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Evaluation of Bridge Abutment Slope Protection at Stream Crossings
Title
Evaluation of Bridge Abutment Slope Protection at Stream Crossings
Creator
Wang, Peng
Date
2023
Description
Extensive research has revealed that scour and flooding contribute to over 50% of bridge failures in the United States, with scour-induced...
Show moreExtensive research has revealed that scour and flooding contribute to over 50% of bridge failures in the United States, with scour-induced failures alone causing the collapse of 20-100 over-water bridges annually out of a total population of approximately 504,000 bridges. Within Wisconsin, a significant number of bridges, specifically over 1200, have been identified as scour-critical, with 200 of them experiencing slope instability issues.This study focuses on the problematic bridge sites in Wisconsin, particularly examining the underperformance of abutment slopes. To identify and document these problematic bridges, a comprehensive survey was conducted, followed by site visits. Subsequently, a thorough Limit Equilibrium Method (LEM) simulation was carried out based on an investigated bridge. The simulation results indicate that the infiltration of water into the slope berm areas significantly decreases slope stability due to seepage forces. Furthermore, the absence of riprap toe protection can result in overall slope failure. The implementation of concrete pouring to address riprap scoring has proven unreliable, leading to frequent failures.Additionally, simulations were performed for grouted riprap, slope walls, grouted tiebacks, and piles. The results demonstrate their potential to enhance slope safety, with their suitability requiring careful evaluation. Notably, a simulation comparing a 1:2 slope design with a 1:1.5 slope inclination reveals that the former significantly improves slope safety.In Chapter 5, a comprehensive life cycle cost analysis is conducted, comparing the 1:2 slope design to the 1:1.5 design. The analysis reveals that the 1:2 design method is more cost-effective over a 60-year study period.In conclusion, this research provides valuable insights into the assessment and mitigation of abutment slope protection issues in Wisconsin. The findings emphasize the importance of considering seepage forces, appropriate riprap installation, and alternative stabilization measures together with a comprehensive life cycle cost analysis. The research contributes to enhancing slope safety and informs decision-making processes for bridge design and maintenance.
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Thermal Resistance of Listeria Monocytogenes At Low Water Activity: Effect of Humectants
Title
Thermal Resistance of Listeria Monocytogenes At Low Water Activity: Effect of Humectants
Creator
Wang, Peng
Date
2012-04-25, 2012-05
Description
The thermal resistance of L. monocytogenes Scott A was examined in glycerol solutions, sucrose solutions, and peanut butters at different...
Show moreThe thermal resistance of L. monocytogenes Scott A was examined in glycerol solutions, sucrose solutions, and peanut butters at different water activities (aw) from 0.27-0.99. The analysis of D-values in glycerol and sucrose solutions shown L. monocytogenes has greater thermal resistance in sucrose solutions at each same water activity level (0.85 and 0.80). The calculated D-values were 13.80 ± 0.31, 6.38 ± 0.73, 3.02 ± 0.10 min in sucrose solution (aw = 0.80), and 9.39 ± 0.22, 4.86 ± 0.29, 2.40 ± 0.19 min in sucrose solution (aw = 0.85), compared to D-values of 1.20 ± 0.04, 0.36 ± 0.03, 0.12 ± 0.01 sec in glycerol solution (aw = 0.80), and 9.60 ± 0.20, 4.20 ± 0.26, 1.80 ± 0.10 sec in glycerol solution (aw = 0.85) at 72, 75 and 78◦C. In each menstrum the thermal resistance of Listeria increased significantly as compared to phosphate buffer. However, the comparison of D-values in glycerol and sucrose solutions failed to reflect a linear relationship between water activities and thermal resistance of L. monocytogenes. In peanut butter samples, the D-values were 16.53 ± 0.31, 9.06 ± 0.75, 7.13 ± 0.27 min and 35.36 ± 2.14, 23.10 ± 1.31, 17.73 ± 1.96 min for 3.13% and 9.38% sugar concentration respectively at temperatures of 80, 90, 100◦C. The Z-values were 56.08 ± 4.87◦C and 67.18 ± 8.44◦C in peanut butter with 9.38% and 3.13% sugar concentration. These results indicate increases of thermal resistance of Listeria with increased sugar concentration in a pure solution. The same protection effect of sugar did not appear to play a role in much increased thermal resistance of Listeria in peanut butter.
M.S. in Food Safety and Technology
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