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This paper proposes a framework for screening and evaluating seismic performance of river earth embankments on liquefiable foundation soils. The framework is executed in the order of simplest screening by soil liquefaction potential map to preliminary and detailed evaluation of seismic performance of embankment according to the sufficiency of data and the complexity and accuracy of the methods. The seismic performances of embankments are classified into four levels based on the seismic-induced crest settlement. The method used for preliminary evaluation is based only on the factors of safety of foundation soils against liquefaction and the embankment slope against sliding. The static softening method (SSM) and dynamic effective stress method (DESM) are suggested for detailed evaluation of seismic performance. SSM is a static FDM or FEM analysis for estimating liquefaction-induced settlement by weakening the strength of the liquefied foundation soil under the action of the self-weight of the embankment. However, DESM is a dynamic history analysis for estimating liquefaction-induced settlement by simulating the generation and dissipation of pore water pressure in the liquefaction process of foundation soils under the action of the self-weight of the soil embankment and its seismic inertial force. The damaged embankment of the Maoluo River in the 1999 Chi-Chi earthquake was used as a case to demonstrate the feasibility of this framework. The results showed that the simpler the adopted method is, the more conservative the estimated settlement. [ABSTRACT FROM AUTHOR]

This study simulates and discusses the behavior of low-rise buildings on liquefiable ground with different ground water table levels during earthquakes via centrifuge modeling. The test results reveal that lowering the water table can effectively limit the settlement of structures on liquefiable ground. However, this also reduces the seismic isolation effect of soil liquefaction. As the water table is lowered, the acceleration amplification in structures increases slightly. In addition to this, the effect of reinforcing the first floor slab was studied and the results show that such reinforcement can generate a significant anti-liquefaction effect in areas with a high water table. Engineers can use this combination of improvement methods to achieve better designs. • The results of dynamic centrifuge tests are used to clarify the anti-liquefaction effect of the concerned methods. • The anti-liquefaction effect of lowering the ground water table is explained by the concept of the cyclic stress ratio. • Several notes on anti-liquefaction design are proposed as a reference for practical engineers. [ABSTRACT FROM AUTHOR]

The average shear wave velocity of the top 30 m of the subsurface profile (Vs30) is a critical parameter to characterize the seismic site class. Since Vs30 is a quantitative index and measurable by geophysical techniques, the use of Vs30 becomes popular and is widely used in practice. However, the Vs30 of a site may vary due to the different Vs measurement methods used. This could result in a different seismic site class and design force. To quantify the effect of measurement methods on Vs and seismic site classification. This study collected high quality geotechnical investigation reports with standard penetration test (SPT) N-values, and shear wave velocities measured by suspension logging, SCPT, down-hole test and cross-hole logging. The correlations between Vs and SPT-N by different methods were then built and compared. The results show that Vs by suspension logging is relatively high in comparison with those by SCPT and cross-hole logging. The effect on the site classification resulting from the different Vs measurement methods is then demonstrated with several examples. [ABSTRACT FROM AUTHOR]

Shield tunnels are widely constructed throughout urban areas with most of their sections being fully or partially embedded in liquefiable deposits. The possible damage to shield tunnels caused by soil liquefaction should be considered in their seismic design. Thus, this paper proposes a FDM-based analysis method to study this issue. Several dynamic time history analyses were performed for a shield tunnel embedded at different positions in ground with a liquefiable layer. It was found that the liquefied soil behaves like a fluid, and the tunnel uplifts due to buoyancy if the tunnel is fully embedded in a liquefied soil deposit. However, if the tunnel is only partially embedded in the liquefied deposit, with its top or bottom section in a non-liquefied deposit, the interaction behavior is quite complex and differs from that of a tunnel fully embedded in liquefied soil. To check the safety of the lining, the internal forces of the lining were monitored and compared with its strength curves throughout the shaking history. The proposed framework can be used as a reference for a practical engineer to consider the dynamic behavior of a shield tunnel in a liquefiable deposit. • The study suggests a procedure to assess the seismic behavior of a shield tunnel in the ground with a liquefiable deposit. • The safety assessment of the tunnel was performed by comparing the lining internal forces with the capacity curves. • The location of a shield tunnel would affect its dynamic behavior in a liquefiable deposit during seismic loading. [ABSTRACT FROM AUTHOR]

• A new and elegant CPT method for soil liquefaction evaluation is presented with its probabilistic extension. • The model uncertainties of various CPT methods are calibrated based on case histories in Taiwan. • The consideration and applications of model uncertainties of CPT methods for liquefaction assessments are provided. This paper aims to calibrate model uncertainties of the current Cone Penetration Test (CPT) methods for assessing soil liquefaction potential and introduce a new and concise one called the hyperbolic function (HBF) method based on the unique Chi-Chi earthquake database in Taiwan. The development and features of the HBF method were introduced at first. The performance and model uncertainty of each CPT method is then evaluated with a database of historical and Chi-Chi earthquake cases using the indices of the predicted success rate and bias-factor models, respectively. The success rate evaluations show that the HBF is one of the most accurate methods. The calibrated bias-factor models can indicate the conservatism of each CPT method applied to the Taiwan sites. Afterward, the liquefaction hazard curves associated with these CPT methods for Taiwan sites are derived based on the case histories of liquefaction and non-liquefaction in Taiwan. A real case study to illustrate the applications of these calibrated models evaluating liquefaction hazards to an offshore wind farm near Taiwan western coast is also demonstrated in this paper. These above results bring not only recommendations on CPT liquefaction assessment methods incorporated into the Technical Specifications for Site Investigation and Design of offshore wind farms in Taiwan, but procedures to calibrate regional biased models for other offshore wind farms in the world. [ABSTRACT FROM AUTHOR]

Abstract This research conducts dynamic time-history analysis and a modified cross-section racking deformation (MCSRD) method to analyze the collapse mechanism of the Daikai Subway during the 1995 Kobe earthquake using FLAC2D. A simplified approach to consider the nonlinear behavior of a structure element is imported and combined with the FLAC2D built-in nonlinear soil constitutive models to accurately consider the nonlinear interaction between the soil material and structure. Based on the proposed framework, the damage evolution process of the Daikai Subway station can be traced by the dynamic time-history analyses. The collapse pattern roughly agrees with field observation. Regarding the MCSRD method, the critical member of the "central column" is identified but the internal forces did not reach its limit state; this may be because inertial force is neglected, which is a characteristic of the pseudo-static method. Therefore, it is recommended to conduct dynamic time-history analysis for a shallow buried tunnel in soft soil because the inertial force may largely influence the seismic characteristics. [ABSTRACT FROM AUTHOR]

This study documented the case history of the new Sanyi railway tunnel. The New Austrian tunneling method (NATM)-built mountainous tunnel was seriously damaged during the 1999 Chi-Chi earthquake. In order to better understand the vulnerability and the deformation of the underground structure subject to strong ground motion, the modified cross-section racking deformation (MCSRD) method was used to evaluate the seismic performance of the tunnel. The analyses carefully took the nonlinear soil-structure interaction into account in order to derive damage pattern of the tunnel. Based on the analysis results, in addition to the extremely strong ground motion, numerical testing identified the causes of the disaster to include rectangle-like geometry at the refuge section, non-reinforcement of the second lining, and imperfect backfilling. The results also showed that the second lining of the NATM-built tunnel sustained substantial seismic loading and should be suitably reinforced in seismically active areas. The effect of the reinforcement of the second lining was demonstrated with a reinforcement example. [ABSTRACT FROM AUTHOR]

The modified cross-section racking deformation (MCSRD) method can accurately derive the vulnerability and the deformation of underground structures resulting from different magnitudes of earthquakes; while the nonlinear soil-structure interaction can be determined by numerical calculation. Compared with dynamic analysis, the MCSRD method is a more efficient and simpler way of achieving the seismic performance-based design (SPBD) for underground structures. To better apply the method using FLAD2D, the research includes several numerical examples, which study critical numerical points of the approach. The framework of the MCSRD method to assess the seismic capacity of underground structures will be demonstrated with an example. [ABSTRACT FROM AUTHOR]

This paper presents major preliminary observations on the liquefaction-induced damages in the Meinong earthquake ( M = 6.4). The severe damages to buildings centered on Huian and Sanmin Streets in Tainan City where the places were reclaimed fish or farm ponds with poor construction quality from many decades ago. To better understand the effect due to the soil liquefaction at these sites, the information provided by the in situ 13 Standard Penetration Test boreholes and 5 Cone Penetration Test soundings accompanying with the PGAs derived from the near seismographs was used to conduct the soil liquefaction evaluation by the Seed method (Seed et al. in J Geotech Eng ASCE 111(12):1425-1445, 1985) when subject to the Meinong earthquake. The liquefaction potential index (LPI) was then evaluated accordingly. From the results, it was found that the estimated damage severity was not consistent to the field conditions if the local site effect was not taken into account. To better reflect the site response in such sites, the sites' PGAs in the PGA contour map were multiplied by 1.5 times to quantify the amplification effects due to the soft geological condition. In addition, the PGAs based on other simple approaches were evaluated as well for comparison. Besides, the effects of fines content and magnitude scaling factor were also discussed in this paper. After that, several common simplified methods were also used to calculate the LPI when subject to the Meinong earthquake in order to evaluate the applicability of these simplified methods. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a framework for assessing the probability of exceeding a specified liquefaction-induced settlement at a given site in a given exposure time. This framework deals not only with the effect of liquefaction (in terms of settlement) but also with probabilistic characterization of all possible ground motions at a given site (in terms of a joint distribution of a max and M w). Additionally, a new concept, referred to herein as liquefaction-induced settlement hazard curve, is introduced for assessing the annual rate of settlement exceedance at a given site. This settlement hazard curve concept has the potential to be a very useful tool in the field of geotechnical earthquake engineering. Satisfactory results are obtained in the demonstration examples analyzed with the proposed framework. Whereas the proposed framework is simple and effective, further refinements to this framework, especially on the treatment of epistemic uncertainty, are warranted. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: This paper presents an empirical method and a modified cross-section racking deformation (MCSRD) method to assess the seismic capacities of the old Sanyi railway tunnels that were constructed about one hundred years ago. The proposed MCSRD method is simple and fast. It can automatically take into account the interaction between underground structure and the surrounding ground under seismic action, by using a 2-D finite difference method. The seismic capacities based on the MCSRD method are higher than those based on the empirical method by one JMA intensity scale. The field monitored performance of these tunnels during the 1935 Hsinchu-Taichung and 1999 Chi-Chi earthquakes agree very well with the seismic capacities assessed by the MCSRD method. [Copyright &y& Elsevier]

Abstract: This paper proposed a semi-analytical approach for analyzing the problems of the tunnel water inflow. The approach was developed by using the classical ground water theory. The groundwater problem in a finite domain is transformed to a problem in an infinite domain by the image method and the superposition principle. Using the convolution–deconvolution method, the time-variant inflow problem is transformed to a constant flow problem. The calculation formula was developed for the conceptualized hydro-geological models for the tunnel inflow problems. The computation is simple and fast in comparison with the other 2D and 3D numerical methods. The parameters required in the approach are few and easily estimated. Two cases of the tunnel water inflow were simulated by the approach. The calculated inflows agree well with the general trends of the measured inflow data. [Copyright &y& Elsevier]

This paper examines the performance of shear wave velocity-standard penetration test (VS-SPT) models and shear wave velocity-piezocone penetration test (VS-CPTU) models developed in the literature and evaluates their transformation variabilities based on VS-SPT-CPTU datasets collected from thirteen alluvium sites in the Taipei Basin, Taiwan. These data show that VS is strongly correlated with the depth of soil (D) whereas it is weakly correlated with SPT-N or CPT-qc, which indicates that most of the transformation models in the literature are unsuitable to these sites since they are usually formulated without soil depth. Thus, VS-SPT and VS-CPTU empirical formulas and their transformation uncertainties for these sites in the Taipei Basin are re-calibrated in this paper, and they perform more unbiased with lower variability as shown in this paper, which indicates they provide a suitable approach to those sites for VS prediction. Finally, the application of these re-characterized models on VS30 prediction is demonstrated with a practical example. [ABSTRACT FROM AUTHOR]

On February 6, 2016, a moment magnitude (Mw) 6.4 earthquake struck southern Taiwan and devastated the Tainan area. Although the intensity of ground shaking was only moderate (peak ground acceleration, ~ 0.2 g), widespread damage associated with liquefaction (e.g., settlement and tilt of residential buildings) was observed. In this study, soil liquefaction in two residential areas during the Meinong earthquake was assessed comprehensively via field investigation and thorough numerical analysis. Liquefaction triggering analysis using field measurement was performed initially to identify the liquefied layer. The agreement between the gradation of ejecta and in situ soil sample corresponding to the liquefied layer confirmed the analysis results. The liquefied layer is shallow, and the damage level (i.e., settlement) is highly correlated to the distance between the footing and liquefied layer. In the second part of the study, a simplified numerical analysis was proposed to simulate the interaction between the shallow footing structure and liquefied soil. By gradually reducing the soil strength of the liquefied layer in the analysis, the residual strength of the liquefied soil was found to be 10–20% of the original one to reproduce the observed building settlement. The obtained residual strength is compatible with the previous study based on the back analysis of embankment or slope failures. [ABSTRACT FROM AUTHOR]

Simplified methods for assessing soil liquefaction potential based on the standard penetration test (SPT) are prevalent in practice and widely accepted by several seismic design codes. When encountering sites that have not been investigated using SPT, such as offshore sites or sites with a high level of gravel content, engineers can only substitute the methods based on piezocone penetration test data (CPT-qc methods) or shear wave velocity measurements (VS-based methods); however, these two approaches perform inconsistently with methods based on SPT data (SPT-N methods). As a result, this paper exploits the datasets consisting of SPT, CPTU, and in situ seismic test measurements from 13 alluvium sites in the Taipei Basin to compare the performance of prevalent SPT-N, CPT-qc, and VS-based methods. The discrepancies (uncertainties) of these methods are characterized as Gaussian distribution models, which is believed to be a feasible strategy for predicting equivalent results for SPT-N methods when SPT data are not available. Finally, the application of the proposed models to liquefaction potential index evaluation is demonstrated using a real case study. [ABSTRACT FROM AUTHOR]

This paper presents a probabilistic framework for assessing the liquefaction hazard at a given site in a given exposure time. Ten sites from different seismic-prone regions of the USA are studied to validate the developed probabilistic framework. Additionally, this framework is extended from the focus of liquefaction potential at a given soil element (or finite layer) to the concern of the whole soil column based on the concept of liquefaction potential index (LPI) proposed by Iwasaki and his co-workers. In this extended framework, the probability of surface manifestation of liquefaction at a given site subjected to all ground motions at all hazard levels in a given exposure time is determined. As an example to illustrate this probabilistic framework, the widely used, standard penetration test (SPT)-based method by Youd et al. is adopted as a building block in the framework. This framework is illustrated with examples and its versatility is demonstrated. Finally, the procedure for extending the developed framework to the evaluation of ground settlement is outlined. [ABSTRACT FROM AUTHOR]

An earthquake with an epicenter offshore of Hualien City in eastern Taiwan occurred at midnight on February 6, 2018. The Richter magnitude (ML) of the earthquake was 6.26 and the seismic intensity ranged up to level VII, the strongest seismic intensity level regulated in Taiwan. Almost all the major damage resulting from this seismic event was occurred near both sides of the Milun Fault, where records from nearby strong motion stations displayed the characteristics of near-fault ground motions. The main seismic damage was the collapse of four buildings with soft bottom stories, one of which resulted in fourteen of the seventeen total fatalities. Comparing the acceleration response spectra with the design response spectra sheds light on the effects of near-fault ground motions on the collapsed buildings. Based on the eventual forms of collapsed buildings, building collapses that have generally led to major casualties in past seismic events around the world can be classified into sit-down, knee-down and lie-down types. In addition to the four collapsed buildings, seismic reconnaissance on other buildings, bridges, ports, and non-structural components have also been conducted. This study explores the issues and challenges arising from the reconnaissance results and thereby enhances learning from the seismic event. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a review of the state-of-the-art of Liquefaction Potential Index (LPI), a parameter created by Iwasaki and his co-workers to characterize the potential for surface manifestation of liquefaction, and the results of an extensive calibration of the LPI with a focus on a new model based on piezocone testing (CPTU). The results show that the threshold criteria developed by Iwasaki and his co-workers for interpreting the calculated LPI are not universally applicable. To the contrary, the LPI must be re-calibrated when any component model of the LPI framework is replaced with a new model. The new CPTU model is a significant advance in the cone penetration-based liquefaction evaluation; in fact, it is the first simplified model that explicitly incorporates pore pressure measurement as one of its input parameters. This CPTU model is applicable to a wide range of soil types and thusly enables a more convenient and effective modeling of liquefaction effects within the LPI framework. Probabilistic characterization of the new CPTU model is carried out. Finally, the results of the calibration of the LPI calculated with this CPTU model, along with the concept of the probability of surface manifestations, are presented and discussed. [Copyright &y& Elsevier]

This paper presents an update of the Hyperbolic Function (HBF) method to evaluate the liquefaction potential of sandy soils. The HBF method was created after the 1999 Chi-Chi, Taiwan Earthquake (M w = 7.6) using the database of case histories developed based on field observations and in situ and laboratory tests in areas affected by the 1999 event. The updated HBF method reported herein reflects the 20-year efforts of research and practice in Taiwan after the 1999 event. Here, the original database created by Hwang and his co-workers was first re-examined and updated. The updated Chi-Chi database was supplemented with the cases derived from the 2016 Meinong, Taiwan Earthquake, and some selected data from other parts of the world. This new database was then used to update the parameters of the HBF model through rigorous statistical methods. The HBF model is unbiased (as it corresponds to a probability of 50%). The updated HBF method, a deterministic model, is further extended into a probabilistic version through rigorous statistical calibration. This probabilistic version is expressed as a mapping function that relates the factor of safety (F S) against liquefaction to the probability of liquefaction (P L). The design recommendation for engineering practice in Taiwan is provided based on the calibrated P L - FS mapping function. The updated HBF method is demonstrated through examples to be an easy-to-use procedure for liquefaction potential evaluation. Use of Bayes' theorem for updating the liquefaction probability and the new concept of liquefaction likelihood ratio are also discussed. • An updated database of liquefaction and non-liquefaction cases from Taiwan is created. • An easy-to-use HBF model for liquefaction evaluation is presented, which emerged from two decades of research in Taiwan. • Procedures for the calibration of empirical models for liquefaction evaluation are introduced and illustrated. • The concept of the liquefaction likelihood ratio (LR) is presented with a graph of LR contour curves for Bayesian updating. [ABSTRACT FROM AUTHOR]