DEGRADATION OF COMPACTED MARLS: A MICROSTRUCTURAL INVESTIGATION

R. Cardoso and E. E. Alonso

ABSTRACT: Embankments made with marl and other soft clayey rocks result in an agglomerated structure of finite size particles. These particles evolve however, resulting in major changes of the overall behaviour of the aggregate. The development of settlements and the loss of strength in time are the main concerns in practice. The mechanisms leading to the breakage and eventually the destructuration of one single rock particle are investigated using the concepts of unsaturated soil mechanics since wetting and drying cycles, controlled by atmospheric changes, result in strong suction changes and are one of the main reasons for rock degradation. Numerical simulations of the behaviour of individual rock fragments when wetted until full saturation were performed. Several contributing factors, namely suction change rate, initial suction and confinement were investigated. The knowledge learned with the simulation of the degradation of single rock fragments was extended to simulate the behaviour of particle arrangements under some representative stress and suction paths. Some results of suction controlled tests used for the calibration of the models are presented. The calculated behaviour of single particles and aggregates under wetting is discussed and qualitatively compared with experimental observations of the individual rock fragments and the compacted material. The results obtained provide a new insight into the nature of degradation induced by wetting and drying. They provide also a mechanical explanation, at the level of rock fragments, for the overall behaviour of aggregates.

Key words : evolutive behaviour, hard soil, marl, rockfill, soft rock, suction  (IGC: D3/D9/E2/F5/G13)