Süreksizlikler arası mesafe ve süreksizlik kutupsal yönelimlerinin tünel etkilenme bölgesi yer değiştirme mekanizmasına etkisinin araştırılması

Abstract

Süreksizlik; tünel destek sistemlerinin seçiminde aktif rol oynayan jeomekanik bir parametre, kaya sınıflama sistemleri ile tahkimat tasarımı yapılırken de incelenmesi gereken ana bileşenlerden biridir. Bu tez çalışmasında, kayaçlardaki 2 boyutlu süreksizlik geometrisinin tünel ve ortam üzerinde etkisinin olup olmadığı, varsa bu etkinin ne oranda olduğu sayısal çözümleme ile araştırılmıştır. Etkisi araştırılan parametreler; süreksizlik aralığı ve yönelimidir. Kaya sınıflama sistemlerinden RMR (Kaya Kütle Puanı)'ın puanlama çizelgelerinde bulunan sınır değerleri baz alınarak süreksizlik aralıkları belirlenmiştir. Buna göre, ele alınan tünel projesi modifiye edilerek 6 cm ile 400 cm arasında değişen 8 farklı süreksizlik aralığı (6, 13, 20, 40, 60, 130, 200 ve 400cm) 0º ile 180º arasında değişen 12 süreksizlik yönelimi (0; 22,5; 30; 45; 60; 67,5; 90; …) olacak şekilde tünel çevresinde kuramsal olarak oluşturulmuş, tünel etkilenme zonundaki yer değiştirme hareketinin her bir durumda ne oranda değiştiğinin ortaya çıkarılması hedeflenmiştir. Bu şekilde oluşturulan tünel proje modelleri, sonlu elemanlar yöntemi ile çözümleme yapan RS2 yazılımı kullanılarak çözülmüştür. Çözümlemede sabit tutulan parametreler, tünel geometrisi, arazi gerilmeleri ve malzeme özelliklerini de içeren jeomekanik parametrelerdir. Toplam 68 çözümleme yapılmış, yapılan yer değiştirme analiz sonuçları, tam tünel cidarında ve cidarından dışına doğru genişleyen 2, 4, 6 ve 8. metrelerde sorgular oluşturularak incelenmiştir. Ele alınan tünel projesi yan yana açılan ikiz bir tünel projesidir. Sonuçlar, ilk tünel açılıp tahkimatı tamamlandıktan ve ikinci tünel açılıp tahkimatı tamamlandıktan sonra iki ayrı durumun ilk tünel üzerindeki etkileri olmak üzere incelenmiş ve bu incelemeler karşılaştırılmıştır. Ardından, bu karşılaştırmalar yorumlanmış ve sonuç olarak; süreksizlik aralıkları azaldıkça toplam yer değiştirmelerin arttığı, 60 cm ve daha az süreksizlik aralıkları olduğu durumlarda bazı süreksizlik yönelimleri için ani artışlar olduğu gözlemlenmiştir. Ayrıca etkilenme bölgeleri için tünel cidarına yaklaşıldıkça teoriyle paralel olarak yer değiştirme değerleri artmış ve tünel çeperindeki artışın, uzaktaki noktalara oranla daha büyük bir miktarlarda arttığı tespit edilmiştir. Son olarak da karşılaştırma grafiklerinde maksimum ve minimum değerleri almış süreksizlik yönelimlerinin birbirleri arasındaki fark üzerinden etkilenme bölgelerinin arasındaki ilişkiyi bulmak için grafikler çizilmiş ve denklemleştirilmiştir. Bu eşitlikler sayesinde de 8'm'den içe doğru yer değiştirme değerlerinin birbiri üzerinden hesaplanması mümkün kılınmıştır.

Joint is both a geomechanical parameter, which play an active role for a selection of tunnel support systems, and one of the basic components that should be examined by a support design which is carried out by rock classification systems. The aim of this thesis is to examine and understand the effect of some joint geometries to the tunnel and the environment which surrounds the opening if it exists. These joint geometries which are studied are joint spacing and orientation. Joint spacing values are chosen and hypothetically changed by the RMR parameters for the related classification system and the same tunnel geometry and conditions. Joint spacing values are also hypothetically changed between 0 and 180°. After applying those joint geometries on the tunnel project, total displacement values for affected area around the tunnel are computed via numerical methods, so the metacharacter for joint properties is occurred. Therefore, the model for tunnels which have the same parameters is occurred. While this thesis process, at first literature search is completed. The used software to complete analysis is based on Finite Element Methods. For this reason, all the numerical methods (Finite Element Methods, Discrete Element Methods, Finite Differences Methods and Boundary Element Methods) are searched in this section. Then, to understand the behavior of the area, rock mass classification systems (Rock Mass Rating, NGI-Q System and Geological Strength Index) are examined. Then, the all the joint properties and finally introduction to the RocScience RS2 software are studied briefly. After this stage, information about the tunnel project is mentioned in detail. The operated tunnel project is located on the North-East side of İstanbul and near to the Blacksea side of Kocaeli Peninsula. Length of the tunnel is approximately 340 m. This section includes engineering geology studies which are completed by preparing a geological and geotechnical reports which cover the association of all in-situ data obtained from the field with the literature searches and the statics from the previous experiments to understand the whole rock mass and to decide the supporting system. Homogenous zones are evaluated based on the circumstances of structural components and the directions that effect the excavations and the supporting systems of those circumstances, not the involved geological units of the area. Evaluated homogeneous zoning based on drillings and the logs are mentioned. Then evaluation of rock mass classification; RMR, NGI-Q System and GSI and in-situ stress are calculated and stability analysis are evaluated by using those values. Then, the most problematical section for engineering geology in homogeneous zones is defined as a critical section of these homogeneous zones. And finally, supporting systems are suggested for the critical section because of the fact that, it is the most unstable and the most supporting needed section. Therefore, the supporting system for this section would be safety enough for of the homogeneous zones. In the next stage, the numerical modelling studies for the tunnel project is applied. In this section, the model is occurred in the software by using values which are mentioned in the previous stage. Then defined joint samples which are joint spacing and joint orientation are applied to this model alternately. Joint spacing values are defined according to the RMR parameters for the related classification system (8 samples; 6, 13, 20, 40, 60, 130, 200 and 400 cm). And the joint orientation values are chosen for each 22.5 º and 30 º from 0º to 180º (12 samples; 0, 22.5, 30, 45, 60, 67.5, 90, 112.5, 120, 135, 150, 157.5). In each step, one of these joint geometries changed while the other one is stable. This means that 96 models are occurred in the software. These joint geometry values are defined hypothetically around the tunnel opening to observe total displacement values on the tunnel affection zone for each sample. After joint geometries are added to the tunnel project model which is created as mentioned above are computed by using the RS2 software which is based on the finite element methods. However, for some of those models could not be computed. In some samples, because of the fact that nodes are too close to each other for intense models, analysis could not computed. And for some others, because of the fact that files of some models are too intense, low tolerance numbers and so the exceeded the maximum iteration number, some models could not be computed which are mentioned in detail in the following sections. While the analyze processes, tunnel geometry, stress values of the area and geomechanical parameters which include material properties are kept constant not to impact the results. For these reasons, despite of the fact that there should be totally 96 models, only 68 analyses are applied and completed by using the numerical method. After the analyses are completed, the results are interpreted. In the interpretation stage, the total displacement values at 50 points which have the same coordinates on the tunnel boundary and imaginary circles at 2, 4, 6 and 8 m outside of the tunnel are calculated. Then the total displacement values are compared for all models at all affected areas which are tunnel boundary, 0, 2, 4, 6 and 8 m outside of the tunnel boundary. Result values are calculated at 8th (after the first tunnel is excavated and supported) and 14th (after the second tunnel is excavated and supported) stages of the excavation to understand the effect of the second tunnel on the first one. The result graphs are drawn to compare the all models with each other and then they are interpreted. Comparison process is applied at three aspects. While the comparison process, at first, the joint spacing values are kept constant, then the joint orientation values are investigated at 50 points on affected areas. After that, the affected areas are kept constant and the joint spacing and joint orientation values are investigated. And finally, considering these graphs, square of the difference of maximum and minimum values are calculated and those differences are formulized. By using these formulas, the relations between affected areas can be understood and easily calculated. The project, is a twin tunnel project which are excavated side by side. The results are taken into consideration for the left handed tunnel for after either the first tunnel, or the second tunnel are excavated and supported. The results are compared and interpreted both separately and together. As a result of these comparison processes; •It is understood that the joint spacing and total displacement are inversely proportional, when the joint spacing decreases, total displacement values are increased. •For some joint spacing and smaller ones, sudden increasing in total displacement values are observed for some joint orientation values. For some models, these increasing rates reach 600%. •While the joint spacing values decreasing, those changes can be seen for more joint orientation models. •According to the comparison for the affected area around the tunnel, total displacement values are increased getting around the tunnel boundary. •As getting to the tunnel boundary, total displacements for the sides of the tunnel boundary are increasing with a higher range with respect to the points at the distant boundaries. •Increasing of the total displacement values are observed for both 8th and 14th stages while the joint spacing is decreasing. •When the total displacement values are compared for after the first tunnel is excavated and supported and the second tunnel is excavated and supported, the increasing rate of total displacement for second tunnel is more than the first one especially for the right side of the first tunnel which is the closer section of the tunnel to the second tunnel. •Finally, the difference of maximum and minimum values are calculated and formulized to find out the relation between affected areas. These formulas can be used to calculate the total displacement values by using each other for the affected area points.