For the past few years in the area of the city of Rijeka, Croatia, a few open pits in limestone rock mass were excavated. On the basis of the geotechnical investigation results designs of support systems of the cut in limestone rock mass were prepared. The support systems of the cut in the rock mass were made by the reinforcements from rock bolts and multilayered reinforced sprayed concrete (shotcrete). During the works execution monitoring system for the support system behavior was established. This enabled to obtain the data necessary for the stress-strain back analysis of the real behavior of rock mass. An active design procedure was established which made possible changes required in the reinforcement system. Performed back stress-strain analysis also showed need for the additional correction in the correlations between deformation characteristics and rock mass classification.
In the course of several past years in the area of Rijeka, Croatia, many buildings were constructed after the excavation of open pits or high cuts in the limestone rock mass. In order to evaluate the design documentation, as well as the construction of the cited buildings, complex geotechnical research works were performed presumably consisting of engineering-geological mapping, laboratory testing of the rock mass samples, and probe drilling combined with geophysical measurements. Starting from the results of the research works, the designs were evaluated in order to reinforce the open pit walls constructed in the limestone rock mass. During the design of excavation, the laws of the behavior of reinforced rock mass were considered and Hoek-Brown failure criterion rock mass were considered, together with accepted criteria of estimation of deformability of the rock mass (Hoek et aI., 2002).
The reinforcement and the stability of the excavation cut were mainly performed by the use of the rock bolts in rock supports, as well as by the use of the multilayered shotcrete. During the performance, an active design approach was used and in the course of the works, that is, the observational methods of the behavior of the rock mass were practiced (Kovačević, 2003). The observation of the rock mass behavior during the performed works on excavation enables the stress-strain back analysis and more accurate estimation of the rock mass parameters. The results of the performed back analysis pointed out the necessary changes during the performance of the rock supports, provided for the reinforcement of the cuts in the rock mass. In this work the experiences collected during the construction of open pits in limestone rock mass performed on several buildings including the observed deviations from generally accepted properties of the reinforced rock mass will be reviewed.
In this work behavior of the limestone rock masses on four important projects performed on a relatively narrow area have been analyzed, particularly in the cases of the following operations: rock cuts done in the course of the enlargement of the working terraces of the shipyard «Viktor Lenac» near Rijeka.