Anchorage Pull Testing for Fully Grouted Roof Bolts

Mark, Chris
Organization: International Conference on Ground Control in Mining
Pages: 9
Publication Date: Jan 1, 2002
Fully-grouted roof bolts comprise more than 80% of the primary roof supports used in U.S. coal mines. However, nearly 1,500 MSHA reportable, non-injury roof falls occur each year, and most of these are attributable to failure of the roof bolt system. Anchorage failure is one failure mechanism for fully-grouted bolts. As roof deformation works its way upward, the bolts can become heavily loaded near their upper ends, If the applied load exceeds the anchorage, the bolts will simply pull out. Research dating back 30 yrs indicates that this type of anchorage failure is most likely when the roof rock is weak, just where roof support is most critical. In soft shale or coal roof, the small amount of data available in the literature indicates that 20-30 in of resin anchorage may be required to achieve the full capacity of the bolt. In other words, the "full resistance zone" of a 60 in bolt may actually be just 30-40 in. Despite its potential importance, there is no widely accepted anchorage test for fully grouted bolts. Standard pull tests have sometimes been employed, but they provide no information on the anchorage near the top of the bolt. An alternative, first described more than 25 yrs ago in the U.S., is the short-encapsulation pull test (SEPT). With this test, the bolt is installed with only a short (1 ft or less) tube of resin. In recent years variations of this test have become international standards. This paper describes recent studies using short encapsulation pull tests in the U.S. Tests were conducted in the National Institute for Occupational Safety and Health (NIOSH) Safety Research Coal Mine at Bruceton and at underground mines in Pennsylvania and West Virginia. The study found that the SEPT can be used to make a simple evaluation of resin bolt anchorage. Suggested procedures for conducting SEPT are included. The study also confirmed that poor anchorage can be an issue, particularly where the roof rock is very weak. Some simple techniques for improving anchorage, and thereby the effectiveness of fully grouted bolts, are discussed.
Full Article Download:
(2412 kb)


Additional chapters/articles from the SME-ICGCM book Proceedings 21st International Conference on Ground Control in Mining

Pre-Driven Experimental Longwall Recovery Room Under Weak Ro
Longwall Mining-Induced Abutment Loads and Their Impacts on
Influence of Structural Stress Concentration and Structural
The NIOSH Shield Hydraulics Inspection and Evaluation of Leg
Study on Top-Coal Loss and the Optimum Drawing Interval of L
Stress Measurements for Safety Decisions in Longwall Coal
Re-Use of Rectangular Bolted Roadways in a Cover Depth > 100
Numerical Modeling of the Gob Loading Mechanism in Longwall
Deep Cover Pillar Extraction in the U.S. Coalfields
Evaluation of Pillar Recovery in Southern West Virginia
A Case History Investigation of Two Coal Bumps in the Southe
A Linear Coal Pillar Strength Formula for South African Coal
Anchorage Pull Testing for Fully Grouted Roof Bolts
Comparison of Some Aspects of Bolting Mechanisms Between Ful
Eclipse System Improves Resin Anchored Rebar Bolting
Design Considerations for Tensioned Bolts
Field Testing of the Fully Grouted Thrust Tensioned Bolts
Improvement in Pre-Tensioning of Strand Bolts in Australian
The Introduction of Roof Bolting to U.S. Underground Coal Mi
Support of Coal Mines in the United Kingdom
The Use of NDT Methods to Determine the Condition of Rockbol
Rockbolted Support of Retreat Longwall Gateroads at 1000m De
Roof Screening: Best Practices and Roof Bolting Machines
Numerical and Physical Modeling as Planning Tools for Rockbo
Stone Mine Design in Highly Fractured Rock
The Importance of Underground Stone Mine Roof Geology
Utilization of Ground-Penetrating Radar to Determine Roof Co
An Examination of the Loyalhanna Limestone's Structural
Highwall Stability in an Open Pit Stone Operation
Overview of Safety Considerations with Highwall Mining Opera
Highwall Monitoring to Combat Rockfall Accidents at Opencast
Seepage and Reinforcement Behavior of Grouting Into Slaking-
Floor Heave in Shallow Room-and-Pillar Mining
Analysis of a Stability Problem in an Underground Coal Mine
Comparison of Acoustic Emission and Stress Measurement Resul
Acoustic Scanner Analysis of Borehole Breakout to Define the
Estimating Rock Strengths Using Drilling Parameters During R
New developments with the coal mine roof rating
Application of geotechnical and geophysical parameters to im
Development of a Risk Rating System for Use in Underground C
Empirical and analytical design of large openings at a propo
Shear Mechanism for Mining-Induced Fractures Applied to Rock
Evaluating Techniques for Monitoring Rock Falls and Slope St
Developments in Sealant Support Systems for Ground Control
Stability Control of Clusters of Deep Openings Around Shaft
The Use of Pneumatic Stowing in Germany Considering Subsiden
A 3-D Semi-Analytical Method for Subsidence Prediction and S
Theory and Technology of Mining Subsidence Control by Grouti
Surface Subsidence Due to the Combined Effects of Undergroun