Microstructure of the Salzburger Seeton: Characterization based on cone penetartion tests

Piezocone penetration tests (CPTu tests) allow continuous measurements of the tip resistance, the sleeve friction and the pore water pressure over depth. Furthermore, they minimize the required time as well as costs for a soil characterization. Due to the difficulty related to undisturbed sample recovery of soils (i.e. of weak silty fine‐grained sediments) for laboratory testing, in situ investigations are becoming increasingly popular in geotechnical engineering. The article illustrates results of cone penetration tests, executed at three test sites in the city of Salzburg. It is shown that CPT‐based soil behaviour type charts according to Robertson lead to a realistic characterization of the underground conditions. The grain size distribution of the Salzburger Seeton varies between fine sand‐silt mixtures, which are found in the upper parts, to clayey silts in greater depths. According to CPT‐based soil behaviour type charts of Robertson clayey silts behave clay‐like contractive and are characterized by homogeneous properties with increasing depth. Qtn‐IG diagrams underline that the Salzburger Seeton with a high clay content presents a weak microstructure. On the other hand, the upper Seeton layers, which can be classified as silt‐sand mixtures and silty sands respectively, show a stronger bounding between the particles.