--- title: "Geological parameters for canal alignment" subject: "Engineering Geology II" chapter: 4 key: "semester_4/engineering_geology_ii:canal-alignment-parameters" source: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/canal-alignment-parameters site: BCT Engineering --- # Geological parameters for canal alignment Engineering Geology II · Chapter 4: Engineering geology in site selection, investigation & construction/excavation - Asked in: 2075 Bhadra, 5 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/canal-alignment-parameters - Whole chapter: https://www.bctengineer.com/md/semester_4/engineering_geology_ii/chapter-4 ## Question What are the engineering geological parameters that should be considered in canal alignment selection? Describe. ## Short answer Key parameters include soil and rock type (prefer firm impervious soils), permeability (avoid cavernous limestone), slope stability (avoid landslides, adverse dipping beds), geological structure (cross faults at right angles), gentle topography, low groundwater, manageable drainage crossings, seismic safety, and availability of construction materials. ## Answer A canal carries water over long distances, so geology decides its stability, seepage loss and cost. #### Geological parameters 1. **Soil and rock type:** firm, compact, impervious soil (clay, silty clay) gives low seepage loss and stable banks. Avoid loose sand and gravel (high seepage), very soft clay (settlement), black cotton or swelling soil, and rock needing costly excavation. 2. **Permeability and seepage:** avoid cavernous limestone, fractured rock and coarse gravel unless lined. Canal loss reduces supply and raises the water table. 3. **Slope stability:** in the hills, use stable slopes; avoid landslide areas, steep cuts in weak rock, and talus. On a hillside, beds dipping out of the slope (toward the valley) cause slides. 4. **Geological structure:** avoid faults, shear zones, and highly jointed rocks along the line; cross faults at right angles. 5. **Topography:** a gentle gradient is needed; side-hill cut-and-fill canals need a stable ground. 6. **Groundwater:** high water table causes waterlogging and bank failure; salinity affects soil. 7. **Drainage crossings:** number and type of cross-drainage works; geology at their foundations; flood-prone areas. 8. **Seismic and flood hazards.** 9. **Construction materials:** earth for embankment, stone, gravel and sand nearby. 10. **Excavation conditions:** depth of cutting, rippability, rock excavation cost. Investigation: geological mapping, test pits at intervals, borings at structures, permeability tests, and soil tests (compaction, shear strength, swelling). ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which soil is preferred for a canal? A. Firm, compact impervious soil such as clay or silty clay B. Loose sand and gravel C. Black cotton soil D. Cavernous limestone Answer: A. It gives low seepage and stable banks. (Key point: Soil type) 2. Why is seepage important? A. It improves supply B. It reduces supply and raises the water table C. It has no effect D. It lowers cost Answer: B. Lining may be needed in permeable ground. (Key point: Seepage) 3. Which bedding on a hillside canal causes slides? A. Dip into the hill B. Horizontal bedding C. Dip toward the canal D. Massive rock Answer: C. Out-of-slope dip promotes sliding. (Key point: Hillside dip) 4. A high water table causes A. Waterlogging and bank failure B. Stronger banks C. Less seepage D. No effect Answer: A. Salinity also affects soil. 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