<p><p><img class="aligncenter wp-image-3424 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; style="border: 2px solid #696969;" alt="Location map for electro-osmosis project to stabilize a subgrade along Interstate 40 in Arizona." width="820" height="601" /><h2>Project Summary/Scope:</h2>The objective of this project was to create a viable soil stabilization technique using electro-chemical methods to stabilize the clay subgrade soils. The method was intended to be able to implement by Arizona highway maintenance personnel. A test study section was selected on Interstate 40 westbound lane about 56 km east of Holbrook, Arizona. Electro-osmosis combined with a 0.4 N potassium chloride (KCl) solution was used to inundate into the subgrade clay. The 285 steel plates used for sleeving the base material presented a potential traffic problem and made it necessary to countersink each hole with a concentric 25.4-cm diameter and 2.5-cm deep depression.</p><p>Subsurface Conditions: The subgrade layer consisted of lean clay to a depth of about 4.6 meters. LL = 39, PL = 17, PI = 22, percent passing No. 200 sieve = 70%, and percent clay content = 20%. Density of the soil = 1700 kg/m³, and the moisture contents were in the range of 10 to 15%.</p><p>The target design depth of treatment was about 0.9 meters. The test section is divided into three sections. The center section has vertical No. 8 rebar about 1.5-meter long as anodes. In contrast, the other two sections have horizontal anodes made up of 6.1-meter sections (welded end to end) of No. 8 reinforcing bars placed in a 1.2-meter trench. Similarly, cathodes were also made up of 6.1-meter sections (welded end to end) of No. 8 reinforcing bars placed in a 1.2 -meter trench. 15.2-cm diameter holes were drilled on 2.4-meter centers approximately 1.7-meters deep throughout the test section. A total of 285 holes were drilled throughout the site to pour KCl solution.</p><p>Using a 60kW DC generator, a 400-amp current and a voltage gradient of about 0.1 volts/cm was applied for 30 days. The electrode installation process began by digging trenches and drilling holes for a section with vertical anodes. The water-KCl solution was placed into the holes using a gasoline nozzle. The holes were filled twice a day for a period of approximately one month, which amounted to about 136 m³ (36,000 gal) of solution.</p><p><figure id='attachment_3426' style='max-width:1247px' class='caption aligncenter'><img class="wp-image-3426 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Plan views of the electrode placement for the Interstate 40 subgrade stabilization in Arizona using electo-osmosis." width="1247" height="445" /><figcaption class='caption-text'> (From O’Bannon, C., G. Morris, and F. Mancini. Electrochemical Hardening of Expansive Clays. In Transportation Research Record 593, Figure 1 and Figure 2, p. 49. Copyright, National Academy of Sciences, Washington, D.C., 1976. Reproduced with permission of the Transportation Research Board.)</figcaption></figure><h2>Performance Monitoring:</h2>Based on the X-ray diffraction data and electro-micrograph, it appeared that the stacking geometry of the clay particles was modified by the electro-chemical treatment. Results indicated that the crystalline fabric of the clay was affected by the treatment. This is evidenced by the electron and X-ray diffraction patterns, which for the pretreated material depicted a thick-layered structure. This is noted by the wider rings or high-intensity X-ray diffraction peaks of the treated material as opposed to the relatively thin diffraction rings or low-intensity X-ray peak obtained from the nonpretreated material. The expansive pressure of the soil increased by about 50% and the percentage of swell decreased by more than 36 %.<br><h2>Project Technical Paper:</h2>O’Bannon, D. E. Morris, G. R., and Mancini, F. P. (1976). ‘‘Electrochemical hardening of expansive clays.’’ Transportation Research Record 593, Transportation Research Board, pp 46–50.<br><h2>Date Case History Prepared:</h2>November 2012</p></p>