Citation, Dr. James R. Rice, M.A. Biot Medal, 2007

It is my great honor and pleasure to nominate James R. Rice, Mallinckrodt Professor of Engineering Sciences and Geophysics at Harvard University for the 2007 Maurice A. Biot Medal.  Jim Rice’s contributions to the mechanics of porous materials are so extensive, fundamental, and diverse that it is difficult to summarize them succinctly, even though they constitute only a part of his contributions to broader area of mechanics, including fracture, plasticity, computational mechanics and geomechanics, material science, and geophysics. There are, however, features common to all of Jim’s work: originality, thoroughness, clarity and elegance. He attacks big and important problems. He has a genuine gift for extracting the maximum insight from simple idealizations that then form the foundation for more elaborate explorations. Although some of his work involves complicated analysis or calculations, he has the ability the distill results to a kernel that those of us with less facile minds can appreciate. He is a theoretician but is relentless at basing his analyses on experimental and field observations and interpreting it in terms of implications for observations.

Because of the wide impact and fundamental nature of Jim’s work, it is difficult categorize in the mechanics of porous materials. As noted in the supporting letter by xxxx (name removed to protect privacy) “In a quite unpredictable way, a famous paper by Rudnicki and Rice (1975), not focused on porous rocks, became in 1999 the source of intensive research on porous rocks.” Nevertheless, with some considerable oversimplification, I would group his contributions to the mechanics of porous materials in three areas:  poroelasticity, inelastic behavior of fluid-saturated porous materials, and response of void containing technological materials.

In poroelasticity, several supporting letters (xxxx, xxxx and xxxx) discuss the landmark status of the paper with Mike Cleary, "Some Basic Stress-Diffusion Solutions for Fluid-Saturated Elastic Porous Media with Compressible Constituents" (Reviews of Geophysics and Space Physics, 1976). This work was followed by a series of papers (some published under the sole authorship of Jim’s students, e.g., Ruina and colleagues, e.g., Simons) that developed additional solutions and explored their importance for earthquake precursory phenomena and spreading earthquake faults or shear zones. As an example of the simultaneous fundamental and applied nature of Jim’s work, a 1978 paper, "Deformation of Spherical Cavities and Inclusions in Fluid-Infiltrated Elastic Materials" extended a famous and widely used result of Eshelby on the strain inside ellipsoidal inclusions in elastic materials to a spherical inclusion in a linear poroelastic material.  Other papers went on to apply this solution to earthquake precursory processes.

Recent contributions include a paper with M. Cocco "Pore pressure and poroelasticity effects in Coulomb stress analysis of earthquake interactions" (Journal of Geophysical Research, 2002) which rigorously accounted for poroelastic effects in calculating Coulomb stress changes (shear stress minus friction coefficient times effective stress). In particular, they showed that the appropriate form of the effective stress in a narrow fault zone is proportional to the change in stress normal to the plane of the fault zone when the shear modulus in the fault zone is significantly smaller than in the surrounding material but by the mean stress changes when the elastic mismatch is small. Other very recent work, "Effective normal stress alteration due to pore pressure changes induced by dynamic slip propagation on a plane between dissimilar materials" (Journal of Geophysical Research, 2006) shows that the pore pressure induced by differences in poroelastic properties in narrow layers bounding a plane of dynamically propagating slip can cause alterations of effective normal stress comparable in magnitude to the alterations of normal stress due to dynamic propagation of slip on a bimaterial interface.

Among Rice’s important contributions to the inelastic behavior of porous geomaterials is "On the Stability of Dilatant Hardening for Saturated Rock Masses" (Journal of Geophysical Research, 1975), a concise and insightful analysis of dilatancy of saturated materials, a phenomenon discussed by Osborne Reynolds at the beginning of the last century and familiar to anyone who has walked on wet beach sand. Rice showed that if dilatancy (pore volume increased) was induced by shear faster than fluid could flow into the newly created void space, the resulting decrease in fluid pressure would increase the effective compressive stress and inhibit further inelastic shearing. This phenomenon, termed dilatant hardening, was, however, unstable in the sense that small spatial nonuniformities would grow exponentially in time when the underlying drained response was unstable.  Rice mentioned but did not pursue the implications for shear induced compaction which are relevant liquefaction and have been explored by Vardoulakis, Garagash and others. Rice went on to examine the implications of this phenomenon for the growth of shear bands (J. R. Rice, "The Initiation and Growth of Shear Bands", in Plasticity and Soil Mechanics, edited by A. C. Palmer, 1973) and deformation processes preceding earthquake instability ("Earthquake Precursory Effects due to Pore Fluid Stabilization of a Weakening Fault Zone", Journal of Geophysical Research, 1979). More recently, with Paul Segall ("Dilatancy, Compaction, and Slip Instability of a Fluid Infiltrated Fault" (Journal of Geophysical Research, 1995), he has shown that the coupling of fluid flow with a more sophisticated rate and state description of compaction and dilation not only is consistent with laboratory results but can alter the stability of slip on earthquake faults.

"Fault Stress States, Pore Pressure Distributions, and the Weakness of the San Andreas Fault" (in Fault Mechanics and Transport Properties in Rocks, eds. B. Evans and T.-F. Wong, 1992) is another landmark paper that addresses the weakness of the San Andreas fault in both an absolute (compared with laboratory friction measurements) and a relative (to adjacent material in the crust) sense. Rice showed that the latter is consistent with a rotation of principal stress axes as the fault is approached. Supporting evidence for this prediction is now emerging from results of the San Andreas fault drilling project. This paper has had a major influence on the way geophysicists think about faults and on the design and motivation for the San Andreas fault drilling project. Using observed variations of permeability, he also predicted that fault weakness is consistent with high pore pressure in a relatively impermeable fault and suggested the possibility of soliton-like pulses of pore pressure that propagate slowly upward along the fault.

In several recent papers Rice has explored the role of thermal heating of fault zone pore fluid by frictional sliding on the mechanics of faulting ("Heating and weakening of faults during earthquake slip", "Does shear heating of pore fluid contribute to earthquake nucleation?" (with P. Segall), and "Thermal pressurization and onset of melting in fault zones" (with A. Rempel), all in Journal of Geophysical Research, 2006).

Even more recently, in as yet unpublished work with a student, Yajing Liu, Rice has shown that small heterogeneities in pore pressure combined with a rate and state dependent description of frictional sliding can provide a physical basis for aseismic deformation transients that have been observed in several subduction zones (zones where one tectonic plate sinks below another), including Cascadia in the northwest US.

Rice’s contributions to the material science and engineering of void containing technological materials are described in more detail in the supporting letters by xxxx and xxxx. Here I just repeat the comment of xxxx that the work of Rice and Tracey initiated development of a quantitative theory for the role of void growth and coalescence in ductile fracture and of xxxx that this paper “created the subject of void growth analysis in metals”.  Both go on to say that this work lead to the development of a constitutive model by Art Gurson, a graduate student under Jim’s direction. The paper, which as xxxx notes was published by Gurson as sole author despite Jim’s substantial contributions, has been cited over one thousand times.

Jim’s work and many awards provide ample and concrete evidence of his contributions. But, even these far underestimate his influence on the field of poromechanics and mechanics, in general. Jim is unfailingly supportive and encouraging and generous with his ideas. Buried in personal communications and acknowledgements are clues to the keen insights, crucial suggestions, and even detailed notes he has provided to others without taking credit. As one example, I quote an acknowledgement in a wonderful paper on “Thermoelastic response of porous rock” (Journal of Geophysical Research, 1986) by Dave McTigue: “The author is particularly indebted to J. R. Rice for providing a detailed development of the appropriate energy balance for the system treated.” I am sure there are many others and even more that have gone unnoted or unacknowledged.

There is, of course, no requirement that the Biot medal be given to a fine human being and a wonderful person, but it is my pleasure to nominate someone who is. From my perspective, beginning as a student of Jim as an undergraduate and graduate advisor and progressing to friend and colleague, he has been unfailingly supportive and encouraging, not only in professional matters but personal ones as well. There is simply no question that whatever I have accomplished in this profession owes much to his influence. My long struggle to overcome my awe of him has been aided all along the way by his kindness. I know for a fact that my opinion is shared by many of his students and colleagues.

Jim’s record needs no promotion but I urge you in the strongest possible way to award the 2007 Biot medal to Jim Rice for his “Fundamental contributions to the mechanics of porous metals and geomaterials with applications to soil mechanics, geophysics and materials science and engineering.” There is no one more deserving.

Sincerely,

(Nominator’s name removed)

2007