The construction of gravel turf is comparatively simple. In case of suitable subsoil the construction of a 30 cm of vegetation base layer is sufficient. This is called “one layer method”, as the whole layer consists of the same material.
If the subsoil is unsuitable or heavy loading intensity is expected, the subsoil has to be exchanged and a plane constructed. Suitable materials for the plane are natural gravel as well as recycling materials, as they are commonly used for road constructions.
Plane
The plane of gravel turf should have the following parameters
- Load bearing capacity (EV2 ~ 45 MN/m²)
- Permeability (kf 10-4 to 10-6 m/s)
- Maximum inclination 5%
- Evenness (max. 3 cm on 4m slat)
Vegetation base layer
The vegetation base layer should correspond to the following criteria:
- Vegetation base layer thickness: 15 to 30 cm (30 cm is recommended); if vegetation base layer width exceeds 20 cm it should be split up into two layers of e.g. 15 cm
- Humidity of materials: The materials should be “earth-moist” during the whole construction process
- Layer continuity: to provide an optimal vertical continuity it is recommended to roughen the surface of the already compacted sub layer before constructing the next.
- Construction technique: to avoid decomposition, it is recommended to build in the materials by means of a digger directly from the truck.
- Compaction: a roller compactor of 8 tons is recommended; the compaction is conducted without vibration
- Load bearing capacity: approximately 45 MN/m²
- Evenness and inclination: it is recommended to ascertain the evenness and inclination of the different layers (max. inclination 5%, max. deviation from the 4m slat: 3cm)
- time of construction: spring has proven to be best suitable for the construction of gravel turf (from begin of frost free nights until the end of May)
Sowing
The seeds are sowed by hand with 10 g seeds per m². The vegetation base layer has to be watered before and after the sowing to ensure optimal contact between seeds and substrate.
In the course of the GREEN CONCRETE project two different seeds assortments are tested. One assortment is based on the recommendation of the FLL (RSM 5.1, FLL 2008) and consists solely of grasses seeds. The second assortment has been developed by the University of Natural Resources and Applied Life Sciences Vienna. This seeds mixture is composed of grasses and herbs, which are suitable for all project research locations.
Growth maintenance
At least 50% of the gravel turf surface needs to be covered by plants in order to be acceptable. Thus growth maintenance is obligatory. It is recommended to prevent any usage of gravel turf for 3 month and regularly irrigation. In case of pour nutrient supply the donation of fertiliser may be necessary.
Operational maintenance
The degree of maintenance effort of gravel turf depends predominantly on the intensity of usage. The mowing frequency for instance depends on the stress the plants have. It is assumed, that the test sites of the GREEN CONCRETE project with defined loading (2 loadings per week) have to be mowed 3 times per year.
The removal of fallen leaves and waste may also be necessary.
Winter service
If snow clearence is necessary, it should be conducted with a snow plough. The shield of the snow plough shall be kept 3 to 5 cm above surface to avoid damage of the plant cover. Commonly used road grit may be dispersed.
