SPECIAL ISSUE :LANDMARKS Jet grouting is a landmark technology, and as such has changed deep foundation practice in many ways. In the past 10 years, this highly specialized technology that uses hydraulic energy to erode soil and mix/replace the eroded material with grout to form “soilcrete,” has seen a significant increase in its use. Since Mitsuhiro Shibazaki, a “grandfather” of jet grouting technology, presented at the 2003 International Conference on Grouting and Deep Mixing, specialist contractors have followed his direction by creating new geometries in the ground while considering the variable quality of the product. Today, experienced jet grouting contractors are drawing from the technology’s wide arsenal of techniques for innovative treatments in soil conditions that previously were untreatable with other technologies. As practitioners gain experience, the technology has become more reliable and more widely used for a variety of applications: tunneling, bridge piers and abutments, waterfront structures, and restricted-access foundation renova- tions, to name a few. Jet grouting has distinct advantages over conventional ground support systems, especially in difficult site conditions. For example, all work can be done in-situ from the ground surface, and in confined spaces including spaces with extremely limited headroom. Historical buildings can be underpinned with minimal resulting settlement. Where structures or surface movements are not a concern, practitioners can treat large volumes of problem soils. Another pioneer of the technology, Hiroshi Yoshida, recently reported research initiatives that have refined the tooling. More efficient nozzle designs have improved fluid focus while reducing the tooling sizes. For example, practitioners have AUTHOR: George K. Burke, P.E., D.G.E. Senior Vice President-Engineering Hayward Baker Inc. Odenton, Maryland 86 • DEEP FOUNDATIONS • NOV/DEC 2012 A recent jet grouting operation in Cambridge, Mass., shows how the technology has advanced over the years. This equipment has a state-of-the-art data acquisition system that records all grouting parameters in real time. The one simple jet grouting principle, though, is that more energy creates more geometry. The power generated at the pump, the time spent in the ground, and air shrouding are the most critical elements that the jet grouting contractor can control. The jet grouting contractor cannot control the subsurface conditions subjected to the Make sure the borehole: • Has an open sustainable annulus for returns • Is stable so it will not collapse • Is large enough so that spoil returns will not clog the annulus and cause pressure build-up Jet Grouting: A Landmark Technology formed super-sized columns 5 m (16.4 ft) to 7 m (23.0 ft) diameter with relatively small-diameter tools (see Figure 1). Jet Grouting Basics: More Energy, More Geometry Jet grouting is highly varied in tooling used, procedures used, fluids used for erosion and mixing, and the energy applied for jetting these fluids. There are just too many combinations to simplify the technology, and this can be confusing to the non-practitioner. erosion, and this variability can be as critical as the controllable parameters! Variability aside, we need to understand the elements you can control: the standard objectives of jet grouting. Objective 1: Access the Treatment Zone. Jet grouting usually involves rotary mud drilling to access the treatment zone, which involves some planning before the work begins. To ensure continuous cuttings return during the jetting process, you must control the jetting environment with a good borehole and drilling technique.
