Investigation of Shield Convergence in Underground Longwall Coal - - PowerPoint PPT Presentation

▶
investigation of shield convergence in underground
SMART_READER_LITE
LIVE PREVIEW

Investigation of Shield Convergence in Underground Longwall Coal - - PowerPoint PPT Presentation

Nov 09, 2023 150 likes •427 views

Investigation of Shield Convergence in Underground Longwall Coal Mining, A Case Study Luke Clarkson Graduate Geotechnical Engineer, BMA Thesis Presentation (goodyoda13 2014) Limitations Limitation #1. Limitation #2. Chart Showing Loading

slide-1
SLIDE 1

(goodyoda13 2014)

Investigation of Shield Convergence in Underground Longwall Coal Mining, A Case Study

Luke Clarkson Graduate Geotechnical Engineer, BMA Thesis Presentation

slide-2
SLIDE 2

Limitations

1-5 Minute Segment vs 5-10 Minute Segment

  • Evaluation of the earlier and shorter term loading and convergence

rates during the set to yield period may eliminate any compromise of the data caused by early yield in dedicated high set longwalls. Chart Showing Loading Rates against Convergence Rates for Broadmeadow LW8 Weighting Event 25/04/2013 to 04/05/2013 Time until Stability Restored: 67 hours Distance Travelled in this time: 5.6m Zero Convergence recorded 138 hours and 22.15m past event initiation.

Limitation #1. Limitation #2. Limitation #3.

(PDR Engineers, 2013)

Tilt sensors geometrically calculate the typical h1, h2 and h3 values. Caterpillar Tilt Sensor Resolution:

  • Approx. 8mm, 0.1°

CSIRO Tilt Sensor Resolution 0.01°

slide-3
SLIDE 3

Events Analysed

Detrimental Influence of Dyke Intrusion Cavities #2 & #3 Cavity #1 LW8 Weighting Event

Parameter Longwall 8 Weighting Event Longwall 9 Weighting Event Seam Thickness (m) 6.88 6.90 Depth of Cover (m) 235 270 Floor Strength (MPa) 32.5 29 Roof Strength (MPa) 16 22 MP42 (overburden sandstone unit) Thickness (m) 16.5 27.5 – 30 Microseismic Events Preceding Weighting 150 4

(SCT, 2013)

Load Cycle Map Showing Recorded Pressures over LW8 Panel Comparison between Geological parameters in LW8 and LW9 Events

slide-4
SLIDE 4
  • There is no correlation between number of yields and convergence rate.
  • Loading in excess of 2 bar/ minute during set-to-yield over 5-6 cutting cycles is indicative of an oncoming weighting
  • Previously estimated correlations between loading rate (5-10 min) and convergence rate are deemed to be subject to

geological and operating conditions:

  • Increased thickness of a competent, overburden unit will increase the intensity of a weighting after the unit breaks.
  • (Related to the previous point) A longer set-to-yield time can be indicative of normal conditions, or indicative of strata

unit competence and extended cantilevering.

  • 6.6% (or less) time spent in yield is reflective of stable although still periodic weighting influenced longwall mining

conditions.

  • ≥2 yields/ cycle for 3 consecutive cycles as an indicator of oncoming weighting.

Conclusions Made on Prediction of a Weighting Event

Event 1.5 bar/ min pressure increase rate correlates to… Periodic yet Stable Conditions (up to) 8.12mm/ hour convergence rate Broadmeadow LW8 Weighting Event 22.04mm/ hour convergence rate Cavity #1 19.7mm/ hour convergence rate Broadmeadow LW9 Weighting Event 9.76mm/ hour convergence rate

slide-5
SLIDE 5

Conclusions Made on Prediction of Cavities

  • Loading rates are not recommended as a parameter to monitor in anticipation of cavities.
  • Number of yields on the shield directly under the influence of a cavity are not recommended to monitor in

anticipation of cavities.

  • A predictive tool for cavities is observation of the number of yields of adjacent shields.
  • An additional indicator would be total convergence in a single cycle or for 3-5 cycles.
  • Deterioration of conditions as a result of structural geology should be an ongoing consideration.
slide-6
SLIDE 6

Analysis of Shield Closure vs Difference in Shield Heights

Convergence in Underground Longwall Mining

slide-7
SLIDE 7

Analysis of Shield Closure vs Difference in Shield Heights

Charts Showing Cumulative Difference in Tip Height compared to Average Shield Closure in Cycle

N.B. A positive displacement reflects downward movement

  • 600
  • 400
  • 200

200 400 600 800 1000 1200 1400

  • 1000
  • 500

500 1000 1500 2000 12:05 16:20 20:35 1:00 5:15 9:30 13:45 18:00 22:15 2:40 6:55 11:10 15:25 19:40 0:05 4:20 8:35 12:50 17:05 21:20 1:45 6:00 10:15 14:30 18:50 23:05 3:30 7:45 12:00 16:15 20:30 0:55 5:10 9:25 13:40 17:55 22:10 2:35 6:50 11:05 15:20 19:35 27/04 28/04 29/04 30/04 1/05 2/05 3/05 4/05 Shield Closure (mm) Displacement (mm) Time Cumulative

  • Diff. in Tip

Height (mm) Shield Closure (mm)

13.95mm/ hr 6.31mm/ hr 10.15mm/ hr 13.33mm/ hr 21.44mm/ hr

  • Shield closure is represented as an average ‘per cycle’.
  • Time until Stability Restored: 67 hours
  • Distance Travelled in this time: 5.6m
  • Zero Convergence recorded 138 hours and 22.15m past event initiation

Instability Duration, 5.6m of retreat until clear Overburden Sandstone fracturing point, reflected by increased convergence/ convergence rates Cumulative convergence allows

  • verlying sandstone to break
slide-8
SLIDE 8

Analysis of Shield Closure vs Difference in Shield Heights

  • 600
  • 400
  • 200

200 400 600 800 1000 1200

  • 600
  • 400
  • 200

200 400 600 800 1000 1200 4:10 6:20 8:30 10:40 12:50 15:00 17:10 19:20 21:30 23:40 2:00 4:10 6:20 8:30 10:40 12:50 15:00 17:10 19:20 21:30 23:40 2:00 4:10 6:20 8:30 10:40 12:50 15:00 17:10 19:20 21:30 23:40 2:00 4:10 6:20 8:30 10:40 12:50 15:00 17:10 19:20 21:30 23:40 2:00 4:10 19/07/2014 20/07/2014 21/07/2014 22/07/2014 23/07/2014 Cumulative Shield Closure (mm) Displacement (mm) Time Cumulative Difference in Shield Height (mm) Cumulative Shield Closure in Cycle (mm)

Overburden sandstone fracture

  • 500

500 1500 2500 3500 4500 5500

  • 500

500 1500 2500 3500 4500 5500 12:05 16:05 20:05 0:15 4:15 8:15 12:15 16:15 20:15 0:25 4:25 8:25 12:25 16:25 20:25 0:35 4:35 8:35 12:35 16:35 20:35 0:45 4:45 8:45 12:45 16:50 20:50 1:00 5:00 9:00 13:00 17:00 21:00 1:10 5:10 9:10 13:10 17:10 21:10 1:20 5:20 9:20 13:20 17:20 21:20 27/04 28/04 29/04 30/04 1/05 2/05 3/05 4/05 Cumulative Shield Closure (mm) Displacement (mm) Time Cumulative Diff. in Tip Height (mm) Cumulative Shield Closure (mm)

LW8 LW9

Charts Showing Cumulative Difference in Tip Height against Cumulative Shield Closure over time

N.B. A positive displacement reflects downward movement

Initial condition reflected height less than cut height. Negative fluctuations throughout reflect an attempt to return to appropriate operating height Linear increase between tip height and shield closure readings Instability Duration, 5.6m of retreat until clear Overburden Sandstone fracture 04:25 Shield tip height Reduction > Average Shield Closure

slide-9
SLIDE 9

LW8 LW9

0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5

  • 10
  • 8
  • 6
  • 4
  • 2

2 4 6 8 10 12:05 15:45 19:25 23:05 2:55 6:35 10:15 13:55 17:35 21:15 1:05 4:45 8:25 12:05 15:45 19:25 23:05 2:55 6:35 10:15 13:55 17:35 21:15 1:05 4:45 8:25 12:05 15:50 19:30 23:10 3:00 6:40 10:20 14:00 17:40 21:20 1:10 4:50 8:30 12:10 15:50 19:30 23:10 3:00 6:40 10:20 14:00 17:40 21:20 27/04 28/04 29/04 30/04 1/05 2/05 3/05 4/05 H1:H3 Ratio Canopy Attitude (°) Time Canopy Angle (°) H1:H3 Ratio 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 2 4 6 8 10 12 14 16 4:10 6:10 8:10 10:10 12:10 14:10 16:10 18:10 20:10 22:10 0:20 2:20 4:20 6:20 8:20 10:20 12:20 14:20 16:20 18:20 20:20 22:20 0:30 2:30 4:30 6:30 8:30 10:30 12:30 14:30 16:30 18:30 20:30 22:30 0:40 2:40 4:40 6:40 8:40 10:40 12:40 14:40 16:40 18:40 20:40 22:40 0:50 2:50 19/07/2014 20/07/2014 21/07/2014 22/07/2014 23/07/2014 H1:H3 Ratio Canopy Attitude (°) Time Canopy Angle (°) H1:H3 Ratio

Analysis of Shield Closure vs Difference in Shield Heights

Charts Showing Canopy Angle against H1:H3 Ratio over time (PDR Engineers 2013)

slide-10
SLIDE 10

Analysis of Shield Closure vs Difference in Shield Heights

Distance along Face (m)

100 200 300

  • Pillars exhibit influence 60m from each gate end
  • Shields in the centre of the panel are expected to experience the worst conditions
  • Strength Factor = Factor of Safety
  • Given excavation modelled with no structural support aside from coal pillars

Rocscience – Phase2D Finite Element Model

500 1000 1500 2000 12:05 17:40 23:15 05:00 10:35 16:10 21:45 03:30 09:05 14:40 20:15 02:00 07:35 13:10 18:45 00:30 06:05 11:40 17:20 22:55 04:40 10:15 15:50 21:25 03:10 08:45 14:20 19:55 01:40 07:15 12:50 18:25 27/04 28/04 29/04 30/04 01/05 02/05 03/05 04/05 Displacement (mm) Time Shield #115 Shield #110 Shield #100 Shield #90

Microseismic monitoring will allow for a better understanding of anticipated geological influences, and the associated magnitudes of effects, on different shields across the face.

White area represents excavated region in front of coal face Heading

slide-11
SLIDE 11

Analysis of Shield Closure vs Difference in Shield Heights

Cavity Identification through Shield Height Data (Cavity #1) (PDR Engineers 2013)

  • 1000
  • 500

500 1000 200 400 600 800 1000 22:00 1:15 4:20 7:25 10:30 13:35 16:40 19:45 22:50 2:05 5:10 8:15 11:20 14:25 17:30 20:35 23:40 2:55 6:00 9:05 12:10 15:15 18:20 21:25 0:40 3:45 6:50 9:55 13:00 16:05 19:10 22:15 1:30 4:35 7:40 10:45 13:50 16:55 20:00 23:05 26/05 27/05 28/05 29/05 30/05 31/05 Difference in Tip Height (mm) Average Shield Closure in Cycle (mm) Date Average Shield Closure in Cycle (mm) Cumulative Difference in Tip Height (mm) Manual correction reflected by increased shield closure in cycle Observable, rapid increase in height as shield sets to cavity

  • 4
  • 2

2 4 6 8 10 12 14 16 18

  • 0.05

0.15 0.35 0.55 0.75 0.95 1.15 1.35 1.55 22:00 1:15 4:20 7:25 10:30 13:35 16:40 19:45 22:50 2:05 5:10 8:15 11:20 14:25 17:30 20:35 23:40 2:55 6:00 9:05 12:10 15:15 18:20 21:25 0:40 3:45 6:50 9:55 13:00 16:05 19:10 22:15 1:30 4:35 7:40 10:45 13:50 16:55 20:00 23:05 26/05 27/05 28/05 29/05 30/05 31/05 Canopy Angle (°) H1:H3 Ratio Date H1:H3 Ratio Canopy Angle (°) Shield set to cavity

slide-12
SLIDE 12

Analysis of Shield Closure vs Shield Pressure - Yielding

Convergence in Underground Longwall Mining

slide-13
SLIDE 13

100 200 300 400 500 600 700 800 900 1000 1 2 3 4 5 6 7 8 Shield Closure Number of Yields Date MG Leg - Number of Yields TG Leg -Number of Yields Chart Showing Number of Yields for Each Leg compared to Leg Closure for Periodic yet Stable Conditions between 17-09-2013 and 10-10-2013

Analysis of Shield Closure vs Shield Pressure

Effects of Resets and Yielding

Chart Showing Percentage of Time Spent in Yield at Different Stages of Different Events

Percentage of time in yield compensates for:

  • Consistent high pressure application
  • Proximity to yield pressure at which shield sets

From this study, no direct proportionality between this parameter and magnitude of the event can be deduced.

slide-14
SLIDE 14

Analysis of Shield Closure vs Shield Pressure

Effects of Resets and Yielding

100 200 300 400 500 600 700 800 900 1000 2 4 6 8 10 12 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 Shield Closure (mm) Number of Yields Cycle Number MG Leg Number

  • f Yields

TG Leg Number

  • f Yields

Shield Closure Chart Showing Amount of Convergence compared to Number of Yields per Cycle for Broadmeadow LW8 Weighting Event 27/04/2013 - 04/05/2013

LW9 LW8

200 400 600 800 1000 2 4 6 8 10 12 14 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Shield Convergence (mm) Number of Yields Cycle Number MG Leg No. Of Yields TG Leg No. Of Yields Shield Convergence (mm) Chart Showing Amount of Convergence compared to Number of Yields per Cycle for Broadmeadow LW9 Weighting Event between 19/07/2014 and 23/07/2014 Event Initiation Event Initiation Observable, heightened number of yields on TG leg only. Minimal variance in number of yields prior to event, than that observed in stable yet periodic conditions.

slide-15
SLIDE 15

Stable yet Periodic Characteristics 1 Stable yet Periodic Characteristics 2 Broadmeadow LW8 Weighting Event (24/04/2013 - 08/05/2013) Alternate Cavity #1 (26/05/2013 - 09/06/2013) Alternate Cavity #2 (28/06/2013 - 07/07/2013) Alternate Cavity #3 (28/06/2013 - 07/07/2013) Broadmeadow LW9 Weighting Event (19/07/2014 – 23/07/2014)

Throughout Throughout Prior Post Prior Post Prior Post Prior Post Prior Post Minimum 1st Quartile 0.26 0.5 0.26 0.26 Median 1.04 1.04 2.52 2 2 3.04 1.04 3rd Quartile 2 2 2 5.26 2.78 1.04 1.04 3.04 4.78 3.04 Maximum 5.04 4 3.04 10 4 2 8 12 12 5.04 14 Average 1.17 0.79 1.25 3.51 1.63 0.63 0.86 2.24 3.06 1.67 0.9632

Analysis of Shield Closure vs Shield Pressure

Number of Yields

Table Showing Statistical Distribution of the Number of Yields per Cycle

  • ver 48 hours prior and post Alternate Events

Chart Showing Statistical Distribution of Number of Yields at 48 hours prior and post Alternate Events

slide-16
SLIDE 16

Cycle # Prior to Event LW8 Weighting Event Cavity #1 Cavity #2 Cavity #3 LW9 Weighting Event Leg 1 Leg 2 Leg 1 Leg 2 Leg 1 Leg 2 Leg 1 Leg 2 Leg 1 Leg 2 1 2 3.04 3.04 4 4 2 4 3.04 14 2 1.04 2 3.04 2 4 3.04 6 8 14 3 1.04 3.04 1.04 3.04 4 4 10 4 2 2 3.04 2 3.04 3.04 5

  • 2

2 1.04

  • 1.04

7.04 6

  • 1.04

2 8 4

  • 1.04

7

  • 3.04

3.04

  • 8
  • 1.04

Table Showing Number of Cycles Leading up to the Event (12 hours prior)

Averages of the cycles immediately prior to given events presented the following trends:

LW8 Weighting Event: 2 yields/ cycle for 4 cycles prior. Cavity #1: 2.5 yields/ cycle for 4 cycles prior. Cavity #2: 3.5 yields/ cycle for 3 cycles prior. Cavity #3: 3.5 yields/ cycle for 4 cycles prior. LW9 Weighting Event: inconsistent results.

Analysis of Shield Closure vs Shield Pressure

Number of Yields Trigger

slide-17
SLIDE 17

Analysis of Shield Closure vs Shield Pressure

Yield and Loading Rate Bridge

7 hours prior to the event, yields in cycle

  • n shields adjacent

to cavity begin to peak. Yields in Cycle across Panel Average Leg Pressure across Panel Cavity Formation Peaking of number

  • f yields on adjacent

shields

On prediction of cavity areas:

  • Focus on peaking in number of yields of shields either side of the cavity area
  • Behaviour visible on load cycle maps up to seven hours prior to cavity

formation.

  • This study recommends this trigger as the most reliable predictor to cavity

formation.

  • Terminology defines this behaviour as a conceptual ‘yield and loading rate’

bridge (Hoyer 2012).

slide-18
SLIDE 18

Analysis of Shield Closure vs Shield Pressure – Loading Rate

Convergence in Underground Longwall Mining

slide-19
SLIDE 19

Analysis of Shield Closure vs Shield Pressure

Loading Rate

1 2 3 4 5 6 7 8 9 1 7 13 19 25 31 37 43 49 55 61 67 73 79 85 91 97 103 109 115 121 127 133 139 145 151 157 163 169 175 181 187 193 199 205 211 217 223 229 235 241 247 Loading Rate (bar/min) Cycle Number MG Leg Shield #100 (bar/min) TG Leg Shield #100 (bar/min) Convergence (mm) Chart Showing Loading Rates (5-10 mins) compared to Convergence for Periodic yet Stable Longwall Weighting Conditions 18-09-2013 to 10-10-2013

  • Periodic weighting observable in load

cycle map, yet no strata deterioration

  • bserved, giving “periodic yet stable”

conditions.

  • MG and TG end visibly protected by pillar

support.

Parameter Loading Rate (bar/min) Minimum 1st Quartile 1.12 Median 2.32 3rd Quartile 3.12 Maximum 8.12 Average 2.21 3D Imaging Map Showing Loading Rates for Periodic yet Stable Longwall Weighting Conditions 18/09/2013 to 10/10/2013 Statistical Distribution of Loading Rates for Periodic yet Stable Longwall Weighting Conditions 18-09-2013 to 10-10-2013

slide-20
SLIDE 20

10 20 30 40 50 60 70 1 bar/min 2 bar/min 3 bar/min 4 bar/min 5 bar/min

  • Avg. Convergence Rate

in Cycle (mm/hr) Loading Rate in Cycle

LW9

20 40 60 80 100 120 1 bar/min 2 bar/min 3 bar/min 4 bar/min 5 bar/min

  • Avg. Convergence

Rate per Cycle (mm/hr) Loading Rate per Cycle

LW8

Parameter 1 bar/min 2 bar/min 3 bar/min 4 bar/min 5 bar/min Average 15.56 23.43 41.61 48.60 69.74 Parameter 1 bar/min 2 bar/min 3 bar/min 4 bar/min 5 bar/min Average 9.31 12.23 23.65 14.02 22.23

200 400 600 800 1000 1 2 3 4 5 6 7 8 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 Convergence (mm) Loading Rate (bar/min) Cycle Number MG Leg Shield #100 (bar/min) TG Leg Shield #100 (bar/min) Convergence (mm)

LW8 Weighting Event

Analysis of Shield Closure vs Shield Pressure

Loading Rate

Peak in Loading Rate prior to Weighting Event Peak in Convergence at Initiation of Weighting Event As loading rate increases, so too does convergence rate at this time.

slide-21
SLIDE 21

Analysis of Shield Closure vs Shield Pressure – Cycle Times

Convergence in Underground Longwall Mining

slide-22
SLIDE 22

200 400 600 800 1000 1200 Stable Longwall Conditions 05/05/2013 - 13/05/2013 Stable Longwall Conditions 17/09/2013 - 10/10/2013 Prior to LW8 Weighting Event 18/04/2013 – 28/04/2013 Envelope of Weighting Event 18/04/2013 – 10/05/2013 Prior to Cavity #1 Shield #93 from 28/05/2013 – 07/06/2013 Prior to Cavity #2 Shield #85 28/06/2013 – 09/07/2013 Prior to Cavity #3 Shield #85 28/06/2013 – 09/07/2013 Prior to LW9 Weighting Event 17/07/2014 - 21/07/2014 Cycle Time (Minutes) Event

Analysis of Cycle – Convergence Interface Including Set-to-Yield Analysis

Statistical Distribution of Cycle Times

  • Cycle Time: the time between two resets of the shield pressure
  • No quantified value or relationship was deduced as a result of the variability of

cycle times throughout. 50 100 150 200 250 300 350 400 Stable Longwall Conditions, 05/05/2013 - 15/05/2013 Stable Longwall Conditions, 17/09/2013 - 10/10/2013 Prior to LW8 Weighting Event, 27/04/2013 – 29/04/2013 Throughout LW8 Weighting Event, 27/04/2013 – 04/05/2013 Prior to Cavity #1, 26/05/2013 - 28/05/2013 Prior to Cavity #2, 28/06/2013 - 30/06/2013 Prior to Cavity #3, 03/07/2013 - 05/07/2013 Prior to LW9 Weighting Event, 19/07/2014 – 23/07/2014 Throughout LW9 Weighting Event, 19/07/2014 – 23/07/2014 Shearer Cycle Time (mins) Event

  • Shearer Cycle Time: the time it takes for the shearer to run from the maingate, to the

tailgate, and back to the maingate end of the panel after a cut and flit run.

  • No quantified value or relationship was deduced as a result of the variability of

cycle times throughout.

slide-23
SLIDE 23

0.02 0.04 0.06 0.08 0.1 0.12 0.14

  • 1.0
  • 0.3

0.5 1.2 2.0 2.7 3.5 4.2 4.9 5.7 6.4 7.2 7.9 8.7 9.4 10.2 10.9 11.6 12.4 13.1 13.9 14.6 15.4 16.1 16.8 17.6 18.3 19.1 19.8 Vertical Displacement of Strata (m) Distance Inbye from Coal Face (m) MP42 = 16.5m Thickness MP42 = 30m Thickness 100 200 300 400 500 600 Stable Longwall Conditions 05/05/2013 - 13/05/2013 Stable Longwall Conditions 17/09/2013 - 10/10/2013 Prior to LW8 Weighting Event 18/04/2013 – 28/04/2013 Prior to Cavity #1 Shield #93 from 28/05/2013 – 07/06/2013 Prior to Cavity #2 Shield #85 28/06/2013 – 09/07/2013 Prior to Cavity #3 Shield #85 28/06/2013 – 09/07/2013 Prior to LW9 Weighting Event 17/07/2014 - 21/07/2014 Time Elapsed (Minutes) Event

Chart Showing Statistical Distribution of Set-to-Yield Times Hydraulic Support Into Goaf

Analysis of Cycle – Convergence Interface Including Set-to-Yield Analysis

Cumulative Displacement alongside Set-to-Yield Statistical Distribution N.B. LW9 Event reflects statistically longer set-to- yield times than LW8 event. Set-to-Yield Duration: the time that it takes for the shield to increase from 350bar, the setting pressure, to 450 bar, the yield pressure Only variable is MP42 (overburden sandstone) thickness.

slide-24
SLIDE 24
  • There is no correlation between number of yields and convergence rate.
  • Loading in excess of 2 bar/ minute during set-to-yield over 5-6 cutting cycles is indicative of an oncoming weighting
  • Previously estimated correlations between loading rate (5-10 min) and convergence rate are deemed to be subject to

geological and operating conditions:

  • Increased thickness of a competent, overburden unit will increase the intensity of a weighting after the unit breaks.
  • (Related to the previous point) A longer set-to-yield time can be indicative of normal conditions, or indicative of strata

unit competence and extended cantilevering.

  • 6.6% (or less) time spent in yield is reflective of stable although still periodic weighting influenced longwall mining

conditions.

  • ≥2 yields/ cycle for 3 consecutive cycles as an indicator of oncoming weighting.

Conclusions Made on Prediction of a Weighting Event

Event 1.5 bar/ min pressure increase rate correlates to… Periodic yet Stable Conditions (up to) 8.12mm/ hour convergence rate Broadmeadow LW8 Weighting Event 22.04mm/ hour convergence rate Cavity #1 19.7mm/ hour convergence rate Broadmeadow LW9 Weighting Event 9.76mm/ hour convergence rate

slide-25
SLIDE 25

Conclusions Made on Prediction of Cavities

  • Loading rates are not recommended as a parameter to monitor in anticipation of cavities.
  • Number of yields on the shield directly under the influence of a cavity are not recommended to monitor in

anticipation of cavities.

  • A predictive tool for cavities is observation of the number of yields of adjacent shields.
  • An additional indicator would be total convergence in a single cycle or for 3-5 cycles.
  • Deterioration of conditions as a result of structural geology should be an ongoing consideration.
slide-26
SLIDE 26

Recommendations for Further Work

  • Evaluation of loading rates in a similar fashion to this study, yet in the 1-5minute range.
  • An evaluation of the geometric contribution of distance from the pivot point of the cantilever through

more in depth distance-based analyses.

  • Detailed analysis of shorter timeframes prior to historic weighting events
  • An introduction for the ability to monitor the rate of yield (amount of fluid coming out of the legs through

the yield valves)

  • Assessment of higher resolution convergence instrumentation
  • Analysis of a greater sample space of events including all weightings which did not result in cavities.
  • Further investigation into quantifiable energy release within events through microseismic monitoring.