Immersed Tube Tunnels Research Articles

Combined prediction model of joint opening-closing deformation of immersed tube tunnel based on SSA optimized VMD, SVR and GRU

Prediction of joint opening-closing deformation is crucial to ensure the operation safety of immersed tube tunnels. This paper proposes a novel deformation prediction model based on the framework of "decomposition-prediction-integration", which combines the Sparrow Search Algorithm (SSA), Variational Modal Decomposition (VMD), Support Vector Regression (SVR) and Gated Recurrent Unit (GRU). First, the deformation sequence is decomposed into trend, period, and residual components by VMD. In this process, a innovative evaluation index (EI) is proposed to guide the decomposition by combining the Root Mean Square Error (RMSE) and the Sample Entropy (SE), while the VMD is hyper-parametrically optimized by SSA under the EI to improve the decomposition quality. Secondly, the trend component is fitted and predicted using the Least Squares Method; the SSA-SVR model is used to establish the nonlinear response relationship between the period component and the influence factor; the GRU model optimized by SSA is applied to excavate the temporal characteristics within the residual component, which in turn achieves the prediction of the residual component. Finally, the opening-closing deformation prediction results are obtained by integrating the prediction results of each component. The application results demonstrate that the proposed model is excellent in terms of reliability and applicability, with smaller prediction errors and higher accuracy than the other six models. It provides an innovative method for joint opening-closing deformation prediction.

Evaluation on the state of sand filling layer and the influence on segment deformation of immersed tunnels

The immersed tunnel is considered an effective solution for traffic problems across rivers and seas. The sand filling layer, as an important part of immersed tunnel foundation treatments, directly affects segment attitude stability. Due to difficulties in quality control of concealed construction and the complex hydrodynamic environment, the sand filling layer is prone to compaction defects, further leading to changes in segment attitude. However, limited by structural concealment and state complexity, most studies consider the sand filling layer part of the foundation to study its impact on settlement while neglecting its influence on segment attitude. This research proposes an evaluation method for the sand filling layer state based on elastic wave testing and the elastic wave characteristic parameters selected come from analysis of the time domain, frequency domain and time–frequency domain. By classifying the elastic wave characteristic parameters through the K-means clustering method, the relationship between the state of the sand filling layer and the elastic wave characteristic parameters is established. The state of the sand filling layer is divided into dense, incompact, and void. A numerical model is established based on the Guangzhou BI-UT immersed tunnel with incompact and void sand filling layer states to simulate deformation and torsion. The results indicate that the settlement of the tunnel segment is low in the eastern region and high in the western region due to the presence of a less dense sand filling layer, with a maximum differential settlement of 0.04 m. The evaluation method plays a crucial role in guiding the construction of immersed tube tunnels.

A novel test method for characterizing tempo-spatial variations in elastic modulus of underwater concrete

Concrete structures used in underwater engineering, such as immersed tube tunnels, are subject to a range of challenging coupling circumstances including mechanical load (M), fluid flow (F), fluid pressure (P), and chemical attack (C). Concrete in different areas also experiences compressive or tensile stress under mechanical load. However, most experimental setups only consider limited coupling scenarios, such as M-C, M-F-C, or M-P-C, and the sample is typically in a single stress state, either compressive or tensile. To overcome these limitations, a novel stress-seepage-chemical coupling erosion setup (SSC-CES) was developed to perform durability tests on concrete. This setup allows for simulation of the service conditions of an immersed tube tunnel, including M-F-P-C coupling and distribution of compressive and tensile stresses. This study presents also a detailed description of the setup's components, configurations, and working principles, and discuss how sealing and alignment problems for the sample were addressed to ensure accurate fluid pressure and stress loading. The indentation technique was furthermore applied to obtain the local mechanical properties of different erosion areas, enabling analysis of tempo-spatial variations in elastic modulus. Finally, a test was conducted to examine the M-F-P-C coupling effect using the developed SSC-CES and indentation technique. Results indicated that the elastic modulus weakened from the erosion surface and gradually approached the initial value with increasing depth. Additionally, it showed a transition from slight increase to gradual decrease with erosion time. Notably, the elastic modulus in the tensile stress area was considerably lower than that in the compression stress area. These test results confirm the reliability of the developed SSC-CES and the rationality of the analysis method using micro-indentation technology. The system effectively supports the study of durability evaluation of immersed tube tunnels under M-F-P-C coupling.

Risk Assessment of Immersed Tube Tunnel Construction

Due to the complexity of risk factors in constructing immersed tube tunnels, it is impossible to accurately identify risks. To solve this problem, and the uncertainty and fuzziness of risk factors, a risk assessment method for immersed tube tunnel construction was proposed based on WBS-RBS (Work Breakdown Structure-Risk Breakdown Structure), improved AHP (analytic hierarchy process), and cloud model theory. WBS-RBS was used to analyze the risk factors of immersed tube tunnel construction from the aspects of the construction process and 4M1E, and built a more comprehensive and accurate construction risk index system. The weight of each index was calculated by the improved AHP of a genetic algorithm. The cloud model theory was used to build the cloud map of risk assessment for immersed tunnel construction and evaluate construction risk. Taking the Dalian Bay subsea tunnel project as an example, the risk assessment method of immersed tunnel construction was verified. The results showed that this method not only solved the problem of failing the consistency check in the higher-order judgment matrix but also improved the consistency pass rate by 33.3% and accurately reflected the risk assessment results. The assessment results show that the construction risk level of the Dalian Bay submarine-immersed tunnel is medium. The risk level of indicators “slope instability” and “water-stop damage” are high risk, while “pipe section cracking”, “low underwater alignment accuracy”, “uneven crimping of a water-stop”, and “uneven substrate treatment” are medium risk. This provides a reference for the risk assessment study of immersed tunnel construction.

Full-Scale Loading Test of Jet Grouting in the Artificial Island–Immersed Tunnel Transition Area of the Hong Kong–Zhuhai–Macau Sea Link

In the Hong Kong–Zhuhai–Macau Bridge mega project, several ground treatment methods were applied in the transition area between the artificial island and immersed tube tunnels to reduce the potential uneven foundation settlement underlying the tunnel, as the backfilled sand layer is more than 10 m around it. One of the foundation improvement methods involves the combination of preload and high-pressure jet grouting (HPJG) columns. Current field tests, such as core bowling, standard penetration test, and plate loading test, are not suitable for evaluating the strength of this reinforced foundation. This study presents a full-scale load test to examine the construction quality and effects of an HPJG-reinforced foundation. A novel method was designed based on the Boussinesq equation to simulate the additional stress distribution from the immersed tube tunnel. The tangent modulus method considering the impact of modulus nonlinearity was employed to calculate the nonlinear settlement of the treated foundation. Preferable settlement results were obtained using a set of pre-embedded high-precision hydrostatic leveling systems. Both the measured data and calculated settlement demonstrate the reasonableness of the present in situ test.

Study on the Coupled Smoke Characteristics and Evacuation of Underwater Immersed Tube in Tunnel Fire

Fire accidents pose a great threat to the normal operation of underwater immersed tube tunnels, and failure to control or improper control will lead to serious disaster consequences. Based on the potential risks, this work explores the characteristics on the exhaust outlets and safety doors of underwater immersed tube tunnels from the smoke extraction and personnel evacuation. First, a one-way immersed tube tunnel was established by employing FDS numerical simulation software. And the characteristic parameters of smoke extraction in tunnel fire were analyzed by referring to the structural parameters of a certain domestic immersed tube tunnel. The longitudinal velocity and the exhaust outlet opening strategy were then analyzed. Finally, Pathfinder was used to simulating and calculating the required safe evacuation time (T_RSET), and through its comparison with the calculated available safe evacuation time (T_ASET), the optimal safety door spacing and width were determined, which is expected to provide a reference example for studying the coupled smoke extraction characteristics of underwater immersed tunnels fire.

Fire Resistance Test and Numerical Simulation on the Tube Structure of Steel–Concrete–Steel Immersed Tube Tunnel

To provide references for the fire prevention design of steel–concrete–steel immersed tube tunnels, four types of test conditions—no fire protection, fireproof coating insulation, single-layer seam fireproof boards, and double-layer seam fireproof boards—were carried out using partial full-size structural test members. Additionally, the thermal insulation effects of various fireproofing technology solutions were contrasted and analyzed. Combined with the numerical simulation analysis, the temperature distribution law inside the tube structure under various fireproofing measures and the temperature rise law of measuring points at different depths were studied, and the protective effect of the fireproof layers on the tube structure under high fire temperature was demonstrated. The results of the numerical simulation and the experimental data agree well. The results show that adding fireproof layers can significantly lower both the steel shell’s surface temperature and the depth of fire impact. Without fire protection, the surface temperature of the bottom steel shell exceeds 300 °C at 69 s, and the member bursts. The fireproof coatings are cracked and flaking and cannot meet the fire resistance limits. Both single-seam and double-seam schemes of calcium silicate boards can meet the fire resistance limit requirements and the latter has a better heat insulation effect.

Closure state measurement of final joint of the immersed tunnel of the Hong Kong-Zhuhai-Macao Bridge

The immersed tunnel of the Hong Kong-Zhuhai-Macao Bridge adopts the construction mode of sinking from the east and west artificial islands to the middle to form a closed dragon mouth, and then sinking the final joint through. The final joint state parameter measurement is the key factor determining the success or failure of the project. Aiming at the problems of low efficiency, low measurement accuracy, poor reliability and inability to adjust the state of the closure in real time, this paper proposes a real-time measurement method for the formation of the closure state. Firstly, the measurement feature points are arranged on the end faces of the two pipe joints that form the closure, and the coordinates of the feature points in the pipe joint coordinate system are obtained by measurement. Secondly, in the process of sinking and laying, the measuring tower method and the manhole casting point method are used to measure and adjust the state of the closing mouth. Finally, the three measurement results are uniformly converted into the engineering coordinate system, and the accuracy is compared and analyzed by using the measurement error transfer model, and the best measurement method for the closing state of the immersed tunnel construction is obtained. This method changes the construction method of forming closure first, then measuring through and then adjusting accurately in the construction of immersed tunnels, and provides a reference for large-scale underwater installation projects such as immersed tube tunnels and underwater pipes.

Study on bearing characteristics of marine subsoil for semi-rigid immersed tunnel

In the project of Hong Kong-Zhuhai-Macau Bridge, the back-silting of natural foundation section is serious, and the tunnel structure is prone to uneven settlement along the longitudinal direction, and the longitudinal depth of the tunnel will be different due to the navigation demand. The traditional flexible joint scheme will cause great deformation of segment joints and reduce the safety reserve of the shear bearing capacity of the joints. Therefore, the Hong Kong-Zhuhai-Macau immersed tunnel has adopted a semi-rigid system design, that is, after the completion of the prestressing construction of segment joints, the prestressing tendons were not be cut off. The pre-stressed reinforcement can not only ensure the opening of segment joints within a certain range, but they are also adapted to the uneven settlement of the seabed. Notably, prestress plays a very important role in the whole immersed tube tunnel. Therefore, this paper is focused on a comprehensive study of the prestress applied in the semi-rigid scheme. A 1:100 small scale model test of the E13 element in the natural foundation of the immersed tube tunnel is taken as an example. Through the study of two factors, the degree of prestress tension and the size of back silting, the settlement characteristics and the distribution of compressive stresses of marine subsoil on the immersed tunnel are analyzed. The results of the model test showed that the increase in the degree of prestress tension is advantageous to management of the stress and uneven settlement of the joints. Through a comparison of the results of different prestress tension values, the rationality behind the selection of semi-rigid tunnel as a practical engineering scheme is demonstrated. This research lays a foundation for further study on the selection and optimal design of immersed tube tunnels, and the results provide a references point for similar immersed tunnel projects.

Improved vertical displacement calculation model for immersed tube tunnel considering tidal load

Most of the major cross-sea cluster projects in China, such as the Hong Kong–Zhuhai–Macao bridge, Shenzhen–Zhongshan bridge, and Dalian Bay Tunnel, have adopted the immersed tube tunnel method. In traditional theoretical analyses, the soil continuity of the foundation is neglected. In this study, the elements of an immersed tube tunnel are considered equivalent to the Timoshenko beams placed on a Vlasov double-parameter foundation, and a formula for calculating the vertical deformation of the immersed tube tunnel is derived. Moreover, the Timoshenko beam calculation model placed on a Winkler foundation is adopted for comparison, in order to verify the rationality of the proposed calculation method. Considering the Yongjiang immersed tube tunnel project as an example, the vertical displacement of an element–joint in this tunnel under the influence of the tidal load is analysed, and the theoretical calculation results of both models are compared with the field observation results. The comparison reveals that the proposed model based on the hypothesis of a Vlasov double-parameter foundation yields results more comparable to the observed data than the other model. These research results are expected to have certain guiding significance in the design and calculation of immersed tube tunnels.

Research on Cracking Control of Immersed Tube Tunnels Concrete by Pre-heating treatment

Herein, the pre-heating treatments are researched. With diversity of zone and temperature, highest average temperature of the section 10cm below surface was 14.7°C, which is lower than that of the concrete block. And the distance of 20cm and 40cm to surface of section, the temperature is 11.8°C and 9.8°C， respectively. When the heating water of 60°C, the increase of 48h to 72h, the highest temperature is about 47.2°C and 49.6°C.

Cracking Evaluation of Full-Section Casting without Postcast Strip Method on Immersed Tube Tunnels Concrete

Sheng, Z.; Yu, F.; Deng, C.; Zhu, C., and Xiong, J., 2020. Cracking evaluation of full-section casting without postcast strip method on immersed tube tunnels concrete. 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. 108–112. Coconut Creek (Florida), ISSN 0749-0208.Tubes immersed with the full-section casting method have been widely applied in many projects. However, cracks can occur longitudinally and transversely from the interfacial region. Thus, cracking evaluation can be combined with simulation to analyze the temperature field and estimate the relationship between internal and external restraint with the safety coefficient. Herein, the initial immersed tube has less possibility of cracking; the adjacent one should be cast within 6 days to prevent cracking.

Shaking table model test of immersed tunnels with different site conditions and seismic wave input directions

ABSTRACT Given the particularity of the environment of the immersed tunnel, once damage occurs by earthquake, it will cause catastrophic consequences. Therefore, it is necessary to evaluate the seismic performance of immersed tunnel. To study the seismic response law of immersed tube tunnels under different site conditions and seismic wave input directions, we tested four groups of immersed tube tunnel shaking table models. In the experiment, we took three kinds of site conditions into account, including homogeneous dry sand site, homogeneous saturated sand site and heterogeneous site. The test result was as follows: When considering the different site conditions under horizontal earthquake excitations, soil liquefaction significantly influences the propagation of seismic waves, whereas the dynamic responses of the tunnel in the heterogeneous site were larger than those of the other two groups. The input directions of seismic waves have a great influence on the dynamic response of soil layer and tunnel. Furthermore, the relative displacement between tunnel sections was analysed.

Research on Key Design Technology of Shenjiamen Harbour Subsea Tunnel Engineering in Zhoushan

The Shenjiamen harbour subsea tunnel in Zhoushan, Zhejiang is the first pedestrian submarine immersed tube tunnel in China. In view of the characteristics of the fine soft immersed tube tunnel with large slope, the section of the immersed tube structure was reasonably chosen, the length of the pipe was partitioned, various subsidiary structures were finely arranged, the technology and parameters of the grouting were strictly controlled, and the deformation of end corner was taken as the important control parameter for the design of fine soft pipe joint. The new design technology of final joints with the combination of thrust bearing platform and water sealing wall can ensure the construction quality of final joints, as well as reduce the risk and cost of project. In the field of tunnel engineering, a new bank protection structure that double row steel pipe pile was combined with mould bag sand cofferdam had been researched and designed. Through these key technologies, it has accumulated a wealth of design experience for submarine immersed tube tunnels, which possesses an important reference value for similar projects.

Quantitative Investigation on Grouting Quality of Immersed Tube Tunnel Foundation Base using Full Waveform Inversion Method

Abstract Full waveform inversion (FWI) method is used to reveal the internal structure of underground mediums in geotechnical engineering. It comprehensively utilizes the amplitude, travel time, and phase of a wave field. It also offers the potential to produce better resolution of the target medium and feasibility for the detection of buried low-velocity layers. A new FWI method for elastic waves in stratified mediums is presented, which adopts a quasi-linear method coupled with a random search algorithm. The strength of this approach is that the Jaccobian matrix is iteratively calculated instead of the Hession matrix, and the inversion work is helpful for getting out of the local minima within appropriate search scope. To verify our method, it is applied to numerical 2-D stratified models and the appropriate search step and range constraint for inversion are determined by parameter sensitivity analysis. With a series of waveform pretreatments, including filter process, waveform energy normalization, and waveforms mitigation based on correlation analysis, we extended it to use with 3-D stratified media models. Its feasibility and accuracy in recovering the unknown parameters of low-velocity layers are certified. Based on the results of the numerical cases, this FWI method can be used for detecting the grouting quality in immersed tube tunnels. The S-wave velocity profiles of low-velocity layers under the tunnel floor are obtained. Because the S-wave velocities of grouting layers will increase before and after grouting, the grouting quality is effectively evaluated by the FWI method and provides a practical reference for other similar projects.

Deterioration assessment of an immersed-tube road tunnel in Taiwan

Taiwan has been constructing tunnels since the 1960s and more than 300 are now in operation. Unfortunately, some of the early tunnels are now showing signs of significant deterioration. This paper provides a case study of a busy 30-year-old urban undersea immersed-tube road tunnel, which is suffering from cracks, water ingress and corrosion. Non-destructive inspection techniques were carried out to determine the level of deterioration and to make an overall assessment of the tunnel’s operational safety. The paper describes the tunnel’s main defects, the results of settlement, and the structural inspections and monitoring judgements made. The paper is intended to serve as a reference for assessing the deterioration of immersed-tube tunnels.

The Correlation of Chloride Diffusion Coefficient and Concrete Maturity Value and its Application in Marine Engineering

The correlation of chloride diffusion coefficient and concrete maturity value within 56 days of curing was investigated by the chemically combined water content method, rapid chloride migration (RCM) test and concrete maturity test, respectively. The experimental results showed the chloride diffusion coefficient of concretes decreased not only with increasing curing ages, but also with increasing curing temperature, which can promote the hydration degree of cementitous. There is a significant correlation between the chloride diffusion coefficient of indoor curing specimens and the concrete maturity value when expressed as a power function (R2=0.976), and the calculated values of concrete maturity for outdoor specimens which obtained by using the power function agrees well with the measured values, then it can use the measured concrete maturity value to predict the chloride diffusion coefficient of concrete. And then in this project, when the immersed tube tunnels were placed in seawater, the recommended value and the control value of concrete maturity was 21064°C•h and 13926°C•h, respectively. Furthermore, the ages of the tunnels placed in seawater can be appropriately adjusted by calculation when considering the external curing temperature and heat of hydration of cementious.

Study of Sedimentation Speed and Compression Characteristics of Back-Silting Soil from Undersea Immersed Tube Tunnels

The immersed tube tunnels in Yangtze river delta region are affected severely by back-silting. Back-silting is difficult to control during construction and the consequences are hard to evaluate as well. In this study, sedimentation experiment was conducted incorporating back-silting soil solutions with different concentration ratios, and compression tests on the initial sedimentation layers was also conducted based on back-silting soil specimens taken from the back-silting soil sedimentary layers located in the surrounding area of Shenjiamen harbor undersea immersed tube tunnel in Zhoushan City. The undersea back-silting was assessed from the aspect of sedimentation speed and the strength of initial sedimentary layers. Results from the study are essential for further study of back-silting load and the effect of back-silting on settlement.

Istanbul (Bosphorus) immersed tube tunnel and survey works

The railway lines in both sides of Istanbul have been connected to each other by an underwater tunnel passing through the Bosphorus. This type of tunnel is known as immersed tube tunnel. Immersed tube tunnel is a part of MARMARAY project that is continued nowadays. MARMARAY is a rail transport project in Istanbul. It consists of the construction of an undersea rail tunnel under the Bosphorus strait. Suburban rail lines along the Sea of Marmara from Halkali on the European side to Gebze on the Asian side will be modernized with this project. An immersed tunnel consists of several prefabricated steel shell or concrete tubes. These tubes are constructed on land. They are floated and moved to the immersion site. They are installed one by one. They are lowered and connected to one another underwater. Then, the water is pumped out and the segments are covered with the backfill materials. An immersed tunnel is generally installed in a trench that has been dredged previously in the bottom of a waterway between structures constructed in the dry. All spaces between the trench bottom and the soffit of the tunnel can be a previously prepared gravel bed, or sand bedding pumped or jetted underneath the tunnel. Piled foundations are sometimes used, where soil conditions require them. As construction proceeds, the tunnel is backfilled. The completed tunnel is usually covered with a protective layer over the roof. Survey works requires high precision in every construction project such as dam, bridge, tunnel etc. Horizontal and vertical control of tunnels are performed by using geodetic control points. Survey works should be performed precisely. Key words: Tunnel, immersed tube, immersed tube tunnels, geodetic control,MARMARAY.

Urban soft ground tunneling in China – experiences from Shanghai and other cities

This paper introduces the different kinds of urban soft ground tunnels in China built by shield method, immersed tube method and pipe jacking method. Although the history of urban soft ground tunneling is only around 40 years in China, enormous tunnels were built together with great progress especially since last decades. A lot of experiences and lessons gained from practices are not only valuable to Chinese tunnel engineers but also to tunneling industry in the world. In this paper we focus on the tunnel activities in Shanghai. Some significant technical features are highlighted. The most of the road tunnels in China were built by mining method. The modern tunneling methods like shield tunneling method or immersed tunneling method were only used in the cities where the ground is composed of soils. Up to now, the road tunnels built by the shield method are only found in Shanghai, and the immersed tube tunnels exist in three cities, named Shanghai, Guangzhou and Ningbo. Some project details and technical challenges are presented in this paper. As for MRT tunnels, there are about 210 km length of MRT tunnels in operation in mainland of China. MRT systems are being in operation only in four cities, while another 16 MRT lines are under construction or planning now. We focus on the planning, design and construction of MRT tunnels in Shanghai. Details of project and shield tunnelling machine are given in this paper. There are also other types of tunnels constructed or under construction by shield method or pipe jacking in China. With the development of our building infrastructure in the new century, the construction of different types of TBM projects and immersed tube tunnel projects are booming. We are looking forward to more innovative tunneling technologies to be employed in China. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.