| In recent years,with the development of Xi’an subway construction projects,some subway intervals need to go through the collapsible loess area.At the beginning of the construction,influence of loess on tunnel does not appear with no soaking condition,influenced by the objective factors,such as rainfall fissure infiltration,the river water seepage,tunnel excavating surface catchment effect,may lead to a change in water rate around the tunnel after the subway was built,that could result in the long-term operation of state changes and tunnel structure stress change,threaten the safe operation.Therefore,it is of great significance to study the influence of the collapsible loess layer on the subway tunnel and the treatment technology of the tunnel basement.Based on Xi’an subway Lintong line’s engineering background(line 9:Zhi Yang five road~ Zhi Yang square interval),this paper studies the radial surrounding rock pressure and the surrounding rock pressure and the stress and deformation of tunnel lining structure in the subway tunnel crossing the collapsible loess layer,and analyzes and summarizes the treatment technology of the tunnel foundation.The main results are as follows:1.Through the geotechnical centrifuge model test and numerical simulation,the pressure of the surrounding rock of the tunnel lining and the surrounding rock pressure in the surrounding rock are studied.The results are as follows:(1)With the process of soaking in the loess layer,the stress of tunnel lining is redistributed,and the pressure of the tunnel radial surrounding rock and the surrounding rock pressure of the tunnel are all increasing;(2)Through the change of lining stress ratio and the decrease of pressure arch range,it is indicated that the bearing capacity of surrounding rock is weakened due to stratigraphic immersion,resulting in the strata pressure which was originally assumed by the surrounding rock in the soil and transferred to the lining structure.Through analyzing the deformation of the model and the stress and deformation of lining structure,it is found that the collapsibility of base and the non-uniform settlement of foundtion will have greater impact on the surrounding rock and lining structure in terms of surface settlement,structural stress and non-uniform deformation.2.According to compare the different buried depth of basement compression stress with initial collapse pressure,tunnel base within a certain range of compressive stress is smaller than the initial collapse pressure,and the range gradually decreases with the depth of tunnel increases.Consequently,from the point of of view of the perspective of collapsible loess foundation treatment,we should determine the influence scope of the compressive stress of the foundation under the tunnel burying depth firstly.When the thickness of the collapsible soil layer of the tunnel foundation is smaller than the calculation range,the collapsible loess of the foundation can not be specially treated,and it can be treated according to the general loess foundation.3.The treatment principle and treatment method of basement of subway tunnel are discussed and summarized,with the underground excavation of subway as the research object,the preliminary design of the scheme is carried out according to the specific conditions,and the feasibility of the tree root pile treatment technology is verified by the demonstration of the bearing capacity and effect after treatment.Water immersion in loeess layer has detrimental effects on subway engineering.studying based on the influence of loess mechanical properties of tunnel structure and surrounding rock and putting forward the effective treatment of collapsible foundation,can provide the basis for loess area iron pre design and post operation. |
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