What type of soil can easily be penetrated by the thumb due to its lower unconfined compressive strength?

The correct answer is related to the classification of soils according to their unconfined compressive strength and how easily they can be penetrated. Type C soils are generally characterized by having low cohesion and low shear strength, making them more susceptible to changes in moisture and easier to penetrate with an object like a thumb.

Type C soils include loose sands, silts, and gravel that may not provide adequate support for vertical loads and lack stability, especially when wet. This classification is important for excavator operators and other construction professionals because it impacts safety and the methods used during excavation.

Understanding the characteristics of Type C soils helps operators gauge the risks involved when working with these materials, particularly in terms of potential cave-ins or failures in excavation sites. Thus, identifying and classifying soil types accurately is crucial for effective planning and execution of excavation work.