Greining á jarðtæknilegum eiginleikum og sveiflumögnun setlaga á Suðurlandi - verkefni lokið

Fréttatilkynning verkefnisstjóra

11.7.2024

Jarðtæknilegar aðstæður á Íslandi eru um margt sérstakar; setlög eru jarðfræðilega ung, að stórum hluta mynduð í hamfaraatburðum, einkennast af sylti og stærri kornastæðum og eru oft lausþjöppuð. Þá liggja víða eitt eða fleiri stíf lög, t.d. hraunlög eða kargalög, ofan á mýkri setlögum eða á milli þeirra. Upplýsingar um jarðtæknilega eiginleika jarðlaga eru nauðsynlegar við hönnun mannvirkja en vegna sérkenna íslenskra jarðvegsaðstæðna er mikilvægt að afla upplýsinga um eiginleika þeirra með staðbundnum mælingum. 

Yfirborðsbylgjumælingum var beitt til að ákvarða stífnieiginleika jarðvegs. Áhersla var annars vegar lögð á samþætta notkun aktífra og passífra aðferða til að auka áreiðanleika í mati á stífni og heildarþykkt jarðlaga. Hins vegar var unnið að þróun aðferða sem henta til ákvörðunar á stífni jarðvegs og lagskiptingum á stöðum þar sem uppbygging jarðlaga er óregluleg, s.s. þar sem hraunlög eru klemmd milli mýkri setlaga. Auk þessa var staðbundin sveiflumögnun valinna
jarðsniða metin með tölulegum aðferðum, þar sem niðurstöður yfirborðsbylgjumælinga,
tilraunastofumælinga á jarðvegssýnum og hröðunartímaraðir úr Suðurlandsskjálftunum 2000 og 2008 voru nýttar. Niðurstöður þeirrar greiningar voru m.a. notaðar til samanburðar við hönnunarróf sem skilgreind eru í nýrri útgáfu Evrópustaðls (Eurocode 8). Niðurstöður verkefnisins eru birtar í alþjóðlegum ritrýndum tímaritum og kynntar á innlendum og alþjóðlegum fagráðstefnum. Niðurstöðum mælinga var safnað saman í opinn gagnagrunn, sem nýtist fagaðilum á sviði mannvirkjahönnunar og öðrum rannsakendum. Hugbúnaður, sem þróaður var sem hluti af verkefninu, var einnig gerður aðgengilegur í opnum aðgangi.

English:

Icelandic soil deposits are in many aspects vastly different from those found in other countries, due to the unique geological history of Iceland. The overall aim of the project was to improve understanding of the seismic characteristics of Icelandic soil sites and man-made fillings, focusing on densely populated areas and important infrastructure within or near the South Iceland Seismic Zone (SISZ). Active and passive source surface wave analysis was used for site characterization, with special emphasis on the development of techniques for profiling deep soil sites (depth to bedrock >30 m) and locations where a layer of fractured lava-rock is embedded in or overlying soft sediments. Site amplification effects were studied through numerical analysis, using scenario ground motion time histories from recent major earthquakes in the SISZ, with input parameters derived from in-situ and laboratory measurements. Methodology and results are published in international scientific journals and presented at national and international conferences in geotechnical and earthquake engineering. An open database of measured shear wave velocity profiles was constructed where data and interpreted results can be accessed. In addition, open-source software that was developed as part of the project was released.

Information on how the results will be applied:
Seismic site characterization is a fundamental aspect of engineering design in seismically active areas. Surface wave analysis is recognized as a versatile, fast, and cost-efficient approach for stiffness profiling of Icelandic soil deposits, providing information on soil shear wave velocity and layering down to 20-200 m depth. Surface wave analysis is suitable for a wide range of soil site conditions, including gravelly sites and sites characterized by conglomerated materials or mixed soils including cobles or boulders. The possibility of using single-station ellipticity measurements, accompanied by MASW or MAM testing, for velocity profiling of sites with alternating layers of sediments and lava-rock at shallow depth improves subsequent numerical studies on site response for such conditions. Ground conditions where lava-rock overlies soft sediments are not well represented in the current and forthcoming versions of Eurocode 8, highlighting the need for site-specific analysis based on local geotechnical information. Ongoing work is aimed at better establishing the amplification and attenuation effects in the context of the Icelandic geological and seismic framework. Results of advanced laboratory testing, conducted as part of the project, will be used for parameter calibration of advanced numerical constitutive models. Due to the high seismic level in the SISZ, information of soil non-linearity is important for prediction of site amplifications in engineering design. An open database with measured shear wave velocity profiles and supporting data was constructed as part of the project. Together, the sites currently included in the database represent the three most encountered types of natural soil deposits in Iceland, in addition to engineered fills. Hence, whilst not substituting site-specific measurements, the database is intended to give researchers and professional engineers access to data and interpreted stiffness profiles for design and further analysis. The set of empirical correlations, relating small-strain shear stiffness to effective confining pressure, can further be used to assess stiffness parameters for the different soil types. Software for processing and analysis of active-source MASW data, developed as part of the project, has been made available in the Python

Package Index (PyPi) and the project's webpage masw.hi.is. It is distributed as open-source software, allowing users to modify the code and adapt it to future user cases.

A list of the project's outputs:
The project's findings have resulted in four scientific articles and two manuscripts that are currently in preparation for submission to peer-reviewed geotechnical journals. The findings of the project have been (and will be) presented at national and international conferences in engineering sciences, geotechnical engineering, and earthquake engineering (Dagur verkfræðinnar 2021, ICSMGE 2022, 3ECEES 2022, COMPDYN 2023, ECSMGE 2024, WCEE 2024 and NGM 2024). Additionally, one MSc thesis was written as part of the project. A database of measured shear wave velocity profiles and supporting data has been constructed and made available in open access, along with a set of empirical correlations that can be used to assess the small-strain shear stiffness of commonly encountered local soil materials. Software, developed as part of the project, has been released with an open-source licence.

Heiti verkefnis: Greining á jarðtæknilegum eiginleikum og sveiflumögnun setlaga á Suðurlandi/Geotechnical seismic site characterization and local site response studies in South Iceland Verkefnisstjóri: Elín Ásta Ólafsdóttir, Háskóla Íslands
Tegund styrks: Nýdoktorsstyrkur
Styrktímabil: 2020-2022
Fjárhæð styrks kr. 28.636.500
Tilvísunarnúmer Rannís: 206793