IPT Projektijuhtimine OU

Kopli, Estonia

IPT Projektijuhtimine OU

Kopli, Estonia
Time filter
Source Type

Sedman A.,University of Tartu | Talviste P.,IPT Projektijuhtimine OU | Motlep R.,University of Tartu | Joeleht A.,University of Tartu | Kirsimae K.,University of Tartu
Engineering Geology | Year: 2012

Oil shales are considered as an alternative energy resource because they contain bituminous organic matter that can be extracted by retorting. However, oil shales have typically a high mineral content (up to 80%), thus an inevitable issue is the formation of environmentally hazardous solid waste that is piled into large depositories next to oil extraction plants. In Estonia more than 100 Mt of oil shale retorting waste (called semi-coke) is deposited in open dumps. Mechanical stability of these deposits as well as optimal landfill design depend on the geotechnical properties of the waste. The aim of the study was to examine the geotechnical properties of semi-coke waste dumps with the focus on shear strength and cementation. The results from this study indicate that shear strength is controlled not only by the frictional component but also by the cohesive component. Cohesion is mainly developed due to the secondary cementing mineral ettringite, which gives the deposits additional mechanical stability by forming monolithic zones. It is found that this cementation is not permanent due to the lowering of pH and mechanical crushing at high normal stress. Also slight hydrophobicity of semi-coke was recorded, which may influence the behavior of shear strength and saturation together with the complex inner structure. © 2012 Elsevier B.V.

Talviste P.,IPT Projektijuhtimine OU | Hang T.,University of Tartu | Kohv M.,University of Tartu
Bulletin of the Geological Society of Finland | Year: 2012

The distribution and varve thickness data of Late Weichselian varved clay were analyzed to describe the proglacial sedimentary environment, ice recession and water-level changes in the Baltic Ice Lake at the distal position of Pandivere-Neva (13.5-13.1 ka BP) ice-recessional formations in western Estonia. According to vertical changes in natural water content, fabric and varve thickness, four clay units were distinguished, reflecting a change in the sedimentary environment from ice-proximal to distal conditions. The varved clay complex is locally interrupted by a massive silty-clay unit, interpreted as an icedrift material during the stagnation of the glacier margin at the Pandivere-Neva line. Varve correlation gave a 294-year-long floating varve chronology. According to total varve thickness and the relation between thicknesses of seasonal layers, an about 130-year period of ice-proximal conditions in the study area was followed by a rapid (within ca 20 years) change to more distal conditions. The presented varve chronology does not cover the entire period of proglacial conditions in the area, as all studied clay sections displayed an erosional discontinuity at the upper contact. In total, ca 4 m of selective post-sedimentary erosion of clay is attributed to wave erosion due to a water-level drop after the final drainage of the Baltic Ice Lake. It is concluded that the Yoldia Sea minimum level in the Parnu area was 0 to -2 m a.s.l.

Kohv M.,University of Tartu | Talviste P.,IPT Projektijuhtimine OU | Hang T.,University of Tartu | Kalm V.,University of Tartu
Geomorphology | Year: 2010

The largest recent landslide in Estonia (ca 60000m3), which occurred on 19 December 2005, has been investigated, modelled and monitored. Eight boreholes, geotechnical sampling and nine vane shear tests provided data on the geological setting, soil strength parameters and location of the rupture zones. Topographic surveys were carried out twice a year from April 2006 to April 2009 to monitor the evolution of the slope. Limit equilibrium modelling displayed a complex of six separate retrogressive failures, beginning near to the Sauga River and ending 75m from the former river channel. Modelling results are in agreement with the actual morphology of the multiple landslides. Monitoring records the enlargement of the landslide as the Sauga River downcuts through the slide and erodes its toe. Strength loss in the varved clays underlying the slope is a key factor in failure development. © 2010 Elsevier B.V.

Marko K.,University of Tartu | Tiit H.,University of Tartu | Peeter T.,IPT Projektijuhtimine OU | Volli K.,University of Tartu
Engineering Geology | Year: 2010

The largest landslides in Estonia are associated with glaciolacustrine varved clays. One of the recent slope failures, Audru landslide, was chosen for detailed investigation. Landslide morphology was instrumentally measured and the underlying geological setting investigated with eight boreholes penetrating the varved clay. Varve correlation was used to localize the failure zone and estimate the extent of the displaced material within the landslide body. Field measurements and limit equilibrium models displayed a retrogressive complex of three separate sliding events. The first stage of Audru landslide was initiated by the river undercutting and was followed by retrogressive slides that caused partial liquefaction of the landslide body. The influence of the various modeling parameters on the overall slope stability was also investigated. © 2010 Elsevier B.V.

Sedman A.,University of Tartu | Talviste P.,IPT Projektijuhtimine OU | Kirsimae K.,University of Tartu
Oil Shale | Year: 2012

Oil shale ash and semicoke, solid residues from the oil shale industry, are today disposed of separately in landfills which pose a considerable environmental hazard. In the current study, the possibility of codepositing ash and semicoke was investigated in a small-scale field experiment. The purpose of the experiment was to elucidate which mineral changes in the landfilled material occurred and how these changes affected its permeability characteristics. For this purpose five mixtures with different ash-tosemicoke ratios were prepared and placed in the open air. Changes in the dry density, hydraulic conductivity and mineral composition of mixtures were recorded within a period of four months and after one year. During the experiment the mixtures expanded and showed increased permeability due to intensive secondary mineralization. The higher the ash content of a mixture, the more intensive the expansion and, consequently, the higher the permeability, which contributed to an increased infiltration of the leachate and toxic compounds through the landfilled material, thus leading to unfavourable environmental impacts. The above suggests the possibility of co-depositing ash and semicoke, but only if the ash content of their mixture is low enough. © 2012 Estonian Academy Publishers.

Talviste P.,IPT Projektijuhtimine OU | Sedman A.,University of Tartu | Motlep R.,University of Tartu | Kirsimae K.,University of Tartu
Waste Management and Research | Year: 2013

Oil shale-type organic-rich sedimentary rocks can be pyrolysed to produce shale oil. The pyrolysis of oil shale using solid heat carrier (SHC) technology is accompanied by large amount of environmentally hazardous solid residue - black ash - which needs to be properly landfilled. Usage of oil shale is growing worldwide, and the employment of large SHC retorts increases the amount of black ash type of waste, but little is known about its physical and chemical properties. The objectives of this research were to study the composition and self-cementing properties of black ash by simulating different disposal strategies in order to find the most appropriate landfilling method. Three disposal methods were simulated in laboratory experiment: hydraulic disposal with and without grain size separation, and dry dumping of moist residue. Black ash exhibited good self-cementing properties with maximum compressive strength values of >6 MPa after 90 days. About 80% of strength was gained in 30 days. However, the coarse fraction (>125 μm) did not exhibit any cementation, thus the hydraulic disposal with grain size separation should be avoided. The study showed that self-cementing properties of black ash are governed by the hydration of secondary calcium silicates (e.g. belite), calcite and hydrocalumite. © 2013 The Author(s).

Loading IPT Projektijuhtimine OU collaborators
Loading IPT Projektijuhtimine OU collaborators