Cast iron piles: choose the most appropriate statement about their suitability and behavior

Introduction / Context:
Cast iron (C.I.) piles are hollow sections used historically and in specific modern applications where corrosion resistance and compressive strength are desired. Their material characteristics guide where they should—and should not—be used in piling works.

Given Data / Assumptions:

• Cast iron is strong in compression, relatively brittle in tension and under impact.
• Marine environments are corrosive to many metals.
• Piles may be required to resist vertical loads, lateral loads, and dynamic effects.

Concept / Approach:
C.I. exhibits good corrosion resistance in sea water, forming protective films. It carries compressive loads well but is brittle; therefore it is vulnerable to shock, vibration, and bending. Batter piles introduce significant bending/lateral actions, which are not ideal for brittle sections. The best-fit singular statement emphasizes suitability in sea water, while avoiding over-claiming resistance to shock or lateral action.

Step-by-Step Solution:
Match material property to environment: C.I. resists marine corrosion → suitable under sea water.Check dynamic/lateral performance: brittleness makes it poor against shock/vibration and batter action.Evaluate load capacity claim: while C.I. can carry considerable vertical compression, usage is governed by brittleness; the safest, universally true statement focuses on marine suitability.Select the statement highlighting sea-water suitability.

Verification / Alternative check:
Practice notes caution against using C.I. where impact driving shocks are high or lateral/batter actions dominate, but document long service in marine piles where compressive actions are predominant.

Why Other Options Are Wrong:
Resist shocks/vibrations: Incorrect; brittleness limits shock resistance.Suitable as batter piles: Incorrect; bending/lateral demands are unfavorable.Only very light vertical loads: Unduly conservative; they can carry significant compression, but design must prevent impact/bending.Never below water level: Opposite of reality; corrosion resistance is a key advantage.

Common Pitfalls:
Assuming all metals behave ductilely under impact; overlooking the difference between compressive strength and toughness.

Final Answer:
They are suitable for works under sea water due to good corrosion resistance.