İstanbul grovaklarında NATM ile açılan ikiz tünellerin neden olduğu yüzey deplasmanlarının tahmini
Predictions of settlements for twin tunnel excavated by NATM in Istanbul graywackes
Yazar: EZGİ AKÇAY
Danışman: PROF. DR. RECEP İYİSAN
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Zemin Mekaniği ve Geoteknik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2019
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Kırsal kesimlerden şehir merkezlerine göçün artmasıyla, şehir içlerinde trafik yoğunlaşmış, ulaşım ihtiyacı da bununla beraber artmış, metro, tünel, tramvay, otobüs, araba gibi demiryoluyla ve karayoluyla ulaşımı sağlayan araçlar için daha fazla yol inşa edilmesi zorunlu hale gelmiştir. Yollar yapılırken yeraltı yapısı olan tüneller, özellikle kamulaştırma problemlerinin de önüne geçtiği için şehir merkezlerinde, yapıların yoğun olduğu bölgelerde oldukça tercih edilmektedir. Fakat bu tüneller, açıldıkları bölgelerde tünel üzerindeki yüzeyde bulunan yol, bina, cami gibi yapılarda yerel zemin koşullarına, kayanın süreksizlik durumuna ve yeraltı suyu gibi durumlara bağlı olarak deplasmanlara neden olabilmektedirler. Deplasman miktarlarının artması, yapılarda göçmelere neden olabilmektedir. Oluşan deplasmanların miktarları önceden tahmin edilir ve düzenli ölçümlerle de takibi yapılırsa yapılarda oluşabilecek göçme problemlerinin ve dolayısıyla can ve mal kayıplarının önüne geçilebilmektedir. Bu bakımdan İstanbul grovaklarında Yeni Avusturya Tünel Açma Yöntemi (NATM) ile açılan ikiz karayolu tünellerinin inşaatı nedeniyle tünel üzerindeki yapılarda oluşan deplasmanların düzenli ölçümler sonucunda elde edilen miktarları, yerel zemin koşullarına bağlı olarak incelenmiştir. İlk olarak tünellerin farklı kazı aşamalarının ayrı ayrı neden olduğu deplasmanların miktarları incelenmiş, miktarlar arasında herhangi bir bağlantı olup olmadığı tespit edilmiş ve aralarında tünel çapının 2 katı kadar mesafe bulunan iki tünelin birbiri üzerindeki etkisi araştırılmıştır. Daha sonra literatürde bulunan dönüm noktasının tünel eksenine olan mesafesinin (i) 3 ayrı zemin türü (iri daneli, karışık ve ortalama) için bağıntıları kullanılarak hesaplanan teorik deplasman miktarları ile yapıların köşe noktalarında oluşan deplasmanların sahadan alınan gerçek miktarları karşılaştırılmış, İstanbul grovaklarında açılan tüneller için hangi i bağıntısının daha uygun olabileceği tartışılmıştır. Son olarak, Alibeyköy/İstanbul'da inşa edilmekte olan Cebeci Tüneli'nin Alibeyköy Bölgesi üzerinde bina köşe noktalarında düzenli olarak ölçülen yüzey deplasman miktarları, proje verileri ve tünelin açılarak içinden geçtiği zemin profili kullanılarak pratik amaçlar doğrultusunda yüzeyde oluşan deplasmanları tahmin edebilmek, can ve mal kayıplarını en aza indirebilmek amacıyla örtü yüküne bağlı olarak tünel dönüm noktasının tünel merkezlerine olan mesafesini hesaplayabilen ampirik bir bağıntı İstanbul grovakları için elde edilmiştir.

Abstract:
Population increases have been experienced as a result of rapid urbanization due to migration from rural areas to big cities. Because of increasing population of people living in the cities, number of structures increases day by day. Due to the packness and traffic density in the city centers, a part of the population had to be moved out of the city. Because of that reason, a necessity for transportation in order to gain time for people, shorten distances and thus save fuel, which is an expensive matter today. There is an increasing need for tunnel construction which is aimed at meeting the social needs such as shelter, storage and defense, especially transportation, and with the effect of ground and topography conditions. Generally, it is not economically and technically feasible to construct highway and roads through such regions where there are dwellings, workplaces, schools, historical buildings, in other words, where urbanization is quite intense. Therefore, in recent years, due to increase metro, highway, rail system projects in our country, the need for highway and railway tunnels has increased considerably in cities. With the increasing necessity of tunnels, tunneling has become compulsory due to developing technology and tunneling methods have improved from past to present. One of these methods, the New Austrian Tunneling Method (NATM), was created by Rabcewicz in 1946, based on the principle of rock transport to the rock, which is still widely used today, which can be opened in variable section areas, applicable to unexpected geological profiles encountered during excavation and whose supports like bolt, shotcrete, umbrella arch method can easily be changed accordingly. Although this method is mostly applied in tunnels on weak ground, NATM is applicable for both cohesive and non-cohesive soil and has a wide area of choosing tunneling method. 
The method has become widespread all over the world in a short period of time because it can easily adapt to any kind of tunnel geometry and ground conditions. NATM has its own rules and preserving the natural strength of the rock, the regular support system and the covering of the shell with shotcrete is one of these rules. It is one of the important rules to measure the deformations regularly by using geodetic and geotechnical methods in the tunnel and in the surface area and to evaluate the results by comparing the design with the calculations. This principle provides information about the deformation that may occur in the tunnel and ground surface. Tunnel and surface movements created by tunnel construction stages are inevitable. In addition, the tunnel may cause horizontal and vertical displacements on the surface during and after construction. As a result of these displacements, structures and roads may be damaged. These damages can be avoided by prediction of structures and road settlements. This can be achieved with the help of an empirical correlation which is easy to apply in the site, practical and suitable for the Istanbul graywackes. Thus, the structural collapses on the surface can be prevented and the damages, loss of lifes and properties because of the tunnel construction can be minimized. 
In this study, the measured settlements in the areas of the tunnel interaction caused by twin tunnels opened in the city by the New Austrian Tunneling Method (NATM) were examined and the trough width parameter, which is one of the parameters defining the magnitude of settlements was observed. It is aimed to obtain an empirical correlation of trough width parameter for twin tunnels opened by NATM in Istanbul graywackes. Thus, the center of the twin tunnels, where regular surface measurements were made, were determined as the central axis and buildings 80 m to the left and right from this axis were selected for analysis. In a study conducted for a region where the tunnel progressed 500 meters, this distance was divided into 10 sections according to the density of the structure and each section was analyzed statistically in itself and the effect of tunnel excavation stages on surface settlements was tried to be obtained by comparing these analyses. Although in the site, there are drillings and laboratory tests which  are determine local conditions and geotechnical properties of the layers (cohesion, modulus of elasticity, poisson ratio, uniaxial compressive strength, natural unit volume weight), by using the data obtained from the field tests, empirical correlation was tried to be obtained for trough width parameter which will be used in settlement quantity caused by twin tunnels in İstanbul graywackes.
In this study, where the displacements caused by twin tunnels opened by NATM are examined, firstly general information about the subject of the thesis is given and the purpose of the thesis formation and the statistical analysis and results of this thesis are mentioned. 
In the second part of the study, the concept of tunnel, the purposes of the tunnels, the excavation methods depending on the type of the ground was introduced, the development of the tunnels from the past to the present, various tunneling methods are explained and the positive and negative aspects of these methods are mentioned. 
In the third part of the study, taking into account the various parameters of the rocks, Terzaghi is mainly classified according to certain characteristics of the rocks and the most commonly used rock classification and support systems are explained. 
In section 4, the New Austrian Tunneling Method which is widely used in our country is explained in detail, NATM rock classification is given and the excavation methods, support systems and the positive and negative sides of this method are explained. 
In the fifth section of this study, the measurement methods used in the tunnel and on the surface, where the direction of movement and the quantity of the displacements are determined are explained. 
In the sixth part of the study, the geometric properties of the tunnel used in the study, the local soil conditions and geological structure, the stages of tunnel excavation, the relationship between tunnel excavation and surface settlement quantities are explained and the development of an empirical correlation for the Istanbul graywackes is discussed. In this study, real values are used, parametric study and numerical analysis methods are excluded. 
In the last part of the study, the displacement evaluations of the buildings and the results of the statistical analysis have been mentioned and various suggestions have been made. The short-term displacement amounts of each excavation stage were examined and it was concluded that there was no relationship between the quantities or percentages of these displacements, that different excavations in each cross-section caused independent displacements and that these amounts could not be attributed to a certain increase percentage. The reason for this can be explained as the drilling velocities of the tunnel, the variability of the times between the support systems and the condition of the ground. Parameter values obtained from field experiments were used to obtain surface settlements using the proposed correlations, the results overlap with the actual values, the calculation was changed by using the parameters obtained from laboratory experiments and it was found that the settlements were different from the actual settlements. Besides, it was found that the displacement of the second tube did not cause any displacement on the first tube, and that the surface displacement amounts of the structures on the respective tubes did not increase due to the excavation in the other tube. 
It is concluded that the tunnels had no effect on each other due to construction of the tunnels in the rock environment and distance between the axes of the two tunnels being about 2 times the tunnel diameters. In addition, it was found that the maximum displacement on the surface did not occur on the left tube or the right tube, but rather on the central axis located in the middle of two tunnel axes and on the curve obtained by superposing. As a result, it is recommended to carry out the geotechnical measurements in the tunnel at regular intervals, to increase the quality of the measurements taken, to reduce the error rates, to increase the measurement quality by increasing the measurement intervals. In order to determine the properties of soils in displacement predictions, it is recommended to observe soil survey and use field tests. Finally, by using the actual displacement values measured in twin tunnels drilled in the Istanbul graywackes with NATM, a correlation is proposed to estimate the displacements on the surface depending on the distance of the tunnel axis to the surface for practical purposes.