Thomas M. Barczak Timothy J. Batchler NIOSH Pittsburgh Research Laboratory

1. Comparison of the Transverse Load Capacities of Various Block Ventilations Stoppings Under Arch Loading Conditions Thomas M. Barczak Timothy J. Batchler NIOSH Pittsburgh Research Laboratory

2. Mine Ventilation Stoppings Insufficient capability to withstand transverse loading. What caused this failure?

3. ASTM E 72 TESTING • CFR Part 75.333 Ventilation Controls requires stoppings to be evaluated in accordance with ASTM E-72 specifications. • Provide an average capacity of 39 psf.

4. Problem Statement • This presentation compares the transverse load capabilities of several block materials and wall dimensions commonly used in stopping constructions. • Mine Ventilation stoppings are dependent upon the material strength of the block, the height and thickness of the wall and its boundary conditions.

5. Mine Roof Transverse load Tension Compression Mine Floor Test Protocol for Arch-Loading • Wall bridges between mine roof and floor. • Compressive forces are developed within the wall.

6. Mine Roof Simulator (MRS) • Multi axis load frame. • Controlled vertical and horizontal movement of lower platen. • 3 million lbs capacity.

7. Simulating Rigid Arching In the MRS Transverse load

8. Lower Platen Upper Platen Single Column Concrete Wall Adjusting Nuts 20 Kip Load Cell Metal Plate Rolling Tray Platen Bolt

9. Arch-Loading Evaluation • The applied horizontal force to the base of the half-wall by the MRS is measured. • This equates to the transverse pressure acting of the stopping wall.

10. Various Block Materials • Standard concrete masonry unit (CMU) • Lightweight aggregate CMU • Hollow core block • Autoclaved aerated concrete (AAC) Materials • Foamed Cement • Extruded Foam Cement

11. Transverse Load Capacities • Several factors influence the transverse load capacity. • Three critical parameters are: • Block Strength • Block Thickness • Wall Height

12. Block Material Properties • Wide range of block materials. • Current ASTM criterion (freestanding wall evaluation)

13. Block Height and Thickness • Transverse load decreases as the entry height increases • Transverse load increases as the wall thickness increases

14. Critical Design Parameters • Direct correlation between block compress strength (fc), wall height (L), wall thickness (t), and transverse load capacity.

15. Impact from Convergence • Convergence causes increased thrust force on the hinge points in the wall. • This additional thrust force increases the wall’s resistance to deflect outward, thus resulting in higher transverse load capacity. • Benefits from convergences is lost once the block strength is reached.

16. Vertical Preload Pressure 30-in half-wall height 45-in half-wall height 60-in half-wall height

17. Lateral Displacement Rigid Boundary Stiffness • Rigid arch conditions apply when the abutments (mine roof and floor) do not deform. • Lateral displacement is controlled by the stiffness and elastic response of the wall • If the abutments are not rigid, then more lateral displacement will occur, resulting in a decrease in the transverse load capacity.

18. Reduction of System Stiffness • The impact of the abutment stiffness has a greater impact on the shorter walls. 30-in half-wall height 60-in half-wall height 45-in half-wall height

19. Impact of Preload on Boundary Stiffness • As preload increases, reductions from boundary stiffness to transverse pressure are diminished.

20. Conclusions • A new test protocol was used to evaluate several blocks currently used for stoppings. • Compressive strength of the block, wall height, and block thickness have significant impact on the transverse load capacity. • Boundary conditions and convergence greatly affect the transverse load capacity.

21. Any Questions Ice Block - 12 feet tall - 10 feet wide - weighs 20 tons

22. Any Questions