Ursachen und Mechanismen des Trocknungs-Befeuchtungs-Zerfalls überkonsolidierter Pelite

Summary

Disintegration of overconsolidated pelites is caused by dry-wet and freeze-thaw changes. For this investigation, the influence of material properties of the rock on the one hand and climatic factors on the other hand were investigated both in laboratory tests and site observations.

The observations of the disintegration process are related to material properties such as grain size distribution, mineralogical composition, microstructure, porosity, specific surface and the ability to dry out with and without water supply. The influence of all these properties is examined. The climatic influence on Opalinuston (middle Jurassic) has been investigated in detail and compared with the influence of characteristic indices of the material.

Disintegration is initiated by desiccation and shrinkage, which first lead to compaction and an increase of strength of the overconsolidated pelites. However, contact between the clay particles is weakened by desiccation and the structure collapses when rewetted.

The extent of the initial increase in strength depends on the degree of clay particle orientation. The preferred orientation is independent of the rate of diagenesis.

The decrease in strength by rewetting is decisively influenced by the degree of diagenesis. With increasing diagenesis the ability of water adsorption decreases as does the intensity of the particle disintegration.

The increase of material strength resulting from shrinkage is opposed by a decrease in strength of the rock caused by fissuring. Rewetting with water or water vapour causes an additional disintegration of the already weakened material.