<p><p><figure id='attachment_3489' style='max-width:764px' class='caption aligncenter'><img class="wp-image-3489 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Overhead photograph of project site at I-78 and Route 33 interchange in Easton and Bethlehem Pennsylvania where a jet grouting project was undertaken." width="764" height="450" /><figcaption class='caption-text'> ©2010 NAVTEQ, Pictometry Bird’s Eye© 2010 Pictometry International Corp, Image Courtesy of USGS, ©Microsoft Corp</figcaption></figure></p><p><div class="grayed-title"> <span style="font-family: inherit; font-size: 24px; font-weight: bold;">Project Summary/Scope:</span></div><div></p><p>Construction of new highway interchanges for I-78 and Route 33 required deep excavation (up to 17.8 meters) and cut slopes as steep as 1H:1V.</p><p>Subsurface Conditions: The soil conditions at the site generally consisted of a pinnacled limestone/dolomite bedrock surface between 18.0 and 32.3 meters below the existing ground surface. Soil seams within the rock and float rock or boulders are also present. Immediately overlying the rock surface, soft to very soft residual clay and silt is present. Above this transition zone, the soils are generally stiff to hard sandy and clayey silt, silty clay, and sandy silt. Groundwater is present at depths of 17.7 to 26.5 meters.</p><p>The exploration encountered soft soils below the planned toe of the steep cut slopes. In order to achieve the required factor of safety for the slope, jet grout columns were installed with a proposed design unconfined compressive strength of 3,500 kPa, a design cohesion of 240 kPa, and a friction angle of 35°. Two rows of columns, one at the toe and one row one-third up the slope with a design diameter of 0.75 meters were installed. The columns were designed to be installed as a “cut-off” wall and were installed in a secant pattern. The columns were designed to extend into the underlying limestone bedrock. In order to anchor the columns into rock and to ensure continuity of the columns, steel reinforcement pipes were installed in the columns. A patented method of installation was used in order to allow placement of the steel and the jet columns at the same time rather than drilling through the cured soil-concrete mixture at a later date.<br><h2>Complementary Technologies:</h2>In addition to the jet columns, soil nails and geocells were installed to reinforce the surficial slope.<br><h2>Performance Monitoring:</h2>Prior to construction, a test program was performed to aid in determining the predictable column diameter, ensure thorough mixing and consistency of the soil‑cement mixture, obtain core samples for compressive strength testing, and to ensure proper overlap to form a secant pattern. The test section also helped assist with determination of the appropriate installation methods (i.e., single-, double-, or triple-fluid). The test program revealed that the initial planned use of a single-fluid process was not adequate because of the presence of stiffer soils. The installer then switched to the double-fluid method. The test method also revealed the appropriate nozzle raising step interval for the appropriate mixing and column overlap. During construction, random production columns were cored full height of the column for visual inspection of the core samples and for compressive strength testing.<br><h2>Cost Information:</h2>$1,300,000 (for the entire 32 meters of slope including jet grouting, soil nailing, and geocell slope protection.)<br><h2>Project Technical Paper:<strong> </strong></h2>Meyers, J., Myers, T., and Petrasic, K. (2004). “Jet grout stabilization of steeply excavated soil slope.” <em>Grouting 2003</em>, pp. 318-329.<br><h2>Date Case History Prepared:</h2>November 2012</p><p>&nbsp;</p><p>&nbsp;</p><p></div></p></p>