To investigate the load-bearing characteristics of shallow permafrost and the patterns of road surface deformation in the permafrost regions of the Qinghai-Tibet Plateau, representative areas were selected for onsite road surface deformation surveys and in situ cone penetration tests. Greater penetration resistance ratio or cone tip resistance correlates with reduced penetration depth during the Cone Penetration Test (CPT), indicating stronger load-bearing capacity in the respective area and consequently lesser road surface settlement. Smaller values of penetration resistance ratio or cone tip resistance, coupled with greater thickness in the region, result in more severe road surface deformation. Based on the penetration resistance ratio and cone tip resistance of the permafrost strata, the concept of the envelope area ratio is proposed to evaluate the load-bearing capacity of shallow permafrost. Under identical standard conditions, a larger envelope area ratio of either the P_s-d or q_c-d curves indicates stronger load-bearing capacity of the permafrost strata and lower surface settlement risk. Empirical formulas correlating the envelope area ratio of the P_s-d and q_c-d curves with the maximum value of road surface settlement were established, with determination coefficients exceeding 0.9.

This study conducted indoor consolidation tests on the aging road and natural ground foundational soils from the G214 permafrost section in the Yellow River source area to compare their consolidation characteristics. The results revealed that the consolidation deformation of the aging road foundation soil was significantly lower than that of the natural foundation soil, with a flatter consolidation curve. In the aging road foundation, the 2.5-4.3 m soil layer affected by annual temperature fluctuations exhibited void ratio variations 2.05 times greater than other layers. However, the variation in void ratio in multiple layers of the natural foundation was greater than that in the aging road foundation. The maximum settlement of the aging road foundation originated from the 2.5-4.3 m layer with smaller shallow settlement, while the natural foundation showed dominant shallow settlement followed by the 2.5-7.5 m layer, reaching a total settlement 1.37 times that of the aging road foundation. A layered treatment strategy is recommended: applying techniques adapted from soft foundation treatment to shallow layers while implementing thermal stability protection for permafrost in deeper layers, achieving a coordinated approach between deformation control and permafrost environmental protection.

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.