Effects of Grout Composition, Depth and Injection Rate on Compaction Grouting

Design of an efficient and economical compaction grout program requires a firm understanding of the primary controlling parameters and mechanisms. These include the soil conditions and overburden pressure, the grout composition, injection rate, and injection pressure. This paper describes a series of small-scale model compaction grouting tests performed in a geotechnical centrifuge to examine the effects of grout composition and injection rate on grout take and grout bulb development. The response to a one-stage grout bulb injection in dry cohesionless soil is examined at various full-scale equivalent prototype depths and injection rates using two grout mixes, and preliminary trends regarding grout bulb development and shape are evaluated. Preliminary results indicate that the grout bulb development is a function of the overburden pressure, injection rate, and grout composition. When similar volumes of grout are injected, grouts with smaller clay content developed into smaller grout bulbs than greater clay content grouts. The shape of the grout bulb does not appear to be measurably affected by injection rate, but is influenced by injection depth and clay content. Given a known volume of injection, the final grout bulb volume is a function of the depth of the injection and, to a lesser extent, the injection rate.