Yüksek sürşarj yükleri altında toprakarme duvarların limit denge ve sonlu elemanlar analiz yöntemlerine göre değerlendirilmesi
Evaluation of reinforced earth walls under high surcharge loads according to limit state and finite element analysis methods
Yazar: SERCAN ŞAT
Danışman: DR. ÖĞR. ÜYESİ BERRAK TEYMÜR
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
Dizin: Dolgu zeminler = Filling soils ; Donatılı duvar = Reinforced wall ; Donatılı zemin = Reinforced soil ; Yapı-zemin etkileşimi = Soil-structure interaction ; İstinat duvarları = Retaining walls

Özet:
Esnek istinat yapıları sınıfına dahil olan donatılı toprak duvarlar/toprakarme istinat duvarları, geleneksel dayanma yapılarına alternatif olarak yaklaşık 60 yıl önce kullanılmaya başlanmış ve her geçen yıl artarak günümüzde yaygın olarak kullanılmaya devam etmektedir. 60'lı yılların sonunda sistemin mucidi Fransız Mühendis Mimar Henri Vidal tarafından ortaya çıkarılan güçlendirilmiş zemin yapıları, günümüze kadar geliştirilerek süregelmiş olup; imalat kolaylığı sağlaması ve konvansiyonel istinat yapılarına kıyasla ekonomik olması yönü ile tercih edilmeye devam etmektedir. Özellikle ülkemizin de içinde bulunduğu depremsellik koşulları göz önüne alındığında, sismik aktivitelerde yüksek performans göstermesi nedeniyle, deprem riski yüksek olan bölgelerde esnek yapısı itibari ile verdiği güvenli çözümler sayesinde, geleneksel yönteme göre daha fazla tercih edilmesi kaçınılmaz bir unsur haline gelmiştir. Özellikle 1999 Kocaeli depremine maruz kalan toprakarme istinat yapılarının mal ve can güvenliğini tehlikeye atmadan, deprem sürecinde ve sonrasında güvenli şekilde servis ömrüne devam etmesi sistemin mühendislik açısından ne derece önemli bir yeri olduğunu da ortaya koymaktadır.
Esnek istinat yapılarının hayata geçirildiği ilk zamanlarda çoğunlukla karayollarında kullanılmasına karşın, sismik yükler altındaki yüksek performansı nedeniyle, kısa zamanda demiryolları, baraj yapıları, askeri yapılar, sanayi ve maden yapılarında da sıklıkla çözüm üretici olarak kullanılmıştır. Özellikle tekrarlı sismik yüklemelerde, yapıya etkiyen yüksek yükler ve titreşimlerin sistem içerisinde sönümlenmesi ve donatı dolgu arasındaki aderans kuvveti ile karşılanması, yapıların uzun servis ömürlerinde güvenle hizmet etmelerine imkan sağlamaktadır.
Bu tez çalışmasında yüksek sürşarj yüklerine maruz kalan bir bakır madeni yapısının en kritik yüksekliği temel alınarak toprakarme analizleri gerçekleştirilmiştir. Tasarım kriterleri A.B.D, Türkiye ve Fransa karayolları idarelerinin ilgili yönetmelik ve şartnameleri göz önünde bulundurularak hazırlanmıştır. Çalışma içerisinde hem limit denge hem de sonlu elemanlar analiz yöntemleri ile toprakarme duvar yapısı modellenmiş olup, sonuçlar karşılaştırılarak irdelenmiştir.
Bu yüksek lisans tez çalışması altı bölümden oluşmaktadır. İlk bölümde, esnek istinat yapıları kavramına giriş yapılmış ve sistem hakkında genel bilgiler verilmiştir. İkinci bölümde, toprakarme duvar sistemi çalışma mekanizması, uygulama alanları ve yapı sistemi bileşenleri tariflenmektedir. Üçüncü bölümde, şerit donatılı toprakarme istinat yapılarının tasarımı yapılırken ele alınan iç stabilite ve dış stabilite kriterleri aktarılmaktadır. Dördüncü bölümde, tez çalışması kapsamında analizlerin yapılacağı limit denge ve sonlu elemanlar yöntemi anlatılmakta, bu yöntemler uygulanırken temel alınan bilgisayar programlarından bahsedilmektedir. Beşinci bölümde, Kazakistan'da bir bakır madeni projesinde yer alan yüksek sürşarj yüklerine maruz kalan 20m yüksekliğinde şerit donatılı bir toprakarme duvar tasarımı ve analizleri yer almaktadır. Tezin son bölümü olan altıncı bölümde ise, beşinci bölümde yapılan analizlerin sonuçları özetlenmekte; limit denge ve sonlu elemanlar programları ile analiz edilen modellerin sonuçları karşılaştırılmaktadır.
İlk olarak, toprakarme duvarın genel stabilite analizleri irdelenmiştir. Limit denge ve sonlu elemanlar analizinden elde edilen sonuçlar değerlendirilmiş olup, hem statik hem sismik durum için çıkan değerlerin birbirlerine yakın değerler olduğu saptanmış; sonlu elemanlar yöntemi ile elde edilen sonuçların daha kritik durum teşkil ettiği görülmüştür. Genel stabilite için şartnamelerde belirtilen sınır değerler incelendiğinde, çıkan sonuçların belirlenen sınırlar dahilinde kaldığı görülmüştür.
İkinci olarak sonlu elemanlar yöntemi ile panel yüzeyinde oluşacak yatay deplasman durumları irdelenmiş, statik ve sismik (psödo-statik) durum için şartnamelerde belirtilen sınırlar dahilinde kaldığı görülmüştür.
Son olarak toprakarme duvar iç stabilite analizleri irdelenmiştir. Limit denge ve sonlu elemanlar analizleri ile çözüm yapılan sistemde, kullanılan her bir şerite gelen yükler hesaplanmış, en kritik yük ihtiva eden şerit kıyaslanmıştır. Statik ve sismik durumda en alt kademe şeritin kritik yüke ulaştığı, limit denge ve sonlu elemanlar analizlerden elde edilen sonuçların birbirlerine yakın mertebelerde olduğu görülmüştür.

Abstract:
Retaining structures are one of the basic elements of highway, motorway and railway projects. It is used for slope stabilization, mainly for retaining structures, ramp walls, bridge abutments, and to minimize the amount of embankments in the construction of different types of structures such as infrastructures, hydraulic structures and railways. For many years, retaining structures have been designed as a traditional solution with gravity walls or cantilever walls made almost entirely of reinforced concrete, which are essentially rigid structures and do not perform well against significant differences unless they are built on deep foundations. The cost of traditional reinforced concrete retaining walls increases rapidly as the height of the fill soil to be kept increases and the poor foundation conditions increases.
Mechanically Stabilized Earth Walls (MSE) have become an alternative to traditional reinforced concrete retaining wall systems because they can accommodate much larger settlements with lower construction costs. Instead of very high-cost reinforced concrete retaining walls, the system is formed by applying reinforcements to a much lower cost granuler fill material. In addition to the economic advantage of the system, it is one of the main reasons for its being a place in geotechnical engineering because of its flexible working mechanism and safety structures.
Reinforced Earth retaining walls, which belong to the class of mechanically stabilized earth retaining structures, have been used approximately 60 years ago as an alternative to traditional concrete retaining structures and are increasingly being used today. Reinforced earth structures invented by French engineer architect Henri Vidal in the late 60s, have been developed and continued until today; It continues to be preferred in terms of providing ease of manufacture and being economical compared to traditional concrete retaining structures. Especially considering the seismicity conditions in our country, due to its high performance in seismic activities, it has become an indispensable element to be preferred more than the traditional method in the regions with high risk of earthquake thanks to its safety solutions due to its flexible structure. Particularly, the continuation of the service life of the retaining structures exposed to the 1999 Kocaeli earthquake in a safe manner during and after the earthquake without putting at risk the safety of property and life shows the importance of the system in terms of engineering.
Although mechanically stabilized earth retaining structures were mostly used on highways in the first years of their implementation, due to their high performance under dynamic loads, they were frequently used as solutions in railways, dams, military structures, industrial and mining structures. Particularly in repetitive dynamic loads, the high loads and vibrations that affect the structure are damped in the system and the adherence force between the reinforcement filler provides the structures to serve safely during their long service life.
In the design of conventional concrete retaining structures, the rigidity of the structure is an advantage in terms of providing resistance against the loads acting on it. However, this rigidity feature becomes a disadvantage as the rigidity value increases in structures with very high heights, which will cause the structure to be defeated suddenly in instantaneous effects. As the geometric conditions of the retaining structure and the size of the loads acting on it increase, the system should exhibit more flexible behaviors in terms of stability of the structure during its service life.
Mechanically stabilized earth retaining structures, which are the most common and accepted application of reinforced earth walls, due to its flexible behavior in case of any extreme load acting on it, provided the designers with great ease in the projects which are very difficult to apply. The system has been successfully applied in many projects involving overloads and is still being applied due to the opportunities provided for geotechnical engineering.
Within the scope of this study, the historical development of reinforced concrete retaining structures has been examined and the reinforced earth retaining structure has been put forward with general working principles and structural elements. The basic principles considered in the design of reinforced concrete retaining structures, the assumptions made for structural elements with steel strip reinforcement, design requirements of the retaining structures according to the specifications and regulations were investigated. The behavior of the system under high surcharge loads was investigated by limit state and finite element method. The working conditions considered by the numerical analysis programs used in the design of the project were examined, and the results of static and seismic loading were compared and geotechnical evaluations were made. Static and seismic loading case was referred to the relevant standards and regulations of USA, Turkey and France Highways determination of design principles.
In this thesis, reinforced earth wall analyzes were carried out based on the most critical height of a copper mine structure exposed to high surcharge loads. Design criterias have been prepared according to the regulations and specifications 
of the highway administrations of U.S., Turkey and France. In this study, both the limit state and finite element analysis methods have been modeled with reinforced earth retaining wall and the results have been compared and examined.
This master thesis consists of six chapters. In the first part, the concept of mechanically stabilized earth retaining structures is introduced and general information about the system and the first applications in the world are given. In the second section, the working mechanism of the earth wall system, advantages and disadvantages of sysytem, all fields of application and components of the structural system are described. In the third section, the design of the reinforced earth retaining structures and all internal stability and external stability criteria discussed in this design are explained in detail. In the fourth chapter, the working mechanisms of the limit state and finite element method which the analyzes will be made are explained. The computational methods and criteria of the softwares which are based on these methods are mentioned. The fifth section includes the design and analysis of a reinforced earth retaining wall with a maximum height of approximately 20 m, which is subjected to high surcharge loads in a copper mine project in Kazakhstan. In the last chapter of the thesis, the results of the analyzes in the fifth chapter are summarized; limit state and finite element softwares are compared with the results of the analyzed models. The detailed examination of the results of both calculation methods are provided.
Firstly, the general stability analysis of the reinforced earth wall is examined. The results obtained from limit state and finite element analysis were evaluated and it was found that the values obtained for both static and seismic conditions were close to each other; The results obtained by finite element method were found to be more critical. When the limit values stated in the specifications for general stability were examined, it was found that the results were within the specified limits.
Secondly, the horizontal displacement (ux) conditions to be formed on the surface of the panel by the finite element method were examined and it was observed that the static and seismic conditions remained within the limits specified in the specifications.
Finally, the internal stability analysis of the reinforced concrete wall is examined. In the system where limit state and finite element analyzes are performed, the loads from each strips used are calculated and the strip effecting the most critical load is compared. In static and seismic state, the lowest level of the strip reached critical load, and the results obtained from limit state and finite element analyzes were close to each other.
Finally, in the light of technological developments, many new reinforcement materials can be used in reinforced earth retaining structure systems. Research and development studies allow for the creation of much more economical and safe retaining structures. For many years mechanically stabilized earth (MSE) walls will continue to be used in geotechnical engineering and many successful projects will be implemented.