Because it is loaded axially rather than in bending. H-piles are proportioned with flange and web of comparable thickness and an approximately square overall shape, giving similar capacity about both axes and a robust section that resists damage under hard driving. A beam concentrates material in its flanges for bending about one axis, which would be inefficient and vulnerable when driven.

That driving the pile pushes very little soil aside, because the steel occupies only a small fraction of the plan area it passes through. Ground heave, lateral ground movement and pore pressure build-up are therefore small. That allows piling close to existing foundations, buried services, slopes and retaining structures with far less risk of damaging them than a large displacement pile would carry.

Because the small cross-sectional area concentrates the hammer energy on a small toe area and displaces little material, so penetration resistance is lower than for a solid or closed section of equivalent capacity. That lets H-piles pass through dense sands and gravels, and through made ground, to reach a deeper bearing stratum where other pile types would refuse.

A hardened fabricated point welded to the pile toe to protect it and to help it seat when driving onto rock. Without one, a bare H-section toe can be damaged, or can skid on a sloping rock surface rather than biting into it, leaving the pile out of position or inadequately founded. Rock shoes are specified where rock is expected to be hard, sloping or irregular.

By full-strength welded splices using plates across the flanges and web, or by proprietary mechanical connectors that speed the operation and require no welding on site. Splicing is a normal part of driven piling and allows the final pile length to follow the actual ground rather than a predicted depth, which avoids both ordering excess length and running short.

Yes, and this is exploited in combined walls, where heavy H sections act as king piles taking both the vertical load and the bending from retained soil, with lighter sheet piles spanning between them. In that role the section is selected on its bending capacity about the relevant axis as well as on axial capacity, which is a different calculation from a plain foundation pile.

Very little where the pile is entirely within undisturbed natural soil, since oxygen availability is minimal and corrosion effectively ceases. Made ground, contaminated fill, water and the tidal and splash zones require explicit provision, whether as sacrificial thickness, coating or concrete encasement. The exposed length above ground or water is treated like any other exposed structural steelwork.