A study on the identification of liquefaction-induced failures on ground surface based on the data from the 1999 Kocaeli and Chi-Chi earthquakes

One of the major causes of earthquake damage is liquefaction. However, it doesn't result in severe harm unless it leads to ground surface damage or ground failure. Therefore, prediction of potential for ground surface damage due to liquefaction is one of the important issues in microzonation studies for liquefaction-induced damage in areas with high seismicity. In 1985, based on a database compiled from Chinese and Japanese earthquakes, Ishihara considered the influence of the non-liquefied cap soil on the occurrence or non-occurrence of ground failure (mainly sand boiling), and proposed an empirical approach to predict the potential for ground surface damage at sites susceptible to liquefaction. However, some investigators indicated that this approach is not generally valid for sites susceptible to lateral spread or ground oscillation. In this study, a contribution to improve the approach by Ishihara is made. For the purpose, an index called liquefaction severity index (LSI) and data from two devastating earthquakes, which occurred in Turkey and Taiwan in 1999, were employed. The data from liquefied and non-liquefied sites were grouped and then analysed. Based on the observations reported by reconnaissance teams who visited both earthquake sites and the results of the liquefaction potential analyses using the filed-performance data, a chart to assess the potential for ground surface disruption at liquefaction-prone areas was produced. The analyses suggest that the procedure proposed by Ishihara is quite effective particularly for the occurrence of sand boils, while the bounds suggested in this method generally may not be valid for the prediction of liquefaction-induced ground surface disruption at sites susceptible to lateral spreading. The chart proposed in this study shows an improvement over the Ishihara's approach for predicting the liquefaction-induced ground surface damage. The microzonation maps comparing the liquefaction sites observed along the southern shore of Izmit Bay and in Yuanlin, and the surface damage and non-damage zones predicted from the proposed chart can identify accurately the liquefaction (sand boiling and lateral spreading) and no-liquefaction sites.     

First-level liquefaction hazard mapping of Laoag City,Northern Philippines

During the 1990 Luzon earthquake (M_s 7.8), the central part of Luzon Island, Philippines suffered much from liquefaction-related processes. Examination of inventories shows that the affected areas lie on certain geological environments that are characteristically vulnerable to liquefaction. Based on this local experience and the findings of earlier workers correlating geological setting with liquefaction susceptibility, a first-level map of liquefaction hazard for Laoag City, Northern Philippines, was produced. Distinct micro-geomorphological units were identified within the mainly fluvio-deltaic setting of the study area. The liquefaction susceptibility of each unit was then ranked as high, moderate, low or non-liquefiable, taking also the geomorphological evolution of the area into account. The geomorphological model of the fluvio-deltaic basin was tested against the results of the georesistivity survey carried out in this study. Moreover, compatibility of the liquefaction susceptibility map with historical liquefaction records supported the validity of the proposed ranking. The study showed that microzonation based on geomorphological criteria is indeed very useful in less-developed countries like the Philippines, where funds for a more rigorous determination of liquefaction potential are limited and not always available.     

Cyclic liquefaction screening of sand with non-plastic fines:Critical state approach

There have been significant advances in the application of critical state,CS,in liquefaction potential assessment.This was done by comparing state parameter,j with estimated characteristic cyclic stress ratio,CSR due to an earthquake.A cyclic resistance ratio,CRR curve,which can be determined from cyclic liquefaction tests,separates historical liquefied and non-liquefied data points(j,CSR).On the other hand,the concepts of equivalent granular state parameter,j*,which was developed for sands with fines,can be used in lieu j to provide a unifying framework for characterizing the undrained response of sands with non/low plasticity fines,irrespective of fines content(fc).The present work combines these two propositions,and by merely substituting j*for j into the aforementioned CS approach to capture the influence of fc.A series of static and cyclic triaxial tests were conducted,separately and independently of the concept of j*,for sand with up to fc of 30%.The clean sand was collected from Sabarmati river belt at Ahmedabad city in India which was severely affected during the Bhuj earthquake,2001.The experimental data gave a single relation for CRR and j*which was then used to assess liquefaction potential for a SPT based case study,where fc varies along the depth.The prediction matched with the field observation.     

Soil liquefaction susceptibility and hazard mapping in the residential area of Kütahya (Turkey)

This study presents the results of both field and laboratory tests that have been undertaken to assess liquefaction susceptibilities of the soils in Kütahya city, located in the well-known seismically active fault zone. Liquefaction potentials of the sub-surface materials at Kütahya city were estimated by using the geological aspect and geotechnical methods such as SPT method of field testing. And, the data obtained have been mapped according to susceptibility and hazard. The susceptibility map indicated “liquefable” and “marginally liquefable” areas in alluvium, and “non-liquefable” areas in Neogene unit for the magnitude of earthquake of M=6.5; whereas, liquefaction hazard map produced by using of liquefaction potential index showed the severity categories from “very low” to “high.” However, a large area in the study area is prone to liquefy according to liquefaction susceptibility map; the large parts of the liquefable horizon are mapped as “low” class of severity by the use of the liquefaction potential index. It can be said that hazard mapping of liquefaction for a given site is crucial than producing liquefaction susceptibility map for estimating the severity. Both the susceptibility and hazard maps should be produced and correlated with each other for planning in an engineering point of view.     

A liquefaction severity index suggested for engineering practice

One of the major tasks in earthquake geotechnical engineering is the preparation of liquefaction susceptibility maps. For this purpose, some indices associated with liquefaction susceptibility are used. However, the currently used indices have some limitations. In this study, a liquefaction severity index, which can be used in preparation of susceptibility maps, is suggested. The suggested severity index is applied to two sites selected from Taiwan (Yuanlin) and Turkey (Inegol) to examine performance. The application indicated that the suggested index shows a good performance for the selected sites, and can be considered as a tool for further studies.     

Artificial neural network and liquefaction susceptibility assessment: a case study using the 2001 Bhuj earthquake data,Gujarat, India

This study pertains to prediction of liquefaction susceptibility of unconsolidated sediments using artificial neural network (ANN) as a prediction model. The backpropagation neural network was trained, tested, and validated with 23 datasets comprising parameters such as cyclic resistance ratio (CRR), cyclic stress ratio (CSR), liquefaction severity index (LSI), and liquefaction sensitivity index (LSeI). The network was also trained to predict the CRR values from LSI, LSeI, and CSR values. The predicted results were comparable with the field data on CRR and liquefaction severity. Thus, this study indicates the potentiality of the ANN technique in mapping the liquefaction susceptibility of the area.     

Real-time assessment framework of spatial liquefaction hazard in port areas considering site-specific seismic response

This paper proposes a systematic framework for real-time assessment of spatial liquefaction hazard of port areas considering local seismic response characteristics based on a geographic information system (GIS) platform. The framework is integrated and embedded with sequential, interrelated subprocedures and a database for liquefaction-induced damage evaluation that standardizes and both individually and collectively quantifies analytical results. To integrate the current in situ condition of a selected port area, the framework functions as a spatial database system for geotechnical and structural data and as a recipient of automatic transmission of seismic monitoring data. The geotechnical profile correlated with liquefaction potential is compiled into a geotechnical spatial grid built by geostatistical methods. Linked with the geotechnical spatial grid, the processing of site-specific responses is automatically interpreted from previously derived correlations between rock acceleration and maximum acceleration of each soil layer. As a result, the liquefaction severity is determined based on a combined geotechnical spatial grid with seismic load correlation in real-time according to a simplified procedure, allowing calculation of the liquefaction potential index (LPI). To demonstrate practical applications of the framework in estimating the liquefaction hazard in real-time, liquefaction-hazard maps were visualized for two earthquake scenarios, verifying the applicability of the proposed framework.     

Use of microtremor in liquefaction hazard mapping

This study shows how microtremor measurements can be used as an aid to liquefaction hazard mapping and zonation, as demonstrated in Laoag City, Northern Philippines. From microtremor measurements, qualitative information on subsoil conditions was obtained and a site classification map was generated. The map was combined with the geomorphology-based liquefaction susceptibility map to produce an integrated liquefaction hazard zonation map. This integrated map is deemed to be more accurate in depicting relative liquefaction susceptibility since it combines information on the distribution of potentially liquefiable soils in terms of geology and grain characteristics with information on the stiffness and thickness of these soils. With information about the thickness of the deposits, an idea of the severity of liquefaction-related damage can also be gathered since thicker deposits relate to more serious damage. Plots of historical liquefaction cases, as well as borehole data and resistivity profiles in the study area, support the validity of the integrated map. The use of microtremor, therefore, constitutes an effective and inexpensive approach to liquefaction hazard zonation, and as such is very useful in less-developed countries like the Philippines and other areas where funds for more rigorous investigations are not always available.     

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.     

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.     

An energy-based interpretation of sand liquefaction due to vertical ground motion

In several recent earthquakes, high vertical ground accelerations accompanied by liquefaction were observed. Downhole records have also shown that large vertical accelerations do not necessarily originate from the source, but rather get amplified towards the ground surface. Given the advantages of energy-based interpretation of liquefaction triggering due to S-waves, this approach is used together with finite element analyses to investigate vertical motion amplification and ensuing liquefaction. The results show the importance of the post-resonance response cycles, while hysteretic damping based on total stresses, accounting for the water in the pores, is shown to be very low, explaining the observed amplification.     

LPI-based approach for calibrating the severity of liquefaction-induced failures and for assessing the probability of liquefaction surface evidence

Liquefaction Potential Index (LPI) is used as an assessing tool of liquefaction susceptibility. Based on the existing correlation of the LPI values with the liquefaction potential of a site, liquefaction hazard maps have been compiled. The evaluation of liquefaction susceptibility of the soil layers that had been taken into account for the calculation of LPI value, on the existing classifications, was based on the “Chinese criteria”. However, Seed et al. [Seed, R.B., Cetin, K.O., Moss, R.E.S., Kammerer, A.M., Wu, J., Pestana, J.M., Riemer, M.F., Sancio, R.B., Bray, J.D., Kayen, R.E., Faris, A., 2003. Recent advances in soil liquefaction engineering: a unified and consistent framework. 26th annual ASCE L.A. Geotechnical Spring Seminar, Long Beach, California. 71 pp.] concluded that those criteria are conservative and proposed a modification of them.The basic aim of this paper is to examine the impact of these modifications to the existing LPI-based calibrations of severity scale of liquefaction-induced failures and to propose a new one if it is needed, using box–whisker plot method. The data set that was analyzed is compiled by borings with SPT from liquefied and non-liquefied sites in Taiwan, in Turkey and in Greece.Moreover, a LPI-based formula is proposed, as an outcome from the application of logistic regression analysis to the data set, which can be used for predicting the liquefaction surface occurrence. In addition, a discriminant function is suggested for classifying a site as liquefiable or not. In this approach, the LPI and the thickness of the non-liquefiable cap layer are taken into account as the classification parameters.     

Evaluation of liquefaction potential hazard of Chennai city, India: using geological and geomorphological characteristics

According to the latest UNFA Report on state of world population 2007, unleashing the potential of urban growth by 2030, the urban population will rise to 5 billion or 60?% of the world population. Liquefaction in urban areas is dangerous phenomenon, which cause more damage to buildings and loss of human lives. Chennai, the capital city of the State Tamil Nadu in India, is one of the densely populated cities in the country. The city has experienced moderate magnitude earthquakes in the past and also categorized under moderate seismic hazard as per the Bureau of Indian Standards (BIS in Criteria for earthquake resistant design of structures; Bureau of Indian Standards, New Delhi, 1893 2001). A study has been carried out to evaluate the liquefaction potential of Chennai city using geological and geomorphological characteristics. The subsurface lithology and geomorphological maps were combined in the GIS platform for assessing the liquefaction potential. The liquefaction hazard broadly classified into three categories viz., liquefaction likely, possible and not likely areas. Mainly, the liquefaction likely areas spread along the coastal areas and around the river beds. The rest of the areas are liquefaction not likely and possible. The present map can be used as first-hand information on regional liquefaction potential for the city, and it will be help to the scientists, engineers and planners who are working for future site-specific studies of the city.     

Assessing probability of surface manifestation of liquefaction at a given site in a given exposure time using CPTU

This paper is a follow-up to a previous paper on the subject of liquefaction potential index (LPI), a parameter that is often used to characterize the potential for surface manifestation of liquefaction at a given site subjected to a given shaking level (represented by a pair of peak ground surface acceleration a_max and moment magnitude M_w). In the previous paper by Juang and his coworkers, the LPI was re-calibrated for a piezocone penetration test (CPTU) model, and a simplified model based on LPI was created for computing the conditional probability of surface manifestation of liquefaction (P_G). In this paper, the model for this conditional probability P_G is extended into a complete framework for assessing the probability of surface manifestation of liquefaction in a given exposure time at a given site subjected to all possible ground motions at all seismic hazard levels. This new framework is formulated and demonstrated with an example site in 10 different seismic regions in the United States.     

The liquefaction of clayey soils under cyclic loading

This paper seeks to investigate the liquefaction of clayey soils, a phenomenon that has been the trigger for many natural disasters in the last few decades, including landslides. Research was conducted on artificial clay-sand mixtures and natural clayey soils collected from the sliding surfaces of earthquake-induced landslides. The undrained response of normally consolidated clayey soils to cyclic loading was studied by means of a ring-shear apparatus. For the artificial clay-sand mixtures, it was found that the presence of a small amount of bentonite (≤ 7%) would cause rapid liquefaction, while a further increase in bentonite content (≥ 11%) produced the opposite effect of raising soil resistance to liquefaction by a significant degree. It was demonstrated that the bentonite-sand mixture was considerably more resistant to liquefaction than the kaolin-, and illite-mixtures, given the same clay content. The test results of plastic soils revealed the significant influence of plasticity on the liquefaction resistance of soil. The microfabric of clayey soil was investigated by means of a scanning electron microscope. The analysis showed that the liquefaction potential of soil was strongly related to certain particle arrangements. For example, soil vulnerable to liquefaction had an open microfabric in which clay aggregations generally gathered at the sand particle contact points, forming low-strength “clay bridges” that were destroyed easily during cyclic loading. On the other hand, the microfabric of soil that was resistant to liquefaction appeared to be more compact, with the clay producing a matrix that prevented sand grains from liquefying. In the case of the natural soils, the obtained results indicated that their cyclic behavior was similarly influenced by factors such as clay content, clay mineralogy and plasticity. The relation between the liquefaction potential of natural soil and its microfabric was thus also established. On the basis of the obtained results, the authors posited an explanation on the mechanism of liquefaction for clayey soil.     

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.     

静力触探法对巴楚地震液化判别的适用性

2003年2月24日新疆巴楚-伽师地区发生的6.8级地震中出现了自1996年唐山大地震以来我国大陆境内最为严重的砂土液化现象。以此地震液化调查为基础,检验包括我国规范液化判别方法、Robertson方法和Olsen方法的国内外现有静力触探试验为指标的液化判别方法的适用性。结果表明,我国规范、Robertson方法、Olsen方法在对巴楚地震液化场地判别中,总体上非液化场地判别成功率高于液化场地判别成功率,非液化场地的判别成功率分别为88%、71%和88%,但对液化场地判别成功率分别为55%、73%和45%,明显偏于危险,原因需要进一步查明,建立适合局部地区的液化判别方法应是未来必须进行的工作。     

Liquefaction potential and susceptibility mapping in the city of Yalova, Turkey

This study presents results of both field and laboratory tests that have been used to asses liquefaction susceptibilities of the soils in Yalova city, located in the well-known seismically active North Anatolian Fault Zone. Liquefaction potentials of the sub-surface materials in Yalova city were estimated by using the standard penetration test (SPT) method of field testing. The data obtained have been mapped according to susceptibility, and the susceptibility maps based on the geotechnical data indicated a moderate to high susceptibility to liquefaction for the magnitude of earthquake of M=7.4. Both the high groundwater level and the grain size of the soils, in conjunction with the active seismic features of the region, result in conditions favourable to the occurrence of liquefaction. When the surface and near surface geological conditions were taken under consideration, it was seen that the study areas geology is prone to liquefaction having a moderate liquefaction susceptibility. If geologic and geomorphological criteria are considered, it should be understood that the study area as discussed under the regions geology is susceptible to liquefaction. The geotechnical data largely support the geologic-based liquefaction susceptibility of the study area.     

最近20年地震中场地液化现象的回顾与土体液化可能性的评价准则

回顾了1994年美国Northridge地震、1995年日本阪神地震、1999年土耳其Kocaeli地震、1999年台湾集集地震、2008年中国汶川地震、2010年智利Maule地震、2010～2011新西兰Darfield地震及余震、2011年东日本地震中大量的、不同类型的液化实例调查与研究,发现这些地震的液化具有以下特点：（1）罕见的特大地震（Mw9.0）使远离震中300～400 km的新近人工填土发生严重的大规模液化;（2）特大地震（Ms8.0、Mw8.8）使远离震中的低烈度Ⅴ～Ⅵ度地区发生严重液化;（3）海岸、河岸附近地区的新近沉积冲积、湖积土,填筑时间不到50年的含细粒、砂砾人工填土,容易发生严重液化;（4）天然的砂砾土层液化发生严重液化;（5）发生了深达20 m的土层液化现象;（6）松散土层液化后可以恢复到震前状态并再次发生液化;（7）高细粒（粒径≤75 ?m）含量≥50%或高黏粒（粒径≤5 ?m）含量≥25%的低-中塑性土严重液化,对介于类砂土与类黏土之间的过渡性态土,有时地表未见液化现象;（8）液化土层的深度较深或厚度较小时,容易出现地面裂缝而无喷砂现象;有较厚的上覆非液化土层时,场地液化不一定伴随地表破坏。液化实例证明,第四系晚更新世Q3地层可以发生严重液化;黏粒含量不是评价细粒土液化可能性的一个可靠指标;低液限、高含水率的细粒土易发生液化,采用塑性指数PI、含水率wc与液限LL之比作为细粒土液化可能性评价的指标是适宜的。综合Boulanger和Idriss、Bray和Sincio、Seed和Cetin等的液化实例调查与室内试验研究成果,建议细粒土液化可能性的评价准则如下：PI ＜12且wc/LL＞0.85的土为易液化土,12＜PI≤20和/wc/LL≥0.80的土为可液化土;PI ＞20或wc/LL＜0.80的土为不液化土。     

Back-analysis of liquefaction in the 2006 Mozambique earthquake

A magnitude 7 earthquake occurred in southwest Mozambique in February 2006, triggering extensive liquefaction around the fault rupture. Samples were recovered from the liquefied soils for laboratory testing to calibrate a numerical model for the assessment of liquefaction susceptibility. Laboratory tests and simulations confirm that the alluvial sands from the area affected by the earthquake have a very high susceptibility to liquefaction, although this depends strongly on the in situ density, which is likely to be low since the soils are deposited in a major flood plain. Since many areas of Mozambique, including parts of the major coastal cities, are on similarly loose and saturated deposits, there could be a significant liquefaction hazard in future earthquakes.