Evaluating In-Situ Jet Grout Column Diameters Utilizing Wave Analysis

Jet Grouting is an in-situ injection technique employed with specialized equipment, drill rig, drill rods and injection monitor with horizontal radial nozzles delivering high velocity fluids to erode, mix, and stabilize in-situ soils. This process is used on a wide variety of projects to improve the mechanical properties and/or reduce the permeability of the soil. Prior to commencing production jet grouting, a field test program is typically undertaken to evaluate and refine injection parameters and to assess jet grout element geometric, mechanical, and permeability properties. The test program typically involves the construction of test elements followed by a 3 to 14 day cure time, depending upon soil type and project requirements. Where possible, jet grout test elements are exposed by excavation and geometric properties are obtained by direct measurement and bulk samples are collected and delivered to a laboratory for unconfined compressive strength and permeability testing, as required. Where excavation is not possible, core drilling is employed to obtain soil cement samples from the jet grout test columns for strength testing. Coring jet grouted soil can be difficult and often yields results that are not representative of the in-situ condition and quality of the jet grouted element(s). Therefore, an alternative quality control evaluation method is needed. This paper will discuss the measurement of in-situ jet grout column diameters on a project site in Columbus, Ohio. The measurement and evaluation of jet grout column diameters were obtained using a wave-based analysis approach. This approach will be introduced and data will be presented to show that column diameters can be assessed in-situ with this method, even in different soil types. The measurements, data collection, and analysis are the result of an international collaboration and the authors believe the system may be useful for similar projects in the future for our industry.