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|Title:||Soil freeze-thaw effects on bank erosion and stability : Connecticut River field site, Norwich, Vermont|
|Authors:||Ferrick, M. G.|
Gatto, Lawrence W.
Grant, Steven A.
|Publisher:||Cold Regions Research Engineering Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||ERDC/CRREL ; TN-05-7|
|Abstract:||Bank recession resulting from surficial erosion and mass failure is a consequence of hydraulic forces and geotechnical processes. One important set of geotechnical processes in regions where seasonal frost forms is soil freeze-thaw (FT) cycling and associated ground-ice growth and melt. In cold regions soil FT processes usually cause more bank recession annually than other processes. The magnitude of FT effects is variable, depending on soil type, water content, and freezing rate. The banks along the Connecticut River at Norwich, Vermont are unstable and receding in certain locations. A 40-m-long segment of unstable east-facing bank was selected for intensive monitoring along with nearby north- and south-facing bank locations. This technical note documents our field observations, measurements, and analysis encompassing three years of monitoring. Our data acquisition equipment, focusing on FT processes, was installed in November through December 2002, and data collection continued through July 2005. The primary purposes of the field program were to evaluate: 1) the depth and duration of soil FT, and the effect of orientation and soil moisture on these parameters, 2) the effects of FT on soil strength and erosional processes, 3) the timing and depth of any slope failures of the east-facing bank, and 4) the hypothesis of soil FT as a primary contributor to slope failure. Results indicate that bank orientation and soil moisture can have dramatic effects on the depth, extent, and duration of soil freezing. FT of the monitored banks generally affected the soil to a depth of 0.75 m below the surface. The shallow nature of the bank erosion at this site is consistent with FT weakening of near surface soils. Subsequent rainfall and runoff are then able to readily move these sediments down slope causing progressive bank recession. Finally, transport of fine eroded sediments and native soils from the base of the bank by waves and water level fluctuations maintain the slope in an unstable state to continue the bank erosion and recession.|
|Gov't Doc #:||ERDC/CRREL TN-05-7|
|Rights:||Approved for Public Release; Distribution is Unlimited.|
|Appears in Collections:||Technical Note|