The Control of Shield Tunnel Construction-Induced Ground Settlement Based on an Optimized Gap Parameter Theory and Three-Dimensional Finite Element Analysis

The ground settlement induced by shield tunnel construction should be carefully monitored and controlled during construction as a compulsory measurement to ensure construction safety. In the existing literature, gap parameter theory is adopted to predict ground settlement; however, the influence of slurry grouting on ground settlement during the construction process has been ignored. Regarding this drawback, a novel optimized gap parameter theory is proposed and combined with 3D finite element analysis to investigate ground settlement caused by shield tunnel excavation. Considering that construction technology plays an important role in ground settlement, numerical studies are carried out to investigate the sensitivities of the grouting filling ratio, pressure of the tunnel face, and the strata conditions in ground settlement. The practical engineering of Wuhan Metro Line 7 is introduced to verify the superiority of the proposed method. The results show that the proposed method can reflect ground settlement well, compared to the existing methods and the measured data. Then, 3D finite element analysis and orthogonal test are adopted to conduct sensitivity analyses of the grouting fill rate, support pressure ratio, and strata conditions. The results illustrate that the grouting filling rate has the most obvious impact on ground settlement, while the support pressure ratio and strata conditions also have a certain impact on ground settlement. Taking the binary structure stratum of the terrace geological environment of the Yangtze River in Wuhan as the research object, this study employs a three-dimensional numerical simulation approach to analyze six distinct binary structure stratum models. The parameter value ranges, considering formation conditions, are determined through integrated theoretical analysis. Finally, based on the deviation analysis results between the optimized gap parameter theory and numerical simulation, it is concluded that there is no significant difference in the surface settlement values obtained from the two methods. To summarize, the proposed optimized gap parameter theory, combined with the corresponding numerical simulation technology, provides a good tool for the control of ground settlement caused by shield tunnel excavation in complex strata, such as binary structure strata.