Quick-clay microstructure

Abstract

The article deals with a quick clay which was originally deposited in sea water. By leaching in situ the salt content has been reduced to a very small value. By using a special technique for step-wise replacement of pore water with acrylate plastic, 500A˚thick sections were cut with a precision microtome. The sections were photographed in an electron microscope and the micrographs obtained could be used for a study of the clay microstructure. The microstructure is characterized by a linkage of groups or chains of small particles in and between denser flocs or aggregates or between bigger particles. There is no preferential orientation either of small or of bigger particles. A preliminary study of the quick clay and of unleached parts of the same clay stratum has not revealed any microstructural differences. The extreme thinness of the clay sections means that the micrographs reveal pores larger than about 500A˚. Thus the micrographs give a fairly complete picture of the size and shape variation of the micropores in the clay. By measuring the maximum dimension of all pores which could be identified and by using suitable methods for statistical condensation, representative values of mean pore size and two-dimensional “porosity” were obtained. These characteristics are discussed in relation to the permeability and strength properties of the quick clay and of some fresh- and brackish-water deposited clays which have been investigated previously. Finally, on the basis of the micrographs a hypothesis is made concerning the rate of settlement.