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ENGINEERING GEOLOGICAL INVESTIGATION FOR THE HYDROTECHNICAL TUNNEL PORTAL PROTECTION (KAKANJ, BOSNIA AND HERZEGOVINA)

Indira Sijercic

Abstract

The main waste dump "Vrtliste" (Kakanj Municipality, Bosnia and Herzegovina) is formed in the Ribnica river valley at the edge of the open pit. During its construction it was necessary to relocate the stream of Ribnica river, which included the construction of a hydrotechnical tunnel, river dam, spillway and other elements needed for introducing Ribnica into the Bosna River, as well as the overflow channel over the open pit. The area on which the hydrotechnical tunnel is located comprises of several lithological complexes of compound engineering geological features. Most of the tunnel passes through the sediments of the upper Cretaceous age presented by clastic sediments in the flysch development and the carbonate clastic deposits with the characteristics of flysch. At the tunnel entrance there are Oligomiocene sediments of different lithological composition. Engineering geological characteristics of the terrain were compounded by the rock mass sliding about 6.0 million m3, which barraged the river Ribnica into a length of 550 m. This led to formation of reservoirs and rising level of Ribnica river. Newly engineered geological conditions required adaptation of technical solutions during the construction of the hydrotechnical tunnel. It was not possible to relocate the embankment formed to prevent the flow of river Ribnica, so the new approach was to its strengthening and rising. In order to protect the entrance portal above the tunnel pipeline and the surrounding terrain, detailed engineering geological and geotechnical researches were carried out for that purpose.

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