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

在本研究项目中，作者调查了冻融循环对火山灰土的物理和工程性质的影响，以及浮石土作为路基防冻材料的适用性。1.火山灰土的冻胀性火山灰土的冻胀性是由于土壤水分从未冻区向冻结前沿的运动而引起的，但火山灰土的冻胀性受土壤持水性和渗透性的影响较大。火山灰土的胀缩量大于非火山灰土，但随土样初始含水量和容重的减小而减小。2.冻融循环对火山灰土物理工程性质的影响火山灰土具有很强的持水性，在田间湿润条件下具有很高的含水量。因此，冻融循环引起的物理和工程性质的变化是由于水（液体）到冰（固体）的相变。冻融循环可提高重塑土的导热系数和强度。3.浮石土作为路基防冻材料的适宜性浮石土的物理和工程性质主要取决于风化程度，风化浮石土的持水性很强，而非风化浮石土的持水性很弱。因此，前者为易霜冻土壤，后者为非易霜冻土壤。非风化浮石土冻融循环对承载力（CBR值）影响较小，可用于路基防冻。

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.