Kazık Yükleme Deneylerini Değerlendirme Yöntemlerinden Özkan-alku Yönteminin Geliştirilmesi Ve Önerilen Yeni Yöntem İle Erken Göçme Yükü Tahmini

Abstract

Kazık yükleme deneylerinin değerlendirilmesinde, çeşitli araştırmacılar tarafından birçok yöntem geliştirilmesine rağmen, yeterli deney verisi olmadığı durumlarda kazık nihai taşıma gücünü belirlemek kolay olmamaktadır. Bu çalışma kapsamında, nihai kazık taşıma gücünün belirlenmesinde Özkan – Alku yöntemi kullanılarak, göçmeye ulaşmamış ya da yeterli verinin elde edilemediği deneyler için erken göçme yükü belirlenmesi hususunda yeni bir yaklaşım önerilmektedir. Kazık yükleme deneyinin yapılış amacına hizmet edebilmesi için elde edilen deney sonuçlarının mutlak suretle uygun bir şekilde değerlendirilmesi ve kazığın emniyetli olarak taşıyabileceği yük değerinin tayin edilmesi gerekmektedir. Çalışma kapsamında önceki araştırmacılara ait kazık yükleme deneyi değerlendirme yöntemleri incelenmiş ve deney verilerine uygulanabilirliği belirtilmiştir. Bu çalışmada kazık yükleme deneyi sonuçlarının değerlendirilmesinde kullanılan yöntemlere alternatif olarak, mevcut bir yöntem üzerinden yeni bir değerlendirme geliştirilmiştir. Yöntemlerin performanslarının belirlenmesi adına yapılmış yükleme deneyi verisi kullanılmış ve yöntemler ile elde edilen sonuçların birtakım istatiksel parametreler yardımıyla karşılaştırılması yapılmıştır. Özkan – Alku yöntemine göre iki farklı eksen takımında, iki farklı doğruyla temsil edilen kazık yükleme deneyi başlangıç ve sonlanma grafikleri, bu çalışmada iki düşey eksene sahip tek bir grafikte ifade edilmektedir. Grafik üzerinde başlangıç ve sonlanma eğrilerini temsil eden veri grubunun kesişim noktası “kritik yük değeri” olarak adlandırılmaktadır. Bu nokta sonrasında grafik üzerinde en küçük kareler yöntemiyle doğru elde edebilmek adına 2 noktaya daha ihtiyaç duyulmakta ve önerilen yeni yöntemle bu şekilde oluşturulan doğru esas alınarak göçme yükü belirlenmektedir. Önerilen yöntemi açıklamak adına, yük – oturma eğrisine göre göçme durumunun gözlendiği toplam 48 adet yükleme deneyi verisi esas alınmaktadır. İlk durumda tüm veriler korunarak Özkan – Alku yöntemine göre göçme yükü değerleri belirlenmiştir. Daha sonra belirlenen “kritik yük değeri” ve sonrasında sadece 2 nokta ile temsil edilecek şekilde azaltılan veriler esas alınarak, yöntem bu yeni veri takımına uygulanmaktadır. Değerlendirme sonunda belirlenen göçme yüklerinin çok yakın olduğu görülmektedir. Bu doğrultuda deney sırasında uygulanabilecek yeni yöntem ile, “kritik yük değeri” grafik üzerinde işaretlendikten sonra deneyde 2 nokta daha elde edilerek, göçme yükünün belirlenebileceği gösterilmektedir.

Interpretation of pile load tests are one of the main issues of deep foundation systems. Various types of interpretation methods were used to determine pile failure load. However, in some cases, it is hard to evaluate failure mechanism of pile when sufficient load test data are not exist. In this study, in the ligth of Ozkan-Alku method, a new approach was considered for early estimation of pile failure load in which conditions that inadequate test data were achieved. In order to gain productive results from pile load test, test data should be determined properly to designate ultimate bearing capaciyt of single pile. Within the scope of this study, present pile load test interpretation methods were evaluated and exercised with test results. A new approach of an existing Ozkan-Alku method has developed for alternative to present pile load test interpretation methods. As a comparison of these methods, pile load test data executed from previous projects were used and some statistical parameters were determined to compare failure load of single piles. Static pile load tests are performed on pile to determine the bearing capacity and verify the design assumptions. To make an economical pile design, piles shall be tested until failure. In most cases, failure load cannot be reached due to high costs and lack of proper equipment and reaction systems. A proof load test, which is a limited form of static load test, is usually carried out to determine the performance of the pile. The proof load test is usually performed 1.5-2.0 times of design load and is less expensive. Pile design based on proof load test causes overdesign and increases foundation costs. Due to aformentioned reasons, an accurate and reliable method is required to determine the ultimate pile capacity based on proof load test results. Piles are need to be constructed to transfer the load coming from the high and heavy buildings to the deep ground. Deep foundations is an expansive application and engineers should consider economic and safety conditions together in their design of deep foundations. Dependant on development of the technology, design of deep foundations can be controlled with load test applied to the piles. There are several methods used in the design of bored piles. To start with, mathematical modeling of the pile and soil parameters provide various formulas and theories for ultimate bearing capacity and settlement calculations of a pile. However, such model based analyses seldom give fully reliable results. Many factors, including construction methods and real site conditions also play an important role in the estimation of vertical load capacity. As a result, although economically costly and time consuming, pile load tests are the most dependable way of measuring the load bearing capacity and displacement behavior of piles. Besides, integrity test are the most prefable option to check the quality of pile upon installation. Various deep foundation codes have been determined to minimize the risk of foundation failures. These codes recommend higher safety factors for theoretical capacity calculation methods which have a large amount of assumptions and unknowns, whereas lower safety factors for methods which present more detailed and reliable results. However, latter methods are usually more costly and need qualified workmanship. Therefore, for every piling project, a cost analysis should be performed, which compares the benefit of a method with its disadvantage to decide for the most economic pile design. Pile design is generally exercised with theoretical expressions and emperical formulas. It is vital part of the supervision of calculations that on-site pile load test evaluations to prove estimated and designated pile load. Many interpretation methods are existed in geotechnical literature developed by various investigator to specify pile failure load. Most part of these methods determine pile failure load with remarks obtained from load-settlement curve. In this study, interpretation of pile load test methods were divided into three parts such as mathematical expressions, graphical methods and trial-error methods. While Brinch-Hansen 80% method, Chin-Kondner method and Decourt method were evaluated under mathematical expressions headline, Davisson method, Mazurkiewicz method, Tangent method, Corps of Engineers method, De Beer method, Butler-Hoy method and Fuller-Hoy method were evaluated under graphical methods headline. Brinch-Hansen 90% method and Vander Veen method were also evaluated under trial-error methods headline. Inequality of interpretation pile load test results commonly cause different approaches and evaluations for pile failure load. Therefore, pile load test results should be determined with a new approach that does not vary with pile characteristics, load steps and test period. While evaluation of test data with only one expression or equation is generally not suitable, it was emerged that various practices have exercised. Determination of new approach was exercised through existing Ozkan-Alku method and additional remarks. Some inference were produced over load-settlement curve to determine compatibility with existing method from pile load test data. Then, it was emerged that initial and end graphs of existing method could not be represented with only one expression from pile load tests which were determined till failure load has obtained. It was aimed that any expression determined from initial and end graphs of Ozkan-Alku method, should reveal pile failure load or load-settlement curve trajectory. In this study, inital and end graphs of Ozkan-Alku method which were represented two different equations in different axes, was expressed as a one graph with two vertical axes. A “critical load” was defined on combined graph as interception of two functions, initial and end graphs. After that point, it was revealed that only 2 more test data are required to determine pile failure load. Also, least squares method was used to determine failure load. To clarify new recommended method, 48 pile load test data were determined. At first, all of the test data was performed with Ozkan-Alku method and failure load of each pile was obtained. After that, with “critical point” from new recommended method and 2 more test points, failure loads were obtained with just these data. It is observed that, acquired results are pretty close and new method is quite reliable. Also, pile load test datas were evalueted with Chin-Kondner and Decourt methods to present relationship with recommended method. All acquired results were compared and given in this study.