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，作者研究了冻胀和冻融循环对火山灰土物理和工程性质的影响，以及浮石土作为路基防冻的适宜性。主要研究结果如下：1.火山灰土的冻胀虽然冻胀是由于土壤水分从未冻部分向冻锋方向运动所致，但对于火山灰土而言，其冻胀运动主要受持水性和渗透性的影响。火山灰土的膨胀量大于非火山灰土，但随着土样初始含水率和容重的降低而减小。2.冻融循环对火山灰土物理和工程性质的影响火山灰土具有很大的持水能力，在田间湿润条件下具有较高的持水量。因此，冻融循环过程中由于水(液体)相向冰(固)相转变而引起的物理和工程性质的变化。冻融过程中土样的导热系数增大，液限水含量高的重塑土样强度增大。3.浮石土对路基防冻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大，而未风化浮石土的持水性较小。因此，前者为霜冻敏感土，后者为非霜冻敏感土。由于冻融循环对路基承载能力(CBR值)的影响很小，未风化浮石土可用于路基防冻。

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.