This paper describes an approach applied in the design and construction of one cut at section km 23+200 - km 23+400 from the expressway A4, section Stip – Radovish, part of the Macedonian road network in construction. The cut is constructed in volcanogenic rock mass of andesitic type, with different zones within the massif. It is specific, because of different phases of extrusions along wider fault zones, rock mass has typical composition of block-in-matrix (BIM) rocks. In the frame of this article, the approach based on the integral application of empirical – analytical, and observational methods during the design and construction is presented. Some results from investigations and correlations between the investigated parameters necessary to define optimal slope protection elements are also given. One attempt is done to prepare a simple tool for characterization of BIM rocks initially named as BIMSI (Block In Matrix Strength Index), based on a combination of Volumetric Block Proportion and Strength Ratio of significant blocks and matrix. This idea requires further study. Finally, some elements of applied solution for slope protection are presented.
The practice in Rock Engineering shows that analyses for "block-in-matrix rocks" (BIM – rocks) rocks is a challenging task due to their complex structure and engineering behavior. Problems to be solved in such media are present in the process of investigations, design, and construction because, it is very difficult to define their extent in space, parameters for characterization, preparation of conceptual and numerical models due to the contrast in the strength between the blocks and the matrix material surrounding them, etc. The expression "block-in-matrix rocks" was introduced by Raymond [1]. It is related to similar terminologies such as mega-breccia’s, olistostromes, wildflysch, varicolored clays, and sedimentary chaos [2]. The term "bimrock" was proposed by Medley in his attempt to study the engineering properties of these geological mixtures and was defined as "a mixture of rocks, composed of geotechnical significant blocks within a bonded matrix of finer texture" [2].
Related to this problem, several approaches are important. For example, there are several methodologies present in the literature for estimation of the physical and the mechanical properties through empirical equations in practice [3-6]. An approach for engineering characterization of bimrocks in NW Greece is discussed by Nikolaidis and Saroglou [7]. Some elements that are important for this article are based on analyses of shear strength of different materials [8], or the approach for quantification of Geological Strength Index [9].