Abstract

Fundamental understanding of permafrost thawing behaviour and the ability to model it numerically are vital to predict the effects of permafrost thawing on infrastructure. This paper presents insight into numerical modelling of frozen soil using frozen-unfrozen soil constitutive model using finite element software PLAXIS. Frozen-unfrozen soil model is a thermo-hydro-mechanical (THM) coupled constitutive model. Critical parameters required for numerical modelling of frozen soil are summarized and how to obtain them are presented. Examples of how to utilize numerical modelling to understand the permafrost thawing effects are provided for a buried pipeline and an oil well. The results highlight the risk to integrity of surface and buried structures due to permafrost thawing subsidence effects.

Introduction

Thawing of permafrost and the resulting effects on environment and infrastructure are going to be a major challenge to mankind in this century. Permafrost is ground that remains continuously frozen, for two or more years, located on land or underwater. Permafrost thickness can range from a few meters to in excess of 600m below ground level. Permafrost covers 20% of the earth's land surface including the arctic, Antarctic and mountainous regions. Human activities and climate change are accelerating the thaw of permafrost regions, leading to detrimental environmental and engineering issues.

In 2019, the Inter-governmental Panel of Climate Change (IPCC) concluded that by 2100, near surface permafrost could degrade by 70%, representing a significant change in environmental conditions globally. Therefore, understanding the effect of permafrost thaw and the ability to model its effects are of critical importance to allow for proper risk management and mitigation of existing and proposed infrastructure.

Permafrost thawing has several impacts, but two key impacts are the release of locked in carbon (methane & carbon dioxide) and thaw induced settlements. Thawing of permafrost can lead to foundation settlements which in turn can have major damage to infrastructure and buildings. Subsidence is the major geotechnical phenomenon related to permafrost thaw, caused by several mechanisms. Understanding how permafrost thaw may affect foundations, pipelines and sub-structures is critical to ensure risks is managed and mitigated. Most structures in permafrost areas are not designed to account for permafrost thawing effects, thus subsidence from permafrost thawing would cause additional strains which could lead to failures (example is the 2020 Norilsk diesel oil tank failure near Norilsk in Russia).

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