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THE DESIGN OF CONDITIONING PROCESS FOR MECHANIZED TUNNELLING WITH TBM-EPB
No full textThe growing demands for mobility in large urban areas and the need of expansion of large rail and road infrastructures have led, in recent decades, to a notable boost in the world of tunnels, made evident, among other things, by a number of realized projects in exponential growth, by an unprecedented technological development and by the consequent growth of professionalism involved and jobs, investments and incomes generated.
In the mechanized excavation of tunnels, the EPB-TBM excavation technology can rightly be considered one of the latest innovations in terms of time and certainly one of the most widespread methodologies in the world. Much of the diffusion of this technology is due to its flexibility and the ability to quickly adapt to the variable conditions, making its strong point in the possibility to control the pressures applied to the excavation front-face by soil conditioning and to the considerable advantages linked to the possibility of avoiding the complex process of separation and re-use of bentonite mud from the spoil.
For a successful excavation, conditioning is a decisive process and its good management leads to the reduction of risks, the reduction of a series of undesired effects (surface induced failures/settlements, wear of TBM metal parts in the case of coarse grained soils, clogging in the case of fine-grained soils), the increase in excavation performance and the possibility of optimizing the re-use of the excavated soil; in extreme synthesis to the reduction of risks, times, costs and impact of realization of the work.
This process, determinant for the success of the excavation activities and in general of the realization of the work, is not substantially the object of design. In the preliminary and definitive design phase, soil conditioning is currently only considered for the environmental aspects necessary for the definition of the plan for the use of excavated earth and rocks. The study of soil conditioning is entrusted in small part to the executive design phase of the work, in which the characteristics of the TBM (and therefore also of the injection systems) are defined, and almost entirely directly in the construction phase for the choices of products, dosages and conditioning parameters. The dosage definition is made on the basis of the indications provided by the producers of conditioning agents or by the TBM manufacturers, refined directly during the first section of the TBM excavation (learning phase) and occasionally confirmed by conditioning tests carried out in the laboratory close to the beginning of the excavation activities. The operative procedures for managing and modifying the conditioning parameters are agreed on site by TBM staff with professional figures such as the TBM engineer. Occasionally, accidents due to errors in the conditioning occur, the greater consumption of conditioning agents is systematic up to 3 times the estimated values and there is almost never certainty about the possibility of improving the performance of the TBM by optimizing the conditioning process.
This process is determined by the widespread belief that each construction site and each tunnel is a work "stand-alone" for which the conditioning has to be defined directly in the course of work; this conviction matured over time due to the differences related to the formulation of the products, very similar but never exactly the same, due to the variability of the soil encountered during the excavation, predictable but never accurately, due to the scale effect that naturally exists between the evaluations made in the laboratory and what happens on site, due to the remarkable effect that the subjective evaluations and decisions of the workers involved in the excavation of the tunnels (foreman / TBM chief) and in the lack of studies and in general of the a clear understanding of the conditioning process from the chemical, physical, geotechnical and mechanical point of view.
After years of experimental study and comparison with real cases of tunnelling, I certainly cannot claim to have a clear knowledge about every aspect of the conditioning, but I am absolutely convinced that this aspect can and must be the object of a design process like so many other aspects of excavation of a tunnel, once entrusted to the experience of the miners and which today are the subject of in-depth analyses developed by engineers. These engineers, to make a good job, must have listened to the miners' stories, seen the mechanics at work in a TBM, studied the scientific evidence produced by different research groups in the world, make use of the calculation tools and engineering judgement that are proper to them and, above all, they must resist the temptation to say "in the jobsite, somehow, they will handle it".
The layout of this thesis stems from the belief that, while considering all the uncertainties and peculiarities typical of each tunnel project, in a general perspective the conditioning is a process that responds to precise and always valid rules, of which the typology of soil, the chemical composition of conditioning agents, the characteristics of the TBM and the injection system are simply variables of a system that is decidedly complex but substantially responsive to laws and relationships like everything we know as engineers.
More in detail, I have gained the conviction that all the effects of the conditioning of any type of soil can be seen as the combination of three effects: i) the effect of the chemical interaction between the conditioning agents and the soil; ii) the effect of the variation of the water content caused by the injection of water and the liquid part of the foam and iii) the effect of the introduction of air into the soil and consequently the lowering of its saturation degree. Consequently, during the course of the PhD, one of the first aims was certainly the study and measurement of the three effects listed on a very wide combination of soils and conditioning agents necessary to understand how the chemical composition of conditioning agents and the characteristics of the soil affect these effects.
On the basis of the existing literature and the first experimental evidences obtained in the laboratory, I have therefore begun to think of a conditioning design process that can be integrated into the entire project from the preliminary stages up to the executive design that it was able to define, with subsequent investigations, costs, consumption, dosages and features of the conditioning process during the excavation, to foresee the correct maintenance of the pressures at the front during excavation and during the standstill and to foresee the geotechnical and environmental characteristics of the soil after extraction from the excavation chamber to define the most suitable reuse methods.
This process responds to rules and concepts of general validity to be declined, for each tunnel project, based on the boundary conditions; in this design process characteristics of the soils, TBMs features, environmental and economic constraints, interactions with the external environment are all parameters input of a clear process developed according to well-defined and always valid rules that will lead to a solution that is always different for each gallery to be built; I am indeed deeply convinced that every tunnel is a separate project, but that instead the rules with which every aspect must be designed, including conditioning, are those of physics, chemistry and geotechnics.
The definition of this design process required the development of new specially designed laboratory tests, standards and interpretation and classification systems based on the results of a decidedly high number of combinations of types of soil (8 fine-grained and 8 coarse grained) and more than 30 different conditioning agents including foaming agents and polymers.
The process I have conceived involves three successive phases, the first to be developed in the context of the Technical and Economic Feasibility Study and of the Definitive Project, the second to be developed in the context of the Executive Project and the third to be developed together with the excavation of the gallery.
Each phase involves the use of a series of data and information (inputs - what I have) commonly available for each design level, provides a series of objectives (targets - what I need) necessary for the correct design of the work, foresees the execution of analyses and laboratory tests purposely conceived of which the standards are defined (actions - what I do), foresees the obtaining of a series of indications (results - what I get) and finally it foresees the verification (controls - what I check) of the hypotheses made to acquire information on residual uncertainties and to perform parametric analyses necessary to define the ranges of variability of the results.
The integration of this process within the process of design and canonical execution of a tunnel excavation could allow the reduction of accidents, risks, unforeseen events, excessive consumption, maximize excavation performance, optimize the reuse of conditioned land, reduce the duration and problems of the learning phase.
Furthermore, the development of all the conditioning study activities in a single process will bring order, avoiding overlaps and repetitions in the different phases of the design, reducing burdens and timing associated with these activities, which are often out of control.
This thesis proposes a method, based on experimental evidence, the result of continuous comparisons with real projects of tunnels excavated in recent years and a significant number of combinations of products and soils analysed. Certainly, like every Research product, it should not be considered a finished and defined product, but I hope in the future it will be integrated and modified, even by myself, on the basis of new experimental evidences, of new requirements and boundary conditions (characteristics of TBM and conditioning agents) that will certainly have changed in a few years.
It is important to underline that the contents of this design process are based on widely shared approaches from the international literature, that only some laboratory tests and some classification systems have been developed and proposed by me during the last three years and that the overall proposed design process, in a nutshell, can be considered a reorganization and an organic collection of a series of information that the scientific community, in which I undeservedly include myself, has collected in the last decades and an attempt to transmit it to those who they are engaged daily in the design and construction of tunnels with EPB-TBM.
The highest and certainly ambitious goal, which I would be satisfied to have achieved even in small part, is to modify the perception of studies on soil conditioning to give them the level of attention usually reserved for the most relevant aspects of tunnel excavation; the aspects that must be carefully designed, the aspects that determine the success of an excavation, the aspects that if undervalued can cause risks and considerable damages, the aspects that can substantially determine the time, cost, durability and environmental impact of an excavation work. I am convinced that the most recent history is showing that soil conditioning, in the mechanized excavation of tunnels, deserves this level
Experimental Study of Coarse Soil Properties Influencing Soil Abrasivity
No full textAbstractThe paper reports selected results of a study on tool wear for mechanized tunnelling in coarse soil. Several laboratory soil abrasion tests were performed and the results correlated with mineralogical composition, shape and surface roughness of the grains and the grain size curve of the soils. The analysis of the results clearly confirms the well-known correlation between soil abrasivity and quartz content and, for the soils tested, can quantify the relevant influence of grain size and grain roughness. We also report and discuss results useful for quantifying the positive effect of the addition of different chemical agents, injected as foams in a process known as soil conditioning, commonly performed in mechanized tunnel excavation using tunnel boring machines whit earth pressure technology to minimise tool consumption
Approccio integrato alla gestione delle terre e delle rocce da scavo per il buon uso del territorio e per la prevenzione dei dissesti
No full textLa fragilità del territorio del nostro paese assieme alla localizzazione spesso poco felice di città e infrastrutture, mette a rischio frane, inondazioni, terremoti le nostre strutture e infrastrutture. La corretta gestione del territorio passa attraverso una attenta attività di pianificazione e la salvaguardia dell’esistente impone un’efficace attività manutentiva e una pianificazione degli interventi di presidio per la mitigazione dei rischi. Con questi obiettivi, la disponibilità dei sempre crescenti volumi di terreno provenienti da scavi non impiegati o non impiegabili nell’ambito dello stesso progetto, può essere considerata come un’opportunità per la realizzazione di opere di mitigazione dei rischi
connessi con il verificarsi dei fenomeni naturali prima citati. Si tratta di un obiettivo ambizioso che può essere conseguito creando le condizioni normative e organizzative per facilitare l’incontro tra l’offerta e la richiesta di terra.Structures and infrastructures, in our country, are often put in serious danger, concerning landslides, floods and earthquakes, by the
brittleness of the territory and by an often inappropriate localization. A proper land management can be achieved through a careful planning, and the preservation of the existing structures imposes effective maintenance activities and a design of protection structures to mitigate the risks. With these objectives, the availability of ever-increasing volumes of soil from excavations, not used or which cannot be used within the same project, can be seen as an opportunity for the realization of projects in order to mitigate risks associated with the occurrence of natural phenomena described above. It is an ambitious target that can be achieved by creating the regulatory and organizational conditions to facilitate the matching of supply and demand for soil
Geotechnical characterization of natural clays for the prediction of clogging risk for TBM
No full textDuring mechanical tunnel driving it is known that the excavated soils can stick to the metallic part of the tunnel boring machine (TBM). Despite the fact that several test methodologies have been developed during the last 15 years to provide an assessment or quantification of the clogging risk, no standardized method is available yet. This study evaluated three natural clay samples with different grain size distribution and mineralogical content considering two widespread test set ups for the evaluation of the clogging tendency: the Hobart mixing and the plate pull-out test. After a comprehensive geotechnical characterization of the three clay samples, adherence and plate pull-out force have been measured at different water content/consistency index. Results show that adherence and plate pull-out force in terms of water content w and consistency index I-C follow normal distribution curves which, as the percentage of clay, the content of clay minerals and the plasticity increases, have higher amplitudes and higher peak values. In general, the existence of a correlation between geotechnical classifications parameters and the behavior in terms of potential clogging risk for natural clays makes it possible to predict these risks in the design phase of the tunnel excavation and to plan appropriate mitigation actions
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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