Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D5856-15 – Standard Test Method Technical Guide
ASTM D5856-15 specifies a laboratory method for measuring the hydraulic conductivity of porous materials using a rigid-wall, compaction-mold permeameter. This standard is under the jurisdiction of ASTM Subcommittee D18.04 on Hydrologic Properties and Hydraulic Barriers and is critical for characterizing compacted soils used in environmental and geotechnical barriers.
📐 Scope and Applicability
This test method applies to laboratory-compacted specimens with a hydraulic conductivity less than or equal to 1 × 10⁻⁵ m/s. For materials with higher hydraulic conductivity, Test Method D2434 (Constant Head) is specified. The values stated in SI units are the standard; however, reporting in cm/s remains a traditional practice in the U.S. The standard does not address all safety concerns. Users must establish appropriate safety and health practices and determine regulatory limitations prior to use.
⚙️ Test Procedure and Apparatus
The permeameter consists of a rigid compaction mold. Specimens are generally compacted within the mold itself, following standard efforts outlined in Test Methods D698 (Standard Proctor) or D1557 (Modified Proctor). After compaction, the specimen is saturated, and a hydraulic gradient is applied. The flow rate is measured until a steady state is achieved. Key referenced apparatus standards include D4753 for balances, D2216 for moisture content, D854 for specific gravity, and E145 for ovens.
| 📌 Referenced Standard | 🔧 Application in D5856-15 |
|---|---|
| D698 / D1557 | Standard procedures for laboratory compaction of soil specimens (Standard and Modified Effort). |
| D2216 | Standard test method for determining the water (moisture) content of the soil. |
| D854 | Procedure for measuring the specific gravity of soil solids, essential for void ratio calculations. |
| D3740 | Minimum requirements for agencies engaged in the testing and inspection of soil and rock. |
| D5084 | Alternative test method for hydraulic conductivity using a flexible wall permeameter. |
📊 Key Terminology and Measured Properties
The standard defines hydraulic conductivity (k) as the rate of discharge of water under laminar flow conditions through a unit cross-sectional area of a porous medium under a unit hydraulic gradient and standard temperature conditions (20°C). The term “coefficient of permeability” is historically synonymous. For a complete discussion, refer to Terminology D653. The terms flux (quantity of flow per unit area per unit time) and pore volume of flow (cumulative outflow divided by the specimen’s pore volume) are specific criteria used to verify that steady-state flow conditions have been reached.
| 🟦 Term | 🎯 Definition (from D5856-15) |
|---|---|
| Hydraulic Conductivity (k) | Rate of discharge under laminar flow through unit area under unit gradient at standard temperature (20°C). |
| Flux | Quantity of flow per unit area per unit time. |
| Pore Volume of Flow | Cumulative outflow from a specimen divided by the volume of pore space. |
⚠️ Scope Limitation: This test method is not suitable for materials with a hydraulic conductivity exceeding 1 × 10⁻⁵ m/s. Sidewall leakage in the rigid-wall permeameter can lead to inaccurate results for more permeable soils. Use Test Method D2434 for such materials.
💡 Standardization at 20°C: Hydraulic conductivity is highly dependent on water temperature due to changes in viscosity. Results must be corrected and reported for a standard temperature of 20°C to ensure comparability across different testing conditions and laboratories.
❓ Frequently Asked Questions
🔍 What is the primary distinction between D5856 and the flexible wall method D5084?
D5856 utilizes a rigid-wall compaction-mold permeameter. The specimen is typically compacted directly into the mold and tested within it. D5084 uses a flexible membrane and a confining cell pressure, which effectively seals the sides of the specimen and prevents sidewall leakage. D5084 is often preferred for a wider