Toshiyasu Unno

Applicability of Enzymatic Calcium Carbonate Precipitation as a Soil-Strengthening Technique

AbstractA grouting technique for enzymatic calcite precipitation is evaluated. Urea and calcium salt, at various concentrations, are mixed with a concentration-fixed enzyme to obtain the optimal precipitation of CaCO3. The optimally combined solution is injected into sand samples in small PVC cylinders. Then, the improvement in small-scale samples is observed. The combination, approved for small-scale tests, is further used for larger-scale tests. The porosity distribution within the soil is evaluated by sampling the treated sand at different locations. A precipitation ratio up to 80% can be obtained using a small amount of the enzyme. The results show that the in situ enzymatic CaCO3 precipitation technique may be feasible for use in larger-scale applications. A multiphysics simulator that considers the calcite precipitation reaction during the transport of the solution is adopted to predict the evolution of the porosity. The predicted porosities are compared with the measured porosities. The results sho...

Earthquake-Induced Mudflow Mechanism from a Viewpoint of Unsaturated Soil Dynamics

This paper discusses the general liquefaction state of unsaturated soil related to the mudflow type slope failures observed during earthquakes in areas covered with volcanic ash sand deposits. It is found that the volume compressibility of soil structure, the degree of saturation and the confining pressure are key factors governing the liquefaction of unsaturated soils.