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

BBUGS Suppliers Day - Moranbah Formal Proceedings UOW 2015 Coal Conference: pp. 129 - 137 ICGCM 2015 Conference: pp. 97 - 104

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

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

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.

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.

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 ?

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

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

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.

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

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.

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

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

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

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

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

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

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 24.13 MPa (3,500 psi) and 48.26 MPa (7,000 psi).

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

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

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

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

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

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)

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

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

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

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

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.

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).

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).

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

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

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

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

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.

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.

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

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

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.

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.

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

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

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

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

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

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)

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  

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

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

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

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

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

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

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

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

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

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

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

Borehole Resin Pressures – Empirical Model 15:1 Resin Cartridges

Borehole Resin Pressures – Empirical Model 2:1 Resin Cartridges

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) - 24.13 MPa to 48.26 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.

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

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

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.

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.

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.

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

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

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

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.

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  28 - 30mm bore holes, may well provide the optimal resin bolting solution for M24 bolts.

Conclusion Resin Performance Summary

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