| The subway tunnels,which are to be built or built in Xi'an,are mostly in the collapsible loess stratum.Even some segments of deep loess strata with a thickness of over 30 m.And the groundwater is rich around these sections,and there is a great risk of water immersion in the construction or long operation of the subway.Therefore,the experimental research on the deformation characteristics of the deep loess tunnel under different water immersion conditions is carried out,and the results of the centrifuge model test are verified by numerical simulation,and the following conclusions are obtained.1.The fiber Bragg grating sensing system based on the TJL-3 centrifuge of Chang'an University can monitor the deformation of the tunnel model.The fiber Bragg grating sensor is small in volume,light in quality and few in lead,and has little interference to the centrifuge model test.At the same time,it can completely resist electromagnetic interference.More stable and more accurate.2.The centrifuge test shows that the soaking collapsibility of deep loess stratum will cause tunnel deformation,and the effect of deformation will be greatly increased with the increase of water immersion height(depth).The maximum bending moment of the arch and arch is 95.6kN m when the vertical half of the base longitudinal unevenly soaked in the base reaches 15 cm.During construction,foundation treatment for deep collapsible loess is needed.3.The centrifugal test shows that the submerged collapsibility of the basement layer of the deep buried tunnel and the soaking collapsibility of the overlying soil layer on the shallow buried tunnel will cause the tunnel structural bending moment value to be changed obviously,resulting in the deformation of the tunnel structure,and the deformation of the tunnel structure caused by different water immersion conditions is different.The transverse half collapsibility mainly causes the change of the axial bending moment of the tunnel.The maximum axial bending moment of the tunnel is 187.6kN m and 168.5kN m respectively when the base and overlying horizontal half collapsing.The longitudinal half collapsibility will cause the change of the circumferential bending moment of the tunnel section,and the tunnel cross section ring direction when the base and the overlying longitudinal half collapsing The maximum value of bending moment is 95.6 kN·m and 54.7 kN·m respectively.4.The numerical simulation results show that the deformation of the subway tunnel structure will be caused by the different water immersion conditions,which is in accordance with the law obtained by the centrifuge test.The change of the bending moment value of each point in the numerical simulation is smaller than that of the centrifugal model,because the numerical simulation can fully realize the ideal state of the uniform immersion in the submerged area.However,when the test is influenced by many factors,it is difficult to achieve uniform immersion,which will cause greater changes in bending moment. |
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