Investigation of Karst Cavities and Earth Subsidence with Combined Application of Boring and Geophysics in the Progress of High-Speed Railway Routes

Abstract.

In Germany there are a lot of new high-speed railways in planning or under construction. One of these is the new Nuremberg - Ingolstadt railway line and the updated line from Ingolstadt to Munich. These two lines will form part of a high-speed trans-European railway link from Scandinavia via Berlin to Munich and Verona. The 78 km railway line construction project has been divided into three contract sections: Contract Section North, mainly characterised by pure earth and bridge works; Contract Section Centre, with the emphasis mainly on tunnel construction; and Contract Section South, combining earthworks and tunnelling. Extensive geophysical investigations combined with borings are carried out in critical areas between Nuremberg and Ingolstadt. The target of this geological exploration phase is mainly the detection of karst pits and earth subsidences (dolines). In this area these geological objects are an important aspect for the stability and permanent serviceability of the high-speed railway routes. The exploration concept on the open stretch consists of combined geological enquiry, geotechnical work, geophysical investigations and borings, which are positioned at the found anomalies of geophysics. The survey leads to a common interpretation of all information and results. After several test campaigns the combination of at least two geophysical methods yields to the best results. Dependent on the thickness of the overburden layer seismics, micro-gravity and/or georadar are applied from the surface. Additionally tomographic methods are used between boreholes for special topics. Important for the success of the investigation in difficult geological areas are the excellent co-operation between all scientists, engineers and technicians (geologists, geotechnicians, geophysicists, driller, consultants, etc.).