Mikrostruktur des Salzburger Seetons – Charakterisierung basierend auf Drucksondierungen

Abstract

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.

The soil investigations and soil mechanics insights for the underground construction of the S‐LINK

“…Results from the earlier studies of the Salzburg lake clay [5][6][7] suggest that these lacustrine sediments are characterised by microstructural bonds. The nature of the microstructural bonds may differ between the upper sand-and silt-dominated layers, where the microstructural bonds tend to be stronger, and the deeper clayey silts of the Salzburger lake clay, where they tend to be weaker.…”

“…Previous investigations of the Salzburg lake clay [6] tried to identify correlation factors between oedometer stiffness measured in the laboratory and the results of the cone penetration tests. Reference values from settlement back calculations were used as the basis for comparison.…”

“…Der Einfluss von mikrostrukturellen Bindungen des Salzburger Seetons, die zwischen den Bodenpartikeln wirken und das mechanische Verhalten des Bodens beeinflussen, wurde in den vergangenen Jahren intensiv untersucht [5][6][7]. Diese Bindungen können u.a.…”

“…In früheren Untersuchungen an Salzburger Seeton [6] wurde versucht, Korrelationsfaktoren zwischen der Oedometersteifigkeit im Labor und Ergebnissen von Drucksondierungen zu ermitteln. Als Vergleichsbasis dienten Referenzwerte aus Setzungsrückrechnungen.…”

“…The influence of microstructural bonds in the Salzburg lake clay, which act between the soil particles and influence the mechanical behaviour of the soil, has been intensively studied in the past [5][6][7]. These bonds can be formed through cementation and ageing of the soil and generally lead to increased strength and stiffness compared to unstructured soils with the same void ratio, which cannot be attributed to the stress history alone.…”