--- title: "Bridge components sketch; river bank protection" subject: "Transportation Engineering II" chapter: 5 key: "semester_7/transportation_engineering_ii:bridge-sketch-components-river-bank-protection" source: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/bridge-sketch-components-river-bank-protection site: BCT Engineering --- # Bridge components sketch; river bank protection Transportation Engineering II · Chapter 5: Introduction to Bridge and Tunnel Engineering - Asked in: 2075 Asoj, 8 marks - Video: [What is River Training Works in Bridge Construction | Floor Apron & Flexible Apron, Stone Pitching](https://www.youtube.com/watch?v=2e3AZxByUkI) — REINFORCE - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/bridge-sketch-components-river-bank-protection - Whole chapter: https://www.bctengineer.com/md/semester_7/transportation_engineering_ii/chapter-5 ## Question Draw a neat sketch of bridge with its components. Explain the methods of river bank protection? ## Short answer A bridge has superstructure (deck, girders, bearings, parapets) and substructure (abutments, piers, foundations), with approaches and protective works. River bank protection uses revetments or pitching, gabion walls and mattresses, spurs or groynes, guide bunds, retaining walls, and launching aprons to prevent erosion and scour. ## Answer #### Sketch and components of a bridge A bridge has a **superstructure** (above the bearings) and a **substructure** (bearings, piers, abutments, foundations), plus approaches and protective works. ```text Approach Parapet/Railing Deck slab Approach slab ________________________ slab ____ ____|_____|_____|_____|_____|____ ____ \ | [girder][girder][girder] | / Wing \ |Bearing Bearing | / Wing wall |Abutment [ PIER ] Abutment| wall | | | | | HFL ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Scour level - - - - - - - - - - - - - - - - [Footing] [Pile/Well] [Footing] ``` **Superstructure** - **Deck/slab and wearing coat:** carries the traffic loads (IRC Class A/70R/AA loading as per IRC:6) to the girders. - **Girders/trusses/arches:** main load-carrying members that span between supports. - **Cross girders/diaphragms:** give lateral stability and distribute load. - **Parapets, railings, kerbs, footpaths:** safety for vehicles and pedestrians. - **Expansion joints and drainage spouts:** allow thermal movement and remove surface water. **Bearings:** transmit reactions from the superstructure to the substructure and permit rotation and movement (elastomeric, roller and rocker types). **Substructure** - **Abutments:** end supports that also retain the approach fill, with **wing walls** and **return walls** that hold back the earth. - **Piers:** intermediate supports carrying the vertical load, with a pier cap and bed block. - **Foundations:** open (spread) footings, piles, wells or caissons that carry the loads to sound strata below the scour depth. **Others:** approach embankment and approach slab, **protective works** (guide bunds, spurs, apron, pitching) and river training works; the design HFL, LWL and scour level are marked on the section. #### Methods of river bank protection River bank protection prevents erosion and scour of the banks near bridge approaches and guides the flow to pass smoothly through the waterway (IRC:89 "Guidelines for design and construction of river training and control works for road bridges"; Nepal DoR river training and bio-engineering guidelines). Main methods: 1. **Revetments (pitching):** stone pitching (dry or grouted), concrete blocks or gabion mattresses laid on a filter layer over a graded bank slope, with a toe wall or launching apron to prevent undermining. Used for banks with moderate flow. 2. **Gabion/crate walls and mattresses:** wire-mesh boxes filled with boulders; flexible, free-draining, cheap and widely used in Nepal. Gabion mattress aprons adjust to scour. 3. **Spurs/groynes:** short structures projecting from the bank into the stream that deflect the flow away from the bank, cause silting between them and train the channel. Types: permeable (pile, timber) and impermeable (stone, boulder); attracting, repelling or deflecting, depending on their angle. 4. **Guide bunds:** earthen embankments with a stone-pitched river face, curved at the upstream end, on both sides of the bridge waterway to guide the flow centrally through it (IRC:89). 5. **Retaining walls/embankment walls:** masonry, RCC or gabion walls along the bank where space is limited. 6. **Longitudinal dykes/marginal bunds:** embankments parallel to the flow to confine the river. 7. **Launching apron and toe protection:** loose stones at the toe that launch down the slope when scour occurs, protecting the foundation of the protection work. 8. **Bio-engineering:** vegetation (grass, bamboo, shrubs, trees) planted on the bank, often combined with gabions; cheap and environment-friendly for smaller flows (DoR Roadside Bio-engineering Guideline). 9. **Check dams/sills and permeable fences:** reduce velocity and trap sediment in steep streams. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which set belongs to the substructure of a bridge? A. Deck slab, girders, parapets B. Piers, abutments, foundations C. Railings, kerbs, expansion joints D. Wearing coat and drainage spouts Answer: B. The substructure comprises bearings, piers, abutments and foundations that transfer loads to the ground. (Key point: Superstructure vs substructure) 2. What do bearings do? A. Retain the approach fill B. Transmit reactions from superstructure to substructure and permit rotation and movement C. Divert the river flow D. Carry traffic loads directly Answer: B. Bearings sit between girders and piers/abutments, passing reactions down while allowing rotation and thermal movement. (Key point: Role of bearings) 3. What do spurs (groynes) do? A. Project from the bank to deflect flow away and cause silting between them B. Run parallel to the flow to confine the river C. Only support the bridge deck D. Carry the approach road Answer: A. Spurs project into the stream, deflect flow from the bank and train the channel. (Key point: Spurs/groynes) 4. What is the purpose of guide bunds? A. To store water upstream B. To guide the flow centrally through the bridge waterway C. To support girders D. To drain the road surface Answer: B. Guide bunds, curved at the upstream end, on both sides of the approach guide the flow through the waterway. 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