ICGCM Papers:
Support Performance Assessments
 
 
Analysis of the Design and Performance Characteristics of Pumpable Roof Supports
35th International Conference on Ground Control in Mining
Analysis of the Design and Performance Characteristics of Pumpable Roof Supports
by
Timothy Batchler, NIOSH, Office of Mine Safety and Health Research, Pittsburgh, United States
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[Conference] 35th International Conference on Ground Control in Mining
[Price] Free  [Comments] 0
[Topical Area] Support Performance Assessments
[Author] Timothy Batchler, NIOSH, Office of Mine Safety and Health Research, Pittsburgh, United States
[Abstract] 
Key Conclusions:
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This study presents the impact of several design parameters (support material, diameter, bag construction, and wire pitch) for pumpable roof support systems. The peak capacity, stiffness, and residual load characteristics can be controlled by modifying these design parameters. Not all supports are the same, using different fill material will provide different performance characteristics. Currently, there are two basic types of material used, CSA and Portland based materials. A universal performance behavior is a high stiffness and sustainable yield that is controlled by the confinement provided by the wire wrapped bag. This confinement affects both the peak and residual loads. Currently, progressive load shedding is a common and unavoidable consequence of the material used for this type of support construction. Therefore, reducing load shedding behavior with this type of support construction will have to be achieved by altering the fill materials properties to eliminate the brittle failure and highly bulked behavior of the failed material. With a better understanding of the pumpable support performance characteristics, a roof support design can be customized to specific ground control conditions.
Key Findings:
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There are several design parameters that can affect the performance characteristics of the pumpable support system. There is a strong relationship between the support performance and the different types of cementitious material used for the support construction. The stiffness of the supports constructed from Calcium-sulfo-aluminate (CSA) material was significantly higher than the Portland material for all support sizes. In general, the peak load capacity of the CSA supports were higher than the Portland supports. Confinement also plays a significant role in the support performance influencing both the peak load and residual load behavior. The bag is used as a form for filling the support in place underground and integrates a spiraled wire around the pumpable support to increase confinement of the fill material. There is a direct relationship between the wire spacing (pitch) and the capacity of the support. The failure behavior of pumpable supports, like all brittle material, occurs when the support stress exceeds the tensile shear strength causing a load shed event. A sequence of significant load shedding events occurs during loading and the support typically fails progressively. In general, supports constructed from Portland material have more load shed events occurring before the peak load than those made from CSA material and about the same degree of load shedding after the peak.
Objective of the Paper:
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This paper evaluates the impact of various support design parameters by examining full-scale performance tests conducted at the National Institute for Occupational Safety and Health’s (NIOSH) Mine Roof Simulator (MRS) as part of the various vender developmental and quality control testing. These tests were analyzed to identify correlations between the support design parameters and the resulting performance. Based on more than 160 tests, quantifiable patterns were examined to assess the correlation of the support dimensions, cementitious material type, wire pitch and single-wall vs dual-walled bag designs to the support capacity, stiffness, load shedding events, and yield characteristics.
Problem Statement:
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Pumpable roof supports are currently being used to provide safe working environment for longwall mining. Because pumpable supports are visually similar and installed fundamentally in the same manner, there is a tendency to believe they perform the same way. However, there are several design parameters that can affect their performance, including the cementitious material properties and the bag construction practices that influence the degree of confinement provided. A full understanding of the impact of these design parameters is necessary to optimize the support application and to provide a foundation for making further improvements in the support performance.