- 2081 Kartik (new course) · 2+2 marks
Discontinuities and engineering problems in Nepal Himalaya
Short answer
The major discontinuity systems are MFT/HFT, MBT, MCT, and STDS, all major thrust/faults with crushed, sheared weak ground, seismically active, causing earthquakes, landslides, and water inflow. Engineering problems include floods in Terai, slides in Siwalik, shear zones in Lesser Himalaya, rockfall/avalanches in Higher Himalaya, and karst in Tethys.
Describe the major discontinuity systems and their engineering significance along with the different engineering geological problems in the different tectonic subdivisions of the Nepal Himalaya.
Major discontinuity systems
| Thrust | Between | Tentative location | Age of last movement |
|---|---|---|---|
| MFT / HFT | Terai and Siwalik | Along the southern foot of the Churiya hills | Active (Holocene) |
| MBT | Siwalik and Lesser Himalaya | Along the northern edge of the Siwaliks / foot of the Mahabharat range | Late Pleistocene, reactivated |
| MCT | Lesser and Higher Himalaya | Along the foot of the Higher Himalaya, mostly north of Kathmandu | Miocene, partly active |
| STDS | Higher Himalaya and Tethys | Along the northern slopes of the Great Himalaya | Normal fault, Miocene |
Engineering significance
- All are major thrusts or faults: crushed, sheared and weak ground, tunnelling and slope problems.
- They are seismically active, so earthquakes, surface rupture and landslides are linked with them.
- Springs, seepage and groundwater concentrate along them.
- Structures (dams, powerhouses) should avoid crossing them.
Problems in the tectonic subdivisions
| Zone | Main engineering geological problems |
|---|---|
| Terai | Floods, river shifting and bank cutting, high water table, soft soils with low bearing capacity, liquefaction, arsenic in groundwater, no rock for aggregate |
| Siwalik | Weak, poorly consolidated rocks, landslides and debris flows, gully erosion, swelling mudstone, slaking, flash floods, steep slopes |
| Lesser Himalaya | Landslides in weathered phyllite and schist, shear zones along thrusts, karst and cavities in limestone, tunnel squeezing, seepage |
| Higher Himalaya | Very high relief and steep valleys, rockfall, avalanches, glacial lake outburst floods, moraine slides, difficult access, cold and frost |
| Tethys Himalaya | Karst in limestone, frost and permafrost, rockfall, cold, remoteness |
| Boundary thrusts (MFT, MBT, MCT) | Crushed zone, weak ground, earthquakes, landslides, water inflow |
✓ Answer checked by Claude Opus 5.5 (high effort)
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