What do the field thumb penetration, pocket penetrometer, and shearvane measure?

The field thumb penetration, pocket penetrometer, and shear vane are tools specifically designed to measure the unconfined compressive strength of soil. Unconfined compressive strength assesses how much load or pressure soil can withstand before failure, making these methods crucial in geotechnical engineering and construction.

Unconfined compressive strength tests provide valuable information about the strength characteristics of cohesive soils, which helps determine their suitability for construction projects. The thumb penetration test utilizes the thumb's pressure to gauge the soil's firmness, while the pocket penetrometer measures the resistance of soil to penetration using a small handheld device. Similarly, the shear vane test measures the resistance exerted by the soil when it's sheared at a specific angle, providing a direct measurement of the soil's shear strength.

Although density of soil, water content, and soil cohesion are essential factors in soil mechanics, they are not the primary focus of these specific testing methods. Hence, the correct choice highlights the significance of measuring unconfined compressive strength in field applications related to soil stability and construction integrity.