Teruyuki Suzuki

Basic Study on the Frost Heave Pressure of Rocks: Dependence of the Location of Frost Heave on the Strength of the Rock

Frost heave in rocks is caused by the frost heave pressure (pore ice pressure) generated by the freezing of pore water, which then cracks the rock. This work attempts to clarify the frost heave pressure of rocks by experiments at four temperature conditions. Ohya tuff and Kimachi sandstone, in which the occurrence of frost heave has previously been confirmed, were used as specimens. Measurements of these experiments were the internal temperature of the rocks during the freezing process and the location where the ice lens formed. These two parameters made it possible to determine the temperature of the location where the ice lens formed. A generalized Clausius-Clapeyron equation was used to calculate the pore ice pressure. The results indicated that the temperature at the location of the ice lens formation depends on the types of rock, but not on the temperature gradient during freezing. It was also confirmed that frost heave in rocks with a higher tensile strength appears at locations with a lower temperature, while that in rocks with a lower tensile strength appears at location of temperatures close to 0°C. These findings suggest that the location and temperature of the ice lens formation are dependent on the strength of the rock.

A Basic Study on Frost Susceptibility of Rock: Differences between Frost Susceptibility of Rock and Soil

This paper reports the differences between frost susceptibility of rock and soil. The research consists of two types of frost heave tests. One test uses solid rock samples. The other uses artificially-shattered, grainy rock samples. Rock can be treated as soil by artificially shattering. The authors conducted these two types of frost heave tests on 5 types of rock to investigate the differences between frost susceptibility of solid rock and grainy rock. From the test results, non-frost-susceptible rock did not change its frost characteristics in solid and grainy condition. On the other hand, the frost characteristics of frost-susceptible rock changed dramatically in solid and grainy condition. To determine the factors behind these test results, the authors compared the physical characteristics of solid rock sample and grainy rock sample. These comparisons clarified the structural difference between solid rock and grainy rock affects the frost susceptibility. These facts above indicate that the frost susceptibility of rock and that of soil are different.

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．

Study on the Shape of Freezing Front and Frost Heave Damage of C-box Structure

In Japan, the C-box (Culvert-box) is constructed to allow small rivers and other crossroad intersections to pass beneath roadways. In cold regions, it is reported that due to frost heave in the banking soil around the C-box, cracking damage may develop at the surface of the pavement. The mound-shaped frost heave at the upper part of the C-box may result in cracking on the side wall of C-box caused by the frost heaving force. The purpose of this study was to test and describe countermeasures for these frost heave damages. A 1/20 scale model bank containing a concrete C-box was constructed in a large freezing room. Under controlled room temperatures, the temperature in the banking soil and the shape of freezing front in the soil around the model C-box were measured.

FREEZING FRONT AND FROST HEAVING PRESSURE IN MULTI ANCHORED RETAINING WALL

各種の補強材を用いた新しい土構造物が多く開発され実用に供されているが, 寒冷地における凍上対策を考慮した構造物はほとんど無く対策工法の検討が急がれている. 本研究では多数アンカー式補強土壁を試験設置し, 冬期間の背面盛土の凍結状況や壁面ブロックに加わる凍結土圧などの動態観測を4シーズンにわたって行った. 実験の結果凍結面形成や凍結土圧などの特性について, いくつかの有用な知見が得られた.