Web-based Class Project on Rock Mechanics

1. Web-based Class Projecton Rock Mechanics Polyurethane Resin Grouting for Stabilization Prepared by: Report prepared as part of course CEE 544: Rock Mechanics Winter 2015 Semester Instructor: Professor Dimitrios Zekkos Department of Civil and Environmental Engineering University of Michigan Clark Green With the Support of:

2. Contents • 1.0 Introduction • 2.0 Types of Polyurethanes • 3.0 Effects on Fractured Rock Masses • 4.0 Implementation and Design Considerations • 5.0 Advantages and Disadvantages • 6.0 Case Study • West Virginia Roof and Pillar Coal Mine • Poudre Canyon Tunnel • 7.0 Conclusions

3. 1.0 Introduction • Polyurethane Resin = PUR • Subset of the broader “polyurethane” chemical grout category • Purpose of PUR grouting • To consolidate and strengthen a fractured rock mass by injection grouting • “Rock Gluing” • Applications • Coal mine roof and/or longwall stabilization (1960’s – present) • Standard method for stabilization in Germany since 1970’s • Rock slope stabilization against rock falls (since the 2000’s) • Recently researched by FHWA

4. 2.0 Types of Polyurethanes • Single Stage Polyurethane (PU) • One component polyurethane chemical, one component water • HYDROPHILIC – REQUIRES WATER FOR REACTION • Expansive reaction due to production of CO2 foam • Sealant/Water Cutoff • Polyurethane Resin (PUR) • Two components polyurethane chemical • HYDROPHOBIC – DOES NOT REQUIRE WATER FOR REACTION • Some PUR may react with water by design • Strength/Stabilization • Epoxy • Not used for large-scale grouting Expansion potential of polyurethane (Joyce 1992)

5. 2.0 Types of Polyurethanes Adapted from (Arndt et al 2008)

6. 3.0 Effects on Fractured Rock Masses • Penetrates fractures • As small as 0.5 mm apertures • Chemically binds to rock • Consolidation of rock mass • Increased strength of rock mass • Creates impermeable barrier • Grout curtains aid in design injection sequence • Creates water cutoff • Provided all void spaces are filled Rock – Dark colored material PUR – Light colored material PUR seams infiltrating fracture pattern (Molinda 2004)

7. 4.0 Implementation • General PUR grouting procedure • Drill grout borehole • Sequence and spacing of boreholes to be discussed later • Insert grouting assembly into borehole • Pressure transfer from grout tube into borehole • Target zones along borehole for improvement • Mix components • Perform mixing as close as possible to the injection site • Inject grout through fractures along borehole • Stop injection when PUR is seen visibly extruding from surface of rock or spike in back pressure is observed Example grout pump. Small and easy to mobilize (Bodi2012)

8. 4.0 Design Considerations • Rock mass characterization • Target zones for improvement • Estimate void space • Estimate amount of PUR required • Estimate moisture content for hydrophilic PUR • Injection sequence • Determine borehole dimensions and spacing • Determine location of grout curtains/barriers • Drill and fill one at a time • Monitor injection pressures • Be aware of temperature effects • Viscosity and set time of PUR • Handling PUR components • Some PUR components may be skin and eye irritants • Cured PUR resin is chemically and environmentally inert

9. 5.0 Advantages and Disadvantages Advantages Disadvantages Infiltration is unknown Invasive techniques required for verification Hydrofracturing Too much injection pressure may cause rock falls High Cost • Low viscosity • Penetrates small fractures • High control resolution • Viscosity • Expansion properties • Set time (seconds) • Strength • Strength • 3 – 4 times the strength of cementitious grouts • Easily mobilized and environmentally inert • Aesthetics

10. 6.0 Case Studies West Virginia Coal Mine Poudre Canyon Tunnel 75 ft long tunnel through vertically foliate gneiss Western portal prone to rock falls Previously stabilized with non-tensioned rock dowels PUR chosen to demonstrate effectiveness of technique FHWA demonstration project performed by the Colorado Department of Transportation • Experiencing multiple roof falls per year • Moisture sensitive shale roof • Roof supports restricting passage through mine • PUR injection chosen for stabilization of roof at intersections

11. West Virginia Coal Mine Standing supports not doing so well (Molinda 2008) Plan view of roof falls and planned injection sites (Molinda 2008)

12. West Virginia Coal Mine • Plan view • 11 boreholes per intersection, staggered • 10 ft center-to-center spacing • Cross section • Target zone between 2 – 6 ft above roof chosen to create grout “beam” for stabilization • Initial injection performed at perimeter angled 45 degrees to create grout curtain • Sequential injection of targeted zone Injection design (Molinda 2004) Stabilization design (Molinda 2008)

13. West Virginia Coal Mine • 100% filling of voids • 9 of 16 boreholes • Partial filling of voids • 4 of 16 boreholes • 43% to 93% • No filling of voids • 3 of 16 boreholes • 0%, 1%, and 9% observed • The boreholes showing no filling of voids were supported with standing supports. • Verification of infiltration extremely important Verification of PUR infiltration (Molinda 2008)

14. 6.0 Case Studies West Virginia Coal Mine Poudre Canyon Tunnel 75 ft long tunnel through vertically foliate gneiss Western portal prone to rockfalls Previously stabilized with non-tensioned rock dowels PUR chosen to demonstrate effectiveness of technique FHWA demonstration project performed by the Colorado Department of Transportation • Experiencing multiple roof falls per year • Moisture sensitive shale roof • Roof supports restricting passage through mine • PUR injection chosen for stabilization of roof at intersections

15. Poudre Canyon Tunnel • Injection sequence • Bottom of rock face to top (generally) • Borehole geometry • 1.5 in diameter • 10 – 12 ft depth • Pumping sequence • Initial injection to allow gravity flow downward through fractures • Second injection to force resin outward and upward • Pumping halted when PUR was seen extruding above current borehole • Pumping pressures kept below 50 psi • No intrusive verification performed Poudre Canyon Tunnel with injection sequence overlay (Arndt et al 2008)

16. FHWA Recommendations • Context Sensitive Rock Slope Design Solutions Manual (2011) • Apply PUR to fracture apertures greater than 2 mm • Space injection boreholes 8 – 16 ft apart • PUR may flow 10 – 15 ft away from borehole through fracture pattern • Boreholes should intersect major discontinuities at 90 degree angles • Inject PUR from bottom to top using staged pumping • Keep pressures below 250 psi • PUR is recommended by the FHWA to be used only as a supplemental method of stabilization

17. 7.0 Conclusions • PUR consolidates and strengthens rock masses • Penetrates and fills fractures as small as 0.5 mm in aperture • Control of important engineering properties • Viscosity • Set time • Strength • Expansion properties • Important design considerations • Rock mass characterization • Borehole and injection sequencing • Verification • Proven in the coal mine and transportation industries

18. Questions?

19. References • Arndt, B., DeMarco, M., and Andrew, R. (2008). Polyurethane Resin (PUR) Injection for Rock Mass Stabilization, Federal Highway Administration Central Federal Lands Highway Division, Lakewood, CO. • Bodi, J., Bodi, Z., Scucka, J., and Martinec, P. (2012). “Chapter 14: Polyurethane Grouting Technologies, Polyurethane” InTech, <http://www.intechopen.com/books/polyurethane/ polyurethane-grouting-technologies> (Mar. 3, 2015) • Joyce, J. T. (1992). “Polyurethane Grouts.” Concrete Construction, The Aberdeen Group, <http://www.concreteconstruction.net/concrete-articles/polyurethane-grouts.aspx> • Molinda, G. (2004). “Evaluation of Polyurethane Injection for Beltway Roof Stabilization in a West Virginia Coal Mine.” Proceedings of the 23rd International Conference on Ground Control in Mining, West Virginia University, Morgantown, WV, 190-196. • Molinda, G. (2008). “Reinforcing Coal Mine Roof with Polyurethane Injection: 4 Case Studies.” J. Geotech. Geol. Eng., 26(5), 553-566.

20. More Information More detailed technical information on this project can be found at: http://www.geoengineer.org/education/web-based-class-projects/rock-mechanics