IEG 환경지질연구정보센터

10월 25일(목)․응용지질학│암석학

2007 추계지질과학연합학술대회 초록집 5

Estimates of Rock Mass Properties using the RMR and GSI system

Seung Hee Kim^*

․Seung Hyun KimㆍJong Hyun RheeㆍHo Bon Koo

Rock mass properties are required for many applications in rock engineering practice includ- ing excavation, support, and cut-slope design. For this purpose, obtaining design input param- eters such as deformation modulus, cohesion, internal friction angle and etc. are necessary for numerical modeling. Although such parameters should be determined from in-situ and laboratory tests, the practical way to obtain these parameters is to apply a rock mass classi- fication system at the design stage due to the limitation of access.

Many classification systems such as RQD, RMR(Rock Mass Rating), SMR, Q and GSI(Geological Strength Index) system have been developed. Among them, techniques of reduction through the RMR system are widely used for rock support system design and gen- erally considered conservative. The GSI system is used as an another method of estimating design parameters. The GSI system is the only rock mass classification system that is directly linked to engineering parameters such as Mohr-Coulomb, Hoek-Brown strength parameters or rock mass modulus. However, the application of the existing GSI system is difficult since it is subjective and requires long-term experience.

In the numerical simulation process, continuous analysis methods based on finite element method or finite difference method have been utilized to evaluate stability of tunnel and cut-slope. However, rock mass parameters derived from mentioned classification systems do not reflect several critical factors such as orientation, spacing, location of the joints since rock mass is a inhomogeneous material. In contrast, discontinuous analysis method which can reflect distribution of discontinuities requires a huge of investigation hours and modeling time.

In this study, the estimation of rock mass properties is carried out on several collapsed cut-slopes and tunnel portal area. Collapsed cut-slopes show various rocks including Siltstone, Cole-shale, Limestone, Gneiss, Schist, Phyllite, Granite and Tuff. The estimation of rock mass properties is performed mainly based on the RMR(Bieniawski, 1976) and GSI(Hoek and Brown, 1980) system. Interested rock mass properties are determined in terms of continuous numer- ical analysis - that is, cohesion, friction angle, and elastic modulus. Two results show consid- erable differences when it comes to cohesion and elastic modulus. By comparing rock mass parameters of two systems, reliable rock mass estimating and continuous numerical analysis method is discussed.

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