Novel electrode design for non-destructive resistivity measurement on material in geotechnical standard sample cylinders

We present a novel design of an electrode arrangement for measurement of the resistivity of soil samples contained in a sample cylinder used in standard geotechnical site investigations in Sweden. The objective is to make it possible to measure the resistivity of the same samples that are to be used for mechanical tests, without disturbing the samples in order to get unbiased mechanical test data. A design with four piece-of- pie shaped electrodes integrated in the lids in each end of the sample has been tested and evaluated. Temperature sensors are embedded in the electrode lids to allow temperature compensation of the measured data.

Alternative electrode designs were modelled numerically with the finite element method (FEM) prior to the prototype manufacturing. Measurement tests with water filled sample cylinders show that stacking and reciprocal errors can be kept below 1% provided that suitable measurement settings and sequences are used. The geometrical factors depends on the distance between the electrodes in each end of the cylinder, i.e. varies with the length of the sample, and must be determined experimentally or via FEM modelling.