--- title: "Special structures in hill roads" subject: "Transportation Engineering I" chapter: 5 key: "semester_6/transportation_engineering_i:hill-special-structures" source: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/hill-special-structures site: BCT Engineering --- # Special structures in hill roads Transportation Engineering I · Chapter 5: Hill Roads - Asked in: 2066 Magh (old course), 8 marks - Video: [Unraveling the Secrets of Hill Roads ( Highway Engineering )](https://www.youtube.com/watch?v=L3Bg_YPJH8k) — IQ Cracker - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/hill-special-structures - Whole chapter: https://www.bctengineer.com/md/semester_6/transportation_engineering_i/chapter-5 ## Question Briefly describe the special structures constructed in hill roads. Make the sketch of drainage system layout in hill roads. ## Short answer Special hill road structures include retaining/breast walls, gabion works, check dams, chutes, rock-fall nets, hairpin bends, and bio-engineering. The drainage layout: catch drain intercepts hillside water, side drain collects road/cut water, both conveyed via culverts and chutes to natural stream. ## Answer #### Special structures in hill roads 1. **Retaining walls** - valley side, to hold fill and to widen the road. 2. **Breast walls** - hill side, to support cut faces and avoid slips. 3. **Revetments and toe walls** - protect slopes and river banks from scour. 4. **Gabion structures** - walls, mattresses and check dams in wire crates; flexible and permeable. 5. **Check dams, drop structures, chutes/cascades** - gully control and safe disposal of culvert flow. 6. **Cross-drainage works** - culverts, causeways, Irish bridges and small bridges. 7. **Retaining/catch ditches, rock-fall nets and shotcrete** for rock slopes. 8. **Hairpin bends and passing places** (lay-bys) on narrow roads. 9. **Parapet/guard walls and crash barriers** on the valley edge. 10. **Bio-engineering works** - grass, shrubs and brush layering. 11. **Sub-surface drainage** - French drains, horizontal drains, weep holes. 12. **Tunnels, snow galleries and avalanche shelters** in very difficult or snow-bound areas. #### Sketch of the drainage layout in hill road ```text hill ~~~~~~~~~~~~~~~~~~~~~~ catch water drain ===> (to nala) \ \ cut slope \ breast wall side drain ---> culvert ---+ ==== road ================= | \ retaining wall v \ fill slope chute valley ~~~~~~~~ stream <------+ ``` Flow path: hillside water is intercepted by the catch drain; road and cut-face water goes to the side drain; both are carried through culverts and chutes to a natural stream. Sub-surface drains (French/horizontal) discharge into the side drain or through weep holes. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the function of a breast wall? A. To hold the fill on the valley side B. To support cut faces on the hill side and avoid slips C. To carry a stream under the road D. To protect river banks from scour Answer: B. Breast walls are built on the hill side to support the cut face. (Key point: Breast walls) 2. Which describes gabion structures correctly? A. Rigid concrete blocks with no drainage B. Wire crates of stone forming walls, mattresses and check dams, flexible and permeable C. Pipes used for culverts D. Timber frames filled with concrete Answer: B. Gabions are wire crates filled with stone and are flexible and permeable. (Key point: Gabion structures) 3. In the hill road drainage layout, where does hillside water above the cut slope go? A. Into the side drain on the road B. Intercepted by the catch water drain and led away to a nala C. Directly over the retaining wall D. Into the pavement layers Answer: B. The catch water drain intercepts hillside water before it reaches the road and leads it to a natural channel. (Key point: Drainage layout flow path) 4. What is the role of chutes or cascades at culvert outlets? A. To increase the culvert flow B. Safe disposal of culvert flow down the slope to the stream C. To support the fill D. To catch falling rocks Answer: B. Chutes and cascades carry the concentrated discharge safely down the steep slope to the stream, preventing erosion. (Key point: Chutes and culverts) ## 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× - [Surface water drainage in hill roads](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Ahill-surface-drainage) — Transportation Engineering I, chapter 5, asked 2× - [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× - [Design and construction problems of hill roads](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Ahill-problems) — Transportation Engineering I, chapter 5, asked 11× - [Typical cross-sections of hill roads](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Ahill-cross-sections) — Transportation Engineering I, chapter 5, asked 9× - [Catch water drains in hill roads](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Acatch-water-drain-hill) — Transportation Engineering I, chapter 5, asked 2× ## Related in other subjects - [Layout planning of surface drainage system](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Asurface-drainage-layout-planning) — Irrigation and Drainage Engineering, chapter 9 - [System administration; special vs general user](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Asysadmin-special-vs-general-user) — Operating System, chapter 9 - [File system layout, i-node, backup](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Afs-layout-inode-backup) — Operating System, chapter 5 - [File system layout; i-node vs linked list](https://www.bctengineer.com/question.md?key=semester_6%2Foperating_system%3Afs-layout-inode-vs-linked-list) — Operating System, chapter 5