Evaluation Tests for Colloidal Silica for Use in Grouting Applications

Abstract

Abstract Colloidal silica (CS) is a low-viscosity chemical grout that can be injected to form an impermeable barrier in the subsurface. Such a barrier was proposed to be placed under a disused unlined retention basin at the Savannah River site. Specifications for the CS grout were included in the bid package, including performance tests. The product must meet requirements of low viscosity, low permeability when gelled, and controllable gel time both in vitro and in situ. Bidders submitted samples for evaluation, and this paper describes the tests that were conducted and presents typical results. Gel time in soil was assessed by injection tests in packed-soil columns and the monitoring of gelling in the columns. Injection tests were designed to ensure that grout injection would not be impeded by rapid gellation caused by contact with soil. The requirement was that the injection pressure during 2 h of injection be less than 2.5 times as great as the injection pressure without gelling. Gelling of the grout in the soil columns was monitored by repeated falling-head tests that showed that mobility decreased to zero during the prescribed time for gelling in situ.