Subsurface investigation — auger boring basics (applications and limits) Which combination of statements correctly describes hand/portable auger boring as used in geotechnical site exploration?

Introduction / Context:
Auger boring is a simple, low-cost method to obtain shallow subsurface information for foundations, utilities, and environmental screening. Understanding where it works best prevents wasted effort and unsafe holes.

Given Data / Assumptions:

• Use in near-surface soils for small projects or preliminary exploration.
• Equipment ranges from hand augers to portable power-driven rigs.
• Focus on soils above the groundwater table for unsupported holes.

Concept / Approach:

Augers cut and lift soil by helical blades. In cohesive and self-supporting soils the hole walls remain stable without casing, making auger boring efficient. Below the water table or in loose sands, holes collapse unless cased. Economically, the method is attractive up to a few metres; beyond that, more capable drilling methods are preferable. Typical tool diameters for site work lie in the 7.5–30 cm range, matching sampling and in-situ test requirements for small projects.

Step-by-Step Solution:

Verification / Alternative check:

Most geotechnical manuals specify hand augers for cohesive soils and caution against use below water table without casing. Equipment catalogs confirm typical diameter ranges.

Why Other Options Are Wrong:

• Each individual statement is correct; selecting any single one misses the comprehensive nature of auger boring practice.

Common Pitfalls:

• Attempting auger boring in loose saturated sands without casing support.
• Expecting undisturbed samples from simple augering without proper samplers.

Final Answer:

All the above.