Jet Grouting for Water Cutoff and Excavation Support

Jet grouting is an extremely versatile ground treatment method for water cutoff and excavation support applications. The jet grouting process features unique characteristics that enable it to be used where other ground treatment methods cannot. Jet grouting uses relatively small diameter tooling compared to soil mixing, yet it can create soil-cement columns with diameters many times larger than the tooling. This allows jet grout columns to be installed beneath utilities or structures that must be left undisturbed. In addition, jet grouting creates soil-cement columns through the erosive action of high velocity fluid(s) exiting the nozzles. The erosive action scours the surface of underground structures and enables jet grout columns to conform to and seal against these surfaces. The erosive action also enables jet grouting to successfully treat a wide variety of soils. Jet grouting can be used as a stand-alone method to create water cutoff and excavation support structures. It can also be used to complement other technologies. This paper presents three case histories of jet grouting used in very different applications. The first project used jet grouting to build a partially unreinforced circular shaft and tunnel structure that was tied into an existing brick sewer. The jet grouting successfully stabilized contaminated soils and prevented the contaminants from entering the excavation. The second project used jet grouting to seal full-depth gaps in a cement deep soil mix wall for a cut and cover subway tunnel. The gaps resulted from numerous utility crossings along the project alignment. The third project used jet grouting to form a seal slab at the bottom of a braced sheetpile excavation in sand beneath the water table. The jet grout seal slab was installed prior to any excavation. The seal slab enabled excavation to proceed in the dry and provided permanent resistance to seismic-induced liquefaction of the soil beneath the new structure.