Abstract
Focusing on the special stratum conditions of upper-soft and lower-hard fissured rock strata, this paper conducts quantitative research and analysis on the factors influencing the ground settlement caused by shield tunnel construction considering the coupled hydromechanical properties and presents a corresponding numerical simulation-artificial neural network-Bayesian network- (NS-ANN-BN-) based method. In this method, with a subway shield tunnel as the engineering context, three numerical models are established, in which the shield tunnel is located in soft strata, the shield tunnel is located in semisoft and semihard strata, or the shield tunnel is located in hard strata. According to the numerical simulation (NS) calculations, the ground settlement values under the three types of strata are 38.96 mm, 10.42 mm, and 3.13 mm, respectively. A radial basis function artificial neural network (RBF-ANN) is used to establish the nonlinear mapping relationship between the stratum parameters and the ground settlement, and the training samples and test samples are generated through NS to train the RBF-ANN. After the training is completed, the accuracy of the neural network meets the requirements. The elastic moduli of coarse sand~gravel sand k3 and moderately weathered rhyolite k4 and the cohesion of moderately weathered rhyolite c4 are selected as the key parameters. A large number of training cases are generated through the RBF-ANN, and the Bayesian network (BN) prior probability is calculated by self-learning. A BN model of ground settlement for shield tunnel construction in the upper-soft and lower-hard fissured rock strata is established. The BN back analysis method is used to quantitatively analyze the influencing factors of the ground settlement. The results show that when the tunnel is located in soft strata, the surface settlement is mainly affected by parameter k3. When the ground settlement increases considerably, the three parameters all have a strong influence. When the tunnel is located in semisoft and semihard strata, the influence of the three parameters on the ground settlement is weak. When the tunnel is located in hard strata, the ground settlement is mainly affected by parameter k4. When the ground settlement greatly increases, parameters k3 and c4 have less influence. When the tunnel is located in strata with different soft-hard ratios, the ground settlement is mainly affected by the elastic moduli of coarse sand~gravel sand and moderately weathered rhyolite. This method can provide a reference for the ground settlement analysis of shield tunnel construction in areas with similar fissured rock strata.
Highlights
With the development of China’s urban construction, urban rail transit as a modern transportation infrastructure has developed rapidly in recent years
The findings showed that the excavation sequence of the double-line tunnel has little effect on the ground settlement and that the ground settlement is mainly affected by the earth chamber pressure
The numerical simulation-artificial neural network-Bayesian network (NS-Artificial neural networks (ANNs)-BN) analysis method proposed in this paper is a comprehensive method composed of NS, an ANN, and BNs
Summary
With the development of China’s urban construction, urban rail transit as a modern transportation infrastructure has developed rapidly in recent years. Sun et al [6] used the strength reduction method to study the safety factor of subway stations with different burial depths in upper-soft and lower-hard strata and derived a calculation formula for the minimum rock overburden thickness These studies mainly used NS methods to study the ground settlement or the influencing parameters such as typical engineering single-type studies and did not propose general solutions for different geological conditions. Few studies have analyzed the factors influencing ground settlement during shield tunnel construction in upper-soft and lower-hard fissured rock strata considering the coupled hydromechanical properties. NS, an ANN, and BNs are reasonably combined With this method, the ground settlement of shield tunnel construction in three different upper-soft and lower-hard fissured rock strata considering the coupled hydromechanical properties of Qingdao subway line 1 is analyzed. This method can provide a reference for shield tunnel construction under similar geological conditions
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