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is where the actual measurements are taken. Because it is surrounded by the saturated buffer of the outer ring, the water from the inner ring is forced to move almost entirely downward in one-dimensional, vertical flow.

For most North American regulatory and engineering applications, . astm d338518 pdf

V=ΔQA×Δtcap V equals the fraction with numerator cap delta cap Q and denominator cap A cross delta t end-fraction = Infiltration velocity (typically expressed in mm/minmm/min is where the actual measurements are taken

Infiltration Rate of Soils in Field Using Double-Ring Infiltrometer1 V=ΔQA×Δtcap V equals the fraction with numerator cap

One famous anecdote from the 1990s: a landfill liner design in Florida relied on lab permeability tests showing clay was nearly impermeable. But field tests using D3385 found infiltration rates 100 times higher—because natural cracks and wormholes existed. The design was changed, preventing a major groundwater contamination risk.

Engineers must carefully select a level test site. The rings are driven vertically into the soil using a driving plate and hammer to ensure a snug fit and prevent water leakage. In stiff or dry soils, a trench may be excavated to facilitate installation. Following installation, a constant or falling head of water is maintained in both rings.

Identify a representative test location free of surface debris, large roots, and heavy vegetation.