基于CFD的地震液化研究新进展

综述了近年来关于液化土体流体动力学特征的试验发展状况,以及基于计算流体动力学（简称CFD）的地震液化数值模拟现状,重点介绍了目前比较活跃的可以较高精度模拟液化土体流动状态的三次伪质点数值方法（简称CIP法）。通过对CFD和传统固体力学在地震液化研究中的应用比较,指出了应用CFD的三大优势,即土体大变形问题、液化土体参数分析以及液化土体中结构物的变形应用CFD分析,均可获得较好的结果。进一步提出,在地震液化应用中,未来CFD的发展应该考虑整合液化前的土体性状研究和地震液化中桩-土-结构物的综合分析。     

汶川地震中甘肃清水田川黄土液化的试验研究

2008年5·12特大地震中,位于甘肃省清水县郭川乡的田川村发生了饱和黄土的液化滑移灾害。本文首先在对田川场地进行考察的基础上,综合田川在汶川地震中的震害情况以及滑移区的地形条件,将该地区在汶川地震中的烈度进行了修正。其次对田川黄土进行了物性指标测试以及室内动三轴液化试验,根据试验结果,综合考虑产生液化所需的场地及土性条件、黄土的动强度和液化特性,对田川黄土液化灾害进行了分析,并采用反应分析的方法对其进行了液化判定。研究结果证明了田川黄土液化的事实存在性,为低烈度区黄土液化提供了新的震害依据。

     

以标贯试验为依据的砂土液化确定性及概率判别法

核电厂址非基岩场地的地基液化问题是核电厂选址的关键问题,亟需建立核电厂址地基液化判别方法。回顾了以标贯试验和地表峰值加速度为依据的砂土液化判别方法的演化历史,依据Idriss-Boulanger确定液化临界曲线的基本方法,提出了确定液化临界曲线的基本原则,分别依据美国液化数据库、中国抗震规范液化判别式所用的液化数据及综合两者的液化数据资料,给出了相应的液化临界曲线,验证了液化临界曲线的位置对不同的细粒含量、有效上覆压力、现场试验方法的液化数据的合理性,分析了测量或估计土层循环应力比和修正标贯击数各种因素的不确定性对液化临界曲线的敏感性,结果表明：所提的液化临界曲线不易受各种因素的影响。利用Monte Carlo模拟、加权最大似然法和加权经验概率法,给出了液化临界曲线的名义抗液化安全系数与液化概率的经验关系式及概率等值线,并对核电厂Ⅰ类、Ⅱ类和Ⅲ类抗震物项地基,给出了相应的液化临界曲线。     

饱和砂土地震液化判别的可拓聚类预测方法

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。     

Mapping the liquefaction induced soil moisture changes using remote sensing technique: an attempt to map the earthquake induced liquefaction around Bhuj, Gujarat, India

The Bhuj earthquake (Mw = 7.9) occurred in the western part of India on 26th January 2001 and resulted in the loss of 20,000 lives and caused extensive damage to property. Soil liquefaction related ground failures such as lateral spreading caused significant damage to bridges, dams and other civil engineering structures in entire Kachchh peninsula. The Bhuj area is a part of large sedimentary basin filled with Jurassic, Tertiary and Quaternary deposits. This work pertains to mapping the areas that showed sudden increase in soil moisture after the seismic event, using remote sensing technique. Multi-spectral, spatial and temporal data sets from Indian Remote Sensing Satellite are used to derive the Liquefaction Sensitivity Index (LSeI). The basic concept behind LSeI is that the near infrared and shortwave infrared regions of electromagnetic spectrum are highly absorbed by soil moisture. Thus, the LSeI is herein used to identify the areas with increase in soil moisture after the seismic event. The LSeI map of Bhuj is then correlated with field-based observation on Cyclic Stress Ratio (CSR) and Cyclic Resistance Ratio (CRR), depth to water table, soil density and Liquefaction Severity Index (LSI). The derived LSeI values are in agreement with liquefaction susceptible criteria and observed LSI (R ² = 0.97). The results of the study indicate that the LSeI after calibration with LSI can be used as a quick tool to map the liquefied areas. On the basis of LSeI, LSI, CRR, CSR and saturation, the unconsolidated sediments of the Bhuj area are classified into three susceptibility classes.     

辽宁石佛寺水库砂土液化处理试验

石佛寺水库工程建筑物区主要工程地质问题之一为砂土液化问题。在主坝轴线上选取适当部位进行几种液化处理方案的试验,为检测液化处理效果进行了地基加固处理前后密实度分析和加固处理后地基土地震液化特征分析与评价,对比几种方案的可行性,最终选择解决场区饱和砂土液化的最优方案。     

基于判别分析法的地震砂土液化预测研究

将距离判别分析方法应用于砂土液化的预测问题中,建立了砂土液化预测的距离判别模型。选用震级、研究深度、震中距、标贯击数、地下水位及地震持续时间等6项指标作为判别因子,以大量的工程实例数据作为学习样本进行训练,建立了线性判别函数对待评样本进行了评价。研究结果表明,距离判别分析模型判别砂土液化效果良好,预测准确度高,回判估计误判率低,可望成为砂土液化预测的有效手段。     

以剪切波速与地表峰值加速度为依据的地震液化确定性及概率判别法

剪切波速作为土性的基本参数,为评价土体抵抗地震液化的能力提供了一种方法。回顾了以剪切波速和地表峰值加速度为依据的场地地震液化判别方法的演化历史,依据他人收集的现场液化资料,合计49次地震、618例液化/不液化场地数据,提出了确定液化临界曲线的基本原则,给出了基于修正剪切波速与地表峰值加速度的液化临界曲线,验证了液化临界曲线的位置对细粒含量、有效上覆压力、震级等因素取值变化的合理性,分析了估计土层循环应力比CSR的剪应力折减系数、震级标定系数、有效上覆压力修正系数等因素的不确定性对液化临界曲线的敏感性。结果表明：液化临界曲线对各种影响因素具有很好的适用性。利用Monte Carlo模拟、加权最大似然法和加权经验概率法,给出了建议的液化临界曲线的名义抗液化安全系数与液化概率的经验关系式及概率等值线,并对核电厂Ⅰ类、Ⅱ类和Ⅲ类抗震物项地基,分别建议了相应的液化临界曲线。该方法以丰富的现场液化数据为依据,具有广泛的应用前景。     

A Bayesian network approach for predicting seismic liquefaction based on interpretive structural modeling

The Bayesian network (BN) is a type of graphical network based on probabilistic inference that has been gradually applied to assessment of seismic liquefaction potential. However, how to construct a robust BN remains underexplored in this field. This paper aims to present an efficient hybrid approach combining domain knowledge and data to construct a BN that facilitates the integration of multiple factors and the quantification of uncertainties within a network model to assess seismic liquefaction. Initially, only using given domain knowledge, a naive network model can be constructed using interpretive structural modeling. Thereafter, some effective information about the naive model is provided to construct a robust model using structural learning of BN from historic data. Finally, the returning predictive results and the predictive results are compared to other methods including non-probabilistic and probabilistic models for seismic liquefaction using the metrics of the overall accuracy, the area under the curve of receiver operating characteristic, prediction, recall and F₁ score. The methodology proposed in this paper achieved better performance, and we discussed the power and value of the proposed approach at the end of this paper, which suggest that BN is a good alternative tool for seismic liquefaction prediction.     

A performance-based framework for assessing liquefaction potential based on CPT data

This article describes a new performance-based approach for evaluating the return period of seismic soil liquefaction based on standard penetration test (SPT) and cone penetration test (CPT) data. The conventional liquefaction evaluation methods consider a single acceleration level and magnitude and these approaches fail to take into account the uncertainty in earthquake loading. The seismic hazard analysis based on the probabilistic method clearly shows that a particular acceleration value is being contributed by different magnitudes with varying probability. In the new method presented in this article, the entire range of ground shaking and the entire range of earthquake magnitude are considered and the liquefaction return period is evaluated based on the SPT and CPT data. This article explains the performance-based methodology for the liquefaction analysis – starting from probabilistic seismic hazard analysis (PSHA) for the evaluation of seismic hazard and the performance-based method to evaluate the liquefaction return period. A case study has been done for Bangalore, India, based on SPT data and converted CPT values. The comparison of results obtained from both the methods have been presented. In an area of 220 km² in Bangalore city, the site class was assessed based on large number of borehole data and 58 Multi-channel analysis of surface wave survey. Using the site class and peak acceleration at rock depth from PSHA, the peak ground acceleration at the ground surface was estimated using probabilistic approach. The liquefaction analysis was done based on 450 borehole data obtained in the study area. The results of CPT match well with the results obtained from similar analysis with SPT data.     

Soil liquefaction potential induced by the andalusian earthquake of 25 December 1884

On 25 December 1884, an earthquake of epicentral intensityI ₀ = IX in the MSK scale caused great damage in a large area in the provinces of Granada and Málaga, in the south of Spain. The reports of the Spanish, Italian and French Commissions that studied the earthquake described ground phenomena in seven different sites which can be identified as soil liquefaction.By means of dynamic penetration tests carried out in the above sites, the corresponding soil profiles (based on SPT data and water table depth) were established, and the occurrence of liquefaction was proved in five out of seven of these sites. Also, the intensities at such locations and the magnitude of the earthquake were estimated.From the geotechnical data and the cyclic stress ratio induced by the earthquake, liquefaction conditions were confirmed in all the five sites which presumably liquefied. Then, possible values of the minimum ground surface accelerations necessary for the onset of liquefaction at each location were calculated. The results obtained were completed with data reported in six liquefaction case studies from Japan and the United States, from which design charts relating soil acceleration with normalized SPT values for different intensity levels were drawn.Finally, by using standard attenuation curves, the above data were translated into epicentral distances, and good agreement with the known epicentral area was found. As a result, a consistent approach for liquefaction hazard and source location problems has been developed. The proposed method combines in its formulation historical evidence and earthquake engineering techniques.     

1989～2011期间8次强地震中抗液化地基处理成功案例的回顾与启示

回顾了1989年美国Mw6.9级Loma Prieta地震、1993年日本Ms7.8级Kushiro-Oki地震、1994年日本Mw8.2级Hokkaido Toho-Oki地震、1995年日本Ms7.2级阪神地震、1999年台湾集集地震、1999年土耳其Mw7.4级Kocaeli地震、2001年美国Mw6.8级Nisqually地震以及2011年Mw9.0级东日本地震中场地抗液化工程措施的成功案例,初步分析了各种抗液化工程措施的有效性与优劣性,可以给出如下工程场地抗液化处理的经验：（1）对于易液化的沿海及填海造陆场地,采用适宜的抗液化工程措施应成为地基处理不可缺少的环节;（2）应基于场地条件、经济条件及环境要求,综合考虑场地抗液化地基处理措施的选择;（3）挤密砂桩法和碎石桩法运用广泛、技术成熟且比较经济,宜优先选择作为抗震设防烈度Ⅷ度及以下地区的场地抗液化地基处理措施;（4）强夯法使用机具简单、费用低廉,适宜选择作为抗震设防烈度Ⅷ度及以下地区大面积场地的抗液化地基处理措施;（5）注浆法、深层搅拌法、旋喷法作为抗震设防烈度Ⅸ度及以下地区的场地抗液化地基处理措施是有效的;（6）多种抗液化地基处理措施联合使用的处理效果往往优于单一措施单独使用的处理效果,在条件许可的情况下,宜选择多种抗液化地基处理措施联合使用,以期达到更好的处理效果。     

饱和砂土爆炸液化特性研究

基于有效应力动力分析法,在Byrne有效应力弹塑性模型的基础上,提出了一个能够考虑主应力轴旋转、饱和砂土含有少量气体、饱和砂土液化后的应变软化和应力重分布特性的弹塑性模型。将该模型编制成分析模块,并与通用岩土分析软件FLAC接口,进而对饱和砂土分别在单点、两点（微差）和多点（微差）爆炸地震波荷载作用下进行数值模拟分析,分别考虑了水平、微倾以及斜坡场地等3种工况,并且对爆炸地震波荷载与天然地震波荷载作用下饱和砂土的动力特性进行了对比研究。数值模拟结果表明,该模型能够很好地表现饱和砂土的爆炸液化气特性;不同动载和不同场地条件下,饱和砂土表现的动力特性以及液化行为也不尽相同。     

Piles in fully liquefied soils with lateral spread

The paper provides a new analysis procedure for the assessment of the lateral response of isolated piles/drilled shafts in saturated sands as liquefaction and lateral soil spread develop in response to dynamic loading such as that generated by the earthquake shaking. The presented method accounts for: (1) the development of full liquefaction in the free-field soil that could trigger the lateral spread of the overlying crust layer; (2) the driving force exerted by the crust layer based on the interaction between the pile and the upper non-liquefied soil (crust) layer; and (3) the variation of the excess pore water pressure (i.e. post-liquefaction soil strength) in the near-field soil with the progressive pile deflection under lateral soil spread driving force. A constitutive model for fully liquefied sands under monotonic loading and undrained conditions is developed in order to predict the zone of post-liquefaction zero-strength of liquefied sand before it rebounds with the increasing soil strain in the near-field. The analytical and empirical concepts employed in the Strain Wedge (SW) model allow the modeling of such a sophisticated phenomenon of lateral soil spread that could accompany or follow the occurrence of seismic events without using modifying parameters or shape corrections to account for soil liquefaction.     

Seismic liquefaction analysis of a reservoir dam foundation in the South–North Water Diversion project in China. Part I: Liquefaction potential assessment

In this paper, the dynamic characteristics of a liquefiable silt substratum within the foundation soil of a reservoir dam in the Tianjin area are investigated by means of standard penetration resistance and dynamic triaxial tests. Properties including N-values, factors influencing liquefaction as a cyclic stress, consolidation pressure, structure, and particle composition are considered in this research. Parameters used to evaluate liquefaction potential are obtained through testing. A comprehensive program based on the Chinese code and standard for geological investigation (Ministry of Water Resources of China 1999a; Ministry of Construction of China 2001a) and Seed’s simplified method (Seed and Idriss 1971; in J Geotech Eng Div ASCE 109(3): 458–482, 1983) was carried out to evaluate the potential of liquefaction within the reservoir dam foundation. Liquefaction potentials were also assessed in response to the Chinese codes for seismic design (Hydropower Research Institute of China 2000; Ministry of Construction of China 2001b). The evaluation shows that saturated surface silt in the reservoir dam foundations is vulnerable to liquefaction at seismic intensities of VII and above. The two assessment methods are in good agreement with each other, and the research results can provide useful information for the safe construction and normal operation of the reservoir.     

The great 1950 Assam Earthquake revisited: Field evidences of liquefaction and search for paleoseismic events

Extensive field investigations were carried out for the first time in the meizoseismal area of the great 1950 Assam Earthquake aimed at exploring the paleoseismic history of the NE Indian region through documentation of liquefaction features and radiocarbon (¹⁴C) dating. Trenching at more than a dozen locations along the Burhi Dihing River valley and within the alluvial fans adjoining the Brahmaputra and Dibang Rivers resulted in the identification of more than a dozen very prominent liquefaction features (sand dykes, sills, sand blows etc.) as evidences of large to great earthquakes. ¹⁴C dating of the organic material associated with some of the features indicates a paleoseismic record of about 500 yrs archived by the sediments in this region. Compelling geological evidence(s) of the great 1950 earthquake are well constrained by ¹⁴C dating. Out of the two historically reported seismic events (1548 AD and 1697 AD) from this region, ¹⁴C dating could constrain the 1548 AD event though not distinctly. Further studies using combined ¹⁴C and OSL dating may better constrain the seismo-chronology of the study region.     

CPT-based probabilistic evaluation of seismic soil liquefaction potential using multi-gene genetic programming

In this paper, liquefaction potential of soil is evaluated within a probabilistic framework based on the post-liquefaction cone penetration test (CPT) data using an evolutionary artificial intelligence technique, multi-gene genetic programming (MGGP). Based on the developed limit state function using MGGP, a relationship is given between probability of liquefaction (P_L) and factor of safety against liquefaction using Bayesian theory. This Bayesian mapping function is further used to develop a P_L-based design chart for evaluation of liquefaction potential of soil. Using an independent database of 200 cases, the efficacy of the present MGGP-based probabilistic method is compared with that of the available probabilistic methods based on artificial neural network (ANN) and statistical methods. The proposed method is found to be more efficient in terms of rate of successful prediction of liquefaction and non-liquefaction cases, in three different ranges of P_L values compared to ANN and statistical methods.     

天津泰达地区粉土振动液化特性的研究

本文以动三轴试验和原位测试数据为基础，以天津地区砂性土为例，探讨砂性土振动液化机理及孔隙水压力变化规律，采用多种方法分析判别砂性土液化，为高烈度地区重要工程建筑抗震设计提供重要数据。     

黄河三角洲地区砂土路基液化机理探讨及处置

从砂土路基液化机理人手,结合黄河三角洲地区地基土工程地质特征,对该地区路基砂土液化做现场振动试验,找出影响砂土路基液化的影响因素,主要内因有土体的密实度、含水量和土体中是否存在软弱区;主要外因有荷载的大小、作用时间和荷载频率。并针对砂土液化的内外因,结合青银高速公路强夯处理案例展开分析,提出了处理方法。     

大厚度饱和砂土液化治理试验研究

饱和砂土液化地基治理是工程建设中面临的一大难题。某拟建电厂工程针对大厚度的饱和砂土液化地基,通过采用大直径振冲碎石桩复合地基的处理方法,开展了大厚度饱和砂土液化地基治理的现场试验研究。试桩施工结束后,通过采用载荷试验、超重型动力触探试验等原位测试方法,对桩间土、桩体及复合地基的承载性能、变形参数及液化处理效果进行了评价和分析,取得了大量可靠的试验数据,对类似工程具有一定的参考价值