Study On Prediction Parameters Of Ground Settlement Of Peck Formula For Shield Tunneling In Round Gravel Stratum In Hohhot City

Shield tunneling construction has the advantages of high mechanization,fast construction speed,uninterrupted ground transportation,avoiding underground pipeline relocation,no noise,and little impact from groundwater.Therefore,it is widely used in the construction of urban metro sections and some long-distance underground integrated pipelines gallery,which represents the development direction of future urban rail transit and underground engineering construction technology.The formation deformation caused by shield tunneling construction is one of the hotspots of underground engineering research.At present,many results have been achieved represented by the Peck formula.It provides a good tool for predicting surface deformation in shield tunneling construction with its intuitive concept,easy-to-calculate formula and fewer calculation parameters.This paper takes the shield tunneling section of Shuaijiaying 2nd Line of Hohhot Rail Transit Line 2 to the South Campus of Inner Mongolia University as the engineering background.Based on the local conditions of the gravel stratum,the parameter values of the Peck formula(settling tank width and formation loss rate)are studied through field measurement data analysis,empirical formula calculation,function fitting and numerical simulation and the main research work and conclusions are as follows:Firstly,it can be found that under the stratum conditions of the construction section,with the tunneling of the shield machine,the overall longitudinal deformation of the surface shows the settlement after the first uplift,and the settlement curve of the lateral deformation of the surface basically conforms to the positive distribution by analyzing the measured surface deformation data.The maximum settlement value of the double-line shield is greater than the maximum settlement of the single-line shield,and the maximum settlement occurs between the two-line tunnels.Secondly,the settlement tank width and formation loss rate are calculated by Peck formula.The settlement tank width is about 6~7m,the settlement tank width coefficient is about 0.35,and the formation loss rate is about 0.5%~1.4%.Thirdly,the numerical simulation of shield tunneling construction is carried out by using FlAC3 D.By comparing with the measured data and the calculation results of Peck formula,a reasonable numerical model is selected,and then the ground settlement deformation form of the double-line tunnel with different spacing is obtained,which is obtained by the double Peck formula.The surface settlement deformation modes are compared to verify the rationality of the Peck formula parameters(settling tank width and formation loss rate)in the gravel stratum in Hohhot.Fourthly,the shape of the settlement tank caused by the double-line shield construction of this project is “U” type,which is mainly related to the local soil condition and the spacing of the double-line tunnel.