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D5407-95 – Standard Test Method Technical Guide
ASTM D5407‑95 (Reapproved 2000) specifies the standard test method for determining elastic moduli of undrained, intact rock core specimens in triaxial compression without pore pressure measurement. This method is critical for deriving the stress‑axial strain and stress‑lateral strain curves, as well as Young’s modulus (E) and Poisson’s ratio (ν).
📐 Specimen Geometry and Tolerances
Per Section 3, the test specimen is a rock core cut to length with machined flat ends. Conformance to the dimensional and shape tolerances specified in ASTM D 4543 is mandatory. The water content of the specimen is determined according to ASTM D 2216. Note that this test method does not cover post‑peak stress‑strain behavior (Note 1) and is not suitable for rocks exhibiting significant inelastic strains, such as potash or salt (Section 1.3).
⚠️ Anisotropy and Inelastic Effects: The engineering applicability of the isotropic equations provided in Section 1.2 decreases if the rock is anisotropic. If the difference in elastic moduli in any two directions exceeds 10% at a given stress level, the equations give only approximate results. For highly inelastic rocks, unload‑reload cycles are necessary.
⚙️ Test Procedure and Speed Selection
The loading device, verified per ASTM E 4, must apply load at a rate conforming to the requirements of Section 9.6. The specimen is placed in a triaxial chamber, subjected to a confining pressure, and optionally heated to the desired test temperature. Axial load is continuously increased while axial and lateral deformations are monitored to determine the elastic constants.
💡 Sonic Methods (Note 2): Elastic moduli measured by sonic methods can be employed as a preliminary measure of anisotropy before conducting the full undrained triaxial compression test. The triaxial test itself simulates the stress conditions of underground rock masses (Section 4).
📊 Key Measured Properties and Calculations
For isotropic materials, the elastic moduli are derived from the stress‑strain curves. The fundamental relations are defined in Section 1.2.
| 🟦 Property | 📏 Symbol | 📐 Formula (Isotropic) |
|---|---|---|
| Young’s Modulus | E | Stress / Axial Strain |
| Poisson’s Ratio | ν | − (Lateral Strain / Axial Strain) |
| Shear Modulus | G | E / [2(1 + ν)] |
| Bulk Modulus | K | E / [3(1 − 2ν)] |
| 🟦 Test Aspect | 🎯 Requirement | ⚡ Key Specification |
|---|---|---|
| Specimen Tolerances | ASTM D 4543 | Dimensional and shape tolerances |
| Water Content | ASTM D 2216 | Laboratory moisture determination |
| Load Verification | ASTM E 4 | Periodic verification of machine |
| Drainage Condition | Undrained | No pore pressure measurement |
| Units | SI Units | Regarded as the standard |
✅ Application Context (Section 4): Deformation and strength of rock are functions of confining pressure. While this test accurately measures intact specimen properties, large‑scale in‑situ behavior is strongly influenced by joints, faults, and other inhomogeneities. Laboratory values must, therefore, be applied with proper judgment in engineering design.
❓ Frequently Asked Questions
🔍 What is the scope of ASTM D5407‑95?
This standard covers the determination of elastic moduli (Young’s modulus and Poisson’s ratio) of intact rock core specimens in undrained triaxial compression. It specifies the apparatus, instrumentation, and procedures for obtaining stress‑axial strain and stress‑lateral strain curves up to the ultimate strength.
💡 How is the shear modulus calculated?
For isotropic materials, the shear modulus (G) is derived from Young’s modulus (<