Automatic Sensing and Detection for Subway Tunnel Pathologies

Subway tunnels often suffer from surface pathologies such as cracks,corrosion,fractures,peeling,water and sand infiltration,and sudden hazards caused by foreign object intrusions.Installing a mobile visual pathology sensing system at the front end of operating trains is a critical measure to ensure subway safety.Taking leakage as the typical pathology,a tunnel pathology automatic visual detection method based on Deeplabv3+(ASTPDS)was proposed to achieve automatic and high-precision detection and pixel-level morphology extraction of pathologies.Compared with similar methods,this approach showed significant advantages and achieved a detection accuracy of 93.12%,surpassing FCN and U-Net.Moreover,it also exceeded the recall rates for detecting leaks of FCN and U-Net by 8.33%and 8.19%,respectively.

Review on water leakage control in distribution networks and the associated environmental benefits

Water supply is the primary element of an urban system. Due to rapid urbanization and water scarcity, maintaining a stable and safe water supply has become a challenge to many cities, whereas a large amount of water is lost from the pipes of distribution systems. Water leakage is not only a waste of water resources, but also incurs great socio-economic costs. This article presents a comprehensive review on the potential water leakage control approaches and specifically discusses the benefits of each to environmental conservation. It is concluded that water leakage could be further reduced by improving leakage detection capability through a combination of predictive modeling and monitoring instruments, optimizing pipe maintenance strategy, and developing an instant pressure regulation system. The environment could benefit from these actions because of water savings and the reduction of energy consumption as well as greenhouse gas emissions.

Long-term settlement behavior of ground around shield tunnel due to leakage of water in soft deposit of Shanghai

The lining of shield tunnel is usually composed of segments,in which the joints,cracks,and the grouting holes(hereafter called lining deficit)exist.During the long-term running,soils and groundwater may leak from these kinds of lining deficit.The leaking of soil and groundwater causes the long-term ground loss around tunnel and thus results in the settlement of ground surface.This paper aims to analyze the impact of the leakage of groundwater through segments on the long-term settlement of ground surface.The adopted analytical method is based on the theory of groundwater seepage by using numerical simulation.The analyzed results show that settlement of ground surface increases gradually with the increase of the leaked volume of tunnel segments.When the leaked volume was unevenly distributed,differential settlement occurred locally.Comparative analysis by changing the leaked volume was conducted.The results reveal that there is a linear relationship between settlement and leaked volume when the leaked volume was controlled within the allowable limit.

Analysis of unlined pressure shafts and tunnels of selected Norwegian hydropower projects

Norwegian hydropower industry has more than 100 years of experiences in constructing more than4000 km-long unlined pressure shafts and tunnels with maximum static head of 1047 m（equivalent to almost 10.5 MPa） reached at unlined pressure tunnel of Nye Tyin project. Experiences gained from construction and operation of these unlined pressure shafts and tunnels were the foundation to develop design criteria and principles applied in Norway and some other countries. In addition to the confinement criteria, Norwegian state-of-the-art design principle for unlined pressure shaft and tunnel is that the minor principal stress at the location of unlined pressure shaft or tunnel should be more than the water pressure in the shaft or tunnel. This condition of the minor principal stress is prerequisite for the hydraulic jacking/splitting not to occur through joints and fractures in rock mass. Another common problem in unlined pressure shafts and tunnels is water leakage through hydraulically splitted joints or pre-existing open joints. This article reviews some of the first attempts of the use of unlined pressure shaft and tunnel concepts in Norway, highlights major failure cases and two successful cases of significance, applies Norwegian criteria to the cases and reviews and evaluates triggering factors for failure.This article further evaluates detailed engineering geology of failure cases and also assesses common geological features that could have aggravated the failure. The minor principal stress is investigated and quantified along unlined shaft and tunnel alignment of six selected project cases by using threedimensional numerical model. Furthermore, conditions of failure through pre-existing open joints by hydraulic jacking and leakage are assessed by using two-dimensional fluid flow analysis. Finally, both favorable and unfavorable ground conditions required for the applicability of Norwegian confinement criteria in locating the unlined pressure shafts and tunnels for geotectonic environment different from that of Norway are highlighted.

Novel numerical model to simulate water seepage through segmental gasketed joints of underwater shield tunnels considering the superimposed seepage squeezing effect

The water leakage through segmental joint gaskets has become a major concern that adversely affects the normal serviceability of underwater shield tunnels throughout the construction and operational periods.Therefore,it is of great significance to investigate the sealing performances of the joint gaskets,which directly helps evaluate the waterproof capacity of underwater shield tunnels.To date,the numerical modeling plays an irreplaceable role in the analysis on the waterproof capacity of the joint gaskets.Nevertheless,conventional methods tend to ignore the self-sealing effect induced by the water seepage pressurization,thus failing to reveal the progressive evolution of the water infiltration process through the joint gasket.To remedy this defect,this paper proposed a novel numerical model to simulate the penetration process of the sealing gasket based on the Python language-enabled secondary programming in the ABAQUS software,which could fully consider the superimposed seepage squeezing effect.Based on the proposed model,the waterproof failure process and the dynamic contact stress of the gasket’s water seepage path subject to excessive hydraulic pressure were thoroughly investigated.Moreover,indoor tests on the waterproof capacity of the gasket were also performed to validate the proposed model.It is found that the numerical results from the developed model are consistent with the experimental results.This research will contribute to better understanding of the gaskets’hydraulic penetration process and more accurate prediction of the maximum waterproof capacity in underwater shield tunnels.

A Comprehensive Study on the Consequences of Gap-Graded Sands Considering the Loss of Fine Particles

Water and sand leakage disasters are likely to occur during construction in water-rich sand layer areas,resulting in ground collapse.The stress-strain action characteristics of discontinuous graded sand under different internal erosion degrees,and the evolution mechanism of water and sand leakage disasters caused by the internal erosion need to be further explored.Therefore,this paper takes the discontinuous graded sand in a water rich sand layer area in Nanchang City of China as the research object.Considering the influence of different fine particle losses(0,10%,20%and 30%)under the internal erosion of sand,the salt solution method is used to realize the specified loss of fine particles in the internal erosion.The stress-strain behavior after the loss of fine particles due to internal erosion is studied by triaxial shear test.Meanwhile,the physical model test and PFC-CFD method are both used to study the evolution rules of water and sand leakage disaster considered the influence of internal erosion degrees.Results show that:(1)under the same confining pressure,the peak failure strength of sand samples decreases along with the increase of fine particle loss.(2)In the water and sand leakage test of saturated sand,a natural filter channel is formed above the observed soil arch.The greater the loss of fine particles,the steeper and wider the collapse settlement area.(3)The relationship between the cumulative amount of water and sand leakage and time is nonlinear.The total mass loss of sand increases along with the increase of internal erosion degree.(4)After the soil arch is formed around the damaged opening,the sand continues to converge above the soil arch under the action of water flow,resulting in the dense convergence of contact force chains.

Deep learning based water leakage detection for shield tunnel lining

Shield tunnel lining is prone to water leakage,which may further bring about corrosion and structural damage to the walls,potentially leading to dangerous accidents.To avoid tedious and inefficient manual inspection,many projects use artificial intelligence(Al)to detect cracks and water leakage.A novel method for water leakage inspection in shield tunnel lining that utilizes deep learning is introduced in this paper.Our proposal includes a ConvNeXt-S backbone,deconvolutional-feature pyramid network(D-FPN),spatial attention module(SPAM).and a detection head.It can extract representative features of leaking areas to aid inspection processes.To further improve the model's robustness,we innovatively use an inversed low-light enhancement method to convert normally illuminated images to low light ones and introduce them into the training samples.Validation experiments are performed,achieving the average precision(AP)score of 56.8%,which outperforms previous work by a margin of 5.7%.Visualization illustrations also support our method's practical effectiveness.

HIRFL cooling water-monitoring system design and construct

Background HIRFL is a heavy ion accelerator built by the Institute of Modern Physics,Chinese Academy of Sciences,which constitutes a total length of over 900 m by the SFC,SSC,CSRm,CSRe and so on.It bears a lot of research task of the country,so to ensure its safe operation is very important.Purpose Cool-water system is a key part in HIRFL,and the parameters of the cool-water system need to be monitored before an accident occurs.Methods This article describes three aspects of the system,from the water leakage detection,pressure monitoring,to the water-level monitoring.A complete monitor system was designed and constructed,including the hardware structure;the data transfer mode,as well as specific control program.C++,FLASH and SCADA are used in the monitoring system.Results Fault alarm was performed timely and accurately by the monitoring system,and many accidents were avoided.Conclusion Water system monitoring is an important part of the accelerator control system.It will also play a major role in the construction of large-scale scientific device named HIAF in the further.

Liquid Level Sensor Based on CMFTIR Effect in Polymer Optical Fiber

The macro-bending induced optical fiber cladding modes frustrated total internal reflection effect is used to realize the liquid level probe with a simple structure of single macro-bend polymer optical fiber loop. The test results show that the extinction ratio reaches 1.06dB. ＂First bath＂ phenomenon is not obvious （about 0.8%）. The robustness of the sensor is better, and the ability of anti-pollution is stronger compared with the conventional sensors. The process of making this sensing probe is extremely easy, and the cost is very low.