Marine Construction (CE-503 (D)) - Unit 5 Short Notes

UNIT 5: Marine Construction – Cost Estimation, Valuation, and Project Management

I. Marine Infrastructure Planning and Classification

A. Harbor Classification by Location

Harbors are classified based on geographical position and protection offered:

• Natural Harbor: Sheltered by natural landforms (e.g., Mumbai Harbor, Sydney Harbour).

• Artificial Harbor: Man-made with breakwaters/dikes (e.g., Visakhapatnam Port).

• River Harbor: Located on rivers, inland navigation (e.g., Kolkata Port on Hooghly).

• Canal Harbor: Connected to ship canals (e.g., Panama Canal).

• Commercial Harbor: Handles general cargo, passengers.

• Naval Harbor: Military use, fortified.

B. Characteristics of a Good Harbor

• Protected Waters: Natural/artificial shelter from waves/winds.

• Adequate Depth: Sufficient draft for vessels, minimal dredging.

• Easy Access: Approach channels with safe navigation.

• Ample Space: For berthing, cargo handling, anchorage.

• Good Soil Bearing Capacity: For structures.

• Proximity to Transport Links: Rail/road connectivity.

• Availability of Fresh Water & Fuel.

C. Principles of Harbor Planning

1. Location Selection: Based on topography, geology, wave climate.

2. Layout Design: Optimize berths, turning basins, approach channels.

3. Wave Protection: Breakwater alignment, length.

4. Dredging Strategy: Maintenance dredging volumes.

5. Future Expansion: Modular design for growth.

6. Environmental Impact: Minimize disruption to marine ecology.

D. Requirements of a Good Port

E. Inland Water Transport Systems

• Canals: Man-made waterways (e.g., Suez Canal).

• Rivers: Natural rivers with navigable depth (e.g., Ganga-Bhagirathi).

• Lakes & Reservoirs: Limited commercial use.

• Advantages: Low fuel cost, bulk cargo capacity, reduced road/rail congestion.

• Challenges: Silting, seasonal water level variation, slow speed.

F. Coastal Protection Works

• Groynes/Jetties: Trap sediment, prevent erosion.

• Seawalls: Vertical/sloping structures to reflect wave energy.

• Revetments: Sloped armor layers (riprap, tetrapods).

• Offshore Breakwaters: Reduce wave transmission to shore.

• Beach Nourishment: Sand replenishment.

II. Hydrographic Survey and Wave Mechanics

A. Equipment for Hydrographic Survey Operations

• Single-beam Echo Sounder: Depth measurement below transducer.

• Multibeam Echo Sounder: Wide swath bathymetry.

• Side Scan Sonar: Seabed imagery for objects/terrain.

• GPS/RTK: Positional accuracy.

• ADCP (Acoustic Doppler Current Profiler): Current velocity profiling.

• Tide Gauges: Water level monitoring.

• CTD (Conductivity-Temperature-Depth): Water column properties.

B. Sea Wave Characteristics

• Wave Length (L): Distance between successive crests.

$$L = \frac{g T^2}{2\pi} \tanh\left(\frac{2\pi d}{L}\right)$$

where $g$ = gravity, $T$ = period, $d$ = depth.

• Wave Height (H): Vertical distance crest-to-trough.

• Governing Factors:

  • Wind Speed & Duration: Primary energy source.

  • Fetch: Uninterrupted water distance.

  • Water Depth: Shallow water waves shorter, steeper.

  • Currents: Can amplify/dampen waves.

C. Beaufort Scale for Wind Force

D. Wave Impact Pressure on Sea Structures

[!TIP] Impact pressure is dynamic, higher than hydrostatic due to wave breaking/slamming.

1. Derivation in Shallow Water (Depth $$\displaystyle d < L/20 $$):

   • Wave breaks, air entrapment.

   • Max Impact Pressure:

$$P_{\text{max}} = k \gamma H$$

 where $k$ = impact coefficient (2–5 for vertical walls), $\gamma$ = unit weight of water, $H$ = wave height.

• Assumes instantaneous momentum transfer.

2. Derivation in Deep Water (Depth $$\displaystyle d > L/2 $$):

   • Non-breaking waves, pressure oscillatory.

   • Linear Wave Theory (Airy):

$$P = \frac{\rho g H}{2} \cdot \frac{1}{\cosh\left(\frac{2\pi d}{L}\right)}$$

 at bed; reduces with depth.

• For vertical wall: $$\displaystyle P_{\text{max}} = \gamma H $$ (non-breaking).

E. Air Breakwater Concept and Application

• Concept: Floating breakwater with air-filled chambers (e.g., HDPE tubes) that dissipate wave energy via mass-spring-damper system.

• Application:

  • Small craft harbors, marinas.

  • Temporary protection during construction.

  • Environmentally friendly (minimal seabed disruption).

• Limitation: Effective only for short-period waves (< 4 s).

III. Marine Structures: Design and Construction Methods

A. Breakwaters

1. Wall Type Breakwater Construction Method:

   • Foundation: Prepared by dredging, rubble mound or piles.

   • Vertical Wall: Concrete caissons or blockwork on prepared base.

   • Construction Sequence:

     1. Place foundation layer (grouted rubble).

     2. Lower precast concrete units/caissons (by barge).

     3. Backfill with rock armor (attached to seaward side).

     4. Capping with concrete for stability.

   • Key: Ensure interlocking of armor units (e.g., Xbloc, Accropode).

2. Impact Pressure Considerations:

   • Wall Slopes: Vertical walls suffer higher impact; sloping (1:1.5) reduces force.

   • Wave Reflection: Can increase local scour; use porous structures.

   • Air Entrainment: Design for pressure relief holes in concrete.

B. Docks and Lock Gates

1. Dock Wall Cross-Section and Construction Aspects:

   • Typical Section:

     • Front Wall: Vertical/sloping, reinforced concrete.

     • Backfill: Granular material with drainage.

     • Dolphins: For vessel mooring.

     • Fendering System: Rubber/wood fenders.

   • Construction: Cofferdam method or open dredging with sheet piles.

2. Lock Gate Design and Compressive Force Derivation:

   • Gate Type: Mitre gates (common), sliding gates.

   • Hydrostatic Force on Gate:

     • Pressure varies linearly with depth: $$\displaystyle p = \gamma h $$.

     • Total Force per unit width:

$$F = \int_0^h \gamma y \, dy = \frac{1}{2} \gamma h^2$$

 - For gate width $b$, total force $$\displaystyle F_{\text{total}} = \frac{1}{2} \gamma h^2 b $$.

 - **Compressive Force** at hinge: Depends on gate angle; mitre gates transfer force to abutments.

3. Repair Docks and Staging Systems:

   • Dry Dock: Graving dock, syncrolift, floating dock.

   • Staging: Temporary platforms for hull access; modular steel frames.

C. Piers and Dolphins

1. Purpose and Dimensioning of Piers:

   • Purpose: Berthing for vessels, cargo handling, passenger terminals.

   • Dimensioning:

     • Length: Based on vessel size + safety margins.

     • Width: Determined by cargo equipment, roadways.

     • Depth: Matching dredged basin depth + overdraft.

2. Types and Applications of Dolphins:

   • Single Dolphin: Isolated pile cluster for mooring.

   • Cluster Dolphin: Multiple piles for large vessels.

   • Breasting Dolphin: Protects pier from vessel impact.

   • Materials: Reinforced concrete, steel piles.

D. Ancillary Marine Structures

1. Culverts: Construction Methods and Techniques:

   • Types: Box culvert, pipe culvert (HDPE, RCC).

   • Method:

     • Cofferdam installation for underwater sections.

     • Precast segments or cast-in-situ.

     • Waterproofing with membranes.

2. Drainage and Electrification Systems in Marine Facilities:

   • Drainage: Gravity-fed with sump pumps; oily water separators.

   • Electrification: Submarine cables in ducts; explosion-proof fixtures in hazardous zones.

E. Ship Handling and Repair Facilities

1. Keel and Bilge Blocks:

   • Keel Blocks: Support vessel's keel; spaced per hull design.

   • Bilge Blocks: Support curved hull sections; adjustable height.

   • Material: Hardwood/steel with rubber pads.

2. Traversing Slipways:

   • Ways: Inclined ramp with rails.

   • Traverser: Cradle moves horizontally on rails to/from water.

   • Haulage System: Winches, chains for vessel movement.

3. Overturning Stability Considerations:

   • Check: Resisting moment > overturning moment from wind/waves.

   • For Dry Docks: Vessel weight must be within base footprint.

   • Formula:

$$\text{Factor of Safety} = \frac{\text{Resisting Moment}}{\text{Overturning Moment}} \geq 1.5$$

IV. Site Earthwork and Preparation for Marine Projects

A. Earthwork Volume Calculation Methods

1. Mid-Sectional Area Method:

   • Volume $$\displaystyle V = A_{\text{mid}} \times L $$, where $$\displaystyle A_{\text{mid}} $$ = area at midpoint between cross-sections.

   • Used for long uniform sections (e.g., access roads).

2. Mean Sectional Area Method:

   • Volume $$\displaystyle V = \frac{A_1 + A_2}{2} \times L $$, where $$\displaystyle A_1 $$, $$\displaystyle A_2 $$ = end areas.

   • More accurate for varying terrain.

B. Embankment and Cutting for Marine Access Roads

• Embankment: Fill material (granular, compacted in layers). Side slopes typically 1.5:1 (H:V) or 2:1.

• Cutting: Excavated material may be reused for embankment.

• Compaction: Required to achieve design density (Proctor test).

C. Slopes and Soil Considerations

• Slope Ratios:

  • 1.5:1 (H:V): Steeper, for rock/good soil.

  • 2:1: Gentler, for cohesive soils.

• Soil Types:

  • Sandy: Requires compaction, drainage.

  • Clay: Low bearing capacity, may need stabilization.

V. Cost Estimation for Marine Construction Projects

A. Purpose and Principles of Estimation

• Purpose: Forecast cost, secure funding, tender basis, cost control.

• Principles: Accuracy, completeness, clarity, consistency with specifications.

B. Types of Estimates

C. Estimation Methods and Techniques

1. Long Wall and Short Wall Method:

   • Long Wall: Parallel to room length; length = room length + 2 × half breadth.

   • Short Wall: Perpendicular; length = room breadth.

   • Used for brickwork quantity.

2. Measurement and Deduction Rules:

   • Masonry: Deduct openings (doors/windows) fully; lintels/sills included in masonry.

   • Plastering: Deduct openings > 0.5 m²; add for reveals (if specified).

3. Material Takeoff and Statements:

   • Concrete: Volume from dimensions (m³).

   • Brickwork: Volume = length × height × thickness (m³).

   • R.C.C.: Similar to concrete + reinforcement weight (kg).

4. Earthwork Estimation for Marine Sites:

   • Use mean sectional area method for dredging/embankment.

   • Account for swell/shrinkage factors (typically 10–25%).

D. Cost Components and Percentages

[!TIP] Percentages vary by project type; marine projects have higher dredging/breakwater costs.

VI. Rate Analysis and Valuation in Marine Context

A. Rate Analysis

1. Definition: Determination of unit cost for construction items (e.g., per m³ concrete).

2. Factors Affecting:

   • Material costs (cement, steel, aggregates).

   • Labor wages (skilled/unskilled).

   • Equipment hire (excavators, pumps).

   • Overheads (site office, utilities).

   • Profit margin (5–10%).

   • Location/transportation.

3. Preparation Example (Lime Concrete 1:2:6):

   • Materials: Lime, surkhi, brick ballast 40mm.

   • Quantities per m³:

     • Lime: 0.25 m³ (≈ 360 kg)

     • Surkhi: 0.5 m³ (≈ 720 kg)

     • Ballast: 0.75 m³ (≈ 1200 kg)

   • Cost Calculation: Material cost + labor (mason, helper) + tools + overhead.

4. Overhead Charges and Work Charge Establishment:

   • Overheads: Indirect costs (site supervision, electricity, water, security).

   • Work Charge Establishment: Temporary facilities (sheds, stores) at 1–2% of project cost.

B. Valuation Principles

1. Purpose of Valuation: Determine market value for sale/purchase/insurance/taxation.

2. Key Concepts:

   | Term | Definition | |-------------------|-----------------------------------------------------| | Value | Worth in exchange (market-driven). | | Cost | Historical expenditure. | | Price | Actual transaction amount. | | Market Value | Price in open market between willing parties. | | Book Value | Cost minus depreciation (accounting). | | Scrap Value | Value as raw material at end of life. | | Salvage Value | Value if sold intact (e.g., used equipment). |

3. Methods of Valuation:

   • a. Sinking Fund Method:

     • Annual sinking fund $S$ deposited to accumulate replacement cost after $n$ years at interest $i$:

$$S = \frac{C \cdot i}{(1+i)^n - 1}$$

   where $C$ = initial cost.

 - **Depreciation** = $S$ + interest on accumulated fund.

• b. Year’s Purchase (Y.P.):

  • Present value of ₹1 per annum for $n$ years at rate $r$:

$$\text{Y.P.} = \frac{1 - (1+r)^{-n}}{r}$$

 - **Value** = Net annual income × Y.P.

• c. Dual Rate Interest:

  • Different rates for sinking fund ($$\displaystyle i_s $$) and interest ($i$).

  • Annual depreciation = $$\displaystyle C \cdot i_s $$; interest on written-down value = $(C - \text{depreciation}) \times i$.

• d. Standard Rent Fixation:

  • Based on gross income (potential rent) minus outgoings (maintenance, taxes).

  • Governed by Rent Control Acts.

4. Financial Metrics:

   • Gross Income: Total possible rent (vacancy ignored).

   • Net Income: Gross income minus all outgoings (repairs, insurance, taxes).

   • Depreciation vs. Sinking Fund: Depreciation is accounting expense; sinking fund is actual cash accumulation for replacement.

VII. Project Documentation and Management

A. Detailed Project Report (DPR)

• Content:

  1. Executive summary.

  2. Project justification (need, location).

  3. Technical details (design, specifications).

  4. Cost estimates (detailed, abstract).

  5. Implementation schedule (PERT/CPM).

  6. Financial analysis (IRR, NPV).

  7. Risk assessment, environmental clearance.

• Preparation Process: Feasibility study → preliminary design → detailed design → cost estimation → approval.

B. Schedule of Rates

• Current Schedule of Rates (CSR): Published by government/agencies (e.g., CPWD, PWD).

  • Contains item-wise rates for materials, labor, equipment.

  • Updated annually; basis for estimates and tenders.

  • Includes standard deduction percentages for wastage.

C. Tender Documentation

1. Tender Notice: Advertisement, eligibility, submission deadline.

2. Bill of Quantities (BOQ): Itemized list with quantities, units, rates (blank for bidders to fill).

3. Abstract Sheet: Summary of BOQ totals; used for comparison of bids.

D. Labor and Productivity

1. Task Work:

   • Definition: Output per worker per day (e.g., m³ brickwork/day).

   • Affecting Factors:

     • Skill level, tool/equipment availability.

     • Site conditions (weather, space).

     • Material supply continuity.

     • Supervision quality.

VIII. Case Studies and Applied Examples (Adaptation to Marine Projects)

[!TIP] Past papers ask for adaptation of building estimation methods to marine structures (e.g., breakwater concrete volume similar to R.C.C. beam).

• Rough Estimate Adaptation: Use cubic content rate for breakwater volume (m³) × rate.

• Detailed Estimate Adaptation: Itemize marine-specific items: armor units, quay concrete, dredging (m³), fendering.

• Earthwork for Marine Embankments: Apply mean sectional area with side slopes 1.5:1.

• R.C.C. in Marine Context: Higher cement content (e.g., M30 for seawater exposure), epoxy-coated rebar.

• Valuation Example:

  Year's Purchase for port warehouse:

  Net annual income = ₹10 lakh, life = 30 years, $$\displaystyle r = 8\% $$:

$$\text{Y.P.} = \frac{1 - (1.08)^{-30}}{0.08} = 11.2578$$

Value = ₹10,00,000 × 11.2578 = ₹1.12578 crore.

Exam Focus Summary

• High-Frequency Topics:

  1. Estimation Types (distinguish revised vs supplementary).

  2. Rate Analysis (factors, preparation for concrete/lime).

  3. Valuation Methods (sinking fund, year's purchase calculations).

  4. Earthwork (mid-sectional vs mean sectional area).

  5. Harbor Classification & Planning.

  6. Wave Impact Pressure (shallow vs deep derivation).

  7. DPR & CSR (content and purpose).

• Common Pitfalls:

  • Confusing scrap value (raw material) vs salvage value (intact sale).

  • Forgetting ancillary costs (water, electrification) in total estimate.

  • Misapplying long wall/short wall for curved marine walls.

  • Ignoring swell factor in earthwork for dredged material.

• Formula Box:

  • Wave Impact (Shallow): $$\displaystyle P_{\text{max}} = k \gamma H $$.

  • Earthwork (Mean Area): $$\displaystyle V = \frac{A_1 + A_2}{2} \times L $$.

  • Sinking Fund: $$\displaystyle S = \frac{C \cdot i}{(1+i)^n - 1} $$.

  • Year's Purchase: $$\displaystyle \text{Y.P.} = \frac{1 - (1+r)^{-n}}{r} $$.

  • Hydrostatic Force on Lock Gate: $$\displaystyle F = \frac{1}{2} \gamma h^2 b $$.