Subsurface exploration: Auger boring is generally not suitable under which site condition?

Introduction / Context:
Auger borings (hand or power augers) are common for shallow subsurface investigations. The method is economical and fast in certain soils but has limitations where borehole stability is poor without casing or drilling mud.

Given Data / Assumptions:

• Auger borings advance an open hole without continuous casing.
• Groundwater and granular soils can cause side collapse.
• Objective is to identify conditions where augering is not common.

Concept / Approach:
In cohesionless sands and gravels or in soils with high groundwater and low apparent cohesion, the bore walls tend to ravel and cave, necessitating temporary casing or drilling fluids. Because simple auger methods do not provide sustained lateral support, they are not preferred in such conditions.

Step-by-Step Solution:
Identify soil requiring lateral support: loose sands/gravels, saturated strata.Recognize method limitation: auger borings lack inherent wall support.Conclude: not common where lateral support is required.

Verification / Alternative check:
Geotechnical manuals recommend wash boring, rotary with mud, or cased drilling in unstable, cohesionless, or saturated formations instead of simple augers.

Why Other Options Are Wrong:

• Cohesive soils: augers work well because walls stand temporarily.
• Soft soils and residual soils: can be augered with care and shallow depths.
• “None of the above” contradicts the known limitation.

Common Pitfalls:
Attempting deep augers below water table without casing; misclassifying silty sands as cohesive.

Final Answer:
Soils that require lateral support to prevent side collapse