--- title: "Problems of Lesser Himalaya and Terai" subject: "Engineering Geology II" chapter: 2 key: "semester_4/engineering_geology_ii:lesser-himalaya-terai-problems" source: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/lesser-himalaya-terai-problems site: BCT Engineering --- # Problems of Lesser Himalaya and Terai Engineering Geology II · Chapter 2: Engineering Geology in Himalayas - Asked in: 2078 Chaitra, 2 marks; 2078 Baisakh, 1+1 marks; 2076 Bhadra, 2 marks; 2074 Bhadra, 1+1 marks; 2070 Bhadra, 3 marks (asked 5 times) - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/lesser-himalaya-terai-problems - Whole chapter: https://www.bctengineer.com/md/semester_4/engineering_geology_ii/chapter-2 ## Question What are the engineering geological problems of the Lesser Himalaya and the Terai (Indo-Gangetic plain) zones? Mention mitigating measures. ## Short answer Lesser Himalaya problems include landslides, weak rocks, and seismic activity, mitigated by slope stabilization and drainage. Terai problems are floods, low bearing capacity, liquefaction, and arsenic contamination, addressed by embankments, deep foundations, ground improvement, and safe water wells. ## Answer #### Lesser Himalaya The zone has weak, folded and sheared rocks (phyllite, schist, slate) and steep terrain. - **Problems:** landslides, rock fall, weak foundation rock, tunnel squeezing, karst in limestone, erosion, MBT/MCT earthquakes. - **Mitigation:** gentle slopes and retaining structures, surface drainage, rock bolts and shotcrete, bio-engineering, careful alignment, grouting in karst areas. #### Terai (Indo-Gangetic plain) The Terai consists of thick, unconsolidated Quaternary alluvium (gravel, sand, silt, clay) with a gentle slope. - **Problems:** 1. Frequent floods and river bank cutting; shifting of river channels. 2. Sediment deposition and aggradation of river beds. 3. High water table and waterlogging. 4. Low bearing capacity and large settlement of soft clay and silt. 5. Liquefaction of loose saturated sand during earthquakes. 6. Scarcity of rock aggregate (only boulders and gravel from rivers). 7. Arsenic contamination of shallow groundwater. - **Mitigation:** embankments and spurs, river training, raised foundations or pile/raft foundations, soil compaction and ground improvement, drainage, deep tube wells for safe water, use of river gravel with proper testing. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the Terai made of? A. Hard gneiss B. Thick unconsolidated Quaternary alluvium C. Limestone with caves D. Glacial moraine Answer: B. The Terai has thick unconsolidated alluvium of gravel, sand, silt and clay on a gentle slope. (Key point: Terai ground) 2. Which Terai problem occurs in loose saturated sand during earthquakes? A. Karst collapse B. Rock burst C. Squeezing D. Liquefaction Answer: D. Loose saturated sand loses strength during shaking and liquefies. (Key point: Liquefaction) 3. What mitigates low bearing capacity and settlement of soft clay in the Terai? A. Pile or raft foundations and ground improvement B. Rock bolts C. Gabion walls on hills D. Catch ditches Answer: A. Raised, pile or raft foundations and compaction or ground improvement handle soft soil. (Key point: Foundation mitigation) 4. What groundwater quality problem is noted in the shallow Terai aquifer? A. High salinity from sea only B. Arsenic contamination C. Radioactive gas D. Oil pollution Answer: B. Shallow Terai groundwater is arsenic-contaminated; deep tube wells give safe water. 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