Soil Permeability (Hydraulic Conductivity from a Permeameter Test)

Constant head (ASTM D2434, coarse soils): collect a volume Q over time t under a fixed head h, k = Q L/(A h t). Falling head (ASTM D5084, fine soils): time the head dropping from h1 to h2 in a standpipe of area a, k = (a L/A t) ln(h1/h2). L is sample length, A its area. A 250 cm3 collection in 60 s through a 12 cm x 78.5 cm2 sample under 30 cm head gives k = 2.12e-2 cm/s (60.2 ft/day), a medium-permeability sand. Reports k in cm/s and ft/day plus the Terzaghi/Das drainage class. Correct k to 20 C; a lab specimen can miss field fabric and layering. The geotechnical engineer governs.

constant head (ASTM D2434): k = Q L/(A h t); falling head (ASTM D5084): k = (a L/(A t)) ln(h1/h2); k in cm/s, 1 cm/s = 2834.6456 ft/day.

Darcy's-law permeameter tests -- ASTM D2434 (constant head) and ASTM D5084 (falling head) -- by name, with the Terzaghi/Das drainage-class ranges; no ASTM table text reproduced.

Darcy's law and the two permeameter reductions are public soil-mechanics results printed in every geotechnical text; ASTM D2434/D5084 are purchased standards cited by name only.

Estimate. AHJ and licensed professional govern.

Field names used by the API: method, q_cm3, head_cm, t_s, l_cm, a_sample_cm2, k_cm_s, k_ft_day

• Constant-head reduction k = Q L/(A h t); Darcy's law at a fixed head, for coarse soilsASTM D2434
• Falling-head reduction k = (a L/(A t)) ln(h1/h2); the head falls in a standpipe of area a, for fine soilsASTM D5084
• Drainage class and scope Terzaghi/Das ranges; correct to 20 C; one specimen can miss field fabric, so field k often runs highersoil mechanics