Aydın Özsan

Support capacity estimation of a diversion tunnel in weak rock

Abstract This paper presents the results of the support capacity estimation for the diversion tunnel of the Urus dam site in highly weathered tuff and weak zone. Tunneling in weak rock requires some special considerations, since misjudgment in support design results in costly failures. There are several ways of estimating rock support pressure and selecting support. However, all systems suffer from their characteristic limitations in achieving objectives. Thus, it is more useful to use different methods for estimating support pressure and type of support. The support pressure pi was established by three different methods. These methods are the (1) empirical methods based on rock mass rating (RMR) and rock mass quality index (Q-classification systems), (2) ground support interaction analysis (GSIA) and (3) numerical methods, namely, Phase2 finite element (FEM) program. Rock masses were characterized in terms of RSR, RMR, Q-system and GSI. Drill-core samples were tested in the rock mechanics laboratory to determine physico-mechanical properties. Rock mass strength was estimated by empirical methods. Finally, the required support system is proposed and evaluated by different methods in the highly weathered tuff and weak zone of the diversion tunnel.

Engineering geological assessment of the proposed Uruş Dam, Turkey

Abstract This paper describes the results of the engineering geological investigations and rock mechanics studies carried out at the proposed Urus Dam site. Analyses were carried out in terms of rock mass classifications for diversion tunnel, kinematic analysis of excavation slopes, permeability of the dam foundation and determination of rock mass strength parameters. Urus Dam is a rock-filled dam with upstream concrete slab. The dam will be built on the Suveri River in the central part of Turkey. The foundation rocks are volcanic rocks, which consist of andesite, basalt and tuff of Neogene Age. Studies were carried out both at the field and the laboratory. Field studies include engineering geological mapping, intensive discontinuity surveying, core drilling, pressurized water tests and sampling for laboratory testing. Uniaxial, triaxial and tensile strength tests were performed and deformation parameters, unit weight and porosity were determined on the intact rock specimens in the laboratory. Rock mass strength and modulus of elasticity of rock mass are determined using the Hoek–Brown empirical strength criterion. Rock mass classifications have been performed according to RMR and Q systems for the diversion tunnel. Engineering geological assessment of the proposed dam and reservoir area indicated that there will be no foundation stability problems. Detailed geotechnical investigations are required for the final design of the dam.

Preliminary support design for Ankara subway extension tunnel

This paper presents the results of preliminary support design of the subway tunnel for Ankara subway project in accordance with some empirical and numerical methods, using the phase 2D finite element method (FEM). The 5 m diameter subway tunnel will advance through slightly to moderately weathered dacite and weak zones. Rock masses were characterized in terms of rock mass rating (RMR), geological strength index (GSI) and Q System. Core samples were tested in the rock mechanics laboratory to determine uniaxial compressive strength, deformability parameters, unit weight, tensile strength and triaxial compressive strength properties. Finally, rock mass strengths were determined by empirical and numerical methods. Required support system was suggested.

Classifications of hardgrounds based upon their strength properties

Rock samples from the Baglum-Kosrelik area, 30 km north of Ankara, Turkey have been studied petrographically in detail to differentiate between nodular limestones and hardgrounds. However, it is found that petrographic criteria alone may not always be used to differentiate between nodular limestones and true hardgrounds. Distinction between hardgrounds and other wellindurated carbonate rocks can be made based upon the strength properties of the rocks, including uniaxial compressive strengths, triaxial compressive strengths, modulus ratios, and elastic constant ratios. This study showed that rock petrophysical characteristics could be used to develop criteria for distinguishing hardgrounds. For example, strength tests using the International Society for Rock Mechanics result in very high strength and extreme hardness values, with a minimum uniaxial compressive strength value, of 130 MPa with 10% standard deviation, therefore the rock can be classified as “true” hardground. Classification of these carbonates in this manner would facilitate quantitative discussions between hardground carbonate petrographers and engineering geologists. Hardgrounds throughout the world then could be tested and classified accordingly.