The Characteristics Of Permafrost Degradation In Lesser Khingan Mountains Of China And Its Effect On Road Subgrade Stability

In recent years,the climate change has more significant influence on the global environme nt.In the Northeast of Heilongjiang Province,the northeast of Inner Mongolia and Tibet Platea uin,there are two permafrost regions between different geological conditions and environment al conditions.As climate change intensively,the high latitude frozen soils in the northeast of China and permafrost in Tibet Plateauin have different degree of degradation.These phenomen ons result to extreme weather and geological disasters.And seriously affecting China's environ mental resources and engineering structures,as well as people's life and property safety.Lesser Khingan Mountains region in the northeast of China located on the south e dge of Eurasian permafrost area.It is a part of discontinuous permafrost regions.Perm afrost degradation caused many engineering geological problems and environmental geol ogical problems,such as differential settlement of the embankment,landslide and slope saliva ice,etc.People explored the permafrost along the highway of Xiaoxinganling reg ion,in order to learning the distribution,degradation characteristics of permafrost,and t he influence of the of highway roadbed's stability.The research area on this paper is Beian-Hehe reconstruction highway at K160-K182 section through the northwest of Xiaoxinganlin g.This paper studies the permafrost in the region along the road.Through the study area K161,K178,and K181 sections geological drilling,identifi ed the research section of the permafrost distribution and stratigraphic distribution;Thro ugh on-site monitoring of ground temperature lasted from 2009 to 2016,we get the ground te mperature change of the the monitoring points' subgrade and foundation in the highway constru ction and after highway operation in different depths.Through the K161,K181 sections of drilling soil samples of rock and soil physical and mechanical testing,we got various 1 ayers of natural water content,dry density and other physical indicators and cohesion,angle of internal friction,elastic modulus and mechanical indices.Through the several stu dy of regional sections of the high density resistivity method and geological radar detection,ge tting years' underground soil resistivity distribution and radar wave reflection image with the se asons.Combining with the frozen soil resistivity model constructed in this paper,the dielectri c model and the rock soil body resistivity,dielectric constant in indoor test,grasp the change c haracteristics of rock and soil resistivity and dielectric constant.Field geological drilling data a nd ground temperature monitoring data interpretate and analyse the high density resistivity met hod and geological rada detection results.In order to study the roadbed deformation,whic h caused by roadbed filling,layered filling of operation and permafrost melting,Respec tively for K161 + 440 and K181 + 400 section deformation of subgrade for on-site m onitoring and finite element numerical simulation.Prediction of subgrade settlement and deformation of permafrost completely melts and effects analysis on subgrade stability i n permafrost degradation.The results show that:(1)The temperature of permafrost in the study area is rising,In September 2009,the lowest temperature of permafrost in K161 sections was-0.9?-1.2?,in September 2016,the lowest temperature of permafrost in K161 sections was-0.4?-0.6?.the uppe r and lower position of the permafrost layer affected by seasonal temperature showed the ups a nd downs like wave,from the overall trend,permafrost is influenced by highway constructio n and climate change,and the degradation trend is obvious,presenting thinner in thickness,hig her temperature,which the upper permafrost lawyer under the roadbed is significantly decrease d,lower limit of permafrost degradation increased significantly,permafrost outside road slopi ng mainly degenerate in the form of following limited shift.(2)Permafrost in the study area are mainly located in low-lying valleys,K161 secti on maximum thickness of permafrost within the domain of the road was 9.5m,K181 r oad was 4.0m.K161,K181 stretch of peat,silty clays,gravel and shale strata in permaf rost to thaw after the soil,its sharp drop in shear strength and elastic modulus;With t he thawing of soil consolidation and shear strength and elastic modulus and improved.(3)The geophysical results are basically consistent with ground temperature monitoring re sults,each measuring high resistivity region area and soil resistivity are decreasing within th e line of electrical profile area in the study and the abnormal area of electromagnetic wave i n permafrost area within the radar profile has reduced,show that the permafrost layer in th e section of the line degenerates,the upper limit of permafrost layer decreases,the lower limi t moves up,the temperature increases,the area decreases(4)The field monitoring data and the simulation results are basically the same.The post-working vertical deformation for the permafrost melting of K161 + 440 cross section roadbed is large.By the end of October 2016,the roadbed vertical deformation of the section after construction is up to 24cm.With the melting of the permafrost,the settlement of the section will continue to increase.Roadbed stability is poor,has seriously affected the safety of the road.The post-working vertical deformation for the permafrost melting of K181 + 440 cross section roadbed is small.By the end of October 2016,the roadbed vertical deformation of the section after construction is only 5cm.The roadbed has reached a stable state,roadbed stability is well.