6B.1 INTRODUCTION

Geotechnical pressure grouting consists of forcing grout under pressure into a subsurface formation. The grout can be a liquid solution, fluid suspension, slurry, or of a stiff mortar-like consistency. It will generally harden at some point after injection so as to become immobile. Prior to the last few decades, most grouting was done to fill discontinuities in rock, with the primary purpose of reducing water movement through the formation. Now, in addition to water control, grouting is also extensively used to strengthen soil, either permanently or temporarily as an aid to construction.

Grouting is not new. In fact, records abound of grouting projects throughout the 1800s and even prior to that. Most of the early work involved injection of aqueous suspensions or slurries, often containing cement, lime, or clay, into joints and seams in the bedrock underlying dams in order to reduce water leakage. As early practice involved filling of seams or voids, the grout had to be very flowable, and the maximum particle size considerably smaller than the thickness of the particular discontinuity to be filled. Because the pore spaces in soils are generally much smaller than typical rock joints, injection of particulate grout had limited success in soil.

Accordingly, low-viscosity chemical solution grouts, which could permeate soil formations and chemically harden, were developed. In 1887, a patent was issued to Jeziorski for a sodium silicate based formulation, which could be mixed on-site and injected. Unfortunately, the chemicals would react soon after mixing, requiring very...