Probabilistic evaluation of seismic soil liquefaction potential based on SPT data

The performance-based liquefaction potential analysis was carried out in the present study to estimate the liquefaction return period for Bangalore, India, through a probabilistic approach. In this approach, the entire range of peak ground acceleration (PGA) and earthquake magnitudes was used in the evaluation of liquefaction return period. The seismic hazard analysis for the study area was done using probabilistic approach to evaluate the peak horizontal acceleration at bed rock level. Based on the results of the multichannel analysis of surface wave, it was found that the study area belonged to site class D. The PGA values for the study area were evaluated for site class D by considering the local site effects. The soil resistance for the study area was characterized using the standard penetration test (SPT) values obtained from 450 boreholes. These SPT data along with the PGA values obtained from the probabilistic seismic hazard analysis were used to evaluate the liquefaction return period for the study area. The contour plot showing the spatial variation of factor of safety against liquefaction and the corrected SPT values required for preventing liquefaction for a return period of 475 years at depths of 3 and 6 m are presented in this paper. The entire process of liquefaction potential evaluation, starting from collection of earthquake data, identifying the seismic sources, evaluation of seismic hazard and the assessment of liquefaction return period were carried out, and the entire analysis was done based on the probabilistic approach.     

基于人工神经网络的砂土液化势评价

本文利用静力触探（ＣＰＴ）场地液化数据,建立了液化势判定的反向传播神经网络模型,研究表明,同传统方法相比,人工神经网络方法在判别砂土液化势方面是可行的。     

基于综合法的岩溶山区生态系统脆弱性评价——以贵州省普定县为例

基于主成分分析法,以贵州省普定县区域内的13个行政村落为例,对影响该区生态系统脆弱度的9个变量进行分析,并利用欧式距离公式确定系统的脆弱性.结果表明,耕地面积是影响生态系统脆弱度的最主要因素,占的权重值为0.189,其次是石山地区的平均坡度;在研究区域中有7个村落达到强度脆弱或极强度脆弱,其中偏坡村的潜在脆弱性和胁迫脆弱性为最大;作为一个整体评价单元,研究区的生态系统脆弱度为0.653,属于强度脆弱区.为此,今后应该积极采取相应的治理措施,尤其是注意从控制耕地开发利用规模上来恢复生态环境.     

Assessment of seismic hazard and liquefaction potential of Gujarat based on probabilistic approaches

Gujarat is one of the fastest-growing states of India with high industrial activities coming up in major cities of the state. It is indispensable to analyse seismic hazard as the region is considered to be most seismically active in stable continental region of India. The Bhuj earthquake of 2001 has caused extensive damage in terms of causality and economic loss. In the present study, the seismic hazard of Gujarat evaluated using a probabilistic approach with the use of logic tree framework that minimizes the uncertainties in hazard assessment. The peak horizontal acceleration (PHA) and spectral acceleration (Sa) values were evaluated for 10 and 2?% probability of exceedance in 50?years. Two important geotechnical effects of earthquakes, site amplification and liquefaction, are also evaluated, considering site characterization based on site classes. The liquefaction return period for the entire state of Gujarat is evaluated using a performance-based approach. The maps of PHA and PGA values prepared in this study are very useful for seismic hazard mitigation of the region in future.     

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.     

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.     

Estimation model of sandy soil liquefaction based on RES model

In order to evaluate sandy soil liquefaction, Rock Engineering Systems (RES) was utilized to establish the estimation model of sandy soil liquefaction. Aiming at unascertained factors in the analysis of sandy soil liquefaction evaluation, earthquake magnitude, maximum ground acceleration, the value of standard penetration test, specific penetration resistance, relative density, mean particle size, and water table were selected as influencing factors of sandy soil liquefaction. The interaction matrix was utilized to describe the interaction among the factors. Expert semi-quantitative (ESQ) method was employed to code the interaction matrix. The interaction strength and dominance were analyzed by cause and effect diagram. Finally, the estimation model-based RES was proposed, and the results were in line with actual situation well. In addition, the improved estimation model-based RES was also presented and discussed, which was more convenient with the same prediction accuracy rate.     

On the efficiency and predictability of strain energy for the evaluation of liquefaction potential: A numerical study

Strain energy concept has been employed by the researchers for the assessment of liquefaction phenomenon which is a disastrous type of earthquake-induced failure in saturated soils. The efficiency and predictability conditions of strain energy concept for liquefaction potential assessment are investigated herein using effective stress numerical analyses. Several earthquake ground motions were introduced to the base of a calibrated numerical model using an advanced fully coupled constitutive model. Results of the numerical analyses indicate that earthquake-induced excess pore pressure is more rigorously proportional to strain energy compared with the other examined intensity measures. Subsequently, a simple relationship was derived using the results of dynamic analyses to predict cumulative strain energy density in terms of magnitude, source to site distance, and effective overburden pressure. This relationship, which tries to guarantee the predictability condition of strain energy demand, has demonstrated a successful capability in discrimination between the liquefied and non-liquefied case histories recorded after several well-known earthquakes. This study has provided a practical linkage between numerical analysis and field observations. Finally, it is concluded that although strain energy approach possesses a great conceptual efficiency in liquefaction potential assessment, its precise prediction in actual field conditions involves some difficulties.     

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。     

Indoor radon correlated with soil and subsoil radon potential—a case study

High indoor radon concentrations in a uranium-radium low-level area in the Eifel region, Germany, near the village of Döttingen are caused by ascending radon migration following the convection of groundwater and soil gas along pathways (fractures and faults) in the bedrock sediments of Lower Devonian age. Positive radon anomalies in the soil gas are found to coincide with the locations of houses showing the highest concentrations. These houses are older buildings without concrete foundation slabs. Normally radon concentrations in soil gas are highly correlated with the values of emanated radon calculated on the basis of radium content in the surrounding soils and rocks (diffusive radon potential). However, close to zones of tectonic fractures and faults around the maar-type volcano of Döttingen abnormally high radon concentrations, which were transported by circulating groundwater and postvolcanic exhalation of CO₂ (convective radon potential) were detected.     

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.     

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.     

Assessment of liquefaction potential of Erzincan Province and its vicinity,Turkey

One of the most important causes of damages after the earthquakes is the soil liquefaction. Liquefaction can be defined as temporary loss in strength of saturated sandy and silty deposits under transient and cyclic loadings due to excess pore water pressure. This study includes determination of liquefaction potential in Erzincan city center and its vicinity. Due to the proximity of the North Anatolian Fault Zone, in a probable earthquake, Erzincan Province is thought to be affected. In this context, the earthquake scenarios were produced using the empirical expressions. Liquefaction potential for different earthquake magnitudes was determined. These earthquake magnitudes were selected as 6.0, 6.5, 7.0, 7.5, respectively. Liquefaction potential was investigated using standard penetration test (SPT) data. The first stage of the study, 63 boreholes in different locations was drilled and SPT was performed. Disturbed and undisturbed soil samples were taken from these boreholes. Laboratory testing was performed to determine physical properties of soil samples, and liquefaction potential analyses were examined using three methods, namely Seed and Idriss (J Soil Mech Found Div ASCE 97(9):1249–1273, 1971), Tokimatsu and Yoshimi (Soil Found 23(4):56–74, 1983), Iwasaki et al. (Soil liquefaction potential evaluation with use of the simplified procedure. International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics, St. Louis, pp 209–214, 1981). In order to complete liquefaction analysis within a short time, MATLAB program was prepared. Liquefaction potential analyses were carried out with the MATLAB program. At the final stage of this study, liquefaction potential maps were prepared for different earthquake magnitudes. The expected results will be shared with the local authorities and important engineering remedial measurements will be proposed to prevent further life losses and to mitigate property losses.     

Evaluation of liquefaction potential based on CPT results using evolutionary polynomial regression

In this paper a new approach is presented, based on evolutionary polynomial regression (EPR), for determination of liquefaction potential of sands. EPR models are developed and validated using a database of 170 liquefaction and non-liquefaction field case histories for sandy soils based on CPT results. Three models are presented to relate liquefaction potential to soil geometric and geotechnical parameters as well as earthquake characteristics. It is shown that the EPR model is able to learn, with a very high accuracy, the complex relationship between liquefaction and its contributing factors in the form of a function. The attained function can then be used to generalize the learning to predict liquefaction potential for new cases not used in the construction of the model. The results of the developed EPR models are compared with a conventional model as well as a number of neural network-based models. It is shown that the proposed EPR model provides more accurate results than the conventional model and the accuracy of the EPR results is better than or at least comparable to that of the neural network-based models proposed in the literature. The advantages of the proposed EPR model over the conventional and neural network-based models are highlighted.     

城市地下水赋存环境分析与数值模拟——以长春城区为例

以长春城区为例,分析了城市地下水赋存环境的演变,概化出该区的水文地质概念模型。将土地利用类型和供水管道渗漏对地下水补给的影响纳入城市地下水数值模拟中,经过模型识别,实测水位与计算水位的绝对误差<0.5 m,井点数占观测井总数的85%,经检验满足国家标准(GB/T14497-93)要求。结果表明,模型细化后,水位拟合精度有所提高。     

基于数值模拟的城镇地质灾害危险性评价方法

定量计算城镇尺度地质灾害不同降雨强度下的危险性是地质灾害风险评价中的难点。以红层地区群发性浅层滑坡链式灾害为研究对象,探索一种新的城镇尺度下的地质灾害危险性量化评价方法,为城镇地质灾害风险评价奠定基础。通过查询喜德县米市河区域不同降雨频率下降雨参数,统计分析国家雨量站数据及近50 a的18场群发性地质灾害降雨历时、雨型分布特征。以土层厚度、植被覆盖度及地形数据处理为基础,基于STEM TRAMM数值计算方法及降雨分布曲线计算城镇地质灾害危险性,绘制研究区地质灾害危险性评价图。通过遥感解译数据、地面调查数据及灾害数据库数据与数值计算结果对比,表明应用降雨特征统计及STEM TRAMM数值计算方法精细化评价红层地区城镇地质灾害危险性具有良好的适应性、便捷性及科学性,可为其他不同孕灾背景下的城镇地质灾害危险性评价提供思路。     

倾斜土层地震液化诱发大变形数值分析方法

基于有限元理论,进行了缓坡土层地震液化引起大变形的数值方法研究,即采用二维有效应力动力有限元方法进行分析,在液化分析过程的每一时段考虑地震液化和振动软化得到土单元的模量,通过非线性静力方法计算每时段地震液化引起的大变形,得到土层各深度处的水平和竖向位移。由算例分析了地震动和土层坡度等因素的影响,通过对比分析表明了该方法的有效性,可为工程场地地震地质灾害评价提供参考数据。     

基于PCA-DDA原理的砂土液化预测模型及应用

影响砂土液化的因素有很多,建立多指标的液化预测模型非常有必要。目前所有的多指标砂土液化预测模型,均默认选取的判别因子之间相互独立,不存在相关性,可能导致各判别因子之间存在信息叠加而发生误判。以唐山地震砂土液化的25个案例为样本,选取8个影响因素作为砂土液化预测的初始判别指标,首先采用主成分分析（PCA）对各判别指标进行分析,对存在相关性比较高的指标进行了降维处理。基于降维后的4个主成分换算得到新的样本数据,以18个案例为学习样本,建立主成分分析与距离判别分析（DDA）相结合的砂土液化预测模型。利用建立的预测模型对18个案例进行回判,结果全部正确。对其他7个案例的液化情况进行了预测,并与规范法、Seed方法、BP法、DDA法的判别结果进行分析比较,结果表明基于主成分分析与距离判别方法的砂土液化判别模型预测准确率为100%。将模型应用于工程实例,判别结果也与实际情况一致,表明该模型具有良好的预测功能,可在实际工程中应用。     

基于数值模型的地下水水位预警体系研究——以临汾盆地为例

地下水是中国许多城市主要的供水水源,对地下水的过量开采将导致地下水降落漏斗、地面沉降和地裂缝等环境地质问题.进行地下水水位预警体系的研究对于合理开发和有效利用地下水资源具有重要的现实意义,笔者以临汾盆地为例,根据当地的水文地质条件,利用数学模型建立了地下水水位预警体系,研究结果可为当地水资源的可持续利用提供科学依据.