Integrated Monitoring Concept of Suffusion-Driven Ground Deformation and built environment in the Slănic Salt-Karst Area (Romania)

            Suffusion-related subsidence and collapse processes represent a major geomorphological hazard in salt-bearing environments, particularly where natural dissolution is amplified by anthropogenic factors such as mining legacy and urban development. The town of Slănic (Prahova County, Romania) exemplifies a complex salt-karst landscape affected by ground deformation, impacts on the built environment, and localized collapses, including the major April 2024 event in the city center. The spatially heterogeneous evolution of suffusion features, combined with high societal exposure, requires quantitative monitoring strategies capable of resolving both slow trends and rapid deformation episodes.

The proposed monitoring system includes two complementary components: real-time and recurrent/event-based monitoring. Real-time monitoring relies on permanently operating instruments that continuously measure parameters such as displacement, acceleration, or inclination and transmit data to a centralized platform. Recurrent monitoring consists of measurements performed at predefined intervals or triggered by hazardous phenomena such as structural cracking, landslides, or ground subsidence.

The monitoring concept combines (i)permanent and temporal GNSS campaigns, (ii)terrestrial laser scanning (TLS), (iii)recurrent high-precision topographic measurements and geometric levelling, and (iv)real-time seismic monitoring designed to capture multi-scale deformation signals from neighbourhood scale down to structural detail.

GNSS data are processed using a PPP strategy (GipsyX) to obtain daily solutions in ITRF14 and derive horizontal and vertical deformation time series, with expected precisions of ~2 mm(H) and ~7 mm(V), enabling detection of subtle trends in the unstable urban setting. Campaign GNSS points on dedicated pillars densify the network where continuous deployment is not feasible. Repeated TLS surveys generate multitemporal point clouds for 3D change detection, capturing fractures, localized settlements, and infrastructure deformation linked to salt dissolution and suffosion processes. Topographic measurements using fixed pillars and prisms, together with precise digital levelling, provide independent constraints on vertical displacement and validate GNSS and point-cloud-derived signals.

The preliminary results demonstrate that an integrated multi-method monitoring concept provides a robust, reproducible, and scalable framework for geomorphological monitoring of suffosion-driven deformation in salt-karst terrain. In the monitored sector, the pillar closest to the active suffosion zone recorded a ~2.5 cm permanent displacement in a 3-month period, confirming measurable near-field ground instability. In parallel, prism-based tracking of instrumented buildings indicates systematic inclinations directed toward the suffossion center, consistent with progressive differential settlement and deformation gradients around the collapse-prone area. Data complementarity is essential: three-dimensional displacements measured by the total station on buildings can be validated through tilt measurements, while accelerometers provide short-term confirmation of structural stability.

Overall, the proposed multidisciplinary monitoring system demonstrates feasibility and significant added value, combining real-time detection capabilities with long-term observations. This integrated framework supports informed decision-making, risk mitigation, and targeted monitoring strategies, while offering strong potential for scalability, standardization, and replication at national and international levels through future prototype development, automated alert systems, and intelligent data integration platforms.

Keywords:  Suffosion, Salt karst, Ground deformation monitoring, GNSS-(PPP), TLS

Acknowledgements: This work was carried out within the project No.28Sol(T28)⁄2025, funded by the Ministry of Education and Research, through UEFISCDI (Romanian Executive Agency for Higher Education, Research, Development and Innovation Funding).