Subsea Tunnel Research Articles

Karst cave treatment technology for a subsea shield tunnel

The existence of karst caves brings great potential safety hazard to tunnel construction. When building a tunnel through underwater karst area, engineers will face greater challenges. This paper introduces the treatment technology of submarine karst caves, based on a large diameter subsea tunnel project in Dalian, China. This paper starts with the geological conditions of the tunnel, then introduces the treatment scope of karst, the treatment process, grouting technology and precautions, and finally the quality inspection after treatment and treatment effect are discussed.

A Water Leakage Risk Assessment Model for Shield Tunnel Based on Kalman Filter Data Fusion Method

Multi-source information monitoring and data fusion analysis system has high practical value for the risk management of tunnel structure, especially in complex ground. The analysis of structure health will be getting more comprehensive and real-time with multisource monitoring technologies. Risk warning will be more accurate and timelier. Based on one shield tunnel project, this research analysed the water leakage risk of shield subsea tunnel in unfavourable geological conditions by using the method of geological information and structural monitoring data fusion. Firstly, Kalman filter method was used to denoise the monitoring data, and the effect of different monitoring data was compared; Then, the risk factor of water leakage was analysed, and the relationship between risk factors, geological information and monitoring data was established; Finally, the risk factors based on multi-source monitoring information were fused and analysed by using the improved D-S evidence theory method, and the final analysis results of water leakage risk were obtained. A multisource dynamic risk analysis model of tunnel water leakage was established. The results showed that the Kalman filter method has better noise reduction effect on the high-frequency monitoring data than that of low-frequency monitoring data, and the multi-source dynamic risk analysis model has a good prediction effect on the water leakage risk of tunnel lining in unfavourable ground condition.

Construction of the Tuen Mun–Chek Lap Kok Link Sub-sea Tunnels in Hong Kong

The entire Tuen Mun–Chek Lap Kok Link (TM-CLKL) was commissioned on 27 December 2020 and comprises a 9 km dual twolane carriageway between Tuen Mun and North Lantau, Hong Kong. The challenges for the construction of the TM-CLKL tunnels included sub-sea tunnelling up to 55 m below sea level in mixed ground geology that required replacement of tunnel boring machine (TBM) cutting tools at hyperbaric pressure up to 5.8 bars; replacement of worn TBM cutting tools in complicated ground conditions; construction of approach tunnels in newly reclaimed land subject to long-term consolidation; and construction of cross passages at 100-metre intervals between the two sub-sea tunnels with a risk of sea water ingress at 5.5 bars. This project has deployed sophisticated techniques to surmount the challenges encountered during construction of the five-kilometre-long sub-sea tunnels. These included the use of the world’s largest slurry-type Mixshield TBM, 17.63 m in diameter, for the construction of the northern approach tunnel, followed by two 14 m diameter slurry-type Mixshield TBMs for the construction of the sub-sea tunnels; use of saturation diving techniques for TBM cutterhead interventions up to 5.8 bars which was the first such works in Hong Kong and one of only a few uses of saturation diving in tunnelling worldwide; use of ground freezing techniques in complicated ground conditions for TBM interventions to change worn cutting tools at the TBM cutterhead; TBM tunnelling in newly reclaimed land at the northern landfall and the southern landfall; and the construction of cross passages by mini-TBM using pipe jacking methods between the two main tunnel tubes which was the first such works ever undertaken anywhere in the world. This paper introduces the successful implementation of these techniques for the satisfactory completion of the TM-CLKL sub-sea tunnels.

Computer assisted optimal evaluation of grouting scheme in shallow tunnel through G1 method and GRA

In tunnel construction, grouting technology is an extremely important reinforcement method for improving the mechanical properties and increasing the strength of surrounding rock. This paper presents an optimization evaluation method of grouting scheme for advanced reinforcement in shallow tunnel based on G1 method and grey relational analysis (GRA). In the Haicang Subsea Tunnel Project of Xiamen, the four grouting schemes were optimized and analyzed through the previous optimization evaluation method, the most suitable solution is obtained as the full-control one-time grouting solution and the result has also been verified in practice.

Influence of water pressure on deep subsea tunnel buried within sandy seabed

For a subsea tunnel, the changeable high water pressure is of great significance in the soil-water-tunnel interaction. In this study, a series of parametric studies were conducted to investigate the effect of high water pressures on the seabed settlement and the earth pressures as well as the axial forces and bending moment of a tunnel lining during excavation. The simulation results disclose that the seabed settlement along the transversal tunnel direction increased linearly with the rising water level and the ranges of settlement troughs can be up to around 5 D (D, tunnel diameter) in width. Similarly, the settlement along the longitudinal tunnel direction featuring a semi-trough shape also shows a linear increase with the rising water level, and the maximum influence zone could reach a length of 3 D in front of the excavation face. With the increase of water pressure during tunneling, the total earth pressures along the perimeter of a circular tunnel lining increased significantly and their distributions were prone to be more uniform around the tunnel perimeter. As a result, the deep sea tunnel lining has a typical feature of large axial force and relatively smaller bending moment.

Comprehensive and Quantitative Evaluation of Subsea Tunnel Route Selection: A Case Study on Bohai Strait

The Bohai Sea is the immense inland sea in China and the Bohai Strait is a sea graben from East China to Northeast China which lies between the Jiaodong Peninsula and the Liaodong Peninsula. Considering the forthcoming Bohai Strait subsea tunnel, the authors selected nine indicators including seabed topography, stratigraphic lithology, geological structure, earthquake, environmental impact, engineering scale, ventilation conditions, residents’ satisfaction, and landing position. These indicators are considered as evaluation indexes to evaluate three alternative routes of the Bohai Strait subsea tunnel: line A, line B, and line C. In this paper, the evaluation model of the Bohai Strait subsea tunnel based on analytic hierarchy process (AHP) and extension theory is established. In this regard, the grade of route selection is divided into four categories: excellent, good, average, and bad. Finally, through the model calculations, it is concluded that line B of the Bohai Strait subsea tunnel is the best, and line A is the worst. This method provides a new idea for the evaluation of subsea tunnel site selection and also represents some references for other types of engineering site selection.

A new method for risk assessment of water inrush in a subsea tunnel crossing faults

The geological conditions of subsea tunnels are extremely complicated. When crossing faults, water inrush disasters are prone to occur under the combined action of seawater pressure, geological structure, and construction disturbance. An optimal combination weight-improved grey relational analysis (GRA) method is proposed here to evaluate the risk of water inrush in subsea tunnels through faults. Eight main factors are selected from fault zone properties, fault structure characteristics, engineering factors, and construction factors as risk assessment indexes, and the risk is divided into four levels. The subjective and objective weights are determined using the improved G1-method and entropy weight method, and the optimal combination weight is calculated based on the minimum discriminant information principle and the Lagrange multiplier method. The improved GRA considering the evaluation criteria interval is used to determine the correlation degree of the water inrush risk level, and the maximum correlation degree criterion is adopted to judge the risk level. The method is applied to the Qingdao Jiaozhou Bay subsea tunnel to assess the water inrush risk crossing faults, and the assessment results are basically consistent with the actual engineering situation. This study provides a practical reference for the risk assessment of water inrush in subsea tunnels.

Case study on ventilation and cooling control technology of multi heat source coupling in long distance subsea tunnel construction

To solve the high-temperature environmental hazards caused by concrete hydration heat release in tunnel construction, this paper studies the heat generation mechanism of heat source in the tunnel using theoretical analysis and numerical simulation, and analyzes the temperature control in the tunnel under different ventilation wind speed (1 m/s, 2 m/s, 3 m/s, 4 m/s, 5 m/s) and ventilation temperature (298 K, 293 K, 288 K, 283 K, 278 K). The results show that: increasing the ventilation speed can effectively reduce the environmental temperature in the tunnel, and the ventilation cooling effect is the best when the air duct outlet speed is 3 m/s. Reducing the ventilation temperature can further reduce the tunnel temperature based on increasing the ventilation speed. When the ventilation temperature is set at 293 K, it can meet the needs of ventilation and cooling at the tunnel face. The simulation results show that when the tunnel ventilation speed is 3 m/s and the ventilation temperature is 293 k, the maximum cooling value of the working face can reach 6.66 k, and the maximum cooling rate is 2.18%. Within 5 m from the tunnel working face, the cooling effect of the enclosure structure is the most obvious, which can effectively ensure the comfort of the working environment.

Deformation rule and mechanical characteristic analysis of subsea tunnel crossing weathered trough

It is difficult to comprehend the deformation rule and mechanical characteristics in the construction process of subsea tunnel crossing weathered trough owing to the complex tunnel structure and unfavorable geological conditions. In this study, a geomechanical model test and a numerical model system for the excavation of subsea tunnel were developed based on Haicang Subsea Tunnel to investigate the characteristics of the tunnel displacement, stress, and seepage. After subsea tunnel excavation, the displacement, stress, and hydraulic pressure distribution of surrounding rocks were similar, with the release of stress and lower hydraulic pressure often accompanied with the growth of its displacement. Generally, multiple-physical monitoring information was interactional. In addition, the influence of seawater on the weathering trough was mainly concentrated in an area approximately twice the diameter of the hole, and the influence of water on the vault was greater than that of the sidewall. These results could serve as reference for the construction of subsea tunnel crossings and warning mechanisms of weathered trough.

Multi-sources information fusion analysis of water inrush disaster in tunnels based on improved theory of evidence

Water inrush is one of the most serious geological disasters threatening tunnel construction. Generally, complexity and multi-sources feature of physical information existing in tunnel construction make disaster prediction very difficult, how to accurately predict the disaster becomes a hot topic in the field of tunnel engineering. Dempster-Shafer (DS) theory of evidence is a widely used method for reasoning with multiple evidences, however some unbelievable results usually appear in dealing with highly conflicting evidences by its traditional combination rule. Thus an improved fusion algorithm based on weighted average of evidence conflict probability was firstly introduced into risk prediction of water inrush disaster. Through the improved algorithm, multi-sources precursor information measured from previous model test were fused to predict quantitative risk levels of water inrush for different excavation step of subsea tunnel in the model test. The predicted high risk at the 12th excavation step by improved algorithm agreed well with actual phenomenon of intensive seepage observed in the test, while the traditional method gave a lower level. Moreover, the improved algorithm predicted a more accuracy result in the phase of water inrush (at 16th excavation step shown in test). In brief, the improved algorithm can make more accuracy prediction for water inrush disasters and will provide valuable reference for similar engineering.

Use of saturation diving technique for tunnel boring machine cutterhead intervention in the Tuen Mun–Chek Lap Kok Link Sub-sea Tunnel Project, Hong Kong

The entire Tuen Mun–Chek Lap Kok Link (TM-CLKL) was commissioned on 27 December 2020 and it comprises a 9km-long dual 2-lane carriageway between Tuen Mun and North Lantau, Hong Kong. Construction of the 5km-long sub-sea tunnels was carried out by two 14m diameter Tunnel Boring Machines (TBMs). The tunnel alignment for the TM-CLKL sub-sea tunnel section is in mixed ground condition with the first 500 m in mixed geology of slightly to moderately decomposed granite and completely decomposed granite (CDG), followed by soft ground condition with CDG, alluvial sand, alluvial clay and marine deposit. This mixed ground geology requires regular TBM cutterhead interventions to change the worn-out cutting tools during the tunnelling operation. As the tunnel alignment is up to 55 m below the sea level with the deepest seabed level at -21 mPD, in order to maintain the cutting face stability during the intervention, the intervention pressure could be up to 6 bars. This paper describes different techniques used for TBM interventions under the sea such as trimix bounce mode and saturation mode that appears first time in Hong Kong under a high hyperbaric pressure to change the worn-out cutting tools at the TBM cutterhead.

Analytical solution for wave-induced hydraulic response on subsea shield tunnel

Frequent water level fluctuation such as wave is one of the significant differences that distinguish subsea tunnels from land tunnels. For a better understanding of the influence of the dynamic wave loading, this study develops a new set of analytical solutions for the wave-induced hydraulic response on the subsea shield tunnels. The proposed analytical solutions are verified with numerical simulation, and a good agreement is observed between the hydraulic regimes obtained from both methods. A detailed parametric analysis is presented about the effect of wave characteristics, seabed properties and tunnel parameters on the hydraulic response, including the water pressure distribution around the tunnel, water inflow, seabed liquefaction and the hydrodynamic forces acting on the tunnel. It reveals that soil permeability is the most significant factor in affecting the wave-induced hydraulic response. Besides, the embedded shield tunnel acts as an obstruction to the water pressure propagation and a drain in the seabed at the same time. The former effect leads to the asymmetric distribution of the maximum water pressure around the tunnel, and the latter one dissipates the pore water pressure, but only in quite adjacent areas.

Experimental research and mechanical analysis on the bond‐slip behavior between concrete and corroded I‐shaped steel

AbstractCorrosion of I‐shaped steel in the primary support of the subsea tunnel is inevitable due to high chloride ion content, which will weaken the bond performance between concrete and I‐shaped steel, resulting in a reduction in the service time of the subsea tunnel. Based on Xiang'an subsea tunnel, the bond–slip behavior between concrete and corroded I‐shaped steel was studied by the accelerated corrosion tests and push‐out tests, the experimental results indicated that: (1) The cracks of experimental specimens could be divided into two main forms: splitting failure (corrosion rate less than 5.79%); spalling failure (corrosion rate more than 5.79%). (2) A three‐stage bond‐slip law for concrete and corroded I‐shaped steel was proposed, and the formulae for calculating the bond strength were established. Furthermore, the degradation process of bond‐slip caused by corrosion was analyzed by energy principle and damage mechanics. Based on energy principle, it found that the elastic energy stored in the interface increased before the peak point of bond‐slip curve and decreased after the peak point, while the dissipated energy in the interface always increased with slip value. Finally, the interface relative damage variable was defined based on secant line anti‐sliding modulus and slip equivalent principle. The interface damage development process can be divided into three stages: initial damage, rapid damage development, and slow damage accumulation.

Subsea tunnel linking Föglö with the main island in Åland

The paper describes a well considered subsea road tunnel in Åland, Finland which will hopefully start in the very near future. The paper describes partly the socio-economics and public benefits of such a project in Åland and partly some technical aspects of designing and constructing road tunnels under the sea to connect land masses. The tunnel is expected to be constructed along the lines of similar rock tunnels being constructed and entered into successful operation in many of the Scandinavian/Nordic countries. More important though is the vital role such a project will serve for the society in Åland. The project is not one that serves millions of people in busy mega cities – still it is a pleasure to see a mega project for a small community mature, starting from a sketchy plan made by individual enthusiasts to a solid plan for a multi-million Euro investment.

Analyzing the topology characteristic and effectiveness of the China city network

The topology characteristic and effectiveness of city network play critical roles in guiding transportation infrastructure planning and construction. From empirical evidence of three types of transportation infrastructure in China’s urbanization process—railway, civil aviation, and highway—we propose a new city network construction method based on the transportation infrastructure links between cities. Degree centrality, closeness centrality, and betweenness centrality are selected as measuring indicators for analyzing the topology characteristic of the China city network, and the shortest path length is used to measure the effectiveness of the China city network from the node level and the overall level. Based on public and open data and combining analysis methodologies, we explore the topology characteristic and effectiveness of the China city network. The analysis results show that the topology characteristic of the China city network presents disequilibrium on geographical distribution. Network node effectiveness is positively correlated to the economic development level of cities in the China city network, and different sub-networks present different overall network effectiveness. The analysis results of the Dalian–Yantai subsea tunnel show that although the effectiveness of the China city network can be greatly improved through increasing links between cities with no direct link, transportation infrastructure planning and construction has different impacts on the topology characteristic of the China city network. The topology characteristic and effectiveness of each city in the China city network should be considered comprehensively in the process of transportation planning and construction.

Applicability of liquid air as novel cryogenic refrigerant for subsea tunnelling construction

The artificial ground freezing technique has been widely adopted in tunnel construction in order to impede heavy water flow and to reinforce weak sections during excavation. While liquid nitrogen is one of common cryogenic refrigerants particularly for rapid freezing, it has a serious potential risk of suffocation due to an abrupt increase in nitrogen content in the atmosphere after being vaporized. This paper introduces a novel cryogenic refrigerant, liquid air, and addresses the applicability of it by performing a series of laboratory chamber experiments. The key parameters for the application of artificial freezing using liquid air in subsea tunnel construction are freezing time and energy consumption, which were evaluated and discussed in this paper. The comparative study of these parameters between the use of liquid air and liquid nitrogen demonstrates that liquid air with no risk of suffocation can be a potential substitute for liquid nitrogen delivering the equivalent performance. In addition, the theoretical model was adopted to evaluate the chamber experiments in an effort to estimate the freezing time and the energy consumption ratio (energy consumption for maintaining the frozen state to the energy consumption for freezing soil specimens).

Installation of submarine cables and pipes in shallow waters and connecting them to the shore by the method of horizontal directional drilling

This article presents the horizontal directional drilling (HDD) as one of the most suitable technique used to reduce the impact on the environment during the submarine pipe and cable installation process, especially in the coastal area and shallow waters. HDD is a technique used to drill a subsea tunnel or under other designated area with the goal to pull a pipe or other facility through the drilled underground tunnel. With the development of the offshore natural gas and wind industry, the demand for the construction of transfer pipeline and cables has also increased. The installation of submarine pipelines and cables can have negative effects on the marine environment. This is one of the main reasons that construction and operation of offshore wind energy systems has been and continues to be regarded with scepticism by environmental activists, despite the undeniable benefits of this renewable energy source. The main objectives of this article are to emphasize the importance of using this technique but also to highlight the benefits, in particular by significantly reducing the impact on the marine environment.

Study on the Influence of Nonlinear Seepage and Grouting Reinforcement on Surrounding Rock in Subsea Tunnel

He, X.; Zhou, X.; Xu, Y.; Ma, W., and Wu, T., 2020. Study on the influence of nonlinear seepage and grouting reinforcement on surrounding rock in subsea tunnel. In: Liu, X. and Zhao, L. (eds.), Today's Modern Coastal Society: Technical and Sociological Aspects of Coastal Research. Journal of Coastal Research, Special Issue No. 111, pp. 162–167. Coconut Creek (Florida), ISSN 0749-0208.Seepage is an important problem of tunneling engineering, which shows nonlinear characteristics in the low permeability media. Particularly in the seabed environment, Darcy's law is not accurate when considering the design of grouted subsea tunnels. Therefore, in this article, an analytical model considering nonlinear seepage and grouting reinforcement is established. Under a series of conditions, the analytical solutions of seepage fields and stress fields are derived and verified by numerical calculation. Then the influence of nonlinear seepage and grouting reinforcement on the pore pressure and effective stress of surrounding rock is investigated, and tunnel drainage is also discussed. The results indicate that tunnel excavation under nonlinear seepage is safer than that under linear Darcy's seepage, and grouting is a significant support that can not only improve the bearing capacity of surrounding rock, but also effectively reduce tunnel drainage.

An Approach to Determining Lateral Pressure Considering the Decay in Permeability Coefficient with Depth and Application to the Subsea Tunnel of Xiamen Metro Line 2

Qiu, Y.; Chen, J.; Su, W.; Huang, J.; Yi, S., and Wu, J., 2020. An approach to determining lateral pressure considering the decay in permeability coefficient with depth and application to the subsea tunnel of Xiamen Metro Line 2. In: Liu, X. and Zhao, L. (eds.), Today's Modern Coastal Society: Technical and Sociological Aspects of Coastal Research. Journal of Coastal Research, Special Issue No. 111, pp. 145–150. Coconut Creek (Florida), ISSN 0749-0208.The determination of lateral pressure on a tunnel face is a paramount concern during the process of replacing cutting tools for a subsea shield tunnel. In conventional methods for the calculation of lateral pressure, the influence of soil permeability has seldom been considered, and the decay in permeability coefficient with depth has been ignored. In this article, an approach for determining the lateral pressure considering the decay in permeability coefficient with depth is put forward. Based on the previous method considering constant permeability coefficient, two different types of decay mode are considered in the proposed approach. For the linear type, the explicit expressions of the resultant thrust are then derived and set up. For the negative exponential type, a numerical method is needed to calculate the lateral pressure. Then the proposed approach is applied to the Subsea Tunnel of Xiamen Metro Line 2. Based on the results of the application, the linear type is recommended for use in considering the decay in soil permeability coefficient with depth, and the corresponding explicit expressions are recommended for calculation of the lateral pressure in engineering practice.

Correlation Research of TBM Tunnel Rock Mechanical Characteristics, Chiseling Specific Energy, and Abrasion Performance: Case Study of Jiaozhou Bay Subsea Tunnel in Qingdao

This paper takes Qingdao Jiaozhou Bay subsea tunnel project as the research object to study the relationship among rock mechanical parameters and chiseling specific energy and abrasion performance. SPSS22 was used to analyze the correlation between the parameters. The results show that except for the low correlation with Poisson ratio, all the other parameters in the single factor correlation analysis have high R . By taking the chiseling specific energy and abrasion performance as dependent variables, taking each mechanical parameter as an independent variable, multifactor regression analysis and stepwise multifactor fitting were carried out; it was concluded that the abrasion performance was highly correlated with uniaxial compressive strength and integrity coefficient, and the chiseling specific energy is highly correlated with uniaxial compressive strength and softening coefficient. In the process of verifying the fitting models, it is found that, under the influence of quartz vein and microfissure in the specimens, the chiseling specific energy formula has a higher fitting value, while the fitting formula of abrasion performance has a higher reference value for the specimens in the study area.