Design method for combined thermal stabilization of the railway roadbed foundation of transport structures in the permafrost zone

The operation of railway roadbeds in permafrost regions is accompanied by degradation of the frozen foundation soils, development of thermal subsidence and frost heave deformations. Traditional seasonally operating cooling devices have a fundamental limitation a long time to reach the design mode, during which subsidence accumulates and frost heave deformations develop in water-saturated clayey foundation soils. This limitation is due to the dependence of the freezing rate on the heat transfer coefficient of the cooling device, thermophysical characteristics of the soil mass, and climatic conditions of the site.

A design method for combined thermal stabilization of the railway roadbed foundation of transport structures in the permafrost zone has been developed, covering the full cycle from analysis of initial geocryological data to justification of the parameters of the active and passive stages of cooling device operation. The algorithm represents a closed iterative procedure, at each stage of which the adopted design decisions are verified against regulatory requirements for frost heave deformations and long-term thermodynamic stability of the soil mass.

A method for calculating frost heave deformations during foundation thermal stabilization has been proposed, based on an empirical logarithmic dependence of the volumetric heave coefficient on the radial freezing rate and numerical modeling of the stress-strain state of the roadbed-foundation system.

A criterion for selecting the heat transfer coefficient of the passive stage has been introduced, defining the permissible range and ensuring long-term maintenance of the formed negative temperature zone without thawing and without development of frost heave deformations beyond the maximum allowable value, accounting for predicted climate warming.

An approach to determining the equivalent heat transfer coefficient of combined thermal stabilizers using liquid nitrogen, based on the Nusselt criterion, has been proposed, enabling the transfer of laboratory test results to full-scale objects with modified geometric parameters without conducting repeated experiments.

Verification of the proposed calculation method was performed at the ‘Seven Larches’ test site in the Yamalo-Nenets Autonomous Okrug. Comparison of the calculated vertical displacements with field geocryological monitoring data demonstrated their quantitative agreement, confirming the reliability of the proposed method for calculating frost heave deformations during thermal stabilization of clayey soils with cooling devices.

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