The deformations of building foundations on clay soils can develop over long periods of time, measured in centuries, causing building settlement. The rate of settlement influences the occurrence of plastic deformations of wall and frame ma-terial. Therefore, the development of methods for calculation of foundation deformations in time is an urgent task. It is known that the theory of filtration consolidation gives similar results to practical observations only for weak water-saturated clayey soils of fluid and fluid-plastic consistency, which often require reinforcement. In such cases, jet grouting or impregnation injection technology is used. Injection mixtures based on microcements are used for this purpose. The pa-per proposes compositions of injection mixtures using expanded clay dust. It is shown that expanded clay dust can be used as an active mineral additive in the injection compositions based on the microcements. It is established that the injection compositions on the basis of the microcement modified with the expanded clay dust have the best efficiency at fixing clay soils, as the sizes of their particles are comparable with the sizes of the particles of the microcements and the expanded clay dust.