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D4428 – Standard Test Method Technical Guide
📐 Test Method Scope and Definitions
ASTM D4428/D4428M-14 covers crosshole seismic testing to determine velocities of horizontally travelling seismic waves, specifically primary compression (P-wave) and secondary shear (S-wave), in soil materials. The standard relies on first arrival times or interval arrival times over measured distances for data analysis. Key terms are defined, with “seismic wave train” as the recorded motion of a seismic disturbance with time. General terminology follows ASTM D653.
⚙️ Test Procedure and Equipment Specifications
The test method involves advancing boreholes through soil and using a borehole seismic source at selected depths to generate a seismic wave train. Downhole receivers in offset borings detect the wave train’s arrival. The recommended spacing between offset borings is 3 to 6 meters [10 to 20 feet]. A borehole deviation survey measures the exact distance between boreholes at test depths.
Acceptable equipment includes borehole seismic sources, downhole receivers, and recording systems. The source triggers the recording system, which records the receiver responses to measure travel time. Additional procedures address drilling, casing, grouting, and deviation surveys to ensure accurate results.
| 🟦 Parameter | 📏 Specification | 🎯 Unit |
|---|---|---|
| Borehole Spacing | 3 to 6 | m |
| Borehole Spacing (inch-pound) | 10 to 20 | ft |
| Wave Types Measured | P-wave, S-wave | – |
| Analysis Method | First arrival or interval arrival times | – |
📊 Key Measured Properties and Data Interpretation
The primary properties are P-wave and S-wave velocities. Data interpretation must conform to Practice D6026 for significant digits and rounding. Collection and calculation procedures in these test methods are regarded as the industry standard. Measurements beyond specified sensitivity are not considered nonconformance unless they violate standard objectives.
Results should be reported in SI or inch-pound units independently; combining units from both systems is non-conforming.
⚠ Important Unit Consideration: Values in SI and inch-pound are not exact equivalents. Use each system independently to avoid non-conformance.
💡 Best Practice: Accurate borehole deviation surveys are crucial for correct distance measurement, ensuring reliable velocity calculations from travel time data.
❓ Frequently Asked Questions
🔍 What is the scope of ASTM D4428?
The standard is limited to determining P-wave and S-wave velocities in soil materials using crosshole seismic methods.
💡 What are the recommended borehole spacings?
Offset borings should be spaced 3 to 6 meters [10 to 20 feet] apart.
⚡ How are travel times measured?
The recording system is triggered by the seismic source, and downhole receivers detect wave train arrivals to measure travel times.
📌 Can units be mixed?
No. SI and inch-pound units must be used separately; combining them may result in non-conformance.