What type of soil is the worst for transmitting noise?

• A. Sandy soils
• B. Loamy soils
• C. Gravel soils
• D. Clay soils

Answer: (B)

Sound transmission through soil depends on how the soil’s density, stiffness, porosity, and moisture promote or dissipate the vibration. Loamy soil, a balanced mix of sand, silt, and clay, tends to damp vibrations the most because its fine particles and moisture increase friction and energy loss while still providing a continuous medium for waves to travel. This combination causes vibrations to be absorbed and scattered more effectively, resulting in greater attenuation of noise across a broad range of frequencies. In comparison, sandy soils are more open and transmit energy with less damping, gravel causes more scattering and less consistent transmission, and clay—while dense—does not damp across frequencies as broadly in typical conditions. Thus loamy soil is the most effective at reducing noise transmission underground.