Citation, Dr. John W. Rudnicki, M.A. Biot Medal, 2006


John has been an exceptional contributor to the mechanics of porous media with a series of papers that have made deep impacts both at the fundamental level and in applications to rock mechanics and geophysics. 


My summary of the contributions of John to the field of poromechanics, which is the basis for this nomination, covers three distinct themes.


1. Theory of Strain Localization in Porous Materials


John’s paper with J. R. Rice “Conditions for localization of deformation in pressure-sensitive dilatant materials (J. Mech. Phys. Solids, 1975) focused on shear localization of brittle rock masses and granular materials.  This paper, which won the basic research award from the U. S.  National Committee on Rock Mechanics in 1977, is now a classic having been cited more than 700 times. This work has provided the theoretical foundation for an extensive laboratory testing program at Sandia.  Recently, John and K.A. Issen extended the bifurcation approach to provide an original explanation to the formation of compaction bands that are sometimes observed in porous sandstone layers  and which act as effective barriers to the migration of underground fluids (J. Geophys. Res., 2000).


2. Theory of Coupled Deformation and Fluid Diffusion.


John Rudnicki has contributed over the years with a string of papers dealing either with linear poroelasticity or with failure of fluid-infiltrated porous materials. John’s first paper on poroelasticity was actually a three pages correction to a paper by M. P. Cleary (Int. J. Solids Structures, 1981).  Although the correction pertained to a “minor algebraic error” in Cleary’s paper, it revealed the beautiful mathematical structure of the force singular solution in an infinite poroelastic medium, namely the superposition of the Kelvin elastic solution and a fluid dipole.  This deep insight into the character of the singular solutions has paved the way to the construction of a comprehensive set of Green’s functions by John (Mech. Materials, 1986; J. Applied Mechanics, 1987) and other researchers.


The chapter “Effect of Pore Fluid Diffusion on Deformation and Failure of Rock” in Mechanics of Geomaterials (1985) examines in details the role of dilatancy and pore fluid suction on the failure of rock and rock mass. This chapter, as well as the review article “Coupled Deformation-Diffusion Effects in the Mechanics of Faulting and Failure of Geomaterials (Applied Mechanics Reviews, 2001) have had profound impact on the geomechanics community not only because of the comprehensive nature of the reviews (with a large part devoted to John’s past and new own contributions), but also because of the clarity of the exposition. 


This later contribution also includes an elegant analysis of the influence of reservoir depletion on the state of stress, based on Eshelby’s results on elastic inclusions. This analysis represents a non-trivial advance on the classical predictions made in Petroleum engineering as it includes effects of the shape and the finiteness of the reservoir on the stress change (and degenerates into the classical prediction in the limit of a horizontal reservoir layer of infinite extent).  These particular results are of significance for the stability of wellbores as well as on the containment of hydraulic fractures in hydrocarbon-bearing rocks.


3. Theory of Fault Stability with Applications to Earthquake Mechanics


John with co-authors has written a series of papers dealing with slip dislocation with application to shear faults that were published between 1984 and 1990 in Pure Applied Geophys, JGR, and J. Applied Mechanics. A particularly interesting effect revealed in his work with E. Roeloffs (Pure Applied Geophys, 1984/85) is the prediction of fluctuations of the water levels in wells caused by movements along faults.  Recently, he explored with D. I. Garagash the coupled thermal pressurization and fluid flow effects associated with faulting (J. Geophys. Res., 2003).  They showed that the combined effects of slip weakening, shear-dilatancy, fluid diffusion, and frictional heating yield unexpected destabilization of the fault.


The recommendation letters, enclosed in the nomination package, strongly endorse this nomination.  Some quotes excerpted from these letters are listed below.


Dr. John W. Rudnicki has been an important figure in poroelasticity, and more generally in geomechanics, since his graduate student days. He has widely recognized contributions on interactions between failing rock masses and infiltrating pore fluids, localization of deformation into shear bands, inception of earthquake instability, and seismic radiation from earthquake source processes…. Winding back to John's graduate student days, the work of his Ph.D. thesis opened another area of research in which he quickly emerged as, and remains, a leading world figure.  This is his work, which is the basis for the Biot Medal nomination, on developing poroelastic theory to address the mechanical interactions (and in his recent work, thermal too) between a deforming rock mass and the pore fluid that it hosts.”  (Nominator’s name removed)


In John’s case, the contributions have been not only original but also of fundamental importance to the study of the deformation of the earth in tectonic environments. Probably the biggest impact of John’s research on our understanding of tectonic environment.  Over the decades, John’s insightful analysis of the complex interactions involved in fault slip – which is influenced by pore pressure, temperature, dilatancy, time-dependent friction, and probably other parameters – have been enormously beneficial to the earth science community because his results are expressed in analytical terms that are readily understood and applied.”


Professor Rudnicki developed an elegant theoretical model incorporating the coupling between deformation and diffusion that explains the effects of fluid flow on the onset of shear instability… He made seminal contributions to the theory of linear poroelasticity, by finding point source solutions that can be used as Green’s functions for a variety of problems. Professor Rudnicki also developed fundamental solutions for dislocations in poroelastic media, including solutions for suddenly imposed slip, as well as for propagating dislocations.” 


A personal measure of the impact of John’s work in poroelasticity is the frequency with which I cite him in my book on the Theory of Linear Poroelasticity. John’s overall contributions to our deeper understanding of poroelastic behavior, strain localization, and earthquake mechanics are strongly worthy of the Biot medal.  The award would also be going to a terrific person and colleague.”


“…he has conducted among the most extensive research in poromechanics applied to seismicity and geophysics. …  I have no doubt that John is one of the few who have made the deepest contribution to the field of poromechanics.” 


“This and successive works make him one of the most distinguished and successful scientists of the world in theoretical and numerical analysis if shear band localization in dry and fluid saturated porous media, a rather complicated, very important and challenging physical phenomenon.”


Last but not least, as indicated in several letters of recommendation, Professor Rudnicki has unselfishly served the scientific community.


“He is also a dedicated teacher and an effective scientific citizen.” 


“I have on a couple of occasions been a member of those committees, and John’s thoroughness was a continual reminder that participation, though onerous with no immediate rewards, was a duty not to be shirked.”


“He has unselfishly worked to forward the mechanics community, serving on numerous committees and boards. Professor Rudnicki freely gives his time, delving into problems with characteristic rigor.”


“I would also like to point out the noble and friendly character of Professor Rudnicki.  He is trustworthy without any restriction, open minded and serves his University and several Societies of our community at his best.”


Before concluding this nomination letter, I would like to remark on a personal note that all the papers of John Rudnicki which I have read and studied are exceptionally well written, precise and rigorous, and elegant in their simplicity.  His papers are of enduring quality, not only because of their significance in contributing to knowledge, but also because of their clarity.


In view of his lasting accomplishments to the field of poromechanics, and in particular in its applications to rock mechanics and geophysics, together with his record of dedicated services to the community, I cannot think of somebody more deserving than John Rudnicki as recipient of the Maurice A. Biot Medal.