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D5333-03 – Standard Test Method Technical Guide
ASTM D5333-03 establishes a standardized test method for measuring the magnitude of one-dimensional collapse that occurs when unsaturated soils are inundated with fluid. This procedure is critical for evaluating collapsible soils, which can withstand high loads at low water content but suddenly settle upon wetting. The standard provides a framework for specimen preparation, apparatus calibration, and the calculation of collapse metrics.
📐 Scope and Key Terminology
This test method, under the jurisdiction of ASTM Committee D18 (Subcommittee D18.05 on Structural Properties of Soils), applies to both undisturbed and remolded specimens. The values stated in SI units are regarded as the standard. The method defines specific terms to describe the collapse behavior:
| 🟦 Term | 📏 Symbol | 📐 Definition |
|---|---|---|
| Collapse | — | Decrease in height of a confined soil following wetting at a constant applied vertical stress. |
| Collapse Potential | Ic | Relative magnitude of collapse determined at any user-specified stress level. |
| Collapse Index | Ie | Relative magnitude of collapse determined specifically at 200 kPa (2 tsf). |
Referencing ASTM D653 for general terminology, this standard adds these specific definitions to accurately quantify the collapse phenomenon observed in soils such as loess and certain compacted fills.
⚙️ Test Procedure and Calculation of Collapse Potential
The test is performed in a one-dimensional consolidometer, following the general principles of Test Method D2435. A specimen is loaded to a specific vertical (axial) stress. After primary consolidation under this stress is complete, the specimen is inundated with fluid while the stress is held constant. The resulting decrease in height represents the collapse.
The Collapse Potential (Ic) is calculated using the following formula:
Ic = [ (df - do) / ho - (di - do) / ho ] × 100
This can be simplified to:
Ic = [ (df - di) / ho ] × 100
Where do is the dial reading at seating stress, di is the dial reading before wetting, df is the dial reading after wetting, and ho is the initial specimen height. It can also be expressed in terms of void ratio as Ic = (Δe / (1 + e0)) × 100.
💡 Technical Note: Large applied vertical stress is not a prerequisite for collapse. The potential for collapse is directly related to the soil’s initial water content, density, and the applied stress at inundation.
| 🎯 Variable | ⚡ Description | 📏 Typical Unit |
|---|---|---|
| Ic | Collapse Potential (any stress) | Percent (%) |
| Ie | Collapse Index (at 200 kPa) | Percent (%) |
| do, di, df | Dial readings at seating, before wetting, after wetting | mm (in) |
| ho | Initial specimen height | mm (in) |
📊 Reporting and Applications
The Collapse Index (Ie) provides a standardized index for rating the potential for collapse. This index is a specific calculation of Ic at the standard 200 kPa stress level. Test reports must include the initial water content (per D2216), initial dry density, the applied vertical stress, and the calculated Ic or Ie.
📌 Standard Requirements: SI units are the standard in this test method. Inch-pound units are provided for information only. The procedures account for testing both undisturbed and remolded specimens, allowing for a comprehensive evaluation of in-situ and compacted soil behavior.
This test method is essential for geotechnical investigations in arid and semi-arid regions where collapsible soils are prevalent, helping engineers design foundations that mitigate the risk of sudden, catastrophic wetting-induced settlement.
❓ Frequently Asked Questions
🔍 What is the fundamental difference between Collapse Potential (Ic) and Collapse Index (Ie)?
Collapse Potential (Ic) is a general calculation that can be performed at any applied vertical stress relevant to the project. The Collapse Index (Ie) is a specific value of collapse potential calculated at the standardized stress of 200 kPa (2 tsf), as defined in Section 3.2.2 of the standard, providing a consistent index for classification.
💡 How does the Collapse Potential formula work according to the standard?
According to Eq 1 in the standard, Ic is calculated as: Ic = [(df – do)/ho – (di – do)/ho] × 100. This represents the difference between the strain after wetting and the strain before wetting at a given stress, isolating the settlement caused specifically by the inundation event.
⚡ Can this test method be performed on both undisturbed and remolded specimens?
Yes. Section 1.4 of ASTM D5333-03 explicitly states that the procedures are applicable to both undisturbed and remolded specimens. This allows engineers to evaluate collapse potential for natural soil deposits and engineered compacted fills.
📌 What other ASTM standards are referenced in this test method?
This standard references several key ASTM standards, including D653 (Terminology), D2216 (Moisture Content), D2435 (One-Dimensional Consolidation), D3740 (Agency Evaluation), D4829 (Expansion Index), and D6026 (Significant Digits in Geotechnical Data).