An Improved Approach for Frost Depth Evaluation Considering Unfrozen Water in Frozen Soil

ABSTRACT: The frost depth is known to depend on the unfrozen water content in frozen soil. However, current engineering practice of frost depth calculation often ignores the unfrozen water and assumes that all water in the soil completely freezes below 0°C. Fine-grained soil can contain significant amounts of unfrozen water at freezing temperature, particularly for fine-grained soil in the range of temperatures of practical importance for frost depth. The assumption of fully frozen water in soil often leads to a less conservative underestimation of the frost depth by about 15% to 30% for fine-grained soils. There is a need to develop a practical and industry-friendly approach for frost depth assessment, which takes account of the unfrozen water content in frozen soil. The work by Tice et al. (1976), Anderson and Ladanyi (2003) recommended a correlation between unfrozen water in soil and temperature with a good match with the test data. But this approach requires a non-standard laboratory test (liquid limit test with N=100), which limits its application in engineering practice for commercial projects. This paper proposed an improved approach, which simplifies the correlation and does not need any non-standard tests for the input parameters. It requires only two basic input soil parameters, total initial water content and liquid limit from routine Atterberg limit tests, both of which are usually available in most engineering projects. A sensitivity study was carried out to evaluate the proposed approach using laboratory tests of about 20 soils from the literature. The results shows that the proposed correlation matches well with the lab data and conventional approach and is considered suitable for practical engineering assessment of frost depth.