Thixotropic Properties of Allophane Soil

Abstract

Volcanic ash soil in Japan is principally composed of allophane, with some quantities of various layer silicates, gibbsite, and other sesquioxide minerals. In the Kanto district a type of volcanic ash soil called Kanto loam is found. This soil shows thixotropic response upon remolding. In the natural state, Kanto loam has a porous structure with good bearing capacity but after remolding, the strength is lowered and the structure is broken.In this work the thixotropic properties of Kanto loam in the gel state obtained by adding, cations (Na+, K+, NH4+ and H+) were investigated by the use of consistency curves and centrifugal dehydration curves for soil water. The cation adsorption of allophane is considered to be not of the interlayer type but of the surface adsorption type. A cation can be added to the soil by normal methods (chloric salts, but hydrochloride in the case of H+).The important results may be summarized as follows. The flow properties of a water suspension gel of the fresh soil show generally more thixotropy than do air dried soils. It is found that the flow and dehydration behaviour of a K+ soil and a NH4+ soil more similar to each other than the corresponding behaviour of K+ and Na+ soils. This must be also related to the ionic behaviour of the soil, in the sense that K+ and NH4+ are easily fixed to allophane soil, or freed from it, depending on the surrounding chemical condition.It is supposed that an external force would be effective in changing the adsorption condition of the allophane surface.