EVALUATION TESTS FOR COLLOIDAL SILICA FOR USE IN GROUTING APPLICATIONS

Colloidal silica (CS) is a low-viscosity chemical grout that can be in jected to form an impermeable barrier in the subsurface. Such a barrie r was proposed to be placed under a disused unlined retention basin at the Savannah River site. Specifications for the CS grout were include d in the bid package, including performance tests. The product must me et requirements of low viscosity, low permeability when gelled, and co ntrollable gel time both in vitro and in situ. Bidders submitted sampl es for evaluation, and this paper describes the tests that were conduc ted and presents typical results. Gel time in soil was assessed by inj ection tests in packed-soil columns and the monitoring of gelling in t he columns. Injection tests were designed to ensure that grout injecti on would not be impeded by rapid gellation caused by contact with soil . The requirement was that the injection pressure during 2 h of inject ion 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 rep eated falling-head tests that showed that mobility decreased to zero d uring the prescribed time for gelling in situ.