The shear strength evaluation of rough and infilled joints and its indications for stability of rock cutting in schist rock mass

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Construction of E75 highway section through Grdelica gorge was one of the most demanding projects realized in recent Serbian history. The alignment approximately 25 km long consists of several tens of bridges, two tunnels, three galleries and cuts with total length of 6 km. The alignment passes through highly anisotropic Palaeozoic schist rock formation of different weathering grades. This study focuses on shear strength properties of discontinuities, which are found to be the critical feature contributing to the occurrence of (in)stabilities during highway construction. Field and laboratory investigations were performed in order to determine the shear strength properties of adversely oriented discontinuities. Nonlinear failure law of hyperbolic type is used to describe functional dependence between normal stress and shear stress of rough and filled joints. Parameters of nonlinear envelope were determined by curve fitting to laboratory experimental data (shear test results) and by relating JRC and JCS parameters to the parameters of hyperbolic envelope. The results suggest that JRC and JCS parameters are not correlated. Experimental data show markedly higher dilation effect and overall strength properties compared to the field determination of strength parameters. The type of soft infill also dictates the values of shear strength parameters.
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