Which of the following methods does NOT aid in classifying soil?

The method that does not aid in classifying soil is soil moisture measurement. While soil moisture content is certainly important in assessing the behavior of soil in various scenarios, such as drainage and compaction, it does not directly provide information about the physical or mechanical properties that are crucial for soil classification.

In contrast, the other methods listed are directly related to evaluating soil characteristics. The plasticity test provides insight into the soil's plasticity index, which helps differentiate between cohesive and non-cohesive soils. The dry strength test assesses how well soil retains its shape when dry, which can signal cohesiveness and stability. The thumb penetration test gives a quick field assessment of soil consistency and relative compaction, which is relevant for determining suitability for construction and excavation.