DYNAMIC COMPACTION OF SATURATED POROUS COLUMNS

A theory for flow in a saturated compressible porous medium is developed to simulate the solid-liquid separation operations known as expression in practice. A mathematical model that consists of the mass-conservation equation, quasistate equilibrium equation, stress-strain relation for an elastic matrix, and a variable total stress expression was employed to obtain numerical solutions for pore pressure and compaction variations due to time-dependent and constant displacement conditions at the upper boundary of saturated porous columns. Results were obtained for five problems of practical importance. Cases studied include the compression of a porous column with a specified time-dependent displacement of the upper boundary, compression with instantaneous displacement of the pervious upper boundary of a saturated porous column, compression with time-dependent displacement at the impervious upper boundary, compaction with an upper boundary moving at a constant velocity, and dynamic compression of a saturated porous column with variable permeability and porosity. The effects of piston (upper boundary) and membrane (lower boundary) resistances on pore pressure variation and compaction distribution have been investigated, and the implications of constant porosity and permeability assumptions were demonstrated. It was shown that lower and upper boundary resistance factors have critical influence on the operation.