Skip to main content

Tube sampling disturbance

Researcher: Ms Eyre Hover
Project duration: 2010-2013
Supervisor: Dr Qing Ni and Prof. Ian Guymer
Funding body:

Background

The biggest source of uncertainties and risks for the construction of civil engineering projects lies in the ground. It is observed that among projects that were delayed, nearly half of the cases were due to unforeseen ground problems and not much improvement has been made during the past three decades (Tyrell et al., 1983; NEDO, 1988; Chapman and Marcetteau, 2004). As a result, projects are often built over the initial budget and it is estimated that across the European Union, about 50 billion euros is spent each year due to such problems (Chapman, 2008). Most of the time, soil samples are retrieved by pushing a tube into the ground, a process called tube sampling. It has long been recognized that this sampling process can cause significant disturbances to the soil, so the soil samples obtained do not truly reflect the in-situ soil state. Without understanding the tube sampling disturbances, it is impossible to interpret the laboratory test data properly and obtain the correct engineering property values. It has been a primary concern among geotechnical engineers and extensive research has been done on tube sampling disturbances, although the real movement of soil during tube sampling has never been measured.

Project Aims and Methodology

The aim of this research is to study the real movement of soil during the entirety of the sampling process: driving, storage and extrusion of samples. Since clay is naturally opaque, an artificial transparent material with properties similar to clay (Iskander, 2010) will be used to model the soil medium. Similarly, steel sampling tubes will be replaced with glass tubes of different design to study the effect of sampler geometry on sample disturbance. Displacements within the soil body will be studied by tracking the motion of seeded particles within a plane of the soil body during testing, and analysed using Particle Image Velocimetry (PIV), a non-intrusive displacement/velocity measurement technique originally developed in the field of fluid mechanics.

References

Tyrrel, A. P., Lake, L. M. and Parsons, A. W. (1983) An Investigation of the Extra Costs Arising on Highway Contracts. TRRL Supplementary Report SR814, Transport and Road Research Laboratory, Crowthorne, Berks.

Chapman, T. and Marcetteau, A. (2004) Achieving Eeconomy and Reliability in Piled Foundation Design for Bilding Project. The Structural Engineer, 2 June, 42-37.

Chapman, T. (2008) The Relevance of Developer Costs in Geotechnical Risk Management. Proceedings of the 2nd British Geotechnical Association International Conference on Foundations- ICOF 2008. Brepress, Dunde.

Iskander, M. (2010) Modelling with Transparent Soils, Springer Berlin Heidelber.