Six definable particle types need to be recognised in engineering soils. Failure to appreciate the true nature of soil and to treat soils crudely as a ‘black box’ has led to many different types of failures. The basic five types that need to be recognised are (related to the R-size diagram, see Figure 1) AA’ active clay minerals, BB’ inactive clay minerals, C fine cohesive primary minerals, D silt (at R approximately equals 1), E sand. We estimate that at about 200 microns and above the cohesive forces can be neglected, so that truly granular soils start at 200 microns and extend to 60 mm. We propose 60 mm as the upper limit of truly granular behaviour, which has been arbitrary chosen for the discussion purposes. From 50 to 200 microns we propose that a sixth definable sub-region type occurs, where R<l but cohesive forces are still significant.

Six Definable Particle Types in Engineering Soils and Their Participation in Collapse Events: Proposals and Discussions

Soil organic matter of bulk samples and size fractions (by dry sieving) of chernozems with a rather with different history of use (from intact steppe to permanent bare fallow) was studied by TGA under pyrolysis conditions in an inert atmosphere to approach its transformation depending on the type of use. For the first time, thermal properties of samples of Kursk chernozem (Kursk Research Institute of Agricultural Production and V.V. Alekhin Tsentralno-Chernozemny Nature Reserve of Russia) were studied for a continuous 55-year field experiment with a well-documented history of use and showed that long-term agricultural use significantly changes the thermal parameters of soil organic matter, and this is manifested for aggregates of various sizes. The minimum representative weight for the thermal analysis of bulk soils is ca. 1 g (when grinding samples to 100 μm). The paper proposes a new parameter to assess the degree of organic matter degradation, the ratio of the mass loss in the 380–600 to 170–380 °C temperature ranges that is referred to as two-range thermal stability ratio. It is shown that this relative index discriminates soil samples depending on the land use type and does not require the knowledge on carbon content.

I. J. Smalley

Papers

High resolution derivative thermogravimetry of sensitive clays