Introduction

Composite media are composed of structure and materials mixed at various scales. Some examples of composite media are most structures in the Earth's interior, granular media at the Earth's surface, plant materials such as wood, animal material such as bone, building material such as concrete and modern materials made with carbon fibre. The theory of porous and composite media is an area of research that has been studied by engineers, geologists, geophysicists and applied mathematicians. Other descriptions of porous media have been constructed in the context of thermodynamic interactions in the Earth's lithosphere. In this theory porosity changes may occur due to deformations, chemical reactions or thermal processes. In the case of deformations of porous media, the theory most commonly used by engineers is the Biot–Gassmann theory. Porosity and saturation waves have been observed in laboratory experiments. The chapter also presents an overview of the key concepts discussed in this book.