Engineering geological problems of Siwalik zone

The Siwalik (Churia) zone lies between the MFT and the MBT. It is made of young, poorly consolidated Neogene-Quaternary molasse deposits: sandstone, siltstone, mudstone, clay and conglomerate.

Engineering geological problems

1. Landslides and slope failure: soft, weakly cemented rocks with heavy rain, steep slopes and tectonic dip.
2. Gully erosion and badland topography: easy erosion of friable sandstone and mudstone.
3. Debris flow and flash floods: steep torrents carry large sediment loads to the Terai.
4. Weak and swelling mudstone: low strength, slakes on wetting; difficult for tunnel and foundation.
5. Active tectonics: the MFT and MBT are active, giving earthquakes and fault scarps.
6. Seepage and groundwater: coarse sandstone and conglomerate are highly permeable, so water drains quickly and springs dry up in the dry season.
7. Poor construction material: the rocks are too weak for aggregate, and boulders from the conglomerate are often soft or weathered.
8. Roads: frequent cut-slope failures and road washouts.

Mitigation

Gentle slopes, retaining walls, drainage, afforestation in the Churia range, check dams, river training and proper alignment away from active faults.