Analysis of formation characteristics of marine clay based on resistivity cone penetration test (RCPT)

The resistivity of soil is a basic parameter to describe its electrical conductivity and one of the primary physical properties of soil.The electrical resistivity is dependent on many properties of the soil,such as porosity,degree of saturation,composition(conductivity) of the pore fluid,mineralogy,shape,surface conductance and soil structure,including fabric,cementation and temperature.Therefore,the variation of soil electrical resistivity with depth can be an indicator of its characteristics.As a new kind of in-situ testing technique,the resistivity cone penetration test(RCPT) can be employed to measure the tip resistance,sleeve friction,pore pressure and soil resistivity simultaneously in the field.The measuring equipment and operation principle of the Vertek-Hogentogler RCPT system were introduced.Based on some literatures and field test results from the RCPT at Lianyungang in China,the interpretation of resistivity from depositional characteristics and ionic chemistry was presented.It was shown by the results obtained from field RCPT measurements and physicochemical tests that resistivity was obviously influenced by the depositional characteristics and ionic concentration.The test data indicated that the clay mineral percentage and ion concentration decreased with the increasing electrical resistivity.The Fe3+ concentration was also an indicative factor to have influence on the resistivity values.The Fe3+ existed as colloid in marine clay in Lianyungang,which might influence the cementation between soil particles.High content of Fe(OH)3 colloid could have a significant influence on the electrical characteristics of the clay.It could be concluded that the resistivity obtained from the RCPT could reflect the formation characteristics of marine clay in Lianyungang.