Analysis and prediction of the river levee settlement derived from shield tunneling considering the excavation face stability.

The river levee settlement derived from shield tunnel excavation face instability is an anticipated safety issue. Serious engineering safety hazards may occur if it is not restricted. Thus, this study selected six influence indicators to quantify the stability level of the excavation face using the AHP-Fuzzy method. A database of the levee settlement prediction indicators containing tunneling speed, supporting pressure, grouting pressure, horizontal distance, lagging distance, and stability coefficient of excavation face was built by collecting 60 samples from a river-crossing shield tunnel project in China. Five models were carried out for predicting the levee settlement, i.e., modified Peck formula, RF, SVM, BPNN, and PSO-BPNN. Their prediction performance was verified by comparing the prediction results with the measured ones in a shield tunnel engineering application. The analytical results indicated that the PSO-BPNN model has the highest correlation coefficient, i.e., 0.8831(in training) and 0.8657(in testing) and the lowest error, i.e., RMSE = 1.901, and MAE = 0.8412, respectively. Thus the PSO-BPNN model has the best ability to capture the nonlinear relationship between the independent and dependent variables compared with the abilities of the RF, SVM, and BPNN model in this case study. The modified Peck formula performed unsatisfactory results (RMSE = 3.2588, MAE = 3.1172). The correlation analysis results of the input characteristic parameters of the model also indicate that the stability of the levee settlement is significantly related to the excavation face stability. The results indicate that the hybrid model is a very useful and powerful means to investigate the levee settlement caused by shield tunneling and can be improved by gathering more data from tunneling operations over time. [ABSTRACT FROM AUTHOR]