What is the primary formula for armour stone stability?

The Hudson formula (W = (wr * H^3) / (Kd * (Sr - 1)^3 * cot α)) is the key empirical formula used to determine the required weight of armour units (Clause 6.2.1).

What are typical slopes for a rubblemound breakwater?

Slopes typically range from 1V:1.5H to 1V:3H, depending on wave exposure and armour unit size (Clause 6.2).

What is the minimum recommended specific gravity for armour stone?

The code recommends a minimum specific gravity of 2.6 for armour stone to ensure stability against wave forces (Clause 7.2.1).

How is the stability coefficient (Kd) selected?

Kd is selected from Table 1 based on the type of armour unit, its shape, and its location on the structure (trunk or head).

IS 10972

: 1984

Code of Practice for Design and Construction of Rubblemound Structures

CurrentSpecializedCode of PracticeBIMStructural Engineering · Coastal and Marine Engineering

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This standard provides guidelines for the design and construction of rubblemound structures like breakwaters, jetties, and seawalls. It covers hydraulic design, stability analysis using the Hudson formula, material specifications for armour stone, and construction procedures.

Covers the design and construction aspects of rubblemound structures, including material specifications and construction methods.

Quick Reference Values

Typical stability coefficient (Kd) for rough angular quarrystone (trunk, 2 layers)4.0

Typical stability coefficient (Kd) for rough angular quarrystone (head, 2 layers)3.5

Minimum specific gravity of armour stone2.6

Assumed porosity (n) for armour layer0.40

Typical structure slope (V:H)1:1.5 to 1:3

Typical thickness of armour layer (k t * (W/w r)^(1/3)) where k t is1.04

Key Formulas

Hudson Formula for Armour Unit Weight: W = (wr * H^3) / (Kd * (Sr - 1)^3 * cot α)

Practical Notes

The stability coefficient (Kd) is a critical parameter; its selection requires careful judgment based on structure type, location (trunk vs. head), and armour unit shape.

While this code provides foundational principles, modern practice often supplements it with physical model testing and advanced numerical modeling for complex projects.

Proper design of filter layers and toe protection is crucial to prevent undermining and ensure long-term stability of the structure.