| 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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