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Charlotte, NC, United States

Yeo S.-S.,Geosyntec Consultants | Hsuan Y.G.,Drexel University
Geotextiles and Geomembranes | Year: 2010

The tensile creep behavior of polyethylene-terephthalate (PET) and high density polyethylene (HDPE) geogrids was evaluated using five test methods: the short- and long-term stepped isothermal method (SIM), the short- and long-term time-temperature superposition (TTS), and the conventional method. SIM and TTS are acceleration tests using elevated temperatures. SIM uses a single specimen throughout all temperature steps in contrast to TTS in which a new specimen is employed for each temperature step. The test results indicate that at the same percentage of ultimate tensile strength, PET geogrid exhibited less creep deformation than the HDPE geogrid. The HDPE geogrid exhibited primary, secondary, and tertiary creep stages before rupture, whereas only primary creep and tertiary creep were detected in the PET geogrid. Furthermore, the strain rate of the primary creep stage was found to be independent of the applied loads for the PET geogrid, while it increased exponentially for the HDPE geogrid. The activation energies deduced from different accelerated creep tests were very similar for the PET geogrid. In contrast, the activation energies were higher from the short-term acceleration tests than from the long-term tests for the HDPE geogrid. The four-parameter Weibull model was able to predict the linear and non-linear creep behavior up to 100 years based on 10-h creep testing data. The creep reduction factor of 100 years design life was evaluated and higher values were resulted from the HDPE geogrid than from the PET geogrid. © 2009 Elsevier Ltd.

Espinoza R.D.,Geosyntec Consultants
International Journal of Project Management | Year: 2014

The rationale for using heuristics to establish a risk premium that is added to the risk-free rate to obtain the value of an investment is questioned and an alternative method, termed decoupled net present value (DNPV), is proposed. Rather than using utility theory concepts to decrease the value of uncertain cash flows, the risks associated with project cash flows are discretely quantified using insurance and contingent claim valuation concepts. Synthetic insurance premiums are designed to "protect" the value of expected cash flows which are treated as additional project costs. Because identified project risks are quantified in financial terms and treated as a real cost to the project, DNPV allows business executives to evaluate the effect on the value of the project of different risks and select management techniques that are deemed more effective. Hence, DNPV is both a valuation methodology and a risk management tool. © 2013 Elsevier Ltd and IPMA.

Li C.,Geosyntec Consultants | Zornberg J.G.,University of Texas at Austin
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2013

Fiber reinforcement represents a promising alternative in projects involving localized repair of slopes and reinforcement of thin soil veneers, where planar reinforcement (e.g., with geotextiles and geogrids) is difficult to implement. Current design methodologies allow quantification of the shear strength of fiber-soil composites in terms of the parameters that independently characterize the soil matrix and fibers. The shear strength of fiber-reinforced soil is considered to have two components, including the shear strength of the soil matrix and the tension mobilized within the fibers. Triaxial compression tests and fiber pullout tests were conducted to evaluate how the fiber tension is mobilized for varying shear strain levels. The results of this evaluation provide insights into whether the shear strength of fiber-reinforced soil is governed by the peak or residual shear strength of unreinforced soil. A revision to existing design methodology is proposed in which the individual contribution of fibers and soil matrix is quantified based on the strain level. The appropriateness of using the peak or residual shear strength of the unreinforced soil for predicting the equivalent shear strength of fiber-soil composites is discussed based on strain compatibility considerations. © 2013 American Society of Civil Engineers.

Roseen R.M.,University of New Hampshire | Ballestero T.P.,University of New Hampshire | Houle J.J.,University of New Hampshire | Briggs J.F.,Geosyntec Consultants | Houle K.M.,Horsley Witten Group
Journal of Environmental Engineering (United States) | Year: 2012

This study examined the functionality of a porous pavement storm-water management system in coastal New Hampshire where 6 months of subfreezing temperatures typically occur. The usage of porous pavements for storm-water management in northern climates has many challenges, most of which relate to the extreme cold and significant frost penetration into the porous media. The porous pavement system was monitored for hydraulic and water-quality performance from 2004 to 2008. The use of porous pavements for parking lots for new and redevelopment projects are one watershed-based strategy that can both mitigate impacts for new development and reverse impacts in areas with redevelopment. Surface infiltration capacity and frost penetration were measured monthly to assess winter performance. Because of the well-drained nature of the porous pavement and reservoir base, issues related to frozen media were minimized. Significant frost penetration was observed up to depths of 71 cm without declines in hydrologic performance or observable frost heave. No consistent statistical difference was observed for seasonal hydrologic performance with mean infiltration capacity ranging from 1,490 to 2,690-cm/h. Adverse freeze-thaw effects, such as heaving, were not observed, and for that reason, the life span is expected to exceed that of typical pavement applications in northern climates. Observed hydrologic response resembled shallow depth groundwater drainage, as is the goal for low-impact development designs. Peak flows were reduced by 90% to 0.58-m3/s/km2±0.74 in comparison with standard impervious cover=5.5-m3/s/km2±7.7. There was exceptional water-quality treatment performance for petroleum hydrocarbons, zinc, and total suspended solids with nearly every value below detection limits. Only moderate removal was observed for phosphorous, and treatment for nitrate (NO3) was negative. © 2012 American Society of Civil Engineers.

Abdelaal F.B.,Queens University | Rowe R.K.,Queens University | Islam M.Z.,Geosyntec Consultants
Geotextiles and Geomembranes | Year: 2014

Aging of the same geomembrane immersed in the same four synthetic municipal solid waste leachates tested by Rowe etal. (2008) for 2.65 years is continued for an additional 6.5 years (i.e., providing data over more than 9 years of aging). The additional data is used to (a) update the initial estimates for antioxidant depletion stage, and (b) investigate the effect of leachate constituents on the timing and magnitude of the changes in the physical properties of the geomembrane. While all the examined leachates had surfactant and trace metals in common, reduced Leachate 1 (full leachate) had salts and volatile fatty acids (VFAs), Leachate 2 was not reduced and had neither salts nor VFAs, reduced Leachate 3 had salts, reduced Leachate 4 had VFAs, and Leachate 5 was similar to Leachate 2 except that it was reduced. Incubation in all leachates gave very similar predictions of the antioxidant depletion stage, however, the salts in Leachates 1 and 3 are shown to have the largest effect on the geomembrane mechanical properties, especially stress-crack resistance, resulting in a shorter time to nominal failure than for leachates without salts. Furthermore, reduced Leachates 1 and 3 showed faster degradation in stress-crack resistance than Leachate 2 which was not reduced and without salts. Arrhenius modeling is used to extrapolate the time to nominal failure (i.e., a reduction in stress-crack resistance to 150h) at a range of temperatures. © 2014 Elsevier Ltd.

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