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PILE FOUNDATIONS. TOPICS. Introduction Type of pile Estimating pile length Load transfer mechanism Pile capacity Mayerhof’s method for estimating Qp Vesic’s method for estimating Qp Coyle and Castello’s method for estimating Qp in sand. Correlation of calculating Qp with SPT
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TOPICS • Introduction • Type of pile • Estimating pile length • Load transfer mechanism • Pile capacity • Mayerhof’s method for estimating Qp • Vesic’s method for estimating Qp • Coyle and Castello’s method for estimating Qp in sand. • Correlation of calculating Qp with SPT • Frictional Resistance (Qs) in sand • Frictional Resistance in clay • Elastic settlement of piles • Negative skin friction
Introduction Why we need piles. Upper soil layers are highly compressible and too weak to support the load transmitted by the superstructure Bedrock is not encountered at a reasonable depth below the ground surface Foundation subjected to horizontal forces piles are extended beyond the active zone, which is where swelling and shrinking occur. Foundation for structure that subjected to uplifting forces. Bridge abutments and piers are usually constructed over pile foundations to avoid the loss of bearing capacity
Type of Piles • Steel Piles • Concrete piles • Timber piles • Composite piles
Type of Piles Steel Piles • Normally H and I-section • Steel piles are spliced by welding or by riveting • Steel piles can be fitted with driving points or shoes • Steel piles may be subject to corrosion. Additional thickness need to off-set the effect of corrosion. • Usual length: 15 m to 60 m • Usual load: 300 kN to 1200 kN
Type of Piles Concrete Piles • Can be divided into two type; precest pile and cast-in-situ pile Precast Pile • prepared by using ordinary reinforcement, and they can be square or octagonal in cross section • Usual length: 10 m to 15 m • Usual load: 300 kN to 3000 kN
Type of Piles Concrete Piles • Can be divided into two type; precest pile and cast-in-situ pile Cast-in-situ pile • built by making a hole in the ground and then filling it with concrete. • divided into two broad categories: (a) cased and (b) uncased Cased pile Un-cased pile
Type of Piles Timber piles • The maximum length of most timber piles is 10 to 20 m • Timber piles cannot withstand hard driving stress • if splicing is necessary, it can be done by using pipe sleeves • Timber piles can stay undamaged indefinitely if they are surrounded by saturated soil. However, in a marine environment, timber piles are subject to attack by various organisms and can be damaged extensively in a few months. • The life of the piles may be increased by treating them with preservatives
Type of Piles Composite piles • The upper and lower portions of composite piles are made of different materials • The upper and lower portions of composite piles are made of different materials • Forming proper joints between two dissimilar materials is difficult, and for that reason, composite piles are not widely used.
Estimating Pile Length Under certain circumstances, piles are driven in granular soils to achieve proper compaction of soil close to the ground surface. These piles are called compaction piles.
Frictional Resistance (Qs) in sand For high displacement driven pile For low displacement driven pile
