Pilot-scale modeling of colloidal silica delivery to liquefiable sands

Passive site stabilization is a developing technology for in situ mitigation of liquefaction risk without surface disruption and involves slow injection of stabilizing materials into the liquefiable sand. In this study, colloidal silica was used as a stabilizer. Injections were performed in a pilot-scale facility having dimensions of 243 cm by 366 cm in plan and 122 cm in depth. The pilot-scale facility is the largest of its kind in the United States. It is equipped with electrical conductivity cells which provide real-time monitoring of grout advancement in the soil. Different injection rates were used to investigate the optimal rate for horizontal grout delivery without sinking. In the first experiment, injection rates were about 60-135 ml/min/well. In later experiments, higher injection rates were used (up to 9000 ml/min/well). When low injection rates were used, colloidal silica sank instead of traveling horizontally. With higher injection rates, sinking was less noticeable. After treatment, colloidal silica was allowed to gel. After gelation, the model was excavated and soil samples were extracted to investigate grout penetration. Soil recovered from block samples was tested for unconfined strength in the laboratory. A wide range of strengths were observed and thought to be related to the colloidal silica content of the treated soil. The 3D flood simulator UTCHEM was used to simulate the experimental results. The results of actual experiments showed that even 1% percentage colloidal silica provides significant strength after a month of curing.Colloidal silica grouting model for UTCHEM was validated with different length column tests varying from 3-foot to 30-foot. UTCHEM was also used in a parametric study, to determine the delivery performance using injection and extraction wells on site. Addition to UTCHEM flood simulator, a 3-D finite difference program was developed to simulate colloidal silica injection in porous media. The program generated similar results with UTCHEM in a preliminary injection application. The new program offers further development in computer simulation of colloidal silica grouting.