IS 11315:1987 Part 2 is the Indian Standard (BIS) for methods of test for rocks - part 2: determination of uniaxial compressive strength. This standard specifies the laboratory method for determining the uniaxial compressive strength of cylindrical rock specimens. It details the requirements for the testing apparatus, specimen dimensions and preparation, loading procedure, and the method for calculating and reporting the strength. This test provides a fundamental mechanical property of rock essential for engineering design and classification.
Specifies the method for determining the uniaxial compressive strength of rock specimens.
Overview
- Status
- Current
- Usage level
- Specialized
- Domain
- Geotechnical — Surveying and Geotechnical Investigation
- Type
- Testing Method
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Practical Notes
! The point load test is a valuable index test for field use due to the portability of the equipment, allowing for rapid rock strength classification on site.
! A test is considered valid only if the rock specimen breaks with a fracture plane passing through both loading points. Off-center fractures invalidate the result.
! Accurate application of the size correction factor to obtain Is(50) is crucial for comparing strength results from specimens of different sizes and shapes.
Frequently referenced clauses
rock
International Equivalents
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Key Values7
Quick Reference Values
Recommended core specimen diameter (D)50 mm (approx.)
Minimum specimen length to diameter ratio (L/D) for diametral test1.1
Minimum specimen length to width ratio (L/W) for block test0.5
Loading rate to cause failurewithin 10 to 60 seconds
Validity check - fracture distance from platen tip> 0.5 * D
Standard platen cone angle60 degrees
Standard platen tip radius5 mm
Key Formulas
Is = P / D² — Uncorrected point load strength index (Diametral test)
Is = P / We² — Uncorrected point load strength index (Axial, Block, Lump tests)
We = √(4A/π) — Equivalent core diameter from area A
Is(50) = F * Is — Size-corrected point load strength index
F = (De/50)^0.45 — Size correction factor
Tables & Referenced Sections
Key Clauses
Clause 4: Apparatus
Clause 5: Preparation of Test Specimens
Clause 6: Test Procedure
Clause 7: Calculations
Clause 8: Report
Frequently Asked Questions4
What is the primary purpose of the Point Load Test?+
To determine the point load strength index (Is) for rock classification and to provide an indirect estimate of the rock's Unconfined Compressive Strength (UCS). (Clause 1.1)
What types of rock specimens can be used?+
The test can be performed on rock cores (diametral and axial tests), cut blocks, or irregular lumps. (Clause 5)
How is the final strength value reported?+
As the size-corrected point load strength index, Is(50), which normalizes the result to a standard equivalent core diameter of 50 mm. (Clause 7.2)
What is the recommended loading time for a valid test?+
The load should be applied steadily such that failure occurs within 10 to 60 seconds. (Clause 6.1)
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