Zemin çivileri tasarım prensipleri ve davranışın sonlu elemanlar yöntemiyle analizi
Başlık çevirisi mevcut değil.
- Tez No: 75531
- Danışmanlar: DOÇ. DR. M. TUĞRUL ÖZKAN
- Tez Türü: Yüksek Lisans
- Konular: İnşaat Mühendisliği, Civil Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1998
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Geoteknik Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 189
Özet
Zemin stabilizasyonu geoteknik mühendisliğinde ana bir başlık altında değerlendirilebilecek çok yönlü, uygulamalara açık bir konudur. Son 25 yıldır uygulanmakta olan pasif zemin armatürleri, zemin çivileri ise zemin stabilizasyonunu için kullanılan en yeni ve en geçerli tekniklerden biridir. Özellikle kolay ve tasarruflu imalatı, gösterdiği üstün performansı ile son yıllarda bir çok projede değerlendirilmiş, başarıyla uygulanmıştır. Zemine çivilenmiş yapıların tasarımına yönelik birçok güncel metod mevcuttur. Bunlar sırası ile Davis, Fransız, Alman Metod'ları ile Kinematik Limit Analiz ve Sonlu Elemanlar Analiz Yöntemleridir. Bu metodlardan ilk üçü limit denge prensibine dayanırken, son ikisi limit analiz yaklaşımını içerir. Metodlarda kayma yüzeyi bi-lineer, dairesel, parabolik veya log-spiral olarak kabul edilirler. Stabilite analizleri İle kayma yüzeyini kesen takviyelerin, limit kesme, çekme ve sıyrılma kapasiteleri araştırılır. Teknolojinin gelişmesi, beraberinde zaten kuvvetli işlem hacmi olan bilgisayarları daha da güçlendirmiş, mühendisliki çalışmalar için çok daha cazip kılmıştır. Bu süreci takiben bilgisayar destekli teknik yazılımlar oluşturulmuş ve kullanıma sunulmuştur. LUSAS sonlu elemanlar programı da bu amaca istinaden kullanıma sunulmuş çok amaçlı bir teknik yazılımdır. İçerdiği zengin malzeme ve geometrik özelliklerlerle desteklenmiş bünye denklemleri, çok yönlü ve çeşitli eleman kütüphanesi ile LUSAS konusunda oldukça iddialıdır. Bu tez çalışması ile amaç, zemin çivileme tekniğim tüm yönleriyle sunmak, tasarımına ait prensiplerin altım çizmek ve uygulamaya yönelik bilgileri değerlendirmektir. Ek olarak LUSAS 12 versiyonu kullanılarak zemin çivisi modellenmiş ve davranışı analiz edilmiştir.
Özet (Çeviri)
The determination of forces acting on structures which are connected to or in direct contact with earth mass is one of the paramounth importance in applied Geotecnical Engineering. Considering the increasing demand for deep excavations in connection with extenstive land utilisation within densely populated areas and as a result of increasing value of land, the ecenomy and construction speed of soil nailing has made the method an understanding alternative for both temporary and permanent excavations. Soil nailing has been used in a variety of civil engineering projects in the last three decades, mainly in Europe, to retain excavations and stabilize slopes. The earliest reported works were retaining wall construction in Spain, France and Germany, in connection with highway or railroad cut slope construction or temporary building excavation support. In North America the system was initialy used in Vancouver in the earliest seventies for temporary excavation support. The fundamental concept of soil nailing consists of placing in the ground passive inclusions, closely spaced, to restrain displacements and limit decomression during and after excavation. The nails are generally steel bars, metal tubes or other metal rods that are embedded in grout if necessary, to establish required safety factor against not only tensile forces but also shear stresses and bending moments. Stability of the slope face between nails generally is ensured by providing a thin layer of shotcrete reinforced with wiremesh. Nailing differs from tieback support systems in that the nails are passive elements that are not post tensioned as tiebacks are. Method has been used both granular and cohesive soils and relatively heterogeneous deposits. The principal function of nails in slopes and embankments is to provide stabilizing forces. Through friction between the nails and the soil, acting over a sufficient length, it is possible to develop enough resistance to pullout so that the full tensile strength of the reinforcement can be mobilized to help stabilize the slope. Modes of failure of nailed slopes and embankments include tensile failure of the reinforcement, pullout of the reinforcement from the soil, excessive deformation of the reinforcement and also raveling of the soil from between layers of reinforcements at the face of steep slopes. If the reinforcement fails in tension or deforms excessively, the same type of shear failure can take place as would occur without reinforcement.Steel reinforcement inclusions currently used in soil nailing process can be classified as driven nails, grouted nails, jet grouted nails and encapsulated corrosion protected nails. Driven nails are suitable for temporary construction and have been 22 mm to 32 mm steel bars or structural angles for greater driving rijidity. They are closely spaced at 2 to 4 nails per m2 creating a homogenous composite reinforced soil mass. The nails are driven using vibropercussion pneumatic or hydraulic hammers. This installation technique is rapid an economical, but is limited in the lenght of the nail installed by equipment considerations in which boulders and coarse gravel and weathered rock is absent. Grouted nails are suitable both temporary and permanent construction. They are placed in boreholes that are advanced by either core drilling, rotary drilling, percussion drilling, auger drilling or driven casing. Grouting is performed by gravity or under low pressure from the bottom of the drill hole. Spacing is typically wider, from 1.2 to 1.8 m on center. Drill hole diameter will vary from 10 cm to up to 30 cm when using augers. Jet grouting nails are composite inclusions made from a grouted soil with a central steel nail, installed simultaneously. They are used for temporary aplications and may be used for permanent aplications if the degree of required corrosion protection is low. Nails can be installed using vibropercussion driving at high frequencies (up to 70 hz) and extremely high grouting pressures (>2000 psi). The grout under this technique is injected through a small diameter longitudinal channel in the nail, under a pressure sufficiently high to cause hydraulic fracturing of the surrounding soil. Alternatively, significantly lower grouting pressures ( psi ) have been use in practice with a variety of nails including hallow bars which are used as the drill stem initially and then disconnected and left in the hole to serve as the structurel members. Jet grouting tecniques provide in addition, recompaction and improvement of the surrounding soil and can increase significantly in granuler soils the shear and pullout resistance of the soil. Encapsulated corrosion protected nails are used for permanent structures requaring a high degree of corrosion protection. Encapsulation can be achieved by inserting the nail in a plastic or steel tube and filling the annulus with grout, prior or during grouting the drill hole. The facing functions to ensure local ground stability between reinforcements, limit decompression immediately after excavation and protect the retained soil from surface erosion and weathering effects the type of facing controls the aesthetics of the structure as it is the only visible part of the completed work. Depending on the application welded wire mesh, shotcrete, precast concrete or cast in place concrete facings has been used.There are several methods currently avalible for the design of nailed structures such as the German Method, the Davis Method, the French Method, the Kinematic Limit Analysis and the Finite Element Analysis approaches. The first three methods are based on the limit equilibrium approach whereas the last two are based on the limit analysis method. The basic concept underlying the design of soil nailed structures relies on:. The transfer of tensile forces generated in the nails in an active zone to a resistant zone through friction mobilized at the soil-nail interface.. Passive resistance developed on the surface perpendicular to the direction of the soil-nail relative movement. The frictional interaction between the ground and the nails restrain ground movement during and after construction. The resisting tensile forces mobilized in the nails induce an apparent increase of normal stresses along potantial sliding surfaces (or rock joints) increasing the overall shear resistance of the native ground. Nails placed accross a potential slip surface can resist the shear and bending moment through the development of the passive resistance. The chief design concern is to ensure that the soil-nail interaction is effectively mobilized to restrain ground displacements and ensure structural stability with an apporiate factor of safety. The construction of a soil nailed mass results in a composite coherent mass similar to reinforced fill systems. The locus of the maximum tensile forces separates the nailed soil in two zones:. An active zone (or potential sliding soil or rock wedge), where lateral shear stersses are mobilized and resuts in an increase of tension force in the nail.. A resistant (or stable) zone where the generated nail forces are transferred into the ground. The soil-nail interaction is mobilized during construction and displacements occur as the resisting forces are progresively mobilized in the nails. There are several methods currently avalible for the design of nailed soil structures such as, the German Method, the Davis Method, the French Method, the Kinematic Limit Analysis and the Finite Element Analysis aproaches. The first three methods are based on limit equlibrium method aproach, where as the last two are based on limit analysis aproach. These methods assume the failure surface to be bi linear, circular, parabolic or log-spiral. The variable limit shearing, tensile, and pullout resistances of the reinforcements crossing the failure surface are considered in the stability analysis. The identified design paraneters of a soil nailed system for all methods include, the mechenical or strength properties of the soil and inclusions, as well asparameters characterising the different mechanisms of soil-reinforcement interaction. They can can be classified in the following groups:. Mechanical properties of the insitu soil, particularly soil type, internal friction angle and cohesion...... Mechanical properties of the reinforcements, specifically the tensile and shearing resistances and the bending stiffness. Parameters related to the soil-reinforcement interaction by friction, particularly the limiting unit ultimate friction, Fi, which can be mobilized along the inclusion in the specific soil under consideration. Parameters related to the normal soil-reinforcement interaction by lateral earth thrust on the reinforcement, particularly the limit passive pressure of the soil and the modulus of lateral or subgrade reaction. Geometric properties of the reinforcements such as thichness, shape, length and of the structure such as vertical and horizontal spacings between the reinforcements; inclination of the reinforcements and of the facing. Parameters related to proposed installation method of the reinforcements, type of facing, grouting methods.. External load systems including surcharges, enviromental loading, embankment slopes, water flow and seepage forces. The design of soil nailed retaining structures is based on evaluation of:. Graund stability of the structure and the surrounding ground with respect to a rotational or translational failure along poteantial sliding surfaces.. Local stability at each level of nails Global stability analyses for retaining structures ocnsist of evalualating a global stability factor of the soil nailed retaining structure and the surrounding ground with respect to a rotational or translational failure along potantial sliding surfaces. It requires determination of the critical sliding surface which may be dictated by the stratification of the subsurface soil or in rock by an existing system of joints and discontinuties or position and intensity of surcharge loads. The potantial surface can be located inside or outside the soil nailed retaining structure. Analysis methods which provide a global safety factor, do not provide direct means of estimating working or failure nail tensile forces or provide criteria related to allowable displacements of the structure under working stress conditions. The availability of computers and of finite elment analysis computer programs, has made it possible to perform rational analyses of stress anddeformations in slopes and embankments. These analyses are capable of modelling several important aspects of actual conditions, including nonlinear stress-strain behavior, sequential changes in geometry during construction, and dissipation of excess pore pressures following construction. The finite element method has been used by several investigetors to analyze the behavior soil nailed retaining structures. These analyses involve different constitutive equations for the soil and interface elements to simulate soil-facing and soil-inclusions interaction. Comparisons of finite element predictions with observed behavior instrumented structures have been succesfull in indicating trends in parametric studies. However the use of finite element method in design is currently limited by the relatively high costs and raises significant difficulties with regard to:. The actual construction stages and installation process of the nails are difficult, if not pratically impossible, to simulate.. The complex soil-inclusion and soil-wall interaction is difficult to model. Several interface models have been developed but their implementation in design requires relevant interface properties which are difficult to properly determine.. Various elosto-plastic soil models can be used to predict soil behavior during exavation. However, determination of soil model parameters generally requires spesific an eloborate testing procedures limiting the practical use of these models. The finite element method has therefore been used mainly as a research tool to eveluate the effect of the main design paremeters on the behavior of the structure, ground movement, and working forces in the nails. This manual is proposed as a study of an extent analyse due to the behaviour of nailed soil structures with the LUSAS Finite Element System.
Benzer Tezler
- Design of MSE/soil nail hybrid walls under highspeed railway loads
Yüksek hızlı tren yükleri altında esnek istinat yapıları ve zemin çivili toprakarme duvar tasarımı
EHSAN SEYEDTEHRANI
Yüksek Lisans
İngilizce
2017
İnşaat Mühendisliğiİstanbul Teknik Üniversitesiİnşaat Mühendisliği Ana Bilim Dalı
DOÇ. DR. AYKUT ŞENOL
- Zemin çivileriyle güçlendirilmiş iksa yapılarında sistem performansını ve güvenilirliğini etkileyen faktörlerin vaka analizleri ile araştırılması
A study on the system performance and reliability of soil nail walls using case histories
AYŞE SELİN KESERLİ
Yüksek Lisans
Türkçe
2017
İnşaat MühendisliğiGazi Üniversitesiİnşaat Mühendisliği Ana Bilim Dalı
DOÇ. DR. SAMİ OĞUZHAN AKBAŞ
- Parameters affecting soil nailed wall design
Zemin çivili duvar tasarımı etkileyen parametreler
ÖNDER ÖZCAN
Yüksek Lisans
İngilizce
2000
İnşaat MühendisliğiBoğaziçi Üniversitesiİnşaat Mühendisliği Ana Bilim Dalı
PROF. DR. EROL GÜLER
- Ayrışmış kayada zemin çivili duvar performansının incelenmesi
Investigation of soil nailed wall in weathered rock
ANIL YENİ
Yüksek Lisans
Türkçe
2023
İnşaat MühendisliğiYıldız Teknik Üniversitesiİnşaat Mühendisliği Ana Bilim Dalı
DR. ÖĞR. ÜYESİ MURAT ERGENOKON SELÇUK
DOÇ. DR. ÖMER ÜNDÜL
- Eğimli yüzeylerde zemin çivisi uygulamasıyla ilgili bir inceleme
A research about soil nailing design principles in inclined walls
ONCA ÖZDEMİR