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IS 11309:1985 is the Indian Standard (BIS) for method of conducting a pull-out test on anchor bars and rock bolts. This standard specifies the method for conducting in-situ pull-out tests on grouted anchor bars and rock bolts. It details the required apparatus, testing procedure, and reporting of results to determine the bond strength and load-displacement characteristics of the rock anchor system.
Method of conducting a pull-out test on anchor bars and rock bolts
! Ensure the reaction frame is rigid and its supports are placed far enough from the bolt head (typically >2 times the bonded length) to not influence the rock failure cone.
! A spherical seating is crucial to avoid eccentric loading, which can lead to premature or incorrect failure readings.
! Properly isolate the unbonded (free) length of the anchor to ensure the test measures the bond strength of the intended grouted section only.
Standard Test Method for Rock Bolt and Anchor Pull-Out Test
Directly covers the in-situ pull-out testing procedure for rock bolts and anchors.
BS EN 1537:2013BSI / CEN, UK / Europe
HighCurrent
Execution of special geotechnical works - Ground anchors
Provides a comprehensive framework for ground anchor execution, including detailed testing protocols.
ISRM Suggested Method for Rock Bolt Testing (1974)International Society for Rock Mechanics and Rock Engineering (ISRM)
HighCurrent
Suggested Methods for Rock Bolt Testing
A foundational 'suggested method' that is functionally equivalent and informs many national standards.
ASTM E488 / E488M - 22ASTM International, USA
MediumCurrent
Standard Test Methods for Strength of Anchors in Concrete and Masonry Elements
Covers pull-out tests for anchors in concrete, but lacks the specific focus on rock strata.
Key Differences
≠IS 11309 specifies a single, general-purpose test method, whereas modern standards like BS EN 1537 differentiate between multiple test types (e.g., Investigation, Suitability, and Acceptance tests) with distinct procedures and objectives.
≠Loading procedures in international standards are often more complex. BS EN 1537 and ASTM D4435 specify detailed loading cycles and longer, more defined holding periods for creep measurement, compared to the simpler incremental loading with short holding times in IS 11309.
≠BS EN 1537 provides specific, quantitative acceptance criteria based on creep rate and residual displacement, whereas IS 11309 leaves the establishment of acceptance criteria to the project-specific design.
≠Modern standards like ASTM D4435 have more stringent requirements for equipment calibration and accuracy (e.g., ±2% for load measurement) compared to IS 11309 (±5%).
Key Similarities
≈The fundamental principle is identical across all standards: apply a controlled tensile load to an installed anchor and measure the resulting displacement to evaluate its performance.
≈The core test apparatus is fundamentally the same, consisting of a reaction frame, a hydraulic jack and pump for load application, a load cell or calibrated pressure gauge, and displacement gauges.
≈The primary objective is consistent: to verify the load-carrying capacity of the anchor-grout-substrate system in its installed, in-situ condition.
≈All standards require the generation of a load-displacement curve as the primary output of the test, which forms the basis for all subsequent analysis and acceptance.
Parameter Comparison
Parameter
IS Value
International
Source
Load Measurement Accuracy
Preferably within 2%, but not to exceed 5% of test load.
Accurate to ±2% of the maximum test load.
ASTM D4435 / D4435M - 19
Displacement Measurement Resolution
0.01 mm (using dial gauges).
0.025 mm (0.001 in.).
ASTM D4435 / D4435M - 19
Load Holding Time per Increment
Not less than 3 minutes, until movement ceases.
A minimum of 1 minute after target load is achieved.
ASTM D4435 / D4435M - 19
Creep Test Hold Duration (at peak load)
Not explicitly defined as a separate 'creep test'; holding time is per increment.
15 to 60 minutes for a Suitability Test, depending on ground conditions.
BS EN 1537:2013
Reaction Frame Bearing Distance
Bearing point should be at least 1.0 anchor diameter (preferably 2.5x hole dia) from anchor.
Reaction frame support shall be at a distance of at least 2.5 times the anchor head maximum dimension.
BS EN 1537:2013
Number of Displacement Gauges
At least two dial gauges.
Three or more, equally spaced around the anchor.
ASTM D4435 / D4435M - 19
Test Types Defined
One standard pull-out test procedure.
Three types: Investigation Test, Suitability Test, and Acceptance Test.
BS EN 1537:2013
⚠ Verify details from original standards before use
Key Values5
Quick Reference Values
Minimum bearing plate thickness25 mm
Loading rate not to exceed10 kN/min
Displacement measurement accuracy (dial gauge)0.01 mm
Pressure gauge accuracy2 percent of the maximum test load
Minimum duration for holding each load increment2 minutes
Key Formulas
Bond Stress = P / (π * d * L) — where P is pull-out load, d is bolt diameter, and L is bonded length
Tables & Referenced Sections
Key Tables
No tables data
Key Clauses
Clause 4 - Apparatus
Clause 5 - Procedure
Clause 5.3 - Application of Load
Clause 6 - Observations and Calculations
Clause 7 - Report
Frequently Asked Questions3
What is the primary purpose of a pull-out test on a rock bolt?+
To determine the ultimate pull-out resistance (bond strength) and load-displacement behavior of a rock anchor system in its specific rock mass.
How is the load applied during the test?+
The load is applied incrementally using a calibrated hydraulic jack. Each load increment is held steady for at least 2 minutes to allow for creep deformation (Clause 5.3).
What data is plotted from this test?+
A graph of applied load (or stress) versus the displacement of the anchor head is plotted to analyze the performance of the anchor system.