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The overall strength of a rockmass is determined by the intact rock strength and characteristics of the rockmass structure. In complex rockmasses this structure consists of both joints and other fractures (interblock structure) and intrablock structure such as veins. As excavations go deeper, intrablock structure has been found to have a significant impact on rockmass behaviour. Complex numerical modelling for modern geotechnical design requires input parameters for structure, including normal and shear stiffness, and strength, which have a critical influence on modelled rockmass behaviour. This study focusses on extending joint stiffness and strength concepts to veins by calibrating numerical finite element Unconfined Compressive Strength (UCS) tests with explicit vein geometries that were determined by petrographic analysis of veins in thin section. In some cases, different calibrated properties were found to have equivalent stress-strain profiles in UCS tests. The behaviour of the calibrated stiffness and strength vein properties are examined at an excavation scale using a numerical example of a 10 m-diameter tunnel.
This paper presents a re-evaluation of a case study of an instrumented test drift in the Kiirunavaara mine. A 20 m long section of the test drift, located at the 514 m level in the Kiirunavaara mine, was instrumented in 1983, with the objective of studying the interaction of grouted rock bolts and hard rock masses subjected to changes in stresses induced by mining. During the test a large rock wedge was observed in the footwall side of the drift. Borehole extensometers, distometers, telescopic tube extensometers and rockbolts with strain gauges recorded the movement of the rock mass during the whole field measurement time. However, the actual failure process of the large wedge was not addressed in the original study. In this paper, this case was re-evaluated with the aim of increasing knowledge regarding of failure process of a large wedge in terms of deformation. A global-local numerical modeling approach was employed to reproduce the in situ conditions using the finite element program Phase2 and Universal Distinct Element Code (UDEC) software. The global approach was used to calculate the stresses induced during sublevel caving in the mine. The stresses from the global model were applied to the local model which simulated the test drift behavior, and in which geological structures were explicitly modeled. The deformation experienced by the rock mass due to the wedge in the drift was calculated in the local model and compared to the measured deformation in the field. The field measurement results showed that a small fallout occurred close to the large wedge. The small fallout acted as initiator of the large wedge movement. The numerical modeling results showed that the large wedge did not fall out. The large wedge was characterized by shear displacements.
1.1. Problem description
Rock wedges are formed by the intersection of discontinuities in a jointed rock mass and the free surface of the opening. The wedges are volumes of rock that may fall or slide into the opening. In underground excavations with wedges falling from the roof and/or sliding from the sidewalls the consequences are significant. Sudden sliding or fallout of large wedges may injure people and cause property damage, safety hazards, and interrupt the tunneling and mining activities. Therefore, the failure process of a wedge should be assessed to understand the stability of the construction, and thus to improve the design and performance of underground excavations in jointed rock. The work presented in this paper is part of a research project concerned with Eurocode 7: Geotechnical designs . Based on geotechnical design rock behavior with acceptable limits should be established to assess the stability of a construction. A section of a test drift in the Kiirunavaara mine was instrumented in 1980 to study the interaction of grouted rock bolts and the hard rock mass subjected to mininginduced stresses. During the test a large wedge was observed in the footwall side of the test drift. Instrumentation located near the wedge recorded the movement of the rock mass.