法和剪切波速测试法,并对各种判别方法的判别结果进一步分析,便可综合评价场地饱和砂土的液化趋势。实例表明,综合应用各种液化判别方法进行综合评价,提高了评价结果的准确性。 相似文献
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饱和砂土地震液化判别的可拓聚类预测方法 总被引:4,自引:0,他引:4
基于可拓学的物元模型和聚类分析原理,提出了饱和砂土地震液化判别的可拓聚类方法。选取地震烈度、震中距、砂层埋置深度、地下水位、标贯击数、平均粒径、不均匀系数和动剪应力比等8个影响因素,作为饱和砂土地震液化的评价因子,构建了经典域物元和节域物元。应用物元理论和可拓集合中的关联函数,建立预测模型,通过聚类分析得到饱和砂土地震液化的判别结果。实例研究表明,该模型能客观地反映砂土的液化规律,可拓聚类预测方法应用于饱和砂土地震液化判别是有效可行的。 相似文献
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影响砂土液化的因素有很多,建立多指标的液化预测模型非常有必要。目前所有的多指标砂土液化预测模型,均默认选取的判别因子之间相互独立,不存在相关性,可能导致各判别因子之间存在信息叠加而发生误判。以唐山地震砂土液化的25个案例为样本,选取8个影响因素作为砂土液化预测的初始判别指标,首先采用主成分分析(PCA)对各判别指标进行分析,对存在相关性比较高的指标进行了降维处理。基于降维后的4个主成分换算得到新的样本数据,以18个案例为学习样本,建立主成分分析与距离判别分析(DDA)相结合的砂土液化预测模型。利用建立的预测模型对18个案例进行回判,结果全部正确。对其他7个案例的液化情况进行了预测,并与规范法、Seed方法、BP法、DDA法的判别结果进行分析比较,结果表明基于主成分分析与距离判别方法的砂土液化判别模型预测准确率为100%。将模型应用于工程实例,判别结果也与实际情况一致,表明该模型具有良好的预测功能,可在实际工程中应用。 相似文献
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在砂土液化多指标综合判别法中,采用的判别因子数量一般为5~12,为防止特征冗余,引入核主成分分析(KPCA)对原始样本进行非线性特征提取,同时基于高斯过程分类(GPC)原理,构建了砂土液化预测的KPCA-GPC模型。以唐山地震砂土液化的25个案例为样本,选取平均粒径D50、地下水位dw、标准贯入击数N63.5、砂层埋深ds、地震烈度I、震中距离L、不均匀系数Cu、剪应力与有效上覆应力比τ_d/σ'v共8个指标作为判别因子,对该模型进行验证。研究结果表明:距离判别分析(DDA)、高斯过程分类(GPC)、Seed法的判别准确率分别为83%、83%、67%,而KPCA-DDA和KPCA-GPC的判别准确率均为100%,由此说明消除特征冗余的必要性及KPCA-GPC模型的适用性;同时,与DDA、SVM、BP等确定性判别方法相比,GPC可获得具有概率意义的砂土液化预测结果。 相似文献
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本文利用我国唐山、营口、海城等地区的有关地震中砂土液化的实际资料,通过对《工业与民用建筑抗震设计规范》中所推荐的以标准贯入击数法对饱和砂土液化判别公式的分析,提出了修改意见,并对公式中ds符号给出了明确的含义。 相似文献
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砂土液化预测的Fisher判别模型及应用 总被引:3,自引:0,他引:3
基于Fisher判别理论建立了砂土液化可能性的Fisher判别分析(FDA)模型。在分析砂土液化影响因素的基础上,选取烈度、震中距、地下水位、砂层埋深、标贯击数、平均粒径、不均匀系数、剪应力比等8个实测特征指标作为FDA模型的预测指标。利用砂土液化的实测数据作为训练样本进行训练,建立FDA模型对砂土液化进行预测,并用其他未参加训练的实测数据进行了验证。研究结果表明,FDA模型简便可行、预测精度高,是解决砂土液化预测问题的有效方法之一。 相似文献
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改进了进化遗传算法,提出了新的交叉算子和变异算子,使之具有更好的全局收敛能力。砂土液化是一种危害极大的地震破坏现象,其影响因素很多,选择地震烈度、砂土粒径、相对密度、标贯击数和有效正应力为判据,利用改进了的进化遗传算法建立了砂土地震液化的判别模型。与现场液化情况比较表明,改进进化遗传算法应用于砂土地震液化的判别效果良好。 相似文献
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Peter G. Nicholson 《Geotechnical and Geological Engineering》2006,24(5):1259-1269
Field penetration tests and shear wave velocity measurements are both established and accepted methods for evaluating liquefaction
potential in soils. The results produced by the two methods are generally well correlated. However, recent studies have shown
that when investigating tropical lagoonal deposits, the same accepted methods for evaluating liquefaction potential often
produce significant discrepancies in results. This discrepancy is most apparent in saturated lagoonal deposits of calcareous
gravelly sand (or sandy gravel), which tend to exhibit low penetration resistance values but relatively high shear wave velocities.
These disparate test results can suggest different soil classifications under current building codes. Ambiguity in the code
may allow for a potentially unconservative classification, which may in turn allow for the use and construction of less costly,
lighter weight foundation systems than warranted. Equally as important, the potential for unconservative design as related
to liquefaction appears to be high when shear wave velocity measurements are used as a basis for evaluation in these types
of lagoonal deposits. Because of this, it is strongly recommended that caution should be excercised when determining seismic
design parameters in these types of geologic environments. A hypothesis to explain the discrepancies in the results of evaluation
methods and a suggested design protocol is proposed. 相似文献
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饱和砂土液化是地震引发地基变形失稳、建筑受损破坏的主因之一,合理判定液化可能性是勘察实践和理论研究的重大课题。国内规范要求砂土液化判别仍以标准贯入试验为主,静力触探等原位测试方法为辅,静力触探较其他原位测试手段,在操作便利性、数据采集连续性、测试成本和抗干扰能力等方面更具优势。针对国内规范常用静力触探砂土液化判别方法进行了分析研究,并结合勘察实例进行了计算和对比,探讨了静力触探判别液化方法的土层适用性,并提出有关改进建议。 相似文献
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Tsunami runup and drawdown can cause liquefaction failure of coastal fine sand slopes due to the generation of high excess
pore pressure and the reduction of the effective over burden pressure during the drawdown. The region immediately seaward
of the initial shoreline is the most susceptible to tsunami-induced liquefaction failure because the water level drops significantly
below the still water level during the set down phase of the drawdown. The objective of this work is to develop and validate
a numerical model to assess the potential for tsunami-induced liquefaction failure of coastal sandy slopes. The transient
pressure distribution acting on the slope due to wave runup and drawdown is computed by solving for the hybrid Boussinesq—nonlinear
shallow water equations using a finite volume method. The subsurface pore water pressure and deformation fields are solved
simultaneously using a finite element method. Two different soil constitutive models have been examined: a linear elastic
model and a non-associative Mohr–Coulomb model. The numerical methods are validated by comparing the results with analytical
models, and with experimental measurements from a large-scale laboratory study of breaking solitary waves over a planar fine
sand beach. Good comparisons were observed from both the analytical and experimental validation studies. Numerical case studies
are shown for a full-scale simulation of a 10-m solitary wave over a 1:15 and 1:5 sloped fine sand beach. The results show
that the soil near the bed surface, particularly along the seepage face, is at risk to liquefaction failure. The depth of
the seepage face increases and the width of the seepage face decreases with increasing bed slope. The rate of bed surface
loading and unloading due to wave runup and drawdown, respectively, also increases with increasing bed slope. Consequently,
the case with the steeper slope is more susceptible to liquefaction failure due to the higher hydraulic gradient. The analysis
also suggests that the results are strongly influenced by the soil permeability and relative compressibility between the pore
fluid and solid skeleton, and that a coupled solid/fluid formulation is needed for the soil solver. Finally, the results show
the drawdown pore pressure response is strongly influenced by nonlinear material behavior for the full-scale simulation. 相似文献
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哈达山水利枢纽坝基砂层震动液化研究 总被引:1,自引:0,他引:1
砂层震动液化问题是哈达山水利枢纽工程首要的工程地质问题。根据工程勘察取得的大量试验资料,通过标贯、GJS原状取砂、OYO 3000系列密度测井及瑞利波测试等综合方法,对砂层震动液化问题进行了深入的研究,为坝基加固处理提供了重要依据。其中瑞利波测试技术用于砂土震动液化是一个新的尝试。 相似文献
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动力作用下砂土的残余体变及其时域连续模型 总被引:1,自引:0,他引:1
通过对砂土动力剪切荷载作用过程中的土骨架的弹性和塑性分析,研究了土骨架接触面部分可能发生的弹性恢复和永久变形以及破碎引起的最剧烈的塑性变形;并且,提出了可以通过液化前后颗粒粒径的质量百分含量的对比试验,来验证破碎模型的合理性;为进行砂土动力非线性变形和液化的数值模拟,结合砂土的剪切非线性的本构,总结了更为简化的时域连续的函数经验公式,使得在时域内进行土壤动力特性和动力非线性反应分析,以及用剪胀性理论解释动力液化和变形问题易于进行。 相似文献