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Non - Linear Threshold for amplification analyses in moderate earthquakes in alpine valleys (NLT)

Applicant Laue Jan
Number 125016
Funding scheme Project funding
Research institution Institut für Geotechnik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Civil Engineering
Start/End 01.01.2010 - 30.06.2012
Approved amount 137'475.00
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All Disciplines (2)

Discipline
Civil Engineering
Geophysics

Keywords (6)

Geotechnical Earthquake Engineering; Soil Dynamics; Liquefaction; Ground Amplification; Non Linear Soil Behaviour; Wave propagation

Lay Summary (English)

Lead
Lay summary

The project Non-Linear Threshold for amplification analyses for moderate earthquakes in alpine valleys (NLT) aims to enhance the use of non-linear soil models in amplification analyses. Due to the complexity of the non-linear soil models, especially when incorporated in 2 or 3 dimensional dynamic calculations, the knowledge of threshold conditions need to be studied in detail to reduce computational efforts.

 

The so-called non-linear soil behaviour is governed by the change of stiffness of soils under loading, deformation and in case of high water table levels by an increase in porewater pressure, which can

reach values equivalent to the effective stress (liquefaction). Whereas studies exists on the threshold for stress and strain to consider nonlinearity in dry conditions (e.g. Vucetic, 1994), no such value exists for the interaction between earthquake loading causing porewater pressure build-up and subsequently softening of the material and a change of the stress state. The increase in porewater pressure depends on the incoming stresses and strains as well as the length of an earthquake. As long as particle reorientation is involved, porewater pressures increase already under low loading states, even though liquefaction might only be reached after significant numbers of load cycles. The influence of pore pressure increase, change in directivity and elongated earthquakes, as shown by Faeh et al. 2006 due to topographical effects, will be studied with a series of cyclic laboratory experiments using advanced triaxial and a hollow cylinder apparatus. These tests will be accompanied by field experiments, which have been partially funded with matching funds from the Competence Centre for Environment and Sustainability (CCES) in the project COGEAR .

 

This study is absolutely essential for countries like Switzerland, where big earthquakes are rare whereas moderate earthquakes occur quite frequently and valley effects amplify and lengthen an earthquake in time. To be able to study the amplification further, different material models developed to describe non-linear soil behaviour in the last decades need to be judged to which extent the non-linearity caused by an increase of pore pressures can be covered with these models. While the judgment will be based on one-dimensional calculations and on the existing codes, the most promising model(s) will be transferred into a hybrid calculation building on the developments from the Swiss Seismological Survey (SED). The area of non-linearity can be separated from the linear equivalent calculations. For specific valley conditions (Visp, VS), a model is in preparation to incorporate topographical effects into the study. The Valais, and specifically the area of Visp, has been selected for its high seismic hazard and their well reported non-linear effects observed after the 1855 event. In the past, the Valais has experienced a magnitude 6 or larger event every 100 years, the last in 1946, and the region of Visp is hit by damaging earthquakes every 40 years (Intensity VI-VIII), with the last nearby event in 1960 reaching a macroseismic intensity of VIII with a magnitude over 5.3 at Brig.

Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Modelling of Non-Linear Phenomena – Soil- Structure Interaction in Alpine Valleys
Marin A., Laue J., Mezger F. (2012), Modelling of Non-Linear Phenomena – Soil- Structure Interaction in Alpine Valleys.
Modelling of soil-structure interaction in alpine regions
Marin A., Laue J., Mezger F. (2012), Modelling of soil-structure interaction in alpine regions, in Second International Conference on Performance-Based Design in Earthquake Geotechnical Engineering, Taormina, Italia.
Application of a neighbourhood algorithm for parameter identification in a cyclic mobility model
Roten D., Fäh D., Laue J. (2011), Application of a neighbourhood algorithm for parameter identification in a cyclic mobility model, in 4th IASPEI/IAEE International Symposium on Effects of Surface Geology on Seismic Motions, Santa Barbara.
Geotechnical measurements in the Visp Area Preliminary Subsoil Investigation Using the Weight Sounding Test
Laue J., Marin A. (2011), Geotechnical measurements in the Visp Area Preliminary Subsoil Investigation Using the Weight Sounding Test.
Derivation of a Reference Shear-Wave Velocity Model from Empirical Site Amplification
Poggi V., Edwards B., Fäh D. (2011), Derivation of a Reference Shear-Wave Velocity Model from Empirical Site Amplification, in Bulletin of the Seismological Society of America, 101(1), 258-274.
Overview of existing data in the Visp area
Laue J., Akdeniz F., Marin A. (2010), Overview of existing data in the Visp area.
Estimation of nonlinear site response in a deep Alpine valley
Roten D., Fäh D., Bonilla F., Alvarez-Rubio S., Weber T., Laue J. (2009), Estimation of nonlinear site response in a deep Alpine valley, in Geophys. J. Int., 178, 1597-1613.
Coupled seismogenic geohazards in alpine regions
Fäh D., Moore J.R., Burjanek J., Iosifescu I., Dalguer L., Dupray F., Michel C., Woessner J., Villiger A., Laue J., Marschall I., Gischig V., Loew S., Alvarez S., Balderer W., Kästli P., Giardini D., Iosifescu C., Hurni L., Lestuzzi P., Karbassi A., Baumann C., Geiger A. Ferrari A., Lalou L. Clinton J., Deichmann N., Coupled seismogenic geohazards in alpine regions, in Bollettino di Geofisica teorica ed applicata, 53.
Earthquake damage scenario in Visp (Switzerland): From active fault to building damage
Burjánek J., Fäh D., Dalguer L., Laue J., Lestuzzi P., Baumann C., Gassner-Stamm G., Karbassi A., Marin A., Michel C., Poggi V, Roten D., Earthquake damage scenario in Visp (Switzerland): From active fault to building damage, in 15th World Conference on Earthquake Engineering, Lisbon.

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
BAUHAUS Summer Academy - Model Validation and Simulation 06.08.2012 Weimar, Germany
Second International Conference on Performance-Based Design in Earthquake Geotechnical Engineering 28.05.2012 Taormina, Italy
GeoDACH 2012 10.05.2012 Eisenstadt, Austria
Fourth Annual Meeting of COGEAR 25.01.2012 Visp, Switzerland
Third Annual Meeting of COGEAR 26.01.2011 Visp, Switzerland
Latsis Symposium 2010 15.11.2010 Zürich, Switzerland
Second Annual Meeting of COGEAR 27.01.2010 Visp, Switzerland
COGEAR Workshop 01.07.2009 Lausanne, Switzerland
First Annual Meeting of COGEAR 28.01.2009 Visp, Switzerland


Associated projects

Number Title Start Funding scheme
109177 Earthquake shaking in Alpine Valleys : Phase II (SHAKE-VAL-II) 01.11.2005 Project funding

Abstract

The project Non-Linear Threshold for amplification analyses in moderate earthquakes in alpine valleys aims to enhance the usage of non linear soil models. This requires the understanding of the soil behaviour for the use of non linear models and, to reduce costs, time and complexity, especially for two-dimensional numerical analyses, the knowledge of threshold conditions for the different effects leading to clearly visible non linear behaviour during an earthquake. This non linear behaviour has been observed and back-analysed for earthquakes all over the world (e.g. Youd et al. 2005, Stewart et al. 2008). The so-called non linear behaviour is governed by the change of the material behaviour of soils under loading, deformation and in case of high water table levels, which is the case for most of the alpine valleys, by an increase in pore water pressure. The increase in pore water pressure can reach values equivalent to the effective stress, which is known as liquefaction. Whereas studies exists on the threshold for stress and strain to consider non linearity (e.g. Vucetic, 1994), no such value exists for the interaction between earthquake loading causing pore water pressure built-up and subsequently a softening of the material and a change of the stress state. To be able to cover the mechanism and the threshold values, this effect will be studied in more detail in the frame of the project by means of a series of laboratory experiments. The increase in pore water pressure depends on the incoming stresses and strains, but even for smaller strains, as long as particle reorientation is involved, pore pressures increase. This increase appears already for very low loading states, even though it would require a huge number of cycles to reach liquefaction. Therefore this part of the study is essential especially for countries like Switzerland, where big earthquakes are seldom whereas smaller earthquakes occur quite frequently (comp. Fäh et al. 2006) and topographical effects can amplify the earthquake motion further. To be able to study the amplification, different material models, which have been developed in the last decades needs to be judged and tested into which extent the non-linearity caused by an increase of pore pressures can be covered by the models. This judgement will be based on one-dimensional calculation and based on existing codes. It requires the determination of the respective input parameter. The determination needs a well-equipped state of the art soil mechanical laboratory and is available at IGT for this project. The most promising model(s) will be transferred into a hybrid calculation building up on the developments from the Swiss Seismological Survey (SED). This model allows the usage of different calculation methods in one scheme. The area of non linearity can be separated from the linear equivalent calculations. Use of the hybrid methodology reduces time and effort for two-dimensional calculations. For specific valley conditions such a model will be set up to incorporate topographical effects into the study. The Valais, and specifically the area of Visp, as well as the Visper and Matter valleys, have been selected for their high seismic hazard. In the past, the Valais has experienced a magnitude 6 or larger event every 100 years, the last of which being the magnitude 6.1 earthquake in 1946 close to Sion and Sierre. The region of Visp is hit by damaging earthquakes every 40 years (Intensity VI-VIII), with the last nearby event in 1960 reaching a macroseismic intensity of VIII with a magnitude over 5.3 at Brig. During all such events, significant damage occurred from ground motion and different kinds of secondary phenomena such as liquefaction in the Rhone plain, slope instabilities and extended rock fall could be observed. The study aims to focus on two different valley geometries, the very close valley of the Matter and the larger Rhone valley. This allows to combine topographical effects with a non linear analysis and to study the link between the input source, the change of the earthquake due to the topography and the interplay with the soil behaviour. For example, waves can be trapped and the shaking of a valley can last longer than the earthquake itself. This effect also changes the loading direction of a soil element subjected to this loading. Thus another factor potentially causing a change in the material behaviour needs to be covered. This will be studied with some preliminary tests in the double way cyclic Hollow Cylinder Apparatus and will be brought into perspective with existent conceptual and constitutive models from the soil mechanical domain. This project is closely related to the CCES funded project COGEAR “Coupled seismogenic Geohazards in Alpine Regions” COGEAR was evaluated by international peer review, following strict criteria used by the ETH Research Commission. CCES supports multidisciplinary projects with a scale and scope larger than normal research and provides up to one third of necessary funding. The project COGEAR was accepted in May 2007 and started in January 2008, with a duration of four years. Results and data will be made available to interested research groups and institutions outside the ETH Domain. The PhD student funded by NLT is funded for 1 year out of this project to study the non linear effects in alpine valleys from geotechnical perspective. In NLT request is made to fill the three years for the student and to provide the necessary boundary conditions for a successful research work. NLT is also related to a sinergia proposal submitted to the Swiss National Science Foundation. COGEAR + deals with building a monitoring system for different potential earthquake induced hazards. In relation to NLT, 2 deep boreholes are planned to install at the two sites. They should be equipped with seismic stations at bedrock, at a depth of 20m were it is usually anticipated that non linear soil behaviour will be effective and at the surface. Additionally pore pressures and permanent deformations will be recorded. In addition it is planned to develop and install a dynamic deformation measuring system. These systems are planned to be operational longer than the duration of the project, with a high probability that they will monitor the next damaging earthquake in the Valais and this instalment can be seen as setting up a scientific base for detailed monitoring and analysis.
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