Tunnelling and Underground Space Technology最新文献

The aging and complexity of underground water pipes pose significant challenges to modern society, necessitating long-term monitoring and maintenance to prevent the socioeconomic costs. So, effective nondestructive and geophysical methods are needed to localize the possible leakage areas before any rational opening up is conducted. In this study, we propose a workflow to generate instantaneous frequency slices (IFS) from raw ground penetrating radar (GPR) data. Characterizing the horizontal and vertical patterns of water leakage using IFS revealed two key mechanisms—reflections due to the dry and wet interface and absorption due to water distributed in soil—that significantly influence instantaneous frequency. A well-designed real site (Q-Leak), in collaboration with the Water Supplies Department (WSD) of the government, was conducted to replicate typical leakage scenarios, validating the effectiveness of our IFS-based approach. The results of proposed method demonstrate that IFS is a reliable approach for characterizing leakages in buried water pipes, effectively addressing several challenges associated with amplitude slice analysis. Our proposed methodology enriches the toolkit available for large-scale, future-oriented water leakage detection.

Tunnel fire poses a serious threat to social public safety, and the losses they cause are often incalculable. The prediction of tunnel fires contributes to decision-making in rescue and firefighting, and helpfully reduces fire losses as much as possible. The financially expensive experiments and the time-consuming simulation slow down the pace of development in tunnel fire prediction. Moreover, numerical and experimental study is often unidirectional, with the characteristic of predicting less dimensional data through higher dimensional data. This work proposes a deep learning model (DLM) to instantly achieve bidirectional prediction between the full field information of tunnel fires and a small amount of key physical quantities. Under the designed data processing method, the DLM is trained by a big tunnel fire numerical database with various ventilation, thermal, and geometric conditions. The results show that the DLM can learn the physical fields data and the physical quantities data well with the increasing training epoch. In addition, the DLM performs the promising bidirectional prediction. From the symmetry comparison, the result shows the full physical fields are well predicted by the decoder part of DLM via four key physical quantities. The prediction of the key physical quantities is overall satisfactory, but the prediction accuracy of the tunnel inclination angle is relatively poor compared with the other quantities. The prediction accuracy of key physical parameters through the temperature field is better than through smoke visibility. The important parameters in practice, namely smoke layer distribution and smoke back-layering length are also predicted, and the R${}^2$ of 0.95 and 0.92 are respectively obtained. The bidirectional prediction system proposed in this work demonstrates the promising application for intuitive and rapid prediction of various information in tunnel fires, as well as for summaries of physical laws in tunnel fires.

The performance of longitudinal joints in shield tunnel segments is crucial for ensuring structural stability and durability. This study presents an innovative segment structure combining normal concrete (NC) and ultra-high performance concrete (UHPC) (hereafter called NC-UHPC composite segment). Full-scale joint tests were conducted to analyze the mechanical response and failure characteristics of longitudinal joints in these segments. Compared to reinforced concrete (RC) segment joints, NC-UHPC composite segment joints exhibited a significant increase in initial cracking load by 197.93% under sagging moments and 435.3% under hogging moments. The ultimate load-bearing capacity increased by 55.71% and 67.10%, and the initial bending stiffness improved by 20.57% and 10.59% under sagging and hogging moments, respectively. Furthermore, NC-UHPC composite segment joints exhibited smaller crack distribution areas and fewer cracks, indicating superior crack resistance. No cracks or damage were observed at the NC-UHPC interface. Evaluation of joint toughness and ductility indices further highlighted the favorable performance of NC-UHPC composite segment joints. Finally, a refined numerical model was established to compare the deflection and bending stiffness of RC segment joints with NC-UHPC composite segment joints under varying axial forces. The findings suggest that NC-UHPC composite segments are more suitable for tunnel engineering with greater burial depth, higher water pressure, and larger axial forces.

The planning of mountain tunnels aims to avoid intersecting with landslide-prone areas. However, it is often unavoidable for mountain tunnels to traverse sloped terrain, thereby creating a tunnel-slope system. During the construction of tunnels traversing sloped terrain, disasters such as slope sliding and tunnel collapse frequently occur as a result of tunnel excavation. In order to provide theoretical reference for deformation control and disaster prevention of tunnel-slope systems, taking the left portal of Yangguang Tunnel as a case study, deformation and mechanical characteristics of tunnel-slope systems that incorporate existing anti-slide piles within the context of a replacement structure of pile-wall were studied. A replacement structure of pile-wall was proposed to prevent the sliding of reinforced slopes caused by tunnel excavation. The on-site monitoring data showed that the horizontal displacement of the slope caused by pile cutting and tunnel excavation is 17.7 mm, which proved the reliability of the replacement structure proposed. Under the reinforcement of the replacement structure of pile-wall, tunnel excavation only causes compression deformation of first lining, but the pipe-roof will experience overall sliding deformation. The plastic loosening zone and the disturbance zone of surrounding rock on the deep side of the tunnel are 1.23 times and 3.24 times of the diameter of the tunnel respectively, which are much larger than the loosening zone of the shallow buried side and the tunnel non-biased section. It indicated that the surrounding rock of the deep side of the tunnel is the key area affecting the stability of the tunnel-slope systems. The proposed the replacement structure of pile-wall, as well as the deformation and mechanical characteristics of tunnel-slope systems under its reinforcement, could provide insights for deformation control and disaster prevention of tunnel-slope systems.

The screw conveyor gushing may cause a sudden drop in pressure in the earth chamber, leading to excessive settlement of the surface and nearby buildings or structures, and even catastrophic accidents such as tunnel collapse. This paper presents a comprehensive investigation into slagging failures associated with earth pressure balance shield screw conveyors, categorizing them into rheological failure and permeability failure. Further, a permeability failure theoretical model and a Bingham fluid-based rheological failure model are developed. The above models can describe the conditions and mechanism of screw conveyor spurt taking into account shield parameters, formation characteristics, chamber pressure, and conditioned soil properties. In addition, a sensitivity analysis is conducted on the critical permeability coefficient and critical shear strength of the discharged soil, with a focus on a specific case project. The results underscore the significant impact of the screw conveyor pitch, water head at the entrance, and chamber pressure on the critical permeability coefficient and shear strength. Building on these findings, this paper proposes an anti-surge control index and strategy for shield screw conveyors, taking into account the ratio of shield covering soil thickness to shield diameter. It is recommended that when the shield soil covering layer thickness exceeds twice the shield diameter, real-time modification of the soil parameters, based on the shield tunneling depth, especially the shear strength, is essential for anti-surge control. This study provides engineers with valuable insights into conditioned soil and implements effective surge management strategies for screw conveyors.

The entrance section of the highway tunnel is a high-risk area for traffic accidents, and its traffic accident rate has significant seasonal differences. However, the dominant causes of this difference are still lacking in targeted research. On the other hand, due to the lack of a mature design system and normative guidance, the landscape design of tunnel entrances is more and more random, landscape elements tend to be complex, and color design tends to be diversified. The influence of tunnel entrance landscape design on driving behavior and its applicability in different seasonal environments needs to be studied. Given this, this study focused on two main variables − the typical seasonal environmental colors and different portal colors, and designed 12 schemes composed of three seasonal environments (green spring, golden yellow and red autumn, and white winter) and four portal colors (gray, blue, red, and tawny). Thirty subjects were invited to conduct a driving simulation experiment to study the influence of different seasonal environmental color characteristics and tunnel portal color on the amplitude and stability of driving behavior. The results show that the drivers’ behavior amplitude is large in spring and winter, and the traffic safety risk is relatively high. The typical color characteristics of the environment in different seasons are one of the reasons for the seasonal difference in the traffic accident rate. The driver’s operational stability is relatively poor in the autumn environment, which is related to the high scene complexity of the season. Compared with the grey portal scheme, the color design of the portal will increase the driver’s driving speed and the driving safety risk. However, its influence on the stability of driving behavior is bidirectional, and the color design coordinated with the environment can improve the stability of driving. When the portal is ready for landscape decoration, it is recommended to use a color scheme that is in harmony with the environment.

Segment joint is the main water leakage channel in underwater shield tunnels, and joint deformation influences tunnel waterproof capacity greatly. Real-time structure health monitoring is a great way to investigate the joint opening and to offer early warnings for abnormality, such as data outlier and joint properties degradation. This study investigated the variation of joint opening, provided early warning indexes and evaluated the joint mechanical properties degradation using the field monitoring data of an underwater shield tunnel over 10 years, which is rarely seen in the literature. Study results show that: (1) Field monitoring data reveals that the distribution of joint opening increments obeys a heavy-tailed distribution rather than the normal distribution. The exponential distribution model and the log normal distribution model can fit the longitudinal joint increments and circumferential joint increments much better. (2) The early warning index is determined based on the statistic theory and 0.999 quantile is set as the warning value. The obtained warning values of the studied underwater tunnel are 0.005 mm and 0.08 mm for the longitudinal and circumferential joint respectively. The small warning value means that small abnormality can be identified and the early warning would be more efficient. (3) A mechanical model is proposed to evaluate the joint mechanical properties degradation based on monitoring data. Results show that normal stiffness of circumferential joint decreases from 18.3 GPa/m to 14.7 GPa/m. Results of this study provides valuable reference for early-warning and joint degradation evaluation of under water shield tunnel.

This paper presents the development of a novel methodology and the results of an experimental study to quantify foam destruction ($\mathrm{FD}$) observed during the conditioning of fine-grained soils. A laboratory setup was designed to simulate pressurized mixing conditions prevalent in the cutterhead tool gap and excavation chamber of an earth pressure balance tunnel boring machine (EPBM). The developed $\mathrm{FD}$ quantification methodology utilizes the concept of back pressure saturation to determine the volume of the ruptured air from the foam bubbles during the conditioning of soil. The influence of major soil types, fines content ($\mathrm{FC}$), soil consistency index ($I_c$), foam injection ratio ($\mathrm{FIR}$), and foam liquid half-life ($t_{1/2}$) on $\mathrm{FD}$ were investigated. The results showed no $\mathrm{FD}$ in sand, 15–30% $\mathrm{FD}$ (% of injected foam volume) in silt, and significant $\mathrm{FD}$ of 30–85% in clay. $\mathrm{FD}$ was found to be directly proportional to $\mathrm{FC}$ and inversely proportional to $\mathrm{FIR}$ and $t_{1/2}$. No relationship was observed between $\mathrm{FD}$ and $I_c$. The study provides clear experimental evidence of the presence of $\mathrm{FD}$ phenomena in fine-grained soils and a methodology for calculating $\mathrm{FD}$. The quantification of $\mathrm{FD}$ range in major soil types and insights into influencing factors revealed in this study will help practitioners account for the expected $\mathrm{FD}$ in various soil types while deciding $\mathrm{FIR}$, and decide whether to use foam at all while preparing conditioning strategies for EPB tunneling projects in fine-grained soils.

This study investigates the impact of multiscale surface roughness on shear behaviors of crystalline rock fractures. Employing wavelet decomposition, we analyze the multiscale features of 3D fracture surface roughness and characterize each roughness level using statistical parameters. Using a validated shear simulation model, we simulate the direct shear processes of mated fractures with a realistic fracture surface digitalized from the scanning of a granite sample under various normal stresses and decomposed surface roughness levels. The shear behaviors, including the peak and residual shear strengths, shear-induced normal displacement (shear dilation) and surface degradation of the decomposed fractures are analyzed. The results reveal a significant correlation between shear strengths and the multiple levels of surface roughness. For the first time, we demonstrate the crucial role of 3D multiscale surface roughness in determining fracture shear strengths and find that the surface unevenness notably affects the peak shear strength of unfilled and mated fractures, while the surface waviness controls the residual shear strength. The unevenness also can enhance the fracture dilation and surface degradation within a relatively short shear distance (∼1 mm). The findings offer valuable insights for a better understanding and estimation of the shear behaviors of unfilled and mated crystalline rock fractures in engineering practice.

An investigation into the movement characteristics of granules during Earth Pressure Balance (EPB) shield tunneling contributes significantly to understanding the interaction between the shield machine and the soil. This understanding also enables researchers to gain deeper insights into the cutting and guiding effects of the shield cutterhead on the soil, thus providing a scientific basis for optimizing shield tunneling parameters and cutterhead designs. To achieve this, indoor model shield tunneling experiments were conducted using independently developed shield tunneling equipment and spatial positioning devices developed by our research group. The research investigated the spatial movement trajectories, radial diffusion, and axial movement characteristics of granules at the face subjected to the action of a spoke-type cutterhead. Furthermore, the study proposes the use of average diffusion degree and movement rates of granules as metrics for evaluating the cutting and steering performance of the cutterhead. The influence of cutterhead rotational speed and advance rate on the movement characteristics of granules was further explored based on these two indicators. The study’s findings reveal the following: (1) Granules at the face predominantly exhibit a spiral movement trajectory when the EPB shield tunneling machine operates in a dynamic equilibrium state. (2) The cutting and steering performance of the cutterhead’s various areas is enhanced progressively from the center to the outer edge, as evidenced by a gradual decrease in the average diffusion degree of granules and an increase in the average axial movement rate (AMR). (3) The AMR and average diffusion degree of granules are influenced by both the rotational speed of the cutterhead and the advance rate of the shield machine. Optimal matching of the rotational speed and advance rate maximizes the average AMR of granules, minimizes the average diffusion degree, reduces the torque on the cutterhead to its lowest point, and consequently, optimizes the efficiency of shield tunneling. This research presents a novel perspective and methodology for understanding the movement characteristics of granules during shield tunneling operations. The outcomes of this study provide valuable insights for the structural design of shield machine cutterheads and the optimization of tunneling parameters.