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D5220 – Standard Test Method Technical Guide
🧐 Scope and Summary of Test Method
ASTM D5220/D5220M−21 defines the standard for measuring the water mass per unit volume of soil and rock in-place by the neutron depth probe method. This nuclear method relies on the thermalization of fast neutrons emitted from a probe placed at depth within an access tube. The value is determined by comparing the thermal neutron count rate with established calibration data as detailed in Annex A1.
Values must be reported in either SI units or inch-pound units. Each system is to be regarded separately as standard, and the two systems shall not be combined. All observed and calculated values must adhere to the rounding guidelines of Practice D6026.
⚠️ Nuclear Safety: Users must establish appropriate safety, health, and environmental practices. Specific hazards for this test method are listed in Section 8. Compliance with all regulatory limitations regarding the neutron source is mandatory.
⚙️ Test Procedure and Calibration
The procedure involves placing a fast neutron source and thermal neutron detector at the desired depth in a bored hole lined by an access tube. The thermal neutron count rate is directly influenced by the hydrogen content of the surrounding soil or rock, allowing the water mass per unit volume to be derived.
Accuracy is dependent on a robust calibration program. The standard mandates that calibration data be established in accordance with Annex A1 to correlate specific probe count rates to known water contents. Interferences affecting this measurement are discussed in Section 6 of the standard.
💡 Data Quality Tip: Proper installation of the access tube is critical to minimize interferences from air gaps or borehole irregularities. The material and dimensions of the tube must be consistent with those used during calibration.
📊 Key Measured Properties and Reporting
The primary property measured is the water mass per unit volume. This test is commonly used in geotechnical engineering for compaction control and moisture monitoring. Results from this method can be correlated with laboratory tests such as D2216 for moisture content.
| 🟦 Standard | 🎯 Key Relevance |
|---|---|
| D653 | Standard Terminology |
| D2216 | Lab Moisture Content |
| D6026 | Significant Digits & Rounding |
| D3740 | Quality Assurance for Agencies |
| 🟦 Parameter | 📏 Specification |
|---|---|
| Measured Quantity | Water Mass per Unit Volume |
| Method | Neutron Thermalization (Depth Probe) |
| Calibration | Mandatory (Annex A1) |
| Safety | Specific Hazards in Section 8 |
❓ Frequently Asked Questions
🔍 What