Engineering Rock Mechanics

Questions and answers: introduction 7

41.3 The photograph below illustrates construction of the 61 m
span, 25 to 50 m deep, underground Giavik Olympiske Fjellhall
(Olympic Mountain Hall) in Precambrian gneiss in Norway. This is
the largest roofspan public-access civil engineering cavern in the
world. Describe the engineering rock mechanics factors that would
have to be considered in the design and excavation of such a cavern.

A1.3 The main factors to be considered in excavation of such a cavern
are the geological setting, the natural rock stress, the deformability and
strength of the intact rock, the geometry and nature of the pre-existing
fractures, the groundwater, variations in the rock properties, the use
of a rock mass classification technique to indicate rock mass quality,
time-dependent effects, and the excavation and support methods. The
cavern is to be constructed in hard rock, but it has a large span (of 61 m
compared to the usual 15-25 m) and is located close to the surface. Under
these circumstances, we would need to consider in the first instance any
instability that might arise from rock blocks falling by gravity from the
cavern roof.
In fact, after considerable site investigation, the use of the Q rock
mass classification scheme, associated numerical modelling and design
work4, the cavern was first excavated to a 36 m span and then, after
installation of 6 m rockbolts and 12 m long cable bolts plus fibre-rein-
forced shotcrete, increased to the 61 m span. The long axis of the cavern

This refers to the year 2000. It is likely that in the future this project will be superseded

Bhasin R. and Lerset E (1992) Norway’s Olympic Cavern. Civ. Eng., December, 60-61.

by even larger projects.