Search

• River bed elevation changes can contribute significantly to flood damage. • To model episodic river bed changes, we propose a new stochastic model. • We test the model using data from a highly active montane river. • Over long and short times, the modeled distributions fit the data well. • The model can forecast future geomorphic risk to riverine infrastructure. In some steep valleys, flood-induced changes in river bed elevation pose significantly greater risks to infrastructure than floodwaters alone. Over the short term, the river may aggrade or degrade by several meters during a single flood. Whereas floodwaters recede after each event, moreover, riverbed changes add up over successive floods. To quantify the resulting geomorphic risk and its evolution over time, we propose in this paper a new stochastic model of river bed elevation change. The bed is assumed to rise and drop according to a random walk, driven by the composition of two gamma processes that respectively pace the hydrologic forcing and the geomorphic response. The model can therefore incorporate various sources of uncertainty, associated with precipitation and debris flow activity within the contributing watershed. To test the model, we apply it to a highly active montane river, the Laonong River in southwestern Taiwan. Model calibration is achieved from a combination of long and short term data, including radiocarbon-dated deposits and modern river records. The modelled distributions fit the data well, including the likelihood of extreme changes. The model also produces a reasonable hindcast of the geomorphic damage suffered over the last ten years by Highway 20, a vulnerable road link sited along the river, and can be used to forecast future geomorphic risk. [ABSTRACT FROM AUTHOR]

Abstract: Typhoon Mindulle was the most severe typhoon across the Tachia River watershed following the 921 Chi-Chi earthquake, and resulted in extremely high precipitation of 1431mm that induced many landslides, debris flows, and debris floods in affected areas. This paper analyzes the debris flows in the Songhe area induced by Typhoon Mindulle by employing a numerical model for debris flow simulation. The FLO-2D numerical program was adopted to simulate the flow conditions of debris flows in the Songhe area, including flow depths, flow velocities, and sediment depositions. Comparing the field data with simulation results, this paper defines an Index of Accuracy to examine simulation accuracy. Ignoring the influence of houses in the alluvial fans, the simulation accuracy was 79.3% and 61.4%, respectively for the First and Second Branches of the Songhe Stream. Considering the house effect in the Songhe area raised the simulation accuracy to 82.3% and 75.5%, respectively for the First and Second Branches. In addition, the simulation considering the hydraulic structures established after Mindulle was executed. This study also adopted 24h accumulated precipitation at various recurrence intervals (10, 100, and 500years) to perform scenario simulation of debris flows. Based on the method of Swiss Disaster Degree Classification, consisting of influential intensity and occurrence probability parameters, this study classified the risk degree of hazardous debris-flow areas into three categories, including high, medium, and low. The proposed approach generates the risk distribution map that may be used for setting up a disaster mitigation strategy for the Songhe area. [Copyright &y& Elsevier]

Abstract: This paper is aimed at creating an empirical model for assessing failure potential of highway slopes, with a special attention to the failure characteristics of the highway slopes in the Alishan, Taiwan area prior to, and post, the 1999 Chi-Chi, Taiwan earthquake. The basis of the study is a large database of 955 slope records from four highways in the Alishan area. Artificial neural network (ANN) is utilized to “learn” from this database. The developed ANN model is then used to study the effect of the Chi-Chi earthquake on the slope failure characteristics in the Alishan area. Significant changes in the degrees of influence of several factors (variables) are found and possible reasons for such changes are discussed. The novelty of this paper lies in the fact that the developed ANN models are used as a tool to investigate the slope failure characteristics before and after the Chi-Chi earthquake. [Copyright &y& Elsevier]

Abstract: The objective of this paper is to present a new rock mass classification system which can be appropriate for rock slope stability assessment. In this paper an evaluation model based on combining the Analytic Hierarchy Process (AHP) and the Fuzzy Delphi method (FDM) was presented for assessing slope rock mass quality estimates. This research treats the slope rock mass classification as a group decision problem, and applies the fuzzy logic theory as the criterion to calculate the weighting factors. In addition, several rock slopes of the Southern Cross-Island Highway in Taiwan were selected as the case study examples. After determining the slope rock mass quality estimates for each cases, the Linear Discriminant Analysis (LDA) model was used to classify those that are stable or not, and the discriminant functions which can determine failure probability of rock slopes were carried out by the LDA procedure. Afterward, the results may be compared with slope unstable hazards occurring actually, and then the relation and difference between them were discussed. Results show that the proposed method can be used to assess the stability of rock slopes according to the rock mass classification procedure and the failure probability in the early stage. [Copyright &y& Elsevier]

This paper estimates the coefficients of volume compressibility from variation in compressible layer thickness and changes in piezometric heads by using detail ground surface surveys and a multilayer monitoring well at a selected site (Shigang) within the Choshui River alluvial fan in west Taiwan. The paper integrates various types of in situ monitoring tools, including leveling surveys, continuous global position system (GPS) stations, multilevel layer compression and groundwater pressure head-monitoring wells, to investigate the situation and progress of the subsidence problem in the region. The results from the cross-analyses of the measured data show that surface settlement caused by the compression of strata is between the depths of 60 and 210 m where the clayey stratum within 120–180 m was most pronounced and contributes up to 53% of the total compression. The results indicate that the clayey stratum is under normal consolidation. The results also reflect the fact that 20% of settlement contribution comes from the sandy stratum within 90–120 m; the elasto-plastic behavior of this sandy stratum is clear. The coefficients of volume compressibility of the clayey and sandy stratum analysed from the stratum''s compression records; they were 6.38×10-8 and 5.71×10-9 m2/N, respectively. Ultimately, this parameter estimation would permit to control and predict land subsidence based on change in pressure head which are related to groundwater extraction. [Copyright &y& Elsevier]

The Gangweigou floodway, across the Quiren and Rende districts in Tainan, Taiwan, was designed to bypass partial discharge in the Gangweigou River during heavy rainfall events for the purpose of flood control. This floodway was an excavated open channel supported by single or double rows of precast RC cantilever pile walls on each side of its banks; these piles were installed by the jetting-assisted method. Twenty days after the completion of the floodway, it was put to work for the first time during a heavy rainfall. Unexpectedly, the cantilever pile walls in several sections failed and caused the collapse of the slope behind the walls. This paper explores the failure mechanism and the real causes of failure in this case. Based on the conditions of hydrology and hydraulics, failure processes and the results of stability analyses, it was concluded that ignoring a possible bed incision or bank erosion was likely the primary problem with the improper design. The most critical condition was when the water level in the floodway quickly dropped, which resulted in rapid drawdown. The failure of the case could have been avoided if both the rapid drawdown condition and the potential of the channel bed incision were considered. [ABSTRACT FROM AUTHOR]

Earthquakes can generate seismic disturbances that propagate vast distances and trigger landslides that can achieve high-speeds. It remains difficult to identify the co-seismic ground motion of these landslides and their triggering earthquakes. In this paper, we report on the analysis of co-seismic ground motions generated by the initiating fracture and deposition impact of the Tsaoling landslide. The landslide, with a source volume of 125 × 10 6 m 3 , was triggered by the 1999 Chi-Chi earthquake in Taiwan. The ground motion was recorded by a strong ground motion station, CHY080, near the scar area. The polarization of the seismic waves indicates that the peak acceleration was parallel to the dip direction. Modified ensemble empirical mode decomposition (EEMD), with additional clustering analysis, was applied to decompose the seismic signals. Two instances were found in the seismic records of a series of peculiar wave packets, with the first being associated with the landslide initiation and the second the landslide impact on the deposit valley. To confirm the first landslide breakage, the decomposed signals were compared with the predictions of the analytic elastic wave model and Newmark analysis. The landslide impact was verified with a computational fluid dynamic simulation. Comparison between the EEMD decomposed signals, elastic wave theory, Newmark rigid body analysis, and numerical simulation demonstrates the claimed landslide motion. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the digital image correlation (DIC) method was used to monitor the full-field deformation of a retaining wall. Two retaining walls located in mountainous areas of Taiwan were investigated. The first, Fushan slope, was characterized by substantial long-term deformation, and the second, Bulao slope, was located beneath an expressway and was severely damaged by Typhoon Morakot. This paper first describes the preparation procedures for in situ applications of the DIC method. Various environmental factors such as fog, rain, light direction, and spot mark clarity affected measurement precision, and consequently produced monitoring images that were unsuitable for further analysis. The DIC analysis results clearly indicate the deformation pattern of the retaining walls. The proposed method is accurate and effective for performing long-term monitoring of retaining walls, and the results can be used to accurately predict the tendency, location, and quantity of retaining wall displacement. Therefore, the proposed DIC method can be implemented to prevent disasters caused by landslide. [Copyright &y& Elsevier]

Site characterization, which aims to characterize the subsurface stratigraphic configuration and the associated geo-properties, has long been a significant challenge in geological and geotechnical practice. Due to the complexity and inherent spatial variability of the geological bodies and the limited availability of borehole data, uncertainty is unavoidable in the characterized subsurface stratigraphic configuration and the associated geo-properties. In previous studies, the stratigraphic uncertainty and the geo-properties uncertainty were characterized separately. This paper proposes a conditional random field approach for a coupled characterization of stratigraphic and geo-properties uncertainties. The spatial correlation of the stratum existence between different subsurface elements and the spatial correlation of geo-properties are characterized by two autocorrelation functions, determined with the maximum likelihood principle. With the knowledge of the spatial correlation of the stratum existence, the stratigraphic configuration can be sampled using a modified random field approach. Then, the spatial correlation of the geo-properties is updated based on the sampled stratigraphic configuration. With the updated spatial correlation of the geo-properties, the spatial distribution of the geo-properties can readily be simulated with the conditional random field theory. The effectiveness of the proposed approach is demonstrated through a case study of probabilistic site characterization of an offshore wind farm site in Taiwan. To extend the applicability of the proposed approach, a probabilistic evaluation of liquefaction potential at this site under a given seismic shaking level is performed. • A probabilistic method for characterizing the geological model is proposed. • Characterizations of stratigraphic and geo-properties uncertainties are coupled. • Stratigraphic configuration is simulated with modified random field approach. • Spatial variability of geo-properties is simulated with conditional random field. • The spatial correlation structure is estimated with maximum likelihood principle. [ABSTRACT FROM AUTHOR]

This paper presents a new application of the Bayesian approach to objectively determine logic-tree weights for ground motion prediction equations (GMPEs) used in seismic hazard analysis. This is a considerable improvement over the current practice based on subjective judgment to determine the logic-tree weights for GMPEs. To demonstrate the feasibility of this Bayesian application, case studies at three sites in Taiwan were conducted. The results demonstrate that the logic-tree weights for three Next Generation Attenuation GMPEs can be determined in an objective and repeatable manner using this Bayesian calculation, which is based on the difference between predicted and observed peak ground accelerations. • A Bayesian application to determine logic-tree weights for PSHA • The determination based on observed earthquake ground motions • Case studies using the method also presented [ABSTRACT FROM AUTHOR]

Abstract: Fragility curves can be developed using analytical or empirical methods. When the actual building damage records and the associated ground motion data are available, empirical methods are often adopted. Traditionally, district-based records of building damage are analyzed for developing such fragility curves. In this paper, a new procedure based on the concept of “isointensity-isoexposure” is developed. The new procedure is demonstrated through a case study of the building damage records collected from the 1999 Chi-Chi, Taiwan earthquake. The results show that the fragility curves developed with the proposed procedure are more in-line with observations than with the traditional district-based procedure. The developed fragility model may be used for earthquake loss estimation and future emergency planning in the study area. The limitations of the proposed approach include: (1) the developed fragility curves are area-specific and may not be readily applicable to other regions, and (2) ground motion intensity data may not be available at every location in an area of interest. [Copyright &y& Elsevier]

Abstract: The region around Taiwan is well known for its unique geological setting which has resulted in a high seismicity. The Central Geological Survey, Taiwan (CGST), has launched a series of investigation on characterizing the active faults on the island. The CGST revealed that there are 33 active faults and their fault parameters are suggested in the latest publication in 2010. However, the uncertainties of return period and earthquake magnitude are not provided. The main objective of the paper is to study the impact of “unspecified” parameter uncertainties on recurrence earthquake probabilities. In addition, a numerical approach involving the use of Monte Carlo simulation was proposed to estimate the exceedance probabilities in which the parameter uncertainties were taken into account. The Meishan fault in Central Taiwan with the best-estimate return period of 162years and earthquake magnitude of 7.1 was used as an example. The analyses verified the impact of parameter uncertainties on the exceedance probability in fault-induced earthquake recurrence. When uncertainty is high, the exceedance probability associated with large magnitudes is high. It was also observed that the probabilistic analysis in this study can generate a realistic, continuous distribution of exceedance probabilities that cannot be obtained by a deterministic approach. The best-estimate distribution of exceedance probability was established by enveloping the curves estimated by both deterministic and probabilistic approaches. Accordingly, the best-estimate exceedance probability for a 7.5-magnitude earthquake recurring in 2011–2060 induced by the Meishan fault in Central Taiwan was estimated as 11%. [Copyright &y& Elsevier]

Abstract: Taiwan has experienced frequent extreme weather events in recent decades. There is a clear trend of a decreasing number of rainy days but with much higher concentration of rainfall. The debris flows caused by torrential rains have caused severe damages to infrastructures (roadways, bridges, lifelines, and buildings) and loss of life in many recent typhoon events in Taiwan. To gauge the risk of a debris flow, it is often necessary to estimate the sediment volume of the debris flow, which is the focus of this paper. A large database involving 59 rivers and streams in Taiwan is developed based on the rainfall data between 2001 and 2009. Each data point in the database includes the sediment volume of a debris flow and its attributes including physiographical parameters, geological index, and rainfall factors. Based on multiple linear regression analysis, an empirical model is developed for estimating the sediment volume of debris flow considering watershed area, landslide area, geological index, cumulative rainfall, and rainfall duration. Characteristics and limitations of this model are examined and comparison with other models is made. [Copyright &y& Elsevier]

Abstract: Typhoon Mindulle struck northeast Taiwan on July 2, 2004, and brought an abundant air current in the following days that caused serious flood disasters to the mountainous areas in central Taiwan. One of sever flood events during Typhoon Mindulle was about hundreds of hectares of farmland loss induced by an 1620m break of Shan-An levee at the Chenyulan River. This paper examines the nature and causes of Shan-An flood by integrating catastrophic investigation and scenario simulation. The catastrophic investigation of the disaster scene, including field survey, outcrop investigation, and remote sensing image interpretation, was executed to reveal the inundation for disaster response and recovery. SPOT-IV and FORSAT-II satellite images and airborne images provided temporal and spatial information for inundation investigation. The HEC-RAS hydraulic model was applied to estimate the water surface profiles of Shan-An levee around the lower reach of Chenyulan River. Also, the impacts of debris and water in the hyper-concentrated sediment flow were estimated to illustrate the effects of sediment yield on Shan-An levee. The result shows that the levee was designed to sustain the heavy rainfall bought by Typhoon Mindulle but failed to the impact of high concentrated sediment flow induced by sediment yield from the landslide. The seismic-triggered landslide on the left riverside was reactivated by intensive rainfalls to deposit a great amount of sediments on the riverbed that narrowed down the river width, increased the impact force, and diverted water toward Shan-An levee. The levee failure should draw more attention from engineers while designing a new flood control structure in the waterway of Chenyulan River due to the occurrence of the hyper-concentrated sediment flow and landslide residuals after the Chi-Chi earthquake (ML 7.3). In addition, the perceived investigation and analysis of an earthen levee failure provides essential information to setup a proper recovery plan of Shan-An levee and a basin management strategy of Chenyulan River in the future. [Copyright &y& Elsevier]

Abstract: Landslide is a frequently encountered problem in Taiwan during the heavy rainfall and typhoon seasons (July to September). Assessing the risk of landslide is a challenging task facing both the engineering communities and local authorities. In this paper we present a framework for analyzing the rainfall-induced landslide risk and demonstrate it with a case study of Lushan hot-spring district in Nantou County in central Taiwan. This framework consists of three parts: (1) an approach for determining the conditional probability of landslide under different scenarios, (2) a procedure for estimating the landslide-induced losses, and (3) a procedure for computing the total landslide risk. The results of the detailed case study of the total landslide risk in the Lushan hot-spring district show that the proposed methodology is an effective approach for landslide risk assessment. Use of the methodology for assessing the cost-benefit of an engineering mitigation work proposal is also presented. [Copyright &y& Elsevier]

Abstract: In this paper, technologies from multiple disciplines are used to reconstruct the shape of the Hsiaolin landslide dam, a short-lived landslide dam (SLD), that was triggered by Typhoon Morakot. Here, the formation, failure mode and breaching process of this SLD are investigated. The results indicate that the overtopping time and the debris budget constrained the dam geometry. The inferred volume of the Hsiaolin landslide dam (15.4millionm3) is much smaller than the actual landslide volume (25.2millionm3) even considering the rock-mass dilation and debris entrainment. Meanwhile, a 46% error could be induced if an over-simplified equation (a function of the dam height, length and width) is used to calculate the dam volume. The saddle of the dam crest, which is where overtopping occurred, could be used as a reference to measure the dam height and length. Accordingly, the determined dam dimensions of height (44m), length (370m) and width (1500m) are suggested to be the representative geometrical indices that influenced the stability of the Hsiaolin landslide dam. The flow rate of the dammed river, another variable relevant to dam stability, was determined from a run-off simulation. It is suggested that, instead of the peak flow before the dam formation, the flow rate during the blockage period (2974m3/s) should be used as the training data for building a statistical model for stability predictions. Finally, the low hydraulic gradient at the toe of the dam''s surface and the high safety factor of the dam slope indicate that the piping and slope instability were irrelevant to the failure of the Hsiaolin short-lived landslide dam. It is postulated that overtopping (about one hour after the blockage) dominated the failure process of this heavy-rainfall-induced landslide dam. [Copyright &y& Elsevier]

Abstract: In this paper the results of a case study of the annual probability and return period of soil liquefaction in Yuanlin, Taiwan, the town that suffered significant liquefaction damage in the 1999 Chi-Chi earthquake, are presented. As part of this case study, a framework for determining the average annual probability of liquefaction (AAPL) that is attributed to a known fault is developed. This framework is formulated by considering the uncertainties in both liquefaction resistance and liquefaction loading. For liquefaction loading, the seismic hazard from a known fault is considered; and for liquefaction resistance, soil parameters, characterized mainly by cone penetration test (CPT) and standard penetration test (SPT), and their uncertainties are considered. Additionally, model uncertainty of the empirically-developed liquefaction resistance models, based either on CPT or SPT, is considered in the analysis for the annual liquefaction probabilities. The results of the case study show that the proposed framework is applicable for site-specific analysis of liquefaction potential or for mapping liquefaction potential in a given town (or city). Furthermore, the AAPL and return period determined based on SPTs are found to be comparable with those determined with CPTs. The results of the case study provide some guidance for future engineering planning and regulation consideration in the Yuanlin, Taiwan area. [Copyright &y& Elsevier]

Abstract: This paper presents the establishment of an empirical HC model for estimating rock mass hydraulic conductivity of highly disturbed clastic sedimentary rocks in Taiwan using high-resolution borehole acoustic televiewer and double packer hydraulic tests. Four geological parameters including rock quality designation (RQD), depth index (DI), gouge content designation (GCD), and lithology permeability index (LPI) were adopted for establishing the empirical HC model. To verify rationality of the proposed HC model, 22 in-situ hydraulic tests were carried out to measure the hydraulic conductivity of the highly disturbed clastic sedimentary rocks in three boreholes at two different locations in Taiwan. Besides, the model verification using another borehole data with four additional in-situ hydraulic tests from similar clastic sedimentary rocks was also conducted to further verify the feasibility of the proposed empirical HC model. The field results indicated that the rock mass in the study area has a conductivity between the order of 10−10 m/s and 10−6 m/s at the depth between 34 m and 275 m below ground surface. Results demonstrate that the empirical HC model may provide a useful tool to predict hydraulic conductivity of the highly disturbed clastic sedimentary rocks in Taiwan based on measured HC-values. [Copyright &y& Elsevier]

Abstract: The 1999 Chi-Chi earthquake triggered the catastrophic Tsaoling landslide in Taiwan. The geomorphological change measured from the data of the 1989 and 2000 aerial photos reveals that the scar and deposit volumes are about 0.126 km3 and 0.15 km3 respectively. The debris material ran over a distance of 1.6 km with 500 m descent in elevation. In this paper, we use the continuum model of hydraulic flow, SHALTOP2D, based on the equations of Bouchut and Westdickenberg to simulate numerically the landslide dynamics. When the mass is moving, the flow is assumed hydrostatic with a basal Coulomb friction. The best fit is obtained using the basal friction angle equal to 6°, the only parameter of the simulation, uniformly applied in the calculation domain. The landslide front reaches the Chinshui river valley, the foothill of the slope, within only about 25 s after initiation and the motion settles in about 113 s. The maximum speed is estimated 75 m/s. The spreading of the deposit agrees well with the field measurement. [Copyright &y& Elsevier]

The importance of the geological model in a geotechnical engineering project has long been recognized. However, the uncertainty associated with the geological model has rarely been quantified and explicitly considered in the geotechnical design. This paper explores the role of the geological model uncertainty and the benefit of reducing such uncertainty in a geotechnical design. To this end, the landslide that occurred on 25 April 2010 at 3.3 K of Freeway No. 3 in Northern Taiwan, referred to herein as NH-3 Slope, is re-analyzed with an assumed geological model (a dip-slope model in this case) under various uncertainty scenarios. Traditionally, the design (i.e., a choice of design parameters such as slope height, slope angle, and supporting anchors) of a rock slope seeks to satisfy a target factor of safety (FS). In the case of NH-3 Slope, the apparent dip angle of the slip surface along the dip direction of slope constitutes the geological model of concern. Different survey techniques produce data with varying degrees of error (or uncertainty) in the measured apparent dip angle. For example, data from a Regional Geological Map (RGM) typically yields an estimate of the bedding plane attitude with a significant level of uncertainty due primarily to low data density. In contrast, LiDAR can significantly reduce the uncertainty of the derived bedding plane attitudes. By lowering this uncertainty, the variation (or uncertainty) in the computed FS may be reduced, which tends to yield a lower failure probability (P f), given other conditions being the same. The benefit of lowering the geological model uncertainty in a geotechnical design is demonstrated through a retrospective analysis of the NH-3 Slope. • We explored the role of geological uncertainty on a dip slope failure in Taiwan. • We treated bedding attitudes as the main geological uncertainty in the stability analysis. • We found the use of LiDAR can lower the uncertainty of derived bedding attitudes. • We demonstrated the engineering benefit of reducing geological uncertainty. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this paper is to present data on the occurrence of landslides triggered by typhoon and earthquake events, and to discuss the basic earthquake triggering mechanisms involved. Four events of typhoon and earthquake triggered landslides in the Chenyoulan River catchment of central Taiwan during 1996 to 2004 were studied in order to identify their controlling factors. The landslides areas were measured by comparing aerial photos taken over the past 18 years, and sediment discharge was counted at hydrometric stations. Investigation results demonstrate that hillslope geomaterials that had been disturbed by strong seismic shaking induced expansion of landslide areas during subsequent events. Analysis of Normalized Difference Vegetation Index (NDVI) also registered the changes of uncovered conditions on the hillslope caused by landsliding. When flow discharge is lower than 100 m3 s−1, post-seismic sediment concentration is roughly four times higher than pre-seismic concentration with the same flow discharge. This fate indicates that the amount of sediment discharge at normal flow discharge is affected by supplied sediment volume, which tends to increase with seismic activity. [Copyright &y& Elsevier]

Abstract: Failures of weak-rock slopes adjacent to roadsides in southwestern Taiwan most often occurred during or immediately after heavy rainfall. Field survey of weak rock slopes along the national South-2 Freeway conducted in this study showed that the slope protection methods employed in the study areas mainly included vegetation (82.0%), prestressed rock anchors with vegetation (6.8%), grille beam (5.9%), rock anchors with grille beam (3.6%). The highest failure rate occurred in the slopes that were protected by the vegetation method. The most frequently encountered weak rock formation along the South-2 Freeway is the alternating sandstone–shale formation (36.3%), followed in sequence by sandstone (24.4%), conglomerates (21.9%) and mudstone (17.4%). The field survey also found that the mudstone slopes present the highest failure rate among all rock types, and the most commonly encountered modes of failure were surface erosion and shallow slides. Factors affecting slope failure include inadequate drainage of storm water runoff, disparate rock types and vegetation on slope surfaces, slope angles and heights. This paper presents results of the field survey of the rate of failures of weak rock slopes in Southwestern Taiwan and examines the attributes of slope failures and the effectiveness of commonly used slope protection methods in the region. Requirements or essential features of an effective slope protection method are then presented along with the preliminary results of its field implementation. [Copyright &y& Elsevier]

Abstract: The Jiufengershan rock avalanche was one of the largest and most damaging landslides triggered by the Chi-Chi earthquake (M L =7.3, M W =7.6) of 21 September 1999. The rock avalanche transported a mass of sedimentary rock 50 m thick and 1.5 km long, located on the western limb of the Taanshan syncline. The surface of rupture coincides with the bedding plane and dips moderately toward the Jiutsaihu valley. This paper is mainly devoted to the study of post-seismic surface processes that affected the sliding surface as well as the debris deposit, from September 1999 to February 2003. Large fractured blocks and a debris layer observed on the surface of rupture were subjected to mass wasting processes and denudation. The quantification of erosion was made using two different approaches. First, the subpixel correlation method was used to determine the horizontal displacement field from aerial photographs taken, respectively, 2 and 3.5 months after the earthquake. Displacements ranging from 1 to 6 m were observed around unstable blocks located at the western flank of the surface of rupture. Second, the co-seismic and post-seismic volume distributions in the sliding zone were determined from three digital elevation models, including a LiDAR image taken in 2002. Post-seismic erosion and deposition from September 1999 to April 2002 were mainly associated with mass wasting and denudation at the surface of rupture, deposition in small basins and lakes located in the debris deposit, and evacuation of materials from the debris deposit along natural and artificial drainage channels. The vertical compaction is 1% of the initial height of the deposit. [Copyright &y& Elsevier]

The method by Iwasaki et al. [Iwasaki, T., Arakawa, T., Tokida, K., 1982. Simplified procedures for assessing soil liquefaction during earthquakes. Proceedings of the Conference on Soil Dynamics and Earthquake Engineering, Southampton, UK, pp. 925–939] for evaluating the liquefaction failure potential is widely used in Japan, Taiwan, and other countries due to its ease of use and general applicability. In this method, an index, called the Liquefaction Potential Index (IL), is calculated based on an integration of the calculated factor of safety (Fs) over depth with a weighting function. Iwasaki et al. (1982) provided a set of criteria to interpret the calculated index IL based on a calibration with his dataset of field performance cases. However, in their method, the factor of safety (Fs) is based on the liquefaction evaluation method adopted in the Japanese Highway Bridge Design Code [JSHE, 1990. Highway Bridge Design Guide Book. Japan Society of Highway Engineering, in Japanese]. Whether other liquefaction evaluation methods can be used in conjunction with the index IL or not needs further investigation. In this paper, the Cone Penetration Test (CPT) data from Yuanlin, Taiwan, the area that suffered the most from liquefaction in the 1999 Chi-Chi, Taiwan, earthquake, are analyzed. Three CPT-based methods are used for the calculation of the factor of safety for these cases derived from the Chi-Chi earthquake. These factors of safety are used to define the liquefaction potential and risk indexes. The calculated indexes are then used to construct the failure potential maps, and these maps are checked with the field observations. The study shows that the Liquefaction Risk Index (IR) defined in conjunction with the Juang et al. [Juang, C.H., Yuan, H., Lee, D.H., Lin, P.S., 2003. Simplified CPT-based method for evaluating liquefaction potential of soils. Journal of Geotechnical and Geoenvironmental Engineering, ASCE, vol. 129, no. 1, pp. 66–80] method yields the best result in interpreting field observations. [Copyright &y& Elsevier]

The 1999 Chi-Chi, Taiwan earthquake caused great destruction to buildings, bridges, and other facilities, and a death toll of more than 2400. Lessons should be learned from this event, which, albeit disastrous, represents a rare full-scale experimentation in geotechnical engineering and related fields. Of particular interest to geotechnical engineers is the phenomenon of soil liquefaction that caused significant damage to buildings, lifelines and harbor facilities. These liquefaction phenomena, in the forms of sand boils, lateral spreads, tilting and settlement of buildings, and ground settlement, were observed in the Chi-Chi event. Shortly after the earthquake, an extensive field investigation in the Yuanlin area, including in situ tests and laboratory tests, was conducted by Moh and Associates and other parties. These in situ and laboratory tests along with ground performance observations form the basis for the present study.In this paper, 24 cases of ground performance in the areas that suffered the most from liquefaction are studied. The ground performance in selected cases of the 24 cases is accounted for through a series of liquefaction analyses. The analysis of the potential of liquefaction and ground failure is performed using Cone Penetration Test (CPT) data. The results of the analyses show that the field observations of ground performance in the Yuanlin area in the Chi-Chi event can be accounted for satisfactorily using the evaluation procedure by Ishihara (Ishihara, K., 1985. Stability of natural deposits during earthquakes. Proc., 11th Int. Conf. on Soil Mechanics and Foundation Engineering, San Francisco, CA, vol. 1, pp. 321–376.). [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]

Liquefaction potential analysis is a required task in the foundation design process of offshore wind turbine in Taiwan. The standard penetration test (SPT) is mostly used in the preliminary soil investigation of the pilot offshore wind farm in Chang-Bin, Taiwan. Due to the different experimental conditions and operating conditions, the N value (SPT-N) of SPT varies greatly. This study applies statistical methods in conjunction with the New Japan Road Association simplified-empirical method (NJRA method) to incorporate the uncertainty of SPT-N values into the offshore liquefaction potential assessment to quantify the risk of seabed liquefaction. The study statistics the field experimental geotechnical parameters SPT-N and determines the probability density function of the SPT-N distribution of each layer of soil in the offshore wind farm. In order to quantify the risk of seabed soil liquefaction potential, the Monte Carlo random sampling method is used, and by the NJRA method to carry out the seabed liquefaction potential in Changhua, Taiwan. After comparing, the results obtained by the current SPT-based soil liquefaction potential assessment by deterministic approach are conservative. In the ground investigation of offshore wind farm development, the method proposed in this paper can access the thickness of liquefiable soil layers under any given probability for optimizing offshore wind turbine foundation design. • We propose a new method to quantify the risk of the seabed soil liquefaction potential. • This method can assess the thickness of liquefiable soil layers under any given probability. • We present probability distribution of soil SPT-N obtained from offshore wind farms in Taiwan. • The effect of uncertainty of SPT-N on the soil liquefaction potential assessment is presented. [ABSTRACT FROM AUTHOR]