<p><p><figure id='attachment_3503' style='max-width:749px' class='caption aligncenter'><img class="wp-image-3503 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Photograph of equipment used for mass stabilization along US Highway 1 near Jewfish Creek in the Florida Keys." width="749" height="536" /><figcaption class='caption-text'> Stabilization equipment and site layout showing mangroves, stabilization area, and surcharge material (Figure from Garbin and Mann 2010).</figcaption></figure></p><p><h2>Project Summary/Scope:</h2>US Highway 1 was to be widened in the environmentally sensitive area of the Jewfish Creek drawbridge in the Florida Keys. The roadway was to be widened by 40 feet, adding a median and two new shoulders. The roadway was initially constructed by placing granular fill along the alignment to displace the existing soft organic silt and clay to the sides. Since initial construction, more organic soils have been deposited, supporting the growth of mangroves adjacent to the road along most of the alignment. Mass stabilization was selected as the method of treatment for economic and environmental reasons. Prior to stabilization, the typical soil profile consisted of 5 ft of granular fill on top of 10 to 15 ft of soft organic silt underlain by limestone.</p><p>An extensive pre-construction laboratory investigation was performed using bulk soil samples from various locations along the alignment to determine the appropriate binder type and quantity. Depending on embankment height, the target shear strength ranged from 400 psf to 1500 psf. A 75:25 slag-cement mixture at dosages of 220 to 270 lb/yd³ was selected to achieve the required shear strengths.</p><p>The mangroves were cleared, with most being chipped and left on the construction area to be mixed into the stabilized soil mass. Following the mixing operation, a 2-foot-thick layer of crushed lime rock was placed on the construction area to provide a working platform. The working area was divided into sub-sections, and each was probed for depth of improvement. Mixing was performed with an excavator-mounted mixing tool rotating at 50 to 100 rpm. The dry binder was delivered pneumatically. Binder delivery was monitored electronically. For each improvement section, a geotextile and two feet of crushed lime rock were placed immediately after thorough mixing to compress the stabilized soil prior to initial set. By project completion, 360,000 yd³ were successfully treated.<br><h2>Alternate Technologies:</h2>Alternatives to mass stabilization considered on this project were excavation and replacement or a column-supported embankment. Constructability and time constraints made mass stabilization the most viable option.<br><h2>Performance Monitoring:</h2>Quality assurance was performed primarily using column penetration testing (KPS) and load testing. KPS tests were performed at a rate of one test per 2,500 square feet of treatment area. Any tests that yielded unsatisfactory results were repeated at a later curing time within 2 feet of the original test. It was required that the treated soil reach the design minimum shear strength prior to the placement of embankment fill. KPS tests were performed at young curing ages because, at later curing times, the test often met refusal. In some cases, in order to achieve penetration, a tool with smaller or no vanes was used. Test embankments were placed to monitor settlement and show that primary settlement would occur prior to paving operations and to evaluate secondary settlement. Pull out tests using equipment similar to the KPS equipment were also performed to calculate the shear strength of the treated soil. The soilcrete was cored in some locations to obtain samples for compression testing.</p><p>The large surface area of the KPS probe made testing deeper levels of the stabilized soil difficult, with the probe often meeting refusal. Nevertheless, penetration for the full depth was required to demonstrate that softer material did not underlie material that caused refusal. In order to test the deepest sections of the stabilized soil, the vanes on the KPS probe were either reduced in size or removed. When the vanes were removed, this became similar to a cone penetration test, and it can result in the same difficulties as a traditional CPT in stabilized soil masses (see quality control/quality assurance document).</p><p>Shear strength requirements were met and verified through multiple testing methods. Measurements showed that settlement ceased soon after the placement of fill and that ultimate settlement was less than 3 inches after approximately 13 months, meeting project requirements.<br><h2>Project Technical Paper:</h2>Burke, G.K., Sehn, A.L., Hussin, J.D., Hull, V.E., and Mann, J.A., (2007). “Dry Soil Mixing at Jewfish Creek.” Proceedings, GeoDenver 2007, ASCE GSP 172 Soil Improvement, Denver, Colorado, February 18-21. 11p.</p><p>Garbin, E. and Mann, J.A. (2010). “Mass Stabilization for Environmentally Sensitive Projects in Florida.” Transportation Research Record: Journal of the Transportation Research Board, No. 2201, Transportation Research Board of The National Academies, Washington D.C., 2010, pp. 62–69. Reproduced with permission of the Transportation Research Board.<br><h2>Date Case History Prepared:</h2>December 2014</p></p>