Jean-Marie Konrad

An efficient technique for generating homogeneous specimens for DEM studies

Abstract A new technique, designated as the Multi-layer with Undercompaction Method (UCM), capable of generating homogeneous specimens for DEM studies is presented herein. The specimen are compacted in several layers using undercompaction criteria based on average planar void ratio. The proposed approach was compared to other available methods and was proven to generate very homogeneous specimens provided a nonlinear average undercompaction criterion was used. Furthermore, the UCM method was efficient for a variety of density conditions ranging from very loose to dense states.

A MODEL FOR WATER TRANSPORT AND ICE LENSING IN FREEZING SOILS

A one-dimensional model for water transport and ice lensing in incompressible saturated and solute-free soil specimens is proposed for the simulation of small-scale frost heave tests in the laboratory. The model considers (1) open-system freezing in which the variables T and Pw are independent, (2) an ice lens that continues to grow as long as enough energy is available in the frozen fringe to produce the work required for mass transfer to the ice lens, and (3) a new ice lens that forms when the vertical strain in the frozen soil reaches the instantaneous tensile failure strain. The proposed frost heave model is amenable to computer simulation procedures which provide predictions of rate of frost heave and rate of pore freezing front penetration as functions of applied load, thermal and water flow regimes, and soil properties. Position, time of initiation, and ultimate thickness of individual ice lenses emerge also as a part of the solution. A quantitative comparison of observed and simulated responses for various boundary conditions is shown for a reference soil known as Devon silt. The model was found to exhibit many of the characteristics observed in frost heave tests on Devon silt and predicted the effects of overburden pressure on frost heave rate.

A new capillary and thin film flow model for predicting the hydraulic conductivity of unsaturated porous media

[1] Most classical predictive models of unsaturated hydraulic conductivity conceptualize the pore space as either bundles of cylindrical tubes of uniform size or assemblies of cylindrical capillary tubes of various sizes. As such, these models have assumed that liquid configuration isthesameinboththewetanddryrangesandthatasingleconceptcanbeused to describe water transport over the entire range of matric head. Yet theoretical and experimental findings suggest that water transport in wet media, which mostly occurs in water saturated capillaries, is quite different from that in dry media, which occurs in thin liquid films. Following these observations, this paper proposes a new model for predicting thehydraulicconductivityofporousmediathataccountsforbothcapillaryandthinfilmflow processes. As with other predictive models, a mathematical relationship is established between hydraulic conductivity and the water retention function. The model is mathematically simple and can easily be integrated into existing numerical models of water transport in unsaturated soils. In sample calculations, the model provided very good agreement with hydraulic conductivity data over the entire range of matric head. Two other well‐supported models, on the other hand, were unable to conform to the experimental data. Citation: Lebeau, M., and J.‐M. Konrad (2010), A new capillary and thin film flow model for predicting the hydraulic conductivity of unsaturated porous media, Water Resour. Res., 46, W12554, doi:10.1029/2010WR009092.

FLUID DYNAMICS BASED PREDICTION OF LIQUEFACTION INDUCED LATERAL SPREADING

Abstract This paper presents and verifies a numerical method to predict the lateral spreading of liquefied subsoil based on fluid dynamics. A numerical fluid dynamics code is modified to incorporate the Bingham viscosity with the minimum undrained strength of liquefied subsoil. The numerical method is applied to shaking table tests of a liquefied slope with and without an underground structure and flow failure of a road embankment near Asele in northern Sweden. As the result of simulations, the numerical method is found to reproduce the time history of flow velocity of liquefied subsoil, lateral spreading load to the underground wall and flow failure process of the embankment.

2-D frost action modeling using the segregation potential of soils

Abstract The segregation potential, SP, has been used to solve two-dimensional frost heave problems. SP-based approach to predict frost heave has been extended to 2-D problems such as freezing around chilled pipelines buried in unfrozen ground. It requires, however, the input of non-linear stress-strain-strain rate-temperature relations for characterizing the behavior of the frozen soil and an incrementally deforming mesh. Simulations of actual field tests using burial chilled pipelines were successfully performed with the newly developed 2D-SP frost action model and provide distributions of ice content, stresses and displacements. Assuming a bi-linear stress-strain relationship for the frozen soil, parametric studies have shown that frost heave was more sensitive to post-yield characteristics of the frozen soil than to the magnitude of its yield stress.

Freezing-induced water migration in compacted base-course materials

Ramped-freezing tests were conducted on three base-course materials with fines contents of less than 7% and compacted at different initial states but always at degrees of saturation near or well below 60%. Three different quarries were studied. The natural fines from crushed gneiss with biotite, limestone, and monzonite were all frost susceptible. Frost heave was relatively small, but significant water intake occurred in all samples during freezing with access to an external water source, regardless of initial saturation level. The frost susceptibility of coarse-grained soils cannot be solely evaluated with respect to frost heave but needs also to consider the amount of water drawn to the freezing front during the freezing process and the consequences of this water during thaw. The normalized heave of the base-course layer of pavements is a practical and efficient indicator of the frost susceptibility of the base-course aggregates. If it is larger than 1%, the base-course material can be considered as fro...

Role of Deicing Salt in Pavement Deterioration by Frost Action

Frost action is a major cause of pavement deterioration in cold climates. Thermal cracking, differential heaving, and loss of bearing capacity during spring thaw are often identified as the main mechanisms involved. Except for thermal cracking, frost-susceptible subgrade soils are generally considered to be the source of the problems. Field observations suggest that frost action within the pavement granular layers could also contribute to pavement deterioration. Differential freezing conditions associated with the contamination of the base material by deicing salt are believed to be the cause of this problem. Indeed, field observations of heaved pavement surfaces near discontinuities, such as cracks or pavement edges, suggest that an ice enrichment process is occurring in pavement granular layers during the freezing season. In a laboratory testing program, salt concentration gradients reproduced in freezing temperature create conditions favorable to an ice enrichment process and contribute to a substantial increase in the frost susceptibility of granular materials. Under steady isothermal cooling conditions, samples placed in layers of increasing salinity have exhibited heave at rates as high as 6 mm/day. Normal freezing tests on the same material free of salt have shown no significant segregation potential. Surface heave resulting from ice enrichment can be highly detrimental to pavement performance. Induced distortion contributes to rapid deterioration of the pavement surface. When occurring along transverse cracks, the phenomenon may seriously alter the ride quality of the pavement.

Deterioration Model for Pavements in Frost Conditions

Pavements in cold climates are often subjected to transverse differential heaving. This phenomenon is the result of the more severe frost action under the unprotected road surface. It induces bending stresses in the pavement structure and ultimately causes longitudinal cracking at the pavement surface. A simple model to predict the initiation and the propagation rate of cracking induced by frost heave is proposed. The model is based on mechanistic principles and calibrated using field performance data. It can be used in designing and managing pavements in frost conditions.

Pore pressure measurements during freezing of an overconsolidated clayey silt

Abstract Frost heave tests on overconsolidated clayey silt specimens have been conducted with and without applied back-pressure. Frost heave characteristics are, at first approximation, independent upon the magnitude of applied back-pressure provided that the unfrozen soil remains saturated. For the soil studied the critical suction at which desaturation occurs is about 40 kPa. Pore pressures were also measured in the unfrozen soil during freezing. The experimental results confirm steady state flow conditions in overconsolidated soil specimen seven during the early stage of freezing. However, suctions in excess of 100 kPa can be generated at the frost front depending upon the freezing conditions. This, in turn, may lead to desaturation of the unfrozen soil near the frost front and render the analysis of a frost heave test even more complex. It is suggested to conduct frost heave test using a back-pressure equal to the hydrostatic pressure in the field and with a value of suction at the frost front close to that in the field in order to assess the relevant segregation potential.

Cold Region Engineering

Permafrost underlies about one-quarter of the world’s land surface and most of the engineering aspect has been well-covered in Andersland & Anderson (1978), Johnston (1981) and Andersland & Ladanyi (1994). This chapter considers more specifically the problems associated with seasonal freezing and thawing of soils in which there is no perennially frozen ground. Frost action may cause extensive damage to buildings, infrastructure such as roads and utility lines and other civil-engineering structures. All such facilities should be designed and constructed to avoid serious functional problems, costly maintenance and unduly short service life. The behavior of soils is strongly influenced by temperature and, therefore, an appreciation of heat transfer in soils is of utmost importance to cold region engineering.