Subsurface investigation — when is the auger boring method unsuitable? Auger boring (hand or portable power augers) is commonly used in cohesive, self-supporting soils above the water table. In which of the following ground conditions is auger boring.

Question

Solve this multiple-choice question and choose the correct option.

Accepted Answer

Introduction / Context:Auger boring is a simple and economical exploration method for shallow depths. However, it relies on the surrounding soil remaining stable (self-supporting) and on the auger cutting efficiently. Recognizing when auger boring becomes unsafe or ineffective helps you select better alternatives (cased borings, wash boring, rotary, percussion). Given Data / Assumptions: Hand or portable power helical augers. No casing or drilling mud for wall support unless noted. Objective is to advance the hole safely while obtaining representative information. Concept / Approach: Augers work best in cohesive or otherwise self-supporting soils above the water table. In very hard/cemented layers the bit cannot cut effectively; in fully saturated cohesionless soils the walls slough and the hole collapses without casing; in very soft soils there is insufficient stand-up time and excessive squeezing into the auger flights, leading to unsafe and poor-quality holes. Step-by-Step Solution: Check very hard/cemented strata → resistant to cutting → progress is poor and tools may be damaged.Check fully saturated sands → no cohesion → immediate collapse without casing → unsafe and unreliable.Check very soft soils → lack of stand-up time → sidewall squeezing and collapse.Therefore all listed cases are unsuitable → choose “All of the above”. Verification / Alternative check: Most geotechnical manuals recommend casing or switching to wash/rotary or percussion in saturated sands and to percussion/rotary coring for very hard or cemented layers; hand augers are explicitly limited to shallow, self-supporting soils above the water table. Why Other Options Are Wrong: (a), (b), (c) individually identify true limitations, but each alone is incomplete. (e) “None” is incorrect because several unsuitable cases exist. Common Pitfalls: Attempting to auger below the water table in sand without casing and expecting stable holes. Assuming the presence of silt gives cohesion; saturated silty sand may still collapse. Final Answer: All of the above.

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