Site of measurement
The object of measurement is located in the Hattorf/Wintershall mining facility of the company K+S Minerals and Agriculture GmbH. This is a cavity (underground, vertical conveyor system) about 500m below the earth's surface with a depth of 70m.
Problem & task
The cavity probably no longer has the original storage volume due to material deposits from years of operation. The environment is dusty and it is expected that material will be deposited within the conveyor system at any time. The cavity is not accessible to humans from any opening. Access is only possible through the 1m diameter openings.
The objective is to obtain the three-dimensional survey of the conveyor system with highest possible resolution for inspection of the system condition; it serves as a data basis for the system operator. Furthermore, strict compliance with all work safety regulations, with minimal risk for the measuring team, is required.
Equipment
For this job, a mobile laser scanner was used. Thanks to its specifications, the GeoSLAM ZEB Horizon is ideally suited for the special conditions underground. The scanner is also suitable for surveying a cavity that is only accessible from above through a narrow shaft.
The scanner was mounted on a special cradle. The cradle was modified to minimize rotational movements when lowered. A 50m rope was attached to the cradle, which was used to lower the measurement system into the cavity.
In addition, trained members of the mine rescue team were on site to provide security and enable the scanner to be lowered and retrieved safely.
Measurement procedure
- Entering the mine with the equipment
- Preparation of the survey: mounting of the scanner on the cradle and mounting of the rope system for lowering and raising the scanner
- Starting the measurement at the upper end of the opening to the cavity
- Lowering of the scanner, 50m deep. The measurement is running.
- Raising the scanner, 50m high. The measurement is running.
- Finishing the scanning process at the upper end of the opening to the cavity.
- Ascent from the mine and analysis of the scan data in the office.
Workflow of the analysis
Following the survey, the scan data was processed using the GeoSLAM HUB software. The processing of the raw data, i.e. the processing of the point cloud from the data of the laser sensor and the IMU, is automated as far as possible. In the case that a scan is not processed automatically (e.g. because few geometric changes are found in the object space), the focus of the SLAM algorithm can be influenced by adjusting various parameters. After successful processing, a completed point cloud of the cavity is now available in *.laz format. All other common point cloud formats can also be exported with little effort.
Since the scanner could only be lowered linearly on the rope, the earth deposits shadow smaller areas inside the cavity.
Results
The result of this scanning is impressive. This cavity, which is not accessible to humans, was successfully surveyed with the help of the GeoSLAM ZEB Horizon. The point cloud documents the dimensions of the cavity according to the requirements. Further missions with the GeoSLAM ZEB Horizon with similar objectives are already being planned and implemented.
Conclusion
Following this successful test, the company K+S Minerals and Agriculture GmbH decided to purchase one of our mobile scanning systems. We then went to a mine with K+S Minerals & Agriculture GmbH and the GeoSLAM ZEB-Horizon mobile 3D laser scanner. On site we trained the employees of K+S in the correct use of the 3D scanner and then reviewed the 3D data in the office:
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