Tunnelling in fault zones - state of the art

摘要

Alpine fault zones are complex structures, exhibiting highly heterogeneous rock mass conditions. In addition the permeability can vary in wide ranges. High displacements, stability problems, and ground water inflows are common phenomena observed during tunneling through fault zones. Besides the choice of an appropriate construction method for such conditions, the safety and long-term stability of the underground structure are major issues. The paper addresses investigation methods and targets to obtain the key parameters determining the rock mass behavior, as well as rock mass characterization methods, criteria for the selection of appropriate construction methods, depending on the expected conditions. It is essential to focus the investigation in the route selection phase on risk relevant parameters. The investigation for the route selection is based on the review of existing data, the evaluation of satellite images including digital elevation model data, aerial photographs and on studies of selected outcrops. Main investigation target is the assessment of the fault pattern and the principal understanding of fault kinematics. During the preliminary design a first geometrical and a preliminary ground model, containing rock mass parameters and hydraulic conductivities of the fault zone has to be established. Site investigations require detailed engineering geological mapping and subsurface investigations by geophysical survey, trenches/trial pits, core drilling and borehole tests. Laboratory tests contribute to the characterization of intact rock properties.