1. BBUGS Suppliers Day - Moranbah
Improved Roofbolting Methodologies
Reducing Hydraulic Fracture
of Strata
David Evans – Technical Manager, DSI Australia
BEng (Mech), MBA, MIEAust
26th November, 2015

2. BBUGS Suppliers Day - Moranbah
Formal Proceedings
UOW 2015 Coal Conference: pp
ICGCM 2015 Conference: pp

3. Presentation Outline
Resin Injection / Hydraulic Fracture of Strata
Progression of Resin Bolting Studies – Gloving / Mixing / Pressure
Borehole Resin Pressures – Parametric Analysis
– Fluid Flow Concepts
– Empirical Relationship
Experimental Method and Results
Empirical Calculations & Model
Load Transfer Tests
Conclusion

4. Presentation Outline
Resin Injection / Hydraulic Fracture of Strata
Progression of Resin Bolting Studies – Gloving / Mixing / Pressure
Borehole Resin Pressures – Parametric Analysis
– Fluid Flow Concepts
– Empirical Relationship
Experimental Method and Results
Empirical Calculations & Model
Load Transfer Tests
Conclusion

5. Resin Injection / Hydraulic Fracture of Strata
Resin loss into strata voids is a well known phenomenon during roof-bolting
Witnessed by encapsulation variance
The greatest resin ‘back-pressure’ is induced at the top of the bolting horizon – on full bolt insertion.

6. Resin Injection / Hydraulic Fracture of Strata
Resin loss into strata voids is a well known phenomenon during roof-bolting
Witnessed by encapsulation variance
The greatest resin ‘back-pressure’ is induced at the top of the bolting horizon – on full bolt insertion.

7. Resin Injection / Hydraulic Fracture of Strata
Underground images show resin injection into voids at the top of the bolting horizon.
Does resin injection into voids induce hydraulic fracture of strata during bolt insertion ?
Can resin pressures be generated at this order of magnitude – exceeding the compressive strength of the strata ?
Are current bolting practices, in part, propagating roof damage ?

8. Presentation Outline
Resin Injection / Hydraulic Fracture of Strata
Progression of Resin Bolting Studies – Gloving / Mixing / Pressure
Borehole Resin Pressures – Parametric Analysis
– Fluid Flow Concepts
– Empirical Relationship
Experimental Method and Results
Empirical Calculations & Model
Load Transfer Tests
Conclusion

9. Presentation Outline
Resin Injection / Hydraulic Fracture of Strata
Progression of Resin Bolting Studies – Gloving / Mixing / Pressure
Borehole Resin Pressures – Parametric Analysis
– Fluid Flow Concepts
– Empirical Relationship
Experimental Method and Results
Empirical Calculations & Model
Load Transfer Tests
Conclusion

10. Progression of Resin Bolting Studies - Gloving
Gloving studies (Pettibone, 1987), (Pastars and MacGregor, 2005)
Regions of discontinuity between bolt, cured resin and borehole / strata.
Gloving modes - wrapped plastic / complete sleeving of the bolt.
Loss of load transfer – worst case 85 to 90% reduction.

11. Progression of Resin Bolting Studies – Mixing Effectiveness
Mixing studies (Campbell and Mould, 2003)
Regions of unmixed and uncured resin following standard bolt installation.
Geometrical configuration of 15:1 resin in a 28.5mm borehole – permits poor mixing.
Catalyst compartment is too small to be adequately ruptured and dispersed.
15:1
Resin
28.5 mm
Bore
AT Bolt
Profile

12. Progression of Resin Bolting Studies – Mixing Effectiveness
Further mixing studies, ACARP report C21023 (McTyer, Feb 2015).
New test method (borehole sleeving) and associated instrumentation.
The bore hole diameter is simulated by a PVC inner tube, structurally supported by an outer steel reinforcing pipe.
Ease of inspection of resin annulus.
Large data set generated.

13. Progression of Resin Bolting Studies – Mixing Effectiveness
15:1 Resin / 28mm Bore
15:1 Resin / 30mm Bore

14. Progression of Resin Bolting Studies – Mixing Effectiveness
15:1 resins exhibit partial un-mixing in 28mm boreholes.
15:1 resins exhibit very poor mixing in 30mm boreholes.
2:1 resins mix well in a 30mm borehole.
2:1
Resin
30 mm
Bore
AT Bolt
Profile

15. Progression of Resin Bolting Studies – Mixing Effectiveness
15:1 resins exhibit partial un-mixing in 28mm boreholes.
15:1 resins exhibit very poor mixing in 30mm boreholes.
2:1 resins mix well in a 30mm borehole.
2:1
Resin
30 mm
Bore
AT Bolt
Profile

16. Progression of Resin Bolting Studies – Mixing Effectiveness
2:1 Resin / 30mm Bore
15:1 Resin / 30mm Bore

17. Progression of Resin Bolting Studies – Mixing Effectiveness
28mm Bore 15:1 Resin
28mm Bore 2:1 Resin
n = 34
n = 30

18. Progression of Resin Bolting Studies – Mixing Effectiveness
30mm Bore 15:1 Resin
30mm Bore 2:1 Resin
n = 14
n = 13

19. Progression of Resin Bolting Studies – Resin Pressure
Resin pressure studies (Giraldo et al., 2006).
Cartridge radially expands in borehole, ruptures and slips over bolt (gloving).
Proposed a mathematical model for the burst pressure of the cartridge – however, this was not the peak observed pressure.
Different resin bolting systems generated peak pressures between MPa (3,500 psi) and MPa (7,000 psi).

20. Progression of Resin Bolting Studies – Resin Pressure
(Giraldo et al., 2006).

21. Presentation Outline
Resin Injection / Hydraulic Fracture of Strata
Progression of Resin Bolting Studies – Gloving / Mixing / Pressure
Borehole Resin Pressures – Parametric Analysis
– Fluid Flow Concepts
– Empirical Relationship
Experimental Method and Results
Empirical Calculations & Model
Load Transfer Tests
Conclusion

22. Presentation Outline
Resin Injection / Hydraulic Fracture of Strata
Progression of Resin Bolting Studies – Gloving / Mixing / Pressure
Borehole Resin Pressures – Parametric Analysis
– Fluid Flow Concepts
– Empirical Relationship
Experimental Method and Results
Empirical Calculations & Model
Load Transfer Tests
Conclusion

23. Borehole Resin Pressures – Parametric Analysis
Presents as a highly complex fluid mechanics model.
Three main parametric groups:
Fluid characteristics of the resin
Dimensional geometry – resin, borehole and bolt.
Rate of insertion of the bolt

24. Borehole Resin Pressures – Parametric Analysis
Fluid characteristics of the resin
Dynamic Viscosity (N.sec.m-2 )
Density (kg.m-3)
(both temperature dependent)

25. Borehole Resin Pressures – Parametric Analysis
Dimensional geometry – resin, borehole and bolt.
Resin cartridge diameter (m)
Resin cartridge length (m)
Bore hole diameter (m)
Bolt core diameter (m)
Bolt rib profile (various dimensions) – height, width, flank angles, radial profile, pitch spacing (m, degrees)
Relative surface roughness of the borehole (dimensionless)

26. Borehole Resin Pressures – Parametric Analysis
Rate of insertion of the bolt
Bolt insertion velocity (m.s-1)
Bolt rotational speed (rad.s-1)

27. Borehole Resin Pressures – Parametric Analysis
Indeterminate Parameters /
Sources of Variance
Non-homogenous fluid (suspension of solids in liquids)
True viscosity and fluid density values are indeterminate
Change of state of properties – chemical reaction occurs during mixing
Temperature variances – fluid properties and reaction time

28. Presentation Outline
Resin Injection / Hydraulic Fracture of Strata
Progression of Resin Bolting Studies – Gloving / Mixing / Pressure
Borehole Resin Pressures – Parametric Analysis
– Fluid Flow Concepts
– Empirical Relationship
Experimental Method and Results
Empirical Calculations & Model
Load Transfer Tests
Conclusion

29. Presentation Outline
Resin Injection / Hydraulic Fracture of Strata
Progression of Resin Bolting Studies – Gloving / Mixing / Pressure
Borehole Resin Pressures – Parametric Analysis
– Fluid Flow Concepts
– Empirical Relationship
Experimental Method and Results
Empirical Calculations & Model
Load Transfer Tests
Conclusion

30. Borehole Resin Pressures – Fluid Flow Concepts
The velocity of the bolt through the resin generates the back flow of the resin in the annulus.
The velocity of the resin flow is directly proportional to the insertion speed of the bolt.
The fluid velocity in the annulus generates the associated borehole back pressures.

31. Borehole Resin Pressures – Fluid Flow Concepts
Highly Turbulent Flow
“In turbulent flow we cannot evaluate
the pressure drop analytically, so we
must resort to experimental results
and dimensional analysis to correlate
the experimental data”
(Fox and McDonald, 1985, 360).

32. Borehole Resin Pressures – Fluid Flow Concepts
Fluid Flow – Sudden Constrictions
Pressure losses for fluid flow through sudden constrictions are based on the square of the fluid velocity divided by two.
(Fox and McDonald, 1985, 367).

33. Presentation Outline
Resin Injection / Hydraulic Fracture of Strata
Progression of Resin Bolting Studies – Gloving / Mixing / Pressure
Borehole Resin Pressures – Parametric Analysis
– Fluid Flow Concepts
– Empirical Relationship
Experimental Method and Results
Empirical Calculations & Model
Load Transfer Tests
Conclusion

34. Presentation Outline
Resin Injection / Hydraulic Fracture of Strata
Progression of Resin Bolting Studies – Gloving / Mixing / Pressure
Borehole Resin Pressures – Parametric Analysis
– Fluid Flow Concepts
– Empirical Relationship
Experimental Method and Results
Empirical Calculations & Model
Load Transfer Tests
Conclusion

35. Borehole Resin Pressures – Empirical Relationship
So, the basic empirical model becomes:
Pb = ƒ ( Va2 / 2)
Where:
Pb = Borehole Internal Pressure (kg.m-1.s-2)
Va = Fluid Velocity in Annulus (m.s-1)
ƒ = functional correlation between pressure and resin fluid velocity

36. Borehole Resin Pressures – Empirical Relationship
Alternately expressed…
Pb = Rpv ( Va2 / 2)
Where:
Pb = Borehole Internal Pressure (kg.m-1.s-2)
Va = Fluid Velocity in Annulus (m.s-1)
Rpv = pressure-velocity ratio (kg.m-3)
at peak pressure & insertion

37. Borehole Resin Pressures – Empirical Relationship
Pb = Rpv ( Va2 / 2)
Assumptions:
Indeterminate and minor parameters are initially set aside.
However - the influences of indeterminate and minor parameters are actually captured in the experimental data sets.

38. Borehole Resin Pressures – Empirical Relationship
Pb = Rpv ( Va2 / 2)
Assumptions:
Predominant measureable relationship is between back pressure and annulus fluid velocity.
Derived Rpv values are ‘exclusive’ to each individual resin type / experimental data set
This exclusivity accounts for fluid ‘viscosity’ and ‘density’ by resin type.

39. Presentation Outline
Resin Injection / Hydraulic Fracture of Strata
Progression of Resin Bolting Studies – Gloving / Mixing / Pressure
Borehole Resin Pressures – Parametric Analysis
– Fluid Flow Concepts
– Empirical Relationship
Experimental Method and Results
Empirical Calculations & Model
Load Transfer Tests
Conclusion

40. Presentation Outline
Resin Injection / Hydraulic Fracture of Strata
Progression of Resin Bolting Studies – Gloving / Mixing / Pressure
Borehole Resin Pressures – Parametric Analysis
– Fluid Flow Concepts
– Empirical Relationship
Experimental Method and Results
Empirical Calculations & Model
Load Transfer Tests
Conclusion

41. Borehole Resin Pressures – Experimental Method
Experimental methodology – borehole sleeving (McTyer et al., 2014).
PVC pipe (sleeve) constrained within a heavy walled steel pipe, capped, anti-rotation features.
Permits quick change-over of PVC sleeves / multiple tests – large data sets.

42. Borehole Resin Pressures – Experimental Method
Experimental methodology – borehole sleeving (McTyer et al., 2014).
Boreholes of 28mm and 30mm, resins of 15:1 and 2:1 compartment ratios.
Instrumentation:
thrust force (kN)
displacement (mm)
rotational speed (rpm)
against time (sec)
Enables calculations of bore hole pressures.

43. Experimental Results – 15:1 Resins, 1000mm Long
28mm Bore
28mm Bore
28mm Bore
Avg. of
20 Tests
Avg. of
5 Tests
30mm Bore
30mm Bore
30mm Bore

44. Experimental Results – 2:1 Resins, 1000mm Long
28mm Bore
28mm Bore
28mm Bore
Avg. of
20 Tests
Avg. of
10 Tests
30mm Bore
30mm Bore
30mm Bore

45. Experimental Results – 30mm Bore, 1000mm Long
15:1 Resin
15:1 Resin
15:1 Resin
Avg. of
5 Tests
Avg. of
10 Tests
2:1 Resin
2:1 Resin
2:1 Resin

46. Presentation Outline
Resin Injection / Hydraulic Fracture of Strata
Progression of Resin Bolting Studies – Gloving / Mixing / Pressure
Borehole Resin Pressures – Parametric Analysis
– Fluid Flow Concepts
– Empirical Relationship
Experimental Method and Results
Empirical Calculations & Model
Load Transfer Tests
Conclusion

47. Presentation Outline
Resin Injection / Hydraulic Fracture of Strata
Progression of Resin Bolting Studies – Gloving / Mixing / Pressure
Borehole Resin Pressures – Parametric Analysis
– Fluid Flow Concepts
– Empirical Relationship
Experimental Method and Results
Empirical Calculations & Model
Load Transfer Tests
Conclusion

48. Borehole Resin Pressures – Empirical Calculations
Qa = vc / tf and Va = Qa / Aa
Qa = volumetric flow rate
of resin into annulus (m3.s-1)
vc = volume of Resin Cartridge (m3)
tf = time for full insertion through
the resin cartridge (s)
Va = velocity of resin within the annulus (m.s-1)
Aa = annulus area (m2)
and Pb = Fo / Ab
Pb = Borehole Internal Pressure (kg.m-1.s-2)
Fo = Output Force (N)
Ab = borehole area (m2)

49. Borehole Resin Pressures – Empirical Calculations
Volumetric Flow Rate Qa = vc / tf
Fluid Velocity in Annulus Va = Qa / Aa
Peak Borehole Pressure Pb = Fo / Ab ƒ
2 Pb
Peak Pressure / Velocity Ratio Rpv =
Va2

50. Borehole Resin Pressures – Empirical Calculations
Pb = Rpv ( Va2 / 2)

51. Borehole Resin Pressures – Empirical Calculations
Pb = Rpv ( Va2 / 2)

52. Borehole Resin Pressures – Empirical Calculations
Pb = Rpv ( Va2 / 2)

53. Borehole Resin Pressures – Empirical Calculations
Pb = Rpv ( Va2 / 2)

54. Borehole Resin Pressures – Empirical Calculations
Pb = Rpv ( Va2 / 2)

55. Borehole Resin Pressures – Empirical Calculations
Pb = Rpv ( Va2 / 2)

56. Borehole Resin Pressures – Empirical Calculations
Pb = Rpv ( Va2 / 2)

57. Borehole Resin Pressures – Empirical Calculations
Pb = Rpv ( Va2 / 2)

58. Borehole Resin Pressures – Empirical Calculations
Pb = Rpv ( Va2 / 2)

59. Borehole Resin Pressures – Empirical Calculations
Pb = Rpv ( Va2 / 2)

60. Borehole Resin Pressures – Empirical Calculations
Pb = Rpv ( Va2 / 2)

61. Borehole Resin Pressures – Empirical Model
15:1 Resin Cartridges

62. Borehole Resin Pressures – Empirical Model
2:1 Resin Cartridges

63. Borehole Resin Pressures – Discussion Points
The peak pressure charts clearly indicate the nature of the relationship - increasing borehole and reducing insertion velocity substantially reduces the peak pressure.
The pressures derived are of a similar magnitude to the borehole pressures measured by Giraldo (2006) MPa to MPa.
The 2:1 pressure curves are slightly more elevated compared to the equivalent 15:1 curves – this notionally captures the fact that the 2:1 resins are slightly ‘thicker’ or more ‘viscous’ compared to the 15:1 resins.
It is anticipated that further experimentation will continue to refine the empirical model.

64. Presentation Outline
Resin Injection / Hydraulic Fracture of Strata
Progression of Resin Bolting Studies – Gloving / Mixing / Pressure
Borehole Resin Pressures – Parametric Analysis
– Fluid Flow Concepts
– Empirical Relationship
Experimental Method and Results
Empirical Calculations & Model
Load Transfer Tests
Conclusion

65. Presentation Outline
Resin Injection / Hydraulic Fracture of Strata
Progression of Resin Bolting Studies – Gloving / Mixing / Pressure
Borehole Resin Pressures – Parametric Analysis
– Fluid Flow Concepts
– Empirical Relationship
Experimental Method and Results
Empirical Calculations & Model
Load Transfer Tests
Conclusion

66. Load Transfer Tests – 300mm Embedment
Inherent concern - increasing annulus size, the load transfer performance is assumed to reduce.
Pre-cast concrete block (42 MPa), a series of drilled holes 300mm deep.
28mm hole / 15:1 resins – 10 tests
30mm hole / 2:1 resins – 10 tests
Boreholes cleaned, inspected and measured prior to resin installation.

67. Load Transfer Tests – 300mm Embedment
All tests used standard AT bolts, 600mm in length to pass continuously through jack body – no couplers used.
Installed using recommended manufacturers spin times, 24 hour period before pull testing commenced.
The hollow bore jack and pressure gauge had current 3rd party calibration.
Displacements were measured using a dial gauge indicator mounted on a rigid steel block.

68. Load Transfer Tests – 300mm Embedment
All tests used standard AT bolts, 600mm in length to pass continuously through jack body – no couplers used.
Installed using recommended manufacturers spin times, 24 hour period before pull testing commenced.
The hollow bore jack and pressure gauge had current 3rd party calibration.
Displacements were measured using a dial gauge indicator mounted on a rigid steel block.

69. Load Transfer Tests – 300mm Embedment
30mm Bore
2:1 Resin
28mm Bore
15:1 Resin

70. Presentation Outline
Resin Injection / Hydraulic Fracture of Strata
Progression of Resin Bolting Studies – Gloving / Mixing / Pressure
Borehole Resin Pressures – Parametric Analysis
– Fluid Flow Concepts
– Empirical Relationship
Experimental Method and Results
Empirical Calculations & Model
Load Transfer Tests
Conclusion

71. Presentation Outline
Resin Injection / Hydraulic Fracture of Strata
Progression of Resin Bolting Studies – Gloving / Mixing / Pressure
Borehole Resin Pressures – Parametric Analysis
– Fluid Flow Concepts
– Empirical Relationship
Experimental Method and Results
Empirical Calculations & Model
Load Transfer Tests
Conclusion

72. Conclusion
Plastic gloving and poor resin mixing is a known concern with 15:1 ratio resin cartridges – particularly in boreholes greater than 28mm in diameter.
For boreholes smaller than  28mm, resin pressurisation can be elevated to levels that potentially induces hydraulic fracture and delamination of weaker strata.
2:1 resins are observed to mix well within  30mm boreholes, providing load transfer results that appear to exceed that of 15:1 resins within a  28mm borehole.

73. Conclusion
The derivation of an empirical relationship is useful in determining the risk of hydraulic fracture and resin loss - this risk is seen to substantially reduce for boreholes greater than  28mm.
Taking all factors into account, the combination of 2:1 resins, utilised within  mm bore holes, may well provide the optimal resin bolting solution for M24 bolts.

74. Conclusion
Resin Performance Summary

75. Delivering the support you need
Presentation End
Coal Hardrock Post-tensioning Geotechnics
Delivering the support you need