<p><p><figure id='attachment_3427' style='max-width:927px' class='caption aligncenter'><img class="wp-image-3427 " style="border: 2px solid #696969;" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Plan view diagram showing electrode placement on either side of a roadway to apply electo-osmosis to the underlying soils." width="927" height="589" /><figcaption class='caption-text'> Dearstyne and Newman (1963) (With permission of ASCE)</figcaption></figure></p><p><h2>Project Summary/Scope:</h2>A runway at the Seattle-Tacoma International Airport consisted of a 6-inch concrete pavement section originally built in 1943, which began showing evidence of distress in 1954. In 1955, a 3-inch bituminous overlay was applied by sealing the underling concrete slab joints. In 1960-61, distresses were again apparent in the form of surface cracks in many places and “pumping” at joints. It was found that the subgrade underneath the pavement was saturated to a depth of about 5 feet and that was the primary cause of the problem. Electro-osmosis was used to chemically “waterproof” the underlying subgrade without removing the pavement on a test section (as shown in the following figure) of the runway. The test section size was 55 feet (length along the runway) x 150 feet (width of runway).</p><p>Subsurface Conditions: Wet/soft saturated clay</p><p>The arrangement of electrodes and chemical injection points are shown in the figure on the following page. A direct current potential of 270 volts was maintained between the electrodes. The chemical used was known as Aliquat H226, a dehydrogenated tallow dimethyl ammonium chloride. H226 is a wetting agent that, once absorbed, becomes hydrophobic. This essentially makes the material waterproof.</p><p>After completion of the treatment and tests, the electrode holes were used for forced grouting under the runway slab. Treatment was continued for a period of 18 days during which a constant electric potential was maintained and chemical solution was added as necessary. A total of 775 gallons of solution was used. The weight of the aluminum positive electrodes decreased from 87.2 lbs to 85.7 lbs due to corrosion but the current was well balanced.</p><p><figure id='attachment_3429' style='max-width:892px' class='caption aligncenter'><img class="wp-image-3429 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Cross-section diagram showing electrode placement on either side of a roadway to apply electo-osmosis to the underlying soils." width="892" height="436" /><figcaption class='caption-text'> Dearstyne and Newman (1963) (With permission of ASCE)</figcaption></figure><h2>Complementary Technologies Used:</h2>Chemical Injection<br><h2>Performance Monitoring:</h2>Voltmeter measurements were used to measure potential drop. Core samples were taken to a depth of about 3 feet to measure soil consistency. The temperature of the positive electrode was measured hourly to monitor any heat energy dissipated into surrounding earth.<br>Following are some key observations:<br><ul> <li>Air dried samples of soil consisted of individual particles before treatment, but samples after treatment appeared as a cohesive mass weakly cemented.</li> <li>pH increased from 8.9 to 9.0 after treatment.</li> <li>Electrical conductivity increased after treatment.</li> <li>Water-soluble material decreased from 1250 ppm to 600 ppm during treatment.</li> <li>Before treatment, a ½-inch test rod would sink over 12 inches into the soil at any test hole. After treatment, it was impossible to force the rod into the soil by hand.</li> <li>Deflection decreased from about 0.2 inches before treatment to 0.01 inches thirty days after treatment (under a 45,000 lb truck Long-term site monitoring indicated that after a rain event there was considerable standing water on the side subgrade at the test section (indicating “waterproofing”) while other areas showed soft silt smudges and “pumping” of the slab sections.</li></ul><h2>Cost Information:</h2>The cost of the test section is estimated at $25 per linear foot of runway with an additional $10 to $25 per linear foot (deepening on conditions) for subgrade grouting after treatment.<br><h2>Project Technical Paper:</h2>Dearstyne C. S. and Newman G. J. (1963). “Subgrade stabilization under an existing runway,” Journal of the Aero-Space Transport Division, ASCE, Vol. 89, No. AT1, 1–8.<br>http://cedb.asce.org/cgi/WWWdisplay.cgi?12907<br><h2>Date Case History Prepared:</h2>November 2012</p></p>