In view of its extreme complexity the mathematical description of the
mechanical behaviour of granular materials is an extremely difficult
task. Today many different models compete with each other. However, the
complexity of the models hinders their comparison, and the potential
users are confused and, often, disencouraged. This book is expected to
serve as a milestone in the present situation, to evaluate the present
methodes, to clear up the situation, to focus and encourage for further
research activities.