Spectacular stabilisation of a hillside in the Wutach Valley, southern Black Forest.
Easter 2014 will be engraved in the memory of the residents of the Black Forest community of Wutach for many years to come: on Easter Sunday between 6 and 7 p.m. the first of many mighty fir trees crashed down onto the L 171 country road, triggering a landslide of massive proportions. The lifeline to the village of Ewattingen and connecting road to the district of Donaueschingen remained blocked for several months until provisional stabilisation of the hillside in the summer of 2014 allowed the road to partially open.
Several observant citizens of Ewattingen informed Hartmut Trenz, road construction expert for the regional council of Freiburg, as early as March that an increasing number of stones were falling onto the road at a specific point and so the hillside was inspected and surveyed by qualified personnel from a wide range of fields. After a huge crack had opened up in the hillside within a few days, on Maundy Thursday the L 171 between Ewattingen and the Wutach mill was closed for safety reasons. A wise decision considering what happened only three days later. Several firs on a steep southern slope above the busy L 171 were no longer able to hold onto the slope and masses of earth, boulders and debris followed the trees down the hillside.
Immediate measures included removal of the fallen pines and boulders from the road as well as the felling of other trees that were in danger of falling in the landslide zone. A special company from Würzburg was commissioned to remove approx. 1,200 m3 of excess earth from the geologically unstable zone using a walking excavator.
For weeks, the community of Ewattingen was just a white dot on the map.
Following further geological studies, a decision was made to strengthen the hillside above the road using shotcrete and anchoring equipment, and the company Bombardi Tiefbau from Titisee-Neustadt was commissioned to stabilise the problematic hillside.
After approx. 120 metal anchors were inserted, a shotcrete wall was sprayed across the entire width of the hillside to stabilise it. Most of the time, the experts were only able to work from a suspended cage during this challenging job and as always, had to deliver quality results under extreme conditions. A Putzmeister P 715 piston pump provdied the experts from Bombardi with assistance: equipped with an automatic dosage system for set accelerating admixture and a 60 metre long DN 50 hose, the hydraulic piston pump demonstrated a perfect combination of powerful technology from large pumps with an extremely compact and user-friendly design as well as the ease with which pumpable material with a grain size of 8 mm can be conveyed. The T-chassis made it easy to transport the machine to the construction site and manoeuvre it to the top of the slope. Specially designed for construction sites and continuous use, the state-of-the-art P 715 pumped a total of 1,000 m³ of material onto the unstable hillside.
Motorists have enjoyed partial "free passage" along the L 171 since July 2014.
After a special fence for stopping sliding debris was erected and a net for preventing new landslides was installed, one lane of the L 171 was cleared again for traffic after having been closed for several months, albeit with a temporary traffic light control. Geologists are continuing to monitor the hillside because the unstable ground in the area around the Wutach gorge is expected to spring some rather unpleasant surprises in the future. Hartmut Trenz, road construction expert and site manager for the landslide in the Wutach Valley, explained that it will almost certainly not be the last landslide witnessed by the residents of Ewattingen and it is important now to reforest the area around the landslip to provide additional stability.
Picture: The magnitude of the landslide can only be fully appreciated by standing directly at the top of the slope and looking down towards the L 171. (Image: Putzmeister)
Source: Putzmeister Holding GmbH