Satoshi Akagawa

Experimental study of frozen fringe characteristics

Abstract The objectives of the paper are to show the efficacy of a newly developed X-ray radiography technique for the study of frost heaving, and to discuss experimental data which reveal the characteristics of the frozen fringe. An open-system frost heave test was conducted for about 700 hours. Lead sphere position markers, in which thermocouples are installed, were placed every 5 mm along the axis of a cylindrical 97 mm long specimen. Seventy-four X-ray radiographs were taken during the test. These X-ray radiographs show ice lenses and the lead spheres clearly. The measured co-ordinates and temperatures of the spheres enable precise temperature profiles to be determined for each X-ray radiograph. By referring the temperature profile to the X-ray photograph, the thickness and temperature range of the frozen fringe are determined. The data obtained by this experiment include heave rate, water intake rate, thickness and temperature range of the frozen fringe, and strain rate distribution within the specimen. From these, the periods of in situ and/or segregation freezing and water movement are discussed.

On the Factors Influencing the Scaling of Ice Forces

A series of ice indentation tests have been performed since the winter of 1996 at Lake Notoro in Hokkaido, Japan (JOIA reports: 1996, 1997, 1998 and 1999), as part of the JOIA project. The main factors affecting the total ice load (F) on a structure were investigated using data derived under systematic test conditions, using natural sea ice. The width (W) of the model structure, ice thickness (h), indentation speed (V) and uniaxial compressive strength (σc) are the major factors influencing ice load on a stmcture with a vertical face. The paper determines the dependence of (W/h), (V/h) and (h) on indentation pressure (Pt). It also describes the pressure distribution examined by a 2-dimensional panel sensor that could simultaneously measure pressures at 2112 points for various indentation speeds. From field data, the paper investigates factors explaining the scaling effect, by which the ice load decreases with increasing indentation area.

An experimental study on static solid-liquid phase equilibrium in the pores of a porous medium

The so-called Clausius-Clapeyron equation, that is, the static equation of state for solid-liquid-porous media systems without liquid flow through the pores, has been experimentally examined by measuring the pore liquid pressure at the solid-liquid interface in order to verify the accuracy of our method of measuring unfrozen pore liquid pressure. Several series of experiments have been carried out using water-saturated Ohya-Tuff as a porous medium specimen cooled from the top down. In these experiments, the solid-liquid interface was always fixed at the top surface of the specimen. The experimental results imply that the measurement method should be useful in determining the relative value of the unfrozen pore water pressure.

Effect of Tensile Strength on Ice Lens Initiation Temperature

Conditions of ice lens segregation when a new one is start to grow is explored in experimental approach in this paper. Two consecutive open-system frost heave tests have conducted with the same Diluvial Silt of which mean tensile strength is 0.75MPa. Four predominant ice lenses have segregated in 114.2mm high specimen during the first heave test. Then, applying positive temperature to pedestals: i.e. thawing, the second heave test has conducted under the same test condition as the first one. Ice lenses have appeared exactly the same location as the first test. Therefore, it is revealed that ice lens initiation takes place where lower tensile strength remains. The temperature of ice lens initiation during the second frost heave test which have been interpolated by the boundary temperatures have found to be higher than those of the first ones. The difference is almost the same as 0.95 o C. Expected pore ice pressure at the initiation calculated with generalized Clausius-Clapeyron Equation using the temperature difference is 1.05MPa. The calculated pore ice pressure is little higher than the sample tensile strength. Therefore, it is expected that pore ice is pushing structure of mudstone against its tensile strength and overburden pressure to fracture via unfrozen film water.

A Practical Method for Three-Dimensional Frost Heave Simulation based on Takashi's Equation

Various models have been proposed for frost heave estimation. However, a practical evaluation method for multi-dimensional deformation has not yet been established. This study aimed to discuss the possibility of expanding the existing evaluation method into three dimensions based on previous experience on simulating interactive behavior between a chilled gas pipeline and frost heave. Takashis equation was adopted among several frost heave models considered; this model has been used to estimate one-dimensional frost heave according to the Japanese Geotechnical Standard. A new three-dimensional frost heave apparatus was developed to apply Takashis equation to multi-dimensional heave, and a modified equation was proposed based on the experimental results. Considering the effect of anisotropic properties on frost heave, this proposal was adopted for a simulation program by coupling the heat transfer calculation and mechanical equilibrium analysis in a finite element method (FEM) model. The simulation results are presented in this paper as an example to confirm the proposed models applicability.

Soil freezing by a step temperature drop in the open system under overburden pressure

Abstract Freezing of saturated, solute-free soils under over-burden pressure by a step temperature drop was discussed for an idealized soil in which all pore spaces among particles had the same size and for real soils, with the following results: The rate of frost heaving and the depth of the freezing front were expressed in three ways depending upon the elapsed time, i.e. stages I, II and III. The type of frozen soil for real soils results in stages I, II and III, respectively, from in-situ freezing of pore water, from both in-situ freezing and segregational freezing of pore water, and from segregational freezing of pore water.

Movement Due to Heave and Thaw Settlement of a Full-Scale Test Chilled Gas Pipeline Constructed in Fairbanks Alaska

In this paper the authors report the heave and thaw settlement properties of a test chilled gas pipeline. A full-scale field experiment of the chilled gas pipeline system was conducted in Fairbanks Alaska from 1999 to 2005. The length of the test pipeline was 105m and the diameter was 0.9m. The circulated chilled air was –10 o C. One-third of the pipeline was buried in permafrost and the rest of it was placed in non-permafrost. At the end of July 2003, circulation of the chilled air ceased, however, monitoring of the thaw settlement properties of the test pipeline continued until the middle of April, 2005. The results obtained include: 1) As the frost-bulb around the pipeline in non-permafrost section formed, the test pipeline in the non-permafrost section moved upward, resulting in bending of the pipeline at the boundary. 2) In summers, overburden frozen ground of the pipeline became thinner due to the development of active layer above. The pipeline buried in permafrost section moved upward abruptly, fracturing the thinning overburden frozen ground. 3) The phenomenon mentioned 2) occurred successive summer, and the pipeline uplift in permafrost section continued in summers. 4) In relation with 1), the upward movement in non-permafrost section was confirmed by frost heaving of the pipe foundation. 5) Settlement of the test pipeline was also confirmed by thaw settlement of the foundation. 6) During the thawing process, the temperature of the thawing frost bulb became 0 o C at first and then thawed rapidly in summer together with the development of active layer. As a result , settlement of the pipeline happened rapidly in summer. Introduction In the existing natural gas production field in permafrost regions such as West Siberia, gas pipelines float in water or are exposed in ditchs as shown in the photos of Fig.1. However the gas pressure at the present time has dropped considerably comparing to the one in the initial production days. This pressure drop enables the damaged pipeline system to survive. However, those initially buried gas pipelines are now mostly exposed and lost the structural stabilities and security reliability. As for the natural gas pipeline installation in permafrost regions, the buried system has been recommended for security reasons. In order to prevent thawing of the permafrost shown in Fig.1, the gas must be chilled for transportation in permafrost regions.On the other hand, even with the chilled gas pipeline system, miner problems may still happen in limited sections of the pipeline where frost heave damage occurs when the pipeline freezes surrounding soils in non-permafrost section (Talik). Two primary chilled pipeline test experiments are discussed in the literature: the Calgary Frost Heave Facility and the Caen, France experiment. A third chilled pipeline experiment was conducted at the Fairbanks Frost Heave Facility, but the data remains unavailable to the public. The Caen, France chilled pipeline experiment is well documented in public literature by Geotechnical Science Laboratories (1983, 1986a, 1986b, 1988) and Dallimore and Williams (1985). The purposes of the Caen experiment were to investigate differential heave resulting from the abrupt transition between two different lithologic soils (Caen silt and SNEC sand) with varying frost susceptibilities and the associated stresses incurred by the pipeline and the soil mass. Abrupt lithologic transition zones are common in the natural environment such as the transition between active fluvial gravel deposits and silt overbanks deposits.

Interactive Behavior between Frost Bulb and Chilled Pipe by an Axially-Symmetric Freezing Experiment

It is known that chilled gas pipelines buried at a boundary between permafrost and non-permafrost are subject to severe bending deformation since they are held tightly in the permafrost whereas the growth of frost bulbs in the non-permafrost region causes frost heave of the pipes. However, the flexural rigidity and the behavior of the pipeline and the surrounding frost bulb as a composite structure have not yet been studied, although they are important factors in evaluating structural safety and stability. The purpose of this study is to experimentally determine the interactions between a chilled gas pipeline and a frost bulb under the simplified condition of axial symmetry, and also to evaluate the adfreeze strength of the frost bulb and its dependence on boundary stress and temperature.

Improvements in Measuring Unfrozen Water in Frozen Soils Using the Pulsed Nuclear Magnetic Resonance Method

AbstractThe pulsed nuclear magnetic resonance (P-NMR) method is commonly used to determine unfrozen water content in frozen soils. Traditionally, unfrozen water content is calculated using first re...

Frost Heave Induced Pipe Strain of an Experimental Chilled Gas Pipeline

A full-scale chilled gas pipeline experiment was conducted in Fairbanks, Alaska to develop the design criteria for pipeline construction in arctic regions. The test pipeline had a length of 105 m and a diameter of 0.9 m. One-third of the pipeline was located in permafrost and the remaining was in non-permafrost. The monitoring data were collected from December 1999 to January 2005 including both freezing and thawing phases. In the transition zone between frozen and unfrozen soil, the foundation material experienced a vertical movement caused by differential frost heave. The test results indicated that the bending action was the main factor for the circumferential and longitudinal strain distribution in the pipeline. The circumferential strain ranged from about 100 to 500 during freezing. The maximum tensile and maximum compressive strains along the pipeline were approximately located at the edges of the transition zone.