1. Web-based Class Project on Rock Mechanics
Polyurethane Resin Grouting for Stabilization
Prepared by:
Clark Green
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
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 Purpose of PUR grouting
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
Property
Polyurethane (PU)
Polyurethane Resin (PUR)
Epoxy
Mixing Components
One
Two
Reaction with Water
Hydrophilic (required)
Hydrophobic
Density
Low to Medium
pcf
Medium to High
20 – 70 pcf
Low to High
5 – 60 pcf
Compressive/Tensile Strength
Low
10 – 500 psi
15 – 20,000 psi
5,000 to 20,000 psi
Viscosity
Very Low to High
Relative Cost
Mid to High
High
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 (Bodi 2012)

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

10. 6.0 Case Studies West Virginia Coal Mine Poudre Canyon Tunnel
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
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

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
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
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

15. Poudre Canyon Tunnel Injection sequence Borehole geometry
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, < polyurethane-grouting-technologies> (Mar. 3, 2015)
Joyce, J. T. (1992). “Polyurethane Grouts.” Concrete Construction, The Aberdeen Group, <
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,  
Molinda, G. (2008). “Reinforcing Coal Mine Roof with Polyurethane Injection: 4 Case Studies.” J. Geotech. Geol. Eng., 26(5),

20. More Information
More detailed technical information on this project can be found at: