Study On Stratum Settlement Of MJS Strengthening And Shield Tunnel Underpassing Of High Speed Railway Subgrade

The MJS(Metro Jet System)method is developed on the basis of conventional high-pressure jet grouting method.It is applied more and more widely in advanced stratum reinforcement of tunnels for its capability of controlling pressure in the ground,achieving all-around construction,ensuring the diameter of grouting,and avoiding environmental pollution.However,there are no detailed studies on issues of stratum settlement and ground settlement during the construction of MJS horizontal grouting piles.In this thesis,the numerical simulation method is used to establish a numerical model of the construction of grouting piles and follow-up shield construction.Combining to monitoring data in the construction site,the following researches are studied:(1)The influence factor of settlement caused by the construction of jet grouting piles and follow-up shield construction are analyzed.The three influence factors,including slurry replacement rates,calculi rate of jet grouting pile and the strength of the reinforced area,are mutual influence and restraint,which determine the settlement of the two construction processes together.(2)Numerical simulation of the construction of jet-grouting piles for the Beijing-Guangzhou Railway and the Wuhan-Guangzhou High-speed Railway is carried out,and the law of stratum settlement and ground settlement are obtained.Analyzing and comparing the law of stratum settlement and ground settlement during each construction step,it is concluded that the maximum values of stratum settlement always appear at the top of the grouting pile and the maximum value of ground surface settlement is mainly determined by the loss of stratum and quality of the squirting pile.(3)Comparing difference of stratum settlement and ground settlement during the construction process under different slurry replacement rates,it is concluded that the values of stratum settlement and ground settlement increase with the increase of replacement rates,and the settling rate of stratum and ground settlement increases as well with the process of construction step.By means of fitting,it is concluded that the relationship between the maximum value of ground settlement and the replacement rate is linear when the construction of jet grouting piles is completed.(4)Comparing different values of stratum settlement and ground settlement under different slurry replacement rates during the process of shield construction,it is concluded that the reinforcement of jet grouting piles could greatly reduce the disturbance of surrounding soil during the shield process and there is an exponential relationship between the maximum ground settlement and the replacement rate in process of shield construction.(5)Comparing maximum sum of ground settlement generated by the two construction processes at the different replacement rates,it is known that the optimal replacement rate is 10% in the construction of Beijing-Guangzhou Railway and 20% in the construction of Wuhan-Guangzhou High-speed Railway.