Kazık taşıma gücünün Eurocode 7 ve Rus kazıklı temeller yönetmeliğine göre belirlenmesi hakkında bir inceleme
An investigation on the determination of pile bearing capacity in accordance with Eurocode 7 and russian pile foundations design codes
Yazar: EDA ÇELİK YURTSEVER
Danışman: DOÇ. DR. MUSTAFA TUĞRUL ÖZKAN
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Zemin Mekaniği ve Geoteknik Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2016
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Bu çalışmada Eurocode 7 ve Rus tasarım yönetmeliklerine göre kazık tasarımının genel esasları, kazık taşıma gücünün belirlenmesinde kullanılan yöntemler incelenmiş ve çözülen örnek problemlerle kazık taşıma gücü hesap yöntemlerindeki benzerlik ve farklılıkların belirlenmesi amaçlanmıştır. 
Avrupa Birliği ülkelerinde geoteknik mühendisliği uygulamalarında uyulması gereken genel kurallar 'Eurocode 7 Geoteknik Tasarım' başlıklı yönetmelikte verilmektedir. Eurocode 7'de değişik tipteki temellerden, istinat yapılarına kadar zeminle etkileşim halinde olan yapıların genel tasarım kuralları tanımlanmaktadır. Ülkemizde kullanılan tasarım yönetmeliği TSE EN 1997-1 de Eurocode 7 örnek alınarak oluşturulmuştur.  
Günümüzde Türk inşaat firmalarının yoğun olarak faaliyet gösterdiği Rusya Federasyonu ve eski Sovyet Cumhuriyeti ülkelerinde ise geoteknik mühendisliği uygulamalarında SNIP olarak bilinen Rus yönetmelikleri kullanılmaktadır. Rusya kazıklı temeller yönetmeliğini revize ederek güncel tasarım yönetmeliği SP 24.13330.2011'i yayınlanmıştır.
Eurocode 7 kazık tasarımıyla ilgili olarak sınır durum tasarımı, tasarım yöntemleri, kazık yükleme deneyleri, eksenel ve yatay yüklü kazıklar, kazıkların yapısal tasarımı ve inşaatın kontrolü konularını ele almaktadır. Eurocode 7'ye göre kazık tasarımı taşıma gücü ve kullanılabilirlik sınır durumlarına göre kazık taşıma gücüne, zemin parametrelerine ve yüklere uygulanan kısmi faktörlerle yapılmaktadır. Tasarımda izlenmesi tavsiye edilen metotlar için kısmi faktörlerin ele alınış şekli incelenmiştir. Karakteristik taşıma gücünün belirlenmesinde kullanılan güvenlik faktörleri kazık taşıma gücünün belirlenmesinde kullanılan yönteme göre değişkenlik göstermektedir. 
Rus kazıklı temel yönetmeliğinin genel tasarım esasları, kazık taşıma gücünün belirlenmesinde kullanılan yöntemler, farklı kazık tipleri için verilen hesap yöntemleri, incelenmiştir.
Karşılaştırma yapmak amacıyla kohezyonlu ve kohezyonsuz zeminlerde farklı tipteki kazıkların  her iki yönetmeliğe göre taşıma kapasitesi hesabı yapılmıştır. Öncelikle her iki hesap yönetmeliğine göre taşıma gücü hesabı için gereken zemin paramaterleri tespit edilmiş, seçilen zemin tabakaları için literatürde önerilen değerlerden yararlanarak zemin parametreleri belirlenmiştir. Hesaplar neticesinde elde edilen bulgularla hesap yöntemlerinin ve elde edilen sonuçların nerde birbirine yaklaşıp nerede farklılaştığı vurgulanmıştır. 
Taşıma kapasitesi hesabında kullanılan, Eurocode 7'nin de önerdiği, DIN 1054 normu ve SP 24.13330.2011 yönetmeliği bazı noktalarda örtüşse de tasarım parametresi kabulleri ve elde edilen kapasiteler açısından birbirinden farklı sonuçlar verebilmektedir.

Abstract:
In this study, the general principles of pile design according to Eurocode 7 and SP 24.13330.2011 regulations are investigated. It is intended to go through the basic methods used in order to determine the bearing capacity of a pile, and pinpoint their respective similarities and/or differences by introducing some design examples. 
In European countries, general rules to abide by in geotechnical engineering applications are explicitly defined in 'Eurocode 7: Geotechnical Design'. General design rules are given for all types of structures interacting with soil, ranging from all types of foundations to retaining structures. Various design approaches, partial safety factors and other correlation factors described in Eurocode 7 are all mostly informative, and the utilization of these guidelines are left to the discretion of the member states of the European Union. This initiative has recently led to the formation of 'National Annexes to Eurocode'. Geotechnical design regulations in Turkey too, are basically constituted on their Eurocode 7 basis, in an attempt to keep up with the current design methodologies predominantly used abroad.
In most member states of the Russian Federation and the former Soviet Republic, where recently Turkish construction companies take up intense activity, Russian design codes (formerly known as SNIP) are in use for geotechnical engineering applications. Though not being a member state of the European Union, Russia too, has adopted the most basic concepts of the Eurocodes. Rules and specifications have been extracted, restructured and elaborated in accordance with the Russian engineering experience. Their design codes, which were in use for a vast time period of 25 years, have lately been revised, and the updated design code specifically attributed to the design of pile foundations has been reissued by the name of 'SP 24.13330.2011'.
The study consists of seven main chapters. The first chapter presents the goal and scope definition of the study, which in brief is the utilization of both design codes on specific examples that show variability in such parameters as soil type, pile type, pile length and diameter. Chapter two provides general information, which may as well be treated as conventional wisdom, on pile foundations.
The third chapter introduces Eurocode 7 for piled foundation design: design principles, limit states in pile design, the partial factors used in the design for actions, soil parameters, pile resistances,  the methods used in pile bearing capacity determination and specific rules for pile design are given. The design approaches are introduced for the ultimate limit state design. The methods for determining pile bearing capacity is given; pile load test, determination of pile capacity based on in-situ test by the name model pile and characteristic value of pile skin and base resistance by alternative procedure.  Based on the methods for determining the pile bearing capacity, the calculation rules and partial factors related to chosen methods are given.
The next chapter focuses on the Russian design code for pile foundations: general design principles, methods for determining the bearing capacity of a pile, analysis and design methods for different pile types, methods for determining the pile bearing capacity according to static and dynamic load tests and/or similar field (in-situ) tests, and other specific rules for pile design are given. Design tables for skin friction and base resistance for different soil types and pile depths is used for the bearing capacity calculations. The limit states for the pile design are given; ultimate limit state (bearing capacity) and serviceability limit state. Ultimate limit state is provided by the condition that the design load transmitted to the pile for the most unfavorable condition should be lower then the pile capacity divided by the safety factors. 
Chapter five presents design examples, performed in accordance with both design codes using bearing capacity formulas. The said examples vary by soil type, being cohesive cohesionless soils, and by pile type, being bored piles and precast concrete driven piles. In order to add further diversity to the examples, various lengths of piles are taken into account. The soil profile applied in the examples also adds to the variety. According to Eurocode 7 recommendations, 'DIN 1054: Subsoil - Verification of the safety of earthworks and foundations - Supplementary rules to DIN EN 1997-1' (namely, the German standard for geotechnical design) is used as a complementary reference  in order to determine the charactersitics pile base and shaft resistance. Soil parameters for the requirements of the design codes is determined firstly, then the parameters are determined by using several correlations given in the literature. The design tables for pile bearing capacity given in the Russian Codes is generally based on the relative density and grain size of cohesionless soil and liquidity index of cohesive soils. Inspite of this, the characteristic values of pile skin and base resistance is determined by CPT cone resistance for bored and displacement piles in sand, undrained shear resistance for bored piles in clay, and liquidity index for displacement pile in clay given in German Design Code.
In the sixth chapter, obtained results are carefully organized so that findings can be tracked as effortlessly as possible. The similarities and differences between the design methods described in Eurocode 7 and SP 24.13330.2011 are emphasized by the computation results. Identified differences are interpreted with regards to causality. According to bearing capacity calculations, pile shaft friction and base resistance variability with depth  have been identified. In brief, for the bearing capacity of bored piles in cohesive soil and driven piles in cohesionless soil, the pile bearing capacities for both methods is close to each other and the difference between  codes is at the rate of 40% for bored piles in cohesionless soil  . The big difference between pile capacities for precast driven pile in cohesive soil is determined as DIN 1054 and SP 24.13330.2011 both give different shaft friction and base resistance values for medium stiff clay. 
As a result of the study, it can be easily concluded that Eurocode 7 and SP 24.13330.2011 codes show similarity in the sense that they both adopt the ultimate and serviceability limit states in the design of pile foundations, and that they both apply partial safety factors to loads and resistances for the ultimate limit state design. However, they visibly differ in terms of the number and content of the design checks, and in terms of the actual values of the partial safety factors.
Eurocode 7 avoids to provide a definitive design model, since the member states of the European Union all utilize different design methods. Nonetheless, design criteria to be followed are clearly defined, and the use of partial safety factors is obligatory. Hence, European countries prepare additional regulations (National Annexes) in order to clarify the partial safety factors and the attributions of design checks according to their needs. On the other hand, the Russian code explicitly defines the analysis and design methods to be used in determining the design loads and pile bearing capacity, and provides accurate calculations techniques for problematic site conditions as well.
For determining soil parameters to be used in pile design, Eurocode 7 allows for the use of a cautious estimate as well as the use of geological data based on previous experience. Statistical methods are also an option. SP 24.13330.2011 refers to a relevant code (GOST 20502-96) for the same purpose, thereby ensuring that soil parameters are determined according to the desired safety level, the number of soil tests and the variation factor(s) of the obtained results.
When it comes to the utilization of pile load tests and other related field tests in order to determine the pile bearing capacity, Eurocode 7 and SP 24.13330.2011 both use similar methods, which rely on the number of tests, and yet slightly differ in content.
The following conclusions can be drawn from the design examples provided in this study:
- The values of load bearing capacities for bored piles in cohesive soils calculated according to SP 24.13330.2011 are on average 20% higher than those calculated according to DIN 1054.
- For the depths used in the examples, the values of load bearing capacities for bored piles in cohesionless soils calculated according to DIN 1054 are on average 40% higher than those of SP 24.13330.2011 calculations. The reason for this difference is undoubtedly the fact that the shaft resistance defined in DIN 1054 is much higher. The tip resistance values obtained by both codes are relatively close for the depths used in the examples.
- The values of load bearing capacities for precast driven RC piles in sand are close according to both design codes.
- The values of the tip and shaft resistances for precast driven RC piles in medium-stiff clays calculated according to SP 24.13330.2011 are relatively higher than those of DIN 1054 calculations, for which the total difference is found to be approximately three times.
As a final word, it can be said that Eurocode 7 and SP 24.13330.2011 codes bear similarities with respect to the general principles of the ultimate limit state design. Having said that, SP 24.13330.2011 and DIN 1054 (which gets involved due to EC7 reference) still happen to yield slightly different results in terms of the adopted design parameters and the final capacity values.