The "double-ring" design is critical for accuracy because it forces water in the inner ring to flow . The outer ring acts as a buffer, saturating the surrounding soil to prevent lateral (sideways) spreading from the inner measurement area. Requirement under ASTM D3385-18 Method Constant Head Method (water level is kept steady) Ring Depth Driven typically to 150 mm (6 inches) Measurement
The "double-ring" design is critical for accuracy because it forces water in the inner ring to flow . The outer ring acts as a buffer, saturating the surrounding soil to prevent lateral (sideways) spreading from the inner measurement area. Requirement under ASTM D3385-18 Method Constant Head Method (water level is kept steady) Ring Depth Driven typically to 150 mm (6 inches) Measurement