Experimental Study on Measurement and Adjustment of Grout pH in On-site Mixing Process for Gelation Time Control of Colloidal Silica Type Chemical Grout

In order to improve ground to planned shape and property by grouting using colloidal silica type grout, it is necessary to use the grout with determined gelation time according to injection time. Therefore, the grout pH, which correlates with gelation time, must be controlled properly onsite of grout mixing. However, conventional mixing plant is not equipped with a function to adjust pH, so the pH adjustment requires time and labor, especially when sulfuric acid-based reactant is used. To address this issue, we have developed "pH-adjusted grout mixing system" that enables real-time grout pH measurement during on-site mixing and amount control of consistent materials. As a result of on-site grout mixing test using developed mixing system, it was confirmed that grout with target pH could be mixed within the target time by determining the procedure for supplying liquid B, considering the increase in grout pH with a time delay caused in grout mixing, based on the assumption of the mixing procedure in which alkaline liquid B is supplied into acidic liquid A.