Dai Nakamura

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.

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.