Performance of an air convection embankment over ice-rich permafrost: instrumentation, monitoring, and modeling

Performance of an air convection embankment over ice-rich permafrost: instrumentation, monitoring, and modeling

Jensen, David D.

Date: 2015-05

Type: Thesisms

Table of Contents: Chapter 1. Introduction and background -- 1.1. Literature review -- 1.1.1. History of embankment design and construction over permafrost -- 1.1.2. Air convection embankment (ace) -- 1.2. research objectives -- Chapter 2. Project area -- 2.1. Location and geomorphology -- 2.2. Geology, vegetation, and permafrost -- 2.3. Climate -- Chapter 3. Field work and instrumentation -- 3.1. Field work -- 3.2. Soil sample collection and test hole logs -- 3.3. Instrumentation -- 3.3.1. Temperature sensors -- 3.3.2. Measurand ShapeAccelArray -- 3.3.3. Horizontal slope inclinometer -- 3.3.4. Automated data acquisition system (ADAS) -- Chapter 4. Instrumentation results and analysis -- 4.1. Temperature sensors results and analysis -- 4.1.1. TAC, thermistor string, and SAA performance -- 4.1.2 analysis of results from temperature sensors -- 4.2. Deformation monitoring -- 4.2.1. Instrument performance -- 4.2.2. Analysis of results -- Chapter 5. Laboratory testing -- 5.1. Thermal conductivity and thaw strain testing -- 5.2. Water content and dry unit weight testing -- 5.3. Grain size analysis of thermal berm material -- Chapter 6. numerical modeling -- 6.1. Software overview -- 6.1.1. Case study analysis -- 6.2. Modeling parameters -- 6.2.1. Model geometry and mesh -- 6.2.2. Material properties for SEEP/W -- 6.2.3. Material properties for TEMP/W -- 6.2.4. Boundary conditions -- 6.2.5. Modeling stages and time stepping -- 6.3. Results and analysis -- 6.3.1. Numerical Modeling Results -- 6.3.2. Analysis of modeling results -- Chapter 7. Summary and conclusions -- References -- Appendices.

Abstract:

Construction and monitoring of roadway embankments over ice-rich permafrost present unique challenges. The air convection embankment (ACE) is a relatively new design developed to reduce thaw settlement over ice-rich permafrost. Monitoring ACE temperatures and deformation allows for evaluation of embankment performance to improve ACE designs, and numerical modeling of an ACE can be used to estimate long-term thermal stability. For this research, geotechnical instrumentation was installed in an ACE with thermal berm located near Chicken, Alaska. A digital temperature acquisition cable (TAC) and a MEMS-based in-place inclinometer were installed at the base of the embankment and evaluated for performance over a one-year period, and two-dimensional thermal modeling of the ACE and thermal berm was conducted. Temperature and deformation measurements from the site were analyzed to assess embankment performance, while modeled and measured embankment temperatures were compared to assess model validity. Results suggest that the TAC and in-place inclinometer demonstrate acceptable performance for monitoring embankment temperature and deformation, respectively, over ice-rich permafrost. The modeled embankment temperatures demonstrated a similar trend to measured temperatures, with temperatures beneath the thermal berm warmer than beneath the ACE; however, the mean modeled temperatures differed from those measured by -5°F for the thermal berm and -2°F and -9°F for a snow-covered and plowed ACE, respectively. Model results for a plowed ACE showed increased performance and a 7°F decrease in mean annual temperature compared to a snow covered ACE. Numerical modeling results and measured embankment temperatures and deformation suggest the ACE will remain stable while the thermal berm will experience thaw settlement until thermal equilibrium is reached. Foundation soil temperatures are expected to grow colder beneath the ACE and warmer beneath the thermal berm.