Tünel kazılarından kaynaklanan yüzey oturmalarının betonarme binalarda etkilerinin incelenmesi

Abstract

Hızlı nüfus artışı ve şehir içi yerüstü müsait alanların kısıtlı olması sebebiyle yaşanan trafik problemi hemen hemen bütün metropollerin ortak sorunu haline gelmiştir. Bu nedenlerden ötürü yeraltı ulaşım ağının yaygınlaştırılmasına yönelik yatırımlar her geçen gün artış göstermektedir. Tünel kazıları sırasında oluşan yüzey oturmaları şehir içi tünelciliği açısından dikkat edilmesi gereken en önemli konulardan biridir.Yüzey oturmaları alt yapı sistemlerini, binaları ve can güvenliğini riske atmayacak şekilde sınırlandırılmalıdır. Bu amaçla yerel zemin koşulları iyi analiz edilmeli, elde edilen bilgiler ışığında uygun tahkimat elemanları belirlenmelidir. Yerel zemin koşulları dışında metro güzergahının geçtiği bölgede yapı stoğunun özellikleri önem arz etmektedir. Yapılan hesaplar sonucunda beklenen yüzey oturmalarına binanın vereceği tepki burada esas olandır. Zaman içinde güncellenen yönetmeliklerle inşaatlarda kullanılan malzeme kalitesinde artış gözlenmiş, elde edilen yeni bilgiler ışığında bina tasarımları açısından gelişmeler kaydedilmiştir. Fakat tünel kazılarının yapılmasının planlandığı güzergahta eski yapı stoğu daha büyük riskler barındırmaktadır. Dönemin koşulları göz önüne alındığında başta beton ve çelik olmak üzere binalarda kullanılmış inşaat malzemelerinin özellikleri iyi belirlenmeli ve ayrıca temel ve döşeme türü vb o döneme ait tasarım anlayışına göre uygun modellemeler yapılarak oturmalar sonucunda oluşacak ek yüklerin bina taşıyıcı elemanlarındaki etkileri tespit edilmelidir.Özellikle yumuşak zeminlerde tünel içi deformasyonlar ( konverjans ) ve yüzey oturmalarıyla tünel kazıları sırasında sık sık karşılaşılmaktadır. Gelişen teknolojiyle beraber Tünel Açma Makinelerinin (TBM) kullanımı yaygınlaşmış, tecrübeli operasyonal ekiplerle ayna basınçları mevcut zemine göre ayarlanarak bu etkiler minimize edilmeye çalışılmıştır. Ayrıca TBM ile yapılan kazılarda kazı ve kalıcı tahkimat imalatı arasındaki süre NATM(Yeni Avusturya Tünel Methodu)'a kıyasla daha kısa olduğu için yüzey oturmaları açısından daha istenen sonuçlar vermektedir. Ayrıca bu teknolijinin yaygınlaşmasıyla beraber İstanbul'da ana hat tünellerinin çoğu TBM ile açılmaktadır. Bu sebeple bu çalışmada Tünel Açma Makinelerinin çalıştığı kesit özellikleri dikkate alınarak yüzey oturmaları hesaplanmıştır.

Due to rapid population growth and lack of available spaces , traffic jam became a common problem for big cities. Therefore, investmens to the metro lines have been increasing with the time in order to solve the transportation problem.Surface settlements induced by tunnel excavations are one of the important topic of tunneling work located near the urban areas. High surface settlements can be dangerous for upper structures, infrastructure systems and human life. Therefore, level of surface settlements should be limited. In order to provide this, local soil conditions should be analyzed well and support type should be chosen accordingly.Beside the local soil conditions, conditions of available building stock is so important. The reaction given by carrier system of building should be determined well. With the development of the opportunities , quality of building materials used in constructions has been increased in time. Also, design codes became stricter over time. However, the route of new metro line projects also pass near the old buildings and they are under risk more when the compared with new buildings. The material properties (concrete, reinforcement etc.) and type of carrier system(slab,columns,shear wall and foundation) of the old building should be determined well. Morever, the computer model should be preapered according to information comes from the building.Especially in soft grounds, deformations in tunnel and surface settlemens are commonly observed during excavation of tunnels. Thanks to the development of the technology, TBM usage is increased and with the experienced staff, settlements are controlled effectively with arranging the face pressure according to the local soil conditions. In addition to that, the time between excavation and installation of final supports is short when compared with NATM (New Austrian Tunneling Method). Therefore, TBM provides better results in terms of surface settlements. In addition, usage of TBM are more common than NATM for excavation of main line tunnels.Therefore, TBM cross sections were chosen to predict the surface settlements.In the first part of the study, the aim and content of the study are described. The aim is examining the effect of tunnel induced surface settelements on the old building stock by parametric study. The parametric study contains two different soil types that are sandy and clayey.Moreover, three, four and five floor buildings that they have same plan view were included to the parametric study. In addition to that, three different tunnel depth were taken into account. As known, while some of the metro tunnels pass very close the surface level, others pass very deep. Therefore, 9 meter, 12 meter and 20 meter tunnel depths were chosen to consider many possible scenario during the excavation of tunnels. As expected, the excavation of tunnels that passes more than 20 meter below the surface has limited effects on the surface settlements so that considering the depth of 20 meter as a maximum value is sufficient. The minimum value of 9 meter depth was chosen to investigate effect of shallow tunnels. 9 meter depth is already challenging value for excavation.However; it is possible to face with more difficult situations in real life applications in terms of tunnel depth.For that cases, more dangerous results should be expected in comparison with 9 meter.In the second part of the study, two different excavation methods were explained. The first method is NATM (New Austrian Tunnelling Method). The idea of NATM is that the stress which surrounds rock mass is used as a tunnel support. Therefore, tunnel can carry the load itself. Moreover, temporary supports are used during excavation process.Shotcrete, wire mesh, lattice girder, rock bolt, soil nail, face,umbrella arch, and forepoling are used as a temporay support according to the local soil conditions. For example, if the soil conditions are good to excavate safely, there is no need to use umbrella arch application or forepoling during the excavation of tunnel face. Reinforced concrete works are final works of construction of tunnels.NATM is slower than TBM in terms of time.However, it can be economical than TBM for short length tunnels.Also, NATM are easly used for cross passage tunnels, switch tunnels and station tunnels. For these tunnel cross sections, TBM is not suitable to use. The second method is TBM (Tunnel Boring Machine ). TBM is a machine that used for excavation of tunnels. The first part of TBM is called cutting wheel which includes disc cutters, scraper, bentonite outlet etc. TBM's are used not only for metro tunnels but also sewer lines, water line etc. Unlike the NATM, reinforced concrete works are finished as soon as possible after the excavation. Segments that are precast element are used as a permanent support. After the installation of segment rins, grouting process should be done to fill voices between excavated area and segments.For the soft soil conditions, extra necessary precautions must be taken because of the stability problem of tunnel face.Some of TBM's have EPB (Earth Pressure Balance Shields) mode to provide stability to tunnel face. In the thesis, TBM excavation was taken into account because it is common for excavation of main line tunnels.In the third part of the thesis, Peck (1969) and Loganathan&Poulos (1998) formulas used for calculating surface settlements were explained. For clayey soils, both two formulas were used and the formula that gives critical results was chosen. For sandy soils, Peck (1969) formula was only used because other formula is not convenient for clays according to their study.In the fourth part, surface settlements were calculated according to information coming from third part. Surface settlements were calculated for different scenerios such as tunnel depth and distance from the axis of tunnel. Three different tunnel depth, which is 9-12-20 meter, were chosen as mentioned before. In addition to that, six different distances from tunnel axis were chosen to investigate effects of location of tunnel in horizontal direction on surface structures. In the fifth part, informations about buildings were given like plan view, column lengths,material properties for concrete and steel and the loads entered to 2D model. Unfortunately,Some of the old buildings were constructed by poor quality materials like low strength concrete around 15 Mpa or steel around 220 Mpa.In addition to that, most of the buildings were constructed around 1960s did not receive enough engineering service. Therefore, column lengths were chosen small to represent real scenarios. Moreover, minimum reinforcement ratio was chosen according to earthquake code in Turkey in 1975. In the thesis, fck was taken 18 Mpa and fyk was taken S220.Foundation type was chosen spread footing. Three,four and five floor buildings that have same plan view were chosen. 216 model were created via SAP 2000 program. 216 model contains three different buildings,two different axis on building,two different soil type,three different tunnel depth and six different distances from tunnel axis. Forces and moments on ground floor columns were taken from SAP 2000 analysis and they were compared with capacity of columns. The drawings shows the status of columns under the loading according to their capacity were preapered. If the column do not exceed its capacity,it is painted by green clour. If column exceed its capacity under the loading, it is painted by orange, red and magenta according to the level of exceedance. If the column exceeds its axial capacity, it is painted by black color.According to the results, shallow tunnels (9,12m) have destructive impacts on buildings if the tunnel passes around x=-10,-5 and 0 meter coordinates. Therefore, Some precautions should be taken before the excavation.In the sixth section, time history analysis were performed for three different story buildings in order to emphasize the importance of surface settlements from a different perspective. The earthquake record belongs to Silivri Earthquake which hit Istanbul on 26 September 2019 were used to perform time history analysis. Axial and moment capacities of the first floor columns were compared to surface settlements results. In the seventh and last section of the study, conclusions and recommendations were summarized.