Xiaobin Ding

Accurately forecasting the operational performance of a tunnel boring machine (TBM) in advance is useful for making timely adjustments to boring parameters

Maintaining the alignment of the shield tunneling axis with the designed tunnel axis is crucial in urban subway construction. However, previous studies have only verified the accuracy of the models in a specific project, ignoring model transferability. This paper proposes a multistep transferable prediction method (PCA-GRU) for shield attitude and employs feature importance analysis of the PCA-GRU model through feature dimensionality reduction experiments. Datasets obtained from the Guangzhou and Fuzhou Metro Line X Projects were used to validate the accuracy of the proposed method. The results revealed that PCA can unify the model input, enabling the model to be applied to different projects, and the proposed model could produce an accurate prediction within 24 steps, with an average R² of 0.94 and 0.97 in the Guangzhou and Fuzhou projects. This indicates that the proposed model possesses transferability and generalization ability, which can aid decision-making during urban subway construction.

Ball penetrometers have been employed in both centrifuge tests and field experiments for soil profile interpolation. Nevertheless, it has become apparent that the performance of the ball penetrometer in centrifuge tests significantly deviates from that in field tests. In this study, a more comprehensive analysis utilizing the larger deformation finite element method was undertaken to gain deeper insights into the behavior of ball penetrometers when used in nonhomogeneous clay within the centrifuge testing environment. This investigation accounts for the influence of the unique scale and shaft ratio of the ball penetrometer in centrifuge tests. The numerical model developed in this study was rigorously validated against previously published data, demonstrating a high degree of agreement. Subsequently, a parametric study was conducted to investigate potential influencing factors. As a result, a novel method for quantifying the bearing capacity factor was proposed. This method offers the promise of obtaining more precise data regarding the continuous shear strength in centrifuge tests, thereby providing valuable guidance for soil profile determination within this experimental setting.

The present study investigates the dynamic properties of granite samples with varying degrees of defects through triaxial cyclic loading experiments conducted under different conditions, including varied confining pressures, loading frequencies, dynamic stress amplitudes, and number of cycles, and the dynamic response model of granite samples influenced by the confining pressure and frequency are constructed. The results show that the dynamic elastic modulus of granite increases, but its dynamic damping ratio decreases as the confining pressure increases. The dynamic elastic modulus and dynamic damping ratio of the granite increase as increasing frequency. The dynamic elastic modulus of granite increases with the increasing dynamic stress amplitude while its dynamic damping ratio decreases. The dynamic elastic modulus and dynamic damping ratio of granite decreases with an increasing number of cycles. The modified Duncan–Chang model can well describe the dynamical behavior of granite influenced by the confining pressure and frequency. The correlation coefficients of the modified model reached 0.98. It is worth saying that the correlation coefficient of the model is low at 20 Hz frequency. It indicates that frequency has a strong effect on the dynamic response of granite compared with the confining pressure. These data and models will be applied to the next step of detection and prediction of the tunnel rock stress state.

Currently, the development of deep earth space is an important strategic, scientific, and technological goal

We propose a novel inverse analysis method that utilizes shockwaves to detect the operational condition of tested rock. To achieve this back analysis, an in-depth investigation of the dynamic properties of granite specimens was conducted. The dynamic properties of the granite specimens were investigated using a triaxial cyclic loading machine, under different confining pressures, loading frequencies, stress amplitudes, and numbers of cycles, and a dynamic response model was constructed from the test data. The results show that the dynamic elastic modulus increased with the increase in confining pressure, while its damping ratio decreased. The dynamic elastic modulus and damping ratio increased with the increase in loading frequency. As the dynamic stress amplitude increased, the dynamic elastic modulus of the granite increased, but the dynamic damping ratio decreased. As the number of cycles increased, the dynamic elastic modulus and dynamic damping ratio of the granite decreased and gradually stabilized. The modified Duncan–Chang model was used to construct the dynamic response model of the specimens. It is worth saying that the correlation coefficient of the model is low at a loading frequency of 20 Hz. This indicates that the frequency has a greater effect on the dynamic response of the specimen compared with the confining pressure. The conclusions obtained from these tests can be used to study more comprehensively the interaction and causal relationship between different factors, and to prepare for the next steps of tunnel rock stress-state prediction.

Tunnel boring machines often encounter clogging during excavation in strata with rich clay content. The clogging can damage the cutterhead and interrupt excavation. Cutting tool clogging, also known as mud cake formation, has a strong effect on excavation work efficiency. While current studies are focusing on the mechanism of clogging, engineering practice still heavily relies on qualitative empirical judgement. To quantitatively assess the risk of mud cake formation, we carefully selected 22 influential parameters to reflect the effect of geological, machinal, and operational risk factors in the tunneling process and established a rubric for risk factor contributions using the analytical hierarchy process (AHP). The results imply the liquidity index, plasticity index, cutterhead torque, and total thrust force contribute to around 45% of the total influence on mud cake formation, while machinal factors are less influential than geological and operational factors. We verified the framework with a tunnel section from the Guangzhou Metro Line 22 that had mud cake formation reported. Rings labelled as high risk for mud cake formation by our framework concurred with those rings with mud cake actually observed. Project log and operational parameter variations were incorporated to explore the connection between mud cake formation and treatment.