Merits and demerits of percussion drilling

In percussion drilling a heavy chisel bit is repeatedly raised and dropped to break the soil or rock, and the cuttings are removed by a bailer.

Merits

• Can penetrate hard soils, boulders, gravel and rock.
• Simple, rugged equipment, cheap and suitable in remote areas.
• Gives a good idea of groundwater and depth to rock; reaches large depths.

Demerits

• Slow in soft soils and gives disturbed, mixed samples.
• Soil below the bit is disturbed, so undisturbed sampling is difficult and strata boundaries are hard to identify.
• Not suitable for soft clays or loose sands below the water table (need casing).
• Cannot give proper records of thin layers.