国内外静力触探液化判别方法对比检验

静力触探试验（cone penetration test,简称CPT）具有独特优势,使其成为了海上风电工程的主要勘察方法。海上风电工程位于液化易发区,因此研究基于CPT液化判别方法的适用性和可靠性就成为亟待解决的突出问题。详细介绍了4种国内外具有代表性的CPT液化判别方法,并采用理论分析及大量CPT液化实测数据检验,对现行的美国国家地震工程研究中心（National Center for Earthquake Engineering Research,简称NCEER）方法、《岩土工程勘察规范》（GB50021-2001）方法（岩规法）、《软土地区岩土工程勘察规程》（JGJ 83-2011）方法（软土规程法）和《建筑工程抗震性态设计通则》（CES 160:2004）方法（通则法）等4种方法进行对比检验,提出了4种主要方法的评价结果。结果表明：NCEER法液化判别临界线在低烈度区存在不合理的回弯现象,在高烈度区存在临界值增大过快的问题,在Ⅶ度区深层偏于危险,在Ⅸ度区深层明显偏于保守,在Ⅶ、Ⅸ度区浅层和Ⅷ度区判别结果较好;岩规法液化判别临界线存在很大的问题,液化判别临界线随深度递减,液化判别...     

液化判别中基于人工神经网络的粘粒含量取值研究

岩土工程勘察实践中,得到正确的粘粒含量是进行液化判别的前提与基础。利用静力触探成果进行液化判别时,粘粒含量往往采用场地平均值或邻近钻孔相应深度处土样的粘粒含量值,与判别点处粘粒含量实际值间存在一定差别,影响了采用静力触探液化判别的准确性。采用人工神经网络可建立起需液化判别土层各点粘粒含量与相应空间坐标间的关系,从而得到场地内需液化判别土层粘粒含量的分布规律,为液化判别提供更为准确的粘粒含量。     

盐城市某港区砂土液化评价体系建立

砂土液化引起的地基土大变形是港口工程破坏的重要原因。因此,港口地区的液化判别方法选择的合理性、判别结果的准确性就显得尤为重要。针对某港区砂土液化问题,选择临界标贯击数法、Seed简化法、BP神经网络法、基于GIS的液化判别法等四种液化评价方法,进行砂土液化势评价并分析对比,建立基于GIS三维液化评价体系。结果表明:研究区15m以上砂土液化趋势较大,15m以下液化趋势较小。     

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。     

砂土地震液化预测的人工神经网络模型

在简要分析BP算法的基础上,应用BP网络的理论与方法,选取烈度、震中距、平均粒径、不均匀系数、地下水埋深、砂层埋深、标贯击数、剪应力比等8个实测指标,建立了砂土液化预测的神经网络模型。通过实例计算与模型评价、验证了该模型的科学性、高效性并较规范法、Seed简化法等传统方法具有更高的预测精度,说明人工神经网络是解决非线性问题的有效方法之一。     

饱和砂土液化判别方法的局限性及综合应用实例

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。     

基于中国砂土液化数据库的标准贯入试验液化判别方法研究

历史地震液化调查数据是液化判别方法构建、改进以及验证的重要基础,也是检验现有液化认识和理论的主要标准。通过吸收我国集集、巴楚和松原等地震液化数据,将基于标准贯入试验（standard penetration test,简称SPT）锤击数的液化数据量库从121个增至465个。采用该液化数据库,对比研究了我国建筑抗震设计规范液化判别方法（简称建规法）、2个双曲线模型以及循环剪应力比CSR简化方法等4种基于SPT液化判别方法的可靠性。结果显示：2个双曲线模型能够很好地判别液化和非液化数据,成功率超过85%,对液化数据和非液化数据的判别成功率保持均衡;建规法以及CSR简化方法判别结果存在不足;地震烈度为7度区液化数据和非液化数据混合情况较多,不同液化判别公式判别效果均不够理想,而对8度区和9度区液化数据,4种方法判别成功率较高;与以往液化概率判别公式对比,基于CSR计算方法,采用新液化数据给出的液化风险评估概率判别公式虽然采用数据量不同,但公式预测临界线匹配良好;建规法存在明显不足,对饱和砂层埋深大于10 m的深层土液化判别结果过于保守。研究成果可为改进我国规范中液化判别方法提供参考。     

我国规范液化分析方法的发展设想

通过分析我国地震形势、液化震害潜在威胁以及震害防御工作现状,阐明了我国发展液化分析方法的客观需求,简要评述了我国规范中现有液化判别方法,总结了我国近来两次大地震液化考察经验,提出了与规范修订相关的研究设想。通过我国地震安全性评价工作的发展现状以及我国大陆地震重点监视区与第四纪沉积分布性态分析,说明了我国发展液化分析方法的必要性和紧迫性。根据2003年新疆巴楚地震和2008年汶川大地震中液化震害考察结果,比较我国规范现状,提出了与未来规范的完善和发展相关的10个研究课题,包括：液化对设计谱的影响、 特殊土类液化判定标准、区域性的液化判别标准、场地液化概率评价、基于液化土层PGD的结构物损害估计、液化引起地裂缝的生成条件、基于剪切波速的液化判别方法、VI度区内场地液化及危害性判定、深层土液化判定以及场地液化的现场判定和识别技术     

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。     

关于砂（粉）土地震液化的判别公式——审稿后的思考

对于液化判别,不论是用什么方法,也不论是砂土或粉土,其基础都是根据已有的有限震例调查资料。可以说,这完全是一种经验关系,甚至可以说这仅是一种非常粗略的概率判别或趋势判别。即使是列入《规范》[1]的判别方法,对于一个具体实例来说,都可能存在着相当的误判概率。作为一个岩土工程师,我们要求的是根据各种因素的判别结果,作出合理的工程判断。如果文献[2]的重点也是强调根据各种因素进行综合判断,那无疑是完全应该肯定和鼓励的。但如果是讨论SPT法和CPT法哪个更好,则可能是不一定必要的。因为对于这些判别方法(公式)的来由和当时的概…     

南京砂强度特征与静态液化现象分析

在松散、中密和密实状态下,以南京粉细砂三轴固结不排水试验结果为基础,进行了强度、变形与静态液化特征的分析。松散南京砂强度特性表现出典型的应变软化,当轴向变形小于1 %时强度达到最大值,而后急剧降低;在50,100 kPa围压时发生了静态液化。但随着固结压力的增大,静态液化消失。与南京砂具有相同土骨架的松散纯净砂却在低围压下未出现静态液化,其形成机制是：粉粒的存在未使土体孔隙比发生较大变化,却引起更大的体缩性;中密和密实南京粉细砂表现出加工硬化的强度特征,临界应力状态线倾角高达55°,具有较高的抗静态液化能力。     

Fundamental yet simplified model for liquefaction instability

A fundamental procedure is proposed for the identification of liquefaction in saturated soils based on the instability in the material's microstructure. The disturbed state concept (DSC) provides a unified constitutive model for the characterization of entire stress–strain behaviour under cyclic loading, and the values of disturbance at threshold states in the deforming microstructure provides the basis for the identification of liquefaction. The procedure is verified with respect to laboratory behaviour of two sands, saturated Ottawa and Reid Bedford. A mathematical analysis of the DSC constitutive matrix is also performed. Procedures for the application of the DSC for simplified analysis and design, and in finite element procedures are presented. It is believed that the proposed model can provide a fundamental yet simplified procedure for liquefaction analysis, and as a result, it is considered to be an improvement over the available empirical and energy-based procedures. © 1998 John Wiley & Sons, Ltd.     

Geotechnical reconnaissance and liquefaction analyses of a liquefaction site with silty fine sand in Southern Taiwan

Geotechnical reconnaissance of a recurrent liquefaction site at a Quaternary alluvial deposit in southern Taiwan was conducted to establish a comprehensive case history for liquefaction on silty fine sand with high fines content. The liquefaction occurred at a silty fine sand layer with D₅₀ = 0.09 mm and fines content greater than 35% and was triggered by a M_w = 6.4 earthquake on March 4, 2010, which induced maximum horizontal acceleration up to 0.189 g at the site. In situ subsurface characterizations, including standard penetration test, cone penetration test, and shear wave velocity measurement, were performed as well as cyclic simple shear tests on undisturbed specimens retrieved by a modified hydraulic piston sampler. Comparisons of cyclic resistance ratios (CRRs) indicate that CPT sounding with standard penetration rate could overestimate the resistance ratio and drainage conditions during penetration should be considered for high fines content soil in the liquefaction analysis. Additionally, variations of CRRs from different in situ tests indicate that correlations among in situ tests and CRR could be soil specific and precautions should be taken when using these curves on silty fine sands.     

Shear strength and pore-water pressure characteristics of sandy soil mixed with plastic fine

Recent earthquake case histories have revealed the liquefaction of mixtures of sand and fine particles during earthquakes. Different from earlier studies which placed an emphasis on characterisation of liquefaction in terms of the induced shear stress required to cause liquefaction, this study adopted a strain approach because excess pore-water pressure generation is controlled mainly by the level of induced shear strains. The current study includes the results of a set of laboratory tests carried out on sand specimens with the same relative densities and variation in the plastic fines (kaolinite or bentonite) contents ranging from 0 to either 30 % and consolidated at mean confining pressure of 100, 200 and 300 kPa using static triaxial test apparatus, in order to study the influence of fine content and other parameters on the undrained shear strength and liquefaction potential of clayey sand specimens; also, pore-water pressures in the specimens are discussed. Results of tests show that the peak strength decreases as the fines (kaolinite or bentonite) content increases up to a threshold content of fines (FC_th) after which, increases in plastic fine content lead to improve the peak shear strength of specimens, and also the ultimate steady-state strength has been improved due to the increased in plastic fines content. Also, pore pressure build-up in clayey sands is generally slower than that observed in pure sand.     

Reliability analysis of soil liquefaction based on standard penetration test

A review of probabilistic and deterministic liquefaction evaluation procedures reveals that there is a need for a comprehensive approach that accounts for different sources of uncertainty in liquefaction evaluations. For the same set of input parameters, different models provide different factors of safety and/or probabilities of liquefaction. To account for the different uncertainties, including both the model and measurement uncertainties, reliability analysis is necessary. This paper presents a review and comparative study of such reliability approaches that can be used to obtain the probability of liquefaction and the corresponding factor of safety. Using a simplified deterministic Seed method, this reliability analysis has been performed. The probability of liquefaction along with the corresponding factor of safety have been determined based on a first order second moment (FOSM) method, an advanced FOSM (Hasofer–Lind) reliability method, a point estimation method (PEM) and a Monte Carlo simulation (MCS) method. A combined method that uses both FOSM and PEM is presented and found to be simple and reliable for liquefaction analysis. Based on the FOSM reliability approach, the minimum safety factor value to be adopted for soil liquefaction analysis (depending on the variability of soil resistance, shear stress parameters and acceptable risk) has been studied and a new design safety factor based on a reliability approach is proposed.     

基于Logistic回归模型的砂土液化概率评价

以国内外23次地震中200组场地液化实测数据为基础,通过Logistic回归分析,建立关联修正标准贯入击数N160cs与循环应力比CSR的液化概率模型。以50 %液化概率水平为液化与非液化的临界点,建立了指数形式的抗液化应力比CRR计算式,新建概率模型预测饱和砂土液化与非液化的成功率分别为85.71 %和76.14 %,具有较高的可靠性。与已有模型比较,使用了新的数据和修正系数,消除了一些不合理的偏差,总体判别结果偏于安全。为了将确定性分析方法与概率分析方法联系起来,建立了抗液化安全系数FS与液化概率PL的关系式。算例结果表明,新建概率模型简单、实用、可靠。     

Prediction of cyclic resistance ratio for silty sands and its applications in the simplified liquefaction analysis

Liquefaction resistance of granular soils is commonly characterized by the cyclic resistance ratio (CRR) in the simplified shear stress procedure of liquefaction potential assessment. This parameter is commonly estimated by cyclic tests on reconstituted samples or empirical correlations between liquefied/non-liquefied case histories. The current study employs results of cyclic triaxial tests on reconstituted soil specimens and presents a predictive equation for cyclic resistance ratio (CRR) of clean and silty sands. The CRR equation is a function of relative density, effective mean confining pressure, non-plastic fines content, number of harmonic cycles for liquefaction onset, and some other basic soil properties. It is demonstrated that the developed relationship obtains reasonable accuracy in the prediction of laboratory-based CRR. Based on the developed CRR model, new relationships are then presented for the coefficient of effective overburden pressure (K_σ) and magnitude scaling factor (MSF), two important modification factors in the simplified shear stress procedure. These new modification factors are then compared with those recommended by previous researchers. Finally, the possible application of the proposed CRR model in field condition is shown for a specific case. This study provides a preliminary insight into the liquefaction resistance of silty sands prior to the complementary laboratory studies.     

Laboratory Investigation into the Effects of Silty Fines on Liquefaction Susceptibility of Chlef (Algeria) Sandy Soils

In a number of recent case studies, the liquefaction of silty sands has been reported. To investigate the undrained shear and deformation behaviour of Chlef sand–silt mixtures, a series of monotonic and stress-controlled cyclic triaxial tests were conducted on sand encountered at the site. The aim of this laboratory investigation is to study the influence of silt contents, expressed by means of the equivalent void ratio on undrained residual shear strength of loose, medium dense and dense sand–silt mixtures under monotonic loading and liquefaction potential under cyclic loading. After an earthquake event, the prediction of the post-liquefaction strength is becoming a challenging task in order to ensure the stability of different types of earth structures. Thus, the choice of the appropriate undrained residual shear strength of silty sandy soils that are prone to liquefaction to be used in engineering practice design should be established. To achieve this, a series of undrained triaxial tests were conducted on reconstituted saturated silty sand samples with different fines contents ranging from 0 to 40 %. In all tests, the confining pressure was held constant at 100 kPa. From the experimental results obtained, it is clear that the global void ratio cannot be used as a state parameter and may not characterize the actual behaviour of the soil as well. The equivalent void ratio expressing the fine particles participation in soil strength is then introduced. A linear relationship between the undrained shear residual shear strength and the equivalent void ratio has been obtained for the studied range of the fines contents. Cyclic test results confirm that the increase in the equivalent void ratio and the fines content accelerates the liquefaction phenomenon for the studied stress ratio and the liquefaction resistance decreases with the increase in either the equivalent void ratio or the loading amplitude level. These cyclic tests results confirm the obtained monotonic tests results.     

Assessment of soil liquefaction potential based on numerical method- a case study of an urban railway project

Paying special attention to geotechnical hazards such as liquefaction in huge civil projects like urban railways especially in susceptible regions to liquefaction is of great importance. A number of approaches to evaluate the potential for initiation of liquefaction, such as Seed and Idriss simplified method have been developed over the years. Although simplified methods are available in calculating the liquefaction potential of a soil deposit and shear stresses induced at any point in the ground due to earthquake loading, these methods cannot be applied to all earthquakes with the same accuracy, also they lack the potential to predict the pore pressure developed in the soil. Therefore, it is necessary to carry out a ground response analysis to obtain pore pressures and shear stresses in the soil due to earthquake loading. Using soil historical, geological and compositional criteria, a zone of the corridor of Tabriz urban railway line 2 susceptible to liquefaction was recognized. Then, using numerical analysis and cyclic stress method using QUAKE/W finite element code, soil liquefaction potential in susceptible zone was evaluated based on design earthquake.     

定轴排水剪切试验中各向异性砂土的力学响应

南京云母砂主要由片状颗粒组成,具有较为明显的各向异性特性。采用香港科技大学的自动控制空心圆柱扭剪仪进行了应力主轴方向角分别为10°、30°、60°、80°的密实云母砂定轴剪切试验,研究云母砂的初始各向异性规律。为研究中主应力的影响,又对同一密度的试样在中主应力系数b＝0.1、0.5、1.0三种不同情况下进行定轴剪切试验。试验结果表明,在大主应力方向角从0°～90°的变化过程中,强度先减小后增大,且随着b值的增加强度增大;变形表现出明显的各向异性,随着b值的增加体变增大