At conventional construction sites, the removal of soil and other excavated materials causes enormous mass movement, with a significant climate impact and contribution to global CO₂ release. This study aimed to generate a Circular Soil concept for reusing excavated materials by creating engineered soils for landscape construction at large building sites. Engineered soils act as a substitute for natural soils and fulfill vital technical and soil functions when installing an urban green infrastructure (GI). In a field study, the vegetation performance on engineered soils was evaluated to establish a methodological approach, to assess the applicability of the Circular Soil concept. First, the technical specifications (grain-size distribution) were modeled for intensive green roof and turfgrass applications. Then, the soil components were optimized, mixed, installed and tested for greenery purposes, focusing on plant growth performance indicators (vitality, projective cover ratio and grass-herb ratio) to assess the vegetation performance. The results showed that the engineered soils match the performance of the reference soil alternatives. In conclusion, the Circular Soil concept has a high potential to contribute considerably to sustainable on-site soil management and the circular economy. It can be applied on a larger scale for urban GI development and sustainable resources management in the landscaping and construction sector.

Green Infrastructure measures such as seepage troughs are an integral part of sustainable urban rainwater management. In Austria, seepage troughs are currently almost exclusively produced with a 30 cm thick active soil filter passage made of topsoil. A standard seed mix is used as vegetation, which usually consists of only three different turfgrass species. During a three-year trial, engineered soils with improved properties (increased water storage capacity, infiltration rate and pore volume) were tested for their suitability as seepage troughs compared to topsoil. In addition to the standard turf seed mix, a flowering turf seed mix (34 species) and flowering meadow seed mix (53 species) were applied. The engineered and reference soils were analyzed for infiltration rate, vitality, cover ratio and inflorescence. The results were further assessed with the evaluation chart showing quantitatively the suitability of the tested soils for rainwater management. The investigations showed that engineered soils in combination with flowering meadow seed mix lead to the best results. Therefore, this type of vegetation for seepage troughs is recommended for future applications. The reference alternatives cannot be recommended.

Equations for calculating evapotranspiration in technical soils show great differences regarding their results. Causes are the different climatic conditions and vegetation specifics during their development. Every equation of evapotranspiration only delivers 100% correct results if it is used under the same climatic condition as it was developed in. To determine the evapotranspiration, the loss of weight of different technical soils and plants was measured in a test series on load cells in a climate chamber. The result of these test series is the development of an easy-to-use equation. An equation for calculating evapotranspiration at any temperature is possible while using a polynomial correlation. To determine the evapotranspiration rate (in mm/m² per 24 h), only temperature, vegetation type, and technical soil have to be defined to obtain an output of evapotranspiration in mm/day. Using the well-known equation by Makkink, evapotranspiration in technical soils is 0.12 mm/day, whereas the newly developed equation calculates (1) 2.59–5.58 mm/day for the variant with no vegetation, (2) 3.15–4.00 mm/day for Sedum floriferum, (3) 4.40–4.55 mm/day for Geranium x cantabrigiense. The application of this equation will help to determine the evapotranspiration in chosen technical soils (used in the sector of rainwater management) with or without vegetation.

Existing formula, like the well-known Penman-Monteith equation, for calculating evapotranspiration possess great differences concerning their results. Causes for that are the different climatic conditions and vegetation specifics during their development. Every formula of evapotranspiration only...