Adaptive sampling strategy for characterizing spatial distribution of soil liquefaction potential using cone penetration test

Characterizing spatial distribution of soil liquefaction potential is critical for assessing liquefactionrelated hazards(e.g.building damages caused by liquefaction-induced differential settlement).However,in engineering practice,soil liquefaction potential is usually measured at limited locations in a specific site using in situ tests,e.g.cone penetration tests(CPTs),due to the restrictions of time,cost and access to subsurface space.In these cases,liquefaction potential of soil at untested locations requires to be interpreted from limited measured data points using proper interpolation method,leading to remarkable statistical uncertainty in liquefaction assessment.This underlines an important question of how to optimize the locations of CPT soundings and determine the minimum number of CPTs for achieving a target reliability level of liquefaction assessment.To tackle this issue,this study proposes a smart sampling strategy for determining the minimum number of CPTs and their optimal locations in a selfadaptive and data-driven manner.The proposed sampling strategy leverages on information entropy and Bayesian compressive sampling(BCS).Both simulated and real CPT data are used to demonstrate the proposed method.Illustrative examples indicate that the proposed method can adaptively and sequentially select the required number and optimal locations of CPTs.

An improved method of evaluating liquefaction potential with the velocity of shear-waves

According to the results of cyclic triaxial tests, a linear correlation is presented between liquefaction resistance and elastic shear modulus, which shows the relation of Gmax (kPa) with (σd/2)1/2(kPa)1/2. When applied to soils from different sites, the correlation can be normalized in reference to its minimum void ratio (emin). Accordingly, an improved method is established to evaluate the liquefaction potential with shear-wave velocity. The critical shear-wave velocity of liquefaction is in linear relation with 1/4 power of depth and the maximum acceleration during earthquakes, which can be used to explain the phenomenon that the possibility of liquefaction decreases with the increment of the depth. Compared with previous methods this method turns out simple and effective, which is also verified by the results of cyclic triaxial tests.

Application of machine learning to the Vs-based soil liquefaction potential assessment

Earthquakes can cause violent liquefaction of the soil, resulting in unstable foundations that can cause serious damage to facilities such as buildings, roads, and dikes. This is a primary cause of major earthquake disasters. Therefore, the discrimination and prediction of earthquake-induced soil liquefaction has been a hot issue in geohazard research. The soil liquefaction assessment is an integral part of engineering practice. This paper evaluated a dataset of 435 seismic sand liquefaction events using machine learning algorithms. The dataset was analyzed using seven potential assessment parameters. Ten machine learning algorithms are evaluated for their ability to assess seismic sand liquefaction potential, including Linear Discriminant Analysis(LDA), Quadratic Discriminant Analysis(QDA), Naive Bayes(NB), KNearest Neighbor(KNN), Artificial Neural Network(ANN), Classification Tree(CT), Support Vector Machine(SVM), Random Forest(RF), e Xtreme Gradient Boosting(XGBoost), Light Gradient Boosting Machine(Light GBM). A 10-fold cross-validation(CV) method was used in the modeling process to verify the predictive performance of the machine learning models. The final percentages of significant parameters that influenced the prediction results were obtained as Cyclic Stress Ratio(CSR) and Shear-Wave Velocity( VS1) with 56% and 38%, respectively. The final machine learning algorithms identified as suitable for seismic sand liquefaction assessment were the CT, RF, XGBoost algorithms, with the RF algorithm performing best.

Dynamic properties and liquefaction behaviour of cohesive soil in northeast India under staged cyclic loading

Estimation of strain-dependent dynamic soil properties, e.g. the shear modulus and damping ratio, along with the liquefaction potential parameters, is extremely important for the assessment and analysis of almost all geotechnical problems involving dynamic loading. This paper presents the dynamic properties and liquefaction behaviour of cohesive soil subjected to staged cyclic loading, which may be caused by main shocks of earthquakes preceded or followed by minor foreshocks or aftershocks, respectively. Cyclic triaxial tests were conducted on the specimens prepared at different dry densities （1.5 g/cm3 and 1.75 g/cm3） and different water contents ranging from 8% to 25%. The results indicated that the shear modulus reduction （G/Gmax） and damping ratio of the specimen remain unaffected due to the changes in the initial dry density and water content. Damping ratio is significantly affected by confining pressure, whereas G/Gmax is affected marginally. It was seen that the liquefaction criterion of cohesive soils based on single-amplitude shear strain （3.75% or the strain at which excess pore water pressure ratio becomes equal to 1, whichever is lower） depends on the initial state of soils and applied stresses. The dynamic model of the regional soil, obtained as an outcome of the cyclic triaxial tests, can be successfully used for ground response analysis of the region.

Intensity measures for seismic liquefaction hazard evaluation of sloping site

This work investigates the correlation between a large number of widely used ground motion intensity measures(IMs) and the corresponding liquefaction potential of a soil deposit during earthquake loading. In order to accomplish this purpose the seismic responses of 32 sloping liquefiable site models consisting of layered cohesionless soil were subjected to 139 earthquake ground motions. Two sets of ground motions, consisting of 80 ordinary records and 59 pulse-like near-fault records are used in the dynamic analyses. The liquefaction potential of the site is expressed in terms of the the mean pore pressure ratio, the maximum ground settlement, the maximum ground horizontal displacement and the maximum ground horizontal acceleration. For each individual accelerogram, the values of the aforementioned liquefaction potential measures are determined. Then, the correlation between the liquefaction potential measures and the IMs is evaluated. The results reveal that the velocity spectrum intensity(VSI) shows the strongest correlation with the liquefaction potential of sloping site. VSI is also proven to be a sufficient intensity measure with respect to earthquake magnitude and source-to-site distance, and has a good predictability, thus making it a prime candidate for the seismic liquefaction hazard evaluation.

Liquefaction Assessment in Golem Area, Albania, by Means of In-situ Tests

The liquefaction is a very significant phenomenon in clayey silty soils, silty sands and also sands. The high potential of liquefaction is generally recognized when these types of soils are laid under the hydrostatic water table. Low plasticity silts, silty sands and sands are found as recent alluvial deposits in the western coastal part of Albania, especially in the sandy beaches of Adriatic Sea near Durres City. The aim of this study is to evaluate the soil liquefaction potential in the area of Golem. Ten CPTUs （cone penetration test with pore pressure measurements） are carried out for the site investigation of soils. In this paper, results of the CPTU based liquefaction analysis are presented. The data of two CPTUs （10 in total） are analyzed and factor of safety was found by considering different levels of hazard and ground water. The results of liquefaction potential analysis show that the soils in the area of Golem have a high risk of liquefaction.

Soil Liquefaction Hazard Evaluation by the New Seismic Dilatometer Marchetti Test （SDMT）

Soil liquefaction, and the permanent deformations that frequently result from it, have caused significant damage in past earthquakes. The procedures used in contemporary geotechnical earthquake engineering practice are generally based on simplified procedures for the evaluation of the liquefaction potential. The work describes a framework for performance-based earthquake engineering and its use in the development of a performance-based procedure for liquefaction hazard evaluation. The performance-based procedure will be used to show how consistent application of conventional procedures for evaluation of liquefaction potential can influence performance prediction. Implications for liquefaction-resistant design will also be discussed. The purpose is to summarize current procedures for practical prediction of liquefaction behavior, to describe recent advances in the understanding of liquefaction behavior, and to describe the incorporation of this improved understanding into new solutions for detailed modeling of soil liquefaction, Simplified procedures for evaluation of liquefaction hazards will be reviewed relatively briefly, with more details devoted to emerging knowledge about the mechanics of liquefiable soil behavior, and methods for incorporating those mechanics into improved models for performance prediction. In particular it focuses about the influence on the evaluation of Cyclic Resistance Ratio （CRR） by different in-situ tests （Cone Penetration Test （CPT）. Standard Penetration Test （SPT） and Seismic Dilatometer Marchetti Test （SDMT）） and by different shear waves velocity measurements （Down Hole D-H. Cross Hole C-H, Seismic Dilatometer Marchetti Test SDMT）.

The Hidden Earthquake Induced Liquefaction Risks in the Rohingya Refugee Camp Hills & Surrounding Areas of Ukhiya, Cox’s Bazar, Bangladesh—A Geotechnical Engineering Approach

Liquefaction is one of the major catastrophic geohazards which usually occurs in saturated or partially saturated sandy or silty soils during a seismic event. Evaluating the potential liquefaction risks of a seismically prone area can significantly reduce the loss of lives and damage to civil infrastructures. This research is mainly focused on the earthquake-induced liquefaction risk assessment based on Liquefaction Potential Index (LPI) values at different earthquake magnitudes (M = 5.0, 7.0 and 8.0) with a peak ground acceleration (amax) of 0.28 g in the Rohingya Refugee camp and surrounding areas of Ukhiya, Cox’s Bazar, Bangladesh. Standard Penetration Test (SPT) results have been evaluated for potential liquefaction assessment. The soils are mainly composed of very loose to loose sands with some silts and clays. Geotechnical properties of these very loose sandy soils are very much consistent with the criteria of liquefiable soil. It is established from the grain size analysis results;the soil of the study area is mainly sand dominated (SP) with some silty clay (SC) which consists of 93.68% to 99.48% sand, 0.06% to 4.71% gravel and 0% to 6.26% silt and clay. Some Clayey Sand (SC) is also present. The silty clay can be characterized as medium (CI) to high plasticity (CH) inorganic clay soil. LPI values have been calculated to identify risk zones and to prepare risk maps of the investigated area. Based on these obtained LPI values, four (4) susceptible liquefaction risk zones are identified as low, medium, high and very high. The established “Risk Maps” can be used for future geological engineering works as well as for sustainable planning, design and construction purposes relating to adaptation and mitigation of seismic hazards in the investigated area.

中国模式下砾性土液化指数评价新方法

砾性土地震液化是我国土木工程震害防治技术体系建设面临的新问题,砾性土液化指数作为砾性土液化判别的最终表征量及抗液化对策的实际控制指标,是当前体系发展中亟待突破的瓶颈。该文继承中国模式,基于2008年我国汶川地震实测数据,提出以超重型圆锥动力触探击数比余量为基本变量的砾性土液化指数评价新方法。采用我国独有资料,构建砾性土的理论计算液化指数与宏观调查液化指数间函数关系,分析我国规范中既有液化指数与液化等级对应关系的可行性,建立适于砾性土液化指数与液化等级的对等关系,以实测资料多方论证新方法的合理性。提出的新方法,保持了中国模式的优势,可为实际工程应用和我国规范修订提供直接的技术支持。

黄土液化作用及其次生灾害风险评估方法初探——以积石山M_(S)6.2地震为例

2023年12月18日甘肃积石山6.2级地震引发的黄土液化泥石流地质灾害,造成了大量人员伤亡和财产损失。以此为背景,系统梳理了液化调查、风险评估和风险区划的工作思路:选定地区液化的内在和诱发因子,收集并分析资料,拟定调查工作底图,以调查问卷的形式开展液化影响因素摸底工作,开展针对性的外业调查或辅以物探和钻探工作,得到土壤液化发育潜势实际材料图;其后借用常规地质灾害的评估方法,开展调查区域的易发性、易损性评价和风险评价,得到调查区风险区划图。利用此方法对积石山地震诱发的泥石流灾害进行验证,分析其液化灾害的地质环境背景、形成机理和危害特征,并对其发生的风险进行评价。文章首次提出土的液化作用及其次生灾害区域调查因子的选择和风险评估的流程,可为开展土层液化作用及其次生灾害隐患区排查、国土空间规划,特别是高烈度山区集中居住点地质安全评估和选址建议提供参考。

场地液化势评价概率模型

本文提出了场地液化势评价概率模型。基于世界范围内多次震后场地液化性状实测资料 ,采用人工神经网络 (ANN)来搜索标贯击数Ncr与抗液化能力之间的非线性关系 ,进而导出安全系数与液化概率之间的关系。建立的修正液化指数公式可对可液化场地进行液化概率评价。修正液化指数有明确的概率意义 ,适用于饱和砂土等可液化场地液化势评价的风险决策。

瞬态瑞利面波勘探技术在公路工程勘察中的应用

结合工程实例介绍了一种新的勘探技术———瞬态瑞利面波法 ,并总结了测试技术要点 ,包括测试分析系统、测试条件等 ,最后分析了应用效果及应用中的一些问题。

上海苏州河故道砂质粉土液化综合判别

本文根据工程实际的大量现场测试和室内试验 ,提出了上海苏州河故道砂质粉土综合运用宏观评判和微观定量判定进行液化评价的原则和方法。对上海地区地基土液化判别有一定的实际意义。

淮安市砂土地震液化势的综合评估

建立了BP神经网络模型LM算法的砂土地震液化判别方法,采用LVQ模式分类网络对数据进行分类,选取唐山地震时76个场地、320组现场液化勘察资料为研究对象,训练和检验网络模型的数据各160组,结果表明,该方法的砂土液化预测准确度为96.8%。根据淮安市典型场地土的钻孔资料,采用《建筑抗震设计规范法》液化判别法(规范法)、美国国家地震研究中心建议的液化判别简化方法(NCEER法)和谢君斐-陈国兴液化判别方法(谢-陈法)等3种液化判别方法及本文提出的BP神经网络模型液化判别方法对22个钻孔、120标贯点进行了液化判别,结果表明:14种地震液化判别方法的计算结果基本一致;2NCEER法比谢-陈法的计算结果要保守;3谢-陈法与规范法的计算结果很吻合,预测正确率相差不大;4规范法相对BP神经网络模型法的计算结果要保守;5BP神经网络模型法比其他3种方法的预测结果更符合实际的液化规律。最后,综合4种方法的液化判别结果给出了该地区地震液化势的评估结果,并给出了部分典型地质剖面土层地震液化势分布图。

地基砂土液化判别方法探讨

本文以我国《水利水电工程地质勘察规范》(GB 50287-2008)中的标准贯入锤击数液化判别法为基础,以该法进行应力修正的方法为依据,提出了采用附加应力等效埋深来考虑有限面积基础建筑物附加应力随深度扩散影响的液化判别新思路,以工程设计中参数取值常用平均值和小值平均值来考虑标贯击数和黏粒含量的离散性,同时借用有限元网格离散求解思路确定砂层可能液化的区域。以宁朗水电站闸坝工程为例进行了案例分析,结果表明:在地震设防烈度VII度时,闸基下中细砂层近震时不发生液化,远震时在闸基4个角点下的局部小区域内发生液化。

基于BP神经网络的饱和砂土液化判别方法

基于唐山地震中大量的砂土液化现场实测资料,选取描述地震动特性的烈度、震中距、地面峰值加速度和描述砂土层埋藏环境条件的地下水位、标贯点深度(土层深度)、上覆非液化覆盖土层厚度、有效覆盖压力,以及表示砂土自身属性的标准贯入锤击数、平均粒径、不均匀系数、修正标贯击数共11个指标的不同组合作为输入变量,采用快速BP算法和LM算法构造了饱和砂土液化判别的BP神经网络预测模型。通过所建网络模型的训练、验证和应用,结果表明:(1)所建14个BP神经网络模型都是有效的,液化判别的准确度与模型输入变量的不同组合有关;(2)增加网络模型的节点(考虑因素较多)并不一定能够提高BP神经网络模型的液化判别准确度,反而增加了BP神经网络模型的复杂性和学习时间;(3)两种算法的BP神经网络模型都有很高的液化判别准确度,LM算法的计算速率要比快速BP算法快得多,但在计算过程中需要更多的内存,建议采用LM算法;(4)采用所提BP神经网络模型的权值与阈值进行其它预测样本的液化判别时,判别结果可能偏于保守;(5)从影响砂土液化的主要因素、获取指标难易程度考虑,在与《建筑抗震设计规范》砂土液化判别公式考虑指标一致的情况下,建议采用BP神经网络模型M4或M5a,该模型简单、方便,且其预测准确度远高于《建筑抗震设计规范》

砂土滑动液化的初步分析

本文针对大量的滑坡现场观察到的滑体滑动引起严重的砂土液化现象描述了液化引起的危害。初步给出了砂土滑动液化的定义;分析了砂土滑动液化形成的机理以及砂土滑动液化势评价的初步设想。

基于动三轴试验的现场液化判别剪切波速法

通过控制土体剪切波速的动三轴液化试验 ,得到了更能真实地反映土体的抗液化能力的临界剪应变参数。文中探讨了各因素对临界剪应变的影响 ,并结合动三轴试验结果和剪切波速判别方法 ,对取土地区自由场地进行液化评估 。

饱和黄土的静态液化特性试验研究

利用GDS三轴测试系统,对原状黄土进行了等压/偏压固结不排水剪(ICU/ACU)、常剪应力排水剪(CQD)试验。ICU和ACU试验表明:土体的应力-应变模式为强烈应变软化型,得到了其稳态线和潜在不稳定区,提出液化发生的必要条件就是土体状态位于或被带到潜在不稳定区域内。CQD试验表明,土体破坏的启动摩擦角远小于稳态摩擦角。当其应力路径试图穿越不稳定区时发生不完全排水剪缩破坏,具有突发性,检验了提出的不稳定区域的有效性。基于潜在不稳定区域的位置和斜坡土体的应力状态,提出了饱和黄土静态液化分析方法。

GIS环境中砂土液化评价方法

本文介绍了一种适用于 GIS环境下分析液化可能性指标的砂土液化分析方法 ,详细阐述了分析过程和它与GIS的接口情况。