Abstract
The Krsko-Brežice field is one of the most seismically active areas in Slovenia. The most damaging recorded earthquake with an intensity of VIII (EMS) occurred on 29th January 1917. It caused damage and claimed two lives. In the last 100 years, 9 earthquakes with intensity higher than VI (EMS) have been recorded. At the investigated area, a top layer up to 5 m thick, consisting of recent deposit of very loose silts and sands (ML, SM, SP), covers the medium dense to dense Quaternary gravel, beneath which there are over-consolidated, uncemented Miocene silts and marls. The top layer could be prone to liquefaction, as reported for the close surroundings of Brežice, where the liquefaction phenomenon was observed during the Zagreb earthquake in 1880 and during the Kupa Valley earthquake in 1909. The paper presents the results of laboratory index tests, cyclic simple shear tests and field investigations (SPT, CPT, (S)DMT, vs measurements), which were carried out to assess the liquefaction potential of the top layer at the location of the Brežice Hydroelectric Power Plant (HPP). All results show that the top layer is prone to liquefaction for an earthquake with a 475 year return period. Cyclic simple shear test results show that the liquefaction potential of horizontal ground for an earthquake with a 475 year return period can be reduced by the densification of the top layer to at least 95% of maximum Proctor density.
Highlights
Earthquake induced liquefaction is the phenomenon in which loose saturated granular soil loses shear strength due to pore pres sure increase, to the point where it is unable to support structures and to remain stable
This paper presents the assessment of liquefaction potential of the top layer at the location of the Brežice Hydroelectric Power Plant (HPP), based on labo ratory index and cyclic simple shear tests, as well as field cone penetration tests (CPT/CPTu), standard penetration tests (SPT), flat dilatometer tests ((S)DMT) and shear wave velocity measurements
The analyses indicate that there is a clear threat of liqu efaction in the top layer, assuming a water table 0.1 m below the ground surface for an earthquake with a 475 year return period
Summary
Earthquake induced liquefaction is the phenomenon in which loose saturated granular soil loses shear strength due to pore pres sure increase, to the point where it is unable to support structures and to remain stable. Recent investi gations have highlighted that earthquakes can trigger shear strength loss in a broad range of types of saturated soils, from sand to low plasticity clays (BRAY et al, 2004, CHU et al, 2004, BOULANGER & IDRISS, 2006), earthquake-induced ground failure is observed less frequently in clays than in sands. This paper presents the assessment of liquefaction potential of the top layer at the location of the Brežice HPP, based on labo ratory index and cyclic simple shear tests, as well as field cone penetration tests (CPT/CPTu), standard penetration tests (SPT), flat (seismic) dilatometer tests ((S)DMT) and shear wave velocity measurements (vs)
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