Theory of Finite Deformations of Pourous Solids M. Biot Indiana University Mathematics Journal 1972 text pdf 10.1512/iumj.1972.21.21048 10.1512/iumj.1972.21.21048 en Indiana Univ. Math. J. 21 (1972) 597 - 620 state-of-the-art mathematics http://iumj.org/access/