Strength of Soft Swiss Lacustrine Clay: Cone Penetration and Triaxial Test Data

Abstract

A new link road is to be constructed top down between parallel cast-in place pile walls under a series of railway lines in Kreuzlingen, Canton Thurgau, which is an important hub in the regional transportation network. The results of a site investigation on the soft, normally consolidated, post-glacial lacustrine clay deposit underlying the railway lines, including a cone penetration test, undisturbed sampling from an adjacent borehole, and laboratory testing, are reported. Strength characteristics of the clay were determined, correlated, and linked to stress history and current stress. The investigation demonstrated a close agreement between strength parameters derived from the laboratory and the in situ testing when a piezocone factor of NkT = 17 was applied. This agreement confirms previous local experience. The results obtained lead to a more differentiated knowledge of the clay deposit, providing valuable data for constitutive modeling. These data will be particularly useful for future local construction work using the observational method and value engineering.

Mechanical characterisation of lacustrine clay by interpreting spatial variability in CPTU measurements

“…It is higher than might be expected on the basis on previously suggested range of values, although a sensitivity of 3 to 5 may be partially responsible. Springman et al (1999) suggested a linear trend for a characteristic undrained shear strength s u for Kreuzlingen clay that was supported by triaxial stress path data as well in compression and extension (see Fig. 2).…”

“…(8) Figure 8 reports the trend functions calculated by this study on the A201 s u profile at the Wauwil Springman et al (1999). site and the one derived from Springman et al (1999) at Kreutzlingen.…”

“…CPTUs have been adopted in such glacial clays in recent years, in order to design transportation infrastructure in Switzerland (Heil et al 1997;Springman et al 1999). Recently, Hird & Springman (2006) investigated the feasibility of detecting silt layers as thin as 5 mm by comparing pore pressure profiles from CPTUs using piezocones with 5 cm 2 and 10 cm 2 cross sectional areas, which were performed at the Wauwil site (Fig.…”

“…The 5 cm 2 piezocone appeared to be able to achieve a more accurate prediction of the location and extent of the silt/clay layers, although variability in cone resistance (q c ) and pore pressure (u 2 ) profiles affects the precision mostly where silty and sandy lenses or inclusions are crossed. Furthermore, Springman et al (1999) tried to derive appropriate properties for designing structures in Kreuzlingen clay by comparing field and laboratory tests. They derived s u values from cone tip resistance q c and pore pressure u 2 by means of the standard equations:…”

“…roads, retaining walls), with the intent to achieve optimal (i.e., more economic) design. The optimisation of design between client, engineer and contractor through value engineering, may well become of increasing interest (Springman et al, 1999).…”