The determination of the thixotropic limits of sediments

Abstract Efforts to determine the highest thixotropic values that may be reached by sediments have shown that the manner of preparation of the systems is of considerable importance. In particular, the preliminary shaking of the system, instead of the usual procedure of stirring only, results in the production of substantially higher values, even in the case of but moderately thixotropic calcareous and sandy materials. The increase varies from 5 per cent. with weakly thixotropic systems to more than 70 per cent. with fat clays. The significance of the increase, in relation to the theory of thixotropy, is discussed. It has become evident that the lower thixotropic limit cannot be determined by the inverted‐tube method, although its approximate magnitude can be estimated. Some such estimates have been compared with the results obtained in liquid‐limit tests on the same samples, from which it appears that the moisture‐content for flow at 10 bumps in the liquid‐limit test (i.e. about 11 ± 5 per cent. of the liquid limit) approximates to that at the lower thixotropic limit. The necessity for devising more precise experimental methods, and for agreement on definitions of liquid flow and plastic flow, is emphasized. The term rheotropy is suggested to include the phenomena of thixotropy s.s., false‐body, rheopexy, and age‐hardening (i.e. for the isothermal reversible gel/sol‐or‐more‐fluid‐gel transformation). Brief reference is made to certain natural occurrences of thixotropic or potentially thixotropic deposits and to the practical problems to which they give rise. Also, opportunity has been taken to include thixotropic values for a further selection of sediments.