Earthwork excavation in soft soil, hard rock, wet soil

Excavation in soft soil

• Manual: Using spade, pick-axe, and shovel for shallow excavation of earth, clay, sand and murrum; labour is cheap in Nepal.
• Mechanical: Backhoe excavators, bulldozers and loaders for large areas.
• Sides are sloped or supported by timber shoring (planking and struts) for depth over 1.5 m, to avoid collapse.
• Spoil is placed at least 1 m away from the edge; the bottom is levelled and compacted.

Excavation in hard rock

1. Manual: Crowbars, wedges, chisel, pick axes, sledge hammers for small works. Wedging with feathers and plugs splits blocks.
2. Pneumatic breakers and drilling with compressed air, jackhammers.
3. Blasting: Holes are drilled, charged with explosive (gelatin, ANFO), stemmed and fired with detonators and fuse. Needs licensed personnel, warning, and safety distance. Controlled blasting limits damage.
4. Rippers and hydraulic hammers on excavators.
5. Non-explosive demolition agents (expansive cement) where blasting is not allowed near buildings. The rock bottom is cleaned and made level or benched.

Excavation in wet soil

Needs removal of water so that work is in dry conditions.

1. Sump and ditch method: Drains lead water to a sump from which it is pumped.
2. Well-point system: Pipes jetted around the trench with a vacuum pump lowering the water table.
3. Deep wells and sheet piling / cofferdam for deep works near water.
4. Shoring with close timbering for loose, saturated soils.
5. Scheduling in the dry season.

  Soft: sloped sides      Wet:  sump + pump
   \       /               \____/ 
    \_____/                  [sump]