•A theoretical TBM torque model was developed in rock–soil interface mixed ground.•A new prediction index, MTPI, was proposed to evaluate the cutability of mixed face.•TBM performance prediction ...method based on MTPI and torque capacity was proposed.•The predictive capability of the proposed method was validated by field data.
Tunnelling in rock–soil interface (RSI) mixed ground often results in high cutterhead torque and torque fluctuation. Therefore, choosing a reasonable penetration rate to reduce the torque and improve tunnelling efficiency is paramount. In this study, considering the interaction between the cutterhead and RSI, an excavation torque model was first established based on the CSM model for a disc cutter and a new three-dimensional limit analysis model for a scraper. Further, considering the friction at the cutterhead in RSI, a total torque model was developed. Based on the study of excavation torque change characteristics when the cutterhead located in RSI, a simplified relationship among torque, face composition, penetration and rock strength was established. Subsequently, a new prediction index, Mixed-face Torque Penetration Index (MTPI), which includes the torque exerted by the TBM in the calculated penetration rate, was proposed to evaluate rock-soil mixed face cutability. This index allows for the inclusion of a TBM–rock mass and TBM–soil interaction factor. The methodology based on MTPI and TBM torque capacity to predict the penetration rate of the machine in different geological conditions and TBM specifications was proposed. Finally, the predictive capability of the proposed torque model and penetration prediction model were validated by the good agreement between the predictions and field measurement data from the Guangzhou Metro Line 21 tunnel in China. This study can match the tunneling parameters with the geological conditions within the limitation of TBM and provide guidance for TBM operation or evaluate whether the TBM satisfies the project schedule.
•Propose a method to identify the settlement risk section along metro lines.•Extend Artificial Neural Network–Cellular Automata on uncertainty analysis.•Present a detailed case study for ...verification.
“Metro economy” has led to intensive land development along the metro lines. However, engineering activities associated with land development inevitably disturb the service environment, causing severe settlement of adjacent metro tunnel structures in soft soil areas. As a reference point for pre-treating this type of tunnel settlement, a method is proposed to classify settlement risk sections along metro lines based on a land-use development simulation and corresponding uncertainty analysis. First, the land-use development along the metro line was simulated by Artificial Neural Network–Cellular Automata (ANN-CA). Second, the land-use development process was considered a random event rather than a deterministic prediction as in a typical ANN-CA, with its probability quantified based on the cells’ conversion probability. The classification of the surrounding land-use development probability was used to allocate the settlement risk sections of metro lines. This method was applied to the Han–You section of the Nanjing Metro Line 2. The predicted settlement risk sections corresponded suitably with the actual settlement troughs, demonstrating the effectiveness of this method. Thus, this method provides a novel consideration for the pre-treatment of metro tunnel settlement from the perspective of interactions between the metro line and surrounding land development.
Excavating super-large-span tunnels in soft rock masses presents significant challenges. To ensure safety, the sequential excavation method is commonly adopted. It utilizes internal temporary ...supports to spatially partition the tunnel face and divide the excavation into multiple stages. However, these internal supports generally impose spatial constraints, limiting the use of large-scale excavation equipment and reducing construction efficiency. To address this constraint, this study adopts the “Shed-frame” principle to explore the feasibility of an innovative support system, which aims to replace internal supports with prestressed anchor cables and thus provide a more spacious working space with fewer internal obstructions. To evaluate its effectiveness, a field case involving the excavation of a 24-m span tunnel in soft rock is presented, and an analysis of extensive field data is conducted to study the deformation characteristics of the surrounding rock and the mechanical behavior of the support system. The results revealed that prestressed anchor cables integrated the initial support with the shed, creating an effective “shed-frame” system, which successively maintained tunnel deformation and frame stress levels within safe regulatory bounds. Moreover, the prestressed anchor cables bolstered the surrounding rock effectively and reduced the excavation-induced disturbance zone significantly. In summary, the proposed support system balances construction efficiency and safety. These field experiences may offer valuable insights into the popularization and further development of prestressed anchor cable support systems.
Objective:
This work aims to investigate the clinical features and the temporal changes of RT-PCR and CT in COVID-19 pediatric patients.
Methods:
The clinical, RT-PCR, and CT features of 114 COVID-19 ...pediatric in-patients were retrospectively reviewed from January 21 to March 14, 2020. All patients had chest CT on admission and were identified as positive by pharyngeal swab nucleic acid test. The clinical features were analyzed, as well as the features and the temporal changes of RT-PCR and CT.
Results:
Fever (62, 54%) and cough (61, 54%) were the most common symptoms. There were 34 (30%) cases of concurrent infections. The most common imaging features on CT were ground-glass opacities (46, 40%) and consolidation (46, 40%). The bilateral lower lobes were the most common pattern of involvement, with 63 cases (55%) involving one to two lobes, and in 32 (28%) cases CT was normal. Throughout the whole duration of COVID-19 in children, the diagnostic positive rate of RT-PCR has been far higher than that of CT (all
P
< 0.05). For RT-PCR follow-up, reliable negative results were obtained only 7 days after the onset of symptoms. Though lung involvement on chest CT progressed rapidly in several cases, lung involvement in children with COVID-19 is mild, with a median value of 2 on CT score.
Conclusions:
RT-PCR is more reliable than CT in the initial diagnosis of pediatric patients with COVID-19. On follow-up, reliable negative RT-PCR results are available 7 days after the initial symptoms. The use of CT should be considered for follow-up purposes only if necessary.
This paper presents three comparative in situ grouting tests for long-term settlement treatment of a cut-and-cover tunnel of Nanjing Metro Line 10. The characteristics of the tunnel settlement and ...induced structural damage are described in detail. Comparative grouting tests were conducted to identify the effects of the grouting sequence and grouting material on the tunnel settlement treatment. The test results show that the total amount of uplift of the tunnel associated with the bottom-up grouting sequence is greater than that associated with the top-down grouting sequence. When a mixture of cement and water glass was used as grout, the average cumulative deformation and average deformation rate of the tunnel 6 months after the completion of grouting were −11.2 mm (uplift) and 0.018 mm/day (settlement), respectively. These values satisfy the control requirements and are better than those obtained using a cement and bentonite mixture as grout. Hence, a bottom-up grouting sequence and a cement and water glass grout mixture are advised. The findings presented in this paper provide useful guidance for similar projects.
This paper presents a landslide that occurred in loess hills resulting in structural damage to the Zhangjiazhuang tunnel of the Lanzhou–Xinjiang high-speed railway line. The characteristics of tunnel ...deformation and structural damage are provided in detail. To ensure future safety of the tunnel, investigations consisting of field reconnaissance, borehole investigations, seismic activity and rainfall records analysis, and numerical simulations were conducted to identify the regional geology and landslide characteristics. Using these investigations, the probable formation mechanism of this sliding failure is determined to be (
i
) an ancient groove that provides a natural slip bed leading to stress concentrations and dislocation failure at the back of the slope; (
ii
) seepage channels that are well-developed on this loess hillslope, through which an extreme rainfall event 6 months prior to the landslide saturated the strata materials; and (
iii
) finally, the limit state of the materials is reached in an earthquake under undrained condition, and the landslide is triggered. The findings presented in this paper can provide a reference for the control and treatment of landslides in loess areas.
The progressive failure of active soil arching in a quasi-static particle flow was investigated to elucidate the deformation behavior and load evolution mechanism. A transparent trapdoor test ...apparatus and self-developed particle image velocimetry system were used to capture the soil mass displacement field. Disturbed region and active region were introduced to characterize the displacement patterns evolution for both shallow and deep conditions. Meanwhile, the evolution of the surface settlement, horizontal displacement, and volumetric change of backfill as the trapdoor receding were quantified. The shear band propagation was interpreted considering the dilatancy behavior. In addition, the vorticity reveals local rotation characteristics in the shear region. Afterwards, i) the evolution mechanism of arching was speculated from macro-and microscopic perspectives. ii) The critical displacement for mobilizing the minimum load was discussed. These results can provide a profound understanding for mathematical modelling that is expected to illustrate the progressive development of active arching with displacement.
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•Evolution of arching in a quasi-static particle flow were investigated.•Continuous deformation and strain were captured by self-developed PIV system.•Two different evolution of displacement patterns were identified.•Vorticity field distribution was basically consistent with that of shear band.•Evolution mechanism of arching in distinct stages were different and elucidated.
This paper presents a Bayesian inversion approach to identify earth pressures on in-service underground structures based on structural deformations. Ill-conditioning and non-uniqueness of solutions ...are major issues for load inversion problems. Traditional approaches are mostly based on an optimization framework where a smooth solution is uniquely determined using regularization techniques. However, these approaches require tuning of regularization factors that may be subjective and difficult to implement for pressure inversion on in-service underground structures. By contrast, the presented approach is based on a Bayesian framework. Instead of regularization techniques and corresponding tuning procedure, only physically plausible bounds are required for specifying constraints. The complete posterior distribution of feasible solutions is obtained based on Bayes' rules. By inferring the potential pressures with the complete posterior distribution, a natural regularization advantage can be shown. Specifically, this advantage is demonstrated in detail by a series of comparative tests: (1) the Bayesian posterior mean exhibits an inherent quality to smooth out ill-conditioned features of inversion solutions; (2) satisfactory inference of the pressures can be made even in the presence of non-uniqueness. These properties are valuable when observed data is noisy or limited. A recorded field example is also presented to show effectiveness of this approach in practical engineering. Finally, deficiencies and potential extensions are discussed.
AbstractIn soft-soil areas, excessive transverse deformations have occurred in numerous shield tunnel linings accompanied by serious structural defects. However, to date, a method to effectively ...diagnose the health status of these poor-performing structures is unknown. This study focuses on health diagnosis for the typical stagger-joint-assembled shield tunnel linings in soft-soil areas of China. First, based on theoretical analyses, it is assumed that diametral deformation can be a significant indicator for the structural performance of a lining; subsequently, this is verified by abundant field data. In particular, a strong positive correlation between the diametral deformation and development of defects is observed. Subsequently, a full-scale test is performed to reveal further quantitative correlations. Besides the service limit values determined in the range of 0.24%–0.79% by specifications and prior studies, the test reveals detailed structural performance deterioration when the deformation is getting larger, where 1.5% is considered a threshold for the failure the entire structure. Additionally, the values of 0.5%, 0.8%, and 1.1% are observed to be key points indicating the gradual degradation of waterproofing, cracks, and overall mechanical performance of the lining. Based on these key points, a five-level health-degree model is constructed to determine the health status of a ring that can be regarded as a supplement of the previous limit values, which is more detailed and practical for the common large-deformed in-service linings in soft-soil areas. These findings can also serve as benchmarks for related studies on linings with different structural parameters in the future.
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