<p><p><figure id='attachment_3449' style='max-width:1024px' class='caption aligncenter'><img class="wp-image-3449 size-large" style="border: 2px solid #696969;" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Schematic diagram showing binding, clogging and caking in an aggregate and geosynthetic system overlying a subgrade." width="1024" height="527" /><figcaption class='caption-text'> Definition of binding, clogging, and caking (Black and Holtz 1999; With permission from ASCE).</figcaption></figure></p><p><h2>Project Summary/Scope:</h2>The test site is located on Washington State Highway SR-507 in Bucoda, WA, about 32 km south of Olympia. The research was synchronized with reconstruction at the site performed by the Washington State Department of Transportation (WSDOT) in June 1991. Poor performance of the test site was due to soft silty subgrade soils, seasonably high ground water table, and moderate traffic volume with high percentage of heavy trucks. There were six test sections, each 7.6 meters in length. Widths of northbound (NB) and southbound (SB) lanes were kept 3.5 meters and 3.2 meters respectively. Test sections with four non-woven separator geotextile (HB, NP4, NP6, NP8), one woven separator geotextile (SF), and one without geotextile were constructed in both lanes of the road.</p><p>Subsurface Conditions: The base course was dense to very dense crushed aggregate consisting of well- to poorly-graded gravel with sand and traces of silt. Most of the coarse aggregate was sub-angular to angular. Base course material particle sizes ranged from approximately 0.075 to 38 mm. Subgrade soils were highly variable in composition, color, moisture content, and plasticity. Fines content in subgrade soils ranged from 57 to 100%. Portions of the HB and NP4 subgrade soils in both lanes probably consisted of fills or colluviums and the subgrade soils in remaining test sections were probably natural residual soils. Varying degrees of iron-oxide staining were observed on the surface of the subgrade at all test sections. More penetration of iron-oxide staining was observed at the NP6-NB, NP8-NB, SF-SB test locations. Ground water levels were high in all test sections and was typically 0.9 meters below<br>the ground surface. Ground water was encountered 30 mm above the subgrade soil in the SB control section test pit. The base course aggregate was wet approximately 30 to 50 mm above all the geotextiles in the SB lane except the NP4-SB location.</p><p>Total thickness of base course was 0.45 and 0.60 meters in the NB and SB lanes respectively. Initial lift thickness of the base course placed over the geotextiles was 0.15 meters and 0.30 meters in NB and SB lanes respectively. A large steel-drum roller was used without vibration to compact the base course. Water was used to facilitate compaction. The road was paved with 0.17 meters of asphaltic concrete as specified by WSDOT. The roadway was sloped at a gradient of 4.4% in the northeast direction.<br><h2>Performance Monitoring:</h2>Test pits 1.2 meters by 1.8 meters in size were made at each test section to observe the condition of the soil, ground water, and geotextile. Several samples of the base course within 20 mm of the geotextile were collected from each test pit section for laboratory analysis. Excavated geotextile samples were collected for laboratory tests. Subgrade soil conditions were observed and several in situ tests (pocket penetrometer, Torvane, and nuclear densiometer tests) were performed and samples of subgrade soils were also collected for laboratory tests. Five successive permittivity tests were performed on four samples of excavated geotextiles using a permeameter that was designed and constructed based on the “STS geotextiles permeameter” design to evaluate degree of blinding and clogging of the geotextiles. Wide width tensile tests were conducted on six specimens from each excavated and virgin geotextile to obtain retained strength after 5 years of performance.</p><p>Various geotextile separators have been effective in preserving the integrity of the pavement system since construction even though fines migration from subgrade had taken place through some of the separators into the base course. Heat-bonded geotextiles were significantly more susceptible to clogging than needle-punched or slit-film geotextiles. Long-term performance of geotextile separators may not be critical in many cases because of increased subgrade strength and reduced compressibility due to consolidation.<br><h2>Project Technical Paper:</h2>Black, P.J. and Holtz, R.D. (1999). “Performance of geotextile separators five years after installation.” Journal of Geotechnical and Geoenvironmental Engineering, Vol. 25, No. 5, 404-412.<br><a href="https://ascelibrary.org/doi/abs/10.1061/%28ASCE%291090-0241%281999%2912… Case History Prepared:</h2>November 2012</p></p>