Guided by the solidification of loess contaminated with heavy metal ions (HMs), a natural inorganic diatomite (NID) was developed as curing agent under an alkaline activator (AA). The curing time, NID content and AA type on the mechanical properties of contaminated soil and solidification effect of HMs were investigated. The solidification source was analysed by microstructure measurement. As curing time increased, the solidification effect increased, with an optimum curing time of 28 days. The higher the content of NID, the stronger the solidification ability. Nevertheless, the strength showed a tendency of initial increase and subsequent decrease. The strength was maximum when NID content reached 10%. The AA created an alkaline environment to promote solidification. In comparison to Na2SiO3 solution, NaOH solution is more effective in the adsorption of HMs. The larger ionic radius of Pb2+ relative to Cu2+, limited HMs migration ability, thereby facilitating solidification.

Diatomaceous soils as a special soil containing diatom frustules are widely distributed in marine deposits. Although their soil properties have been partially tested and reported which exhibit high void ratio and compressibility, a thorough investigation is in lack. Moreover, the interpretation of the cone penetration test (CPTu), a widely-used in-situ test, to the properties of such soil is still unknown, hindering a proper estimation of the diatomaceous soils in engineering geology and geotechnical practice. This study reports the soil properties and mechanical behavior of the undisturbed diatomaceous soil obtained from Walvis Bay in Namibia, which shows that the soils had an extremely high void ratio (similar to 4.39) and low specific gravity (similar to 2.16), and consequently low density and high compressibility. Due to the porous property of diatom frustules, the diatomaceous soils also exhibited a high liquid limit and plastic limit. Although these properties provide an identification to super soft soils, the diatomaceous soils had discrepant mechanical properties, i.e., the values of strength parameters in diatomaceous soils were higher than those in typical soft soils. At the end, by comparing the results of strength parameters obtained from the laboratory tests on undisturbed soil samples and the in-situ CPTu records, this paper proposes the interpretation methods of CPTu results to the strength parameters (effective friction angle and undrained shear strength) in the diatomaceous soils.