GEOTECHNICAL APPROACHES FOR THE DESIGN OF A RAILWAY TUNNEL SECTION INANDESITE

This paper presents a possible approach for the assessment of the cond itions of rock around a railway tunnel (Ankara, Turkey), through a sec tion of moderate-quality andesite rock and gives the preliminary desig n considerations for support requirements. For this purpose, different types of rock behaviour and conditions of rock have been investigated by employing analytical, numerical and empirical methods in conjuncti on with data obtained from site investigation and a laboratory testing program. The results of the analytical investigations have shown that no plastic zone and indicator of rock conditions (such as popping, ro ck bursts or slabbing) around the opening are expected for intact rock conditions. However, when a jointed rock mass is considered, the anal yses performed using rock mass properties indicated that the developme nt of a plastic zone is possible. These results have also been confirm ed by two-dimensional finite-element analyses. It is noted that the ma ximum principal stresses develop at the sidewalls. Numerical analyses also suggested that negligible displacements will take place around th e opening. Particular reference was made to the Geomechanics or Rock M ass Rating (RMR) System for the assessment of rock mass conditions and the selection of a support system. The andesite rock mass investigate d (RMR values between 41 and 52 with an average of 47) falls within th e moderate rock mass category. On the basis of this classification, ro ck bolting and shotcreting are suggested as support systems.