Studies on the Frost Heaving of Volcanic Ash Soils and the Suitability of Pumice Soils for a Subgrade Frost Protection

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In this research project, the authors investigated the frost heaving and the effect of freeze-thaw cycle on the physical and engineering properties of volcanic ash soils, and also the suitability of pumice soils for a subgrade frost protection. The results obtained were summarized as follows :1.Frost Heaving of Volcanic Ash SoilsThough the frost heaving was due to the soil water movement from unfrozen parts of soil to freezing front, in case of volcanic ash soils, that movement was remarkably affected by water retention and permeability. The heave amount of volcanic ash soils was larger than that of non-volcanic ash soils, however, it decreased with decreasing initial water content and bulk density of soil samples. The decrease in heave amount of volcanic ash soils by air-drying occurred at pF4.2 of soil water condition.2.Effect of Freeze-Thaw Cycle on the Physical and Engineering Properties of Volcanic Ash SoilsThe volcanic ash soils had very large water retention, and had much water at field-moist condition. Therefore, the change in physical and engineering properties by freeze-thaw cycle because of the transformation of phase from water(liquid) to ice(solid). The thermal conductivity increased by freezing, and the strength of remoulded soil samples with much water at liquid limit increased by freeze-thaw cycle. On the other hand, shrinkage and compressibility decreased by freeze-thaw cycle, especially for organo-volcanic ash soils.3.Suitability of Pumice Soills for a Subgrade Frost ProtectionThe physical and engineering properties of pumice soils were mainly depend on the degree of weathering, and the water retention of weathered pumice soils was very large, while that of the non-weathered ones was small. Therefore the former was frost-susceptible soils, the latter non-frost-susceptible soils. The non-weathered pumice soils could be used for a subgrade frost potection owing to little decrease in bearing capacity(CBR value) by freeze-thaw cycle.