--- title: "Direct surface methods for road alignment" subject: "Engineering Geology II" chapter: 4 key: "semester_4/engineering_geology_ii:direct-surface-methods-road" source: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/direct-surface-methods-road site: BCT Engineering --- # Direct surface methods for road alignment Engineering Geology II · Chapter 4: Engineering geology in site selection, investigation & construction/excavation - Asked in: 2068 Bhadra, 3 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/direct-surface-methods-road - Whole chapter: https://www.bctengineer.com/md/semester_4/engineering_geology_ii/chapter-4 ## Question Describe the direct methods of surface investigation with reference to selection of road alignment in rock slopes. ## Short answer Direct surface methods: geological mapping at 1:5,000-1:2,000, structural measurements (dip, joint sets) for stereonet analysis to assess planar and wedge failures. Study natural slopes, landslides, springs, and rock strength (Schmidt hammer, RMR) to zone slope stability, select alignment, and design cuts (e.g., 0.25H:1V in hard rock). ## Answer Direct surface methods are field studies by the geologist at the ground surface. For a road in rock slopes they are used to find stable alignment and safe cut slopes. 1. **Geological (field) mapping at 1:5,000-1:2,000:** traverses along the proposed centre line and on both sides; record rock type, weathering grade, soil cover and its thickness. 2. **Structural measurements:** strike and dip of bedding, foliation and joints by Brunton compass; spacing, persistence, roughness, aperture and infilling are noted. Joint sets are plotted on stereonet to check **planar, wedge and toppling failure** with respect to the proposed slope direction. 3. **Study of natural slopes and existing cuts:** performance of old road cuts and natural scarps shows safe angles for each rock type. 4. **Mapping of landslides, rock fall, debris flow, gullies and erosion zones;** old slide scars and tension cracks on the road line. 5. **Hydrogeological observation:** springs, seepage zones and wet areas, stream crossings and flood marks. 6. **Rock strength estimates:** Schmidt hammer, hammer-blow tests and RMR classification of outcrops. 7. **Locating construction materials,** quarries and spoil areas. The result is an engineering geological map and a slope-stability zoning of the route, used for choosing the alignment and designing cut slopes (e.g. about 0.25H:1V in hard rock and 1H:1V or flatter in weak rock). ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How are joint orientations used for road cuts? A. Averaged to find colour B. Plotted on stereonet to check planar, wedge and toppling failure against slope direction C. Used to estimate rainfall D. Ignored Answer: B. Kinematic checks identify unstable cuts. (Key point: Structural measurement) 2. What do old road cuts and natural scarps show? A. Cost of land B. Rainfall C. Safe slope angles for each rock type D. Population Answer: C. Their performance guides design. (Key point: Existing cuts) 3. Which tools estimate rock strength on outcrops? A. Seismic refraction B. Plate load test C. Boreholes D. Schmidt hammer and RMR classification Answer: D. These are surface field estimates. (Key point: Rock strength) ## Related in Engineering Geology II - [Direct methods of sub-surface investigation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Adirect-subsurface-methods) — Engineering Geology II, chapter 4, asked 3× - [Geology in road alignment selection](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Aroad-alignment-geology) — Engineering Geology II, chapter 4, asked 5× - [Geological investigation of tunnel and road](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Atunnel-road-investigation) — Engineering Geology II, chapter 4 - [Surface versus sub-surface investigation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Asurface-vs-subsurface-investigation) — Engineering Geology II, chapter 4, asked 3× - [Indirect methods of surface investigation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Aindirect-surface-methods) — Engineering Geology II, chapter 4 - [Indirect sub-surface methods: tunnel and dam](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Aindirect-subsurface-tunnel-dam) — Engineering Geology II, chapter 4 ## Related in other subjects - [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 surface and subsurface site investigation](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Amethods-of-surface-and-subsurface) — Engineering Geology I, chapter 1, asked 4× - [Objectives of investigation for hill road](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aobjectives-of-investigation-for-hill) — Engineering Geology I, chapter 1 - [Site investigation for road construction](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Asite-investigation-for-road-construction) — Engineering Geology I, chapter 1