ГЕОЭКОЛОГИЯ


ИНЖЕНЕРНАЯ ГЕОЛОГИЯ. ГИДРОГЕОЛОГИЯ. ГЕОКРИОЛОГИЯ

Geoekologiya, 2018, Vol. 5, P. 66-72

PHYSICO-CHEMICAL NATURE OF THE CLAYEY SOILS PLASTICITY LIMITS

F. S. Karpenkoa,#

aSergeev Institute of Environmental Geoscience, Russian Academy of Science, Ulanskii per. 13, bld. 2, Moscow, 101000 Russia

#E_mail: kafs08@bk.ru

Different methods of practical determination the plasticity limits of the clay soils in the various world norma-tive systems and the emerging contradictions are considered. Determination of the lower limit of plasticity – WP (plastic limit – PL) is carried out by similar methods in all normative systems. Accordingly, the results of the definitions are practically the same. Different methods of determining the upper limit of plasticity lead to significant differences in the test results. The explanation of these divergences is given from the standpoint of physicochemical theory of effective stresses, considering the microstructure of clays that formed due to the formation of contacts between mineral particles as the result of the interaction of forces of attraction and re-pulsion between the particles and the wedging actions of their hydrated films. It is shown that the liquid limit determined by different methods correspond to different physicochemical state of the clay soil. The liquid limit value determined according to the GOST standards (upper limit of plasticity – WL) characterizes the moisture content in the clay soils during lithogenesis at the stage of transition from early to middle diagenesis.

This transition is characterized by the replacement of far coagulation contacts (prevailing in clay microstruc-ture) for near coagulation contacts, resulting in the appearance their plastic properties. The liquid limit index determined according to the ASTM, BS and ISO standards (LL) corresponds to the soil moisture at the stage of initial sedimentogenesis and characterizes the moment of the far coagulation contacts formation begin-ning. The different physicochemical nature of the upper limit of plasticity – WL and liquid limit – LL para-meters explains the impossibility of their reliable and objective comparison in practical studies.

Key words: plasticity index, liquidity index, microstructure, structural contacts, lithogenesis, sedimentogenesis, di-agenesis, catagenesis, real effective stress, plastic limit, liquid limit

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