--- title: "Engineering importance of thrusts" subject: "Engineering Geology I" chapter: 7 key: "semester_3/engineering_geology_i:engineering-importance-of-thrusts" source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/engineering-importance-of-thrusts site: BCT Engineering --- # Engineering importance of thrusts Engineering Geology I · Chapter 7: Geology of Nepal - Asked in: 2066 Bhadra (old course), 3 marks - Video: [Geological Structures in Engineering and Its Significance ](https://www.youtube.com/watch?v=iNqGhH-gzbM) — katebaring - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/engineering-importance-of-thrusts - Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-7 ## Question Mention the civil engineering importance of thrusts. ## Answer A **thrust** is a low-angle reverse fault in which an older rock is pushed over a younger rock. The importance of the HFT (MFT), MBT and MCT in civil engineering is: 1. **Crushed, sheared and weak rock** gives low bearing capacity, tunnel collapse, large overbreak and squeezing, so extra support is needed. 2. **Slope instability:** landslides and debris flows are concentrated in the thrust zones. 3. **Seismic risk:** the thrusts are active, so earthquake loading, surface rupture and ground shaking affect dams, bridges and buildings. Structures must not be placed across them. 4. **Groundwater:** thrust zones are conduits for water; heavy seepage, springs and inrush in tunnels. 5. **Rock contrast:** rocks of different strength and permeability meet at the thrust, giving differential settlement and leakage under dams. 6. **Site investigation** must locate the thrust accurately, with trenching and geophysical methods, before alignments of roads, tunnels or dams are fixed. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is a thrust? A. A vertical strike-slip fault B. A low-angle reverse fault where older rock is pushed over younger rock C. A normal fault with younger rock over older rock D. A fold with a vertical axial plane Answer: B. A thrust is a low-angle reverse fault in which older rock rides over younger rock. (Key point: Definition of thrust) 2. What problem does crushed and sheared rock in a thrust zone cause for a tunnel? A. High bearing capacity and no support needed B. Collapse, large overbreak and squeezing, needing extra support C. Reduced seepage because the rock is tight D. Only surface erosion Answer: B. Crushed, sheared rock has low strength, giving tunnel collapse, overbreak and squeezing, so extra support is needed. (Key point: Weak rock in thrust zones) 3. How should structures be placed with respect to active thrusts? A. Directly across the thrust to anchor both sides B. Not across them, because of surface rupture and ground shaking C. Anywhere, as thrusts only matter for tunnels D. Only on the hanging wall Answer: B. Thrusts are active, so earthquake loading and surface rupture mean structures must not be placed across them. (Key point: Seismic risk and siting) 4. Why does a thrust cause leakage and settlement problems under dams? A. Rocks of different strength and permeability meet at the thrust B. Both sides always have the same permeability C. Thrusts always dry the groundwater D. Thrusts make the rock uniformly strong Answer: A. Contrasting strength and permeability across the thrust give differential settlement and leakage. (Key point: Rock contrast) ## Related in Engineering Geology I - [Scope and importance of geology in civil engineering](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Ascope-and-importance-of-geology) — Engineering Geology I, chapter 1, asked 24× - [Folds: recognition and civil engineering influence](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Afolds-recognition-and-civil-engineering) — Engineering Geology I, chapter 5 - [Engineering significance of marble](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aengineering-significance-of-marble) — Engineering Geology I, chapter 4 - [Define engineering geology; scope and importance](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Adefine-engineering-geology-scope-and) — Engineering Geology I, chapter 1, asked 24× - [Engineering significance of fault](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aengineering-significance-of-fault) — Engineering Geology I, chapter 5, asked 6× - [Engineering significance of marble, granite, sandstone](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aengineering-significance-of-marble-granite) — Engineering Geology I, chapter 4 ## Related in other subjects - [Important properties of civil engineering materials](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aimportant-properties-civil-materials) — Civil Engineering Materials, chapter 1, asked 8× - [Importance and scope of civil engineering materials](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aimportance-scope-subject) — Civil Engineering Materials, chapter 1, asked 8× - [Classification of civil engineering materials](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aclassification-civil-materials) — Civil Engineering Materials, chapter 1, asked 2× - [Scope of engineering geology in civil engineering](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Ascope-engineering-geology) — Engineering Geology II, chapter 1