• 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.
    • A Bio-Wicking System to Prevent Frost Heave in Alaskan Pavements: Phase II Implementation

      Galinmoghadan, Javad; Zhang, Xiong; Lin, Chang (2019-11)
      Water within pavement layers is the major cause of pavement deterioration. High water content results in significant reduction in soil’s resilient behavior and an increase in permanent deformation. Especially in cold regions, frost heave and thaw weakening cause extensive damage to roads and airfields. Conventional drainage systems can only drain gravity water not capillary water. Both preliminary lab and field tests have proven the drainage efficiency of a newly developed H2Ri geotextile with wicking fabrics. In this report, continuous research was conducted to verify the effectiveness of the wicking fabric in mitigating frost boil issues in Alaskan pavemnets. Two test sections were selected at two low volume roads on the campus of the University of Alaska Fairbanks. Soil moisture and temperature sensors were installed within the road embankments. The monitored data was used to analyze the soil migrations and evaluate the drainage performance of the wicking fabric. Preliminary monitoring results showed that the wicking fabric was effective in mitigating the frost boil problem.
    • Creep Behavior of Shallow Anchors in Ice-rich Silt

      Zhang, Xiong; Chen, Liangbiao; Lin, Chuang; McHattie, Robert (2013-07)
      Grouted anchors have become a common technique in the application of earth retention systems, slope stability problems and tie-down structures in unfrozen soils due to its cost and time efficiency. However, within much of Alaska area, permafrost is a common type of soil and might contain large amount of visible ice. The highly time and temperature dependent properties of ice-rich soil make it a challenge for the application of anchors in permafrost area. This project valuates the effect of water content and temperature on the creep behavior of shallow anchors in cold room lab. Also, field test was conducted to determine effectiveness of three types of grouting materials, including Bentonite clay, Microsil Anchor Grout and special cement formula. The temperature along the anchor was monitored to evaluate the degradation of the surrounding frozen soil. Research results may be applicable in the design of shallow anchors in ice-rich permafrost at various ice content and temperature range. Also, the load distribution and the pullout test results could give a general guidance for the shallow anchor design in permafrost area.
    • Development of Landslide Warning System

      Riad, Beshoy; Zhang, Xiong (2019-11)
      Landslides cause approximately 25 to 50 deaths and US$1 - 2 billion worth of damage in the United States annually. They can be triggered by humans or by nature. It has been widely recognized that rainfall is one of the major causes of slope instability and failure. Slope remediation and stabilization efforts can be costly. An early warning system is a suitable alternative and can save human lives. In this project, an early warning system was developed for a 40-foot-high cut slope on the island of Hawaii. To achieve the objective, subsurface investigations were performed and undisturbed samples were collected. For the purpose of unsaturated soil testing, new testing apparatuses were developed by modifying the conventional oedometer and direct shear cells. The unsaturated soil was characterized using two separate approaches and, later, the results were discussed and compared. The slope site was instrumented for the measurement of suction, water content, displacement, and precipitation. The collected climatic data along with the calibrated hydraulic parameters were used to build an infiltration-evapotranspiration numerical model. The model estimations were compared with the field measurements and showed good agreement. The verified model was used to determine the pore-water pressure distribution during and after a 500-years return storm. Later, the pore-water pressure distribution was transferred to a slope stability software and used to study the slope stability during and after the storm. Based on a 2D slope stability analysis, the slope can survive the 500-year storm with a factor of safety of 1.20. Instrument threshold values were established for water content sensors and tensiometers using a traffic-light-based trigger criterion.
    • Development of a Computer Vision-Based Three-Dimensional Reconstruction Method for Volume-Change Measurement of Unsaturated Soils during Triaxial Testing

      Zhang, Xiong; Xia, Xiaolong (2019-10)
      Problems associated with unsaturated soils are ubiquitous in the U.S., where expansive and collapsible soils are some of the most widely distributed and costly geologic hazards. Solving these widespread geohazards requires a fundamental understanding of the constitutive behavior of unsaturated soils. In the past six decades, the suction-controlled triaxial test has been established as a standard approach to characterizing constitutive behavior for unsaturated soils. However, this type of test requires costly test equipment and time-consuming testing processes. To overcome these limitations, a photogrammetry-based method has been developed recently to measure the global and localized volume-changes of unsaturated soils during triaxial test. However, this method relies on software to detect coded targets, which often requires tedious manual correction of incorrectly coded target detection information. To address the limitation of the photogrammetry-based method, this study developed a photogrammetric computer vision-based approach for automatic target recognition and 3D reconstruction for volume-changes measurement of unsaturated soils in triaxial tests. Deep learning method was used to improve the accuracy and efficiency of coded target recognition. A photogrammetric computer vision method and ray tracing technique were then developed and validated to reconstruct the three-dimensional models of soil specimen.
    • Development of a Design Method for H2Ri Wicking Fabric in Pavement Structures

      Lin, Chuang; Zhang, Xiong; Han, Jie (2016-11)
      A new roadway drainage design concept is proposed to reduce the roadway water content and enhance the overall pavement performance by implementing H2Ri geotextile with lateral wicking ability. Compared with conventional drainage materials, this type of geotextile has high tensile strength and higher specific surface area, which enable to continuously transport water under unsaturated conditions. SEM (Scanning Electron Microscope) images indicated that the geotextile functions effectively for soils with particle size larger than 12 microns. A series of tests were performed to establish the relationships among different parameters, including resilient modulus test, large-scale direct shear test, salt concentration test and pressure plate test. Test results indicated that the soil-geotextile system can work effectively to reduce the water content within the pavement structure by 2%. By doing so, the corresponding resilient modulus can be increased by 3 times and the permanent deformation can be reduced to half of that value. Meanwhile, the interface frictional strength between geotextile and soil was not sensitive to water content change.
    • Evaluate H2RI Wicking Fabric for Pavement Application - Year 2

      Zhang, Xiong; Connor, Billy (2015-10-31)
      The Tencate H2Ri wicking fabric has proven to work well on two roadway sections on the Dalton Highway. In each the fabric has reduced the water content in the embankment resulting in a maintenance free section. This project used a 24 foot flume in the laboratory to evaluate the effectiveness of the fabric on well graded sand and organic silt. The fabric effectively removed the moisture in the well graded sand. However, the organic silt blinded the wicking fibers which eliminated the capillary moisture movement. The results also demonstrated that overlapping the fabric for joints is not efficient
    • Evaluation of Precut Transverse Cracks for an Asphalt Concrete Pavement in Interior Alaska (Moose Creek –Richardson Highway)

      Liu, Jenny; McHattie, Robert; Zhang, Xiong; Netardus, John (2015-08-31)
      Road-width thermal cracks (major transverse cracks) are perhaps the most noticeable form of crack-related damage on AC pavements throughout colder areas of Alaska. The main objective of this study is to recommend design strategies and construction practices aimed at controlling thermal cracking in AC pavements. In this report, literature review summarizes selected items of the engineering literature directly relevant to precutting of pavement-type structures and control of thermal cracking in general. Crack surveys and data collection were conducted at the test sections in an AKDOT&PF resurfacing project to compare various precut strategies (variations of cut spacing and depth), with the locations of natural major transverse cracks both before and after construction. Laboratory testing and numerical analysis were also presented to provide basic data about the physical properties of the AC and help explain some of the observed characteristics associated with natural thermal cracking. 17.
    • 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.
    • Financial Impact of Fines in the Unbound Pavement Layers

      Liu, Jenny; Zhang, Xiong; Chamberlain, Andrew; Li, Lin (Alaska University Transportation Center, Alaska Department of Transportation and Public Facilities, 2014)
    • Laboratory Performance of Wicking Fabric H2Ri in Silty Gravel, Sand and Organic Silt

      Connor, Billy; Zhang, Xiong (16-05)
      The use of wicking fabric, H2Ri, is growing in its use to remove water from roadway and airport embankments. Past research has shown H2Ri to be effective in sands and fine grained materials in roadways up to 32 feet in width. However, there is a desire to use H2Ri for airports which require a minimum width of 75 ft. This project tested H2Ri in a 73-foot flume in a crushed surface course with 14 % fines. In addition, the fabric was tested in a 22-foot flume with a sand and with an organic clay. The intent was to bracket the material for which the H2Ri will work. The study showed that the fabric will easily move water 73 feet in a silty gravel. The study showed that the fabric was also able to readily remove water in sand. However, the fabric blinded when used in organic silt and proved ineffective. The study also showed that using simple overlap of the H2Ri as a splice, while effective, was not as efficient at moving water as the fabric itself. Consequently, moisture tended to build up around the splice.
    • Resilient Modulus Characterization of Alaskan Granular Base Materials

      Li, Lin; Liu, Juanyu; Zhang, Xiong (Alaska University Transportation Center, Alaska Department of Transportation and Public Facilities, 2010)
    • Stabilization of Erodible Slopes with Geofibers and Nontraditional Liquid Additives

      Zhang, Xiong; Hulsey, Leroy; Connor, Billy; Zhang, Mingchu; Collins, Rodney; Li, Lin (Alaska University Transportation Center, Alaska Department of Transportation and Public Facilities, 2013)
    • Use of H2Ri Wicking Fabric to Prevent Frost Boils in the Dalton Highway Beaver Slide Area, Alaska

      Zhang, Xiong; Presler, Wendy (Alaska University Transportation Center, Alaska Department of Transportation and Public Facilities, 2012)