Birçok projede, taşıma gücü problemi sebebiyle değil oturma miktarları kabul edilebilir sınır değerleri aştığı için radye temelin altında oturmayı azaltıcı kazıklar kullanmak ekonomik bir gereklilik haline gelmiştir. Bu sistemlerin sık kullanılır olması, zamanla oturmayı azaltıcı kazıklar tanımlamasının “kazıklı radye temel” gibi daha geniş bir tanımlamaya dönüşmesine neden olmuştur. Klasik yöntemlerde, kazıklı temel hesabı, yapı yükünün tamamının kazıklar tarafından taşındığı kabulüne göre yapılmaktadır; fakat radyenin zemine temas ettiği durumda, yapı yükü radye ve kazık grubu arasında paylaşılarak zemine aktarılır. Kazıklı radye temel, radye (veya kazık başlığı) ve kazıklardan oluşan iki sistemin birleştirilmesi ile oluşmaktadır. Bu çalışmada önerilen hesap yönteminde, yapı yükünün, radye ve kazıklar tarafından paylaşılarak taşınacağı kabul edilmekte, farklı paylaşım oranlarına göre radyenin ve kazık grubunun oturmaları ayrı ayrı hesaplanmaktadır. Kazık grubunun oturma hesabında eşdeğer radye yönteminden yararlanılmaktadır. Kazık boyu, eşdeğer radye seviyesindeki gerilmenin jeolojik yükün % 20’sinden küçük veya eşit olması şartına bağlı elde edilmektedir. Çeşitli Qkazık/Qtoplam oranları için elde edilen oturma miktarları karşılaştırılarak, radye ve kazık grubunun oturmalarının eşit olduğu paylaşım oranı belirlenmektedir. Elde edilen sonuç, bir yandan oturma miktarını vermekte, öte yandan kazık boyunun belirlenmesini sağlamaktadır. Önerilen hesap yöntemi 2 farklı örnekte uygulanmış ve Plaxis 3D Foundation yazılımı ile de sonlu eleman çözümleri yapılmıştır. Basitleştirilmiş kazıklı radye hesabının, oturma analizi için uygun sonuçlar verdiği görülmüştür.

In many cases it has become an economic necessity to install piles beneath a raft not because a lack of bearing capacity of the foundation but because the settlement of the raft is excessive. Such usage of piles was first termed by Broms (1976) as “settlement reducing piles”. Wide use of pile foundations all over the world has made piling an important branch of geotechnical engineering. Gradually, the concept and usage which was coined as “settlement reducing piles” transformed into a much wider definition of “piled rafts” where “load sharing” between piles and raft has become as important as limiting settlements. Several methods of analysis of piled raft foundations have also been introduced by several authors, but it appears that predicting foundation behaviour is still an area worth to study. It should be pointed out that the behaviour of piled raft foundations differs significantly from that of a single pile and from that of group of piles. The ultimate shaft friction developed by piles within a piled raft can be significantly greater than that for a single pile or a pile in a group of piles. When piles are driven into sand, the soil adjacent to piles is compacted to a distance of a 3 to 6 pile diameters. The ultimate bearing capacity increases by the compaction of the soil between the piles in sand and gravel. The ultimate shaft load of a goup of piles driven in sand or stiff clay may be larger than the sum of individual piles carrying the same load per pile (Vesic, 1981). Such findings have led to the introduction of ‘equivalent raft method’ for pile groups. In this method the load of a group of friction piles is usually assumed to be acting on the soil at an effective depth (equivalent raft) of two-thirds of the pile embedment in the bearing stratum, while for a group of end bearing piles the equivalent raft is taken at the elevation of the pile points. Various methods of analysis of piled raft foundations exist where the piles are considered primarily as friction piles, rather than end bearing piles. As with any foundation system, a design of a piled raft foundation required the consideration of a number of issues, including: - ultimate load capacity for vertical, lateral and moments loadings, - value of the maximum settlement, - value of the maximum differential settlement, - raft moments and shears for the structural design of the raft, - pile loads and moments for the structural design of the piles (Poulos, 2001). The first step in the analysis is to determine the dimensions of the piled raft system to satisfy structural requirements. The deformation properties of the soil beneath the pile group in homogeneous sand deposit not underlain by more compressible soil at greater depth can be made directly from the results of soil tests. In the proposed method, settlements of the raft and the pile group are separately calculated, employing the classical formula. The first consideration in calculating the magnitude of settlements is the distribution of effective vertical pressure beneath the equivalent raft. In case of deep compressible soils the lowest level considered in the settlement analysis is the point where the vertical stress is not more than 20 per cent of the overburden. The length of piles is then determined by considering that the stress at the equivalent raft level is equal or smaller than 20 per cent of the effective overburden stress. In the proposed method, it is assumed that the structural loads will be carried by piles and the raft in a shared basis. Settlements of piles and raft are calculated for various load sharing ratios, separately. Firstly it is considered that load is carried by the raft only (Qpiles/Qtotal=0). Then it is considered that the load is carried by the pile group only (Qpiles/Qtotal=1). Calculation is continued for various load sharing ratios. And a diagram showing the load sharing between piles and raft is drawn and the ratio which represents the same amount of settlement both for the raft and pile group is determined.. To illustrate the method by the approach outlined above, two examples are given. The examples are also calculated by a computer analysis and the results are compared with those obtained by the proposed method.