Roof bolt load and differential sag measurements

Technical Report · Fri Sep 03 04:00:00 EDT 1965

OSTI ID:5326304

de la Cruz, R; Stefanko, R

Today roof bolts are the major method of support in coal mines. Nevertheless, it is rare when instrumentation exists to evaluate the bolt load upon installation or anytime thereafter. The torque wrench at best gives only a crude approximation and can be in great error. Yet, unless the effectiveness of bolting can be evaluated, it is impossible to improve anchorage efficiency. The type of research program described is very significant and could lead to the scientific selection of a bolting system instead of the trial-and-error techniques employed to date. As a result of the field work, it became apparent that a bolt load cell was needed that would combine accuracy and sensitivity with economy and simplicity. Since such a device was not available, it was decided to develop one. A cell was constructed on the same principle as a proving ring. It is essentially a steel ring with two holes drilled diametrically opposite to allow the insertion of the bolt. This ring is placed between the head of the bolt and the plate during installation. Upon torquing the bolt, the ring deflection is measured by a precision dial gage and the bolt load is revealed precisely. The test arrangement permitted the measurement of bolt loads and bed separation simultaneously. The beds began to separate almost immediately after roof exposure, and blasting had an adverse effect. One separation plane occurred in the bolt zone of influence but two major separations were located above the plane of anchorage. With bolt load loss, the top broke and the place became very hazardous to work.

• Research Organization: Pennsylvania State Univ., University Park (USA). Dept. of Mining
• OSTI ID: 5326304
• Report Number(s): SR-53
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
012000* -- Coal
Lignite
& Peat-- Mining
ANCHORS
COAL MINING
EQUIPMENT
MECHANICAL STRUCTURES
MINING
MINING EQUIPMENT
NORTH AMERICA
PENNSYLVANIA
PERFORMANCE TESTING
ROOF BOLTS
SUPPORTS
TESTING
UNDERGROUND MINING
USA