Percussion drilling in geotechnical exploration: which of the following drawbacks can occur during boring and observation?

Introduction / Context:Percussion (shell and auger) drilling remains popular for economical site investigation. However, its dynamic, slurry-assisted cutting can compromise stratigraphic clarity and groundwater readings compared to more controlled methods.

Given Data / Assumptions:

• Percussion action with bailer/shell; water or slurry may be used.
• Soils may be soft or cohesionless, prone to caving.
• Groundwater level monitoring desired.

Concept / Approach:Impact energy and circulation can cause wall sloughing and mixing of materials, especially in sands/silts. Slurry penetration below the hole bottom can mask true groundwater conditions. Repeated impacts disturb the soil fabric beyond the immediate cutting face, affecting sampling representativeness.

Step-by-Step Solution:List known drawbacks: caving/mixing, groundwater masking, deeper disturbance.All listed drawbacks are recognized for percussion drilling.Therefore, select “all the above.”

Verification / Alternative check:Comparative studies note better groundwater and undisturbed sampling from rotary wash with casing or rotary coring than from percussion methods.

Why Other Options Are Wrong:

• Choosing any single effect understates the cumulative drawbacks.

Common Pitfalls:

• Relying on percussion logs for fine stratigraphy without corroborating SPT/undisturbed samples.

Final Answer:all the above