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Donatılı zemin yapılarının sistem davranış özellikleri

Başlık çevirisi mevcut değil.

  1. Tez No: 56003
  2. Yazar: R.SERHAT KESİM
  3. Danışmanlar: DOÇ.DR. M. TUĞRUL ÖZKAN
  4. Tez Türü: Yüksek Lisans
  5. Konular: İnşaat Mühendisliği, Civil Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1996
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 206

Özet

ÖZET Zemin mekaniği, inşaat mühendisliğinin en yeni bilim dallarından biri olması özelliği ile ayrı bir öneme sahiptir. Kısa geçmişine karşılık çok yoğun bilimsel çalışmaların yapıldığı zemin mekaniğinin en yeni konularından birini de Donatılı Zemin konusu teşkil etmektedir. Pratik uygulamalarını çok eski dönemlerde (M.Ö 2500 yıllarında Ziggurat adı verilen tapınakların yapımında) görebileceğimiz bu konu, gerçek anlamda ilk kez 1963 yılında bir Fransız mimar-mühendis olan Henri Vidal tarafından bilimsel bir önem kazanmıştır. İlk proje uygulamalarını 1967 yılında gördüğümüz Donatılı Zemin konusu özellikle A.B.D, Fransa, Kanada ve Japonya gibi ülkelerde gelişme ortamı bulmuş, bu konuda çok sayıda uygulama projesi de gerçekleştirilmiştir. Bugün dünyanın pek çok ülkesinde olduğu gibi ülkemizde de donatılı zemin konusu gittikçe daha fazla dikkat çekmektedir. Bununla birlikte çalışma mekanizması anlaşıldıkça ve ekonomik olması özelliğinin farkına varıldıkça, daha geniş araştırma ve uygulama alanları bulacağım söylemek bir kehanet olmayacaktır. Bu çalışmadaki amaç ; taşıyıcı bir sistem olarak donatılı zemin konusunun irdelenmesi, zemin ve donatı elemanlarının oluşturduğu kompozit sistemin davranış mekanizmasının ilk ve en son yapılan çalışmalar ışığında gerek deneysel ve gerekse analitik metodlarla incelenmesi ve yorumlanmasıdır.. Bu incelemede yüzeysel temellerin taşıma güçlerinin donatı elemanları kullanılarak arttırılması konusu, sonlu elemanlar metodu ile nonlineer analiz yapan bir bilgisayar programı (Lusas 11.0) kullanılarak araştırılmış ve programın çalışma düzeneği hakkında da kısa bilgiler verilmiştir. XV11

Özet (Çeviri)

SUMMARF SYSTEM BEHAVIOUR PROPERTIES OF REINFORCED EARTH STRUCTURES As a definition, reinforced earth is a composite structure of which sliding resistance has been increased, obtained by inserting metalic or polymer elements into earth in parallel direction to principal traction unit deformations for the purpose of increasing resistance and strength of earth in critical directions. Elements used as reinforcement can be metalic or polymer elements. In case that reinforcement elements are metalic, then, it should be necessary to inspect its non-corrosive mechanism. On the other hand, in case that reinforcement elements are polymer elements, hydraulic negative effect of water on reinforcement elements becomes very important. Molecular weights, and crystallisation rates, loading velocity and heat effect in behaviour mechanism of polymers play very significant role. Polymer reinforcement elements are called, in short, as geosynthetics. It is very important measuring properties of geosynthetics from engineering viewpoint. Properties such as weight per unit surface or length, thickness, rigidity, traction resistance (tensile strength) deformation properties, elasticity modules, seam residence, impact strength, penetration resistance, hydraulic permeability, resistance against chemical substances, friction properties, play great and important role in comprehension and interpretation of behaviour mechanism. In reinforced earth, reinforcement elements are inserted into earth mainly for purposes of carrying, separation, filtration and drainage. On the other hand, used filling materials must be selected by taking into consideration long term stability of construction, short term stability after construction and physical and chemical properties of filling material. Total longitudinal thrust-off will increase depending on how small is internal friction angle in filling material. The reason for this is that apparent friction XV1Ucoefficient is in direct proportion with internal friction angle of earth. Lateral tensions and deformations in reinforced earths are limited by reinforcement elements placed in parallel to 03 direction and hence, while deviathoric tension where potentially composite earth is broken, increases and in parallel to this, sliding resistance raises as well. This phenomenon is explained by two different theories. One of these theories is pseudo-cohesion theory. In accordance with this subject theory as long as angle made by strength between earth dunes and reinforcement with normal angle of reinforcement remains smaller than friction angle between earth and reinforcement. Then earth dunes will act as they are attached to each other. This attachment is called either apparent cohesion or pseudo-cohesion. Other theory is named Increased Ambience Pressure Theory. In accordance with this theory, strength increase in reinforced earths is not effected by apparent cohesion, but is realised by increase in lateral tension. When behaviour of reinforced earth retaining structures is examined, it is observed and seen that maximum sliding tension occurred on each reinforcement element, occurs at different points and by joining these points, then, two different zones emerge inside earth masses behind wall. One of zone is a region being neighbour to wall surface and called as active zone and sliding tensions in this zone is towards the wall. Other zone is a passive or resisting zone where sliding tensions are directed towards opposite direction of wall. Capability of reinforcement and earth in these structures is a function of unevenness of reinforcement surface unit weight of filling material, height of filling materials on reinforcement, internal friction angle of filling materials. As per results obtained on model studies conducted in laboratory on reinforced earth specimens, while reinforcement rate increases, so, internal friction angle of composite earth increases as well to certain point and after this point, remains fixed or decreases. Similarly, together with reinforcement rate, sliding resistance increases, but compaction quantity decreases. In addition, by increase of reinforcement rate, it is seen that elastoplastic deformations increase. Other laboratory studies have given the result that by increasing of slimness of reinforcement, bearing capacity has increased as well. XIXIt is possible to summarise other test results conducted in laboratory as shown below : 1. While reinforcement surface rate increases, CBR and secant modules increase as well. 2. While reinforcement is 4%, CBR has become five times greater than reinforcement specimens. 3. While reinforcement rate increases, a larger deformation in volume is formed for the same lateral deformation 4. If it is defined as K=a3/öı, increase of K value will decrease limited lateral deformations. 5. By increase of K value, deviathoric tension value decreases for the same axial deformation. 6. By increase of K value, pore water pressure decreases for the same axial deformation 7. Since pore water pressure is so small in tests with drainage, deviathoric tension comes out big. 8. It is suitable to use reinforcement in type having high hydraulic permeability in earth with cohesion and water saturated. As tests are conducted under laboratory condition on reinforced earth, full scale tests are performed in the field too. In these tests especially longitudinal earth tensions, vertical earth tensions and longitudinal and vertical earth deformations and longitudinal tension and deformations in reinforcement are determined and then determination of longitudinal thrust size transferred to wall surface of maximum reinforcement traction strength and vertical tensions formed throughout reinforcement as well as real field values are achieved one to one. Studies and examination conducted put forth that it is a for away possibility that a flow incident will occur in reinforcement and that reinforcement can be loaded only by a tension up to 11% of flow tension. On the other hand earth and reinforcement deformations exhibit a reverse form with each other towards inside from wall surface. xxIn studies, about finite elements conducted on matter of properties of filling behind wall used in reinforced earth resistance structures, three fillings behind wall have been tested. First of these fillings is cohesion filling, second one granular filling without cohesion filling and third one a mixed filling being granular in front and with cohesion behind. In conclusion of study, in case application of a mixed filling, both longitudinal and vertical deformations have decreased to a great extent. Idea in respect with increasing bearing capacity by application of reinforcement elements under surface foundation has become a topic of study during recent years. Both laboratory and finite element studies have put forth effective parameters on the subject-matter and through these studies, some significant results regarding increasing bearing capacity have been obtained. It has been determined that increasing bearing capacity of earths under surface foundations by reinforcement elements depends on five parameters and these parameters are respectively distance of first reinforcement layer to foundation base, distances between reinforcement, number of reinforcement layers, lengths of reinforcement and elasticity properties of reinforcement material. When soft earths under foundation are reinforced by compact sand and reinforcement elements, then bearing capacity increases and deformations are reduced. Conclusions obtained from studies with finite element and also laboratory studies can be summarised as follows : 1. Bearing capacity of soft earth under foundation is a function of proportion of sand filling thickness made for improvement purpose to foundation width. 2. Taking this proportion as 0,5 gives effective result. 3. Besides their reinforcement duty, reinforcement elements function as separator and will provide positive contribution from this viewpoint to carry power. 4. Friction resistance of geognd type reinforcement elements is higher as compared with others. 5. Both FEA and test studies have shown that optimum depth makes single layer BCR proportion to maximum level. This XXIdepth is around 30% of foundation width being independent to reinforcement dimensions. 6. In case that sitting proportion is bigger than 6%, this rank becomes higher than 30%. 7. It has been determined that maximum BCR value comes out if first reinforcement depth is taken as 25% of foundation with in case of multi-layer reinforcement. 8. Optimum reinforcement element space interval giving maximum BCR value is in rank of 20% of foundation width. 9. Number of optimum reinforcement layers varies between one and five and is effective in depth up to 1.5 times of foundation width. 10. While elasticity of reinforcement increases then BCR value increases as well. 11. Results of studies, about LUSAS finite element conducted by KESİM on subject of increasing bearing capacity of sand earth, supports above stated other results. XXH

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