These are some of the research groups that (to my knowledge) have been involved in research on solitary waves and related topics in granular materials -

1. Prof M. Nakagawa (Colorado School of Mines, USA) and
2. Dr J. H. Agui, Jr. (NASA Glenn, Cleveland, USA), Shock absorption, experimental;
3. Prof J. Hong, Solitary waves, theoretical (Seoul Nat’l U., Korea );
4. Prof H. J. Herrmann, Solitary waves, simulational (U. Stuttgart, Germany );
5. Profs C. Coste and S. Fauve, Solitary waves, experimental  (Ecole Normal, Lyon, France);
6. Prof Th. Poeschel, Solitary waves, simulational (Freie U., Berlin, Germany);
7. Prof. N. Brilliantov, Solitary waves in granular media (Moscow State University, Russia);
8. Dr H. Sakaguchi, Shock absorption, simulational (U. Tokyo, Japan);
9. Prof D. Wu, Shock absorption, theoretical (Colorado School of Mines, USA);
10. Prof F Melo, Solitary waves, theoretical (U. Santiago, Chile);
11. Prof Stephane Job, Solitary waves and shock absorption (SUPMECA, France)
12. Prof V. Nesterenko, Solitary waves and shock absorption, experimental and theoretical (UC-San Diego, USA);
13. Prof K. Lindenberg, Grain dynamics, theoretical (UC-San Diego, USA),
14. Prof E.J. Hinch, Solitary waves (Cambridge U., UK);
15. Prof C.E. Brennen, Nonlinear acoustics in granular beds (Caltech, USA)
16. Prof. L. Vergara, Solitary waves ad secondary solitary waves in granular chains (U. Santiago, Chile)
17. Prof. Insuk Yu, Solitons in granular chains (Seoul National U, Korea)