Subsea Tunnel Research Articles

Microbial acidification by N, S, Fe and Mn oxidation as a key mechanism for deterioration of subsea tunnel sprayed concrete

The deterioration of fibre-reinforced sprayed concrete was studied in the Oslofjord subsea tunnel (Norway). At sites with intrusion of saline groundwater resulting in biofilm growth, the concrete exhibited significant concrete deterioration and steel fibre corrosion. Using amplicon sequencing and shotgun metagenomics, the microbial taxa and surveyed potential microbial mechanisms of concrete degradation at two sites over five years were identified. The concrete beneath the biofilm was investigated with polarised light microscopy, scanning electron microscopy and X-ray diffraction. The oxic environment in the tunnel favoured aerobic oxidation processes in nitrogen, sulfur and metal biogeochemical cycling as evidenced by large abundances of metagenome-assembled genomes (MAGs) with potential for oxidation of nitrogen, sulfur, manganese and iron, observed mild acidification of the concrete, and the presence of manganese- and iron oxides. These results suggest that autotrophic microbial populations involved in the cycling of several elements contributed to the corrosion of steel fibres and acidification causing concrete deterioration.

The corrosion expansion force and cracking separation between corroded section steel arch frame and shotcrete in tunnel primary support

High chloride content in the subsea tunnel environment leads to inevitable corrosion of I-shaped steel in primary support. Corrosion generates expansive force between I-shaped steel and concrete, eventually cracking the concrete protective layer, and weakening the bond strength, severely impacting the tunnel support system’s durability. The main purpose of this article is to obtain the corrosion expansion force generated at the interface between corroded I-shaped steel and concrete, as well as the mechanical response characteristics of concrete under the action of corrosion expansion force. Firstly, nine I-shaped steel concrete components were fabricated for electro-accelerated corrosion test, obtaining the variation curve of corrosion expansion force with corrosion rate and protective layer thickness. The experimental results indicated that the development of corrosion expansion force can be divided into three stages: initial free corrosion stage (corrosion rate ρ = 0.5 % – 0.7 %), stage with a noticeable increase in corrosion expansion force (corrosion rate ρ = 0.7 % – 12 %), and expansion-induced cracking (corrosion rate ρ > 12 %). Meanwhile, a three-stage corrosion expansion force model for concrete and corroded I-shaped steel was proposed, which was correlated to the experimental curve well. Finally, the mechanical characteristics of the surrounding concrete during the development process of different corrosion expansion forces were explored through ANSYS software. The numerical results indicated that these cracks due to corrosion expansion force primarily occurring in the contact region between the concrete and the I-shaped steel flange, specifically in three areas: the central part of the flange and its two corners; The tensile stress in the concrete surrounding the web plate is less than that at the flange, leading to the initial longitudinal cracking observed on the outer surface of the flange.

The collapse mechanism in a subsea tunnel passing through the fault: a model test study

The collapse mechanism in a subsea tunnel passing through the fault: a model test study

Assessing and predicting surrounding rock settlement troughs in the subsea tunnel: A case study of Haicang Tunnel

To ensure the safety of subsea tunnel construction, it is crucial to prevent extreme deformation of the surrounding rock. An assessment and prediction study on the surrounding rock deformation induced by the excavation of the subsea tunnel using the three-bench method was conducted, based on Haicang Subsea Tunnel in Xiamen, China. A series of numerical simulations and on-site monitoring were conducted to reveal the evolution of the displacement field of the surrounding rock. The influences of various factors on the settlement trough of the surrounding rock above the subsea tunnel were also investigated, including seawater, bench length, and bench spacing. The rapid ring closure of the primary support by adopting short benches is imperative to control the arch settlement and settlement trough width. The settlement resulting from the excavation of the upper and middle benches contributed to 90% of the total deformation, as revealed by both numerical simulation and in-situ monitoring. Subsequently, an empirical formula was proposed to predict the settlement trough curves of surrounding rock at different depths above the seabed tunnel.

Analysis of visual and acoustic measures for self-evacuations in road tunnels using virtual reality

Emergency fire situations in tunnels can be especially dangerous when occurring in long underground or subsea tunnels, particularly when evacuation on foot is the only alternative. This paper presents the results from a study comparing different visual and acoustic measures to facilitate efficient and safe emergency evacuation and their effect on people's self-rescue behaviour in response to a tunnel fire. Eighty-one participants evaluated seven different scenarios in virtual reality with or without visual and acoustic supporting measures (i.e. signs, lights, acoustic beacons) to find their way to emergency doors. Objective behavioural data, such as orientation, and walking speed, were collected. The results suggest that the distance between the emergency doors increases uncertainty and affects the time to self-rescue significantly, with four times longer times for 500 m than 250 m between doors. Additionally, the use of continuous guiding lights positively supported orientation and walking speed, with 97 % of the participants finding their way and showing a reduction of time to reach the emergency door of 10–20 s. The study underscores the importance in the proper visual and acoustic evacuation measures for the wayfinding of emergency exits, improving self-rescue of people.

Health Risk Prediction of Operational Subsea Tunnel Structure Based on Bayesian Network

Recently, subsea tunnel construction has developed rapidly in China. The traffic volume of subsea metro tunnels is large. Once a safety accident occurs, economic losses and social impacts will be extremely serious. To eliminate accidents in operational subsea metro tunnel structures, a health risk prediction method is proposed based on a discrete Bayesian network. Detecting and monitoring data of the tunnel structures in operation were used to evaluate the health risk by employing the proposed method. This method establishes a Bayesian network model for the health risk prediction of the shield tunnel structure through the dependency relationship between the health risk of the operational tunnel structure and 13 risk factors in five aspects: the mechanical condition, material performance, integrity state, environmental state, and deformation state. By utilizing actual detection and monitoring data of various risk factors for the health risk of the operational subsea metro shield tunnel structure, this method reflects the actual state of the tunnel structure and improves the accuracy of health risk predictions. The validity of the proposed method is verified through expert knowledge and the subsea shield tunnel structure of the Dalian Subway Line 5. The results demonstrate that the health risk prediction outcomes effectively reflect the actual service state of the shield tunnel structure, thus providing decision support for the control of health risks in the subsea metro shield tunnel.

Dynamic Stability Analysis of Subsea Tunnel Crossing Active Fault Zone: A Case Study

The rock strength in an active fault zone is low and the surrounding rock is fractured and has poor stability, making any subsea tunnel crossing the active fault zone extremely susceptible to disasters such as tunnel collapse, sudden water ingress, and mud inrush. This poses a potential threat to the construction project, making the dynamic stability analysis of a subsea tunnel crossing an active fault zone of great significance. This study takes the second subsea tunnel crossing the Cangkou Fault in Jiaozhou Bay as the engineering background and conducts numerical simulations by employing different lining stiffnesses for tunnel excavation, as well as applying dynamic loads. The dynamic stability of the subsea tunnel crossing the active fault zone is evaluated by comparing and analyzing the lining’s displacement, peak acceleration, and stress characteristics. This study explores the disaster-causing mechanisms of active fractures, determining that the hazard of orthogonal misalignment in an active fault zone is the least severe, while the hazard of opposite misalignment is the most severe. This research provides a basis for disaster prevention and mitigation in active fracture zones.

Design and Evaluation of Novel Submerged Floating Tunnel Models Based on Dynamic Similarity

Submerged floating tunnels (SFTs), also known as the Archimedes Bridge, are new transportation structures designed for crossing deep waters. Compared with cross-sea bridges and subsea tunnels, SFTs offer superior environmental adaptability, reduced construction costs, and an enhanced spanning capacity, highlighting their significant development potential and research value. This paper introduces a new type of SFT scale model for hydrodynamic experiments, adhering to the criteria for geometric similarity, motion similarity, and dynamic similarity principles, including the Froude and Cauchy similarity principles. This model enables the accurate simulation of the elastic deformation of the tunnel body and complex hydrodynamic phenomena, such as fluid–structure interactions and vortex–induced vibrations. Moreover, this paper details the design methodology, fabrication process, and method for similarity evaluation, covering the mass, deflection under load, natural frequency in air, and the natural frequency of the various underwater motion freedoms of the model. The results of our experiments and numerical simulations demonstrate a close alignment, proving the reliability of the new SFT scale model. The frequency distribution observed in the white noise wave tests indicates that the SFT equipped with inclined mooring cables experiences a coupled interaction between horizontal motion, vertical motion, and rotation. Furthermore, the design methodology of this model can be applied to other types of SFTs, potentially advancing technical progress in scale modeling of SFTs and enhancing the depth of SFT research through hydrodynamic experiments.

Research on the effects of ocean current on nuclear wastewater in Japan

According to reports, the Fukushima Daiichi Nuclear Power Station nuclear pollution water drainage project has been completed. Subsequently, Tokyo Electric Power will directly discharge nuclear wastewater into the ocean through a subsea tunnel connecting the land. These nuclear wastewater will be discharged to the waters near the Tropic of Cancer, which is greatly affected by the Japanese warm current, and nuclear wastewater will be taken around the world through ocean currents. German research institutions point out that within a month from the date of discharge of Fukushima nuclear wastewater, its radioactive material will spread to most of the Pacific Ocean, which will seriously affect global fish migration, ocean fisheries, human health and ecological security. Due to the impact of the global ocean current, China's East China Sea, the Yellow Sea and the Bohai Sea will also be affected by nuclear waste water pollution. Based on this, this text will start from the impact of the El Nino warm current on the flow of nuclear wastewater, and will soon explain the impact of Japan's dumping of nuclear wastewater on global security, and from a personal perspective on the current view of environmental protection and governance.

Development of a water leakage model test system and investigation of the water leakage behavior in subsea shield tunnels during operation

With the increasing mileage and operation time of China's subsea tunnels, tunnels are entering a period of high disaster. Water leakage is one of the most common disasters. To study the mechanism of water leakage in subsea shield tunnels during the service period, a model test study was carried out by proposing a novel tunnel seepage leakage model test system in this paper. The system consists of a model frame, ground stress loading system, hydraulic pressure loading system, temperature control system, and monitoring system. Through 3D printing, the tunnel segments were innovatively made of resin. The process of uneven settlement, seawater erosion, joint deformation, gasket stress relaxation, and water leakage during the service period were successfully simulated by heating the model segments and local overloading. The test results showed that the joint deformation with service life could be approximately divided into three stages: non-linear rapid growth, linear growth, and non-linear slow growth. And the joint deformation and the aging of the gasket resulted in the decrease of the contact stress of the segment joint. Both exacerbated the leakage in the joint. By the time the service life reaches 16th year, the waterproofing performance no longer met the waterproofing standard for subsea tunnels. The developed test device and method are practical in predicting water surges in subsea tunnels during service life. This paper provides new insights into long-term waterproofing performance testing of shield tunnels under complex conditions.

Dynamic response of subsea tunnel in liquefiable layered seabed under combined earthquake and wave action

Liquefaction poses a potential threat to the safety of subsea tunnel during the earthquake. In the ocean environment, wave pressure is considered as a normal loading applied at the seabed surface. This study proposed a fully coupled dynamic effective stress finite element model for subsea tunnel in liquefiable layered seabed under combined earthquake and wave action. Biot u-p formulation integrated with a modified generalized plasticity model was adopted for liquefaction analyses of the seabed. The proposed model was validated through a wave flume model test in terms of excess pore water pressure (EPWP). The results showed that the tunnel – soil dynamic interaction significantly increased EPWP near the tunnel. Increasing the wave height significantly increased the liquefaction depth of the seabed; however, the wave loading can either suppress the displacement of the tunnel during the earthquake or increase the uplift of the tunnel during the subsequent wave loading. When investigating seismic response of subsea tunnels in liquefiable soils under combined earthquake and wave action, the ground motion was suggested to be input simultaneously with the wave pressure. This study also highlights the effect of the thickness of liquefiable layer and frequency content of earthquakes on dynamic responses of subsea tunnels.

Magnesium ion corrosion in subsea tunnel grouting: Insights, mechanisms, and optimization strategies for enhanced durability

In the construction of subsea tunnels, grouting reinforcement is crucial for enhancing tunnel strength, impermeability, and stability. This article investigates the impact of prolonged exposure to seawater, specifically magnesium ion corrosion, on the degradation of the C-S-H gel and the weakening of grouting compounds. Utilizing erosion acceleration theory, an experimental setup simulating seawater flow is designed to explore erosion patterns and mechanisms. Macroscopic and microscopic experiments and analyses reveal that magnesium ion corrosion products, Mg(OH)2 and M-S-H, lack cementation ability, leading to detachment from the grouting compound. This detachment results in increased porosity, crack formation, and reduced strength and impermeability. The study recommends reducing the water–cement ratio and increasing grouting pressure to enhance composite strength and impermeability, with attention to boundary effects and prevention of magnesium ion corrosion product shedding. These findings have significant implications for optimizing subsea tunnel construction by improving grouting reinforcement design and ensuring long-term durability.

Mathematical simulation modeling analysis of sub-sea tunnel blasting based on grey correlation

Blasting in the ocean tunnel has a great impact on Marine life and seabed vegetation, so it is necessary to control the impact of blasting vibration on the surrounding Marine environment. In this paper, taking Xiamen Tunnel as an example, the blasting vibration response characteristics of undersea tunnel are studied, and the velocity attenuation rules of tunnel structure in different directions are obtained. The grey correlation theory is innovatively applied to analyze the correlation degree of factors affecting the blasting vibration effect of the undersea tunnel, and the key factors and secondary factors affecting the blasting vibration effect of the tunnel are determined. The grey correlation theory is used to analyze the correlation degree between the blasting vibration effect of the cross-tunnel, which is conducive to improving the safety and stability of tunnel construction. It provides a new idea and method for vibration control of similar projects.

Review of tunnels and tunnelling under unfavourable geological conditions

Considering the rapid expansion of the economy and the increasing demand for infrastructure development, the scale of the tunnelling is expanding, and tunnel is inevitably excavated under unfavourable geological conditions. Consequently, this brings multitude of risks and challenges to tunnels and tunnelling. This paper summarizes the engineering issues associated with five unfavourable geological conditions: soft soil strata, soft and hard composite strata, spatially variable strata, karst strata and subsea conditions. Various analysis methods for deformation problem of tunnel and tunnelling under these unfavourable geological conditions are discussed. The mechanisms of the progressive failure of tunnel faces and collapses of caves in karst tunnels are also presented, as well as the risk assessments and prevention strategies for karst tunnel and water inrush occurrences of subsea tunnel. Furthermore, the analysis of the response of subsea tunnels to dynamic loads such as wave forces and earthquakes is summarized. Additionally, the analysis and prevention techniques for constructing subsea tunnels in fault zones are also considered. Finally, this paper offers a glimpse into potential research directions for future analysis relevant to the topic discussed, aiming to provide guidance for secure construction and maintenance tunnels under unfavourable geological conditions.

A Review of Deep Learning Applications in Tunneling and Underground Engineering in China

With the advent of the era of big data and information technology, deep learning (DL) has become a hot trend in the research field of artificial intelligence (AI). The use of deep learning methods for parameter inversion, disease identification, detection, surrounding rock classification, disaster prediction, and other tunnel engineering problems has also become a new trend in recent years, both domestically and internationally. This paper briefly introduces the development process of deep learning. By reviewing a number of published papers on the application of deep learning in tunnel engineering over the past 20 years, this paper discusses the intelligent application of deep learning algorithms in tunnel engineering, including collapse risk assessment, water inrush prediction, crack identification, structural stability evaluation, and seepage erosion in mountain tunnels, urban subway tunnels, and subsea tunnels. Finally, it explores the future challenges and development prospects of deep learning in tunnel engineering.

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.

Comprehensive Application of Borehole Fine Detection Methods: A Case Study in Shantou Bay Subsea Tunnel

Water inrush disaster is one of the most severe problems during the construction of sea tunnels, primarily due to faults, karst, and weathered zones. Once a water inrush disaster occurs, it can lead to construction delays, traffic disruptions, and major economic losses, as well as potential consequences such as seawater intrusion, casualties, project suspension, and tunnel closure. Thus, advanced geological prediction is indispensable. During the construction of the Shantou Bay subsea tunnel, a sudden water inrush accident occurred in the sea–land transition section. To prevent such incidents and ensure safety, an integrated approach was employed. Firstly, the cross‐hole resistivity method was used to predict water content in front of the tunnel, as it is highly sensitive to water. Subsequently, borehole ground‐penetrating radar was applied to finely characterize the geological structure. By combining these two methods, the size, scale, location, water content, and spatial distribution of water‐bearing structures in front of the tunnel were identified. With the above measures, the Shantou Bay subsea tunnel passed through the detection section successfully. Herein, we present a case study and offer a valuable reference for similar projects concerning subsea tunnel construction.

Site evaluation of subsea tunnels with sightseeing function based on dynamic complex MARCOS method

Subsea tunnels with sightseeing function (STSF) are valuable for integrating transportation across different locations, particularly in cross-sea regions. Given their technical complexity, significant capital commitment, and substantial social impact, site evaluation of STSF has become a critical priority. In this study, a dynamic complex measurement alternative and ranking according to the compromise solution (MARCOS) framework is proposed for STSF site evaluation in a Pythagorean hesitant fuzzy environment. A novel score function for a Pythagorean hesitant fuzzy set is defined to handle an incomparable problem. Moreover, a growth coefficient matrix is constructed to reflect the internal development potential of decision objects, considering changes in expert and criteria weights during the dynamic decision-making process. An STSF evaluation system is designed to satisfy stability, sociality, and economic developments. An empirical study is conducted in Zhejiang Province, China, to verify the robustness and effectiveness of the proposed evaluation framework by comparing its results with other methods.

Research on a Grading Evaluation System for Water Inflow in Three-Hole Parallel Subsea Tunnels Considering Inter-Tunnel Influence

Water inflow analysis is critical for subsea tunnel construction. However, existing studies largely concentrate on the inflow issues pertaining to single-hole tunnels. To address current practical engineering problems, a three-hole parallel configuration is common for subsea tunnels, which may alter water inflow patterns due to the influence of their seepage fields. Herein, numerical simulations are conducted to investigate the water inflow characteristics of a three-hole parallel subsea tunnel. Specifically, the impact of various factors on the water inflow phenomenon, including the permeability coefficient of the surrounding rock, the depth of the seawater, the depth of the tunnel, the spacing between tunnels, and the relative size of the tunnels, are comprehensively studied. Furthermore, based on the principles of the analytic hierarchy process and fuzzy mathematics, an exhaustive assessment framework is developed to evaluate the water inflow of three-hole parallel subsea tunnels. The results indicate that there is a mutual influence between the three parallel tunnels, differing from the predicted water inflow, which is overestimated in a single-hole tunnel model. Therefore, the water inflow assessment for a three-hole parallel subsea tunnel system should account for the inter-tunnel influences. The findings of this study offer valuable insights for the design of waterproofing and drainage systems in three-hole subsea tunnels.

Experimental study on the availability of polyurethane foam used as compressible layers in subsea tunnels

AbstractThe yielding support comprising a compressive layer is considered as a solution to the time‐dependent damage of the lining in squeezing tunnels. The feasibility of the use of polyurethane foam (PUF) as the compressible layers in subsea tunnels was investigated in this study. Confined compression tests were conducted to investigate the compression performance degradation of PUF immersed in artificial seawater for 400 days. The yield strength and elastic modulus of PUF decreased within 180 days but then increased to over 80% of their initial values within the subsequent following 220 days, the degradation rate and strengthening rate of these parameters are of the same order of magnitude. The degradation rate of the yield strength and elastic modulus can be significantly inhibited by ions in artificial seawater, thus causing samples immersed in low‐salt‐concentration solutions to exhibit worse compression performance than those of samples immersed in a high‐salt‐concentration solution. The stress at the end of the yielding plateau and yielding plateau strain range were slightly affected by hydrolysis aging. The shape of the yielding plateau stage of the aged samples changed from a horizontal line to an inclined line owing to the variation in the yield strength. Even after immersion for 400 days, all the aged samples still exhibited compression failure and neither crumbled into pieces nor fractured into parts. The strengthening effect, unchanged failure mode, and almost constant yielding plateau strain range guarantee the safe utilization of PUF in marine environments.