Following massive rockslide: Speed record for installing safety measures in Slovenia

On February 20th , 2016 over 500 cubic meters of rock and debris collapsed onto the district road between the county seat Trbovlje and Ljubljana. Just five weeks later, on April 4 th , the road is officially reopened by the Prime Minister of the country. The road is now being protected by the strongest rockfall barrier of the Swiss company Geobrugg.

The huge rock mass forced Slovenian national authorities to implement urgent measures: Not only was the road blocked, the residents were also cut off from electricity and water. The debris removal on the important route R1-223 had to be completed in the shortest possible time; but first, sustainable protection measures needed to be developed and installed.

Site investigations followed by software analysis conducted by geologists and 21engineers indicate a significant remaining hazard potential. The heavily fractured residual rock mass at the mountain top cannot be taken down as it could damage an important nearby railway. However, parallel to the site investigation and software analysis, limited rock scaling was also being performed.

Sustainable solution implemented quickly

Drilling works commenced on March 8 th to install anchors and base plates for the barrier’s post foundations. Based on the study results national authorities decided to apply the strongest Geobrugg rockfall protection system from the RXE-Series. This versatile barrier tested and approved according to the strongest guidelines has a significant track record of installations in extremely difficult terrain. With its ring nets made of high-tensile steel wire this system has been designed to absorb energies of up to 8,000 kilojoules. This means 20 metric tons impacting at 103 km/h the rockfall protection system.

Flexibility complements proven processes

The task force consisting of Slovenian authorities, geologists, engineers, contractors and specialists from Geobrugg were able to put politics aside to enable a cohesive, efficient and extremely speedy implementation of the protection measures.

The posts, ring nets, ropes and accessories produced and preassembled at Geobrugg in Romanshorn, Switzerland were delivered to Trbovlje by mid-March. The biggest helicopter of the Slovenian Armed Forces delivered the four preassembled ring net bundles along with the five posts, weighing each almost 2 metric tons, to the heavily inaccessible terrain. Despite high winds the helicopter crew made the decision: “We’re flying!” The experience of the entire ground and helicopter crew was needed to connect the posts to the base plates within a millimeter of accuracy.

The mega-barrier technical acceptance inspection took place on April 4th, the same day officials, stakeholders and the public are welcomed to the inaugural reopening of the newly repaired and secured road connecting Trobovlje with the state capital Ljubljana. The hazard mitigation has become a project of superlatives because of its size and the speed of construction as well as for the perfect cooperation of all parties involved.

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