Variability of the Ypresian plastic clay of Paris

ABSTRACT

The Grand Paris Express project, creation of a new transport network, provides a large amount of field data from a wide geotechnical campaign with in situ and laboratory tests. The results about the Ypresian plastic clay of the Paris sedimentary basin, obtained from a section of 5.2 km on the future subway line 15, are compiled and analysed in this paper. The geotechnical variability of this specific soil is assessed through the coefficients of variation ($COV$) of four groups of soil parameters namely: the clay index properties (water content, plasticity index, clay content), the shear strength (effective friction angle and cohesion, undrained shear strength), the deformation modulus, and the coefficient of earth pressure at rest $K_0$. The $COV$ derived from vertical spatial variability is compared to the results of a 8-dimensional multivariate normal distribution which correlates the measured parameters at the same depth. The marginal distribution of a soil parameter given other geotechnical parameters reduces systematically the $COV$. The variability of the effective friction angle was derived from a special statistical analysis of the failure stress points. This paper concludes with specific guidelines on the typical $COV$ and means values for different geotechnical parameters that may supply further reliability analysis.

KEYWORDS:

• Ypresian plastic clay
• coefficient of variation
• shear modulus degradation curve
• friction angle
• undrained shear strength

Disclosure statement

No potential conflict of interest was reported by the author(s).