| Under the background of the continuous development of the urban rail transit network in China,subway has become the main means of transportation for people to travel.However,the construction of subway tunnels will inevitably cause surface deformation.When the deformation exceeds the safety limit,it will bring irreversible economic losses and even casualties.Therefore,it is of great value for the safe construction and smooth operation of subway to scientifically analyze and forecast the deformation.In this study,take the monitoring data of Urumqi Rail Transit Line 1 for exanple,the wavelet theory,fractal theory and Arc GIS numerical simulation were used to comprehensively analyze the ground subsidence characteristics caused by subway excavation from the perspective of time and space,and the 3-D Peck formula was established to predict the future deformation.The main research contents are as follows:(1)I integrate the geological exploration report and other technical data of Line 1,summarize the six stratigraphic types that it often crosses,and obtain the represtative stations and sections according to the particle gradation curve of the main stratigraphy.I compare and analyze the de-noising effect of different threshold methods,threshold selection rules,threshold reconstruction methods,wavelet functions and decomposition levels respectively via wavelet de-noising,develop an optimal de-noising model by selecting the best wavelet de-noising parameters,and adopted the model to de-noise the surface deformation monitoring curve,so as to reduce the noise of the original monitoring data.And according to the principle of fractal interpolation,I use Matlab program to calculate the daily surface deformation of each station and section,which is equivalent to monitor the deformation every day,so as to solve the large number of continuous missing problems in the original monitoring data.(2)According to the Box-Counting approach of fractal theory,I calculate the fractal dimension of the deformation monitoring curve by Matlab program.It is finded that the fractal dimension D is greater than 1 when the monitoring frequency f is n(n = 1 ～ 8),and the two accord with power exponent D=a*f^-b,and according to the fluctuation characteristics of fractal dimension and its change rate of monitoring curve under different monitoring frequencies,I find that when the monitoring period in the north and south sections of Line 1 is less than 6 days and 4 days respectively,we can make full use of the monitoring resources and reasonably formulate monitoring plans on the basis of capturing the key information of surface deformation.(3)Based on the position coordinates and deformation values of the monitoring points in each station interval,I use Arc GIS geostatistical analysis tool to obtain the evolution cloud map of the surface deformation disturbed by subway tunnel construction,and according to the map,the distribution characteristics and evolution law of the obvious deformation areas are analyzed,and the spatiotemporal evolution characteristics of the surface deformation caused by subway tunnel construction are obtained.That is,the obvious deformation area of Nanhu North Road Station and International Airport Station move along the direction of tunnel excavation;the obvious surface deformation areas of Wangjialiang station and Sangong station are distributed in point shape on one side of the central axis of the station;and most of the surface deformation of each section is controlled by the northern section.(4)Based on the principle of spatial analytic geometry,I deduce the 3-D Peck formula from the 2-D Peck.Take no account of the influence of groundwater and noncontemporaneous construction,the surface deformation formula of single monitoring section and 3-D Peck formula of cumulative settlement are developed. |
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