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。     

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。     

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。     

A genetic algorithm approach for assessing soil liquefaction potential based on reliability method

Deterministic approaches are unable to account for the variations in soil’s strength properties, earthquake loads, as well as source of errors in evaluations of liquefaction potential in sandy soils which make them questionable against other reliability concepts. Furthermore, deterministic approaches are incapable of precisely relating the probability of liquefaction and the factor of safety (FS). Therefore, the use of probabilistic approaches and especially, reliability analysis is considered since a complementary solution is needed to reach better engineering decisions. In this study, Advanced First-Order Second-Moment (AFOSM) technique associated with genetic algorithm (GA) and its corresponding sophisticated optimization techniques have been used to calculate the reliability index and the probability of liquefaction. The use of GA provides a reliable mechanism suitable for computer programming and fast convergence. A new relation is developed here, by which the liquefaction potential can be directly calculated based on the estimated probability of liquefaction (P _L ), cyclic stress ratio (CSR) and normalized standard penetration test (SPT) blow counts while containing a mean error of less than 10% from the observational data. The validity of the proposed concept is examined through comparison of the results obtained by the new relation and those predicted by other investigators. A further advantage of the proposed relation is that it relates P _L and FS and hence it provides possibility of decision making based on the liquefaction risk and the use of deterministic approaches. This could be beneficial to geotechnical engineers who use the common methods of FS for evaluation of liquefaction. As an application, the city of Babolsar which is located on the southern coasts of Caspian Sea is investigated for liquefaction potential. The investigation is based primarily on in situ tests in which the results of SPT are analysed.     

Seismic liquefaction potential assessed by fuzzy comprehensive evaluation method

Liquefaction of loose, saturated granular soils during earthquakes poses a major hazard in many regions of the world. The determination of liquefaction potential of soils induced by earthquake is a major concern and an essential criterion in the design process of the civil engineering structures. A large number of factors that affect the occurrence of liquefaction during earthquake exist a form of uncertainty of non-statistical nature. Fuzzy systems are used to handle uncertainty from the data that cannot be handled by classical methods. It uses the fuzzy set to represent a suitable mathematical tool for modeling of imprecision and vagueness. The pattern classification of fuzzy classifiers provides a means to extract fuzzy rules for information mining that leads to comprehensible method for knowledge extraction from various information sources. Therefore, it is necessary to handle the soil liquefaction problem in a rational framework of fuzzy set theory. This study investigates the feasibility of using fuzzy comprehensive evaluation model for predicting soil liquefaction during earthquake. In the fuzzy comprehensive evaluation model of soil liquefaction, the following factors, such as earthquake intensity, standard penetration number, mean diameter and groundwater table, are selected as the evaluating indices. The results show that the method is a useful tool to assess the potential of soil liquefaction.     

Rapid estimation of maximum and minimum void ratios of granular soils

Maximum and minimum void ratios (e_max and e_min) of granular soils are commonly used as indicators of many engineering properties. However, few methods, apart from laboratory tests, are available to provide a rapid estimation of both e_max and e_min. In this study, we present a theoretical model to map the densest and the loosest packing configurations of granular soils onto the void space. A corresponding numerical procedure that can predict both e_max and e_min of granular soils with arbitrary grain size distributions is proposed. The capacity of the proposed method is evaluated by predicting the maximum and minimum void ratios of medium to fine mixed graded sands with different contents of fines. The influence of the grain size distribution, characterized quantitatively by uniformity parameter and the fractal dimension, on e_max and e_min is discussed using the proposed method. Moreover, application of this method in understanding the controlling mechanism for the void ratio change during grain crushing is presented.

     

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.     

现有液化识别方法对比分析

场地液化实时监测和报警是减轻液化灾害的新途径,其核心技术是建立依据强震记录对液化场地进行反演识别的方法。采用统一样本,其中尽可能多地包含软土场地地震动记录,按场地类别对目前国内外现有的Suzuki法、Miyajima法、KY法和SY法等4种主要液化识别方法的可靠性进行了对比分析,提出评价结果及改进建议。分析表明：对全部样本,SY法、Suzuki法、KY法和Miyajima法识别成功率依次为98%、85%、77%和52%;Suzuki法、KY法和Miyajima法的成功率受场地类别影响显著,随场地变软而明显降低,对D类场地识别成功率均在55%以下;Suzuki法、Miyajima法和KY法均采用与绝对周期相关的参数作为判别指标,而软土与液化场地上存在明显交叉,极易导致误判;SY法选取地震动参数的相对变化作为识别指标,即使对D类场地成功率也达到92%,但其方法中仍有若干细节需要进一步探讨和改进     

Paleoliquefaction features on Tenerife (Canary Islands) in Holocene sand deposits

On Tenerife, one of the Canary Islands, a series of clastic dikes and tubular vents is attributed to liquefaction of sediments during a high-intensity paleoearthquake. Geotechnical, geological, tectonic, and mineralogical investigations have been carried out to identify the soil composition and structure, as well as the geological processes operating in the area. Geochronological analysis has indicated an age ranging from 10,081±933 to 3490±473 years BP for the liquefaction features. The area in which these liquefaction features are found has undergone tectonic uplift and is affected by two faults. One of these faults was responsible for displacing the Holocene materials. The paleoearthquake responsible for this liquefaction has been analysed in terms of its peak ground acceleration (pga) and magnitude by back calculation analysis based on the cyclic stress and Ishihara methods. A range of 0.22–0.35g was obtained for the pga, with the value of 0.30g being selected as most representative. From this, an earthquake-modified Mercalli intensity of I_MM=IX was estimated for the liquefaction site. The magnitude-bound method and energy-based approaches were used to determine the magnitude of the paleoearthquake, providing a moment magnitude M in the range of 6.4–7.2; M=6.8 is taken as the representative figure.     

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.     

砂土液化预测的Fisher判别模型及应用

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。     

基于静力触探试验的液化判别新方法

近来地震液化灾害频发,再次成为研究重点,发展具有良好应用前景的基于静力触探试验（CPT）的液化判别方法对预防液化灾害具有重要意义。以Boulanger数据库171组数据为回归样本,分析既有方法存在的问题,提出了基于CPT液化判别的双曲线模型和计算公式,并通过提取2011年新西兰地震147组液化新数据,对该方法进行对比检验。研究表明,我国岩土工程勘察规范的CPT液化判别方法对浅埋砂层偏于保守,对深层土又明显偏于危险,而国际上具有代表性的Robertson方法,其液化临界线存在低烈度区不合理回弯、高烈度区又偏于保守的问题。提出的新公式在不同地震动强度和砂层埋深下均可给出合理判别结果,克服了国内外既有方法的缺点,并纳入到具有样板规范性质的《建筑工程抗震性态设计通则》修订稿中,可为我国相关规范修订和工程应用提供支持。     

New approaches to determine the ultimate bearing capacity of shallow foundations based on artificial neural networks and ant colony optimization

In this study, two different approaches are proposed to determine the ultimate bearing capacity of shallow foundations on granular soil. Firstly, an artificial neural network (ANN) model is proposed to predict the ultimate bearing capacity. The performance of the proposed neural model is compared with results of the Adaptive Neuro Fuzzy Inference System, Fuzzy Inference System and ANN, which are taken in literature. It is clearly seen that the performance of the ANN model in our study is better than that of the other prediction methods. Secondly, an improved Meyerhof formula is proposed for the computation of the ultimate bearing capacity by using a parallel ant colony optimization algorithm. The results achieved from the proposed formula are compared with those obtained from the Meyerhof, Hansen and Vesic computation formulas. Simulation results showed that the improved Meyerhof formula gave more accurate results than the other theoretical computation formulas. In conclusion, the improved Meyerhof formula could be successfully used for calculating the ultimate bearing capacity of shallow foundations.     

饱和土蠕(滑)动液化的研究

本文在文献[1],[2]的基础上对黄土区饱和土蠕动及滑动液化作了进一步研究。文中首先列举了黄土滑坡现场饱和土液化的一些典型实例及其所造成的宏观危害。从不同的角度提出了饱和土蠕(滑)动液化的定义,在大量现场及室内试验的基础上分析了饱和土蠕(滑)动液化的机理和影响因素,最后给出了液化势的评价方法。     

确定多重现期暴雨公式参数的二次优化算法

四参数非线性多重现期暴雨公式在城市排水规划设计中有着广泛的应用。搜索算法与最小二乘法是优化计算的两个简单有效的方法,不过单独直接用于求解四参数非线性多重现期暴雨公式的参数比较困难。提出耦合最小二乘法及搜索算法确定多重现期暴雨公式参数的二次优化算法,该方法可以一次得到多重现期暴雨强度公式的参数,参数优化过程不需要图解。研究表明,计算结果比较客观;成果精度高,例题的平均绝对均方差为0.035mm/min。与遗传算法、蚁群算法等比较,该方法计算原理容易理解,计算简便,可以用Excel进行参数优化计算。     

石家庄市地下水资源管理模型

本文把迭加原理应用于地下水流中,建立了地下水位响应函数,形成含水系统的响应矩阵,从而把有限元水流模拟模型和最优化模型藕合起来,并在微机上实现了两者的有机结合。用两种方法对单位脉冲值进行模拟,提高了水位响应系数的计算精度。最后根据石家庄市地下水管理现状,制定了地下水资源的现状管理方案和人工补给方案,并作出了综合决策方案,为石家庄市地下水资源科学管理提供了依据。     

荆沙长江公路大桥主桥墩基地震液化研究

本文利用经验判别法和试验－分析法对荆沙长江公路大桥主桥墩基场地的地震液化进行了综合判别。对现在使用的有关地震液化判别“规范”的应用范围进行了拓展，虽然是初次尝试，但作者认为效果良好。     

Identification of the behavior of sandy soil to static liquefaction and microtomography

In this paper, undrained triaxial compression tests were performed on specimens obtained in Oued Rass sand (Chlef, Algeria). The objective of this study is to investigate the effects of specimen deposition methods, the initial density, and the confining pressure on the undrained behavior of this sand. The test results show that the initial confining pressure and the relative density affected, in a significant manner, the resistance to liquefaction. However, it increases with confining pressure and relative density. The results also show that the specimens prepared by dry deposition method have a greater resistance to liquefaction than those prepared by moist tamping. A nondestructive comparative analysis of the deposits by X-ray microtomography carried out at the granular scale made it possible to characterize more precisely the difference of the obtained structures for the two deposition modes.     

饱和砂土液化研究现状及展望

通过多年的研究,人们对饱和砂土液化有了很深的认识。在Seed简化法,剪切波速法和标准贯入试验等判别的方法的研究方面也取得了很多的成果。本文主要介绍了我国广泛应用的标准贯入试验的方法,以及应用数值方法如何更好的判断场地的抗液化性。提出应用室内的微型贯入试验来判断饱和砂土液化的展望。     

Modification of the liquefaction potential index and liquefaction susceptibility mapping for a liquefaction-prone area (Inegol,Turkey)

Although some liquefaction assessment methods were proposed to evaluate the liquefaction potential of sandy soils, the conventional method based on the standard penetration test (SPT) has been commonly used in most countries and in Turkey. However, it alone is not a sufficient tool for the evaluation of liquefaction potential. The liquefaction potential index was proposed to quantify the severity of liquefaction. Nevertheless, the liquefaction potential index and the severity categories do not answer the question: "Which areas will not liquify?" Besides, the categories do not include a "moderate" category; on the other hand, the "high" and "low" categories are included. This situation is also contrary to the nature of classification schemes. In this study, the liquefaction potential index and the liquefaction potential categories were modified by considering the existing form of the categories based on the liquefaction potential index. While the category of low was omitted, the categories of moderate and "non-liquefied" were adopted. A factor of safety of 1.2 was assumed as the lowest value for the liquefaction potential category of non-liquefied. In addition, the town of Inegol in the Marmara region became the case study for checking the performance of the liquefaction potential categories suggested in this study.