Dobruja is a historical region shared by Romania and Bulgaria; it is located on the western Black Sea coast, around the Danube River. The main geological, seismic and geotechnical features, as well as natural hazards are presented in this review. A comparative analysis is made between the northern and southern parts of Dobruja. The region has witnessed various kinds of natural hazard over the past decades, and this paper describes the geotechnical characteristics and chronology of two of the more frequently occurring events, namely earthquakes and soil liquefaction. The structural relationships between the different rock formations in Romania and Bulgaria are analyzed, to show the extent to which they influence the dynamics of these events. The stability of foundations on liquefacted sand, silty clay and karsts on which installations such as wind generators, the nuclear power station and breakwaters are built have been examined in the light of the geoenvironmental risks. The similarity in structural, geotechnical and environmental relationships between Romania and Bulgaria engender common risks that could be properly addressed only through collaboration between scientists from both countries.

This publication provides an overview of the current technical and contractual trends that govern the execution of micro-tunneling projects in both Romania and Bulgaria. Technical issues discussed include available equipment and technologies, aspects related to the complexity and challenges of these works, comparisons between the open trench and trenchless methods, environmental impact, and other. Legal issues discussed include contractual schemes, relationship between the parties involved, dispute resolution, and contract types in compliance with both the national as well as the European Union law. Appropriate technical equipment is recommended to avoid risk in implementation and ensure the quality of finished products.

The edge Folkman numbers are defined by the equality Fe(a1, . . . , ar; q) = min{|V (G)| : G e → (a1, . . . , ar; q) and cl(G) < q}. a2) where C5 is the simple cycle on 5 vertices. We prove some upper bounds on edge Folkman numbers for which R(a1, a2) < R(a1 − 1, a2) + R(a1, a2 − 1) and we cite some lower bounds. Faculty of mathematics and informaticsReceived xx.xx.199x

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