Lecture15-Analysis-of-Single-Piles

Lecture15-Analysis-of-Single-Piles - Introduction Piles are...

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Unformatted text preview: Introduction: Piles are mostly used to transfer a load that cannot be adequately supported at shallow depths to a depth where adequate support becomes available. When piles are installed in a deep stratum of limited supporting ability and these piles develop their carrying capacity by friction on the sides of the pile, they are called friction piles ( Figure 1a). When piles by pass weak soil strata and transfer all their load via their tip into a stratum of good bearing capacity, they are called bearing piles (Figure 1b). Many times the load-carrying capacity of piles results from a combination of points resistance and skin friction. The load taken by a single pile can be determined by a static load test. The allowable load is obtained by applying a factor of safety to the failure load. Although it is expensive, a static load test is the only reliable means of determining allowable load on a friction pile. Some piles are used to carry lateral loads, such as marine bulkheads, bridge abutments, etc. These piles are lateral bearing piles (Figure 1c). Different uses of piles: (a) bearing pile, (b) friction pile, (c) piles under uplift . (d) piles under lateral loads, (e) batter piles under lateral loads. Transfer of Load. The way that the load from a column transfers into the soil through the pile has evolved during the past fifty years, from Terzaghi at the extreme left figure, Prieto (1978) on the extreme right, and on going research. PRIETO Tension piles are used to resist moment in tall structures and upward forces , and in structures subject to uplift, such as building with basements below the groundwater level, or buried tanks. For piles under tension both in sands and clays, the bearing capacity at the tip is lost. For piles of uniform diameter in sands, the ultimate uplift capacity is made up of the shaft resistance and the weight of the pile. Laterally loaded piles support loads applied on an angle with the axis of the pile in foundations subject to horizontal forces such as retaining structures (Figure 1d and e). If the piles are installed at an angle with the vertical, these are called batter piles (Figure 1e). Dynamic load may act on piles during earthquakes and under machine foundations. During pile driving, the resistance to penetration is a dynamic resistance. When a pile foundation is loaded by a building, the resistance to penetration is a static resistance. Both the dynamic resistance and the static resistance are generally composed of point resistance and skin friction. However in some soils, the magnitudes of the dynamic and static resistance may not be quite similar. In spite of this difference, frequent use is made of estimates of dynamic resistance by dynamic formulas and the wave equation for the load capacity of the pile. Therefore, we also describe an understanding soil action during loading. Group Action of Piles....
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Lecture15-Analysis-of-Single-Piles - Introduction Piles are...

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