Rigidity of “Warsaw clay” from the Poznań Formation determined by in situ tests

Abstract

The character of morphogenetic processes occurring within river valleys depends on the mechanical and hydrogeological properties of deposits that build up such landforms. In the case of the Polish Lowlands, a series of Pliocene clay lake sediments (so-called Poznań mottled clays) plays a special role. Their current locations and properties are associated with specific sedimentation conditions and glacitectonic deformations, which the soils have been subjected to many times in Pleistocene. Their presence in the lithological profile influences dynamics of slope processes in valleys’ escarpment zones and channel erosion stabilization. In this article, the “Warsaw clay” from the Poznań Series Formation is presented in comparison with other cohesive Quaternary sediments, which are mostly building neighboring outcrops. This article analyzes the Seismic Dilatometer (SDMT) results and a method of interpretation to determine IR, plasticity index, and liquid limit (LL) parameters. The undrained shear strength Su was determined based on the Cone Penetration Test (CPT), SDMT, and laboratory test results. Spatial variability of the strength and deformation parameters in the study area were determined using dilatometer test (SDMT) results. Finally, the nomogram chart is proposed to obtain the rigidity index (IR) of the preconsolidated Pliocene clays, depending on both p0 and p1 pressures from SDMT and effective vertical stress σv0′{\sigma }_{\text{v0}}^{^{\prime} } and pore water pressure u0.

Keywords

• cohesive soils
• rigidity index
• undrained shear strength
• shear modulus
• cpt/dmt