Different Active Thaw Protocols for High Ice-Content Permafrost Layer: A Laboratory and Site Study

With global warming, engineering measures based on permafrost protection are still challenging to inhibit high ice-content permafrost thawing and subsidence in some areas of the Qinghai–Tibetan Plateau (QTP). Hence, early permafrost thawing is an effective method to reduce the later settlement of the upper infrastructure. In this study, thawing tests were carried out on permafrost using steam and heater tubes in the laboratory and on-site, respectively. The results show that steam can rapidly melt frozen soil within a radius of 5 cm, and it took 4 and 12 h to completely melt 0.09 m³ of frozen soil with 20% and 40% ice content, respectively. After thawing, the water content of frozen soil with 20% and 40% ice content at a distance of 5 cm from the steam diffusion tube was 1.68 and 1.37 times the design ice content, respectively. In contrast, the water content of frozen soil exceeding 15 cm was approximately equal to the design ice content after complete melting. The cone penetration test can be used to evaluate the melting range of permafrost. The high-power heating tube designed in this study can thaw high ice-content permafrost with the radius of at least 20 and 35 cm, respectively, within 2 and 4.5 h, and the melting rate along the depth direction was lower than that in the radial direction.