There is a long history of research on the frost heave mechanism. However, the mechanism of frost heaving is not yet elucidated. Because of this, general understanding which is based on recent research results is not widely permeated, and then erroneous measures are seen in frost heave engineering.
Recognizing this problemes, first, a frost heave process which is deduced from past research results is outlined. Phenomenological features of frost heave and a microscopic structure model of ice lens vicinity are discussed with the research results of properties of unfrozen water, and then a process of ice lens growth is shown.
Second, a macroscopic mechanism of ice lens initiation, which gives the initial condition of the segregating ice lens in heaving, is then proposed. A mechanism of ice lens initiation by breaking the structure in which the pressure of pore ice overcomes the overburden pressure and the tensile strength of the structure is shown, and also another process, which simultaneously functions and depresses the local unfrozen water pressure which is a necessary condition of ice lens segregation is discussed with experimental data.

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Thermal and hydrological dynamics of the active layer were monitored during the thawing period from May to September 2000, near Yakutsk, Eastern Siberia. This region is characterized by continuous permafrost and boreal forest (Taiga). The aims were to clarify the characteristics of the heat and water budgets in the active layer, and to assess the influence of forest disturbance on permafrost, based on field observations in disturbed and undisturbed forests. Heat and water budgets of the active layer were analyzed and compared at a mature larch forest site and a disturbed site, which experienced wildfire and clear-cutting 11 years before these observations. Results of the heat budget analysis indicated that the storage of latent heat was the largest component of the heat budget in the active layer. Despite larger ground heat flux observed at the disturbed site, the difference between thaw depth at the disturbed and forest sites was small. This result was attributed to the higher initial ground ice content at the disturbed site where more latent energy of fusion is required to deepen the thawing layer. Water budget analysis showed that total evapotranspiration at the disturbed site was 75% of that at the undisturbed forest site for the period June-September 2000; thus, more soil water tends to be stored at the disturbed site than at the undisturbed forest site. Finally, the conclusion of this study is that soil water content in the active layer is the determinant factor of maximum thaw depth in this region.

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Frozen ground in discontinuous permafrost zones is characterized by complicated spatial distribution and large seasonal fluctuations in unfrozen water contents.Direct current(DC)resistivity imaging performed in the northeastern Mongolia, Daisetsu Mountains of northern Japan and Kanchanjunga Himal of eastern Nepal demonstrate this technique as an effective method for observing frozen ground characteristics which supplemented with additional observation such as ground temperature measurements.DC resistivity imaging is shown to be useful for delineating isolated frozen ground and buried ice bodies in the areas with large topographic and subsurface inhomogeneties.Seasonal changes in resistivity values at the Mongolian site are related to the spatio-temporal changes in soil water condition both in the active and upper layers of the permafrost.These are advantages unique to DC resistivity imaging that are not found with conventional methods such as one-dimensional geophysical soundings of plane-layer approximations, excavation and time-domain reflectometry(TDR)measurements.

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Tateyama Mountains has a unique climate. Northwesterly winds accompanying a winter monsoon cause a large amount of snow, which accumulates to depths of a few decameters on the leeside slopes of mountain crests, while the polar front causes a large amount of rain from June to mid-July (summer rainy season) . Previous studies suggested that permafrost is stable in the north-facing slope of Kuranosuke Cirque, where snow cover remains until August or September, while it is absent on the mountain crest, where snow disappears by June. However, little is known about formation and preservation processes of permafrost in Tateyama Mountains. The aims of this study were to clarify the formation and preservation processes of permafrost under deep snow and heavy rainfall conditions in the Tateyama Mountains.
Subsurface temperatures down to 2.2 m were monitored in the north-facing slope of Kuranosuke Cirque from October 2000 to September 2002 (P site) . Subsurface temperatures to 1.8 m depth, soil water content, and precipitation were monitored on the mountain crest above the Kuranosuke Cirque from June 2001 to September 2002 (NP site) .
In the Tateyama Mountains, heavy rainfall occurs several times during the summer rainy season (June-July), and NP site is stripped of snow cover by June. The rapid melting of seasonal ground frost at this site involves heat transport by the percolation of warm rainwater during the summer rainy season; thus, permafrost is absent at NP site. Simultaneously, at P site, rapid ground freezing in early winter and continued subsurface cooling under thick snow cover throughout the winter generate a deep frost layer. Snow cover lingers until late summer and prevents the percolation of warm rainwater that would otherwise accelerate melting of the frozen layer. Therefore, deep snow cover makes P site favorable for permafrost.

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Adfreeze shear strength between frozen soil and construction material is an important mechanical property to maintain cutoff of ground water during excavation by the ground freezing technique. However, adfreeze shear strength for design is not confirmed because the influence of normal stress on the adfreeze interface, which depends on excavation depth on site, is unknown. Adfreeze shear tests with normal stress on the adfreeze interface between frozen soil and steel plate are performed. The larger the normal stress, the larger the adfreeze shear strength of frozen sand or frozen clay to steel plate. The increase in gradient of frozen sand is larger than that of frozen clay. Adfreeze shear strength is larger with normal stress on the interface between soil and steel plate before freezing. Furthermore, static friction power between frozen soil and steel plate contributes to increase of adfreeze shear strength. Normal stress is more influential on adfreeze shear strength of frozen soil with larger internal friction angle.

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Heat storage for cooling is already in practical use; ice made at night is used during the day. Frozen soil with latent heat could be a heat sink for cooling in the ground through the seasons. Soil that freezes in winter could be used for cooling in summer. Soil freezing by a refrigerator is effective in winter because the coefficient of performance in winter is higher than that in summer.
This paper describes a simulation analysis of repeated heat storage and recovery in three years with a practical model. If a group of cooling pipes is installed, heat recovery efficiency while heat is used for cooling becomes over 80% in the second year. And the effective cooling temperature by refrigerator is estimated. Additionally, soil freezing only by cold winter air and heat pipes without refrigerator is studied.

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Some meteorological factors were observed in the constructed cut slopes faced four different directions under the same conditions through five winter periods in the cold region with less snowfall relatively. The purpose of this field observation is to clarify the relationship between meteorological factors and both soil freezing and snow cover with taking notice of the difference of cut slope directions.
The results of the observation showed that soil temperatures as well as air temperature in the slope faced toward the south are higher than any other direction because of the largest global solar radiation. On the other hand, in the slope faced toward the north, air temperature is the lowest and soil temperatures are also comparatively low due to the least global solar radiation. Nevertheless, maximum snow depth in the slope faced toward the east is larger and maximum frost depth in the slope faced toward the west is larger, rather than the slope faced toward the north. Therefore, soil frost depth of cut slope is influenced not only by the solar radiation but also by snow depth owing to the difference of cut slope direction.
Based on these findings, the cut slopes faced toward the north and the west are more likely to be dangerous compared with those facing toward the other directions, because maximum frost depths of the both slopes are relatively large. In future, it is necessary to take account of direction of cut slope when the cut slopes are constructed and conserved.

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Ground temperature monitoring was conducted at a slope along the left bank of Kanoko dam, Oketo town, Hokkaido, Japan. Ground ice was discovered there during a construction of a road in 1979. After the environment of the slope was artificially changed in 1979, wind holes where cold wind is blowing out are observed on the slope. Though permafrost was detected in 1987 and 1988, permafrost has degraded by 1990. However, perennial frozen ground occurred in 2001 when it was cool. If cool years under about 4°C in MAAT continue, permafrost will probably occur there.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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