Variability of Saturated Hydraulic Conductivity Measurements Made Using a Flexible-Wall Permeameter

Abstract A study was conducted following the procedures in ASTM E691-14 (Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method) to develop a precision statement for hydraulic conductivity measurement of fine-grained soils using Method C (falling head, rising tailwater elevation) of ASTM D5084-10 (Standard Test Methods for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter). Twelve laboratories conducted tests on three replicate specimens of three fine-grained soils (9 specimens total per laboratory) from the ASTM Reference Soils Program: Soil ML (silt), Soil CL (low plasticity clay), and Soil CH (high plasticity clay). The data indicated that the measurement variability for hydraulic conductivity is modest but not negligible, and probably contributes to the spatial variability reported in past studies of hydraulic conductivity. No systematic relationships were observed between variability in hydraulic conductivity and testing time (consolidation, permeation), backpressure, B-coefficient achieved at end of consolidation, compliance with the termination criteria, or specimen compaction conditions. Many laboratories did not comply with the test standard or the supplemental instructions, which may indicate that greater oversight of geotechnical laboratories is needed via accreditation and auditing programs. Analysis of the data indicate that hydraulic conductivity can be measured using Method C of ASTM D5084 within a factor of 2 for the 10–6 cm/s range, a factor of 1.5 for the 10–8 cm/s range, and a factor of 4 for the 10–9 cm/s range.