35
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
1
Bishop lecture
Advanced laboratory testing in research and practice
Conférence Bishop
Les essais en laboratoire avancés dans la recherche et dans l'industrie
Jardine R. J.
Imperial College London, UK
ABSTRACT: This lecture demonstrates the special capabilities and practical value of Advanced Laboratory Testing, focusing on its
application in advancing the understanding and prediction of how driven piles function and perform in sand. Emphasis is placed on
integrating laboratory research with analysis and field observations, drawing principally on work by the Author, his colleagues and
research group. The laboratory studies include highly instrumented static and cyclic stress-path triaxial experiments, hollow cylinder
and ring-shear interface tests and micro-mechanical research. Soil element testing is combined with model studies in large laboratory
calibration chambers, full-scale field investigations and numerical simulations to help advance fundamental methods for predicting pile
behaviour that have important implications and applications, particularly in offshore engineering.
RÉSUMÉ: Cet exposé décrit les possibilités offertes par les essais en laboratoire de pointe, et en particulier sur leurs apports dans la
compréhension et la prévision du comportement des pieux battus dans du sable. L'accent est mis sur l’intégration entre les essais en
laboratoire et les observations sur le terrain, à partir des travaux de l'Auteur, ses collègues et leur groupe de recherche. Les essais décris
incluent des essais triaxiaux statiques et cycliques avec des appareils suréquipés, des essais au triaxial à cylindre creux, des études
d'interfaces pieu/sable à l'aide d'appareils de cisaillement annulaire et des recherches sur la micro-mécanique. Les essais en laboratoire
sont combinés à des expériences en chambre de calibration, des études
«
grandeur nature
»
sur site et des simulations numériques afin
d'aider à l'amélioration des méthodes de prévision du comportement des pieux, qui ont des conséquences importantes en pratique,
notamment pour l'industrie offshore.
KEYWORDS: Sand; laboratory element tests; non-linearity anisotropy breakage time-dependence; driven piles; field and model tests
MOTS-CLÉS: Sable ; tests élémentaires en laboratoire; non-linearité, anisotropie, fragmentation; comportement en fonction du temps;
pieu battu; pieu foncé; tests sur le terrain
1 INTRODUCTION
The Bishop Lecture was inaugurated by Technical Committee
TC-101 (formerly TC-29) of the ISSMGE, honouring the legacy
of Professor Alan Bishop (1920-1988), the leading figure of his
generation in geotechnical laboratory experiments and
equipment design. Bishop was well known for his meticulous
attention to detail, analytical rigour and application of
fundamental research in civil engineering practice. His
contributions to soil sampling and testing were summarised in
the last major keynote he gave, at the Stockholm ICSMFE;
Bishop 1981. Similarly admirable attributes were clear in the
first Bishop Lecture presented by Tatsuoka 2011, making the
invitation to deliver the 2
nd
Lecture both a considerable
challenge and a poignant honour for this former student of
Bishop and Skempton. The lives, work and archived papers of
the latter two pioneers are described together in a website hosted
by Imperial College:
.
Our key aim is to demonstrate the special capabilities and
practical value of Advanced Laboratory Testing, mirroring
Bishop’s work and TC-101’s intent in the International
Symposia (IS) it convened in Hokkaido 1994, London 1997,
Torino 1999, Lyon 2003, Atlanta 2008 and Seoul 2011. We
focus on the mechanics of piles driven in sand, a practical
problem that was thought fully resistant to ‘theoretical
refinement’ by Terzaghi and Peck 1967. The illustration draws
principally on work by the Author, his colleagues and research
group. In keeping with Bishop’s approach, emphasis is placed on
integrating laboratory research, analysis and field observation.
The selected topic is significant industrially. Pile stiffness,
capacity, cyclic response and long-term behaviour can be
critically important to, for example, wind-turbine foundations.
However, the key geomechanics issues are complex and cannot
be addressed fully or reliably with currently available
conventional design tools. Database studies and prediction
competitions have quantified the significant biases and scatters
associated with conventional practice. The Coefficients of
Variation (CoV) established by contrasting axial capacity
predictions with field tests typically fall around 0.5 to 0.7. Some
methods’ predictions scatter around half the measurements while
others tend to double the test values (Briaud and Tucker 1988).
The capacity CoVs can be halved and biases largely eliminated
by applying modern ‘offshore’ methods (Jardine et al 2005b,
Lehane et al 2005). But displacement predictions remain
unreliable under axial, lateral or moment loads. It is also unclear
how cyclic or extended loading should be considered: Kallehave
et al 2012, Jardine et al 2012. Improving understanding and
predictive ability will benefit a broad range of applications,
especially in offshore energy developments.
The Author’s research with displacement piles in sand
started with highly instrumented field model piles at Labenne
(SW France, Lehane et al 1993) and Dunkerque (N France,
Chow 1997), where full-scale testing followed. We review some
of the full-scale test results below before considering new
research prompted by some surprising and significant results.
The Dunkerque profile comprises medium-dense fine-to-
medium clean silica Holocene marine sand overlain by hydraulic
sand fill. Jardine et al 2006, Jardine and Standing 2012 and
Rimoy et al 2013 give details of the geotechnical profiles, pile
driving records and testing methods. Static and cyclic axial
loading tests were conducted on multiple piles, including six
19.3m long 457mm outside diameter driven steel pipe-piles: R1
to R6. Static axial testing involved a Maintained-Load (ML)
procedure where load (Q) was applied initially in 200 kN steps
that reduced as the tests progressed. Loads were held constant
i
Lecture
