Fighting highway subgrade settlement on the roof of the world

The Qinghai-Tibet Plateau houses China’s largest permafrost region, where highways have served for over seven decades. However, recent decades have seen rapid warming (0.35°C/decade, twice the global average) and increasing precipitation, thickening thaw layers and reducing bearing capacity beneath roadbeds. Existing construction strategies largely rely on maintaining frozen soil through embankment elevation, insulation, heat pipes, block stone layers, and passive cooling structures. Yet field observations show that uneven settlement, thaw-induced deformation, cracking, and slope sliding remain widespread, particularly in ice-rich foundations. With permafrost degradation becoming inevitable under climate change, passive preservation alone can no longer ensure long-term safety. Due to these challenges, deeper research into foundation-treatment-oriented design is urgently needed.

Researchers from the Research Institute of Highway Ministry of Transport, China, published (DOI: 10.26599/HTRD.2025.9480065) their findings in Journal of Highway and Transportation Research and Development (2025), analyzing large-scale field monitoring data from the Qinghai-Tibet Highway, Gongyu Expressway, and G214/G109 routes. The article, accepted on June 20, 2025, systematically reviews historical design evolution, reveals causes of roadbed failures, and introduces a new engineering principle — treating permafrost foundations through coordinated pavement-subgrade-foundation design to improve stability under long-term warming.

Field drilling, geophysical surveys, and deformation monitoring show severe wave-like settlement, longitudinal cracking, thaw subsidence, and slope failure across multiple road sections. In high-temperature permafrost zones, the permafrost table has sunk to 7–10 m, forming thick thawed interlayers that retain water, trap heat, and accelerate degradation. Settlement depth correlates strongly with initial ice content — roadbeds over ice-rich frozen soils experience more frequent and deeper subsidence.

Traditional “protect-permafrost” strategies rely on elevation, insulation, block-stone structures, heat rods, ventilation pipes, and surface cooling. While effective initially, long-term performance varies due to hydrology, groundwater, and seasonal freeze-thaw cycles. The study emphasizes shifting from passive protection to active foundation treatment, including excavation and replacement, drainage improvement, deep reinforcement, and combined structural solutions for ≥3 m thaw-affected foundations.

The authors outline future needs: refined geological–hydrological investigation, performance-based evaluation systems, real-time monitoring, and new treatment materials/equipment suitable for high-altitude construction. A collaborative pavement-subgrade-foundation design model is proposed, enhancing resilience under persistent warming trends.

“The Qinghai-Tibet Plateau is entering a new phase of permafrost degradation,” the author writes. “Highways must no longer rely solely on passive thermal protection. Instead, we should view the foundation as an active engineering object — one that can be re-shaped, reinforced, and improved. Only by treating permafrost foundations directly and developing long-term assessment standards can we manage settlement risks and secure transportation stability for decades to come.”

The proposed paradigm shift could benefit major highways, railways, oil/gas pipelines, and other infrastructure crossing fragile permafrost terrain. By integrating monitoring-based foundation reinforcement, drainage control, and thermal-mechanical co-design, engineers may reduce maintenance frequency, prevent road cracking and subsidence, and lower long-term repair costs. The approach also supports climate-resilient development in plateau regions, ensuring safer transport corridors for trade, emergency logistics, and ecological conservation. Continued investment in monitoring systems, materials research, and deep treatment technology will be key to future applications.

Funding information

This study was supported by the National Key Research and Development Program of China, No. 2023YFB2604800, the Key Research and Development Program of Xizang, No. XZ202301ZY0038G.

About Journal of Highway and Transportation Research and Development

The Journal of Highway and Transportation Research and Development (English Edition) (HTRD), established in 2006 and sponsored by the Research Institute of Highway, Ministry of Transport, is a quarterly academic journal dedicated to advancing global highway and transportation research. Since 2024, it has been co-published by Tsinghua University Press and operates as an open access journal, with earlier articles (2006–2023) accessible via the ASCE Library. HTRD publishes innovative and practical studies covering civil and transportation engineering, intelligent transport systems, automotive engineering, logistics, environmental engineering, transportation economics, and road construction machinery. Upholding the principles of academic exchange, technological innovation, and international engagement, HTRD aims to become a high-impact journal showcasing scientific discoveries and supporting transportation development worldwide.