Negatif çevre sürtünmesinin kazık taşıma gücüne etkileri
Negative skin friction effects on pile bearing capacity
- Tez No: 83072
- Danışmanlar: PROF. DR. REMZİ ÜLKER
- Tez Türü: Yüksek Lisans
- Konular: İnşaat Mühendisliği, Civil Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1999
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: İnşaat Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 94
Özet
negatif çevre sürtünmesinin kazık taşıma gücüne etkileri ÖZET Kazıklı temeller, konsolidasyonunu tamamlamamış ya da üzerine dolgu gelen sıkışabilen zeminler boyunca inşa edildiklerinde, negatif çevre sürtünmesi olarak tanımlanan, taşımak zorunda oldukları ilave bir yüke maruz kalırlar. Bu yük bazen kazığın taşıması öngörülen servis yükü kadar olabilir. Bu çalışmada, izmir Çevreyolu - Aydın Otoyolu projesinin bir parçası olan Çiğli şantiyesinde, viyadük ayaklarının oturacağı zeminin negatif çevre sürtünmesi değerini saptamak için gerçekleştirilen negatif kazık yükleme deneyi sonuçlan ile araştırmacıların önerdikleri metotlarla hesaplanan değerler karşılaştırılacak, ayrıca negatif sürtünmeyi oluşturan etkenler, negatif sürtünmenin kazık boyunca dağılımı ve bu etkiyi azaltmak için kullanılan yöntemlerden söz edilecektir. xı
Özet (Çeviri)
NEGATIVE SKIN FRICTION EFFECTS ON PILE BEARING CAPACITY SUMMARY This study deals with negative skin friction which is a serious problem for piles installed through a soft layer or a fill overlying a soft layer. Negative skin friction is due to the relative pile ground displacement. It is an additional load that the pile must carry whilst positive friction is a supporting force. Ground settlement and dewatering are two main factors causing negative skin friction. A value of 4-5 mm settlement for clays is enough to mobilise it. But for the sites completed their consolidation the problem is not seem serious. In addition of these, pile displacement time must to be considered in the design. Mostly the problem is the case of pile installed through the soft layer. But pile installed through a fill causes greater negative skin friction values. The reason that it makes is the high negative skin friction capacity of the non cohesive fill. Pile is even installed trough a fill overlying a soft layer or through a soft layer then the fill is set. In the case of soft soil overlying even a non compressible hard soil or compressible bearing layer negative skin friction occurs only through the soft layer. But for a pile driven through the soft soil underlying a fill it occurs through both two layers. The value of the negative skin friction changes with depth and so is not constant. In general it increases with depth but this is not a linear increment. Pile settlement neutralise pile ground displacement so after a certain depth the decrease begins. When the pile is loaded the increment seen at 1 or 2 meters below the ground surface is eliminated with elastic compression of the pile. xnNegative skin friction value neutralises at a point near the tip for a pile driven to non compressible tough rock layer since the ground settlement is not allowed. But for a compressible bearing stratum, it neutralises at an upper point. In the case of soft soil underlying a fill a more speed elimination can be expected since both two layers move down. The assumed point where negative skin friction is totally eliminated is called neutral point. Great values of negative skin friction occur when a pile is installed through a soft layer overlying a hard non compressible stratum. This event may also cause damage at pile tip. If the pile length exceeds 40-50 m floating (friction) piles must replace point bearing piles. Another solution to the problem is to drive separate protection piles around, an in some cases below the structure. In order to protect piles against negative skin friction several methods can be applied. But first thoughts are about pile structure. Enlarging pile diameter and tip dimensions, changing their lengths and constructing stepped piles are of this kind. Coatings are also used as precaution for driven piles. Asphalt applied with a thickness of 1mm for a steel and 2 mm for a concrete pile can reduce negative skin friction about 25% of the undrained shear strength. Damage occurring while driving is the main problem. This can be prevented by enlarged pile points, precoring or predrilling. Bitumen is another choice for coating. It is used with bentonit slurry. Researchers taking into account pile spacement had succeed to reduce up to 90% negative skin friction value. But in order to not reducing end bearing capacity, at lower parts coating will not be applied. For silty clay and clayey silt, electro - osmosis method proposed by Bjerrum can also be used. A reduction value of 50% for negative skin friction is obtained. It's cost is very high and not applicable to all type of soils. X11IMany researchers has studied the subject and proposed several methods to calculate negative friction value. Bjerrum acclaimed that negative skin friction is not relevant with undrained shear strength of the clay. His equation considers an axial stress distribution that's why opposed by many scientists. Meyerhof defended that negative skin friction is relative to a parameter named J3 varying with depth and effective stress in piles driven to hard clays. Terzaghi and Peck acclaimed that negative skin friction depends on drained pile- ground adhesion, lateral earth pressure coefficient and effective vertical stress. In general form negative skin friction value can be estimated from equation a-Ks-tant))'. Ks.tan
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