Highway foundation treatment techniques in permafrost regions of the Qinghai-Tibet Plateau: Current practices and future trends

In the context of global warming, existing highways in the permafrost regions of the Qinghai-Tibet Plateau are facing multiple challenges, including surface settlement, roadside water accumulation, groundwater saturation, thickening of melting interlayers, and continuous permafrost degradation. These issues pose serious obstacles to the remediation and rehabilitation of existing highway subgrades in the region. This paper reviews the evolution of foundation design methods in permafrost regions abroad and traces the development of highway subgrade design approaches specific to permafrost areas in China. Based on the latest field investigation data, the causes of subgrade settlement along existing highways in the Qinghai-Tibet Plateau are analyzed, and areas for improvement within the current design system are identified. The study proposes the advancement of a third design principle-“proactively improving foundation conditions”, to complement the existing principles of “protecting permafrost” and “allowing permafrost thawing”. It introduces the concept of “treating permafrost foundations” and presents a collaborative design methodology for the pavement-subgrade-foundation system in permafrost regions. This integrated approach enables a more nuanced analysis of how climate-induced changes in foundation characteristics influence subgrade deformation and structural stability. Furthermore, this paper categorizes and discusses the types, characteristics, engineering applications, and performance of existing subgrade treatment techniques, including shallow foundation (0-3 m) and deep foundation (>3 m) treatments. It highlights urgent technical challenges that need to be addressed, such as conducting more refined hydrological and geological investigations, improving the engineering geological evaluation index system, establishing long-term performance assessment methods for permafrost treatment techniques, and developing new treatment materials and equipment for treatment. This research aims to provide scientific support for the effective management and rehabilitation of highway subgrade subsidence in the permafrost regions of the Qinghai-Tibet Plateau.