05-12-2012, 01:31 PM
PILE FOUNDATION
PILE FOUNDATION.pptx (Size: 451.77 KB / Downloads: 399)
DEFINITION
Pile foundation is a deep foundation used to transfer the loading to a deeper, more competent strata at depth if unsuitable soils are present near the surface. This is usually done when depth >3 m below finished ground level.
In pile foundation, piles of different material in different manner are used.
Continued
Piles are relatively long , slender members that transmit foundation loads through soil strata of low bearing capacity to deeper soil or rock strata of high bearing capacity.
In addition to supporting structures , piles are used to anchor structures against uplift forces and to assist structures in resisting lateral and overturning forces.
NECESSITY OF PILE FOUNDATION
When the strata at or just below the ground surface is highly compressible and very weak to support the load transmitted by the structure.
Pile foundations are required for the transmission of structure loads through deep water to a firm stratum.
In case of expansive soil, such as black cotton soil, which swell or shrink as the water content changes, piles are used to transfer the load below the active zone.
LOADS APPLIED TO PILES
Combinations of vertical, horizontal and moment loading may be applied at the soil surface from the overlying structure.
For the majority of foundations the loads applied to the piles are primarily vertical.
For piles in jetties, foundations for bridge piers, tall chimneys, and offshore piled foundations the lateral resistance is an important consideration.
The analysis of piles subjected to lateral and moment loading is more complex than simple vertical loading because of the soil-structure interaction.
Pile installation will always cause change of adjacent soil properties, sometimes good, sometimes bad.
PILE LOAD TEST
Static pile load test is the most reliable means of determining the load capacity of a pile. The test procedure consists of applying static load to the pile in increments up to a designated level of load and recording the vertical deflection of the pile. The load is usually transmitted by means of a hydraulic jack placed between the top of the pile and a beam supported by two or more reaction piles. The vertical deflection of the top of the pile is usually measured by mechanical gauges attached to a beam, which span over the test pile.