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CURATOR
A pinboard by
Yi Tyan Tsai

Ph.D Candidate, University of California - Los Angeles

PINBOARD SUMMARY

Using case histories from subduction earthquakes in Hokkaido to understand damage to levees

Seismic resistance of our built environment has greatly improved through the years, particularly that for buildings and bridges. However, upgrading the performance of lifelines - roadways, utilities and pipelines, is an ongoing task as these spatially extensive structures encounters changing ground conditions and variable ground shaking within the system. Levees are particularly challenging as their proximity to water bodies often places them on loose, soft foundation soils that are prone to strength loss during earthquakes. We studied two levee systems in Hokkaido, Japan from 2 large magnitude subduction earthquakes to understand the mechanisms and factors contributing to damages, and derive functions to relate the probability of collapse given predictive variables (e.g., shaking intensity, softness of foundation). By combining these functions with the possible ground shaking for various earthquake scenarios, damage extent and severity can be estimated. Policy makers can use these to inform their decision to 1) repair susceptible sections, 2) plan emergency response and resources to respond to earthquakes.

8 ITEMS PINNED

Probabilistic stability evaluation and seismic triggering scenarios of submerged slopes in Lake Zurich (Switzerland)

Abstract: Abstract Subaqueous landslides and their consequences, such as tsunamis, can cause serious damage to offshore infrastructure and coastal communities. Stability analyses of submerged slopes are therefore crucial, yet complex steps for hazard assessment, as many geotechnical and morphological factors need to be considered. Typically, deterministic models with data from a few sampling locations are used for the evaluation of slope stabilities, as high efforts are required to ensure high spatial data coverage. This study presents a simple but flexible approach for the probabilistic stability assessment of subaqueous slopes that takes into account the spatial variability of geotechnical data. The study area (~2 km2) in Lake Zurich (northern Switzerland) shows three distinct subaquatic landslides with well-defined headscarps, translation areas (i.e. the zone where translational sliding occurred) and mass transport deposits. The ages of the landslides are known (~2,210 and ~640 cal. yr BP, and 1918 AD), and their triggers have been assigned to different mechanisms by previous studies. A combination of geophysical, geotechnical, and sedimentological methods served to analyse the subaquatic slope in great spatial detail: 3.5 kHz pinger seismic reflection data and a 300 kHz multibeam bathymetric dataset (1 m grid) were used for the detection of landslide features and for the layout of a coring and an in situ cone penetration testing campaign. The assignment of geotechnical data to lithological units enabled the construction of a sediment-mechanical stratigraphy that consists of four units, each with characteristic profiles of bulk density and shear strength. The thickness of each mechanical unit can be flexibly adapted to the local lithological unit thicknesses identified from sediment cores and seismic reflection profiles correlated to sediment cores. The sediment-mechanical stratigraphy was used as input for a Monte Carlo simulated limit-equilibrium model on an infinite slope for the assessment of the present slope stability and for a back analysis of past landslides in the study area, both for static and earthquake-triggered scenarios. The results show that the location of failure initiation in the model is consistent with stratigraphic analysis and failure-plane identification from sediment cores. Furthermore, today’s sediment-charged slopes are failure-prone, even for a static case. This approach of including an adaptable sediment-mechanical stratigraphy into a limit-equilibrium slope stability analysis may be applied as well to the marine realm.AbstractSubaqueous landslides and their consequences, such as tsunamis, can cause serious damage to offshore infrastructure and coastal communities. Stability analyses of submerged slopes are therefore crucial, yet complex steps for hazard assessment, as many geotechnical and morphological factors need to be considered. Typically, deterministic models with data from a few sampling locations are used for the evaluation of slope stabilities, as high efforts are required to ensure high spatial data coverage. This study presents a simple but flexible approach for the probabilistic stability assessment of subaqueous slopes that takes into account the spatial variability of geotechnical data. The study area (~2 km2) in Lake Zurich (northern Switzerland) shows three distinct subaquatic landslides with well-defined headscarps, translation areas (i.e. the zone where translational sliding occurred) and mass transport deposits. The ages of the landslides are known (~2,210 and ~640 cal. yr BP, and 1918 AD), and their triggers have been assigned to different mechanisms by previous studies. A combination of geophysical, geotechnical, and sedimentological methods served to analyse the subaquatic slope in great spatial detail: 3.5 kHz pinger seismic reflection data and a 300 kHz multibeam bathymetric dataset (1 m grid) were used for the detection of landslide features and for the layout of a coring and an in situ cone penetration testing campaign. The assignment of geotechnical data to lithological units enabled the construction of a sediment-mechanical stratigraphy that consists of four units, each with characteristic profiles of bulk density and shear strength. The thickness of each mechanical unit can be flexibly adapted to the local lithological unit thicknesses identified from sediment cores and seismic reflection profiles correlated to sediment cores. The sediment-mechanical stratigraphy was used as input for a Monte Carlo simulated limit-equilibrium model on an infinite slope for the assessment of the present slope stability and for a back analysis of past landslides in the study area, both for static and earthquake-triggered scenarios. The results show that the location of failure initiation in the model is consistent with stratigraphic analysis and failure-plane identification from sediment cores. Furthermore, today’s sediment-charged slopes are failure-prone, even for a static case. This approach of including an adaptable sediment-mechanical stratigraphy into a limit-equilibrium slope stability analysis may be applied as well to the marine realm.2

Pub.: 09 Jan '17, Pinned: 31 Aug '17

Shear wave velocity as function of cone penetration resistance and grain size for Holocene-age uncemented soils: a new perspective

Abstract: For feasibility studies and preliminary design estimates, field measurements of shear wave velocity, V s, may not be economically adequate and empirical correlations between V s and more available penetration measurements such as cone penetration test, CPT, data turn out to be potentially valuable at least for initial evaluation of the small-strain stiffness of soils. These types of correlations between geophysical (Vs) and geotechnical (N-SPT, q c-CPT) measurements are also of utmost importance where a great precision in the calculation of the deposit response is required such as in liquefaction evaluation or earthquake ground response analyses. In this study, the stress-normalized shear wave velocity V s1 (in m/s) is defined as statistical functions of the normalized dimensionless resistance, Q tn-CPT, and the mean effective diameter, D 50 (in mm), using a data set of different uncemented soils of Holocene age accumulated at various sites in North America, Europe, and Asia. The V s1–Q tn data exhibit different trends with respect to grain sizes. For soils with mean grain size (D 50) < 0.2 mm, the V s1/Q tn 0.25 ratio undergoes a significant reduction with the increase in D 50 of the soil. This trend is completely reversed with further increase in D 50 (D 50 > 0.2 mm). These results corroborate earlier results that stressed the use of different CPT-based correlations with different soil types, and those emphasized the need to impose particle-size limits on the validity of the majority of available correlations. For feasibility studies and preliminary design estimates, field measurements of shear wave velocity, V s, may not be economically adequate and empirical correlations between V s and more available penetration measurements such as cone penetration test, CPT, data turn out to be potentially valuable at least for initial evaluation of the small-strain stiffness of soils. These types of correlations between geophysical (Vs) and geotechnical (N-SPT, q c-CPT) measurements are also of utmost importance where a great precision in the calculation of the deposit response is required such as in liquefaction evaluation or earthquake ground response analyses. In this study, the stress-normalized shear wave velocity V s1 (in m/s) is defined as statistical functions of the normalized dimensionless resistance, Q tn-CPT, and the mean effective diameter, D 50 (in mm), using a data set of different uncemented soils of Holocene age accumulated at various sites in North America, Europe, and Asia. The V s1–Q tn data exhibit different trends with respect to grain sizes. For soils with mean grain size (D 50) < 0.2 mm, the V s1/Q tn 0.25 ratio undergoes a significant reduction with the increase in D 50 of the soil. This trend is completely reversed with further increase in D 50 (D 50 > 0.2 mm). These results corroborate earlier results that stressed the use of different CPT-based correlations with different soil types, and those emphasized the need to impose particle-size limits on the validity of the majority of available correlations.VsVsVsNqcVs1QtnD50Vs1QtnD50Vs1Q tn 0.25 tn0.25D50D50D50

Pub.: 03 Jan '17, Pinned: 31 Aug '17

Impact of Higher Frequency Content of Input Motion Upon Equivalent Linear Site Response Analysis for the Study Area of Delhi

Abstract: Abstract While travelling through the subsoil layers, earthquake generated bedrock motions get modified significantly due to local soil and should be quantified using ground response analysis. Present study concentrates on equivalent linear method of site response analysis in SHAKE2000 software. It is a frequency based analysis tool having default frequency set to 15 Hz. While due consideration is given to amplitude, no to very limited information about the frequency content of the input motion to be considered in ground response analysis is available. In the present work, the effect of the maximum frequency of ground motion in site response analysis using SHAKE2000 is examined. Two sets of analyses are carried out in this work based on 30 globally recorded input motions. In the first analyses, input motion up to 15 Hz maximum frequency, which is a default value in SHAKE2000 is considered while second analyses are based on considering each of the 30 input motions up to the Nyquist frequency. Comparing the results from the two sets of analyses highlight that selection of maximum frequency in SHAKE2000 has considerable effect in ground motion amplification at different depths. As a result, even the peak ground acceleration which controls the building behavior and damage scenario, is going to change considerably even in case same input motion is used in the analysis.AbstractWhile travelling through the subsoil layers, earthquake generated bedrock motions get modified significantly due to local soil and should be quantified using ground response analysis. Present study concentrates on equivalent linear method of site response analysis in SHAKE2000 software. It is a frequency based analysis tool having default frequency set to 15 Hz. While due consideration is given to amplitude, no to very limited information about the frequency content of the input motion to be considered in ground response analysis is available. In the present work, the effect of the maximum frequency of ground motion in site response analysis using SHAKE2000 is examined. Two sets of analyses are carried out in this work based on 30 globally recorded input motions. In the first analyses, input motion up to 15 Hz maximum frequency, which is a default value in SHAKE2000 is considered while second analyses are based on considering each of the 30 input motions up to the Nyquist frequency. Comparing the results from the two sets of analyses highlight that selection of maximum frequency in SHAKE2000 has considerable effect in ground motion amplification at different depths. As a result, even the peak ground acceleration which controls the building behavior and damage scenario, is going to change considerably even in case same input motion is used in the analysis.

Pub.: 31 Dec '16, Pinned: 31 Aug '17

Simulation of strong ground motion parameters of the 1 June 2013 Gulf of Suez earthquake, Egypt

Abstract: This article aims to simulate the ground motion parameters of the moderate magnitude (ML 5.1) June 1, 2013 Gulf of Suez earthquake, which represents the largest instrumental earthquake to be recorded in the middle part of the Gulf of Suez up to now. This event was felt in all cities located on both sides of the Gulf of Suez, with minor damage to property near the epicenter; however, no casualties were observed. The stochastic technique with the site-dependent spectral model is used to simulate the strong ground motion parameters of this earthquake in the cities located at the western side of the Gulf of Suez and north Red Sea namely: Suez, Ain Sokhna, Zafarana, Ras Gharib, and Hurghada. The presence of many tourist resorts and the increase in land use planning in the considered cities represent the motivation of the current study. The simulated parameters comprise the Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV), and Peak Ground Displacement (PGD), in addition to Pseudo Spectral Acceleration (PSA). The model developed for ground motion simulation is validated by using the recordings of three accelerographs installed around the epicenter of the investigated earthquake. Depending on the site effect that has been determined in the investigated areas by using geotechnical data (e.g., shear wave ​velocities and microtremor recordings), the investigated areas are classified into two zones (A and B). Zone A is characterized by higher site amplification than Zone B. The ground motion parameters are simulated at each zone in the considered areas.

Pub.: 21 Feb '17, Pinned: 31 Aug '17

Experimental case study of seismically induced loess liquefaction and landslide

Abstract: The 1920 Haiyuan Ms 8.5 earthquake induced a large number of fluidized loess landslides in China, characterized by low slope angles, long run-out distances, and fluidized movement. The mechanism of these landslides has aroused considerable interest, although additional research is needed to understand more fully the behavior of the loess and the failure mechanism. Field investigation was conducted on the Shibeiyuan landslide, and loess samples collected for later laboratory analysis by conventional geotechnical tests, triaxial compression tests, and ring shear tests. The field survey revealed that the Shibeiyuan landslide occurred on a concave slope (< 5°) with a long run-out distance, indicating a small apparent friction angle. It was also found that standing water was present in the landslide area and that the loess had high porosity. Experimental results showed that application of cyclic shear stress to a loose and saturated loess specimen causes excess pore pressure to develop gradually, resulting in a decrease of effective stress until liquefaction. The steady state strength of the loess showed no correlation with stress path, but it was closely related to the degree of saturation, loading rate, and void ratio. This indicates that excess pore pressure can accumulate under seismic loading and that plastic deformation can develop rapidly within a shearing zone, resulting in loess liquefaction and a reduction of shear strength. In the Shibeiyuan landslide, the steady state strength was near zero with the large deformation related to the low angle, long distance, and fluidized movement.

Pub.: 31 Mar '17, Pinned: 31 Aug '17