Key Technology Of Earth Pressure Balance Shield Tunneling In Water-Rich Round Gravel Stratum

Shield machine is very important for tunnel engineering,and it is the core construction equipment.The reason why the shield machine can play its advantages is that it is designed and put into construction according to the stratum conditions.At present,there are many subway construction projects in China,and the stratum conditions of different subway projects are different.In order to improve the matching and adaptability of shield and stratum,it is necessary to study the special stratum conditions and construction environment of each project,and establish the key technology of shield tunneling,so as to provide basis and reference for similar projects in the future.This article relies on the engineering example of the EPB shield tunnel section between the Neidanan campus and the Shuaijiaying water-rich round gravel in the No.2 line of the Hohhot Rail Transit Line.Based on the collection and arrangement of geological data and construction data,the mud film effect produced by the EPB shield in the round gravel stratum is studied,the rule of the shield tunneling parameters is summarized and analyzed,and the adaptability of the earth pressure shield in the stratum is evaluated.The main research content and the results achieved include the following parts:(1)For the high-permeability water-rich round gravel stratum in Shuai-Nei section of No.2 line of the Hohhot Rail Transit Line,a new construction method of EPB shield is implemented: mud film waterproof-spiral soil drainage.Applying the mud film effect in EPB shield,the proportion of residue and soil which can maintain the stability and continuity of mud film is determined,and the water blocking and stability of excavation face are realized.Experimental results show that the best expansion ratio is to ensure the improvement of the residue.The ratio is sodium bentonite: the water mass ratio is 1:8 to 1:10,and the foam concentration is controlled at 3% to 5%.(2)The numerical simulation software FLAC3 D is used to simulate the shield excavation.The distribution of pore water pressure and the surface settlement with or without mud film are compared,and the mechanism of water blocking by mud film is revealed..The simulation results show that when there is a mud film,the pore pressure in front of the excavation face increases faster than when there is no mud film,so that a larger water pressure gradient can be generated quickly at the mud film.The greater the total force of the water pressure difference on the mud film,the greater the horizontal effective stress is provided to maintain the stability of the excavation face and control the surface subsidence.(3)Based on the statistical theory,this paper analyzes the parameters of shield tunneling in the study area,studies the change rule and correlation of the parameters of the EPB shield tunneling under the water-rich round gravel stratum,and summarizes the reasonable range of the parameters.The correlation between driving parameters is analyzed statistically,and the range of better driving speed is determined,and the combination of other parameters is given.(4)The typical regression model in Matlab machine learning is used to train the driving parameters and predict the driving speed.The regression model adapted to the supporting project is determined by comparing with the measured data.The comparison results show that the B-P neural network regression model and linear regression model can get the prediction value of the driving speed according to the input driving parameter simulation,with the accuracy of 88%.Both models are suitable for the driving parameter simulation of the round gravel stratum.(5)The adaptability of EPB shield machine in water-rich pebble stratum is studied,the membership function of each influencing factor index is constructed by using fuzzy mathematics method,the weight of each index is determined by using AHP,and the adaptability evaluation model of shield machine is established.Combined with the actual project,the adaptability of EPB shield machine in water-rich round gravel stratum is evaluated and quantified by using the comprehensive evaluation method.The results show that the adaptability of EPB shield in Nei-Shuai section is 0.76,the adaptation degree is medium to high.