Soils Sealed by Technic Hard Materials in Urban and Traffic Areas

Abstract

Urban areas give rise to unique soil ecosystems, as they are drastically disturbed and modified by human activities. An example of such human activity is soil sealing. Soil sealing is identified as a threat to basement soil, and though enabling high trafficability, contributes to surface water discharge for flood control and the need for installation of facilities. Soil sealing is recognized as one of the most important anthropogenic pressures on soil biodiversity. The effects of soil sealing on major environmental components are concerned with the kinetics of chemical reactions that affect the proper functioning of the soil. Soil profiles beneath asphalt roads display unexpected soil layering, consisting of different materials from the top to the base of the soil profile. A boundary layer indicates that subbase materials mixed with surface soils through the paving process. Even 40 years after the road construction, the sealed soils have maintained properties of the original soil. Soils beneath asphalt pavement are classified as Ekranic Technosols according to the world reference base for soil resources (WRB; IUSS Working Group WRB, World reference base for soil resources 2014. International soil classification system for naming soils and creating legends for soil maps, World soil resources reports no. 106. FAO, Rome, 2014). A buried concrete or asphalt layer serves to stabilize the area beneath interlocking pavement blocks. Different soil materials were observed in the profile beneath the asphalt pavement due to disturbances of the original basement soil by mixing. The profile beneath interlocking pavement is classified as Ekranic Epitechnoleptic Technosol according to WRB, due to covering with interlocking pavement and buried continuous concrete debris. Mixed alkaline subbase materials exhibited an alkaline soil reaction especially in the upper layers, Higher electric conductivity in the profile beneath the building indicates continuous leaching of basic elements from foundation concrete. Thus, soil sealing material influences the soils beneath the sealing layer in different ways. High bulk density over 0.9 g cm⁻³ exceeds the criterion of Andosols despite observation of andic properties confirmed by a NaF soil reaction. Compaction with paving and mixing with demolished construction material changes soil properties such that Andosols are converted into Technosols.