Calculation of seasonal soil freezing depth by engineering and numerical methods

Abstract

Introduction. Provided by severe climatic conditions in the Russian Federation, seasonal soil freezing and emerging cryogenic processes cause frost heaving that negatively affect foundations and buried structures. As the magnitude of frost heaving forces significantly depends on the soil freezing depth, the assessment of soil freezing depth becomes very relevant.Aim. Calculation and estimation of the depth of seasonal soil freezing by engineering and numerical methods.Materials and methods. Calculations of soil freezing depth were performed for two sites composed of sandy loam and loam. Engineering calculations were performed according to four methods set forth in the normative documents, namely Recommendations on Thermal Engineering Calculations and Pipeline Laying in Areas with Deep Seasonal Soil Freezing, Handbook on Construction on Permafrost Soils, Recommendations on Accounting and Prevention of Deformations and Forces of Soil Frost Heaving, Recommendations on Forecasting the Thermal State of Permafrost Soils. Numerical calculations were performed in the Frost 3D and Borey 3D software systems. The experimental sites are located in the Tymovsky district of Sakhalin Oblast, where the Sakhalin-2 pipeline was laid.Results. The engineering methods for calculating the required depth of soil freezing give overestimated results when using a large range of climatic and soil parameters: air temperature, snow cover height and density, wind speed, convective heat transfer coefficients, total solar radiation, surface albedo, maximum elasticity of water vapor, etc. At the same time, the use of Stephan’s formula with a limited set of input parameters gives results close in values. The numerical methods showed close results among themselves, though 32–47 % more than the results of engineering calculations at bare ground surface.Conclusions. Research on the dynamics of soil freezing depth in field conditions is suggested to be carried out and compared with the results of engineering and numerical calculations to improve these methods.