Various methods of subsurface exploration are used at the Hofermühle. In addition to direct (ram core sounding, drilling core extraction and analysis / ramming sounding as well as installations for analyzing slope hydrology and movement), indirect methods (geoelectrics / electromagnetic induction) were used in cooperation with the Vienna University of Technology (Ass.-Prof. Dr. Adrian Flores-Orozco and team) commitment.
In summary, the direct subsurface exploration includes 10 drill cores and 3 pits (07.2016 / 09., 10.2018 / 03.2019 / (03.2020)) as well as a total of 32 ramming soundings (Dynamic Probing Heavy (DPH) or Dynamic Probing Medium (DPM)). The data was recorded at different times (07.2016 / 09., 10.2018 / 03.2019, 03.2020) within the framework of the project, the final theses embedded therein and a project-related course.
To date, the following are permanently installed (Figure 6):
- 9 TDR probes at 3 locations (each at 0.5, 1 and 2 m depth; soil water content in [%])
- 8 piezometers (depth between 4 m and 6 m; height of the water column in [m])
- 1 automatic inclinometer (8 m)
- 3 manual inclinometers (~ 5 m (autumn 2018); ~ 6 m (03.2019); ~ 7 m (07.2019))
Figure 6: Underground installations at the Hofermühle site (Dynamic Probing Heavy (DPH) and Medium (DPM), piezometer (PZM), TDR probes, inclinometer (INC)). (DEM (1m) 2009: made available by the state of Lower Austria). Graphics: Stumvoll M.J. 2020.
Inclinometer measurements provide information about dynamics in the subsurface. Depending on the depth of the installation, it is possible, for example, to define one or more sliding horizons for an active landslide. There are currently 4 cased boreholes in the Hofermühle, which are used for inclinometer measurements. 3 of them are measured approximately monthly using a manual inclinometer probe, one contains a permanently installed automatic chain inclinometer (measuring interval 5 min). The measurements are transmitted directly to the data server in Vienna via the Internet.
Figure 7: Impressions of the field work at the Hofermühle site. 1) Installation of the automatic chain inclinometer, September 2018; 2) Piping of a manual inclinometer, October 2018; 3) Readout of a manual inclinometer, March 2019. © Photographs see individual note.
Piezometers and TDR probes
To examine the groundwater level and its changes, 8 piezometers are distributed over the upper slope (see Figure 6). In order to obtain additional information about the soil moisture at different depths, a total of 9 TDR probes are installed at 3 locations at 3 different depths each (0.5, 1 and 2m). Both piezometer and TDR data are recorded in a measuring interval of 5 minutes. Just like the inclinometer data, it is also sent directly to the server in Vienna, processed and can also be accessed directly in real time on the homepage.
Figure 8: Impressions of the field work at the Hofermühle site, autumn 2018. 1 and 2) Installation of piezometer teaching tubes; 3 and 4) Installation of TDR probes. © Photographs see individual note.
Ram soundings (DPH / DPM), ram core soundings, drill core extraction and laboratory analyzes
A total of 32 pile-driving soundings have been carried out at the site since 2018. Their analysis is part of ongoing work. The drill cores (10) and direct soil samples (3 locations) taken at the site were or will be analyzed and evaluated as part of various final theses. Corresponding results are in progress.
Figure 9: Impressions of the field work at the Hofermühle site, autumn 2018. 1 to 4) Drilling core soundings and drilling core withdrawals; 5) direct soil sampling (undisturbed samples) and 6) ram sounding (DPH). © Photographs see individual note.