1. ANGUELOV K. (1977): Characteristics and indices of the deformation behaviour of some clays with different types of structural bonds. “Hydrotechnics and melioration”. Bull. No 2, pp. 8–13, (in Bulgarian).
2. ANGUELOV K., METCHKARSKI P., ILIEV T. (1982): Possibilities for prognostication of the boards deformations at the East-Maritza open-pit mines. Proc. of the 5th International Symposium for Mine Surveying. Varna, pp. 75–83 (in Russian).
3. VYALOV S.S., PEKARSKAJA N.K., MAKSIMYAK R.V. (1970): About the physical substance of the deformation and collapse of the clay soils. “Foundations and soil mechanics”, Bull. No 1 (in Russian).
4. KARAULOVA Z.M. (1969): The role of the rheologic properties of the clay soils in the development of the riverside slope deformations. Moscow Institute for Civil Engineering, Moscow (in Russian).
5. MORGENSTERN N.R., TCHALENKO J.S. (1967): The optical determination of preferred orientation in clays and its application to the study of microstructure in consolidated kaolin. Proc. Roy Soc. A 300, 218–234.