Dynamic Characteristics Study with Multidegree-of-Freedom Coupling in TBM Cutterhead System Based on Complex Factors

A multidegree-of-freedom coupling dynamic model, which contains a joint cutterhead, an inner ring gear, a support shield body, and pinions, is established, considering the external stochastic excitations, time-varying meshing stiffness, transmission errors, clearance, and so forth. Based on the parameters of an actual project and the strong impact of external excitations, the modal properties and dynamic responses are analyzed, and the cutterhead joint surface loads are obtained and treated by rain flow count. Numerical results indicate that the low natural frequencies are 57 Hz and 61 Hz, and natural vibration modes are pinions-motors rotational mode and translational-overturning coupled mode of cutterhead with inner ring gear correspondingly. Besides, the axial and radial amplitude of dynamic responses are 0.55 mm and 0.25 mm, respectively. The frequencies of radial, torsional, and overturning vibrations are predominantly concentrated in 112 Hz and 120 Hz, which indicates that the vibration responses of cutterhead are mainly affected by the external excitations. Finally, as the rain-flow counting results have shown, the standard deviation of the cutterhead joint surface loads in each direction increases by 12–15 times, compared with that of the external excitations; therefore inertia effect should be considered in cutterhead design. The proposed research lays a foundation for dynamic performance optimization and fatigue crack growth life assessment of cutterhead structure

Designing a Tunnel

Designing a tunnel is always a challenge. For shallow tunnels under cities due to the presence of buildings, bridges, important avenues, antiquities, etc. at the surface and other infrastructures in the vicinity of underground tunnels, parameters like vibrations and ground settlements must be tightly controlled. Urban tunnels are often made in soils with very low values of overburden. Risks of collapse and large deformations at the surface are high; thus negative impact on old buildings are likely to occur if appropriate measures are not taken in advance, when designing and constructing the tunnel. For deep tunnels with high overburden and low rock mass properties, squeezing conditions and excessive loads around the excavation can jeopardize the stability of the tunnel, leading to extensive collapse. The aim of the chapter is to give details on advance computational modelling and analytical methodologies, which can be used in order to design shallow and deep tunnels and to present real case studies from around the world, from very shallow tunnels in India with only 4.5 m overburden to a deep tunnel in Venezuela with extreme squeezing conditions under 1300 m overburden

Performance Analysis of Tunnel Boring Machines for Rock Excavation

The study takes into account different classes of tunnel boring machines (TBM), with the aim of identifying correlation models which are meant to estimate, at a preliminary design phase, the construction time of a tunnel and to evaluate the mechanical and operational parameters of the TBMs, starting from the knowledge of the tunnel length and the excavation diameter. To achieve this goal, first of all a database was created, thanks to the collection of the most meaningful technical parameters from a large number of tunnels; afterwards, it was statistically analyzed through Microsoft Excel. In a first phase, forecasting models were identified for the three types of machines investigated, separately for compact rocks (open TBM) and fractured rocks (single and double shield TBM). Then, the mechanical parameters collected through the database were analyzed, with the aim of obtaining models that take into account, in addition to the type of TBM, the geological aspect and the type of rock characterizing the rock mass. Finally, the validation of the study was proposed in a real case, represented by the Moncenisio base tunnel, a work included in the new Turin–Lyon connection line. The estimated values were compared with the real ones, in order to verify the accuracy of the experimental models identified

Analysis of TBM tunnelling performance in faulted and highly fractured rocks

The thesis focuses on the study of the performance of TBMs in highly jointed and faulted rocks. Despite the great production rates recorded in favourable ground conditions, the TBM advance can be significantly slowed down in limiting geological situations such as extremely fractured and fault zones. After an introduction about the major issues resulting from tunnelling in bad ground conditions, a brief review of some TBM performance prediction models is reported and the most common parameters adopted for evaluating the TBM performance are identified. The geotechnical characterisation of fault zones is very difficult due to their heterogeneous nature (i.e. weak and strong rock components). This particular aspect is highlighted through a literature review about the geological/geotechnical description of fault rocks. In order to investigate possible relationships between difficult rock mass conditions and TBM performance, data of several tunnel projects are collected in a database by including information from the field, laboratory tests and literature. Preliminary analyses are carried out in order to identify correlations between TBM performance (i.e. penetration and advance rate) and rock mass parameters (e.g. rock strength, fracturing degree, etc.). Although some trends are identified, the scattered results confirm the difficulties in predicting the machine performance in complex geological environments. In order to obtain a more complete geotechnical description of disturbed zones, a classification system for highly fractured rock masses and fault zones is developed. Four âfault zoneâ classes are identified by considering the fracturing and the weathering degree of the rock mass. Furthermore, in order to analyse the response to mechanical excavation of the identified classes, a set of numerical simulations are run with the aim to investigate the TBM performance at the cutter-scale. The data recorded in the TBM-performance database are then analysed according to the new classification system. For each âfault zoneâ class, a reduction rate for selected TBM parameters is defined with respect to the tunnelling performance observed in good ground conditions. The results of these analyses are of great relevance as they allow to successfully quantifying the effect of altered rock mass conditions on the TBM behaviour. The results obtained in the previous steps are used to carry out probabilistic analyses of the tunnel construction time and costs by means of the Decision Aids for Tunnelling (DAT). The DAT are a software package that evaluates the influence of uncertainties related to both geotechnical conditions and excavation process on the final tunnel construction time and costs. In this framework, the TBM advance rate reductions previously defined for each âfault zoneâ class are input in the simulations. A reliable estimation of the effect of degrading geological conditions (i.e. faulted and highly fractured/crushed rocks) on the tunnel construction process is obtained. The results of this research provide useful insights regarding the TBM performance reduction in bad grounds, with respect to the âordinaryâ tunnelling conditions. The study highlights the need to better characterise, from a geomechanical point of view, the highly fractured and faulted rocks. This can be done by considering the parameters representative of the degraded state of the rock mass, instead of those commonly used for estimating the TBM performance in good rocks

Stability analysis of shallow undrained tunnel heading using finite element limit analysis

This dissertation investigated the undrained stability of shallow tunnel heading problems subjected to varying loading conditions by performing a two-dimensional plane strain analysis. Failure due to the blowout mechanism was highlighted as a major focus area, due to the lack of previous research on the topic. Finite element limit analysis (FELA), employed through the geotechnical software analysis package, Optum G2, was used to determine lower and upper bound factor of safety (FoS) values for a range of various scenarios. The factor of safety values were calculated using the gravity multiplier method (GMM) and the strength reduction method (SRM). These methods were directly compared and the strength reduction method was found to be the most suitable method for analysing scenarios with either a surcharge or internal tunnel pressure applied. The results obtained in this study were validated by comparing a sample to results published by Augarde, Lyamin and Sloan (2003). This comparison found a very good level of agreement. The factor of safety is a function of three dimensionless parameters; the pressure ratio (PR), strength ratio (SR) and depth ratio (DR). The relationship between the factor of safety and these parameters was investigated. A number of plots and displacement vector fields were created to better assist in understanding these relationships and the specific failure mechanism related to each scenario. This process reinforced the need to not only design tunnels for failure due to collapse but to also check for failure due to blowout. The stability of tunnels has historically been expressed in the form of a stability number, similar to the approach adopted by Taylor (1937). This dissertation presents results by applying the factor of safety approach, allowing for direct and clear interpretation of results and any practical implications. The research culminated in the development of a variety of tunnel heading stability design charts. These design charts have been designed for use by practicing engineers in the preliminary stages of tunnel design. A number of select examples are provided to outline some of the potential uses of the design charts. One particularly useful practical application of the design charts is the ability to determine a safe operating range for the pressure that can be applied to the tunnel excavation face by a tunnel boring machine during construction

Theory and Practice of Tunnel Engineering

Tunnel construction is expensive when compared to the construction of other engineering structures. As such, there is always the need to develop more sophisticated and effective methods of construction. There are many long and large tunnels with various purposes in the world, especially for highways, railways, water conveyance, and energy production. Tunnels can be designed effectively by means of two and three-dimensional numerical models. Ground–structure interaction is one of the significant factors acting on economic and safe design. This book presents recent data on tunnel engineering to improve the theory and practice of the construction of underground structures. It provides an overview of tunneling technology and includes chapters that address analytical and numerical methods for rock load estimation and design support systems and advances in measurement systems for underground structures. The book discusses the empirical, analytical, and numerical methods of tunneling practice worldwide

Risk analysis for tunneling projects

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 574-589).Tunnel construction is increasing world wide. Although the majority of tunnel construction projects have been completed safely, there have been several incidents that have resulted in delays, cost overruns, and sometimes more significant consequences such as injury and loss of life. To help eliminate these accidents, it is necessary to systematically assess and manage the risks associated with tunnel construction. In order to better understand the conditions under which accidents occur, a database of 204 tunnel construction accidents was assembled. This is the most comprehensive database known to date. The database was analyzed to better understand the causes of accidents. Influence diagrams were constructed containing the main factors, and the interactions between them. These served as the basis of the risk assessment methodology presented in this work. The risk assessment methodology consists of combining a geologic prediction model that allows one to predict geology ahead of the tunnel construction, with a decision support model that allows one to choose amongst different construction strategies the one that leads to minimum risk. The geologic prediction model is based on Bayesian networks because of their ability to combine domain knowledge with data, encode dependencies among variables, and their ability to learn causal relationships.(cont.) The combined geologic prediction - decision support model was then applied to the Porto Metro, in Portugal. The results of the geologic prediction model were in good agreement with the observed geology, and the results of the decision support model were in good agreement with the construction methods used. More significant, however, is the ability of the model to predict changes in geology and consequently changes in construction strategy. This was shown in two zones of the tunnel were accidents occurred, where the model predicted an abrupt change in geology, and the construction method should have been changed but was not. Using the model could have possibly avoiding the accidents. This risk assessment methodology provides a powerful tool with which planners and engineers can systematically assess and mitigate the inherent risks associated with tunnel construction.by Rita L. Sousa.Ph.D

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

3D numerical analysis of tunnelling effects on a multi-storey building: the case of Line 9 EPB tunnelling in Barcelona

Juntament amb el desenvolupament de les infraestructures en zones urbanes, la necessitat de construcció de túnels augmenta. Aquestes excavacions subterrànies provoquen moviments en el terreny que poden estar associats amb danys en estructures pròximes al traçat. Tot i la importància del fenomen d'interacció sòl-estructura, les deformacions dels edificis porticats no s'han estudiat exhaustivament i hi ha enfocaments de disseny limitats per avaluar possibles riscos. Aquesta dissertació presenta un model tridimensional d'elements finits de la interacció túnel-sòl-edifici per al cas Llave de Oro, documentat durant la construcció de la Línia 9 del Metro de Barcelona. A causa d’importants moviments produïts en el terreny per la construcció del túnel, diversos elements dels edificis monitoritzats van resultar danyats; amb fissures situades principalment a les zones adjacents a la junta de dilatació entre dos blocs del mateix edifici. En el model numèric es realitza la simulació de l'excavació del túnel, modelitzant l'edifici mitjançant una estructura de pòrtic semirígid amb juntes de dilatació. Els resultats numèrics s'avaluen tenint en compte els moviments observats in situ. L'estudi confirma la importància de la modelització de juntes de dilatació i el seu potencial per a produir esquerdes localitzades en edificis relativament rígids.Junto con el desarrollo de las infraestructuras en zonas urbanas, la necesidad de construcción de túneles aumenta. Estas excavaciones subterráneas provocan movimientos en el terreno que pueden estar asociados con daños en estructuras próximas al trazado. A pesar de la importancia del fenómeno de interacción suelo-estructura, las deformaciones de los edificios porticados no se han estudiado exhaustivamente y existen enfoques de diseño limitados para evaluar posibles riesgos. Esta disertación presenta un modelo tridimensional de elementos finitos de la interacción túnel-suelo-edificio para el caso Llave de Oro, documentado durante la construcción de la Línea 9 del Metro de Barcelona. Debido a importantes movimientos del terreno causados por la construcción del túnel, varios elementos de los edificios monitoreados resultaron dañados; con fisuras ubicadas principalmente en las zonas adyacentes a la junta de dilatación entre dos bloques del mismo edificio. En el modelo numérico se realiza la simulación de la excavación del túnel, modelizando el edificio mediante una estructura de pórtico semirrígido con juntas de dilatación. Los resultados numéricos se evalúan teniendo en cuenta los movimientos observados in situ. El estudio confirma la importancia de la modelización de juntas de dilatación y su potencial para causar grietas localizadas en edificios relativamente rígidos.Because of the currently growing infrastructure system in urban areas, an increasing number of underground tunnels are needed. Generally, underground excavations, such as tunnelling, cause surface soil movements and can be associated with structural damage. Despite the importance of the soil-structure interaction, the deformations of framed buildings have not been extensively studied and there are limited design approaches for their risk assessment. This dissertation presents a three-dimensional finite element model of a tunnel-soil-building interaction, giving insights into the building deformation mechanism for the Llave de Oro case history, documented during the construction of the Metro Line 9 Barcelona. Due to significant ground movements caused by tunnelling, several elements of the monitored buildings were damaged; with cracks mostly located in the areas adjacent to the expansion joint between two blocks of the same building. In the numerical model, the tunnel excavation is simulated, and the multi-storey building is modelled with a semi-rigid frame structure. The effect of expansion joints is evaluated through a parametric study. Results obtained from the numerical model are reviewed in consideration of available monitoring measurements, confirming the importance of modelling expansion joints and their potential for leading to localised cracking within relatively stiff buildings