Initial Situation
At an existing culvert installation in Jessnitz, the original rock cover had largely been lost over time. Flow, turbulence and repeated hydraulic loads had eroded the protective layer.
As a result, the culvert section was increasingly left without sufficient cover in the riverbed and was directly exposed to erosion, undermining and further scour. Rehabilitation therefore required a new protective layer that would reliably cover the affected area while also adapting to the existing riverbed.
The Challenge
For underwater culvert protection, it is not sufficient simply to place new rock material in the affected area. What is required is a protective layer that can be installed in a controlled manner and with a clearly defined geometry.
The new cover layer therefore had to provide a defined build-up height, fully protect the culvert section and be installed without damaging the pipeline beneath. At the same time, the construction process had to allow for a high installation rate and subsequent inspection of the completed area.
The Solution
To restore the protective layer, around 2,500 AquaRockBags®, each with a filling weight of approximately 1 t, were installed.
The net units, manufactured from project-specific Virgin HDPE, were filled directly on site with natural stone from the quarry, properly closed and then installed using a hydraulic excavator.
The AquaRockBag® combines individual natural stones into a defined unit that can be handled with lifting equipment. This keeps the rock volume bundled during transport and placement and allows it to be installed precisely at the intended position.
At the same time, the flexible shape adapts to the riverbed and to adjacent elements. Once installed, the AquaRockBags formed a continuous, interlocking protective layer over the vulnerable culvert section.
GPS-Supported Installation
A key feature of the project was the GPS-supported positioning of the AquaRockBag®.
The intended installation area was digitally defined. This allowed the excavator operator to follow the planned area and the position of the machine and to place the individual AquaRockBags precisely within the specified installation grid.
The digital installation support made it easier to work systematically along the culvert section. At the same time, overlaps and gaps could be reduced and the progress of the installation documented in a traceable manner. In combination with sounding and surveying data, this provides a solid basis for target-to-actual comparisons and subsequent as-built documentation.
Benefits
The combination of AquaRockBags filled directly on site, heavy hydraulic engineering equipment and GPS-supported installation enabled the protective layer to be constructed efficiently.
Under suitable conditions, project data indicated that up to approximately one AquaRockBag® per minute could be installed. The actual installation rate depends, among other factors, on water depth, current, slewing distance, element availability and the required positioning accuracy.
Further benefits of the system included:
- defined quantity of stone per element
- precise individual placement underwater
- flexible adaptation to the riverbed
- reduced uncontrolled spreading of rock material
- grid-based installation
- good compatibility with GPS and surveying technology
- traceable documentation of the installation
- targeted addition of individual elements where required
Information at a Glance
- approx. 2,500 AquaRockBag®
at 1 t each - Virgin HDPE net with natural
stone filling - filling and closing directly on site
- GPS-supported positioning with hydraulic excavator
- up to approx. 1 AquaRockBag®
per minute
Compared with loose rock placement, AquaRockBag® can offer particular advantages where a defined quantity of material needs to be installed precisely and the position of the individual elements needs to be documented. Project-specific hydraulic and geotechnical design remains essential.
Environment and Material
An environmental compatibility certificate is available for the AquaRockBag® product family. In addition, the Virgin HDPE net material used in the project has been tested for weathering, oxidation, chemical and microbiological resistance.
The natural stone filling remains fundamentally open and permeable within the net structure. Pores and voids remain available and, depending on local site conditions, may become filled with sediment and organic material. The actual ecological effect must always be assessed on a site- and project-specific basis.
