Wave impact on shore structures: Which actions can be induced on a seawall or pier when a wave strikes and recedes?

Introduction:
Coastal and harbor structures experience complex dynamic loading from waves. Recognizing the different components of wave-structure interaction is crucial for safe design against sliding, overturning, uplift, and local damage.

Given Data / Assumptions:

• Incident waves with horizontal and vertical momentum components.
• Structures such as seawalls, quay walls, and pier piles.
• Breaking/impact, run-up, overtopping, and backwash phases are possible.

Concept / Approach:
Upon impact, the wave's horizontal momentum generates direct compressive (normal) pressure. Deflection and run-up can impart vertical components, causing shear along surfaces and connections. Breaking waves generate impulsive pressures (slamming). As water recedes, partial vacuum and momentum reversal can induce suction (negative pressure) that tends to pull water away from the structure and uplift elements like slabs or armor units.

Step-by-Step Solution:
Identify horizontal impact → compressive (normal) force on faces.Recognize vertical deflection → shear components along interfaces.Consider breaking-induced collapse → transient high compressive impulses.During backwash → suction/uplift actions due to pressure drop and returning flow.Therefore, all listed effects can occur; choose the comprehensive option.

Verification / Alternative check:
Model tests and field observations confirm impulsive slamming pressures and uplift during backwash, which are included in modern design guidelines.

Why Other Options Are Wrong:
a–d each represents a real effect; none alone is sufficient. The combination reflects real loading envelopes.

Common Pitfalls:
Designing for mean hydrostatic pressure only; neglecting transient impact and suction can lead to unsafe structures.

Final Answer:
All of the above.