Geophysical Monitoring of Environmentally Induced Changes in Dams, Embankments, Landslides, and Their Subsurface: Repeated Multi-Method Surveys

This presentation summarizes a project focused on the seismic imaging and time-lapse monitoring of dams, embankments, and landslides using seismic and complementary geophysical methods. These structures are particularly sensitive to environmentally induced changes, such as variations in water saturation driven by climate variability and human activity, which can significantly affect their stability and long-term performance.

This study presents the results of repeated geophysical surveys conducted in 2023 and 2024 to investigate seepage and under-seepage processes in critical infrastructure related to the Rybnik water reservoir in southern Poland. To analyse the state of the embankment and dam, we used a combination of seismic, CCR, and ERT methods, supported by observations with a DAS system and an innovative Spectral GPR. Using repeated surveys, we were able to image not only spatial inhomogeneities but also changes in the structure related to different water tables and water saturation in the studied Earth-filled objects. Moreover, between the two surveys, maintenance works were performed to limit excessive seepage in the embankment. This action reduced seepage by 30%, but geophysical data enabled a spatial evaluation of the works and identified areas that require future monitoring.

Besides standard analysis in the form of ERT and seismic tomography, we utilised high-resolution seismic data recorded at a 2 m horizontal spacing for reflection imaging. This allowed us to recognise geological structures below man-made structures and the effects of the old river bed located beneath the construction. An additional 3C geophone was used for the seismic survey, allowing for precise analysis of P and S waves. This resulted in Vp/Vs analysis of the objects. Moreover, the combination of P and S wave reflection images provides insight into detailed structures that cannot be recognised with standard methods.

Finally, we utilised the DAS system to further increase the spatial resolution of the seismic data. A comparison of DAS and horizontal geophone data shows that DAS provides long-term monitoring capabilities, essential for ongoing structural health assessments and geohazard detection. For example, the multichannel analysis of surface waves (MASW) using DAS data clearly identifies S-wave velocities down to 13 m with an RMS error of 3.26%, compared to an RMS error of 6.2% for geophone data.

In addition, seismic tomography was applied to the Cisiec landslide (Żywiec district, southern Poland), where time-lapse velocity models are used to track hydrologically driven changes in subsurface properties associated with slope instability.

This research was funded by National Science Centre, Poland (NCN) project number 2022/45/B/ST10/00658.