Carborough Downs LW 4 Salvage Roof Fall and Recovery. February 2014

Transcription

1 Carborough Downs LW 4 Salvage Roof Fall and Recovery February 2014

2 Introduction 1) Mine Plan 2) Time Line 3) Roof Fall potential mechanism 4) Fall Recovery and Salvage

3 Mine Plan LW4 salvage face and location of fall of ground 2

4 PLAN VIEW OF FALL 3 Presentation Title 01/12/2010 (optional)

5 Time Line LW4 Bolt up was completed 12 th December LW tear down started and completed by 23 rd December Salvage of the run of face shields began 23 rd December Salvage stopped for Christmas shutdown 24 th December and restarted 27 th December Salvage continued with minor/normal convergence levels from shield #133 to around shield #86 Typical convergence up to this point was 20-50mm per 24 hrs The goaf behind the E-frame was noted to be standing to the TG (124m) which is not typical at CDCM 4

6 Time Line During the salvage of Shield #86 on 31 st December it was noted that convergence rates between shields #75 to #50 (around MG Chute Rd) was increasing resulting in clearance issues. In the period of 31 st December N/S to 2 nd January N/S the shields between #75 to #50 underwent a significant weighting event converging mm going into yield. At this time Tell Tale monitoring and other visual indicators showed no atypical roof deformation in this area. The goaf remained open from the E-frame to TG In the following days shields #86 to #77 were salvaged, requiring the floor to be shot out to gain sufficient height to retrieve the shields At 3.30 am on 4 th January a fall of ground occurred during the salvage of shield # 76 5

7 Fall of Ground The fall of ground starts at Shield #56 and extends towards the TG to Shield #75 (adjacent to the E-frame) The goaf remained standing from the E-frame to the TG 6 View looking from #57 towards the E-frame

8 Fall of Ground The fall of ground occurred between the canopy tips and the faceline. The height of the fall of ground is approximately 8m. 7

9 Pulled #76 (NS) 3h30am Fall of ground

10 9 Presentation Title 01/12/2010 (optional)

11 Fall of Ground Mechanism Abutment Load Sub-vertical fractures induced ahead of Longwall face due to abutment load Shear on bedding planes Due to bending of strata towards goaf Sandstone Siltstone ~6-7m Sandstone Siltstone Goaf ~1.5-2m Coal

12 Fall of Ground Mechanism Increased Abutment Load Weighting Event Sandstone Siltstone ~6-7m Sandstone Siltstone Goaf ~1.5-2m Coal Increased Rib deformation leading to rib spall

13 Fall of Ground Mechanism Shearing of Sub vertical fractures Delamination along bedding plane Sandstone Siltstone ~6-7m Sandstone Siltstone Goaf ~1.5-2m Coal Gravity

14 Fall of Ground Mechanism Sandstone Siltstone 4m ~6-7m Sandstone Cavity Siltstone Goaf ~1.5-2m Coal

15 Recovery and Salvage Plan Immediately after the roof fall a stabilisation plan was developed and implemented for the area on the MG side of the fall, the E- frame and adjacent shields. Key aim of this was to ensure the extent of the fall was confined and provide a safe working environment from which we could undertake the salvage of the fall. Immediate Response Standing rock-props #25 to fall Install Cable Trusses from #25 to fall Install 4m grouted dowels in face from #25 to fall and in MG chute road 14

16 Recovery and Salvage Plan Risk based approach to fall salvage. Stakeholder involvement and buy in. Plan developed to be undertaken in stages: 1. Shutter-off fallen ground 2. Pump fall material and roof void with grout - Ensuring, with the use of probe holes, no voids are present (QA) 3. Mine through fall area with RH or CM and re-support Ensuring the roadway created is fit for purpose for LW salvage 4. Recommence LW salvage operations. 15

17 CONSTRUCTION OF THE SHUTTER 16 Presentation Title 01/12/2010 (optional)

18 Stand Pipes In Shutter 17 Presentation Title 01/12/2010 (optional)

19 RECOVERY DESIGN While pumping FB200 grout and undertaking QA process, a series of discussions were held regarding the re-support method. Options Considered: 1) Steel Sets 2) Cable Trusses and bolts Key driver was SAFETY and need to resume LW salvage. Decided steel sets were not the right option. A lot of resistance from some members of workforce and management. Experience base was steel sets 18 Presentation Title 01/12/2010 (optional)

20 RECOVERY DESIGN 19 Presentation Title 01/12/2010 (optional)

21 ROADHEADER WORKING INTO AREA 20 Presentation Title 01/12/2010 (optional)

22 ROADHEADER WORKING INTO AREA 21 Presentation Title 01/12/2010 (optional)

23 ROADHEADER WORKING INTO AREA 22 Presentation Title 01/12/2010 (optional)

24 ROADHEADER WORKING INTO AREA 23 Presentation Title 01/12/2010 (optional)

25 ROADHEADER WORKING INTO AREA 24 Presentation Title 01/12/2010 (optional)

26 ROADHEADER WORKING INTO AREA 25 Presentation Title 01/12/2010 (optional)

27 RECOVERY Completed backfill and re-mining + re-support through to the E-frame by 16 th February De-mobed Roadheader, completed roadworks and got underway. LW Salvage recommenced 18 th February Pulled shields past fall area and MG chute road by 22 nd Feb No strata related issues in fall area. Shooting under iron bound shields planned Strata behaving in normal way LW salvage due for completion 28/2/14 Only 1 minor injury slip/trip type 26 Presentation Title 01/12/2010 (optional)