--- title: "Retaining and slope protection structures" subject: "Transportation Engineering I" chapter: 5 key: "semester_6/transportation_engineering_i:retaining-slope-protection" source: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/retaining-slope-protection site: BCT Engineering --- # Retaining and slope protection structures Transportation Engineering I · Chapter 5: Hill Roads - Asked in: 2076 Bhadra, 8 marks - Video: [SLOPE PROTECTION STRUCTURE](https://www.youtube.com/watch?v=7kqSl4DdUFc) — Cedric Salonga - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/retaining-slope-protection - Whole chapter: https://www.bctengineer.com/md/semester_6/transportation_engineering_i/chapter-5 ## Question Discuss the retaining and slope protection structures that are frequently used in the hill road. ## Short answer Common retaining structures are stone masonry gravity walls, gabion walls, and breast walls; slope protection includes stone pitching, shotcrete, wire mesh, gabion mattresses, and bio-engineering. All walls need weep holes and filter backfill. ## Answer Hill roads need structures to hold the soil and to protect slopes from erosion and failure (IRC:SP:48; Nepal DoR hill-road guidelines). #### A. Retaining structures 1. **Retaining walls** - on the valley side, to support the fill and the road. Types: - **Stone masonry gravity wall** (most common; dry or in cement mortar, height up to 6-8 m); - **Gabion wall** (wire crates filled with stone; flexible, permeable, cheap and good on settling ground); - **Concrete/RCC cantilever or counterfort wall** for greater heights; - **Reinforced earth / geosynthetic wall**. 2. **Breast walls** - on the hill side, supporting the cut face and preventing slips and rock fall. 3. **Toe walls** and **buttresses** - stabilise the base of the slope. 4. **Crib walls** (timber/concrete) - interlocking members filled with soil. All walls must have **weep holes** and a filter backfill, be founded on firm ground, and be designed against sliding, overturning and bearing failure. #### B. Slope protection structures 1. **Stone pitching/turfing** on embankment and cut slopes. 2. **Shotcrete/guniting and wire-mesh** on rocky cut slopes. 3. **Gabion mattresses** and **river training works** (spurs, revetments) along rivers. 4. **Rock-fall protection** - rock-fall nets, catch ditches and fences. 5. **Bio-engineering** - grass, shrubs, tree planting, brush layering, fascines. 6. **Check dams, drop structures and chutes** for gully control. 7. **Drainage works** - catch drains, side drains, French drains. ```text hill -> |breast wall| road |retaining wall| <- valley cut slope fill slope ``` Selection depends on the height, soil/rock type, availability of stone, water and cost; gabion and masonry walls are the most commonly used in Nepal. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the difference between a retaining wall and a breast wall on a hill road? A. A retaining wall is on the hill side and a breast wall on the valley side B. A retaining wall supports fill on the valley side; a breast wall supports the cut face on the hill side C. Both are always on the valley side D. A breast wall is only used for bridges Answer: B. Retaining walls hold up the road and fill on the valley side, while breast walls support the cut face on the hill side. (Key point: Retaining vs breast wall) 2. Why is a gabion wall good for settling ground? A. It is rigid and cannot deform B. It is flexible and permeable, and cheap C. It is impermeable and so holds water D. It needs no foundation Answer: B. Wire crates filled with stone are flexible and permeable, so they tolerate settlement and drain freely. (Key point: Gabion wall) 3. Which provisions must ALL retaining walls have? A. A smooth, impermeable backfill B. Weep holes and a filter backfill, founded on firm ground C. A foundation placed on loose fill D. Designed only against sliding Answer: B. Weep holes and filter backfill relieve water pressure, and walls must be on firm ground and designed against sliding, overturning and bearing failure. (Key point: Wall requirements) 4. Which is a slope protection measure for rocky cut slopes? A. Stone pitching on embankments B. Shotcrete with wire mesh C. Gabion mattress for river training D. Turfing on rock Answer: B. Shotcrete (guniting) with wire mesh is used on rocky cut slopes; stone pitching and turfing suit embankment and soil cut slopes. (Key point: Slope protection structures) ## Related in Transportation Engineering I - [Hill road drainage structures](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Ahill-drainage-structures) — Transportation Engineering I, chapter 5, asked 4× - [Special structures in hill roads](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Ahill-special-structures) — Transportation Engineering I, chapter 5 - [Special considerations in hill road design](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Ahill-special-considerations) — Transportation Engineering I, chapter 5, asked 5× - [Define hill road and design factors](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Ahill-define-factors) — Transportation Engineering I, chapter 5, asked 2× - [Factors controlling hill road alignment](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Ahill-alignment-factors) — Transportation Engineering I, chapter 5, asked 2× - [Methods of locating hill road alignment](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Ahill-alignment-methods) — Transportation Engineering I, chapter 5 ## Related in other subjects - [Hill road earthwork, cross slope 1 in 5 (0-60)](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Ahill-road-r-cross-slope-1-5) — Estimating and Costing, chapter 6 - [Hill road earthwork, 0+020 to 0+140](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Ahill-road-c-three-sections) — Estimating and Costing, chapter 6, asked 2× - [Hill road earthwork, 0 m to 90 m, 10/8 m widths](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Ahill-road-e-0-90) — Estimating and Costing, chapter 6, asked 2× - [Hill road earthwork, chainage 130-280](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Ahill-road-formation-8-table-a) — Estimating and Costing, chapter 6