Underwater Tunnel Research Articles

Analytical solution for calculating three-dimensional responses due to dynamic loads acting on an underwater tunnel in stratified soil

Hydroacoustic noise generated by trains running in underwater tunnels significantly impacts aquatic ecosystems, particularly fish breeding grounds and the habitats of endangered species. This underscores the necessity of investigating the characteristics of wave propagation and noise radiation emanating from underwater tunnels. This study proposes a novel analytical method for calculating 3D responses due to a dynamic point load acting on an underwater tunnel in stratified soils that considers dynamic tunnel–soil–fluid interactions. Stratified soils consist of multiple sediment layers, which are simulated as saturated porous media, overlying substrate layers, which are modeled as phase elastic media. The transfer matrix method is applied to simulate wave propagation in a layered fluid–solid system. The functions describing various types of waves scattered at the layer interfaces and the tunnel–soil interface are unified by wave transformation, thereby deriving an analytical solution for dynamic tunnel–soil–fluid interactions. A comparison with existing methods via numerical cases confirms the accuracy of the proposed method. Vibrations and hydroacoustic noise owing to dynamic loads acting on an underwater tunnel buried either in a saturated sediment layer or a single-phase substrate layer are investigated. The influences of tunnel burial depth, layering, as well as the porosity and permeability of saturated sediment are systematically analyzed. This research enhances the understanding of wave propagation and noise radiation in water emanating from underwater tunnels, facilitating the development of vibration isolation measures and protecting aquatic ecosystems.

A method for detecting defects in reinforced concrete structures of underwater tunnels based on ultrasonic echo signal and CNN

Due to the long-term effects of wind and wave corrosion and hydraulic erosion on underwater structures, various degrees of damage such as cracks, holes, and corrosion may occur. When underwater attachments cause lift off disturbances, various interference signals are introduced, increasing the difficulty of defect detection. In order to maintain the safety and stability of reinforced concrete structures in underwater tunnels in a timely manner, a defect detection method for reinforced concrete structures in underwater tunnels based on ultrasonic echo signals and the CNN is proposed. The collection method and formation mechanism of ultrasonic echo signals for reinforced concrete structures in underwater tunnels are analyzed first. After obtaining the ultrasonic echo signals, noise is removed from the signals through empirical mode decomposition and the sparse table algorithm. An ultrasonic defect detection model for concrete structures based on the multi-attention FasterRCNN structure is constructed, the denoised ultrasonic echo signal is input into the model, the multi-attention mechanism is applied to extract the characteristics of the ultrasonic echo signal, and a balanced feature pyramid network is used to achieve feature fusion. The fused features are generated into defect candidate boxes through regional generation networks, and defect position information and category information are output at the fully connected layer of the model to complete defect detection of reinforced concrete structures in underwater tunnels. The experimental results show that this method can accurately remove noise from the echo signal of reinforced concrete structures and shows high denoising performance. When conducting defect detection, it can quickly detect the defect category and position, and provide the defect depth and diameter. The detection results are accurate and do not show significant errors.

A Drone-Based Structure from Motion Survey, Topographic Data, and Terrestrial Laser Scanning Acquisitions for the Floodgate Gaps Deformation Monitoring of the Modulo Sperimentale Elettromeccanico System (Venice, Italy)

The structural deformation monitoring of civil infrastructures can be performed using different geomatic techniques: topographic measurements with total stations and levels, TLS (terrestrial laser scanning) acquisitions, and drone-based SfM (structure from motion) photogrammetric surveys, among others, can be applied. In this work, these techniques are used for the floodgate gaps and the rubber joints deformation monitoring of the MOSE system (Modulo Sperimentale Elettromeccanico), the civil infrastructure that protects Venice and its lagoon (Italy) from high waters. Since the floodgates are submerged most of the time and cannot be directly measured and monitored using high-precision data, topographic surveys were performed in accessible underwater tunnels. In this way, after the calculation of the coordinates of some reference points, the coordinates of the floodgate corners were estimated knowing the geometric characteristics of the system. A specific activity required the acquisition of the TLS scans of the stairwells in the shoulder structures of the Treporti barrier because many of the reference points fixed on the structures were lost during the placement of elements on the seabed. They were replaced with new points whose coordinates in the project/as-built reference system were calculated by applying the Procrustean algorithm by means of homologous points. The procedure allowed the estimation of the transformation parameters with maximum residuals of less than 2.5 cm, a value in agreement with the approximation of the real concrete structures built. Using the obtained parameters, the coordinates of the new reference points were calculated in the project reference system. Once the 3D orientation of all caissons in the barrier was reconstructed, the widths of the floodgate gaps were estimated and compared with the designed values and over time. The obtained values were validated in the Treporti barrier using a drone-based SfM photogrammetric survey of the eight raised floodgates, starting from the east shoulder caisson. The comparison between floodgate gaps estimated from topographic and TLS surveys, and those obtained from measurements on the 3D photogrammetric model, provided a maximum difference of 1.6 cm.

A new fractal model for flow-solid-chemical multi-field coupling in underground engineering

The permeation diffusion behavior of chloride ions with seawater is one of the key factors causing damage to reinforced concrete structures due to seawater erosion of steel bars. This study establishes a new mathematical model for chloride ion transport in reinforced concrete structures exposed to seawater. The model captures the effect of chloride ions on underwater tunnel structures effectively and provides a valuable theoretical basis for the maintenance and safety of these structures. The proposed model uniquely incorporates the microscopic pore structure characteristics of concrete and the effects of static water pressure and porosity on chloride ion diffusion. The results show that: (1) the diffusion coefficient of chloride ions first increases rapidly, then remains basically unchanged and gradually decreases; (2) there is a non-linear positive correlation between porosity, static water pressure, and maximum corrosion thickness; and (3) the fractal dimension of pore curvature is opposite to the fractal dimension of pore size and crack length.

Variation of segment joint opening of underwater shield tunnel during long operational period

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.

Combustion characteristics and mechanism of hydrothermally aged asphalt in underwater tunnels

Asphalt could suffer hydrothermal ageing in underwater tunnels, which varies its combustion characteristics significantly. The hydrothermally aged asphalt (HA) was comparatively studied with base asphalt (BA) and thermal-oxidatively aged asphalt (TA). Major findings are achieved: (1) The C＝O and S＝O bonds are more abundant in TA/HA than BA. HA contains more prominent –OH and H2O but less substantial aliphatics. And it has lower SO than TA by about 20 %, attributing to the oxygen isolation of aqueous immersion during hydrothermal ageing. (2) Remarkably bimodal heat release rate (HRR) peaks are found for HA, while only unimodal HRR peak is observed for TA/BA. Importantly, the primarily main HRR peak of HA occurs at around 110 s, which exhibits to be earlier than those of TA/BA by over 120 s. Meanwhile, the fire growth rate index (FGRA) of HA is higher than those of TA/BA by more than 15 %, implying that hydrothermal ageing dramatically increases the asphalt's fire risk. (3) Herein, the combustion mechanism of bimodal HRR peaks found for HA is analyzed, attributing to thin-layer boilover effect. This could be supported by plentiful pores observed on the combusted HA via scanning electron microscopy technique.

Small‐scale fire tests in the underwater tunnel section model with new sidewall smoke extraction

Small‐scale fire tests in the underwater tunnel section model with new sidewall smoke extraction

Blast protection of underwater tunnels with 3D auxetic materials

Abstract In recent years, the risk of blast attacks on underwater tunnels, important transportation routes, has increased due to the growing prevalence of vicious regional conflicts and global terrorist activities. In this work, we investigate the blast impact behavior of underwater tunnels filled with honeycomb core and covered by solid panels. The core is composed of 3D auxetic materials with high energy absorption compared to conventional honeycombs. In order to improve the stiffness of the auxetic structures, a pair of crossed rods is introduce to each cell. The relative densities of 3D auxetic structures are derived theoretically. The coupling effects of the geometrical parameters on the relative density are investigated. Then the deformation patterns of the underwater tunnels at different blast heights are analyzed. The kinetic energy and absorbed energy are discussed for tunnels with 3D auxetic materials and solid materials. Results show that tunnels composed with 3D reinforced auxetic structures can absorb much more energy than solid ones. Moreover, localized damage is observed which means greater chance of survival and smaller repairs after extreme impact. Finally, a stiffness-improved 3D reinforced auxetic structure is presented to enhance the tunnel’s strength and stability further.

Underwater Backscatter: What is its Practical Communication Distance?

Recent years have seen mounting interest in low-power, distributed subsea internet-of-things (IoT) networks because of their potential in environmental, industrial, and defense applications [1,2]. Energy-efficient ocean IoT networks can enable long-term sensing of ocean variables (temperature, pH, pressure, salinity, etc.) to create more accurate climate and weather prediction models and monitor the impact of climate change on the ocean [3]. Similarly, low-cost and efficient ocean IoT networks can help boost the growth of the world's blue economy by enabling active monitoring of marine infrastructures ranging from oil/gas pipelines to underwater tunnels [4]. Real-time distributed underwater sensor networks can help boost aquaculture (seafood farm) production by monitoring the farm vitals (water temperature, dissolved nutrients, pH, etc.) and detecting environmental hazards (such as harmful algae blooms) early [5].

Experimental Study on the Forced Ventilation Safety during the Construction of a Large-Slope V-Shaped Tunnel

The special large-slope V-shaped structure of underwater tunnels changes the ventilation characteristics during tunnel construction, making the traditional experience limited. Therefore, it is urgent to study the influence of the special structure on the safety of the air environment during construction. In this paper, a series of small-scale experiments were conducted to investigate the ventilation characteristics of V-shaped tunnels. The coupled effects of ventilation parameters (distance of duct outlet from working face Lo, air velocity at the duct outlet uo) and structural characteristics (digging length Ld, slope of the uphill section q) were considered. The extreme slope of the V-shaped tunnel of 8% was considered. The flow field and pollutant transport law were determined by using CO as a tracer in the experiments. The results show that uo has a positive impact on the air return velocity, while Ld has a negative impact, and neither of the other two factors has a significant effect. The transport characteristics of CO in V-shaped tunnels differ from those in flat tunnels, with the former tending to cause unconventional areas of high pollutant concentrations in the horizontal sections. Furthermore, the correlations between CO concentration and distance, ventilation time, and the influence factors discussed in this paper are derived from the experimental results. The conclusions provide guidance for the construction of V-shaped tunnels to prevent air pollution in the construction environment and to improve the working conditions of laborers. Additionally, it can also enrich the ventilation experience in tunnel construction.

Seepage Behavior of Underwater Tunnels in Stratum with Inclined Surface: Insights from Numerical Analysis

This paper is to investigate the seepage behavior of underwater tunnel with inclined boundary at the contact between water body and underwater stratum. Extensive finite element analyses using COMSOL are performed considering various magnitudes of inclination degree of underwater soil surface. The rationality of the numerical analysis method is demonstrated via comparing with analytical solutions. It is found that the inclined boundary has a significant impact on the seepage field of underwater tunnel. The hydraulic head distribution, streamline evolution, velocity and other aspects are comprehensively analyzed, and relevant conclusions are drawn. The streamlines in waters are not vertically downward, but presents a certain acute angle distribution with the stratum direction. And the interface angle toward the depth is larger. Streamlines will also become denser. The streamline flows into the tunnel from all directions. And the attenuation speed of water head in the lower part of tunnel is less than that in the upper part. Thereby serving the optimal design and construction of practical projects.

Adaptive Control of Underwater Tunnel Monitoring Robot Based on IoT and Fuzzy Neural Network Algorithm

Abstract To improve the navigation ability of underwater tunnel monitoring robots at fixed distances, directions, depths, and heights and to improve the accuracy of tunnel monitoring, an adaptive control method for underwater tunnel monitoring robots based on the Internet of Things (IoT) and fuzzy neural network algorithms is proposed. The structure of underwater tunnel monitoring robots is analyzed based on the IoT, the convolutional neural network algorithm is used to extract the tracking target characteristics of the underwater tunnel monitoring robot, and the obstacle avoidance process of the underwater tunnel monitoring robot is analyzed. The membership degree of the input variable is calculated by the fuzzy control algorithm. The control rule optimizes the neural network algorithm, obtains the target characteristics displayed by the visual tracking of the underwater tunnel monitoring robot based on the fuzzy neural network, uses the adaptive control to estimate the optimal parameters, and finally obtains the adaptive sliding mode control of the underwater tunnel monitoring robot. The experimental results show that the proposed method can accurately realize the target tracking task of the underwater tunnel monitoring robot and has better obstacle avoidance ability.

Prediction of Wet Area of Underwater Tunnel Lining

The issue of water seepage poses a significant challenge in tunnel infrastructure. Wet areas are commonly used to evaluate the degree of water seepage in tunnel projects. To investigate the feasibility for numerical simulation to predict a wet area, we selected concrete test blocks with two types of defects—holes and cracks—as the research specimens. Numerical models for various seepage conditions were constructed using TOUGH2, and the results were validated through laboratory experiments. Additionally, the Shenjiamen Subsea Tunnel was simplified into a numerical model, employing TOUGH2 to forecast its future wet area performance within the scope of national standards. The outcomes of our research revealed that point seepage and line seepage exhibited circular and elliptical morphologies, respectively. Moreover, external water pressure and defect size exerted a significant influence on the expansion of the wet area. Notably, the impact of crack width surpassed that of hole diameter. Encouragingly, the numerical models generated using TOUGH2 for unsaturated concrete demonstrated excellent agreement with laboratory test results concerning the geometry, size, and pattern of the wet area. These findings signified the potential of TOUGH2 numerical simulation as a valuable tool in predicting the lifespan of tunnels.

Study on Numerical Simulation of Surrounding Rock Structure Safety of Urban Underwater Shield Tunnel: A Case in Chongqing

Based on the engineering background of shield construction of a subway section in Chongqing, which needs to pass through a park and there is a lake inside this park, this paper adopts theoretical analysis methods and numerical simulation calculation methods to explore the distribution law of the seepage field and the characteristics of water pressure in lining segments during shield tunneling. The results show that, during the whole excavation of a double-track tunnel with EPB shield, the maximum vertical effective stress is about 4.24 MPa, which is located at the arch foot of the tunnel. The maximum effective stress in the horizontal direction is about 3.61 MPa, which is located on both side walls of the tunnel in the horizontal direction; after the left and right tunnels are excavated in sequence, a “double precipitation funnel-shaped” pore pressure distribution is formed around the tunnel; during the construction of the shield tunnel, the vertical displacement and horizontal displacement of the surrounding rock show an increasing trend and gradually tend to be stable values of 24.09 mm and 25.28 mm; the segment vault has settlement, the maximum settlement is 21.8 mm, the arch bottom has uplift, and the maximum uplift is 24.4 mm. The maximum horizontal displacement of the segment appears on both sides of the arch waist, and the maximum horizontal displacement decreases with the increase of excavation steps; the positive bending moment of the lining segment is mainly distributed on both sides of the arch crown, and the negative bending moment is mainly distributed on both sides of the arch bottom. The axial force of the lining segment is compressive stress, and the maximum axial force is mainly distributed on both sides of the arch waist. The maximum normal shear stress occurs on both sides of the segment arch bottom. The study conclusions provide theoretical foundation and a new guidance for long-term safety evaluation of underwater tunnel structures.

Seismic fragility curves of circular tunnels in saturated sand

This paper aims to derive seismic fragility curves for circular tunnels constructed in saturated sand. A bounding surface plasticity constitutive model is used to simulate the progressive accumulation of strains and the subsequent buildup of excess pore pressure in saturated sand under undrained conditions with cycles of loading. For comparative analysis, dynamic analyses under drained conditions are also conducted. The fully coupled numerical method, validated by centrifuge shaking table tests, provides a satisfactory explanation for the dynamic characteristics of soil–tunnel systems. On this basis, ten near-fault seismic motions are scaled incrementally to evaluate the dynamic performance under increasing seismic intensity for deriving the fragility curves. The investigation of the optimal intensity measure involves the correlation of structural response with peak ground acceleration/ velocity/ displacement and peak bedrock acceleration, respectively. The safety of tunnels is evaluated by the developed fragility curves, which account for the site effects of sand liquefaction on both structural response and fragility. The developed fragility curves also highlight the impacts of tunnel buried depth and sand relative density on the structural response and fragility of circular tunnels in liquefiable soils, providing a benchmark for the seismic hazard evaluations of underwater tunnels.

Water infiltration in drained circular tunnels: an analytical solution and its simplification

Underwater tunnels are often subject to groundwater infiltration, which can pose risks both to the tunnel's safety and the groundwater environment. Analytical solutions are commonly used to estimate the rate of water infiltration in tunnels. However, there is a lack of research on the analytical solution of tunnels with drainage systems. The aim of this study was to investigate groundwater seepage in tunnels with circumferentially arranged drainage pipes. The analytical formula for estimating the inflow rate takes into account the seepage processes in the ground, primary lining and geotextile. The accuracy of the analytical solution is confirmed by comparing it with numerical results. The analytical solution's general form is simplified for tunnels with varying permeabilities of the surrounding strata and geotextiles, and a query chart is created to facilitate engineering applications. The research findings can serve as a theoretical basis and reference for the establishment of relevant specifications and the design of tunnel drainage systems.

A Numerical Output Technique for Voxler’s ObliqueImages and Its Application

In geophysical surveys, there will be no measured data at some location where it is inaccessible for placement of survey points or lines. The interpolation data of those locations can be obtained and displayed by using three-dimensional (3D) mapping platform. Based on the study of the file format of ObliqueImage output in Voxler platform, this paper presents a technique for extracting spatial coordinates and physical parameter values of each point in the ObliqueImage. This numerical output technique is used to map the profiled slice across the tunnel axis where boreholes can not be arranged in the electromagnetic wave CT investigation section in a dedicated karst survey of an underwater tunnel in Wuhan, rendering the karst development on the profile across the tunnel axis; after further extension, the point cloud data of bedrock surface and karst caves for building 3D geological model are extracted from isosurface files, which provides data basis for tunnel design and construction digitization.

Driver’s Shy Away Effect in Urban Extra-Long Underwater Tunnel

For urban extra-long underwater tunnels, the obstacle space formed by the tunnel walls on both sides has an impact on the driver's driving. The aim of this study is to investigate the shy away characteristics of drivers in urban extra-long underwater tunnels. Using trajectory offset and speed data obtained from real vehicle tests, the driving behaviour at different lanes of an urban extra-long underwater tunnel was investigated, and a theory of shy away effects and indicators of sidewall shy away deviation for quantitative analysis were proposed. The results show that the left-hand lane has the largest offset and driving speed from the sidewall compared to the other two lanes. In the centre lane there is a large fluctuation in the amount of deflection per 50 seconds of driving, increasing the risk of two-lane collisions. When the lateral clearances are increased from 0.5 m to 2.19 m on the left and 1.29 m on the right, the safety needs of drivers can be better met. The results of this study have implications for improving traffic safety in urban extra-long underwater tunnels and for the improvement of tunnel traffic safety facilities.

Analysis of interaction between tunnel support system and surrounding rock for underwater mined tunnels considering the combined effect of blasting damage and seepage pressure

When an underwater tunnel is constructed using the drill-and-blast method, the rock mass around the tunnel undergoes significant blasting damage. Quantifying the combined effect of blasting damage and seepage pressure on the support–surrounding rock interaction is critical for an underwater mined tunnel. An analytical model is proposed to analyze the entire process of support-surrounding rock interaction in an underwater mined tunnel considering the combined effect of blasting damage and seepage pressure. First, the ground reaction curves are derived considering the combined effect of blasting damage and seepage pressure. Four configurations according to the distribution of plastic zone in the damaged and undamaged zones are distinguished and solved. Subsequently, the fictitious pressure, which is introduced to quantify the spatial effect of tunnel face, is also solved. Thereafter, combining Hoek’s longitudinal displacement profile expression and the proposed ground reaction curve solution, an analytical algorithm for the support–surrounding rock interaction is proposed. The tunnel displacement and support pressure during the entire process of support–surrounding rock interaction are obtained, which are in agreement with the 3D numerical simulations and field monitoring results. Compared with the conventional convergence-confinement method, the performance and advantages of the proposed method are demonstrated. The proposed method is feasible with higher confidence for the preliminary design of underwater mined tunnel, particularly for tunnels excavated in weak zones.

Analysis of Visual Load on Curve and Longitudinal Slope Combination of Extra-Long Underwater Tunnel Based on Visual Sensitive Region

Extra-long underwater tunnels are important traffic nodes in urban road networks and have a high incidence of traffic accidents. The frequent occurrence of curve and longitudinal slope combinations in such tunnels increases crash risk and has a negative impact on traffic safety. Vision is the most important way to obtain traffic information, and visual load is a good measure of driving risk. To explore the impact of curve and longitudinal slope combinations on a driver’s visual load in an extra-long underwater tunnel, eye-movement data and speed data were obtained through a vehicle experiment. Based on driver gaze distribution, the area and location of the visual sensitive region are calculated, and a model of the relationship between the region’s stability and the curve and longitudinal slope at different speeds is established, and applied to the visual-load evaluation. The results show that the curve or longitudinal slope has a significant influence on vehicle speed. High-visual-load areas are mainly located in small-radius curve and large longitudinal slope combination areas and extremely small-radius curve areas. For example, for a combination of left-turn curve and longitudinal slope with a speed of 50–60 km/h, when the curve radius is less than 1150 m and the longitudinal slope is less than −2.4%, or the curve radius is less than 1100 m and the longitudinal slope is greater than 2.2%, the visual load is high and driving safety is poor. This study can provide a theoretical basis for tunnel alignment design and safe operation.