Field-Scale EICP Biocemented Columns for Ground Improvement

Field-scale biocemented soil columns were installed in dry, poorly graded sand using enzyme-induced carbonate precipitation (EICP) and tube-à-manchette (TAM) permeation grouting. Column diameters ranged between 0.3 and 1.0 m, and column heights ranged from 1.0 to 2.4 m. Urease enzyme was obtained in the field from jack beans using tap water and a crude extraction process, with and without dehusking the beans. The biocementation treatment solution was injected in three cycles at approximately 24-h intervals. Test results showed that leaving the husks on the jack bean during extraction did not affect either injection or cementation. The plate load test showed an increase in bearing capacity by a factor of 3 and an increase in stiffness by a factor of 3 following treatment. Downhole seismic readings showed an increase in shear wave velocity of at least $100\mathrm{m}/\mathrm{s}$ in the biocemented soil. Measurements on exhumed columns showed that the column dimensions were similar to the target dimensions. Needle penetrometer readings taken during exhumation indicated an unconfined compressive strength of at least 500 kPa. Carbonate content measurements on exhumed specimens varied from more than 4% (by weight) close to the TAM to less than 2% at the design radius, and an increased injection rate provided more uniform carbonate content. This field-scale program demonstrates that EICP can be employed using conventional grouting equipment and a simple enzyme extraction method to create biocemented columns with diameters of 0.3 to 1.0 m and a target strength of at least 500 kPa in 3 days.