Theoretical Research Of Temperature Control On Artificial Ground Freezing Method Applied To The Cross Passage Of Zhengzhou Metro Line 3

With the increasing development of metro in city of China,artificial ground freezing method(AGF)is more and more used in practical underground engineering.The physical and mechanical properties of the soil will be changed during the freezing process,meanwhile,which will take effects on surface buildings,underground structures and underground pipelines.Based on the design document of Zhengzhou metro line 3,the mechanical properties of sily soil,cooling temperature and different locations of cross passage were studied by tests in laboratory and numerical calculation,the main research results can be summarized as follows:(1)For unfrozen silty sand,the cohesion and internal friction angle are all negatively correlated with the water content,when the moisture contents of soil samples are 13.8%,19.5% and 25.2%,the corresponding values of cohesion and internal frict ion angles are 41 k Pa and 28.47°,30 k Pa and 22.63°,10 k Pa and 16.57°,respectively.The curves of stress-strain showed strain hardening characteristics.(2)For frozen silty sand,the cohesion increased obviously with the decrement of cooling temperatures,however,the increasing amplitude of internal friction angle was little.As the moisture content of soil sample at-1?increased from 13.8% to 25.2%,and when the temperature is-1?,corresponding values of cohesion are 137 k Pa?182k Pa and 296 k Pa,and the internal friction angle are 31.4°,33.1° and 35.5°,respectively.When the temperature is-5?,corresponding values of cohesion are 370 k Pa?451k Pa and 525 k Pa,and the internal friction angle are 30.4°,40.5° and 44.1°.When the temperature is-10?,corresponding values of cohesion are 528 k Pa?642k Pa and 770 k Pa,and the internal friction angle are 37.7°,41.4°and 46.7°.The curves of stress-strain showed strain softening characteristics.(3)The calculation model of cross passage between Erqi square and Shuncheng street station of Zhengzhou metro line 3 by AGF was established to analyze the impact at different cooling temperatures.The results show that the average temperature of frozen wall of sides,vault crown and inverted arch fell to-10? and frozen wall thickness reaches 2m are 40 days,33 days,21 days and 15 days,respectively.The maximum vertical frost heave displacements of ground surface are 4.8mm,4mm,3.34 mm and 2.78 mm when the temperature are-20?,-25?,-30? and-35?,respectively.When the cross passage was excavated under nature condition,the settlement displacement of ground surface is 51 mm.The maximum settlement displacement of ground surface are 6.7mm,3.6mm,1.5mm and 0.9mm when the cross passage is excavated after 40-day freezing at different temperatures mentioned above.(4)The deformation characteristics of cross passage with different buried depths under excavation were analyzed when the surrounding ground was frozen or unfrozen.The results show that the plastic deformation scope of unfrozen cross passage under excavation is 2.5m to 3.8m.When the temperature is-30 ? there is no plastic deformation scope during the construction.When the buried depths of cross passage increased from 10 m to 30 m,the maximum frost heave deformations of the ground surface are 6mm,5mm,2.7mm,1.3mm and 0.5mm respectively.