Phase relations for decomposable soils

Expressions describing the phase composition and interphase relations for a decomposable soil are derived by distinguishing between inert and decomposable fractions. A relationship between void volume changes and decomposition of the solid fraction, effectively a constitutive relationship, is derived and described by a single parameter. Key patterns of volumetric response to decomposition are highlighted. The decomposition-induced void change parameter is shown to be capable of interpreting the sometimes episodic process of volumetric strain in a decomposable soil-like material.