Boriana Tchakalova

• PhD
• Research Associate at Bulgarian Academy of Sciences

The study aims to analyze the current consolidation status of the Pliocene sediments (Brusartsi Formation) by a geological and geomorphological reconstruction of loading and unloading stages in the Kozloduy lowland. Based on that analysis the overconsolidation margin of the Pliocene bedrock is derived for three terrace levels – T6, T2, T1 where sev...

The present study intends to make an assessment of the effect of a natural zeolite addition on field hydraulic conductivity of cement stabilized loess soil. Two single-borehole infiltration methods were used for in situ measurement of field-saturated hydraulic conductivity of cement stabilized loess soil. The results indicate that the addition of n...

This study investigated the geochemical characteristics of Pliocene clay sediments from the Brusartsi Formation, situated in the area of the town of Kozloduy, North Bulgaria). The main objective of the study is to characterize the Brusartsi clays as a natural barrier against pollutant and radionuclide migration. Based on mineralogical and geochemic...

In Bulgaria, comprehensive research and practical experiments of loess-cement have been started in the sixties of the last century in the Geological Institute of Bulgarian Academy of Sciences and later an extensive application has taken place mainly in foundation works and irrigation facilities. The construction of soil-cement impervious screen at...

The present study intends to make an initial assessment of the effect of a natural zeolite addition on shear strength of cement stabilized loess soil. Unconsolidated undrained triaxial compression shear tests were performed for zeolite & cement-treated and cement-treated samples. It is found that the addition of natural zeolite does not reduce the...

Correlations of engineering properties are a useful tool in geotechnical engineering practice. This paper aims to provide a correlation between the effective cohesion and plasticity index for natural, undisturbed clay soils from the Kozloduy area (NW Bulgaria), based on the results from laboratory tests. It has been demonstrated that there is a str...

The construction of a compacted and stabilized layer with local soil from the excavation, mixed with Portland cement, is a soil improvement technique widely applied in foundation works in collapsible loess ground in Bulgaria. Commonly, the role of that cement-modified layer is to replace a part of the collapsible ground, to increase the bearing cap...

Zeolite and Portland cement have been used to stabilize a loess soil from the region of Kozloduy (North Bulgaria). This paper examines the microstructural behavior of cement–zeolite treated loess soil without compaction at water content higher than optimum. Scanning electron microscopy and semi-quantitative energy dispersive spectroscopy analyses o...

The liquid limit is one of the most commonly used index properties of soils. The paper compares liquid limit values determined by the Vasiliev cone penetrometer method and by the Casagrande cup method, based on 45 natural clay samples collected from the Kozloduy Town area (North Bulgaria). An empirical correlation based on these liquid limit result...

The paper compares liquid limit values obtained by the Vasiliev and Casagrande apparatus in line with BDS 648:1984 and BDS EN ISO/ TS 17892–12:2018, on the basis of testing 25 silty loess samples. The results indicated that compared with the Vasiliev apparatus, the Casagrande apparatus gives a higher liquid limit. An equation allowing conversion of...

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...

Plastic soil-cement is a mixture of soil and cement prepared at water content W much higher than the optimum one Wopt, usually at or slightly above liquid limit WL of soil. Recently extensive investigations of plastic loess cement mixtures have been performed for assessment of various options for their using as engineering barriers in safe waste di...

The loess covers about 11% of the territory of Bulgaria mainly in the northern part of the country. It forms continuous strip southern of the Danube River with width up to 65 km. The site selection for waste disposal in loess terrains depends on a complex of geotechnical conditions, requirements and properties of loess sediments. The paper presents...

Plastic soil-cement is a type of soil stabilization used for the treatment of natural soil to improve its engineering properties. It is a hardened material prepared by mixing soil and Portland cement at a water content higher than optimum, usually near the liquid limit, without compaction at optimum water content to maximum dry density. In Bulgaria...

Изследователският проект SITEX-II „Устойчива мрежа за независима техническа експертиза за погребване на радиоактивни отпадъци – Взаимодействия и Реализация“ се изпълнява в рамките на Европейската изследователска програма „Хоризонт 2020“. Проектът стартира през юни 2015 г. и цели практическо реализиране на дейности и модели на взаимодействие, разраб...

Soil-cement cushions are compacted and stabilized layers of the soil base, built under the foundation. Usually, they are constructed with local soil from the excavation, mixed with Portland cement. In Bulgaria, this soil improvement technique has been applied in foundation works in collapsible loess ground, aiming to replace a part of the collapsib...

This paper discusses the microstructural peculiari-ties of cement-zeolite-treated loess soil without com-paction aiming to elucidate the processes of strength formation. The microstructure was investigated using scanning electron microscopy.

The soil-cement cushion represents a compacted and stabilized layer of the soil base, built under the foundation, which is intended to replace a part of the collapsible layer, to increase the bearing capacity of the soil base and/or to play a role of engineering barrier against migration of harmful substances in the geoenvironment. The soil-cement...

Dobrudzha coal deposit is located in a tectonically disturbed zone in north-eastern Bulgaria. It has not been exploited till now due to the great depth of occurrence (1200 ÷ 1400 m) and very complicated geological and hydro geological conditions. Several storey arranged aquifers are discovered in the region. Each of them has a specific chemical com...

Abstract. The present paper considers the properties and technological characteristics of ternary mixtures of loess, Portland cement and zeolite prepared at high moisture content. The uncon-fined compressive strength, permeability and sorption of the mixtures are determined after dif-ferent periods of curing. It is established that the analysed mix...

The paper presents results from laboratory analyses of mixtures of silty loess and small quantities of Portland cement prepared at high water content. The unconfined compressive strength, permeability and sorption are determined after 28-days of curing time. The mixtures analyzed in this study could be applied to build isolation screens without com...

The engineered barriers are an important method of limiting and/or eliminating the movement of contaminants through the surface. Containment barriers can maintain the volume of waste and diminish the potential for migration of the contaminants into the surrounding media or groundwater. Geoenvironmental engineering, in particular engineering geology...