Opening address by the Chairman of the organizing committee of the conference

Conclusions

The present paper deals with the effect of the active factors and conditions of formation on the properties of different types of clayey rocks over the territory of Bulgaria. The most concolidated and lithified clayey marls due to their instability in water and the behaviour of the amorphous cement, are liable to rapid weathering. They do not provide a good foundation for over- and underground engineering constructions. On disturbance of their stability, landslides often develope on the slopes and escarpments, in the form of packs of layers along weaker contacts. It is especially manifested at clayey-marly beds of incoherent structure, which have undergone only chemical syneresis.

The Pliocene clays represent a complex subject for investigation as a foundation and medium for engineering constructions. The deformation behaviour of these clays is determined by their structural state and degree of lithification. Depending on this state and on the applied stress, creep deformations are observed, which either cause failure of the structure or the deformation gradually fades out.

Rheological behaviour of the contemporary silts depends on their properties and structural state, which determine as well conditions for construction works. The structured silts require fast loading, while those structured in a low degree require a slow rate of loading.