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D3385-18 – Standard Test Method Technical Guide
📐 Scope and Applicability of D3385-18
ASTM D3385-18 provides a standardized procedure for the field measurement of the infiltration rate of liquids (typically water) into soils using a double-ring infiltrometer. This test method is particularly applicable to relatively uniform fine-grained soils, with an absence of very plastic (fat) clays and gravel-size particles, and with moderate to low resistance to ring penetration. The soil is regarded as naturally occurring earth materials, processed materials, or mixtures thereof that are basically insoluble.
The standard explicitly defines the boundaries of soil hydraulic conductivity where the method is applicable. It cautions that the procedure is difficult to use or that data may be unreliable in very pervious or impervious soils. The test may be conducted at the ground surface or at given depths in pits, and on bare soil or with vegetation in place, depending on the conditions for which infiltration rates are desired.
⚠️ Critical Geotechnical Limitation: This test method cannot be conducted where the test surface is below the groundwater table or a perched water table (Section 1.5). Additionally, it cannot be used directly to determine the hydraulic conductivity (coefficient of permeability) of the soil (Section 1.7).
⚙️ Installation, Procedure, and Soil Conditions
The double-ring infiltrometer is installed by driving the rings into the soil. In dry or stiff soils that might fracture during driving, the infiltrometer may be installed in a trench excavated specifically for the test. The double-ring geometry promotes one-dimensional vertical flow beneath the inner ring, minimizing lateral spreading of the infiltrating water.
The standard specifies specific hydraulic conductivity thresholds for the reliable application of the test method. The table below summarizes the applicable soil conditions and limitations governing the use of the double-ring infiltrometer as defined in the scope.
| 🟦 Parameter | 📏 Applicable Range | 📐 Condition / Notes |
|---|---|---|
| Hydraulic Conductivity (Upper) | Less than ~10⁻² cm/s | Data may be unreliable above this threshold |
| Hydraulic Conductivity (Lower) | Greater than ~1 × 10⁻⁵ cm/s | Refer to Test Method D5093 for lower values |
| Soil Classification | Uniform fine-grained soils | Absence of very plastic clays and gravel |
| Test Surface Location | Ground surface or pit depth | Cannot be below groundwater table |
📊 Key Measured Properties and Referenced Standards
The primary data generated by this test method is the infiltration rate, measured as the rate of fall of water in the inner ring over time. Adherence to auxiliary ASTM standards is required for proper classification, sampling, and quality assurance of the field data. Section 2 of the standard lists the normative references that must be used in conjunction with D3385-18.
| 🎯 ASTM Standard | ⚡ Title / Purpose |
|---|---|
| D653 | Terminology Relating to Soil, Rock, and Contained Fluids |
| D1452 | Practice for Soil Exploration and Sampling by Auger Borings |
| D2216 | Test Methods for Laboratory Determination of Water Content |
| D2488 | Practice for Description and Identification of Soils (Visual-Manual) |
| D3740 | Minimum Requirements for Agencies Engaged in Testing of Soil and Rock |
| D5093 | Field Measurement of Infiltration Rate Using Double-Ring Infiltrometer with Sealed-Inner Ring |
💡 Standard Units Note: The values stated in SI units are to be regarded as the standard for this test method. The inch-pound units given in parentheses are mathematical conversions provided for information purposes only (Section 1.8).
❓ Frequently Asked Questions
🔍 What types of soil does D3385-18 specify the double-ring infiltrometer test is best suited for?
The standard indicates it is “particularly applicable to relatively uniform fine-grained soils, with an absence of very plastic (fat) clays and gravel-size particles and with moderate to low resistance to ring penetration” (Section 1.4).
💡 Can the double-ring infiltrometer test directly measure hydraulic conductivity?
No. Section 1.7 explicitly states, “This test method cannot be used directly to determine the hydraulic conductivity (coefficient of permeability) of the soil.” The measured infiltration rate is governed by multiple factors including soil structure and initial moisture content.
⚡ What alternative method is recommended for soils with very low permeability?
For soils with a hydraulic conductivity less than about 1 × 10⁻⁵ cm/s, the standard directs users to refer to Test Method D5093, which involves a double-ring infiltrometer with a sealed-inner ring (Section 1.6).
📌 Is it permissible to conduct