Cooling effect analysis of thermosyphons used in Qinghai-Xizang Highway in permafrost regions based on GPR measurement
The warming and humidifying climate on the Qinghai-Xizang Plateau of China is causing permafrost degradation at a faster rate,which is affecting the stability of infrastructure such as highways and railways on it.To resolve this problem,thermosyphons have been widely applied to protect the degrading permafrost in North-east China and the Qinghai-Xizang Plateau.The thermosyphon has the characteristic of active unidirectional cooling.Existing researches often use numerical simulation or borehole temperature measurement methods to an-alyze its cooling effect on permafrost foundations.With the development of geophysical exploration technology,ground penetrating radar(GPR)technology provides a new research method for frozen soil engineering,which can obtain continuous data without causing damage to structures.The section of the Qinghai-Xizang Highway from Tuotuo River to Tanggula Mountain Pass was selected as the research area,and GPR technology is used to study the cooling effect of thermosyphons.Based on the investigation of road problems,three typical road sec-tions were selected,where double-sided and single-row vertical thermosyphons,single-sided and single row oblique thermosyphons,and adjacent non-thermosyphons were placed,respectivley.GPR technology was used to detect and analyze structural damage and underlying permafrost distribution.Meanwhile,combined with on-site investigations,the impact of different thermosyphon placement methods on the cooling effect of frozen soil embankment was evaluated.The results indicate that the cooling effect is as follows:double-sided and single row vertical thermosyphons have better cooling effect,followed by single-sided and single row oblique thermo-syphons and non-thermosyphon.The distribution of the permafrost layer beneath the double-sided and single-row vertical thermosyphon embankment had good continuity,with an increase of 0.47 m in the upper limit of permafrost compared to the natural surface near the road,and the road structure was entire.The permafrost layer under the single-side and single-row inclined thermosyphon embankment had general continuity,and its perma-frost table was close to that of the natural surface.There were areas where structures loosened and cracks hap-pened in the embankment structure.The continuity of the permafrost layer under the non-thermosyphon embank-ment was lower,and the degradation of permafrost was significant,its permafrost table has degraded by 0.80 m compared to the natural surface.The embankment structure showed large areas of looseness and cracks,and there was water accumulation in some areas.Meanwhile,permafrost degradation can trigger road engineering damages.Comparison showed that the single-sided and single-row oblique thermosyphon embankment and the adjacent non-thermosyphon embankment with permafrost degradation showed loose embankment structures and developed some cracks,and were prone to uneven settlement,cracks,potholes,and other problems.GPR test-ing can effectively present the distribution of permafrost beneath roads and the characteristics of embankment structural damage.Furthermore,it can used to analyze the mechanism of road surface problems and to provide scientific basis for highway maintenance.Analysis shows thermosyphons can effectively slow down the degrada-tion rate of permafrost,but different placement methods have a certain impact on the cooling effect,the single-sided layout of thermosyphon for high embankments does not cool the warming permafrost.Therefore,it is nec-essary to scientifically and reasonably carry out the correct design,standardized construction,and effective oper-ation and maintenance of thermosyphon embankments based on the thermal state and structural characteristics of the roads.This can raise the permafrost table under the embankment and reduce or slow down engineering prob-lems caused by permafrost degradation.This study has important practical significance for promoting thermosy-phon to be widely used and for improving the serviceability of highways in permafrost regions.
万方数据
维普
