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| Titel |
Gypsum dissolution risk analysis in the Prealpine part of the Vaud County (Western Switzerland) |
| VerfasserIn |
Pierrick Nicolet, Marc Choffet, Delphine Bohren, Marc-Henri Derron, Michel Jaboyedoff, Bertrand Lauraux, Jean-Marc Lance, Eric Champod |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250080516
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| Zusammenfassung |
| Subsidence or collapse due to bedrock dissolution is a relatively common phenomenon in
Vaud County (Western Switzerland). Indeed, soluble rocks are present in the Jura
and Prealpine parts. Solubility is significantly higher in evaporitic rocks (such as
gypsum) than in Limestones, resulting in possibly important dissolution during a
building’s lifetime. In Limestone, subsidence results mainly from cover collapse over
existing voids. This study aims at evaluating the cost of this phenomenon for the
building portfolio of the region in which gypsum occurs. Currently, 2.5% of the
portfolio value is located over gypsum-bearing formations and is therefore potentially
affected.
Since this phenomenon is not covered by the public building insurance yet, no centralized
event record exists. Therefore, a survey has been conducted with the affected communities to
estimate the events frequency and damage severity. Some records from the archives of
BERTAND LAURAUX SA have been added and allow to compare reparation costs with
insured values. From these cases, a frequency and a buildings vulnerability distribution are
established. The vulnerability distribution is considered to represent the reality, whereas the
frequency is corrected to take into account the different amount of information gathered in the
different municipalities and the incompleteness of the inventory, even in the communities
with more information.
Assuming that the distribution of collapse events occurs with a constant average
frequency and is time-independent, insurance financial years are modeled with a number of
cases assigned randomly following a Poisson distribution. A Monte Carlo simulation is
performed, where the affected buildings value is chosen among the potentially affected
portfolio and its corresponding damage rate is assigned following the distribution previously
established. The maximum damage for each building is limited to CHF 1,000,000 (EUR
827,000), to ignore unrealistic values. Thus, a cost distribution of potential financial years is
obtained.
The risk for a given building is estimated by dividing the total risk by the number of
concerned buildings and reaches EUR 75 per year and building, i.e. EUR 7,500 for a building
built to last 100 years. Therefore, the risk is relatively small and only limited investigation
and investments are to be considered for new buildings. However, more detailed hazard map
might divide the total cost on a reduced number of buildings, which would allow focusing
investments on more critical zones.
An estimation of the risk evolution in the future is made, based on the legalized building
zones, which should cover the needs for the next 20 to 30 years. This data implies a relative
increase of the affected portfolio. However, a recently accepted law limits the rate of
secondary residences and is expected to freeze the development in most of the affected
communities. |
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