Frost Heave: New Ice Lens Initiation Condition and Hydraulic Conductivity Prediction

• Author / Creator

  Azmatch, Tezera Firew

• Studies on frost heave indicate that significant frost heave observed in the field or laboratory is attributed to ice lens formation associated with water migration to the freezing front and the segregational ice that develops. Hence frost heave prediction models require ice lens initiation criteria and hydraulic conductivity estimation method for the frozen fringe. Existing frost heave prediction methods do involve complex procedures of estimating the hydraulic conductivity. Ice lens initiation conditions by existing methods are not also easy to implement. In fact, some of the exiting frost heave prediction methods lack ice lens initiation condition. The objective of this thesis is to investigate and develop ice lens initiation criteria and hydraulic conductivity estimation methods that are simple to implement in frost heave prediction. Simple methods, involving the use of SFCC, for predicting ice lens initiation condition and hydraulic conductivity of the frozen fringe has been proposed and verified in this study. A new fundamental approach is proposed to determine the ice lens initiation condition using the soil freezing characteristics curve (SFCC). It is demonstrated that an ice lens initiates close to the so-called ice-entry value defined using the SFCC. Ice lens initiation conditions for different boundary conditions were determined in a laboratory using the SFCC and were then compared with the ice lens initiation conditions from a one-dimensional open system frost heave tests. The results using the SFCC showed good agreement with the values determined experimentally. A new approach, using the soil freezing characteristic curve (SFCC), is proposed to estimate the hydraulic conductivity of partially frozen soils. The hydraulic conductivity function for partially frozen Devon Silt is derived using the SFCC and the empirical relationships for hydraulic conductivity estimation method developed by Fredlund et al (1994). The SFCC for Devon Silt is determined from unfrozen water content measurement using time domain reflectometry and temperature measurements inside the soil sample. The results using this novel approach compare well with results presented by others that use different methods to determine the hydraulic conductivity function of partially frozen soils. Results from previous studies on frost heave indicate the presence of freezing-induced cracks in the frozen fringe (e.g., Arenson et al., 2008). These cracks affect the hydraulic conductivity of the frozen fringe and hence the moisture transfer process during frost heave. The presence of the cracks necessitates the use of a dual porosity model for estimating the hydraulic conductivity function of the frozen fringe. This study proposed a dual porosity model for estimating the hydraulic conductivity of the frozen fringe. Hence, the hydraulic conductivity of the frozen fringe will have two components: hydraulic conductivity of the soil matrix and hydraulic conductivity of the cracks. Methods are discussed to estimate the two hydraulic conductivity components. The hydraulic conductivity of the cracked frozen fringe is the estimated as the weighted average of the two components based on the respective porosity ratio. The proposed dual porosity hydraulic conductivity model is then used to carry out parametric study of the influence of the cracks on the hydraulic conductivity of the frozen fringe. The results indicated that the cracks have considerable influence on the hydraulic conductivity of the frozen fringe while taking only a few percent of the pore space.

• Subjects / Keywords

  • Frozen soil
  • Ice lens
  • Soil freezing characteristic curve
  • Frost heave
  • Frozen fringe
  • Devon silt
  • Hydraulic conductivity

• Graduation date

  Spring 2013

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3ZG6GG6M

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.