| Loess is a kind of special engineering properties of soil,collapsible,big hole,under voltage tightness and other characteristics,widely distributed in the northwest of China,in Gansu,Shaanxi and other areas of collapsible loess accounted for about three fifths of the total area of loess.With the proposal and implementation of the "The Belt and Road" national strategy thought,China has further strengthened the construction of transportation infrastructure in the western region,and a large number of loess tunnels have emerged in the process of the construction of high-grade highways.However,due to the structural damage of loess after soaking,it is easy to produce collapsible deformation,and the destruction of the loess structure will lead to the damage of long-term mechanical properties,in the later stage of tunnel operation,the large deformation of collapsible loess caused by rheological effect may affect the stability of tunnel structure.Therefore,from the point of the rheological characteristics of collapsible loess,analysing the stability of the tunnel has important theoretical significance and engineering application value.In this paper,relying on the Gansu province science and technology major projects "Gansu collapsible loess area highway construction complete sets of technical research",the Gansu Lanzhou Ding-yuan tunnel as the research object,combined with the rheological characteristics of loess is studied on the stability of tunnel.On the basis of widely consult relevant literature,first of all,the three axial creep test is carried out on the undisturbed loess sample,and the rheological constitutive model is established according to the stress-strain curve.Then the tunnel model was established by using FLAC3 D software,the process of tunnel excavation was simulated,and the rheological behavior of surrounding rock was analyzed.The long-term stability evaluation of collapsible loess tunnel is carried out through the change trend of surrounding rock displacement and the mechanical characteristics of lining structure.The main results of this paper are as follows:(1)Through the analysis of the results of the three axial creep test of the original loess samples,the results show that the loess samples are undergoing a process of rapid creep,steady creep,unloading rebound deformation will occur andthe remaining part of the permanent deformation.The rheological properties of the loess samples are in good agreement with the rheological properties of the four parameter Burgers model,indicating that the tunnel in collapsible loess has obvious rheological effect,should consider the effect of long-term rheological behavior of surrounding rock on the stability of tunnel.(2)By simulating the excavation process of tunnel,the stress and displacement of tunnel surrounding rock under different working conditions are analyzed.When the excavation step is in the step method,the original stress is released,the stress field and displacement field are changed greatly;with the excavation time after initial support,the constraint of the surrounding rock deformation and the whole construction process,with the redistribution of stress of the tunnel,not be damaged.(3)In the process of tunnel excavation,the deepest place is the most dangerest,the accumulated sedimentation value in the arch crown is 28.45 cm,the value of upheaval is 20.07 cm,the shape of The plastic zone is x and area increase gradually.(4)Setting on the thirty years of creep analysis on the surrounding rock after completed the second lining,the research shows that the rheological behavior of the surrounding rock has a great influence on the deformation of the surrounding rock in the first 230 days,the accumulated sedimentation value in the arch crown is 3.2 cm,It accounts for 15 percent of accumulated sedimentation value,rock deformation rate increase with time gradually decreased,finally the surrounding rock is in stable state,the lining structure in the late stress is also in the safe range. |
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