THE STUDY OF THE FLOW HETEROGENITY OF THE CAMBRIAN BLUE CLAY IN SCOPE OF HAZARDOUS WASTE DISPOSAL    

M. V. Vilkina^1*, A. M. Nikulenkov¹, V. G. Rumynin¹

¹St. Petersburg Division, Sergeev Institute of Environmental Geoscience, Russian Academy of Sciences; Srednii pr., 41, St. Petersburg, 199004 Russia

*E-mail: wilkina.mari@hgepro.ru

The present article studies the flow heterogeneity in the Cambrian blue сlay in scope of hazardous toxic waste disposal at the Krasny Bor site. The clay properties were studied both in monoliths sampled in open-pit mine and bore cores by a number of laboratory methods. To investigate the flow characteristics of clays the in-situ Lugeon (or packer) tests were also performed. The visual analysis of the open-pit mine outcropping proved the Cambrian clays to have the block structure. The blocks are separated one from another by the orthogonal fracture system in subhorizontal and subvertical plane directions. The size of the blocks increases with depth, starting with centimeters and reaching several meters at a depth of 20 meters. Meanwhile, numerous borehole core examination during the engineering geological survey shows the absence of the fractures aperture, which could be a conductive zone. The laboratory method such as flow cells tests estimated the hydraulic conductivity of the clays to be 8.8∙10^-7 and 9.0∙10^-8 m/day in along and across bedding directions, respectively. The mean flow anisotropy value remains consistent across all samples and is 9.5. The results of the Lugeon tests allowed us to conclude about the closed state of the fracture system under natural conditions i.e., the clay massif acts as an aquitard. The water injection into an isolated interval with a pressure of four lithostatic values causes opening of the fracture system. In this case the hydraulic conductivity of the fracture system may reach up to 0.5 m/day. When an isolated with packers interval is decompressed, the fractures close in so the clays act as a flow barrier again. Therefore, depending on the environmental conditions the Cambrian blue clays may play the role of the flow hampering barrier or a conductive layer.

Keywords: Cambrian blue сlay, hydraulic conductivity, flow parameters, fracture system, Lugeon tests, waste disposal, Krasny Bor site

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