Acoustic emission long-term measurements in the Morsleben repository
Country / Region: Germany
Begin of project: January 1, 1994
End of project: December 31, 2026
Status of project: February 1, 2024
Project description
Acoustic emission measurements are carried out in the Morsleben repository as part of geomechanical investigations on the integrity of the rock mass, and the stability of underground cavities. The real time registration and location of events is furthermore a contribution to mine safety. The formation of micro cracks is directly detected and located by recording high-frequency seismic energy. The statistical analysis of micro crack clusters enables the identification of macroscopic fissures.
Results and findings
Acoustic emission measurements have been carried out since 1994 in the central part and southern field (Bartensleben) of the Morsleben repository in three sectors of the rock mass, over a length in each case of around 100 metres. Up to 2023 around 220 million microacustic events have been registered and located. These microacustic events represent the deconsolidation of the rock salt in the proximity of the underground cavities, and local fissuring at the boundary of the rock salt and anhydrite. The results of the acoustic emission measurements are interpreted together with findings from other geomechanical investigation methods, such as model calculations, laboratory investigations, and in-situ measurements of deformation and stress.
3D visualization of the registered microacustic events in the central Bartensleben part of the Morsleben repository during November 2023
Source: BGR
Click for an interactive 3D-visualization of the registered microacustic events in the order of mm to cm in the central Bartensleben part of the Morsleben repository during November 2023: Mikroakustische Langzeit-Messungen im Grubengebäude Morsleben (html, 13 MB)
Microacustic events are shown as points and colored after magnitude. Strip-shaped distribution of micro cracks in the roof of backfilled underground mining cavities in. Blue cubes indicate the sensor position of array 3, which were used for location of the shown events. Gray shapes are the mining cavities. Movement of the interactive view is done using the mouse. Rotation of the view is done holding “CTRL” and moving the mouse, lateral movement is done by holding “SHIFT” and moving the mouse. Zoom is done using the middle mouse button. Source: BGR
The backfill of the underground cavities with salt concrete as part of the operations to prevent mining hazards in the central part (Bartensleben) of the Morsleben repository from 2003 to the beginning of 2011, led to additional short-term build-up of stresses in the rock mass. The spatial distribution and development over time of these stresses are recorded and characterised in detail by carrying out acoustic emission measurements. The micro crack activity increased strongly in the vicinity of the backfilled cavities after the backfilling began. The micro crack activity increased again several months after the conclusion of the backfill work. This increase in activity appeared predominantly in a stripy arrangement of micro cracks in the roof of the underground cavities. These stripes developed in each case approximately one year after the completion of the backfilling work in the underground cavities, and are largely still in existence today. It is assumed that this high micro crack activity occurs along macroscopic fissure surfaces, and therefore characterises their spatial location and development over time. A gradual decrease in micro crack activity has been observed for several years now in the backfilled part of the underground cavities.
Project contributions:
Partner:
Gesellschaft für Materialprüfung und Geophysik GMuG mbH, Bad Nauheim