Soil Exploration – Practical depth limit for open test pits Open test-pit exploration is generally considered suitable only up to what approximate depth under safe and practical site conditions?

Introduction / Context:
Open test pits (trial pits) provide direct visual inspection and sampling of near-surface soils. However, safety, ground stability, and dewatering constraints limit their practical depth. Knowing the indicative depth threshold guides the selection between pits and boring methods (SPT, CPT, rotary).

Given Data / Assumptions:

• Shallow exploration without elaborate shoring.
• Normal ground conditions and safe side slopes.
• No heavy groundwater inflow limiting excavation.

Concept / Approach:
Because unsupported sides can collapse and excavation becomes hazardous, open pits are commonly limited to around 3 m depth in routine practice. Deeper exploration typically requires shoring/boxing or transitions to boreholes and in-situ tests.

Step-by-Step Solution:
Recognize that beyond about 3 m, safety and practicality drop sharply without shoring.Adopt the commonly cited limit: ≈ 3 m.Select option “3 m”.

Verification / Alternative check:
Many geotechnical manuals describe trial pits for depths up to ~3 m, emphasizing safe slopes or shoring if deeper excavation is essential.

Why Other Options Are Wrong:

• 2–2.5 m: possible but overly conservative as a hard limit; pits can safely reach ~3 m under good conditions.
• None of the above: incorrect since a practical value exists.

Common Pitfalls:
Ignoring groundwater and trench stability; excavation safety must follow local regulations for shoring and access regardless of nominal limits.

Final Answer:
3 m