| Subway,which also known as urban rail transit,got the favour of people because of many advantages.Subway construction in China's large cities are in full swing,and many cities are under construction or have been built subway lines.Nanning as the capital of the Guangxi Zhuang Autonomous Region and ASEAN Expo permanent host city,because of the large population,is also facing the huge traffic pressure,so the city has planned for the 8 subway lines many years ago and several lines at the same time to carry out construction.Metro Line 1 officially started construction in 2010,was fully opened to traffic in December 2016,so Nanning has become China's first ethnic minority areas to open the subway city.Silty sand is widely distributed in our country.According to the previous geological survey data,Nanning area is distributed with a lot of silty soil strata.After the completion and open of the Nanning Metro tunnel,under the cyclic loading,the dynamic response and long-term cumulative deformation of silty soil layer will occur,affecting the stability and safety of subway operations.Therefore,the dynamic characteristics of saturated silt in Nanning area are obtained by carrying out a series of static and dynamic triaxial tests,then the improved constitutive model is used to simulate the experimental process and the applicability of the improved model is verified by comparing the numerical results with the experimental results.Finally,the numerical simulation carried out by using this model and the empirical formula are used to predict the long-term settlement of silty soil in Nanning area under the subway operating load.The research results of this paper can be summarized as follows:(1)With the increase of consolidation stress,the shear strength of saturated silt increases gradually,and the increment under different consolidation modes is more consistent.When the consolidation stress is same,the shear strength of the soil The shear of the soil under anisotropic consolidation is higher than that under isotropic consolidation,which indicates anisotropic consolidation has a strengthening effect to the soil compared with isotropic consolidation.(2)Under the condition of isobaric consolidation,the tensile strain is obviously larger than that of compressive strain.Due to the weakening of the soil,the soil stiffness is estimated at the beginning of the experiment,so the dynamic stress amplitude is attenuated in the process of cyclic loading under anisotropic consolidation and the phenomenon is more obvious when the dynamic stress ratio is large.(3)With the increase of dynamic stress ratio of cyclic loading,the pore pressure increases obviously.Although the pore pressure of soil sample increases faster when the consolidation stress is large,the increase of pore pressure ratio(the ratio of pore water pressure to consolidation stress)is small.When Consolidation stress and dynamic stress ratio are the same,the increase of pore pressure under the condition of anisotropic consolidation is slower than that of isotropic consolidation.(4)When Consolidation stress and dynamic stress ratio are the same,shear strength weakening degree of saturated silty sand under the condition of anisotropic consolidation is less than that of isotropic consolidation,which indicates anisotropic consolidation has a strengthening effect to the soil compared with isotropic consolidation again and anisotropic consolidation is more accordance with the actual conditions.(5)The difference between results obtained by the finite element software simulation and experiment is small.The improved model and the empirical formula combined can be used to predict the long-term settlement of silt sand in Nanning area under the subway operation load. |
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