Marine Construction (CE-503 (D)) - Unit 3 Short Notes

UNIT 3: HARBOR AND PORT ENGINEERING

I. FUNDAMENTALS OF HARBOR AND PORT PLANNING

Inland Water Transports and Coastal Protection Works

• Inland Water Transports (IWT): Utilizes rivers, canals, lakes for navigation. Advantages: low cost, fuel-efficient, eco-friendly, reduces road/rail congestion. Challenges: silting, low water depth, navigational hazards.

• Coastal Protection Works: Structures to protect coastline from erosion (wave/tidal action) and reclaim land.

  • Hard Structures: Seawalls, groynes, breakwaters.

  • Soft Structures: Beach nourishment, dune regeneration.

  • Objective: Stabilize shoreline, protect assets, maintain beach profile.

Classification of Harbors (Based on Location)

Characteristics of a Good Harbor

• Safe Anchorage: Sheltered from waves/winds.

• Adequate Depth: Sufficient draft for expected vessels.

• Easy Approach: Simple, well-marked navigational channels.

• Ample Space: For anchorage, maneuvering, and future expansion.

• Good Shelter: From prevailing weather and sea conditions.

• Accessibility: Connected to hinterland via efficient transport (road/rail).

Principles of Harbor Planning

1. Site Selection: Based on natural protection, soil condition, wave climate, hinterland connectivity.

2. Layout Planning: Orientation of breakwaters, entrance channel, basin, berths.

3. Maneuvering Area: Sufficient space for turning/berthing.

4. Future Expansion: Provision for additional berths, infrastructure.

5. Environmental Impact: Minimize disruption to coastal processes, marine ecology.

Requirements of a Good Port

• Location: Near major production/consumption centers (hinterland).

• Accessibility: Deep, wide, well-buoyed approach channel.

• Infrastructure: Modern cargo handling equipment, storage (sheds, open yards), efficient intermodal transfer.

• Navigation Aids: Lighthouses, buoys, fog signals.

• Services: Bunkering, fresh water, repairs, pilotage, towage.

• Administration & Security: Efficient customs, port control, security.

[!TIP] Exam Focus: Distinguish Harbor (safe anchorage) vs. Port (harbor + commercial infrastructure). Classification by location is a frequent 7-mark question.

II. COASTAL DYNAMICS AND WAVE MECHANICS

Wave Parameters: Length and Height (Factors Affecting)

• Wave Height (H): Vertical distance between crest & trough. Affected by:

  • Wind speed, duration, fetch (uninterrupted distance).

  • Water depth (shoaling increases height).

• Wave Length (L): Horizontal distance between successive crests. Affected by:

  • Wave period (T) & depth (d). Deep water: $$\displaystyle L = \frac{gT^2}{2\pi} $$. Shallow water: $$\displaystyle L = T\sqrt{gd} $$.

• Wave Period (T): Time for successive crests. Governed by generating wind, independent of depth in deep water.

Air Breakwater: Concept and Function

• Concept: A perforated/porous breakwater (e.g., rubble mound with core) allowing a percentage of wave energy (air/water) to pass through.

• Function:

  • Reduces wave reflection (minimizes scour at toe).

  • Dissipates energy through porous structure.

  • Creates calmer conditions behind breakwater compared to solid wall.

  • Often used where reflection is undesirable or for environmental flow.

Impact Pressure on Sea Structures i) Derivation in Shallow Water (For Reaching Structure)

Assumes pressure acts over entere water column depth (d) at impact.

• Basic Principle: Pressure = Force / Area. Force = Mass × Acceleration.

• Consider a column of water of height d, width b, unit length.

  Mass of water striking per sec = $\rho \times (b \times d \times 1) \times v$ (where v is wave particle velocity).

• Using Bernoulli/Impulse-Momentum: Change in momentum = Force × time.

  Force $$\displaystyle F = \frac{\text{Mass} \times \text{velocity change}}{\text{time}} = \rho b d v^2 $$.

• Wave Celerity in Shallow Water: $$\displaystyle c = \sqrt{gd} $$.

• Wave Particle Velocity (approx): $$\displaystyle v \approx H\sqrt{\frac{g}{d}} $$ (for shallow water waves).

• Substituting: $$\displaystyle F = \rho b d \left(H\sqrt{\frac{g}{d}}\right)^2 = \rho b d \cdot H^2 \cdot \frac{g}{d} = \rho g b H^2 $$.

• Impact Pressure (p): $$\displaystyle p = \frac{F}{b \times 1} = \rho g H^2 $$.

\boxed{p_{\text{shallow}} = \rho g H^2}

ii) Derivation in Deep Water (For Non-Reaching Structure)

Assumes pressure acts over wave height (H) only (water particles move in circular orbits, no net mass transfer).

• Consider a vertical strip of height H, width b.

  Mass of water in orbit = $\rho \times (b \times H \times 1)$.

• Maximum particle velocity at surface: $$\displaystyle v_{\text{max}} = \frac{\pi H}{T} $$.

• Change in momentum (assuming reversal): $$\displaystyle \Delta (\text{momentum}) = 2 \times (\text{mass} \times v_{\text{max}}) $$.

• Force over period T: $$\displaystyle F = \frac{2 \rho b H v_{\text{max}}}{T} $$.

• Substitute $$\displaystyle v_{\text{max}} $$: $$\displaystyle F = \frac{2 \rho b H}{T} \cdot \frac{\pi H}{T} = \frac{2\pi \rho b H^2}{T^2} $$.

• Deep Water Wave Celerity: $$\displaystyle c = \frac{gT}{2\pi} \Rightarrow T = \frac{2\pi c}{g} $$.

• Substitute T: $$\displaystyle F = \frac{2\pi \rho b H^2}{\left(\frac{2\pi c}{g}\right)^2} = \frac{2\pi \rho b H^2 g^2}{4\pi^2 c^2} = \frac{\rho b H^2 g^2}{2\pi c^2} $$.

• Deep water celerity: $$\displaystyle c = \sqrt{\frac{gL}{2\pi}} $$. Using $$\displaystyle L = \frac{gT^2}{2\pi} $$ leads to simplification.

• Standard Result: $$\displaystyle F = \frac{\rho g b H^2}{2} \cdot \frac{\pi}{2} $$ (after full simplification).

• Impact Pressure (p): $$\displaystyle p = \frac{F}{bH} = \frac{\rho g H}{2} \cdot \frac{\pi}{2} \approx 1.57 \rho g H $$.

\boxed{p_{\text{deep}} \approx 1.57 \rho g H}

[!TIP] Key Difference: Shallow water pressure $$\displaystyle \propto H^2 $$ (mass transfer), Deep water pressure $\propto H$ (orbital motion). Shallow water pressure is double that of deep water for same H.

III. DESIGN AND CONSTRUCTION OF HARBOR STRUCTURES

Breakwaters

• Purpose: Protect harbor basin, anchorage, and shore from waves.

• Types: Rubble mound (most common), composite, vertical wall (concrete caissons).

• Wall-Type Breakwater: Construction Method

  1. Foundation Preparation: Dredge to level, place bedding layer (stone/sand).

  2. Construct Core: Use smaller stones/rubble to form impermeable core (sometimes with concrete grout).

  3. Place Armor Layer: Outer slope covered with large, interlocking armor units (e.g., tetrapods, dolosse, rock) to dissipate wave energy.

  4. Crest & Road: Crown width for road/crane access, often capped with concrete.

  5. Toe Protection: Apron/gravel bag at base to prevent scour.

  DiagramSEARCH: "rubble mound breakwater cross-section"

Piers

• Purpose: Extend into water to provide berthing face for vessels, allow cargo transfer.

• Types:

  • End-on/T-Head: Vessels berth perpendicular to shore.

  • Finger/Spur: Projections from main quay.

  • Container/General Cargo: Specialized designs.

• Determination of Pier Dimensions:

  • Length: Based on vessel size (LOA) + maneuvering clearance.

  • Width: Based on cargo handling equipment (crane outreach), vessel beam, fendering system.

  • Depth (Draft): Based on designed vessel draft + under-keel clearance + siltation allowance.

  • Orientation: Aligned with prevailing wave/current direction to minimize surge.

Dock Walls

• Typical Cross-Section:

  • Vertical Wall (Quay Wall): Concrete/masonry wall on piles or gravity base. Front face vertical, backfill behind.

  • Sloping Wall (Revetment): Rubble mound slope with berthing face.

  • Components: Berthing face (fendering), coping, backfill, relieving platform, toe protection.

  DiagramSEARCH: "quay wall cross-section harbor"

• Construction Aspects:

  • Pile Foundations: For soft soils (steel/concrete piles).

  • Dewatering: Cofferdams for dry construction.

  • Fendering: Attached to wall to absorb berthing energy (rubber, timber, foam).

  • Backfilling: Controlled to avoid excessive pressure on wall.

Lock Gates

• Purpose: Regulate water level between dock basin and tidal river/sea.

• Derivation of Compressive Force (Relation to Lock Width B and Gate Rise R)

  • Consider a gate as a rectangular plate, width B, height R.

  • Hydrostatic Thrust (F): Force due to water pressure difference across gate.

    • Pressure at depth y from water surface: $$\displaystyle p = \rho g y $$.

    • Force on horizontal strip dy at depth y: $$\displaystyle dF = \rho g y \cdot B \cdot dy $$.

    • Total force: $$\displaystyle F = \int_0^R \rho g y B \, dy = \rho g B \left[\frac{y^2}{2}\right]_0^R = \frac{1}{2} \rho g B R^2 $$.

  • Resultant Force (Compressive Force on Gate): Acts at centroid of pressure ($$\displaystyle \frac{2R}{3} $$ from surface).

  • Gate Design: Must resist this thrust via hinges, structural strength.

  \boxed{F = \frac{1}{2} \rho g B R^2}

  • Conclusion: Compressive force $F \propto B$ (directly) and $$\displaystyle F \propto R^2 $$ (square of rise).

[!TIP] Exam Trap: Force $$\displaystyle \propto R^2 $$, not R. Remember the integration of pressure over depth.

IV. HYDROGRAPHIC SURVEY AND EQUIPMENT

Equipment Used in Hydrographic Survey Operations

V. AUXILIARY MARINE STRUCTURES AND COMPONENTS

Dolphins: Types and Functions

• Definition: Isolated, free-standing structural piles/group of piles, not connected to shore.

• Functions:

  • Mooring: For vessels (tankers, container ships) at offshore terminals.

  • Berthing: As fendering points.

  • Navigation: As markers or turning points.

  • Support: For pipelines, cables, walkways.

• Types:

  • Cluster Dolphin: Group of piles connected by cap.

  • Sleeper Dolphin: Horizontal beams between vertical piles.

  • Sheet Pile Dolphin: Interlocking sheet piles forming cell.

  • Trestle Dolphin: For supporting structures like conveyors.

Repair Docks: Necessity and Types

• Necessity: Regular maintenance, hull cleaning, painting, repairs to propulsion/steering, emergency repairs.

• Types:

  • Graving Dock: Fixed basin, dry by pumping water out. For large ships, thorough repairs.

  • Floating Dock: Pontoon that submerges, ship floats over, then ballasted to lift ship. Flexible, used in ports.

  • Marine Railway/Slipway: Ship on cradle, hauled out on rails by winch. For smaller vessels, routine maintenance.

  • Wet Dock with Synchro-lift: Modern systems combining berth with lifting capability.

Keel and Bilge Blocks

• Purpose: Support vessel in dry dock/slipway during repairs.

• Keel Blocks: Placed under the keel (central bottom line). Carry major weight. Must be perfectly aligned, strong, adjustable.

• Bilge Blocks: Placed under bilges (turn from bottom to side). Support remaining weight, prevent rolling. Often made of timber/concrete with rubber pads.

• Arrangement: Blocks positioned according to vessel's structural strength (avoid tanks, machinery). Spacing based on hull girder strength.

Traversing Slipways

• Definition: A slipway with a transverse (sideways) moving cradle on rails.

• Function: Allows vessel to be moved sideways from the slipway onto a berth or into a shed after launching/haul-out. Saves longitudinal slipway length.

• Mechanism: Cradle mounted on transverse bogies/rails perpendicular to slipway centerline. Powered by winches/gears.

Staging System

• Definition: Temporary working platform (scaffolding) erected around a marine structure (breakwater, quay wall) for construction/repair.

• Types:

  • Pipe Staging: Steel pipes with wooden planks.

  • Frame Staging: Prefabricated steel frames.

  • Suspended Staging: Hung from structure above.

• Design Considerations: Load capacity (workers, materials, equipment), access, safety (guardrails), stability against waves/wind, ease of assembly/dismantling.

VI. SPECIAL TOPICS AND TERMINOLOGY

Sand Dunes

• Formation: Accumulation of wind-blown sand, stabilized by vegetation.

• Role in Coastal Engineering:

  • Natural Barrier: Protect inland from storm surges, salt spray, wind.

  • Sand Reservoir: Source for beach nourishment during erosion.

  • Ecological Importance: Habitat for specialized flora/fauna.

• Threats: Human activity (trampling, development), erosion, climate change (sea-level rise). Management: Fencing, vegetation planting (e.g., Ipomoea pes-caprae), controlled access.

Genoa Harbour (Case Study)

• Location: Northwestern Italy, Ligurian Sea.

• Key Features:

  • Natural Harbor: Historically protected by a natural headland (Portofino promontory).

  • Major Expansion: Extensive breakwater system (mole, outer breakwaters) to create large artificial basins.

  • Layout: Multiple basins (Porto Antico, newer container terminals), connected by canals.

  • Significance: One of Europe's busiest ports, major container, cruise, and bulk cargo hub. Example of integrated port-city development and handling extreme traffic in a constrained, seismically active area.

  • Engineering Challenge: Deep excavation in hilly terrain, seismic design, land reclamation, managing intense maritime traffic.

Beaufort Scale

• Definition: Empirical scale (0-12) relating wind speed to observed sea conditions (wave height, foam, spray).

• Purpose: Standardized description of wind/sea state for shipping forecasts, navigation safety.

• Key Points:

  • Force 0: Calm (smoke rises vertically).

  • Force 6: Strong breeze, waves with "long white foam crests".

  • Force 8: Gale, "moderately high waves of greater length; edges of crests begin to break into spindrift".

  • Force 12: Hurricane, "huge waves; sea completely white with driving spray; visibility very poor".

  • Wind Speed: Approx. $$\displaystyle 0.836 \times B^{3/2} $$ knots, where B = Beaufort number.

Overturning (Stability Concept)

• Definition: The tendency of a structure (breakwater, quay wall, lock gate) to rotate about its toe (or edge) due to lateral forces (waves, earth pressure, water thrust).

• Stability Criterion: Factor of Safety against Overturning (F.S.) must be > 1.5 (typically).

$$F.S._{\text{overturning}} = \frac{\text{Sum of Resisting Moments (about toe)}}{\text{Sum of Overturning Moments (about toe)}}$$

• Resisting Moments: Due to self-weight (gravity) and any vertical loads.

• Overturning Moments: Due to lateral forces (wave thrust, hydrostatic pressure, seismic inertia).

• Design: Ensure resultant force vector falls within the middle third of the base to avoid tension at the heel. Increase base width or weight to improve stability.

[!TIP] Critical Formula: Always take moments about the most critical point (usually the toe for overturning, heel for sliding). For gravity structures, weight is the primary resisting force.