FORMATION AND COLLAPSE OF METASTABLE PARTICLE PACKINGS AND OPEN STRUCTURES IN LOESS DEPOSITS

Structure collapse and subsidence represent major geotechnical problem s, particularly in areas containing loess, which is a widespread colla psing soil. The necessary open soil structure is formed by aeolian dep osition of the constituent particles. Various aspects of the open stru cture can be modelled by simple Monte Carlo methods. These show how th e typical vertical pores may be formed and allow certain basic structu ral types to be identified. By various methods, artificial airfall loe sses can be recreated in the laboratory and the collapse behaviour stu died by oedometer experiments. Large void ratio specimens (e > 1) can be produced, which have classic collapse behaviour. The artificial spe cimens mimic the behaviour of real loess samples remarkably well. The results suggest that the nature of the loess material may be as import ant with respect to structure collapse and related effects as the mode of sedimentation. The key controls are particle size and shape, the b ond/weight ratio (R), the nature of the interparticle contact bonds, a nd the clay content (which modifies the latter two effects). In the ge ometrical models four pore types, six major substructural types and th ree collapse processes are identified. (C) 1997 Elsevier Science B.V.