Strength tests of enzyme-treated illite and black soil mixtures

Enzymes are organic degradable materials, recently introduced as soil improvement additives for earthen pavement layers and embankments. This study was conducted to evaluate the effect of three enzymes on the unit weight and unconfined compressive strength of illite mixed with black soil. The optimum moisture content (OMC) and maximum dry density of the untreated soil were determined with a standard Proctor test. The same test was conducted to prepare untreated and treated soil samples at OMC. Samples were prepared for two dosages and two curing periods. However, no considerable increase in unit weight was observed for specimens treated with the three enzymes. Larger-sized soil samples were prepared to reduce the inaccuracy in sample preparation and testing. No noticeable improvement was observed for any of the enzymes and dosages. Some of the samples showed a little increase in strength but that was found to be due to the higher densities of those samples. A Fourier transform infrared spectroscopy test was executed to investigate the structure and functional groups of the three enzymes and their effect on soil. Thermogravimetric analysis, differential thermal analysis and X-ray diffraction tests were performed to determine whether any chemical reaction took place between the soil and the enzymes, but no chemical reactions were observed.