Web-based Class Projecton Rock Mechanics

Report prepared as part of course CEE 544: Rock Mechanics

Winter 2015 SemesterInstructor: Professor Dimitrios Zekkos

Department of Civil and Environmental Engineering University of Michigan

Polyurethane Resin Grouting for Stabilization

Prepared by:

Clark Green

With the Support of:

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

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

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)

2.0 Types of PolyurethanesProperty Polyurethane (PU) Polyurethane Resin (PUR) EpoxyMixing Components One Two Two

Reaction with Water Hydrophilic (required) Hydrophobic Hydrophobic

Density Low to Medium 3 - 50 pcf

Medium to High20 – 70 pcf

Low to High5 – 60 pcf

Compressive/Tensile Strength

Low10 – 500 psi

Low to High15 – 20,000 psi

Medium to High5,000 to 20,000 psi

Viscosity Low to Medium Low to High Very Low to High

Relative Cost Low Mid to High High

Adapted from (Arndt et al 2008)

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 materialPUR – Light colored material

(Molinda 2004)

PUR seams infiltratingfracture pattern

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 observedExample grout pump. Small and easy to mobilize (Bodi 2012)

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

5.0 Advantages and DisadvantagesADVANTAGES

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

DISADVANTAGES

Infiltration is unknown◦ Invasive techniques required for verification

Hydrofracturing◦ Too much injection pressure may cause rock falls

High Cost

6.0 Case StudiesWEST VIRGINIA COAL MINE

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

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

West Virginia Coal Mine

Standing supports not doing so well (Molinda 2008) Plan view of roof falls and planned injection sites (Molinda 2008)

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)

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)

6.0 Case StudiesWEST VIRGINIA COAL MINE

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

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

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 performedPoudre Canyon Tunnel with injection sequence overlay (Arndt et al 2008)

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

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

Questions?

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.

More Information

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

http://www.geoengineer.org/education/web-based-class-projects/rock-mechanics