Static and dynamic experimental analysis of an immersion joint

As the weakest part of an immersed tunnel, the immersion joint is the key element in research in this field. Relatively large deformations and internal forces may be induced in the immersion joint subjected to various loading types. Based on a real project, the shear mechanical behaviour is investigated by large scale model test. To explore the performance of the immersion joint, compression-shear loads are applied on a tunnel segment in a specific test set-up. For the applied loading schemes, different levels of axial force, corresponding to the water depth of the joint, are considered as well as varying amplitudes of the shear force. Based on these results, both the static and dynamic shear stiffness of an immersion joint were analysed. The results of the test indicate that the static shear stiffness of the joint increases linearly with the axial force and the same trend is found for the dynamic one. Moreover, the dynamic stiffness is larger than the static one

Experimental assessment of the mechanical behavior of immersion joints and a seismic mitigation method in immersed tunnels

With the rapid progress of urbanization, an increasing number of infrastructure works have been constructed by engineers around the world since the past two centuries, among which many tunnels. Due to the advantages compared to other tunnel types, immersed tunnel techniques are widely adopted and nowadays there are more than 200 immersed tunnels worldwide. The immersion joints, which are between the adjacent tunnel elements, are normally regarded as the weakest parts in the tunnel due to their smaller stiffness than that of the elements. Moreover, the immersion joint is the key component in the water proof system. When an immersed tunnel experiences various loadings, i.e. earthquakes, differential settlement, sinking ships or anchorage impact, deformations occur in the joint and excessive deformations could cause possible damage to the joint, resulting in water leakage which jeopardizes the safety of the immersed tunnel. As known, the configuration of an immersion joint is complicated, mainly involving the primary rubber seal, the secondary rubber seal, the shear keys, the steel shell and the pre-stressing cables. Such a complex configuration leads to difficulties to investigate the behavior of the joint. To have a comprehensive understanding of that, an experimental investigation on the joint subjected to combined loadings is reported in the present thesis. In particular, the behavior of the joint subjected to excessive shear deformation is investigated and subsequently, the failure behavior is also included. It is widely recognized that the shear keys have an important contribution to the shear behavior of the joint. However, the failure behavior of the joint with both the shear keys and the rubber seal is largely unknown due to the lack of experimental investigations. Moreover, it is proved that the flexible immersion joint has a contribution in the seismic response reduction but the application of seismic mitigation devices in the joint has never been considered though such concept has been accepted for buildings for decades. Therefore, the main part of the thesis was divided into two parts, more specifically the mechanical behavior of the joint and the seismic mitigation for immersion joint respectively. Based on an extensive literature review, an experimental program has been elaborated in order to investigate the mechanical behavior of the joint subjected to axial, bending and shear loadings. A geometric scale of 1:10 was selected for technical reasons, such as manufacturing, testing and measurements. Based on that, two tunnel elements, between which an immersion joint was positioned, were designed as well as the rubber seal and the shear keys. The dimensions of a single element are 3800mm x 1150mm x 1250mm with the walls and slabs having a thickness of 150mm. The cross-sectional dimensions of the rubber seal are 37.5mm x 70mm (flange including) with a total length of 9.67m. Two types of shear keys have been investigated, namely steel shear keys and concrete shear keys and each type of the shear keys was divided into two groups depending on their position in the joint and the loading situation. The steel shear keys were connected to the element by bolts while the concrete shear keys were casted together with the element to increase the shear strength. For the model specimens, a unique test set-up has been developed allowing that one element is movable while the other one is fixed, resulting in an axial, bending and shear deformations in the joint respectively. Only horizontal loading was applied in this experiment. The axial load and the bending moment were provided by a set of four hydraulic jacks which are controlled independently while the shear force was applied by an additional jack. Further, a testing procedure was elaborated, consisting of three loading protocols, namely axial compression, compression-bending moment and compression-shear loading cases. For the axial loading case, the hydraulic jacks first provided the gradually increasing axial force then the jacks were unloaded. For the compression-bending case the axial force was applied to an specific value to simulate the initial water pressure in the joint and then a bending moment was imposed. The immersion joint was allowed to rotate, resulting in the occurrence of an opening of the joint. For the shear loading cases, an axial force was also applied at the beginning followed by a reciprocating shear force with increasing amplitude. The shear force was increased until all the shear keys failed. During the experiments, measurements were executed after each successive increase of the load or displacement, comprising axial and shear deformations. Regarding the axial and flexural performance of the joint, the compression-release curve and the bending moment-rotation curves with different levels of axial forces were obtained. Through the obtained load-deformation curves, both the axial stiffness and the flexural stiffness of the joint were derived for use in practice. During this testing cases, a hysteretic loop was observed in both axial and flexural behavior of the joint, indicating that the rubber seal is not perfectly hyper-elastic material as assumed and energy-dissipation did occur. Moreover, an asymmetric bending behavior was observed as the axial force increased. The static and dynamic behavior of the joint were investigated by imposing static and dynamic shear loading respectively. The static and dynamic load-displacement curves of the joint with different loading scenarios were obtained. Accordingly, the static and dynamic shear stiffness of the joint were derived as well. A comparison was made between the static and dynamic shear performance of the joint. The failure behavior of the joint with the steel shear keys and concrete shear keys were investigated by applying reciprocating shear loads with increasing amplitude under a constant axial force. The failure mode of the joint with these two types of shear keys as well as the shear capacity of the joint were obtained. Both series of test results show that the shear keys were not activated at the same time, resulting in a difference between the design shear capacity and experimental one. Finally, a significant contribution of the rubber seal in the shear direction was found, indicating that the shear behavior of the rubber seal should be taken into account in the design procedure. A general literature study with respect to seismic mitigation methods was performed serving as a starting point for the application to immersion joints. To achieve this, a buckling energydissipation device (BEDD) on the basis of the Buckling Restrained Brace (BRB) was introduced and a detailed design procedure for the seismic mitigation device in the joint was provided supposing that the device can work in coordination with the joint in such a way that the maximum energy dissipation is reached. In order to validate the design procedure, a largescale experiment was conducted on an immersion joint subjected to compression-bending moment cases. The bending moment-rotation curves of the joint with seismic mitigation devices as well as the hysteretic performance of the device itself were obtained through axial transducers and strain gauges on the device. It was experimentally proved that the hysteretic performance of the joint was enhanced by using the seismic mitigation device though the performance of the device itself did not meet the expectation. However, it indicated that such application of the seismic mitigation method has a high potential in energy dissipation in immersion joints. In the presented PhD thesis, the mechanical behavior of the joint subjected to axial, flexural and shear loadings and the seismic mitigation method for immersion joints have been studied comprehensively in an experimental way. As the first attempt ever on such issue, the results gained from these investigation give clear insights on the behavior of joint under different loading scenarios. The obtained stiffnesses can be used in further numerical analyses. The proposed seismic mitigation method for immersion joints is shown to be feasible not only to enhance the seismic performance of the joint but also to provide an additional way for energy dissipation of immersed tunnels. The material characteristics of the rubber seal are found to play a much more important role than what is expected from conventional design

Experimental investigation on the flexural mechanical behaviour of an immersion joint

The immersed tunnelling technique is commonly used for river or sea crossings worldwide. Seismic safety criteria of immersed tunnels involve the shear stiffness, axial stiffness, flexural stiffness, and opening deformations of the immersion joints. Therefore, it is necessary to conduct the mechanical analysis of the joint between the immersed tunnel elements. An experi-ment of an immersion joint is presented in this paper, mainly dealing with the experiment design, axial behaviour and flexural behaviour of the immersion joint. The geometric scale of this experi-ment is 1:10. The model joint in this paper includes two 3.8m x 1.15m x 1.2m segments with a rubber gasket and horizontal steel shear keys between them. Different levels of water pressure were considered due to the significant changes of water depth in real project. The displacements of an immersion joint under multi-level loads were measured and analysed considering the hyper-elastic property of a GINA gasket. It can be found that the mechanical behaviour of a GINA gasket is significantly affected by both flexure and axial loadings. Moreover, the flexural stiffness ratio of the joint with respect to that of the tunnel element in service states ranges from 1/27 to 1/272. The results are useful for the further numerical analysis of immersion joint and more related publi-cations are expected in the future

Tunnel Engineering

This volume presents a selection of chapters covering a wide range of tunneling engineering topics. The scope was to present reviews of established methods and new approaches in construction practice and in digital technology tools like building information modeling. The book is divided in four sections dealing with geological aspects of tunneling, analysis and design, new challenges in tunnel construction, and tunneling in the digital era. Topics from site investigation and rock mass failure mechanisms, analysis and design approaches, and innovations in tunnel construction through digital tools are covered in 10 chapters. The references provided will be useful for further reading

New Advances in Marine Engineering Geology

The ocean is the cradle of life and is rich in natural resources. With the worldwide boom in exploration and application of ocean resources, a dramatically increasing amount of coastal engineering and offshore engineering facilities have been constructed in the last few decades. The rapid development of human economic activities and the global climate change have significant impacts on the marine environment, resulting in frequent geological disasters. Under this circumstance, there is an urgent demand for a platform for scientists and engineers to share their state-of-art research outcomes in the field of Marine Engineering Geology. This book is a collection of a series of articles from the 2nd International Symposium of Marine Engineering Geology (ISMEG 2019), presenting some of the recent efforts made towards marine engineering geology and geotechnics, including theoretical advances, laboratory and field testing, design methods, and the potential for further development of these disciplines

Coastal Geohazard and Offshore Geotechnics

With rapid developments being made in the exploration of marine resources, coastal geohazard and offshore geotechnics have attracted a great deal of attention from coastal geotechnical engineers, with significant progress being made in recent years. Due to the complicated nature of marine environmnets, there are numerous natural marine geohazard preset throughout the world’s marine areas, e.g., the South China Sea. In addition, damage to offshore infrastructure (e.g., monopiles, bridge piers, etc.) and their supporting installations (pipelines, power transmission cables, etc.) has occurred in the last decades. A better understanding of the fundamental mechanisms and soil behavior of the seabed in marine environments will help engineers in the design and planning processes of coastal geotechnical engineering projects. The purpose of this book is to present the recent advances made in the field of coastal geohazards and offshore geotechnics. The book will provide researchers with information reagrding the recent developments in the field, and possible future developments. The book is composed of eighteen papers, covering three main themes: (1) the mechanisms of fluid–seabed interactions and the instability associated with seabeds when they are under dynamic loading (papers 1–5); (2) evaluation of the stability of marine infrastructure, including pipelines (papers 6–8), piled foundation and bridge piers (papers 9–12), submarine tunnels (paper 13), and other supported foundations (paper 14); and (3) coastal geohazards, including submarine landslides and slope stability (papers 15–16) and other geohazard issues (papers 17–18). The editors hope that this book will functoin as a guide for researchers, scientists, and scholars, as well as practitioners of coastal and offshore engineering

Field Instrumentation — The Link Between Theory and Practice in Geotechnical Engineering

Geotechnical engineers work in two worlds: a theoretical world where ideas and events can be represented by numbers and calculated to as many decimal points as one desires, and a practical world where observations and events can only be described in general qualitative terms. Numerical data, the end product of measurement, provides a quantitative link between the two worlds of theory and practice. Professor Ralph B. Peck, the father of the Observational method in geotechnical engineering, recognized early in his professional career the importance of field instrumentation and performance monitoring in geotechnical engineering, and he did a lot to promote its use. Thus, the author felt that it was appropriate to illustrate the importance and diversity of field instrumentation projects using selected case histories from the files of the Norwegian Geotechnical Institute (NGI). The examples include retaining structures, braced excavations, slurry trench excavations, large scale tests, dams, glaciers, avalanches and offshore structures. For each case cited the principal scientific, practical, and economic benefits of the monitoring program are pointed out

Low lateral stiffness underground structures for improved seismic performance: application to the Kobe Daikai station

Underground cut-and-cover structures are commonly designed as rigid box sections; however, in practical applications, connections between walls and slabs are frequently rather hinged (because of ease of construction). The abovementioned rigid configurations are highly sensitive to seismic ground motions, due to their important lateral stiffness and internal hyperstaticity; conversely, structures with articulated (or sliding) members have a smaller lateral stiffness, and would be significantly less affected by seismic waves, as would simply accommodate the imposed strains. This flexible solution has been widely considered in practice, but has received little attention from the academic community; this paper tries to close this gap by investigating preliminarily the seismic performance of box-section underground structures with hinged or sliding members. The well-known Daikai Station, damaged by the 1995 Kobe earthquake is analyzed in this paper as a highly relevant case study. An alternative solution is proposed for that station; both simplified and precise calculations have been performed. The simplified calculations are linear static analyses of the station-soil system; the soil-structure interaction is represented by a simple classical model. The precise calculations are nonlinear time-history analyses of an integrated finite element model of the station and the surrounding soil. Both types of analyses refer to the traditional and the proposed solutions of the station. The results of the static and dynamic analyses are satisfactorily compared; they prove that the proposed flexible solution is fully feasible and provides better seismic performance. Finally, another paper by the same authors presented a supplementary case study on a 2-story 3-bay subway station; the outcomes of these two studies could contribute to ground this constructive solution for shallow underground rectangular cut-and-cover structures in seismic areas (both for new construction and retrofit). Noticeably, this approach can be utilized for both cast-in-place and precast structures.This research has been partially funded by the Spanish Research Agency (AEI) of the Ministry of Science and Innovation (MICIN) through project with reference: PID2020-117374RB-I00 / AEI / 10.13039/501100011033. The study of Mr. Xiangbo Bu in the Technical University of Catalonia (UPC-BarcelonaTech) is funded by Chinese Government Scholarship (CSC No. 201906560013). These supports are gratefully acknowledged.Peer ReviewedPostprint (published version

Numerical analysis of Double-O-Tube shield tunnelling

Underground tunnels play an important role in the mass transportation systems in modern cities. The ground movements induced by tunnel excavation in short term and long term are of great concern due to their potentially irrecoverable impact on the surrounding buildings and services. The numerical modelling, in conjunction with well documented case studies to validate the modelling approach, is an efficient methodology for adequate and robust predictions of the ground response caused by tunnelling. The Double-O-Tube (DOT) shield tunnelling is a new technology developed since 1989, and has been applied in over 20 engineering cases in China and Japan. Due to its unique double tube cross-sectional shape, the DOT tunnel is expected to perform differently in mechanical terms compared to traditional twin tunnels. Therefore, a systematic study of its engineering behaviour, of the ground response and of tunnel lining is necessary. This research involves numerical simulations and investigation of DOT construction in soft clay and stiff clay conditions, represented by Shanghai clay and London clay respectively, using Imperial College Finite Element Program (ICFEP). In the first part of the thesis, the Shanghai clay and the whole ground profile are characterised referring to the laboratory data and field experimental evidence. A numerical model is developed in ICFEP for the case of DOT tunnel in the Shanghai Metro system, applying an extended Modified Cam Clay (MCC) model to represent the ground conditions and discretising the tunnel lining with elastic beam elements. The predicted short-term settlement troughs achieve good agreement with the field monitoring data, validating the reliability of the numerical model. Additional sensitivity studies investigate the conditions of the tunnel lining joints and the effects of the pressure exerted by grouting in the constructions process. The second part of the thesis focuses on the modelling of the reinforced concrete segments of tunnel lining using an advanced elasto-plastic concrete model. The model validation is performed with the simulation of loading tests on a single lining segment performed in the laboratory, demonstrating very close agreement between the predicted and measured segment deflections under applied load and an accurate onset of cracking in concrete. Such a concrete model is applied in the analysss of DOT tunnelling in Shanghai to investigate its merits against a simpler lining representation. Finally, the application of DOT tunnelling is explored in stiff clay ground conditions, utilising the Jubilee Line Extension and the Crossrail case studies in London clay, and applying an advanced kinematic surface hardening model for soil behaviour. The comparison of numerical predictions against field monitoring data demonstrates comparable magnitudes of ground movements mobilised by DOT tunnelling with respect to conventional twin tunnelling.Open Acces

Structure-Seabed Interactions in Marine Environments

The phenomenon of soil–structure interactions in marine environments has attracted great attention from coastal geotechnical engineers in recent years. One of the reasons for the growing interest is the rapid development of marine resources (such as in the oil and gas industry, marine renewable energy, and fish farming industry) as well as the damage to marine infrastructure that has occurred in the last two decades. To assist practical engineers in the design and planning of coastal geotechnical projects, a better understanding of the mechanisms of soil–structure interactions in marine environments is desired. This Special Issue reports the recent advances in the problems of structure–seabed interactions in marine environment and provides practical engineers and researchers with information on recent developments in this field