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İstanbul Metrosunda uygulanan derin kazı destek sisteminin bilgisayar modelinin araştırılması

Computer modelling of the deep excavation support system which was applied in istanbul subway construction

  1. Tez No: 66741
  2. Yazar: SİNE AVŞAR
  3. Danışmanlar: PROF. DR. ERKİN NASUF
  4. Tez Türü: Yüksek Lisans
  5. Konular: Maden Mühendisliği ve Madencilik, Mining Engineering and Mining
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1997
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Maden Mühendisliği Ana Bilim Dalı
  12. Bilim Dalı: Yeraltı Maden İşletmeciliği Bilim Dalı
  13. Sayfa Sayısı: 89

Özet

ÖZET Bu çalışmada, tünel ve derin kazı tipindeki kent içi kaya ve zemin yapılarının, destek sistemlerinin nümerik olarak modellenmesi incelenmiş. Nümerik yöntemlerden, sonlu farklar yöntemi ile çalışan FLAC isimli bilgisayar yazılımı kullanılmıştır. FLAC programı yardımı ile İ.B. B.İstanbul Metrosu 1. Aşama 2.Kısım İnşaatı kapsamında gerçekleştirilmiş olan Taksim İstasyonu 2.Konkors yapısında derin kazı cidarlarını desteklemek amacı ile yapılan ankrajlı betonarme perde duvar örneğinin modellemesi yapılmıştır. Çalışmanın temel amacı, yoğun yerleşim birimleri içinde açılmış derin kazı türündeki yapıların davranışını önceden tahmin edebilecek, mühendislere oluşabilecek muhtemel hareketlerin yönü, gelişimi ve etkileri hakkında önceden ipuçları verebilecek bir model oluşturmaktır. Kritik hareketlerin tahminin yanısıra, bilgisayar modellemesinin diğer bir amacı da değişik kazı ve destek sistemini simule ederek, değişik tasarımlar arasından optimum şeklin bulunmasına yardımcı olmaktır. Çalışmanın birinci bölümünde, stres analizi ve stres analizi için kullanılan nümerik yöntemler, jeomekanikte modelleme metodolojisi, FLAC programının özellikleri ve terminolojisi konusunda bilgi verilmiştir. Çalışmanın ikinci bölümünde İstanbul Metrosu Projesinin işletme ve teknik özellikleri hakkında bilgiler verilmiştir. Çalışmanın üçüncü bölümünde jeoloji ile ilgili bilgiler verilerek ortam şartlan tanıtılmaya çalışılmıştır. Çalışmanın dördüncü bölümünde derin kazı destek yöntemleri ve Taksim İstasyonu 2. Konkors yapısında uygulanan sistem ile ilgili bilgiler verilmiştir. Destek sisteminin oluşturulma aşamaları model açısından oldukça önemli olmaktadır. Çalışmanın beşinci bölümünde Taksim İstasyonu 2.Konkors inşaatında yapılan jeoteknik ölçümler ve ölçüm sonuçlarına değinilmiştir. Son bölümde modelin hazırlanma aşamaları anlatılmış, seçilen malzeme özellikleri hakkında bilgiler verilmiştir. Bu bölümün sonunda model sonuçlan varolan bilgilerinde ışığı altında yorumlanmaya çalışılmıştır.

Özet (Çeviri)

SUMMARY In this study, the main purpose is preparation of a predictive model of reinforcement system with anchors which is used in deep excavation of Taksim Station. If a predictive model is achieved succesfully, it can be used for similar projects in the future. It is necessary to make such a model, first the engineer must have the site- spesific data from in-situ tests. If the site-spesific data is useful, the model outputs compared with this and it can be obtained how the model works. In the design of an excavation in rock, it is essential that the excavation can perform an intended function under the loads imposed on it during its duty life. This condition is satisfied if displacements of excavation boundary rock are maintained within prescribed limits, under the prevailing operational static and dynamic loads. Thus, assurance of the performance of an excavation is directly related to the capacity to predict rock-mass displacements, and the associated state of stress, around the excavation. It follows that analysis of stress and displacement distribution around excavation is an essential component of excavation design practice. The purpose of modeling is to realize an economic design for an excavation. In the light of results of the analysis, the design may be modified, within the constraints imposed by operational considerations, until the zones of failure are minimized. Alternatively, rock reinforcement or other rock-mass modification techniques are specified, sufficient to achieve control of rock-mass deformation. A further purpose of modeling is to establish a suitable excavation sequence for the construction of an opening. While the final shape of an excavation is the primary concern, it is necessary to establish, by repetitive analysis, the excavation sequence which preserves the integrity and local stability of the adjacent rock mass as the excavation is developed. The modeling of geo-engineering processes involves special considerations and a design philosophy different from that followed for design with fabricated materials. Analyses and designs for structures and excavations in or on rocks and soils must be achieved with relatively little site-spesific data and an awareness that deformability and strength properties may vary considerably. It is impossible to obtain complete field data at a rock or soil site; for example, information on stresses, properties and discontinuities can only be partially known, at best. Since the input data necessary for design predictions are limited, the numerical model of deep excavation of Taksim Station used primarily to understand the dominantmechanisms affecting the behavior of the system. Once the behavior of the system is understood, it is then appropriate to develop simple calculations for a design process. The level of detail to be included in the model depends on the purpose of the analysis. For example, if the objective is to decide between two conflicting mechanisms that proposed to explain the behavior of the system, then a crude model may be constructed, provided that it allows the mechanisms to occur. It is tempting to include complexity in the model just because it exists in reality. However, complicating features should be omitted if they are likely to have little influence on the response of the model's purpose. Start with a global view and add refinement as necessary. In this study, the software was used for modeling which is named FLAC (Fast Lagrangian Analysis of Continua). FLAC is a two-dimensional explicit finite difference program for engineering mechanisms computation. This program simulates the behavior of structures built of soil, rock or other materials that may undergo plastic flow when their yield limits are reached. Materials are represented by elements, or zones, which form a grid that is adjusted by the user to fit the shape of the object to be modeled. Each element behaves according to a prescribed linear or non-linear stress/strain law is response to the applied forces or boundary restraints. The material can yield and flow, and the grid can deform (in large-strain mode) and move with the material which is represented. The explicit, Lagrangian, calculation scheme and the mixed discretization zoning technique used in FLAC. Plastic collapse and flow are modeled very accurately. Because no matrices are formed, large two-dimensional calculations can be made without excessive memory requirements. There is some general steps and logical rules for preparing, efficient model. They are discussed on follow. In the study, the methodology which contains these steps is used to prepare the model. It is important to have a conceptual picture of the problem to provide an initial estimate of the expected behaivor under the imposed conditions. In this study, several questions asked when preparing the model. For example, is it anticipated that the system can become unstable? Are movements expected to be large or small in comparison with the sizes of objects within the problem region? Is the predominant mechanical response linear or non-linear? Are there well-defined discontinuities that may affect the behavior, or does the material behave essentially as a continuum? Is the system bounded by physical structures, or do its boundaries extend to infinity? Is there any geometric symmetry in the physical structure of the system? These considerations dictate the gross characteristics of the numerical model, such as the design of the grid, the types of material models, the boundary conditions, and the initial equilibrium state for the analysis. They determine how is a model can be used to take advantage of symmetry in the physical system. XIWhen idealizing the physical system for numerical analysis that made in this study, simple test models was constructed and run first, before building the detailed model. Simple models created at the earliest possible stage in the project to generate both data and understanding. The results provide further insight into the conceptual picture of the system. Simple models can reveal shortcomings that can be remedied before any significant effort is invested in the analysis. For example, do the selected material models sufficiently represent the expected behavior? Are the boundary conditions influencing the model response? The results from the simple models can also help guide the plan for data collection by identifying which types of data are more relevant to the analysis. The types of data required for a model analysis include: - Details of geometry, - Location of geologic structure, - Material behavior, - Initial conditions, - External loading, There are large uncertainties associated with spesific conditions, a reasonable range of parametres must be selected for the investigation. The results form the simple model runs often prove helpful in determining this range, and in providing insight to collect the needed data type and amount. When preparing the model runs for calculation, several aspects considered. One of the considerations is that how much time is required to perform each model calculation? It can be difficult to obtain sufficent information to arrive at a useful conclusion if model run times are excessive. The state of the model saved at several intermediate stages so that the entire run does not have to be repeated for each parameter variation. For example, if the analysis involves several loading/unloading stages, it is possible to return to any stage, change a parameter and continue the analysis from that stage. It was best to first make one or two detailed model runs separately before launching a series of runs. These runs stopped and checked intermittently to ensure that the response is as expected. Once there was assurance that the models are performing correctly, several model data files linked together to run a number of calculations in sequence. At any time during the sequence of runs, the calculation was interrupted, the results analyzed, and then continue or modify the model as appropriate. In the study, the reinforcement system of Taksim Station 2nd Entrance Structure was modeled. It was a typical deep excavation application. There was used concrete retaining wall and pretensioning cable anchorages as support system. Height of the wall is 20.30 m., and there are ten levels of anchorages applied on the wall. XIIThe study contains seven chapters. The first chapter is introduction which contains the objects of this modeling study, and general identification of the problem. Chapter 2, contains the following information. The methods that used for classical stress analysis. General information is given about numerical methods for stress analysis (finite elements, boundary elements and finite difference methods). In this chapter information about features of FLAC program, and modeling methodology is also given. In Chapter 3, information about Istanbul Subway Construction Project is given. Project's aims, general and technical features is defined. Chapter 4 contains information about the geology of Istanbul and also the geology of Taksim Station area. Geological, mechanical an physical features of the ground is defined in this chapter. Chapter 5 contains information about the structure that was modeled. Excavation and support system of the structure is discussed in this chapter. Chapter 6 contains information about the geotechnical measurements that taken from field. The field data was compared with the model outputs in next chapter. In chapter 7, information about preparing of the model is given. There was generated a 45*45 grid for representing the wall. The grid contains 2025 elements. All of the supporting element's location is calculated separately and represented on the model. The material properties are adjusted on the model. Mohr-Coulomb failure criteria was selected to represent the mechanical behavior of rock and soil. 500 calculation steps were applied for model. The model outputs was captured by a post script graphic software and opened in Windows media. It has more advantages than opening the graphics in FLAC s graphical interface. Features of the model is given in Figure 1. 5,50 50,50 Excavation Figure 1. Features of The Model xmAfter running this model, the model results were compared with field measurement data. As result the computer model represents the reality correctly and this model can be used for similar designs in the same geologic formation. XIV

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