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Steel-H Pile

Steel H-piles have been widely used because of their ease of handling and driving. A wide range of pile sizes is available, with different grades of steel. The maximum allowable axial load is about 3 000 kN.

Compared to concrete piles, they generally have better driving characteristics and can be installed to great depths. H-piles can be susceptible to deflection upon striking boulders, obstructions or an inclined rock surface. In areas underlain by very dense cohesive soil layers, heavy section H-piles with appropriate tip strengthening are commonly used to penetrate and to withstand hard driving.

Since steel H-piles do not cause large soil displacements, they are useful in urban areas or adjacent to structures where heave of the surrounding ground may cause problems. When large pile groups are to be driven at close spacing in granular soils, compaction may increase the driving resistance. Steel H-piles can be driving in large groups without the need of predrilling (a method commonly used for concrete piles) thereby also reducing the risk of excessive vibrations, which might cause settlement of adjacent buildings founded on sand.

H-piles may be strengthened by welding stiffening plates on to the pile toe, which facilitates punching through thin layers of rock or boulders.

A disadvantage of the H-section pile is the tendency to bend on the weak axis during driving. Thus if piles are driven to a large depths, a considerable curvature may result.

The low resistance to penetration of the H-section pile in loose sandy soils may be a disadvantage in circumstances where high shaft friction and end bearing resistance is required at an economical depth of penetration. Since little compaction of the sand is achieved around and beneath an H-section pile, the shaft friction can be relatively low: In such a case the pile may not achieve satisfactory resistance and may need to be driven to a dense sand stratum or other resistant layers.

A plug of clay, similar to that of the tube pile, may be formed within the flanges of H-section piles. For assessment of bearing capacity, it is important to check by calculation or load testing that there is adequate skin frictional resistance of the soil located within the flanges of the H-section pile. In the case of dense granular soils, which has been disturbed during pile driving, the skin friction (which can be mobilised on the interior of hollow piles or within H-section pile flanges) may not be sufficient to achieve the required shaft resistance, or base resistance (plug at the pile toe). Therefore, the base resistance of tube or box piles and H-section piles in granular soils or rocks is often calculated using only the net cross-sectional area of the steel. In granular soils the skin friction on hollow piles or H-section piles can be calculated along the entire steel surface, provided that this can be verified by measuring the length of soil plug after driving. The assumed internal skin friction must not exceed the plug weight where uplift loads need to be resisted.

Special types of steel H-section piles can be manufactured, which are welded or coupled together to increase their end bearing area or resistance to lateral loads. "Wing piles" consist of short lengths of steel H-section welded to the bottom of standard H-section piles. These "winged piles" are specifically designed to give a high-end resistance for a limited penetration into a bearing stratum of sand. However, the increase in pile resistance may not be in direct proportion to the increase in base area because of the reduction in skin friction along the shaft above the winged sections.

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