Abstract This study examines the details of creating and validating an empirical liquefaction mod... more Abstract This study examines the details of creating and validating an empirical liquefaction model, using a worldwide cone penetration test (CPT) liquefaction database with the intent of incorporating the rigor found in predictive modeling in other fields and addressing shortcomings of existing models. Our study implements a logistic regression within a Bayesian measurement error framework to incorporate uncertainty in predictor variables and allow for a probabilistic interpretation of model parameters when making future predictions. The model is built using a hierarchal approach to account for intra-event correlation in loading variables and differences in event sample sizes. The model is tested using an independent set of recent case histories. We found that the Bayesian measurement error model considering two predictor variables, normalized CPT tip resistance and cyclic stress ratio decreased model uncertainty while maintaining predictive utility for new data. Hierarchical models revealed high model uncertainty potentially due to the database lacking in high loading non-liquefaction sites. Models considering friction ratio as a predictor variable performed worse than the two variable case and will require more data or informative priors to be adequately estimated. The framework developed is flexible and can be extended using different methods of predictor variable selection, model function forms, and validation processes.
The Next-Generation Liquefaction database is a resource for the geotechnical hazard community. It... more The Next-Generation Liquefaction database is a resource for the geotechnical hazard community. It is publicly available online under the following digital object identifier (DOI): 10.21222/C2J040. The database organizes objective liquefaction data into tables and fields (columns of information), with the relationships among the tables and fields described by a schema. The data are organized into tables pertaining to (1) sites, including geotechnical and geophysical site investigation data, surface geology information, and laboratory test data; (2) earthquake events, including source and ground motion information; and (3) observations of sites following events. The schema was vetted through community outreach efforts involving multiple workshops and meetings. Users can view the data, download existing data, and upload new data through a geographic information system (GIS)-based graphical user interface. Information uploaded to the database is reviewed by a database working group to v...
In the last 10 yr, the International Atomic Energy Agency (IAEA) revised its safety standards for... more In the last 10 yr, the International Atomic Energy Agency (IAEA) revised its safety standards for site evaluations of nuclear installations in response to emerging fault displacement hazard evaluation practices developed in Member States. New amendments in the revised safety guidance (DS507) explicitly recommend fault displacement hazard assessment, including separate approaches for candidate new sites versus existing sites. If there is insufficient basis to conclusively determine that a fault is not capable of surface displacement at an existing site, then a probabilistic fault displacement hazard analysis (PFDHA) is recommended to better characterize the hazard. This new recommendation has generated the need for the IAEA to provide its Member States with guidance on performing PFDHA, including its formulation and implementation. This article provides an overview of current PFDHA state-of-practice for nuclear installations that is consistent with the new IAEA safety standards. We a...
The Next-Generation Liquefaction database is a resource for the geotechnical hazard community. It... more The Next-Generation Liquefaction database is a resource for the geotechnical hazard community. It is publicly available online under the following digital object identifier (DOI): 10.21222/C2J040. The database organizes objective liquefaction data into tables and fields (columns of information), with the relationships among the tables and fields described by a schema. The data are organized into tables pertaining to (1) sites, including geotechnical and geophysical site investigation data, surface geology information, and laboratory test data; (2) earthquake events, including source and ground motion information; and (3) observations of sites following events. The schema was vetted through community outreach efforts involving multiple workshops and meetings. Users can view the data, download existing data, and upload new data through a geographic information system (GIS)-based graphical user interface. Information uploaded to the database is reviewed by a database working group to v...
Many ground failures resulted from the 2015 Nepal earthquake sequence, including landslides, rock... more Many ground failures resulted from the 2015 Nepal earthquake sequence, including landslides, rockfalls, liquefactions, and cyclic failures. And whereas the amount and extent of landsliding were relatively consistent with predictions for a Mw 7.8 main shock, the amount and extent of liquefaction were not. We present a summary of liquefaction field observations that we made as part of the Geotechnical Extreme Events Reconnaissance (GEER) investigations. The liquefaction that did occur in the Kathmandu Valley was limited in its spatial extent, and the postliquefaction deformations were small. Prior earthquakes in this region have been reported to have caused greater liquefaction-related failures, and liquefaction hazard–mapping studies predicted widespread liquefaction hazard from an event of this size. We explore two possible reasons at the regional scale for the limited liquefaction from this earthquake sequence: drawdown of the groundwater table and high near-surface shear wave velo...
In practice it is common to estimate site effects using a single proxy, or single variable such a... more In practice it is common to estimate site effects using a single proxy, or single variable such as 30 m shear wave velocity (V S30 ) or site period. Many studies have investigated merits of proposed proxies with contradicting recommendations. Yet, most studies indicate the single proxy approach is less than ideal, resulting in large uncertainty. To provide a better understanding of components that drive site response, we performed a parameterized study on 19 shallow soil profiles with V S ranging from 150 m/s to 400 m/s. We propagated 74 input motions through each soil column using one-dimensional equivalent-linear method to produce 1406 site response analyses. The resulting amplification factors (the ratio of surface to base motion) were then analyzed statistically to identify trends. The mean amplification factor, averaged from 74 records, was used to isolate and quantify the effects of V S on site response. Based on analysis of record-to-record trends, we identified two separate mechanisms through which nonlinearity affects site response including "damping increase" and "site period shift". The interaction of these two mechanisms makes amplification-shaking intensity models highly depth-dependent. The residual standard deviation of amplification factor based on depth-independent models was found to be up to three times larger than the corresponding standard deviation based on depth-specific models. We found strain compatible site period a promising site parameter that complements the predictive information obtained from V S . Finally, a simplified procedure providing a five-point estimate of site transfer function is outlined. The proposed procedure can fill the gap in current practice for an intermediate solution between the numerically rigorous solution and the single proxy approach. Implementation of this procedure is demonstrated in an example. Fig. 8. Strain compatible shear wave velocity versus spectral acceleration, (a) Sand, depth to bedrock 25 m, (b) Sand, depth to bedrock 75 m, (c) Clay, depth to bedrock 25 m, (d) Clay, depth to bedrock 75 m.
Peer Report 3d04 Cpt Testing of Deposits in Imperial Valley, 2004
This report documents the retesting of liquefaction and non-liquefaction field case histories in ... more This report documents the retesting of liquefaction and non-liquefaction field case histories in the Imperial Valley with the cone penetration test (CPT). The River Park and Heber Road sites were originally tested using a mechanical cone following the 1979 Imperial Valley Earthquake . These two sites are rich in information because they have experienced several earthquakes in recent history, have been subjected to moderate levels of strong ground shaking, the liquefiable soils have appreciable fines content, and the sites contain a number of non-liquefied data points.
A dynamic field test of a model levee was performed to study the behavior of very soft and compre... more A dynamic field test of a model levee was performed to study the behavior of very soft and compressible peaty organic soils that commonly underlie levees in the Sacramento / San Joaquin Delta in northern California. This first-of-its-kind test applied dynamic loads to the levee/peat system using a large eccentric mass shaker mounted on the levee crest. Loads from the shaker and the inertia of the levee section are transmitted to the peaty organic soils as base shear stresses, and rotational demands that manifest as normal pressures at the embankment/peat interface. We seek to characterize the transmission of seismic energy between the underlying soft peat and the overlying, comparatively stiff levee fills. A crucial step in the evaluation of the test data is calculation of the amplitude and phase of shaker forces. We compute the centrifugal force from discretely sampled proximity transducer data using a cosine sweep interpolation function.
Proceedings of the 8th U S National Conference on Earthquake Engineering San Francisco Ca, 2006
The recent Sumatra earthquake and subsequent tsunami has provoked greater awareness of the hazard... more The recent Sumatra earthquake and subsequent tsunami has provoked greater awareness of the hazard posed by coseismic fault displacement associated with sea-floor subduction zones. This catastrophic event has focused renewed efforts on tsunami forecasting, modeling, and detection. Yet the mechanism that causes this type of tsunami, coseismic fault displacement of a sea-floor subduction zone, is still treated deterministically. This paper describes a methodology for probabilistic fault displacement hazard analysis (PFDHA) for a sea-floor subduction zone, and presents example displacement hazard curves for the Cascadia Subduction Zone. The goal of this probabilistic methodology is to quantify the uncertainty and associated hazard of coseismic fault displacement of sea-floor subduction zones. This will provide tsunami modelers with a probabilistic measure of the occurrence of fault displacement, and decision makers with a rational basis for tsunami hazard mitigation measures.
This research uses shake table testing of scale soil-structure models to mimic the coupled seismi... more This research uses shake table testing of scale soil-structure models to mimic the coupled seismic response of underground structures and surrounding/supporting soil (termed soil-structural-interaction or SSI). Currently the seismic design of subways and other critical underground infrastructure rely on little to no empirical data for calibrating numerical simulations. This research is working towards filling that empirical data gap. The research is composed of two phases, the first a validation of the free-field response of a flexible wall barrel filled with model soil, the second a test to measure the "racking" deformations induced in a model subway cross-section embedded in the model soil. San Francisco Young Bay Mud (YBM) is used as the prototype soil and the Bay Area Rapid Transit (BART) underground subway cross-section the prototype structure. Results are shown from the completed first phase of the test, and a presentation of the second phase test results is anticipated at the time of the conference. This research is a collaborative project
Abstract This study examines the details of creating and validating an empirical liquefaction mod... more Abstract This study examines the details of creating and validating an empirical liquefaction model, using a worldwide cone penetration test (CPT) liquefaction database with the intent of incorporating the rigor found in predictive modeling in other fields and addressing shortcomings of existing models. Our study implements a logistic regression within a Bayesian measurement error framework to incorporate uncertainty in predictor variables and allow for a probabilistic interpretation of model parameters when making future predictions. The model is built using a hierarchal approach to account for intra-event correlation in loading variables and differences in event sample sizes. The model is tested using an independent set of recent case histories. We found that the Bayesian measurement error model considering two predictor variables, normalized CPT tip resistance and cyclic stress ratio decreased model uncertainty while maintaining predictive utility for new data. Hierarchical models revealed high model uncertainty potentially due to the database lacking in high loading non-liquefaction sites. Models considering friction ratio as a predictor variable performed worse than the two variable case and will require more data or informative priors to be adequately estimated. The framework developed is flexible and can be extended using different methods of predictor variable selection, model function forms, and validation processes.
The Next-Generation Liquefaction database is a resource for the geotechnical hazard community. It... more The Next-Generation Liquefaction database is a resource for the geotechnical hazard community. It is publicly available online under the following digital object identifier (DOI): 10.21222/C2J040. The database organizes objective liquefaction data into tables and fields (columns of information), with the relationships among the tables and fields described by a schema. The data are organized into tables pertaining to (1) sites, including geotechnical and geophysical site investigation data, surface geology information, and laboratory test data; (2) earthquake events, including source and ground motion information; and (3) observations of sites following events. The schema was vetted through community outreach efforts involving multiple workshops and meetings. Users can view the data, download existing data, and upload new data through a geographic information system (GIS)-based graphical user interface. Information uploaded to the database is reviewed by a database working group to v...
In the last 10 yr, the International Atomic Energy Agency (IAEA) revised its safety standards for... more In the last 10 yr, the International Atomic Energy Agency (IAEA) revised its safety standards for site evaluations of nuclear installations in response to emerging fault displacement hazard evaluation practices developed in Member States. New amendments in the revised safety guidance (DS507) explicitly recommend fault displacement hazard assessment, including separate approaches for candidate new sites versus existing sites. If there is insufficient basis to conclusively determine that a fault is not capable of surface displacement at an existing site, then a probabilistic fault displacement hazard analysis (PFDHA) is recommended to better characterize the hazard. This new recommendation has generated the need for the IAEA to provide its Member States with guidance on performing PFDHA, including its formulation and implementation. This article provides an overview of current PFDHA state-of-practice for nuclear installations that is consistent with the new IAEA safety standards. We a...
The Next-Generation Liquefaction database is a resource for the geotechnical hazard community. It... more The Next-Generation Liquefaction database is a resource for the geotechnical hazard community. It is publicly available online under the following digital object identifier (DOI): 10.21222/C2J040. The database organizes objective liquefaction data into tables and fields (columns of information), with the relationships among the tables and fields described by a schema. The data are organized into tables pertaining to (1) sites, including geotechnical and geophysical site investigation data, surface geology information, and laboratory test data; (2) earthquake events, including source and ground motion information; and (3) observations of sites following events. The schema was vetted through community outreach efforts involving multiple workshops and meetings. Users can view the data, download existing data, and upload new data through a geographic information system (GIS)-based graphical user interface. Information uploaded to the database is reviewed by a database working group to v...
Many ground failures resulted from the 2015 Nepal earthquake sequence, including landslides, rock... more Many ground failures resulted from the 2015 Nepal earthquake sequence, including landslides, rockfalls, liquefactions, and cyclic failures. And whereas the amount and extent of landsliding were relatively consistent with predictions for a Mw 7.8 main shock, the amount and extent of liquefaction were not. We present a summary of liquefaction field observations that we made as part of the Geotechnical Extreme Events Reconnaissance (GEER) investigations. The liquefaction that did occur in the Kathmandu Valley was limited in its spatial extent, and the postliquefaction deformations were small. Prior earthquakes in this region have been reported to have caused greater liquefaction-related failures, and liquefaction hazard–mapping studies predicted widespread liquefaction hazard from an event of this size. We explore two possible reasons at the regional scale for the limited liquefaction from this earthquake sequence: drawdown of the groundwater table and high near-surface shear wave velo...
In practice it is common to estimate site effects using a single proxy, or single variable such a... more In practice it is common to estimate site effects using a single proxy, or single variable such as 30 m shear wave velocity (V S30 ) or site period. Many studies have investigated merits of proposed proxies with contradicting recommendations. Yet, most studies indicate the single proxy approach is less than ideal, resulting in large uncertainty. To provide a better understanding of components that drive site response, we performed a parameterized study on 19 shallow soil profiles with V S ranging from 150 m/s to 400 m/s. We propagated 74 input motions through each soil column using one-dimensional equivalent-linear method to produce 1406 site response analyses. The resulting amplification factors (the ratio of surface to base motion) were then analyzed statistically to identify trends. The mean amplification factor, averaged from 74 records, was used to isolate and quantify the effects of V S on site response. Based on analysis of record-to-record trends, we identified two separate mechanisms through which nonlinearity affects site response including "damping increase" and "site period shift". The interaction of these two mechanisms makes amplification-shaking intensity models highly depth-dependent. The residual standard deviation of amplification factor based on depth-independent models was found to be up to three times larger than the corresponding standard deviation based on depth-specific models. We found strain compatible site period a promising site parameter that complements the predictive information obtained from V S . Finally, a simplified procedure providing a five-point estimate of site transfer function is outlined. The proposed procedure can fill the gap in current practice for an intermediate solution between the numerically rigorous solution and the single proxy approach. Implementation of this procedure is demonstrated in an example. Fig. 8. Strain compatible shear wave velocity versus spectral acceleration, (a) Sand, depth to bedrock 25 m, (b) Sand, depth to bedrock 75 m, (c) Clay, depth to bedrock 25 m, (d) Clay, depth to bedrock 75 m.
Peer Report 3d04 Cpt Testing of Deposits in Imperial Valley, 2004
This report documents the retesting of liquefaction and non-liquefaction field case histories in ... more This report documents the retesting of liquefaction and non-liquefaction field case histories in the Imperial Valley with the cone penetration test (CPT). The River Park and Heber Road sites were originally tested using a mechanical cone following the 1979 Imperial Valley Earthquake . These two sites are rich in information because they have experienced several earthquakes in recent history, have been subjected to moderate levels of strong ground shaking, the liquefiable soils have appreciable fines content, and the sites contain a number of non-liquefied data points.
A dynamic field test of a model levee was performed to study the behavior of very soft and compre... more A dynamic field test of a model levee was performed to study the behavior of very soft and compressible peaty organic soils that commonly underlie levees in the Sacramento / San Joaquin Delta in northern California. This first-of-its-kind test applied dynamic loads to the levee/peat system using a large eccentric mass shaker mounted on the levee crest. Loads from the shaker and the inertia of the levee section are transmitted to the peaty organic soils as base shear stresses, and rotational demands that manifest as normal pressures at the embankment/peat interface. We seek to characterize the transmission of seismic energy between the underlying soft peat and the overlying, comparatively stiff levee fills. A crucial step in the evaluation of the test data is calculation of the amplitude and phase of shaker forces. We compute the centrifugal force from discretely sampled proximity transducer data using a cosine sweep interpolation function.
Proceedings of the 8th U S National Conference on Earthquake Engineering San Francisco Ca, 2006
The recent Sumatra earthquake and subsequent tsunami has provoked greater awareness of the hazard... more The recent Sumatra earthquake and subsequent tsunami has provoked greater awareness of the hazard posed by coseismic fault displacement associated with sea-floor subduction zones. This catastrophic event has focused renewed efforts on tsunami forecasting, modeling, and detection. Yet the mechanism that causes this type of tsunami, coseismic fault displacement of a sea-floor subduction zone, is still treated deterministically. This paper describes a methodology for probabilistic fault displacement hazard analysis (PFDHA) for a sea-floor subduction zone, and presents example displacement hazard curves for the Cascadia Subduction Zone. The goal of this probabilistic methodology is to quantify the uncertainty and associated hazard of coseismic fault displacement of sea-floor subduction zones. This will provide tsunami modelers with a probabilistic measure of the occurrence of fault displacement, and decision makers with a rational basis for tsunami hazard mitigation measures.
This research uses shake table testing of scale soil-structure models to mimic the coupled seismi... more This research uses shake table testing of scale soil-structure models to mimic the coupled seismic response of underground structures and surrounding/supporting soil (termed soil-structural-interaction or SSI). Currently the seismic design of subways and other critical underground infrastructure rely on little to no empirical data for calibrating numerical simulations. This research is working towards filling that empirical data gap. The research is composed of two phases, the first a validation of the free-field response of a flexible wall barrel filled with model soil, the second a test to measure the "racking" deformations induced in a model subway cross-section embedded in the model soil. San Francisco Young Bay Mud (YBM) is used as the prototype soil and the Bay Area Rapid Transit (BART) underground subway cross-section the prototype structure. Results are shown from the completed first phase of the test, and a presentation of the second phase test results is anticipated at the time of the conference. This research is a collaborative project
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