Astm D338518 - Pdf

ASTM D3385-18 is the active standard test method for measuring the infiltration rate of soils in the field using a double-ring infiltrometer. It is utilized in geotechnical engineering to assess water penetration using constant, measured flow in two concentric rings, making it best suited for uniform soils with specific hydraulic conductivity. Purchase the official document at ASTM International ASTM International

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2. Theoretical Background

2.1 The Infiltration Process

Infiltration occurs when water at the soil surface enters the pores of the soil matrix. The rate at which this occurs is influenced by soil texture, structure, bulk density, initial moisture content, and the presence of vegetation or cracks. Initially, when soil is dry, the infiltration rate is high due to capillary suction (matric potential). As the soil saturates, gravity becomes the dominant force, and the infiltration rate stabilizes, approaching the saturated hydraulic conductivity ($K_sat$) of the soil.

• Principle: Install two concentric open cylinders driven into soil, maintain constant head in rings, measure water added to the inner ring over timed intervals; divide infiltrated volume by inner ring area → incremental infiltration velocity (cm/h).
• Typical ring sizes: inner ~300 mm dia., outer ~600 mm dia., height ~500 mm; outer ring induces vertical flow beneath inner ring.
• Other apparatus: driving caps, maul/sledge or jack, Mariotte bottle or level gauge/flow control, splash guards, bentonite grout for sealing trenches, depth gauge, timing device.

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.