Atsuko Sato

The behavior of moisture in high-water-content soil during the freeze-thaw process under natural cold conditions.

Ground freezes from the surface downward, and during this process soil moisture is drawn upward. The moisture content of soil that has frozen is high, whereas the moisture content of non-frozen soil below that is low, because water is drawn upward toward the soil that has frozen. If high-moisture soil can be improved to yield low-moisture soil using this phenomenon, low-cost improvement will be possible. Soil moisture change through winter were monitored in outdoor experiments. The results confirmed the feasibility of improving unsuitable soil with high water content through freezing. It was also found that improvement at 15 to 20 cm below the frozen surface was effective, and that the water content of soil poured into an outdoor earth tank decreased from 300 to 150% over a period of two years involving two freezing periods.

Land-Improvement Technology Using the Heat of Soil Stabilizer Reactions in Cold Regions

Laboratory tests on small soil specimens under cold weather conditions found that curing temperature significantly influenced the strength of unsuitable soil improved by adding a stabilizer. The improved soil was found to develop little strength when the ambient temperature was below 0°C. However, the authors considered that the temperature inside a full-scale embankment might not decrease as much as in the small specimens in the laboratory tests because the ambient temperature is expected to have a smaller effect on the soils in the full-scale embankment than on the small soil specimens. In this study, they conducted a field experiment to investigate the extent of freezing and the strength improvement of soils that have been modified with stabilizers. In addition, they measured the effects of a quicklime-mixed soil blanket placed on the constructed embankment. The field experiment confirmed that the embankment underwent little freezing while the soil was developing strength.

Properties of Embankments Constructed in Winter

In snowy, cold regions, embankments constructed in winter may cause settlement and collapse of slopes in the thawing season in early spring. One of the reasons may be unavoidable suspension of the work due to work schedules while constructing an embankment during a cold winter. Accordingly, assuming such construction, a test construction was conducted in the winter season. For the constructed embankment, its inside temperatures and strength were measured. Also, after the embankment melted, it was cut open and the density and water content were measured. As a result, it was found that: (1) even in a 30-cm-high embankment, frost and moisture movement occur; (2) a frozen embankment is strong, but a non-frozen one is not strong; (3) depending on the embankment construction method, layered frost remains and the number of layers increases with the increase of construction days; and( 4) when the embankment freezes, the density and water content decrease.

A technique to reduce moisture content using freeze-thaw action in cold climatic conditions

Ice lenses are known to form when ground cools and the soil surface begins to freeze, thereby causing water in unfrozen soil to move upward toward the freezing front (Japanese Geotechnical Society, 1994). In this process, moisture content in unfrozen soil decreases as water moves out. Based on this principle, the ability to leverage Hokkaidos cold winter climate to reduce the moisture content of dredged soil would significantly reduce costs compared to those incurred in general soil improvement methods (i.e., expenses related to aeration desiccation, mechanical stabilization and solidifier application). Against this background, in order to investigate the feasibility of using the dehydration method based on cold-climate conditions, an experiment was conducted using large sandbags in place of outdoor earth tanks to determine whether moisture content would be reduced as a result of soil freezing. The outcomes indicated that dehydration could be realized simply and economically using large sandbags in a cold climate. It was also revealed that specific soil components could be extracted through freezing-induced dehydration.

An Outdoor Earth-tank Experiment Concerning Frost-heaving Prevention Measures for Reinforced Earth Walls Using Geotextile Materials(Part 2)

寒冷地では，ジオテキスタイルを用いた補強土壁が凍上により変形する例が報告されている．その対策の確立を目的として，これまで，置換，排水，断熱に着目した実物大模型を構築し，ひずみや変形を測定し標準工法と比較した．その結果，置換，断熱工法により凍上による変形を抑制できる可能性があることが分かった．今回施工から1年が経過した補強土壁について計測を継続するとともに，断熱工法に着目して新たに3種類の凍上抑制工を設置した．それぞれの補強土壁を計測した結果，全体の傾向として、凍上によって発生したひずみや変形が融解後も残留し，次の凍結により累積していくことが分かった．