A constitutive model of saturated soils for frost heave simulations (original) (raw)
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Modeling of Frost Heave In Soils
1991
This report results from a research project undertaken over the period July 1, 1990 to September 30, 1991. The research project itself resulted from the combination of two proposals to the Center for Transportation Studies for research into the mechanics of frost heaving in soils. Both proposals had a general objective of creating a better understanding of the behavior of the soil-water-ice systems and frost susceptible soils at freezing temperatures and improving the capabilities of the faculty, researchers and students in an area of study which is important for road design in Minnesota. One proposal had the following major objectives: * deriving a basis for creating an improved engineering tool (numerical/analytical) for predictions of frost heave in soils with the emphasis being on phenomenological modeling of the frost heave process as initiated by Fremond and Blanchard at the Laboratory for Roads and Bridges in Paris. * assembling a laboratory for testing frost susceptible soils. No testing capabilities for assessing the frost susceptibility of soils existed in Minnesota -despite the importance of frost heave in roadway pavement design in Minnesota. The second proposal was aimed at: * stressing the multi-phase character of the phenomenon using a "local averaging technique" to account for the micro-level processes. This approach was designed to determine the applicability of Dr. Voller's previous research in metallurgical solidification phenomena to the frost heave modeling process. The combination of the two proposals retained the separate research approaches but provided for comparisons of the approaches and their applicability to frost heaving modeling. Early in the project period, some changes in project arrangements were necessitated by the move of Dr. Michalowski to Johns Hopkins University. Without Dr. Michalowski's presence in the Department, it was concluded that the investment in the laboratory testing apparatus would not be justified at present. It was also necessary to write a subcontract with Dr. Michalowski for him to be able to complete his work on the project while in Baltimore. In Part I, Radoslaw Michalowski outlines the basic background of frost heave modelling including a summary of the existing modelling approaches. The central element in this part of the report is the extension and application of the Blanchard and Fremond frost heave model. Results from these models are in good agreement with other modeling approaches and consistent with current frost heave understanding. In Part II, Vaughan Voller discusses various similarities between frost heave in soil and solidification of metal alloys. Three components in the thermo-mechanical frost heave model are identified (i) modelling phase change, (ii) modelling ground water flow and (iii) deformation modelling. In the context of the first of these components a numerical technique, previously developed for metallurgical phase change, is applied to a two dimensional case of ground freezing. Results, obtained in a matter of seconds on a IBM PC, are in close agreement with existing frost heave models. This part of the report concludes with a discussion of current and on-going work, in particular the thesis work of the master student, Lingjun Hou, who will couple the numerical techniques of Part II with the phenomenological model of Part I.
Frost heave modelling using porosity rate function
2006
Frost-susceptible soils are characterized by their sensitivity to freezing that is manifested in heaving of the ground surface. While significant contributions to explaining the nature of frost heave in soils were published in late 1920s, modelling efforts did not start until decades later. Several models describing the heaving process have been developed in the past, but none of them has been generally accepted as a tool in engineering applications. The approach explored in this paper is based on the concept of the porosity rate function dependent on two primary material parameters: the maximum rate, and the temperature at which the maximum rate occurs. The porosity rate is indicative of ice growth, and this growth is also dependent on the temperature gradient and the stress state in the freezing soil. The advantage of this approach over earlier models stems from a formulation consistent with continuum mechanics that makes it possible to generalize the model to arbitrary three-dimensional processes, and use the standard numerical techniques in solving boundary value problems. The physical premise for the model is discussed first, and the development of the constitutive model is outlined. The model is implemented in a 2-D finite element code, and the porosity rate function is calibrated and validated. Effectiveness of the model is then illustrated in an example of freezing of a vertical cut in frost-susceptible soil.
Frost Heave due to Ice Lens Formation in Freezing Soils 1. Theory and Verification
A frost heave model which simulates formation of ice lenses is developed for saturated salt-free soils. Quasi-steady state heat and mass flow is considered. Special attention is paid to the transmitted zone, i.e. the frozen fringe. The permeability of the frozen fringe is assumed to vary exponentially as a function of temperature. The rates of water flow in the frozen fringe and in the unfrozen soil are assumed to be constant in space but vary with time. The pore water pres- sure in the frozen fringe is integrated from the Darcy law. The ice pressure in the frozen fringe is detcrmined by the generalized Clapeyron equation. A new ice lens is assumed to form in the liozen fringe when and where the effective stress approaches zero. The neutral stress is determined as a simple function of the un- frozen water content and porosity. The model is implemented on an personal computer. The simulated heave amounts and heaving rates are compared with expcrimental data, which shows that the mode...
Model of the influence of snow cover on soil freezing
A mathematical model of snow-cover influence on soil freezing, taking into account the phase transition layer, water migration in soil, frost heave and ice-layer formation, has been developed. The modeled results are in good agreement with data observed in natural conditions. The influence of a possible delay between the time of negative temperature establishment in the air and the beginning of snow accumulation, and possible variations of the thermophysical properties of snow cover in the wide range previously reported were investigated by numerical experiments. It was found that the delay could change the frozen-soil depth up to 2^3 times, while different thermophysical characteristics of snow changed the resulting freezing depth 4^5 times.
Frost Heave and Ice Lenses Formation in Freezing Soils
Journal of Chemical Engineering Research Updates, 2014
A generalized model for secondary frost heave in freezing fine-grained soils is presented and discussed. The cryostatic suction effect, which increases upward water permeation, ice-lens growth during freezing, and, as a consequence, the increase of soil heave, is considered to be the main mechanism of moisture transfer. We recognize the need to determine the distribution of the moisture within the frozen fringe by approximation of the experimental data for the equilibrium unfrozen water content. This distribution is the result of the complicated interaction between water, ice and the mineral skeleton during the freezing process. The generalization of the Clapeyron relation, which is used in the studies of other authors, estimates only the drop in initial freezing temperature and does not define the connection with the external temperature gradient ∇T, which is responsible for the frost heave process. This very important aspect is discussed in detail in the introduction to our paper. We take also into account the ratio Pe/Ste ≠ 1 (where Pe<<1). This approach allows us to obtain a more general solution. The criterion of the ice lenses formation in fine-grained soils and the model for calculation of the lenses' thickness and spacing are derived. The dynamics of the lenses formation in histogram form is presented and discussed. The theoretical results obtained from the solution for fine-grained soils are compared in good agreement with experimental investigations. The model presented predicts the frost heave and ice lenses formation in freezing soils with reasonable accuracy, satisfactorily reflects observed phenomena, and thus can be suitable for engineering practice.
Acta Geotechnica
This research work presents an experimental and numerical study of the coupled thermo-hydro-mechanical (THM) processes that occur during soil freezing. With focusing on the artificial ground freezing (AGF) technology, a new testing device is built, which considers a variety of AGF-related boundary conditions and different freezing directions. In the conducted experiments, a distinction is made between two thermal states: (1) The thermal transient state, which is associated with ice penetration, small deformations, and insignificant water suction. (2) The thermal (quasi-) steady state, which has a much longer duration and is associated with significant ice lens formation due to water suction. In the numerical modeling, a special focus is laid on the processes that occur during the thermal transient state. Besides, a demonstration of the micro-cryo-suction mechanism and its realization in the continuum model through a phenomenological retention-curve-like formulation is presented. Thi...
Frost Heave due to Ice Lens Formation in Freezing Soils
2000
An operational model for estimation of frost heave in field where stratified soil profile appears is presented. The model is developed from the research model described in part B. Soil layers are first classified into frost-susceptible layers (FSL) or non-frost-susceptible layers (NFSL). In an FSL, both heat flow and water flow are considered and ice lensing can occur. In a NFSL, only heat flow is possible and no ice lcnsing is allowed. The governing equations for heat and mass transfer are established for the time period when the frost front is moving within FSL. Capillarity and unsaturation are also considered. The operational model is verified by field measurements of hcavc amounts. Examples of application are given.
Freezing processes in porous media: Formation of ice lenses, swelling of the soil
Mathematical and Computer Modelling, 2003
moist porous soil is freezing, a volume expansion is generally observed. The volume increase is mainly due to a water migration process from the base of the soil up to the freezing front, which separates the lower unfrozen part from the upper frozen one. The coupled heat-mass transfer process is accompanied, under particular conditions, to the formation of pure ice segregated layers. Conversely, if the freezing process is too fast or the overburden pressure acting on the column of soil is relevant, no macroscopic accumulation of ice is observed. It is generally accepted that a thin transition region (frozen fringe), where water and ice coexist in the porous space, separates the unfrozen from the frozen parts of the soil. The strong interest on ground freezing is motivated by at least two reasons: preventing frost damages produced on roads pavements, pipelines, or other structures, and predicting the effects of artificial-freezing techniques for tunneling or underground constructions. We are going to present a mathematical model of frost heave where water is driven through the porous space by the coupling of a pressure and a chemical gradient. In particular, the interest is focused on detecting which are the boundary values for temperature (or thermal flux) that determine the process of lens formation or frost penetration, once the properties of the soil are known.
Simulation and analysis of frost heaving in subsoils and granular fills of roads
Cold Regions Science and Technology, 1997
Laboratory data were utilized to verify the finite-element program MELEF for simultaneous water flow, heat and solute transport simulations in saturated-unsaturated porous media. Firstly, numerical simulations were used to predict observed frost heaves in the soil columns, using measured and estimated physical properties as well as experimental conditions as input. The comparison of the predictions and the laboratory experiments showed differences less than 5% between calculated and observed frost heaves at the end of the freezing tests. Secondly, a sensitivity analysis for laboratory conditions allowed Ž the verification of various parameters used in the model thermal and hydraulic conductivities, capillary height, pore . distribution index, residual saturation and clay distribution factor . The analysis showed that frost heaving could be chiefly influenced by the parameters defining the soil moisture retention curve, that is, capillary height, pore distribution index and residual saturation. Finally, frost heaving sensitivity tests were performed with MELEF in order to assess likely transient frost heaves of a particular road submitted to different conditions during a particular winter. The previously studied materials were used as inputs with different water table heights and climatic conditions normally encountered in the Quebec region. Results show that improving road drainage could constitute an appropriate solution to the problems of frost deformation, when the sampled materials contain less fine grains. Materials with similar frost-susceptibility indexes but with different physical properties, did not necessarily have similar frost heaving behaviours for the same road drainage conditions. These findings should help to find better solutions to the engineering problems due to ground freezing by making possible a better correlation between the frost-susceptibility of soils, as measured by various laboratory tests, and the amount of heave observed in the field.
Mathematical descriptions for the behaviour of ice-rich frozen soils at temperatures close to 0 °C
Canadian Geotechnical Journal, 2005
With the use of creep and constant strain rate (CSR) tests, mathematical formulations were found that describe the thermomechanical behaviour of ice-rich frozen soils. A Glen-type relationship was chosen for the formulation of minimum creep strain rates at temperatures between -4°C and -1°C. The shear strength of the material could be described by a Mohr-Coulomb failure criterion. Furthermore, it was possible to compare the creep behaviour with the strength of similar soils under constant strain rates. The minimum creep strain rate increases proportionally as the temperature approaches the melting point of the ice, which can be attributed to the increasing amount of unfrozen water, which strongly influences the mechanical response. Even though only a few tests could be used for the determination of the angle of friction and the apparent cohesion, the trend showed that the volumetric ice content influences both parameters, but only the latter seems to be influenced by the temperature and the applied compression strain rate.