Vegetated support grid embankment systems (inclination up to 70°C) are used at road construction especially for noise protection constructions. However increasing manifestations are found, that the planted vegetation is not sustainable. It is assumed, that a marginal rain yield factor, the poor moisture penetration of the wall face, the hindering of plant growth by geosynthetics and a difficult rejuvenation of the plants are the basic causes. Therefore the aim of the project is to survey and to analyze the current condition of existing support grid embankment systems. After the choice of suitable objects regarding age, location and exposition the following factors shall be examined:
- Location (local climate, pH, water-holding capacity, the course of moisturization)
- Vegetation (species, ratio, origin, salt tolerance, pests)
- Reinforcement (corrosion, connection points, emplacement, current condition of the geosynthetics).
Based upon this, it is meant to develop decision guidances, so that the local conditions (aridity, salt contaminated spray, pests etc.) can be taken in better consideration when to choose a noise protection system and sustainable solutions can be found. The analysis of the results will also allow to improve the seed mixtures for the wet sowing at locations influenced by such extreme conditions and to optimize the catalogue of groves for the vegetation.
The project has following objectives:
1) To provide a survey of the current condition of vegetated support grid embankment systems of different age and in different location
2) To provide a typification of the investigated objects concerning the typical location features, typical vegetation features, current condition of the reinforcement
3) To develop a decision guidance, when to use support grid embankment systems, when to use noise protection walls with green facing, when to vegetate with groves, when to vegetate with herbs, when sowing of dry turf
4) To optimize the substratum and cultivation (improving the seed mixtures, improving the list of suitable groves with regard to sustained vegetation.
Following steps will be done during the project activities:
- Screening selection 1: Research
- Investigation selection 2: Location during two growing seasons
- Evaluating climate data of the nearest SMA stations
- Determination of water content (vol.%) Of the soil substrate by taking soil core samples and analysis in the laboratory
- Removal of mixed samples and laboratory analyzes. Microstructure, grain size, pH, nutrients content N, P, K and road salt content
- Investigation selection 2: Vegetation during two growing seasons
- Determination of vegetation coverage means standardized image analysis
- Evaluating the types of the population biology
The construction of vegetated acute angle embankments and support grid structures is based on the principles of soil reinforcements with geo-synthetic materials. Today’s most implemented structures of the norm SN 640 621 are referred to as support grid embankment systems. Their advantages are manifold: they are cost-effective, flexibly applicable, and economically assembled, and possess a low allotment and shipping volume of foreign materials that provide the opportunity for full-covering vegetation. However, unsatisfactory experiences with vegetated acute angle noise control walls and other similar objects raise doubts about the applicability of full-covering vegetation. Detailed analysis shall now document the actual condition of such objects and contribute to a better understanding of acute angle embankments in particular locations, in order to improve upon the system choice as well as to optimize the embankment’s vegetation and care.
Forty screening-objects have been selected from a loose collection of already existing support grid embankment systems on the basis of their advanced age and their ease of accessibility. Each screening-object has been visited, photographed, and evaluated by means of specified questions in regard to the condition of its support grid, frontal geo-synthetic material and its vegetation. Subsequently, fourteen locations were chosen from the list of screening-objects for a more detailed analysis and evaluation of their substrate and ground vegetation. In 2011, during the months of June and October, substrate assays were extracted on six objects, while during the same time frame, the ground vegetation at all fourteen locations was recorded. The substrate was analyzed in terms of its water-holding capacity, grading, nutrient and salt concentration, as well as its pH. The ground vegetation was analyzed on random samples with respect to its species diversity and concentration, the coverage density, and its abundance of life forms. Unique animal species were noted.
The technical components of the evaluated support grid embankments, namely the grid and the frontal geo-synthetic net, are in great majority flawless. Looking at the front vegetation, however, only 2/3 objects show a favourable development; 1/3 of the vegetated areas, especially south-facing locations, are in rather poor condition.
The polled servicing firms express that in terms of their objects’ vegetation cover they are rather critical or in effect disapp
- Chronic drought and salt stress as factors in determining location leafy embankment supporting grid systems on roads
- Unsatisfactory aspect because visible rusty support grid and of exposed geotextiles
- Rupicolous, unstable vegetation layer with a high proportion of one-year, serviced species (so-called weeds.); Failure of most seeded species
- Painstaking care