Study On Temperature Characteristics Of Soil Body And Enclosure Structure Of Foundation Pit Overwintering

With the approach of 2020,the grand goal of realizing a well-off society in China will soon be achieved.In this final sprint stage,China needs to speed up the process of urbanization construction,and now faces the most serious problem is the scarcity of land resources.Therefore,the expansion and rational use of underground space will never stop.Based on the global temperature changes in recent years,the extremely harsh natural climate environment,the growing cold winter climate in some regions,the lowest temperature in winter constantly refresh the historical limit value,and this phenomenon occurs more and more frequently,which will cause many new problems about rock and soil.In seasonal frozen soil areas such as the three eastern provinces of China,a large part of foundation pit engineering will experience a long winter test.Some experience in the design of foundation pit in winter can only be considered as a factor of load foundation pit uplift,but can not find a specific theoretical model as a basic research in the process of construction and design.Therefore,it may also cause excessive deformation or even cracking of the retaining structure in the foundation pit,which may lead to some unpredictable hidden safety hazards and economic losses caused by the use of the foundation pit.In order to solve the problems of temperature stress of foundation pit subjected to the action of foundation soil,deformation and even cracking of enclosure structure,based on frost heave theory of frozen soil,this paper compares and analyses the temperature stress of foundation pit by means of experiment and theoretical calculation.In this paper,data are collected by outdoor model test and in-situ monitoring of foundation pit.Collection and research.Outdoor model tests:frozen fronts migrate and consolidation fronts transfer when soil is frozen,and the conditions of frozen fronts transfer must occur at the interface between solid and liquid,so a constant water supply from outside is needed.According to this freezing theory,using the outdoor winter cold atmospheric temperature Northeast China,the process of frost heave of outdoor soil under the action of extermal atmospheric temperature is simulated by self-made frost heave box.Taking the temperature characteristics of silt foundation pit during the wintering period as the research object,the freeze-thaw cycle process of soil under cold natural environment is tested,and the different atmospheric temperature of soil is obtained.The physical parameters related to the transient temperature field and frost heave are studied under the conditions of temperature field and temperature stress.In the field monitoring part,the real-time monitoring of the variation of the axial force of the pre-stressed anchor cable with the temperature in the retaining structure of the overwintering foundation pit is carried out.Finally,based on the test monitoring data obtained from indoor and outdoor tests,the theoretical derivation is carried out,and the relevant measured parameters are substituted into the deduced temperature field formula.The analytical solution of temperature gradient can be obtained.Finally,the soil temperature stress of the overwintering foundation pit is calculated and compared with the field monitoring data.The analysis results show that the monitoring axial force coincides with the theoretical calculation results,which verifies the above-mentioned rationality.The scientific nature of the theory.For the deformation phenomenon of foundation pit frost heave in winter,traditional protective measures such as electric heating belt and straw mat are adopted to heat the soil,but it will bring a lot of energy loss.It is advisable to adopt the flexible combination of piles.For example,under the premise of allowable deformation of foundation pit,steel sheet pile enclosure combined with anchor cable can be used to achieve the effect of green environmental protection.