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IS 10972:1984 is the Indian Standard (BIS) for design and construction of rubblemound structures. 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.
Overview
Status
Current
Usage level
Specialized
Domain
Structural Engineering — Coastal and Marine Engineering
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
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.
The Rock Manual: The use of rock in hydraulic engineering (2nd edition)
Comprehensive guide for design of rubblemound structures, covering armour stability, filters, and construction.
EM 1110-2-1100US Army Corps of Engineers (USACE), USA
HighCurrent
Coastal Engineering Manual (CEM)
Definitive US guide for coastal structures; Part VI-5 specifically addresses rubble-mound structure design.
BS 6349-7:1991British Standards Institution (BSI), UK
HighWithdrawn
Maritime structures. Guide to the design and construction of breakwaters
Directly addresses the design and construction of breakwaters, a key type of rubblemound structure.
PIANC MarCom WG 040 (2003)PIANC (The World Association for Waterborne Transport Infrastructure), International
MediumCurrent
State of the art of sit-on breakwater design
Provides expert guidance and state-of-the-art review on breakwater design, influencing code development.
Key Differences
≠The IS code exclusively uses the Hudson formula for armour stone stability, which primarily depends on wave height. Modern standards like the Rock Manual and CEM prioritize the Van der Meer formulae, which are more advanced and account for wave period, storm duration, and structure permeability.
≠IS 10972 provides simple rules of thumb for crest freeboard to limit overtopping. International standards use detailed empirical formulae (e.g., Owen's or Van der Meer's overtopping formulae) to predict mean overtopping discharge (q), allowing for a performance-based design where acceptable discharge levels are defined.
≠The concept of 'damage level' is not explicitly quantified in the IS code, which is based on a 'no-damage' criterion from the Hudson formula. Modern codes define damage (S or N) as a quantifiable parameter (e.g., number of displaced stones in a given area), allowing for more economical designs where limited, repairable damage is acceptable.
≠Modern international standards provide specific, more sophisticated formulae for the stability of the breakwater toe and roundhead sections, which experience different hydraulic loads. The IS code offers more generalized guidance for these elements.
Key Similarities
≈All standards are based on the same fundamental principle of a layered, trapezoidal structure (core, underlayers, and armour layer) designed to dissipate wave energy through its porosity and the stability of its outer layer.
≈The formula for calculating armour layer thickness is conceptually identical across all standards, typically expressed as `t = n * kΔ * D`, where 'n' is the number of layers, 'kΔ' is a layer coefficient, and 'D' is a characteristic dimension of the stone.
≈All codes recognize the critical importance of a properly designed filter system (underlayers) to prevent the smaller core material from being washed out through the voids of the larger armour stones, ensuring the structural integrity of the mound.
≈The use of a stability coefficient (like KD in the Hudson formula) is a common concept. This coefficient accounts for variables that are difficult to model purely analytically, such as stone shape (angular vs. rounded), placement method, and location on the structure (trunk vs. head).
Parameter Comparison
Parameter
IS Value
International
Source
Primary Armour Stability Formula
Hudson Formula: W ∝ H³ / (KD * (Sr-1)³)
Van der Meer Formulae: Hs/ΔDn50 = f(ξ, P, S, N). Accounts for wave period, permeability, and storm duration.
CIRIA C683 / USACE CEM
Crest Freeboard / Overtopping
Suggests a minimum freeboard (e.g., 0.1H to 0.2H above SWL) based on wave height.
Calculates mean overtopping discharge (q) using complex formulae, allowing design based on tolerable limits.
The Rock Manual (CIRIA C683)
Armour Layer Thickness (2 layers)
t = 2 * kΔ * (W/γr)^(1/3)
t = 2 * kΔ * Dn50. Conceptually identical, using nominal diameter instead of weight.
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).