Liquefaction Susceptibility of Quaternary Deposits in Bulgaria

The territory of Bulgaria is at risk of a number of unfavorable and destructive geological processes and phenomena constituting the geological hazard. The generally high hazard degree necessitates analyzing, evaluation and mapping of the geological hazard and risk processes. Evaluation and mapping of geological risk is the final stage of a long-lasting gathering of information for each destructive geological process. The purpose of the present study is to analyze the principles and order in assessing and mapping the overall geological hazard. Typical hazardous geological processes for the territory of our country are taken into account (active faults, abrasion/sea erosion, erosion, landslides, rockfalls, collapse, swelling, liquefaction of dispersed soils, etc.). A methodological approach is presented to combine all hazardous geological processes into an integrated hazard map. The study presents the results obtained during the implementation of the project “Elaboration of analysis, evaluation and mapping of geological risk” realized in 2016 by a large research team and supported by the Ministry of Regional Development and Public Works in Bulgaria.

Section: Methodological Approachmentioning

confidence: 99%

Section: Determination Of the Hazard Ratiomentioning

confidence: 99%

Principles for the assessment and mapping of integrated geological hazard in Bulgaria

Ivanov

Berov

Dobrev

et al. 2017

“…2) indicated considerable loss of dynamic resistance of saturated loess at seismic impact. Berov et al (2017) classified the loess deposits in the Danube plain (North Bulgaria) as prone to liquefaction. Idriss and Boulanger (2008) investigated the liquefaction of soils with fines and showed that fine-grained soils with more than 50% grains passing 0.075 mm can be reasonably grouped into soils that exhibit either sand-like stress-strain behavior or clay-like stress-strain behavior during monotonic and cyclic undrained shear loading.…”

Section: O R R E C T E D P R Omentioning

confidence: 99%

Liquefaction potential assessment of saturated loess

Karastanev

Tchakalova

2021

Usually, soils with mainly fine grain-sized content, as loess, are considered to have low liquefaction potential. Regardless of this, many researchers have analyzed and presented much field evidence that silty soil (in particular loess) liquefaction occurred under certain conditions. In Bulgaria, the first loess river terrace (T1) within the Danube River lowland areas is covered by low plasticity silty loess with a thickness of 10–12 m. Тhe groundwater level is often located between 5 m and 8 m in depth so that substantial part of loess deposits are saturated and immersed. Meanwhile, that region of North Bulgaria is under the influence of the Vrancea seismic zone in Romania, which is able to generate strong earthquakes with magnitudes M≥7.0. The present paper aims to assess the liquefaction potential of loess in a ground profile representative of the T1 loess river terraces by the so-called simplified procedure based on SPT, which is incorporated in the software code NovoLiq. The safety factor against liquefaction FSL is estimated at the respective depths in one-dimensional model of the ground profile for free-field conditions at varying peak ground accelerations amax. The critical amax, at which liquefaction of loess is possible according to the assumptions of the applied simplified procedure and the requirements of the National Annex of Bulgaria to Eurocode 8, has been established.

“…Apart from these two groups, the data from several regional studies (i.e.., Tcherkezova, 2015;Sapundzhiev, 2016;Berov et al, 2017;Stoynev and Ivanov, 2019) could serve as a preliminary indicator of the possibility of near-surface field saturation. Tcherkezova (2015) examined the geomorphology (geomorphometric variables) and the possibility of long-term soil saturation near river valleys.…”

Section: Review Of Bulgarian Research Activitiesmentioning

confidence: 99%

“…The higher the clay content in soil, the more susceptible it is to saturation. Berov et al (2017) and Stoynev and Ivanov (2019) summarized and analyzed the liquefaction events of water-saturated sediments for a long-term period in the history of Bulgaria. Review of investigations into the vadose zone's variable state of saturation in connection with the assessment of radon potential...…”

Section: Review Of Bulgarian Research Activitiesmentioning

confidence: 99%

Review of investigations into the vadose zone’s variable state of saturation in connection with the assessment of radon potential in Bulgaria

Kunovska

Trayanova

Mutovska

et al. 2021

Natural radon (222Rn) is a radioactive noble gas that occurs as the immediate decay product of radium (226Ra), part of the 238U family, in the lithosphere. Radon is driven by advection and diffusion with soil gas throughout connected and water-unsaturated pores and/or cracks in permeable rocks and soils. The aim of the present study is to do a review of the existing so far research activities in Bulgaria in connection with the observation and/or evaluation of the degree of water saturation of the near-surface layer, and on that base to distinguish the up-to-date achievements in regards to the radon potential in situ evaluation. Due to this review, the studies in Bulgaria concerning moisture dynamics in the near-surface layers can be divided mainly into two groups. The first one investigates the hydraulic characteristics (parameters) of soils in the vadose zone. Based on that, conclusions or computer simulations for the saturation degree estimation can be drawn. The other group includes in situ observations by sensors on the change of moisture with time. The results of these studies may serve as a base for more precise moisture dynamics assessment at sites with specific radon potential tendencies.