Browsing by Subject "Capillary barrier"
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Item Anti-capillary barrier performance of wicking geotextiles(2012-08) Azevedo, Marcelo Moraes de; Zornberg, Jorge G.; Romanovicz, Dwight K.A capillary barrier develops and restricts water flow when two porous materials with dissimilar pore structures (e.g., a coarse-grained soil overlain by a fine-grained soil) are in contact with one another. This is due to a difference in the unsaturated hydraulic conductivity of the two materials at a given suction. Geotextiles are utilized in a variety of civil engineering applications and have a pore structure similar to that of a coarse-grained soil. This can be problematic in unsaturated soil as the capillary barrier caused by the geotextile may instigate undesirable moisture buildup in the overlying soil and undermine any benefit provided by the geotextile. Various versions of a new geotextile have been manufactured to help dissipate a capillary barrier by "wicking" or laterally draining excess moisture away from the soil. Additionally, nonwoven blends of the unique wicking fiber combined with standard polymeric fibers are tested to assess their ability to minimize the development of a geotextile capillary barrier and not cause additional moisture accumulation in the first place. The unsaturated properties of both woven and nonwoven configurations of these wicking geotextiles were investigated as part of a comprehensive an experimental testing program. The testing program includes small soil column infiltration tests to assess geotextile capillary barrier performance with moisture monitored by time domain reflectometers and capacitance probes. Also, modified hanging column tests were conducted to define the hydraulic properties of the geotextiles in the form of water retention curves. Finally, a microscopy study, involving both optical and scanning electron microscopes, was conducted to observe the wicking behavior of the geotextiles at a micro-scale level. Test results illustrate the enhanced lateral drainage and reduced moisture accumulation of the wicking geotextiles when compared to regular geotextiles. Additionally, the woven version of the wicking geotextile has the potential to perform the functions of separation, filtration, protection, reinforcement, and drainage. All of these functions in a single geosynthetic product could lead to significant cost savings compared to the use of separate products to perform each one of the various functions.Item Performance of geotextiles with enhanced drainage(2016-12) Azevedo, Marcelo Moraes de; Zornberg, Jorge G.; Bhasin, Amit; Caldwell, Todd; Cox, Brady; El Mohtar, ChadiGeotextiles have been successfully used in multiple geotechnical and geoenvironmental applications over the years, and are now commonplace in projects such as waste containment facilities, pavements, and earth retaining structures. While significant information has been documented on the mechanical behavior of geotextiles, information on the hydraulic behavior of geotextiles has been investigated primarily under saturated conditions. Theoretical background, laboratory data, and full-scale measurements have become recently available to understand the interaction between soils and geotextiles under unsaturated conditions. This includes the water retention curve and the hydraulic conductivity function of geotextiles. The mechanisms involved in the development of capillary barriers are relevant to explain the storage of moisture that may develop at the interface between materials with contrasting hydraulic conductivity (e.g. a nonwoven geotextile overlain by a fine-grained soil). This can be problematic in unsaturated soil as the capillary barrier caused by the geotextile may instigate undesirable moisture buildup in the overlying soil and undermine some of the benefits provided by the geotextile. Conventional geosynthetic materials are typically only able to drain moisture under saturated conditions. However, in many instances, unsaturated soil conditions prevail and hinder conventional geosynthetics from properly draining. The main objective of this study is to assess the performance of newly available enhanced drainage geotextile products for their capacity to drain under unsaturated conditions. Various prototype versions of an enhanced drainage geotextile incorporating wicking fibers were developed to help prevent a capillary barrier from forming by promoting cross-plane drainage of any excess moisture from the soil. The unsaturated properties of both woven and nonwoven configurations of these enhanced drainage geotextiles were investigated in an experimental study. The testing program included soil column infiltration tests to assess the development of geotextile capillary barriers, as well as their performance, with moisture monitored using time domain reflectometers. In addition to assessing the cross-plane behavior of enhanced drainage geotextiles, the in-plane enhanced drainage capabilities of the geotextiles were investigated. An experimental test setup involving ultraviolet dye allowed for visualization and quantification of the vertical capillary rise in the wicking fibers. An analytical capillary rise model was developed, which accounts for the tortuous flow path through the fibers. The model predictions were found to match well with the experimental results. A microscopy study incorporating both optical and scanning electron microscopes allowed for observation of the wicking behavior of the geotextiles at a micro-scale level. Complementing the laboratory research, the field performance of enhanced drainage geotextiles was evaluated through several pavement case studies. This study in particular included a field research component, involving construction of an instrumented pavement test section founded on an expansive clay subgrade along a portion of SH-21 in Bastrop, TX. Eight 500 ft long test sections with different types of geotextiles were constructed in order to investigate the possible benefits of utilizing both conventional and enhanced drainage geotextiles within a pavement. Each test section was instrumented with a horizontal and vertical array of moisture sensors, which were monitored to assess the effectiveness of the various geotextiles to remove excess water from the pavement section. Additional monitoring included condition surveys to document pavement distresses and total station surveys to document fluctuations in the surface profile of the pavement due to the presence of expansive clays. Overall, experimental and field results illustrate advantages in both cross-plane and in-plane drainage for the enhanced drainage geotextiles when compared to conventional geotextiles. Furthermore, the woven version of the enhanced drainage geotextile has the potential to perform the additional functions of separation, filtration, protection, reinforcement, and drainage. Offering these multiple functions by a single product could lead to significant cost savings compared to the use of separate products to individually perform each function.