| With the increase in the construction of subway tunnels across the country,the problems faced by tunnel construction in different regions are also different.The research object of this paper is argillaceous siltstone strata with different weathering degrees at the base of Nanchang Metro tunnel.It has poor physical and dynamics properties and belongs to extremely soft rock.In addition,Nanchang has a high groundwater level.Water-rock coupling will cause the weathered soft rock to soften and disintegrate further.The cumulative deformation of the weathered soft rock gradually increases under the long-term subway train load,and the problem of uneven settlement is increasingly prominent.In view of this,this article takes the different weathered argillaceous siltstone in the basement of Nanchang Metro as the research object,and analyzes the microstructure and mineral composition of the weathered argillaceous siltstone through microscopic scanning electron microscope SEM experiments,X-ray diffraction,laboratory dynamic triaxial tests and numerical simulation research methods,To research the dynamic characteristics of weathered argillaceous siltstone and predict the long-term settlement of Nanchang Metro tunnel.The main research contents and related results are as follows:(1)Based on the SEM and X-ray diffraction tests of fully and moderately weathered soft rock under different soak time,the influence of soak time on the mineral composition and microstructure of weathered soft rock is preliminarily discussed.The results show that the mineral composition of the weathered soft rock under different soak times will not change basically;with the increase of the soak time,the microstructure of the weathered soft rock gradually changes from a compact lamellar and scaly structure to loose granular structure,but compared with moderately weathered soft rock,water has a greater impact on the microstructure changes of fully weathered soft rock.(2)The SS-HCA GDS system was used to study the cumulative axial deformation development law of fully and moderately weathered soft rock under the influence factors of dynamic stress ratio,static deviator stress ratio,confining pressure and loading frequency.The results show that the dynamic stress ratio and static deviator stress ratio have a greater impact on the total strain of weathered soft rock.Confining pressure and loading frequency have little effect on the total strain of weathered soft rock.Analyzing the test result data,a mathematical model of cumulative plastic strain considering factors such as loading times and dynamic stress ratio is proposed to provide a theoretical basis for predicting the long-term settlement of the tunnel.(3)The three-dimensional finite element model of the subway tunnel was established using finite element ABAQUS software,and the dynamic response of the weathered soft rock at the base of the tunnel under different train speeds and different strata were analyzed.The calculation results show that the change of train speed has little effect on the dynamic response of the tunnel bottom;the dynamic stress and acceleration at the bottom of the tunnel decrease with the increase of the distance from the vibration source and appear to decay first and then slowly;the tunnel base is the dynamic stress and acceleration of the fully weathered soft rock layer are greater than the dynamic stress and acceleration of the moderately weathered soft rock layer at the base of the tunnel.(4)Combining the cumulative plastic strain model and numerical simulation results to predict the long-term settlement of the Nanchang Metro tunnel.After 100 years of metro operation,it is found that the change of train speed has little effect on the long-term settlement of the tunnel;compared with the case where the bottom of the tunnel is located in a moderately weathered soft rock layer,the cumulative settlement increase of the bottom of the tunnel in a fully weathered soft rock layer is about 42% Uneven settlement will adversely affect the tunnel structure. |
