Long-Term Field Subgrade Monitoring and Quantitative Hazard Assessment along the Qinghai–Tibet Highway in the Permafrost Region

Abstract

Herein, long-term field subgrade monitoring was conducted along the Qinghai–Tibet Highway (QTH) on the Qinghai–Tibet Plateau (QTP) to investigate the sustainable service performance of permafrost highway subgrade and quantitatively evaluate the hazards associated with subgrade differential settlement in permafrost regions at a local scale. In addition, five 60-m-long and 7-m-wide permafrost-subgrade test sites were built, and a parameter defined as the subgrade distress index (SDI) was introduced to develop a data-based quantitative model for assessing hazards associated with subgrade differential settlement. The 10-year monitoring results revealed highly random differential settlement values and locations at the field sites. Differential settlement hazard maps generated using geostatistics based on the monitoring results were beneficial for qualitative analysis of hazard locations and evolution. The hazard assessment results proved that damaged areas can be accurately identified through quantitative model implementation and that the third or fifth year may be a definitive time window for distress maintenance. A three-level early warning strategy for hazards associated with subgrade differential settlement in permafrost regions was suggested: Mild grade I (SDI = 0–0.1), Moderate grade II (SDI = 0.1–0.6), and Severe grade III (SDI = 0.6–1). Long-term monitoring and model assessment are expected to enhance decision-making for highway maintenance management in the permafrost regions.