Browsing by Subject "Volume change"
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Item Elevation and volume change of the ice sheets from GLAS : a comparison of methods(2013-12) Felikson, Denis; Schutz, Bob E.This report compares surface elevation change and volume change esti- mates from three methods: repeat track (RT), crossover (CX), and overlapping footprints (OFP). These three methods use different approaches to group- ing elevation point measurements taken at different measurement epochs and estimating elevation change. Volume changes are calculated from elevation changes in the same manner for all three methods but differences in sampling resolution between the methods affect volume change estimates in different ways. The recently reprocessed Release 633 version of elevation measurements from the Geoscience Laser Altimeter System (GLAS), flown on the Ice, Cloud and land Elevation Satellite (ICESat), are used in this analysis. Both elevation changes and volume changes are compared for both the Greenland Ice Sheet (GrIS) and the Antarctic Ice Sheet (AIS). Additionally, uncertainties in the estimates for each method are quantified and compared. Results are separated by drainage systems and by above/below 2000 m surface elevation for the GrIS. For the AIS, results are aggregated to the East, West, and Penin- vi sula regions. Volume change estimates agree well for the three methods for the GrIS, with estimates of -227.75 ± 2.12 km³/yr, -249.30 ± 3.42 km³/yr, and -218.24 ± 7.39 km³/yr for the RT, CX, and OFP methods, respectively. These estimates are similar to those published from previous studies. For the AIS, however, larger discrepancies are found in the estimates. This stems primarily from a large discrepancy in the volume change estimate of the East AIS, where the RT, CX, and OFP methods estimate volume changes of 33.39 ± 1.42 km³/yr, 46.42 ± 5.46 km³/yr, and -2.72 ± 2.12 km³/yr, respectively. It's not entirely clear why this large discrepancy exists in this particular region, and elevation change estimates for a few particular drainage systems in this region are examined. Previously published volume changes for the AIS also show a large scatter and more work must be done to reconcile the various estimates. Finally, the volume change uncertainties reported do not completely account for the discrepancies in most regions. Additional analysis must be done to completely quantify all error sources.Item Sulfate Induced Heave: Addressing Ettringite Behavior in Lime Treated Soils and in Cementitious Materials(2012-02-14) Kochyil Sasidharan Nair, Syam KumarCivil engineers are at times required to stabilize sulfate bearing clay soils with calcium based stabilizers. Deleterious heaving in these stabilized soils may result over time. This dissertation addresses critical questions regarding the consequences of treating sulfate laden soils with calcium-based stabilizers. The use of a differential scanning calorimeter was introduced in this research as a tool to quantify the amount of ettringite formed in stabilized soils. The first part of this dissertation provides a case history analysis of the expansion history compared to the ettringite growth history of three controlled low strength mixtures containing fly ash with relatively high sulfate contents. Ettringite growth and measurable volume changes were monitored simultaneously for mixtures subjected to different environmental conditions. The observations verified the role of water in causing expansion when ettringite mineral is present. Sorption of water by the ettringite molecule was found to be a part of the reason for expansion. The second part of this dissertation evaluates the existence of threshold sulfate levels in soils as well as the role of soil mineralogy in defining the sensitivity of soils to sulfate-induced damage. A differential scanning calorimeter and thermodynamics based phase diagram approach are used to evaluate the role of soil minerals. The observations substantiated the difference in sensitivity of soils to ettringite formation, and also verified the existence of a threshold level of soluble sulfates in soils that can trigger substantial ettringite growth. The third part of this dissertation identifies alternative, probable mechanisms of swelling when sulfate laden soils are stabilized with lime. The swelling distress observed in stabilized soils is found to be due to one or a combination of three separate mechanisms: (1) volumetric expansion during ettringite formation, (2) water movement triggered by a high osmotic suction caused by sulfate salts, and (3) the ability of the ettringite mineral to absorb water and contribute to the swelling process.