Farklı rijitliklere sahip zeminlerde yapı-tünel etkileşimi sonucu tünel tesirlerinin ve yüzey oturmalarının tahmini
Prediction of tunnel response and surface settlement resulting from structure-tunnel interaction on soils with different stifness
Yazar: ÇİĞDEM CULHA
Danışman: DOÇ. DR. ESRA ECE BAYAT
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Zemin Mekaniği ve Geoteknik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2022
Konu: İnşaat Mühendisliği = Civil Engineering
Dizin: Rijit = Rigid ; Serbest yüzey = Free surface ; Tüneller = Tunnels

Özet:
Gelişmiş ve gelişmekte olan kentlerde yüzeyde var olan mevcut yapılaşma, ulaşım sorunlarını da beraberinde getirmektedir. Taşıma sorununu hafifletebilen yeraltı yapıları, özellikle metrolar, kalabalık şehirlerde kent yaşamını olumsuz etkileyen trafik problemini azaltabildiği için oldukça önemlidir. 
Yapılan tüneller, yüzeyde var olan yapılarla çoğu zaman etkileşim içerisinde olabilmektedir. Bu durum yüzeye yakın yapılarda ve zayıf zeminlerde oldukça önem kazanmaktadır. Tünel ekseninin geçtiği güzergâh boyunca, tünel etki alanında kalan her yapı için tünel kapasite ve bina oturma analizleri yapılmaktadır. Taşıma kapasitesi yetersiz olan, tünelden kaynaklı oturmaları sönümleyemeyecek yapılar yapılan analizler sonucu tünel kazısı sırasında yapılardan alınan oturma değerlerine göre boşaltılabilmektedir. Bu oturmalar ve yapı-tünel etkileşimi; tünel çapı, tünel derinliği, tünel yapım yöntemi, zemin tipi, sütun mesafesi, mevcutsa ikinci tünel konumu, kazı derinliği gibi faktörlerden etkilenebilir. Daha kritik durum ise, tünel kazısından kaynaklanan yer değiştirme sebebiyle yapılar göçme durumuna geçebilir. Bu sebepler neticesinde, tünel kazısı öncesinde yapılan tünel-yapı etkileşim hesapları oldukça önem kazanmıştır.
Zemin durumu, yüzeydeki yapı durumu, yeraltı su seviyesi, zemindeki boşluk oranı, karstik boşluk olasılığı gibi durumlar dikkate alınarak ön analizler analitik hesaplara dayanarak yapılır. Bu ön çalışmalarda, yerinde yapılan jeolojik ve jeofizik çalışmalardan faydalanılır. Zemin veya kaya kütlesinin kazıldıktan sonra desteksiz kalabilme süresine göre, tünel açma yöntemi kabaca belirlenir. Ülkemizde aç kapa yöntemlerle birlikte NATM ve TBM metotları kullanılarak tünel kazıları gerçekleştirilir. Bu tez kapsamında NATM tipi, parçalı kazı metodu kullanılarak kazılan peron tipi tünel incelenmiştir.  
Analizler Plaxis 2D program yardımı ile yürütülmüştür. Plaxis 2D programı tünel çözümlerinde hem Türkiye hem de dünyada sıklıkla kullanılmaktadır. Tez kapsamında Plaxis 2D programı ile elde edilen tünel kesit tesirleri, Möller ve Vermeer, 2005 ile COB-L500, 2000'de önerilen formüllerle elde edilen kesit tesirleri kıyaslanmıştır. Plaxis programının tünel kazı problemlerinde kullanılabilirliği üzerinde durulmuştur.
Farklı rijitliklere sahip zeminlerde kazılan tünelde, zemin rijitliğinin yüzey oturması ve tünel kaplaması üzerindeki etkisini görebilmek için 50 MPa, 75 MPa, 100 MPa ve 200 MPa Elastisite modüllerine sahip birimlerde tünel kazıları yapılmıştır. Bu analizlerde, mevcut yapı altında peron tüneli kazısı yapılması durumu irdelenmiştir. Rijitlik artışına bağlı olarak, yüzey oturmalarında ve tünel tesirlerinde azalma görülmüştür. 
Örtü kalınlığı 10m, 20m ve 30m olacak şekilde, farklı derinliklerde analizler tamamlanmıştır. Tünel derinliğine bağlı, tünel kaplaması üzerindeki tesirler, yüzeydeki yapı ile mesafesine ve yapı temel tipine bağlıdır. Tünel derinliği arttıkça yüzeydeki oturmalar yapı yükü ve temel sisteminden daha az etkilenmektedir. 
Yüzeydeki yapının temel sisteminin tünel kazısı üzerindeki etkisini görebilmek için; yüzeyde yapı olma durumu, yapının 75kPa, 150 kPa ve 225 kPa yüzey gerilmesi altında; yapı temelinin ise yüzeysel ve kazıklı olması durumları için analizler yapılmıştır. Kazıklı temelli yapılarda, kazıklar, tünel kazısı etrafında oluşan plastik zona daha fazla dâhil olduğu için, tünel kazısından daha fazla etkilenmektedir. Temel ile kazıkların birbirine bağlı olduğu durumlarda, bu etki göz önüne alınmalıdır.
Analiz sonuçlarına bağlı olarak, serbest yüzey durumunda, tünel geçici kaplaması üzerindeki moment ile zemim elastisite modülü arasında bir bağıntı elde edilmiştir. Yüzeyde yapı olduğu durumda tünel kazılması hem tünel kapasitesi hem de yapı stabilitesi açısından önemlidir. Yüzeyde yüzeysel veya derin temelli yapı olması dahi tünel deformasyonu dolasıyla tünel etrafında oluşan momente etki eder. Yüzeyde 75kPa bina olması durumunda yüzeysel temel ile derin temel olması durumunun tünel üzerindeki etkisi, sıkı kumda %7, çok sıkı çakıllı kumda %13, ayrışmış kayada %21'dir.Bu fark aynı zeminde derine gittikçe azalmaktadır. Yani tünel yüzeyden uzaklaştıkça temel sisteminin etkisi tünel üzerinde daha az hissedilmektedir. Aynı derinlikte, zemin elasitiste modülü arttıkça temel sistemlerini değiştirmenin, tünel etrafındaki moment değerleri arasındaki farkın azaldığı görülmüştür.

Abstract:
The existing construction on the surface in developed and developing cities also brings transportation problems. Underground structures that can decrease the transportation problem, especially subways, are very important because they can reduce the traffic problem that negatively affects urban life in crowded cities.

Construction of tunnels can often interact with the existing structures on the surface. This becomes very important in structures close to the surface and in weak soils. Along the route through which the tunnel axis passes, tunnel capacity and building settlement analyzes should perform for each structure within the tunnel impact area. Structures with insufficient bearing capacity and which cannot absorb the settlements originating from the tunnel can be emptied according to the settlement values obtained from the structures during the tunnel excavation as a result of the analyzes made. These settlements and structure-tunnel interaction; It can be affected by factors such as tunnel diameter, tunnel depth, tunnel construction method, soil type, column distance, second tunnel location if available, excavation depth. More critically, structures may collapse due to displacement caused by tunnel excavation. As a result of these reasons, the tunnel-structure interaction calculations made before the tunnel excavation became very important.

Preliminary analyzes are made based on analytical calculations, taking into account conditions such as ground condition, surface structure condition, groundwater level, void ratio in the ground, probability of karstic voids. In these preliminary studies, on-site geological and geophysical studies are used. The tunneling method is roughly determined by the length of time the soil or rock mass can remain unsupported after excavation. In our country, tunnel excavations are carried out by using NATM and TBM methods together with cut-and-cover methods. Within the scope of this thesis, the platform type tunnel excavated using the NATM type partial excavation method was investigated.

Analyzes were carried out with the help of Plaxis 2D software. Plaxis 2D is frequently used in tunnel solutions both in Turkey and in the world. Within the scope of the thesis, the tunnel cross-section effects obtained with the Plaxis 2D, the cross-section effects obtained with the formulas proposed in Möller and Vermeer, 2005 and COB-L500, 2000 were compared. The usability of the Plaxis program in tunnel excavation problems is emphasized.
In the tunnel excavated in soils with different stiffnesses, tunnel excavations were carried out in units with 50 MPa, 75 MPa, 100 MPa and 200 MPa Elasticity modules in order to see the effect of soil stiffness on surface settlement and tunnel lining. In these analyzes, the case of the platform tunnel excavation under the existing structure was examined. Depending on the increase in stiffness, a decrease in surface settlements and tunnel effects was observed.

Analyzes were completed at different depths with a cover thickness of 10m, 20m and 30m. The effects on the tunnel lining depend on the depth of the tunnel, its distance from the structure on the surface, and the type of foundation of the structure. As the tunnel depth increases, the settlements on the surface are less affected by the structural load and the foundation system.

In order to see the effect of the foundation system of the structure on the surface ofthe tunnel excavation; the state of being a building on the surface, the building has 5 floors, 10 floors, 15 floors; analyzes were made for the case that the foundation of the building is shallow and piled. In pile foundation structures, piles are more affected by tunnel excavation as they are more involved in the plastic area formed around the tunnel excavation. In cases where the foundation and piles are connected, this effect should be taken into account.

Based on the results of the analysis, a correlation was obtained between the moment on the tunnel temporary lining in the free surface condition and the soil modulus of elasticity. In the case of structures on the surface, tunneling is important in terms of both tunnel capacity and structural stability. Even the presence of a superficial or deep foundation on the surface affects the moment created around the tunnel due to tunnel deformation. In the case of a 75kPa building on the surface, the effect of shallow foundation and deep foundation on the tunnel is 7% in tight sand, 13% in very compact gravelly sand, and 21% in weathered rock. This difference decreases with depth in the same ground. In other words, as the tunnel moves away from the surface, the effect of the foundation system is felt less on the tunnel. At the same depth, it was observed that changing the foundation systems and the difference between the moment values around the tunnel decreased as the soil modulus of elasticity increased.

As a result of the analyzes made in the free surface condition, it was seen that there is an inverse proportion between the soil elasticity module and the settlement that will occur on the surface after the tunnel is excavated. Depending on the increase in the soil elasticity modulus, a decrease was observed in the maximum settlement values for all 3 depths.

For tunnels dug under structures with free surface, shallow foundations and deep foundations, the maximum amount of settlement increases in excavations close to the surface, but the impact area decreases. With depth, the maximum settlement value decreases, but the area affected by the excavation increases. In tunnels opened under a deep foundation, the area of influence is more concentrated under the structure than in buildings with a shallow foundation. In excavations near the surface, the settlement is triangular on the surface, but turns into a U shape with depth.

Depending on the increase in the H/D ratio, that is, in cases where the tunnel excavation depth increases, the maximum settlement amount decreases.
In case of tunneling in case of shallow foundation on the surface, it is clearly seen that for 3 different structure loads, the maximum settlement values increase as the soil stiffness decreases.As the tunnel depth increases, the maximum settlement under the structure decreases. As the tunnel gets deeper, the effect of the structure on the tunnel decreases. Depending on the increase in the tunnel depth, the settlement values for 4 different soils converge.
As the soil stiffness increases, the maximum settlement on the surface is less affected by the building foundation system and the building load. Depending on the increase in soil stiffness, the settlement values approached each other for each studied situation.

In the case of tunneling at the same depth under buildings with the same stiffness and structural load, the maximum settlement when tunneling under the structure with deep foundation is calculated more than in the case with shallow foundations. There are basically two reasons for this. First, where the building foundation is piled, the foundation as a whole is closer to the tunnel excavation. The pile foundation system is more involved in the impact area resulting from tunnel excavation. The second reason is that the pile weight is included in addition to the shallow foundation due to the pile weight. As the structure load increases, the amount of foundation settlement also increases.

In the case of structures on the surface, tunneling is important in terms of both tunnel capacity and structural stability. Even the presence of a superficial or deep foundation on the surface affects the moment created around the tunnel due to tunnel deformation.
The effect of the absence of structure on the surface or the deep/shallow foundation on the moment on the tunnel decreases as the depth increases in the same ground. In other words, as the tunnel moves away from the surface, the effect of the foundation system is felt less on the tunnel.

At the same depth, it was observed that changing the foundation systems and the difference between the moment values around the tunnel decreased as the soil elasticity modulus increased. In relatively weak soils, the foundation system of the structure on the surface affects the moment value on the tunnel more than on more solid soils.
The relationship between the soil modulus of elasticity and the moment on the tunnel temporary lining was investigated. As the tunnel depth increases, the calculated moment values on the tunnel get closer to each other. As the load on the surface increases, that is, the number of floors increases, the load on the tunnel lining increases.