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针对新型核电工程结构AP1000核岛结构设计地基中的5类非坚硬岩场地,即硬岩场地、软岩场地、上限软-中等土场地、软-中等土场地和软土场地,采用一维土层场地模型开展场地土和计算基底条件对设计地震动影响计算分析。分析中,场地模型的计算基底剪切波速分别取为700、1 100、2 438 m/s,计算基底输入地震动分别选择基于核电建设相关技术文件和规范规定的反应谱RG1.60谱、AP1000谱和HAD101/01谱（5个阻尼比）合成的人工地震动时程。计算分析表明：非坚硬岩场地会导致场地地震动峰值加速度及频谱特性显著变化,场地越软影响程度越显著;除软土场地外,场地对地震动峰值加速度和反应谱的影响均为放大作用,软土场地对地震动较低频段反应谱有放大作用,但对峰值加速度和较高频段反应谱具有强烈的减小作用;对于各类场地,计算基底及其剪切波速的变化均会导致地表地震动峰值及频谱特性明显甚至显著变化,其影响程度与计算基底剪切波速成正比;随着场地由硬变软,计算基底剪切波速的变化对场地地震动的影响程度大为减小,至软土场地几乎不产生影响。考虑到场地类型及计算基底选取对场地地震动的显著影响,我国核电厂建设引用AP1000标准设计时应合理分析场地的适宜性。 相似文献
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为探究荷载作用下软土地基直接拼接拓宽路堤受力和变形特征,利用自行设计制造的模型试验系统,通过改变软土地基差异沉降、土工格栅加铺层数对软土地基高速公路直接拼接路堤进行一系列模型试验,研究各种工况下旧路与新拓宽路堤土中应力变化。试验结果表明,拓宽路堤在荷载作用下新旧路各断面土中竖向应力随着荷载的增大而增大,受路堤填土边坡与下伏地基侧向约束条件的影响,荷载作用下土中竖向应力在填土路堤与地基内沿深度方向呈现先减小、后增大、再减小的分布特征;软土地基拓宽路堤差异沉降对新旧路结合部位土中竖向应力影响较大,土中竖向应力随着差异沉降增大而增大;旧路范围内土中竖向应力受差异沉降的影响不大;在拓宽路堤填土的顶部和底部各布设一层土工格栅加筋层时可明显减小路堤土中竖向应力和路堤沉降：相同荷载作用下对比无加筋路堤,铺设2层土工格栅加筋路堤的顶面沉降最大可以减少62%,土工格栅加筋对软土地基拓宽路堤沉降有较好的控制作用。 相似文献
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Stiffened deep mixed (SDM) column is a new ground improvement technique to improve soft soil, which can be used to increase bearing capacity, reduce deformation, and enhance stability of soft soil. This technique has been successfully adopted to support the highway and railway embankments over soft soils in China and other countries. However, there have been limited investigations on its consolidation under embankment loading. This paper developed an analytical solution for the consolidation of embankment over soft soil with SDM column in which core pile is equal to or shorter than outer DM column. The consolidation problem was simplified as a consolidation of composite soil considering the load shear effect of core pile. The developed solution was verified by a comparison with the results computed by three-dimensional (3-D) finite element analysis. A parametric study based on the derived solution was conducted to investigate influence factors—length of core pile, diameter of core pile, diameter of SDM column, modulus of DM column, and permeability coefficient of DM column—on the consolidation behavior of SDM column-supported embankment over soft soil. The developed solution was applied to a case history of SDM column-supported embankment, and a good agreement was found between the predictions and the field measurements. 相似文献
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采用Monte Carlo模拟手段,提出描述场地土层特性变异性对传递函数变异性影响的分析方法。选取日本Kik-Net强震数据库中软（FKSH14）、硬（FKSH12）两类场地,建立场地概率模型。应用Monte Carlo技术随机生成50组场地剖面,分别计算场地的传递函数STF及STF标准差,讨论场地土层厚度、剪切波速,以及二者组合情况下场地传递函数的标准差及场地特征频率的变化。结果显示：对于硬土场地而言,场地特征频率标准差相对于软土场地较大,且剪切波速变异性影响比土层厚度变异性的影响略大,而二者组合工况下最大;而软土场地,土层厚度、剪切波速变化工况下场地特征频率的标准差相当,比二者组合工况下略低;软、硬两类场地,土层厚度与剪切波速二者组合工况下STF的标准差比单一量变化情况下略大,但3种工况下场地STF标准差相差不明显;场地STF的标准差在场地自振频率附近的频率段取值较大,极值点与场地STF的极值点相对应。 相似文献
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堤防的沉降和稳定问题是软土地基上新建堤防工程必须考虑的重要问题。结合南京市长江干堤提升工程小年圩新筑堤项目,开展了软土地基上新建堤防施工全过程的现场监测与分析,主要包括表层沉降、分层沉降、土体侧向位移、土压力、孔隙水压力以及地下水位等内容。基于Plaxis有限元数值软件,建立了软土地基上新建堤防施工填筑过程的数值模型,通过与现场监测结果的对比分析,验证了所建立的数值模型的准确性和可靠性;续而重点分析了填筑速率、填筑间歇时间等关键性施工控制指标对软基上堤防沉降的影响规律。研究结果表明,当单次填筑厚度小于1 m时,单次填筑厚度对整体沉降的影响较小,因此结合实际施工要求,建议单次填土厚度为0.5～1.0 m。相关研究成果可以为类似软基上新建堤防施工质量控制提供参考依据。 相似文献
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Dry soil mix (DSM) columns can be used to reduce the settlement of embankments constructed on soft clays and to improve the stability. During construction the shear strength of the columns needs to be confirmed for compliance with technical assumptions. However, the measurement of the column shear strength can be a contentious issue. All methods of assessing the ultimate shear strength of DSM columns have limitations. These are caused by uncertainties in empirical probe factors required to convert pullout or push in force measured during the lime column penetration test to shear strength and/or testing a small proportion of the DSM column volume and determining whether it is representative of the strength of the entire column. The penetration resistance measured using the lime column test is considered to be more representative of average column shear strength than some other test types. This test can be carried out as a pullout resistance test (PORT) or a push in resistance test (PIRT). Both PORT and PIRT require empirical correlations of measured resistance to an absolute measure of shear strength, in a similar manner to the Piezocone test. In this paper, finite element techniques developed for assessment of T-bar, Ball and Piezocone penetration tests , and are used to assess bounds for the empirical probe factor, N. To simulate the cemented DSM columns, analyses have incorporated a model for a strain softening material. Measured settlements from an embankment constructed on DSM ground improvement are then compared with finite element calculations to infer the shear strength of the columns. These inferred shear strengths are then compared with the results of PORT tests performed beneath the embankment. 相似文献
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襄荆高速公路软弱地基高路堤填筑控制试验研究 总被引：2，自引：2，他引：2
软弱地基路堤填筑高度一般小于5 m,需时较长而影响工期,襄荆高速公路软弱地基路堤填筑高达8 m,加快施工进度与保证施工安全成为一大技术难题,为此进行了一系列的试验研究.现场详勘和试验表明该软弱地基存在1～1.5 m厚的硬壳层及下卧砂卵石层且原状土十字板剪切强度较高(Su = 44 kPa),有利于加快填土速率;选取了塑料排水板及砂垫层加土工格栅的软弱地基处理方案;基于排水条件得到了较大改善,经试验,证明适当降低规范要求的沉降控制标准是可行的.据此,根据监测数据进行动态调整后,填土速率得到了较大提高,施工安全也得到了保证;路堤填筑到设计高度后,通过堆载预压试验,对工后沉降预测值进行了验证,取得了良好的效果. 相似文献
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In the design of soft ground treatment, the soft soil indices are the basic design parameter, and their changes have a strong geographical feature and significant uncertainty. Today, the soft soil indices statistical analysis content is mainly in the correlation and distribution regularity of physico-mechanical indices, which lack systematic study in different regions for different types of soft soils, and the statistical samples are from indoor tests and in-situ tests, without considering the impact of different test methods. In this paper, taking the soft soil in Tianjin as an independent statistical unit body, based on studying the change confines, variability, correlation, probabilistical distribution model of soil indices, some statistical relationship empirical formulas and probabilistical distribution models for physical indices, compression index, strength index were obtained; moreover, the correlation of shear strength results by straight shear test, triaxial test, vane shear test are analyzed; and a method for using random factor to evaluate the uncertainty involved in different test methods of soft soil parameters is proposed. The study results provide a basis and reference for defining the values of geotechnical parameters for soft soil. 相似文献
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软土土性指标作为软基处理设计的基本参数,其变化具有很强的地域特征和显著的不确定性。目前,对软土土性指标统计分析集中在软土物理力学指标的相互关系和分布规律等方面,采用的样本为室内试验和原位测试数据,没有考虑不同试验方法对土性指标不确定性分析的影响。将天津软土作为一个独立的统计单元体,研究了该地区软土物理力学指标的变化范围、变异性、指标间的相互关系和各指标的概率分布模型,得到了天津软土物理指标与压缩指标、强度指标间的统计关系经验公式以及土性指标的概率分布模型;并分析了直剪试验、三轴试验、十字板剪切试验3种不同方法抗剪强度试验结果的相互关系,提出了利用随机因子分析法对试验方法不确定性进行概率评定。研究成果为软土地区工程土工参数的取值提供了依据和参考。 相似文献
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The seismic stability analysis of an embankment lying over a soft foundation soil reinforced by a group of vertical piles is performed within the framework of the upper bound kinematic approach of yield design. The analysis is based on a previously developed ‘multiphase’ model of the reinforced ground, which explicitly accounts for the shear and bending resistances of the piles. Making use of appropriate failure mechanisms involving shear zones across which the reinforcements are continuously deforming, along with ‘plastic hinge’ surfaces, upper bound estimates to the critical seismic coefficient of the structure are derived. The results, which are confirmed by the simulations obtained from a finite element elastoplastic code, give clear evidence of the key role played by the bending strength capacities of the piles in ensuring the stability of the pile reinforced embankment. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Myint Win Bo Ming-Fang Chang A. Arulrajah Victor Choa 《Geotechnical and Geological Engineering》2012,30(1):45-62
Geotechnical ground investigation is important in all construction works particularly, land reclamation projects. The Changi
East reclamation project is a mega project that involves creation of land space as large as 3,000 hectares in multiple phases
between 1991 and 2005. Ground investigation plays a critical role in the Changi project which involved substantial amount
of ground improvement works after reclamation by sand filling. One important aspect of the investigation was to evaluate the
geotechnical characteristics of the underlying compressible soils beneath the original seabed for the selection of suitable
methods of ground improvement. The other important aspect of the investigation was to characterize and verify the compactness
of the reclaimed sand fill. Many types of in situ tests were extensively used in the project. The field vane shear test provides
correlations between the undrained shear strength and depth for the upper and the lower marine clay strata in the Northern
part and the Southern Part of the reclaimed site. Combined with laboratory undrained shear strength tests, the field vane
strength profiles allow the derivation of the undrained shear strength over effective stress ratios for the upper and the
lower marine clays. In addition, results from three other in situ tests, the piezocone cone penetration test, the flat dilatometer
test, and the self boring pressuremeter test provided useful verification of these correlations. A field-performance based
method of assessing degree of consolidation in the underlying clay was developed by combining field monitoring, laboratory
testing and conventional as well as specialized in situ testing. An effective use of in situ testing methods for assessment,
the outcome of ground improvement and for fill quality control in the densification of granular soils is illustrated with
field observation data collected at the project site. 相似文献
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The design against failure of an embankment resting upon a soft soil improved by a group of columns is investigated with the help of the yield design homogenization approach. Assuming that both constituents of the reinforced ground are purely cohesive materials (‘lime column’ technique), an upper bound estimate for the macroscopic strength condition of the reinforced soil as a homogenized medium is first obtained, providing definite evidence of a shear strength anisotropy associated with the reinforcement preferential orientation. The kinematic method of yield design is then performed on the basis of such a criterion, making use of rotational failure mechanisms involving slip circles in the reinforced ground. Upper bound estimates are finally obtained for the embankment stability factor, as functions of the degree of reinforcement and relative thickness of the soil layer. These results are compared with those derived from a simplified analysis, where the reinforced soil is assumed to exhibit an averaged isotropic cohesion. This comparison clearly indicates that the latter simplified analysis may produce quite unsafe estimates for the embankment stability, which can be attributed to the fact that it fails to capture the inherent strength anisotropy of the reinforced soil. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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准确预测路堤沉降对于规避风险和减小成本至关重要。传统的仅基于场地勘察数据的路堤沉降预测方法的预测值常偏离监测值。提出了基于贝叶斯理论的多源信息融合方法进行路堤沉降预测,采用有限元法模拟多层土体的固结沉降,并结合高效的马尔科夫链蒙特卡洛模拟法更新土体参数得到高维后验分布。以新南威尔士州的Ballina地区试验路堤数据为例说明了所提方法的有效性。结果表明,基于贝叶斯理论的多源信息融合方法可以有效融合勘察和监测数据,通过多源数据融合能够较准确地预测路堤沉降。对于Ballina路堤,总体上随着监测数据量的增加,路堤沉降预测预测精度逐渐提高。使用0～116 d监测数据可以准确地预测地表沉降;基于0～496 d监测数据可同时准确预测所有监测点的沉降。对于Ballina路堤,先验信息对沉降预测具有一定影响,但观测误差对预测准度影响微弱。 相似文献
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在深厚软土地基上修筑无砟轨道高速铁路低矮路基,需要重点解决好软土地基工后沉降和长期动力稳定性问题.软土地基具有高压缩性,路堤荷载作用下会产生较大的残余沉降;同时,线路运营后,地基土在高速列车长期循环动荷载作用下易产生较大的塑性变形,二者耦合将严重影响到无砟轨道的几何状态和线路运营安全.基于此,在京沪高速铁路上海虹桥深厚软土地区低矮路基中,首次采用了桩基-连续薄板梁结构型式,并进行了系统的静动态监测、测试.结果表明,该结构工后沉降控制效果良好、长期循环荷载作用下性能稳定,可以满足高速铁路铺设无砟轨道和高速列车长期平顺运行的要求. 相似文献
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路堤下深厚软土侧向变形的沉降影响研究 总被引：1，自引：0，他引：1
通过三轴蠕变试验和平面应变蠕变试验,研究路堤下深厚的海相沉积软土侧向变形对沉降的影响作用。试验结果表明,荷载作用下软土的瞬时沉降是非线性的,剪应力作用产生了不可恢复的侧向变形,侧向变形产生的附加沉降也是重要组成部分。软土的侧向变形在不排水条件下只有鼓胀变形,且持续发展;在排水条件下是鼓胀变形和收缩变形的迭加。在排水条件下软土的侧向变形发展过程和剪应力水平有关,在低剪应力水平下侧向变形对沉降的影响不显著,在高剪应力水平下则侧向变形对沉降的影响不能忽视,剪应力对沉降的影响贯穿于沉降全过程。 相似文献
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软黏土地基由于其含水量高、孔隙比大、强度低、渗透性差,因此,在灵敏度很高的软黏土地基上建造高度较高的路堤,其稳定性很难得到保证。一般采用分级加载的方法使软土地基在路堤荷载的作用下发生固结,强度获得增长。为加速固结,常采用塑料排水板处理地基,使之能在较短的时间内完成固结,加速地基强度增加。针对日本佐贺县高灵敏度的有明黏土地基上修建的分级加载的6.5 m高河堤下软黏土的物理力学性质的变化,说明分级加荷的重要性。现场软土地基为结构性黏土,有很高的灵敏度。而且该软黏土地基的渗透系数极低。因此采用塑料排水板进行了加固处理,施工过程中对地基土的物理与力学性质随固结过程的变化进行了测试。分析了其发展规律,结果表明地基土的单轴强度在250 d内增长了近1倍。 相似文献
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D. T. BergadoJ. C. ChaiN. Miura 《Computers and Geotechnics》1995,17(4):447-471
The behavior of a reinforced embankment on soft Bangkok clay has been analyzed by plane strain finite element method. The finite element analysis considers the selection of proper soil/reinforcement properties according to the relative displacement pattern of upper and lower interface elements. The large deformation phenomenon is simulated by updating the node coordinates, including those of the embankment elements above the current construction level, which ensures that the applied fill thickness simulates the actual field value. A full scale test reinforced embankment with a vertical face (wall) on Bangkok clay has been analyzed by the proposed finite element method, and the numerical results are compared with the field data. The response of a reinforced embankment on soft ground is principally controlled by the interaction between the reinforced soil mass and soft ground and the interaction between the grid reinforcement and the backfill soil. The tension in reinforcement and lateral displacement of the wall face varied during consolidation of foundation soil. The maximum tension force occurred in the reinforcement layer placed at the base of reinforced mass, due to bending of the reinforced mass resulting from differential settlements. It is considered necessary to account for the permeability variation of the soft ground foundation in the finite element analysis. 相似文献
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高填方地基土工离心模型试验技术研究 总被引：7，自引：1，他引：6
以模型试验的相似理论为基础,结合九寨黄龙机场高填方地基工程实例,详细阐述了高填方地基离心模型试验技术,即对九寨黄龙机场104 m高填方地基的离心模型试验,采用等应力局部模型设计方案,以剔除法和等量代替法配制填料,以等效法模拟软弱地基强夯处理,并以增大离心加速度的方法模拟高填方地基的填筑加载过程;试验结果表明,高填方地基的总体沉降特征为"沉降大、压实快";土体的压实沉降主要发生在施工期;试验中高填方地基施工结束时土体的沉降固结度已完成90%以上,施工结束后土体产生的沉降量还不到土体总沉降量的10%. 相似文献