Investigating the Influence of Lateral Loading on the Vertical Capacity of Coal Mine Standing Supports

The National Institute for Occupational Safety and Health (NIOSH) initiated a testing program to assess the effects of lateral loading on various standing supports used in underground coal mines. This study is not intended to endorse a particular type of standing supports nor to provide a comparison between different types of standing supports. This paper aims to measure the lateral loading capacity of two types of standing supports and evaluate how it affects their vertical loading capacity and yielding mechanisms. The study utilizes the Mine Roof Simulator (MRS) at NIOSH Pittsburgh. Type-1 support is characterized by telescopic tubes made from ASTM A-513 steel with a specified locking mechanism, and Type-2 support comprises a single component constructed from ASTM A500 Welded Grade C pipe. Vertical load tests were carried out to assess the designed performance of Type-1 and Type-2 props. Type-1 props demonstrated a "constant yielding" behavior, achieving an ultimate capacity of up to 140 kips. Type-2 props showed a "load shedding" behavior, reaching peak verti- cal loads of up to 191 kips. Buckling analysis revealed that Type-1 props were not designed to buckle, and Type-2 props failed due to buck- ling rather than material yielding. Under vertical pre-loading, lateral loading tests showed that Type-1 props can withstand about 9 kips, and Type-2 props can withstand about 10.79 kips of lateral load. This represents roughly 6% of their vertical loading capacities. Testing props under lateral loads in addition to their intended vertical loads showed that the lateral loads could influence their loading mechanisms. Type-1 props did not exhibit the expected "constant yielding" behavior under lateral load but instead showed "load shedding" decreasing their rated vertical capacity by 70%. At high vertical pre-loading, Type-2 props demonstrated "constant yielding" behavior instead of the anticipated "load shedding," leading to a 60% reduction in their rated vertical capacity. These findings provide valuable insights into the behavior of these props under different loading conditions, aiding in their efficient use and design in underground mining operations.