Water content determination of soft Finnish clays using electrical conductivity measurements
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Suomalaisten savien vesipitoisuuden määrittäminen sähkönjohtavuusmittauksella
This thesis is made in accordance to evaluate a possibility to use electrical conductivity measurements for determination of geotechnical parameters. The main goal of this thesis is to find a way to determine water content of soft Finnish clays using electrical conductivity measurements. This thesis is divided into two parts that are literature study and experimental part. In literature study properties of clay and its formation, as well as modelling and measuring electrical conductivity of soils are examined. In experimental part, electrical conductivity measurements, done for Finnish soft clay deposits, are compared with laboratory data to find affecting relations between those. Totally of seven sites were investigated. Electrical conductivity measurements were done with conductivity module attached on top of a CPTU cone. Based on experimental results, pore water conductivity (salinity) controls the conductivity of tested clays, and a strong, linear correlation between soil and pore water conductivities is found. Water or clay content did not show any effect on results. However, while water content data is divided based on soil conductivity, some kind of correlation between water content and soil conductivity could be found for high conductivity (> 225 mS/m) clays. To confirm existence of this relation, more measurements using high conductivity clays should be done. Of other geotechnical parameters, plasticity and liquidity indexes as well as sensitivity and remolded shear strength seem to correlate with soil conductivity. Liquidity index and sensitivity decreases with increasing soil conductivity and an upper limit as a function of conductivity can be sketched. On the other hand, plasticity index and remolded shear strength seem to increase with increasing soil conductivity, but the correlations are not very strong. Main goal of the theses was not achieved, since water content, at least in general level, does not seem to correlate with electrical conductivity of soil. However, as strong correlation between soil and pore water conductivities was found, it would be interesting to study possibility to use conductivity measurements for evaluation of corrosion environment. In addition, use of conductivity measurements for soil contamination investigations could be studied.