Study On Chemical Reinforcement Measures Of Thawing And Subsidence Of Permafrost Foundation With High Temperature And Ice Content

High temperature-high ice content in temperature rise of permafrost under the action of heat has strong compressibility,and low mechanical strength rapidly,the permafrost of qinghai-tibet railway roadbed stability poses a potential threat,and has set up a section in the embankment settlement,cracking and other diseases caused by in order to keep the permafrost roadbed stability,both of the widely used in projects "permafrost protection" and "cooling roadbed" approach.However,in the context of global warming,such measures are bound to have some limitations.Based on the engineering background of qinghai-tibet railway,this study intends to use the conventional land foundation treatment method as a reference to reinforce the high-temperature and high-ice permafrost subgrade with soil curing agent,so as to provide a new idea for the treatment of thawing and subsidence diseases of the permafrost subgrade.The optimum type and proportion of curing agent were determined by laboratory test in negative temperature environment.The research results have good engineering practical value and academic practical significance.This paper mainly carried out the following research work and obtained relevant research results:Firstly,after preliminary investigation and feasibility test of the experimental scheme,two curing agents were determined to be ordinary Portland cement and sulphoaluminate cement respectively.Secondly,the mechanical properties of high-temperature-high-ice-content permafrost after solidification were studied.The freezing-settlement test,K0 consolidation test and low-temperature triaxial test were carried out on the solidified soil under the action of gravity when the temperature rose.After the addition of 9%sulphoaluminate cement for reinforcement,the coefficient of freezing-settlement was5.2% lower than that of the unsolidified soil.When 9% Portland cement was added,the melting and settling coefficient was 4.12% lower than that of uncured soil.According to the test results,for both kinds of cement,the optimal content is 9%.Considering engineering disturbance,the lower limit of actual engineering content should be set at5%,and the curing effect of sulphoaluminate cement is better than that of ordinary Portland cement.Third,the NMR analyzer imported from Britain was used to conduct laboratory experiments on the unfrozen water content of high-temperature and high-ice-content frozen soil after solidification,and the change curve of the unfrozen water content and temperature was obtained.When ordinary Portland cement was added with 9%,theunfrozen water content of the solidified soil was 5.58% lower than that of the unsolidified soil,and when sulphoaluminate cement was added with 9%,the unfrozen water content of the solidified soil was 5.89% lower than that of the unsolidified soil.Then,the expressions of the elastic modulus of frozen soil and the content of unfrozen water were established,and the solidification mechanism was analyzed.Finally,finite element software is used to establish the model of qinghai-tibet railway subgrade.Under the combined action of heating and heat absorption and upper load,the maximum settlement appears at the center of the subgrade,and there is differential settlement.At the center of subgrade,the initial settlement of uncured soil was-6.56 cm.When the content of ordinary Portland cement was 9%,the settlement decreased by 57.3%.When the content of sulfoaluminate cement was 9%,the settlement decreased by 61.6%.It can be seen that the reinforcement effect is very significant,greatly improving the stability of permafrost subgrade.