Significance and Use
Rock bolts are used for support in a variety of mining and civil engineering situations. The pull test may be used to provide a quantitative measure of the relative performance of different anchor systems in the same rock type. Anchor systems may be different mechanical anchors or different bond materials or lengths for grouted anchors. Such data can be used to choose an anchor type and determine bolt length, spacing, and size.
The objective of the method is to measure anchor performance, and not the performance of the rock bolt itself. Thus, to ensure that the bolt response during the test is minimal and predictable, high strength, short-length (6 to 8 ft (1.8 to 2.5 m)) bolts have been specified. The bolt should be just long enough to ensure that no failure of the rock mass occurs.
Ideally, the rock bolt anchor should fail by shear at the anchor-rock interface or bond. Therefore, the local characteristics of the rock, such as roughness and induced fractures, are significant factors in the anchor strength. To obtain realistic strength values, the test holes should be drilled using the same methods as the construction rock bolt holes.
Rocks with significant time-dependent behavior, such as rock salt or shale, may respond to the anchor system itself and change the anchor strength. In these cases, consideration should be given to testing bolts over a period of time.
In establishing a testing program, the following factors should be considered:
Anchor pull tests should be conducted in all rock types in which construction bolts will be installed. If the rock is anisotropic, for example, bedded or schistose, the tests should be conducted in various orientations relative to the anisotropy, including those at which the construction bolt may be installed.
In each rock type, at each orientation, and for each anchor system, a sufficient number of tests should be conducted to determine the average bolt capacities within a fixed uncertainty at the 95 % confidence level. The allowable uncertainty band depends on the project and involves such factors as the rock quality, expected project lifetime, and importance of the areas to be bolted. Its determination will require considerable engineering judgment. As a rough guideline, at least 10 to 12 pull tests for a single set of variables have been found necessary to satisfy the statistical requirements.
Note 1—Notwithstanding the statements on precision and bias contained in this test method; the precision of this test method is dependent on the competence of the personnel performing it, and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D 3740 are generally considered capable of competent and objective testing. Users of this test method are cautioned that compliance with Practice D 3740 does not in itself assure reliable testing. Reliable testing depends on many factors; Practice D 3740 provides a means of evaluating some of those factors.
1.1 The objective of this test method is to measure the working and ultimate capacities of a rock bolt anchor. This method does not measure the entire roof support system. This method also does not include tests for pretensioned bolts or mine roof support system evaluation.
1.2 This test method is applicable to mechanical, cement grout, resin, (epoxy, polyester, and the like), or other similar anchor systems.
1.3 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.
1.4 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D 6026.
1.4.1 The method used to specify how data are collected, calculated, or recorded in this standard is not directly related to the accuracy to which the data can be applied in design or other uses, or both. How one applies the results obtained using this standard is beyond its scope.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D653 Terminology Relating to Soil, Rock, and Contained Fluids
D3740 Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
D4436 Test Method for Rock Bolt Long-Term Load Retention Test
D6026 Practice for Using Significant Digits in Geotechnical Data
D6167 Guide for Conducting Borehole Geophysical Logging: Mechanical Caliper
anchors (rock); displacement; field testing; loading tests; mines; pull testing; rock; shear testing; Anchor bolts; Displacement--rock environments; Field testing--rock; Loading tests--rock/related materials; Mines; Pull testing; Rock materials/properties/analysis;
ICS Number Code 93.020 (Earth works. Excavations. Foundation construction. Underground works)
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Citing ASTM Standards
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