Developing a Cycle Path with Soft Ground Conditions

cycling path development

The Committee on Planning and Technology in Varde Municipality decided to create a child friendly school road along the busy Vardevej. This resulted in the development of a new cycle path, which opened in December 2018. 

Challenges were encountered as the cycle path crosses a watercourse including a surrounding meadow and marsh area. The geotechnical survey showed that from a depth of 0.3 - 1.0 meters, a 2 – 2.5 m layer of thick peat was discovered with a low carrying capacity. 

The cycle path is also situated in an area that is protected under the Nature Conservation Act §3. The law protects certain habitats where wild animals and plants reside whose livelihood is threatened from new infrastructural developments. This legal act posed some significant challenges for the development, but the project was fortunate in succeeding to get an exemption, and the cycle path development could continue. 

Load compensation with Leca® LWA 

Mille Graarup, Engineer at Varde Municipality, designed the cycle path, but had no previous experience of building on soft ground conditions. The bridge, which crosses the watercourse is a pile foundation that is nine meters deep, and this provided a significant challenge for the project. It was Rambøll who suggested Leca LWA. “From there it was pretty easy”, says Mille Graarup “I found Leca through an online search and contacted René Jespersen to hear if Leca had experience with cycle paths on peat soils, and they did.” 

cycle path

To avoid settlements, a solution was designed where the cycle path was to be at the same level as the terrain, so that no additional load was exerted on the delicate ground - providing additional support for the path. On a stretch of approx. 50 meters before and after the watercourse, 60 cm of the soft, heavy soil was replaced with 40 cm of Leca® 10-20 and 20 cm stable gravel. Through this design method there was no increased load at the bottom of the excavation, and thus no settlements. 

In order to stabilize the design and distribute the pressure, there is was a geogrid system under and over the layer of Leca LWA. 

Easy delivery through pneumatic installation 

Flemming Nørskov, who worked for the project contractor Harry Andersen & Søn and helped to incorporate the Leca LWA, says: “It was easy to work with when it was delivered by the pneumatic blowing truck. We had placed some piles one meter from the center line of the cycle path and then we just had to fill this up until they were covered. It was easy to rectify afterwards.” 

The contractors chose to provide additional stability through placing gravel on top of the Leca LWA - this was then flattened and compressed to provide additional stability to the construction. 

“Compared to an alternative solution, traditional soil would have to be replaced in three meter depths, and 15 m3 would have to be excavated for every meter of development, the solution discovered with Leca LWA opened so many doors for us and solved many issues” says Flemming Nørskov. 

Mille Graarup was pleasantly surprised with the results when using Leca LWA: “When it is first wrapped in geotextile, it is solid to work on, and so far we have no issues with settlement.”