Slope Protection in the Mittelrheintal: Rockfall Detected in Real Time

Challenge

An unstable rock outcrop above a road and a railway

The Mittelrheintal between Bingen and Koblenz is world-famous as a cultural landscape, and geologically it is a difficult region: extremely steep slopes, narrow valleys and slate-like rock that weathers quickly from freeze-thaw cycles and penetrating water. The result is rock detachment, crack formation and slope movements, and here they meet road, rail and villages directly.

At a particularly exposed section above a federal road and a railway line, a geological survey identified an unstable rock outcrop. The rock layers there fracture brittlely and have only limited internal cohesion, making the location acutely unstable. A safe removal of the unstable section is only possible by the end of 2026 for logistical reasons. Until then, the slope had to be temporarily secured and the transport infrastructure below protected.

Solution

Two catch fences that report an event themselves

For passive rockfall protection, two fence levels at different elevations were erected over a length of 45 metres. These are robust wire-rope barriers that absorb large kinetic energies in an emergency and keep rockfall away from the federal road and the railway line. But a catch fence only protects as long as it is intact, and without on-site monitoring a hit would go unnoticed. That is why Infrasolute equipped both fence levels and the rock face above with sensors that detect an event in real time and report it themselves.

High-resolution displacement transducers sit directly above the fences, at the rock fissures. They continuously measure movement along the weak zones, with a measuring range of 0 to 10 mm and a resolution of 0.003 mm. This makes crack widening, loosening plates and incipient rock failure visible early, before anything comes down.

The fence structure itself is monitored by cable displacement sensors in a weatherproof housing to IP65. They are connected to the wire rope, convert its mechanical deflection into an electrical signal, and trigger a real-time alert when a defined threshold is exceeded. Because measurement is linear, both a sudden hit and a gradual deformation are detectable.

In addition, a network of four vertical sensor cables runs along each fence level. The modular cable systems are UV- and temperature-resistant, protected to IP68 and have integrated breaking points: if a cable is mechanically severed, an alert goes out immediately. Four cable levels per fence section make this redundant, and a plug system allows a damaged segment to be swapped quickly. The cables are developed for wire-rope fences and barriers against natural hazards and deliver reliable signals for genuine rockfall, without wind or weather triggering false alarms.

Alerting route

From the hit to an emergency stop for the train

The sensors are queried by two redundant gateways per fence level, every second at 1 Hz. The gateways transmit primarily via LTE, and safety-relevant messages additionally via the GSM-R network of Deutsche Bahn. They are powered by a 12 V Li-ion battery with a solar panel, so they operate self-sufficiently on the slope, and they monitor themselves: battery level, data transmission and communication channels all report their own status. A remote-update function allows them to be recalibrated from a distance.

If rockfall or a critical rock movement occurs, the alert is automatically forwarded to the control centre, including an emergency-stop command for trains on the affected section. That is the decisive difference compared with a fence without sensors: the alert travels before the next train reaches the section.

All measurement data run into the Infrasolute online data portal. There, sensor states are available to the second, alongside event logs with timestamp, trigger and location, graphical representation of crack movement and fence loading, a map for localising the affected segment, and the status of every gateway with battery level and signal reception. Every event and every system message therefore remains fully traceable.

Result

A digitally monitored hazard zone until removal

Passive protection has thus become monitored protection. The rock outcrop and both catch fences are continuously observed until removal at the end of 2026, without anyone needing to climb onto the slope. The system is designed for fail-safety: the data run in data centres with two independent server locations, the on-site power supply is self-sufficient via solar and Li-ion, faults escalate automatically, and because transmission only happens on an event or on query, there is no permanent radio emission on the slope.

The project shows how crack monitoring and event detection in slopes and guardrails together form an early-warning system for a natural-hazard zone. If you have a comparable situation at a slope, a fence or a guardrail, describe your project to us through our project inquiry.