| Frozen soil is the energy exchange result of lithosphere and atmosphere,which is an important part of cryosphere.Global climate warming and human activities are increasingly destroying the conditions of permafrost.The melting process of permafrost has a significant impact on terrestrial ecosystems,hydrology,geomorphology and construction and operation of engineering infrastructure.In the past hundred years,China’s annual average surface temperature increased significantly,which is greater than the average of the world at the same time,which is further enlarged in high latitudes.The surface soil thermal state is the comprehensive product of the energy and material exchange between the atmosphere and the land surface,and plays an important role in the soil geophysical process.Permafrost in Northeast China is in the south edge of Eurasia permafrost,mainly developing"Xing’an-Bergal"permafrost.The thermal stability of permafrost is poor,sensitive to climate change.The melting of permafrost leads to frequent engineering geological disasters in cold regions.The research and achievements of permafrost in China are mainly concentrated in the Qinghai Tibet Plateau,which has less reference because of its different distribution characteristics from those in Northeast China.At present,there are few research results on permafrost regions in Northeast China,mostly concentrated in the Great Hinggan Mountains and some local areas,and lacking large-scale permafrost research results in spatial regional for application in engineering practice.Therefore,this paper simulates the temperature distribution and change characteristics of permafrost based on MODIS surface temperature data,analyzes the influence of different permafrost temperatures on the disease of subgrade combination with field investigation and remote sensing surface deformation observation,and proposes treatment measures for permafrost subgrade in cold regions through highway disease distribution and numerical simulation.In this study,ANUSPLIN interpolation software is used to simulate the spatial distribution of average annual air temperature and ground temperature in Northeast China driven by terrain factors,analyze the changes of air temperature,ground temperature and ground frost number in the study area.Select suitable ground observation data through the correlation coefficient of average annua airl temperature,ground temperature and MODIS ground temperature data in the long time series.The MODIS surface temperature data was modified for vegetation impact,and the MODIS surface frost number in Northeast China was calculated using the modified MODIS surface temperature data.The temporal and spatial characteristics of the surface thermal state in the Northeast permafrost region were analyzed,and the response to the climate change was discussed.Combined with the observation data of frozen soil temperature in the field scientific observation,the numerical relationship between the remote sensing ground frost number and the permafrost temperature is established,the spatial distribution of the permafrost temperature is simulated,and the degradation characteristics of the permafrost and the evolution of the southern boundary are analyzed.Based on the disease investigation of several roads,combined with the C-band inversion of Sentinel 1,the surface deformation monitoring was obtained,and the influence of different permafrost temperatures on the type and distribution of highway diseases was analyzed.Numerical simulation of the impact of different replacement materials on the thermal stability of subgrade,and combined with subgrade treatment measures and disease conditions,comparative analysis of the impact of different permafrost subgrade treatment measures on subgrade deformation.The results show that:From 1970 to 2019,the air temperature and ground temperature showed an increasing trend in Northeast China,and the temperature change was of regional difference.The temperature increases greatly at the relatively low altitude;the rate of temperature rise in regions with relatively high latitudes(north of 46~°N)is higher than the national average level,which is amplified at high latitudes.The ground frost number in the north shows a downward trend,and the change of ground freezing index has a significant impact on the frost number.From 1960 to 2004,the annual average air temperature was consistent with the ground temperature,and the correlation coefficient was high;from 2004 to 2019,the ground temperature increased significantly,and the correlation coefficient decreased.From 2001 to2019,the correlation coefficient between ground temperature of meteorological stations and MODIS ground temperature was low.Affected by the change of observation measure of national meteorological stations from 2004 to 2006,and urban heat island effect,the regional representativeness of ground temperature data of meteorological stations decreased.Considering the impact of surface vegetation,the MODIS surface temperature data was revised with normalized difference vegetation index and forest canopy closure as parameters.The surface frost number under the influence of surface vegetation is taken as the standard for dividing the surface thermal stability in Northeast China,and the division results can also reflect the stability of permafrost.Permafrost with higher stability is mainly distributed in the terrain area with relatively low altitude and gentle slope.Slope aspect has little effect on the distribution of permafrost on a large scale.From 2012 to 2015,the distribution area of stable surface thermal state decreased continuously.Taking 2013 as the time node,the thermal state change of permafrost was divided into two stages:from 2003 to 2013 and from 2014 to 2019,with corresponding permafrost surface score of 32.79×10~4km~2and 27.10×10~4km~2.The permafrost temperature distribution area at-3～0℃accounts for 86.5%～94.1%of the total area.Compared with 2003-2013,the permafrost temperature increased from 2014 to 2019,and the permafrost area increased in the temperature range of-1～-0.5.The southern boundary of the northeast permafrost is relatively stable in the area with dominant altitude at the southern end of the Alpine Mountains and the Xiaoxing’an Mountains.,The permafrost layer in the Xiaoxing’an Mountains under the protection of forests and vegetation coverage,reduces the speed of the southern boundary moving north,and the speed of the permafrost degradation is faster than that at the higher altitude,but lower than the air temperature change speed.In 2010s,the southern boundary of the northeast permafrost was Erguna-Hailar-Arshan-Boketu-north of Gagedaqi(Songling)-Nenjiang-Bei’an-Qing’an-Yichun-Jiayin-Heihe.After passing the southern end of the Xiaoxing’an Ling,the southern boundary crossed its eastern slope and reached Heihe before it completely entered Russia.The degradation of the permafrost in Northeast China shows a spatial degradation trend from the periphery to the core area,and the relatively low permafrost degrades first.Through the combination of manual investigation and SBAS-In SAR technology,maked a statistics and analysis for the types,distribution and pavement deformation of highway diseases.It varies with the change of permafrost temperature.In areas with low permafrost temperature and relatively low terrain,the road diseases are mainly caused by uneven settlement of subgrade.In areas with high permafrost temperature,road diseases are mainly caused by irregular network cracks and wave deformation of pavement.As the temperature of frozen soil decreases,the continuity of highway disaster distribution increases.When the permafrost temperature is higher than-1.5℃,the permafrost thawing has a significant impact on the deformation of highway subgrade and pavement cracks,and the surface deformation is closely related to the permafrost temperature.The subgrade structure of block stone replacement can increase the upper limit of permafrost,reduce the scope of melting interlayer,and reduce the ground temperature of frozen soil,so as to protect the permafrost.This structure can not only improve the thermal stability of the subgrade,but also reduce the melting settlement deformation of the subgrade.Thus enhancing the mechanical stability of the subgrade.In the northeast permafrost region,the treatment measures of hot bar subgrade project have no obvious effect on cooling the subgrade,which have little effect on the permafrost subgrade protection.The melting process of high-temperature permafrost leads to the repeated rise and fall of the foundation water content and the reduction of the bearing capacity,which is the main reason for the uneven settlement of the subgrade and the formation of pavement cracks with multiple morphological characteristics.The research results make up for the lack of regional permafrost research,and can provide guidance and basic data for engineering and ecological environment related research. |
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