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D5607-16 – Standard Test Method Technical Guide
📐 Scope, Specimens, and Discontinuity Types
ASTM D5607 – 16 establishes requirements and laboratory procedures for performing direct shear strength tests on rock specimens under a constant normal load (CNL). It includes procedures for both intact rock strength and sliding friction tests. Specimens must be homogeneous or have planes of weakness, including natural or artificial discontinuities such as rock-concrete interfaces or concrete lift lines. Only one discontinuity per specimen can be tested.
Discontinuities can be in the following states:
| 🟦 State | 📐 Description |
|---|---|
| Open | Clean break, may be free-draining (drained test possible) |
| Healed | Partially or completely recemented |
| Filled | Contains clay fillings or gouge |
The test method applies to hard rock, medium rock, soft rock, and concrete (Section 1.2). The test is usually conducted in the undrained state with an applied constant normal load.
⚙️ Test Procedure and Boundary Conditions
The test is performed under quasi-static, monotonic shearing conditions. The constant normal load (CNL) boundary condition specified is appropriate for problems where the normal stress is constant along the discontinuity. Caution is advised for dilatancy-controlled shearing where this condition may not hold.
⚠️ Constant Normal Load Limitations: The CNL boundary condition may not be appropriate for problems where shearing is dilatancy controlled and the normal stress is not constant along the discontinuity (Section 1.3).
💡 Nominal Area vs. Actual Contact: The term “normal force” is used instead of “normal stress” because of the indefinable area of contact and minimal relative displacement during testing. The actual total contact surface is unmeasurable, so nominal area is used for loading and calculations (Note 1).
The standard makes no provision for the measurement of pore pressures. Therefore, strength values determined are expressed in terms of total stress, uncorrected for pore pressure (Note 2). A clean, open discontinuity may be free-draining and could be considered a drained test.
📊 Key Measured Properties and Data Relationships
During the test, shear strength is determined at various applied stresses normal to the sheared plane and at various shear displacements.
| 📏 Derived Relationship | 🎯 Purpose |
|---|---|
| Shear Strength vs. Normal Stress | Defines the failure envelope for the rock or discontinuity. |
| Shear Stress vs. Shear Displacement | Determines the shear stiffness of the rock mass or discontinuity. |
All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026 (Section 1.4). Reporting of test results in units other than SI shall not be regarded as nonconformance (Section 1.5).
❓ Frequently Asked Questions
🔍 Can I test a specimen with multiple joints or discontinuities?
No, Section 1.1 explicitly states that only one discontinuity per specimen can be tested.
💡 Why is “normal force” used in the title instead of “normal stress”?
Because the actual areas of contact change during testing and are unmeasurable. A nominal area is used for loading and calculations (Note 1).
⚡ Does this test method apply to concrete?
Yes, Section 1.2 explicitly states that this standard applies to hard rock, medium rock, soft rock, and concrete.
📌 Are the test results drained or undrained?
Results are expressed in terms of total stress, uncorrected for pore pressure, as the standard does not provide for pore pressure measurement (Note 2). A test on a clean, open discontinuity could be considered a drained test.