• A Bio-Wicking System to Mitigate Capillary Water in Base Course

      Lin, Chuang; Zhang, Xiong (Center for Environmentally Sustainable Transportation in Cold Climates, 2016-11)
      Water within pavement layers is the major cause of pavement deteriorations. High water content results in significant reduction in soil’s resilient behavior and increase in permanent deformation. Conventional drainage systems can only drain gravity water but not capillary water. Both preliminary lab and field tests have proven the drainage efficiency of a newly developed H2Ri geotextile with wicking fabrics. This bio-wicking system aims at resolving the potential issues that the original design may encounter: (1) H2Ri ultraviolet degradation, (2) H2Ri mechanical failure, (3) loss of drainage function under high suction, and (4) clogging and salt concentration. Both elemental level and full-scale test results indicated that the bio-wicking system is more effective in draining capillary water within the base courses compared with original design, in which the geotextile is directly exposed to the open air. However, a good drainage condition is required for the bio-wicking system to maintain its drainage efficiency. Accumulation of excess water will result in water re-entering the road embankment. Moreover, grass root and geotextile share the same working mechanism in transporting water. In the proposed bio-wicking system, the relatively smaller channels in the grass roots further ensures water moving from H2Ri geotextile, transporting through the stems of grass, and eventually evapo-transpiring into the air at the leaf-air interfaces. In sum, the bio-wicking system seemed to successfully address the concerns in the preliminary design and is a more efficient system to dehydrate the road embankment under unsaturated conditions.
    • Experimental Study of Various Techniques to Protect Ice-Rich Cut Slopes

      Li, Lin; McHattie, Robert; Zhang, Xiong; Zhang, Mingchu (Alaska University Transportation Center, 2014-08)
      Cut slopes are usually required to achieve roadway design grades in the ice-rich permafrost areas in Alaska. However, excavation and exposure of a cut slope destroy the existing thermal balance and result in degradation of ice-rich permafrost. Environmentally acceptable, legal, and economically viable solutions for ice-rich slope protection are still rare. Three potential thermal-erosion mitigation techniques were investigated. Four test sections (Section A: 1 ft wood chips, Section B: coconut blanket, Section C: coconut blanket + Tecco-mesh, and Section D: 1 ft crushed rock as a control section) were constructed at the Dalton Highway 9 Mile Hill during the period of April 17 through April 27, 2013. Temperature and moisture sensors were installed to monitor four test sections and evaluate the effectiveness of the different mitigation techniques. Also, a weather station was built to record climatic information at the test site by April 30, 2013. The filed monitoring period ended on November 11, 2014. No obvious erosion was observed in Sections A and B due to less ice content when compared with Sections C and D which failed one and a half months after construction. The performance of four techniques was discussed in detail.
    • Long-term Stabilization of Disturbed Slopes Resulting from Construction Operations

      Perkins, Robert (Center for Environmentally Sustainable Transportation in Cold Climates, 2018-03)
      Highway construction disturbs soil, which must be stabilized to prevent migration of soil particles into water bodies. Stabilization is enforced by law, regulation, and a permit system. Stabilization is most efficiently attained by reestablishment of vegetation, and permits sometimes specify this method of stabilization. Revegetation is difficult in northern Alaska, and seeded grasses often die in a year or two, while reestablishment with native vegetation takes several years. A literature search and interviews with experts indicates that simply extending this “establishment period” has many practical difficulties. Field investigations and interviews indicate that in northern Alaska little erosion occurs at slopes with failed vegetation, which implies that vegetation was not critical to reducing contamination and the expense of revegetation was unnecessary. However, when revegetation is specified in standard permit language, and contractor, owner, and regulator must close out projects, grasses are utilized. This research supports the recommendation that the Alaska Department of Transportation and Public Facilities work with the Alaska Department of Natural Resources and the Alaska Department of Environmental Conservation to develop special standards for projects north of the Brooks Range and between the Brooks and Alaska ranges, that recognize the low erosion potential of clean road fill – embankments.