Convergence measurements are an essential part of monitoring methods in underground openings. They also provide important information about the mechanical behaviour of the rock mass in the framework of site exploration. In shafts a more accurate estimation of the deformation behaviour of the rock mass is possible because of the symmetric geometry and their location within the shaft safety pillar. Results of convergence measurements with their evaluation and interpretation are presented through the example of two shafts in salt rock, considering the geological situations. As expected, an increase of convergence with depth can be observed generally. Also a significant dependency of the deformation behaviour on the stratigraphic age of the rock layers is obvious. More information can be obtained by calculating the absolute displacements of the convergence measuring point. This practice enables the identification of special geological situations with their influences on deformation size and deformation direction.

1 Introduction

Shafts are the shortest connection between the surface and deep seated mineral deposits and underground openings. They have an infrastructural importance because all of the supply and the disposal of mine workings have to be done through the shafts. Therefore, there is a great demand on stability and low amount of maintenance. Especially for haulage shafts there is a requirement for small und uniform deformations.

Thus, monitoring of shafts with stress and deformation measurements has a great importance. The measuring methods and their results provide important data and information for the characterization of the rock mass. Based on the monitoring results a realistic estimation of the bearing behaviour as well as a reliable prediction for the operating time of the shafts can be made.

Convergence measurements are an important component of the monitoring methods because the deformation of the shaft contour as an essential parameter for functionality and maintenance of shafts can be determined with relatively low effort.

With the example of two shafts in rock salt it will be shown that the convergence measurements make also a significant contribution to exploration and investigation of the rock mass characteristics. Influencing factors which could change the measurement results will be outlined. These factors were considered in the data evaluation in an appropriate way.

Based on the results of the convergence measurements the deformation properties of salt rock can be determined. A more detailed analysis of the convergence data is possible using the calculated absolute displacements of the measuring points. This advanced evaluation enables a correlation of deformation directions with the orientation of rock mass layers.

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