Radar Movement Monitoring TARP Trigger Setting Dilemmas

John Simmons

Sherwood Geotechnical and Research Services

Peregian Beach QLD 4573

BOHOGS Peak Downs Mine 9 May 2017

Simple Guide to Slope Mechanics

R

Du

t

u

RESULTANT FORCE IN DIRECTION OF MOVEMENT:DF = D – R

MOVEMENT IN RESPONSE TO UNEQUILIBRATED FORCE:DF = M a, a = ü

velocity-t1

velocity-t2

Acceleration~ D(velocity)/Dt

ACCELERATION > 0.0 IMPLIES THAT LOCAL OR GLOBAL FACTOR OF SAFETY IS 1.0 OR LESS

Displacement Rate: Pre-Radar Guidance

after Figure 21 of Sullivan, TD, 2007. Hydromechanical coupling and pit slope movements. Keynote Address, Slope Stability 2007, Proceedings of the 2007 International Symposium on Rock Slope Stability in Open Pit Mining and Civil Engineering, Perth. Australian Centre for Geomechanics, pp 3-43. ISBN 9780975675687

Intention of PHMP’s

OPERATIONSHistoryExperienceObservations → TARPs• SOPs• JHAs

• consequences• exposures• likelihoods

DESIGNHistoryExperienceData, Assumptions → Assessment• Standard Designs• Specific Recommendations

• consequences• exposures• likelihoods

ACT → High-Level Risk Assessment → PH Consequences

“Strata Failure” Principal Hazard Management Plan(what, where, when, how, who, why)

Generic Advice on Trigger Levels

ACARP Project C15033 (2011)ESFC-Based Trigger Levels for Monitoring Pit Wall StabilitySherwood Geotechnical and Research Services Report Number 7260-1-2 www.acarp.com.au

Explanation: Composite Failure

Potential failure path includes:

• Pre-existing defects(sliding and separation)

plus:

• Rock material(fracture, sliding, and separation)

Failure can occur very quickly with little warning

Most frequently duringCoal Mining

JPS16 Microseismic Array

JPS16 Radar Monitoring SSR14

JPS16 Deformation Model (Phase2)

JPS16 Rock Mass Response Models

JPS16 ESFC-Related Triggers

Summarise Simmons 2011 Vancouver

DIP = 0°

JPS16 ESFC-Related Triggers

DIP = 5°

In a Nutshell ...

1) Extension Strain Fracturing is real and inevitable and is generated by deformation in response to stress removal

2) Microseismic monitoring is not a practical tool for risk control in an open pit mining environment

3) Pre-collapse movements can be detected for about 2 days prior to collapse but absolute resolution has to be ≤ 5mm/day

4) Radar can detect such movements but only if platform movements can be rigorously assessed

5) The extent of stable extensional fracturing can be reliably predicted with a joint network rock mass model

6) Collapse trigger levels can be developed using a joint network rock mass model, by assuming 20mm in excess of background movement rate, or by assuming > 25mm/d

TARPS REQUIRE TRIGGER LEVELS

DILEMMAS FOR TRIGGER SETTING1. Trigger Levels must be in accordance with levels of RISK as

described in the PHMP

2. Where do I get meaningful numbers for Trigger Levels?

Displacement over time? Computed Velocity? Acceleration?

Applying:

• Anywhere? Use maximum identified by radar?

• Specific Locations? Guided by suspected mechanism?

3. When increasing displacements are detected, how do I use the tools available with the radar software to give adequate warning?

4. How do I minimise the likelihood of false or excessive alarms?

5. How do I report the process to keep people adequately informed?

Example Daily Status Report

Example Daily Status Report

OPEN DISCUSSION: RADAR TRIGGER SETTING1. Where do I get meaningful numbers for Trigger Levels?

Displacement over time? Computed Velocity? Acceleration?

Applying:

• Anywhere? Use maximum identified by radar?

• Specific Locations? Guided by suspected mechanism?

2. When increasing displacements are detected, how do I use the tools available with the radar software to give adequate warning?

3. How do I minimise the likelihood of false or excessive alarms?

Barry Ward – contributions Peter Saunders – contributions