ASTM D7401 Laboratory Determination of Rock Anchor Capacities by Pull and Drop Tests
For ASTM D7401, a rock anchor is fixed in a steel pipe, instead of a borehole, with the same material as its intended application. The rock anchor is hydraulically pushed horizontally during the Pull test, and the displacement of the bolt head is measured at the same time. The anchor system is pulled until the bolt breaks. The plot of load vs displacement is used to calculate the rock anchor's ultimate and working capacities. A known mass is launched vertically, impacting on a plate at a preset distance, which is then affixed to the end of a rock anchor in the Drop test. The maximum energy is measured in kilojoules (kJ).
Scope:
This ASTM D7401 test method is used to determine the working and ultimate static or dynamic capacities of full-scale rock anchors quantitatively. To replicate rock burst and blasting situations, dynamic capacities are calculated.
Procedure:
ASTM D7401 includes installing the Encapsulated Resin Anchor Bolt Specimen by inserting a plug that extends from the top of the specimen tube to below the second set of 25.4 mm holes into the tube.
- Pull Test Method A: The 1m wire is linked to the rock anchor’s end and fed through the tube’s top. The washer over the end of the rock anchor against the tube, the 325 kN hollow ram with a 150 mm stroke, and the 300 mm diameter–12 mm thick steel plate are all mounted. The second potentiometer is attached to the nut. A hand and an electric pump power the hollow ram. During the ASTM D7401 test, the hand pump is employed before resin failure. Once the resin begins to fail, or until the specimen fails or the ram reaches its limit, an electric pump is used.
- Drop Test Method B: The mass to be dropped is predetermined. The clevis is attached to the end of a thin-walled tube that passes through the specimen tube support assembly in the middle. The clevis connects the end of the rock anchor to the thin-walled tube. The end displacement is measured using a camera that monitors a target on the thin-walled tube. These tests are used to calculate the Transverse Stiffness, KT, and Impact energy.
KT=2E1+vdo2-d12di1-2vdi2+do2
Where
KT – Transverse stiffness, MPa/mm
E – Young’s modulus, GPa
v – Poisson’s ratio
do – External pipe diameter, mm
di – Internal pipe diameter, mm.
Ep = (9.81.w.h)1000
Where
Ep – Impact energy, kJ
w – Mass, kg
h – Height,m
Data:
The Data stated in SI units are to be regarded as standard. No other units of measurement are included in the ASTM D7401 standard.
Conclusion:
ASTM D7401 test method is used to determine the working and ultimate static or dynamic capacities of full-scale rock anchors quantitatively. To replicate rock burst and blasting situations, dynamic capacities are calculated.
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