Consequences of sample disturbance when predicting long-term settlements in soft clay

Abstract

An approach for assessing the effects of sample quality is presented. Soil samples were taken using a 50 mm Swedish STII piston sampler and the Norwegian University of Science and Technology (NTNU) mini-block sampler from a soft clay test site. Differences in laboratory test results are identified for several stress paths, assisted by simulations made using an advanced constitutive model. Hitherto such comparisons have focused on differences in basic engineering properties such as strength and stiffness. The effect of choosing alternative model parameters from piston and block samples is demonstrated through the analysis of the long-term settlement of an embankment. The simulations show that substantially larger settlements and lateral displacements are predicted using parameters obtained from the piston samples. Furthermore, the magnitude of the differences is larger than expected. This demonstrates that for this application, relatively small differences in the assessed sample quality, using traditional laboratory data interpretation methods, are amplified when applied to a prototype boundary value problem. It is suggested that a little more care in sampling and testing can result in large cost savings as a result of the more reliable model parameters that can be extracted, particularly when the improved sampling is combined with the use of an advanced constitutive model.

Evaluation of sample quality from different sampling methods in Finnish soft sensitive clays

“…The importance of sample quality in the determination of strength and deformation properties of soft sensitive clays has been extensively documented (e.g., Hvorslev 1949;Lunne et al 2006;Karlsrud and Hernandez-Martinez 2013;Karlsson et al 2016;Mataic 2016). Conclusions from these studies highlight the difficulties encountered while retrieving undisturbed samples using different sampling techniques, pointing out the implications in terms of measured soil properties from laboratory testing.…”

“…These studies revealed that piston samples often result in low quality, especially in highly sensitive clays (e.g. Lunne et al 1997;Lunne et al 2006;Karlsson et al 2016). On the other hand, the use of tube and block samplers in such soils provides enhanced sample quality (e.g., Bjerrum 1973; Lefebvre and Poulin 1979;La Rochelle 1981;Lunne et al 2006;Berre et al 2007; Karlsrud and Hernandez-Martinez 2013).…”

Three-Dimensional Consolidation Theory of Vertical Drain Based on Continuous Drainage Boundary

“…Consolidation significantly influences soil strength and the stability of buildings (Gibson, 1958;Karlsson, Emdal, & Dijkstra, 2016;Sales, Prezzi, Salgado, Choi, & Lee, 2017). Accurate prediction of the consolidation of foundation soil and the settlement of buildings is of great significance to the construction, design and safety of engineering.…”

Monitoring of the nano-structure response of natural clay under mechanical perturbation using small angle X-ray scattering and digital image correlation

“…The material studied is a natural sensitive silty clay from the Utby test site in Sweden. Its formal classification is high-plasticity clay, CH, with high sensitivity S t [18]. The samples are characterised also by a high silt content ( [ 20% by mass), typical for sensitive clays of the region.…”