Differential frost heave manifest as patterned ground: Modeling, laboratory and field studies

Frost heave refers to an uplifting of the ground surface due to freezing of water within the soil. Differential frost heave (DFH) can occur when the freezing is laterally non-uniform. DFH can give rise to patterned ground: surface features made prominent by the segregation of stones, ordered variations in ground cover, or regular topography. Types of patterned ground caused by differential frost heave include earth (or mud) hummocks, frost (or mud) boils, sorted stone circles, and possibly other forms as well. These types of patterned ground could serve as climate-change indicators because DFH is sensitive to environmental changes including regional and global warming and acid rain. The overall objective of this thesis is to explore the conditions necessary for DFH and the implications they have for patterned ground.; Multidimensional equations have previously been developed that describe the frost-heave process based on the Miller frost-heave model. A linear stability analysis (LSA) indicates whether one-dimensional frost heave has the propensity to evolve into differential or multidimensional frost heave. A LSA was completed that assesses the environmental conditions and soil properties necessary for the initiation of DFH. The conditions and parameters investigated include ground-surface-temperature conditions, surface load, freezing depth, frozen-soil elastic modulus, and soil type. Because frost heave is inherently a transient process, both a frozen-time and real-time LSA were carried out. Explanations of the discrepancies between previous LSA studies and this work are included.; A preliminary, finite-amplitude, two-dimensional DFH model is presented. A finite-amplitude model (FAM) is necessary because multidimensional frost heave evolves at a rate that is the same order of magnitude as one-dimensional frost heave. Results from the FAM indicate that the LSA predictions accurately describe the initiation of DFH. The FAM was not wed for long-time simulations because of numerical difficulties.; Field observations of hummocks were made near Inuvik, NWT, Canada in order to substantiate the model predictions. Various characteristics of the hummock including size, spacing, and vegetative ground cover were compared with the LSA predictions and found to agree fairly well. Limited soil properties precluded coroborating the LSA predictions with patterned-ground observations in the literature.; A laboratory apparatus capable of simulating the frost-heave process was built and experiments were conducted using a frost-susceptible soil in an attempt to form patterned ground. Two successful experiments resulted in soil patterning after several freeze/thaw cycles. In one, a 2 x 2 pattern of bumps formed, and in the other, a 2 x 2 pattern of dimples formed. We believe these experiments are the first successful attempts at forming patterned ground due to differential frost heave in the laboratory.