Managing ice-rich permafrost exposed during cutting excavation along Qinghai–Tibetan railway: Experiences and implementation

There is widespread ice-rich permafrost over Qinghai–Tibetan plateau. The exposure and subsequently thawing of ice-rich permafrost result in serious engineering and environmental consequences. However, it is often inevitable to expose ice-rich permafrost during the construction of railway, highway, or any engineering structures in permafrost regions. In this paper, we described the hazards induced from ice-rich permafrost exposure including slope instability, thermal slumping, soil erosion, frost heave and thaw settlement along Qinghai–Tibetan railway. The leading factors resulting in the occurrence of hazards were reviewed. Various remedial measures applied during the construction of Qinghai–Tibetan railway were introduced. The operation effects on avoiding failure or minimizing the damage consequence were discussed. The results show that ice-rich permafrost exposure generally causes cutting failure unless proper countermeasures are applied. Slope instability is the most serious damage for ice-rich permafrost cutting. Frost heaving and thaw settlement tend to damage the surface treatments and have lesser effects on railway operation. Experience shows that Coarse-grain soil replacement with insulation and drainage system are the most common measures to be applied. Cement concrete framework measure is more popular than turf covering and insulation covering due to its construction convenience and less cost. The results indicate that the treatment of turf covering is more suitable for ice-rich permafrost exposure than insulation covering due to high long-term performance rating and surface deformation adaptability. Retaining wall is an effective remedial measure to prevent slope failure of deep cut in permafrost regions. The field investigation shows that design and construction methods to deal with the exposure and thawing of ice-rich permafrost along Qinghai–Tibetan railway are efficient and these experiences are helpful for other projects in cold regions.