Download - GEOPHYSICAL VOID DETECTION DEMONSTRATIONS
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6th Biennial ITGAUM Workshop, June 4-16, 2006, Rochester, NY
GEOPHYSICAL VOID DETECTIONGEOPHYSICAL VOID DETECTIONDEMONSTRATIONSDEMONSTRATIONS
By:Kanaan Hanna, Bart Hoekstra,
Jim Pfeiffer, & Brandy Uphouse
MSHA:Steve Vamosy
George Gardner
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Presentation FocusPresentation Focus
Engineering ProblemProgram Goals and ObjectivesGeophysical Methodology – Field InvestigationsVoid ConfirmationGeophysical Technologies Performance EvaluationsConclusions and Recommendations
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Engineering ProblemEngineering Problem
• Unknown mines,• Inaccurate historical mine maps, or• Incomplete historical mine maps
MSHA Old mine works present major H&S hazards to our nation’s miners…
DOT’s Abandoned mines beneath roadways impact the performance of transportation infrastructure in terms of…• Cost,• Public safety
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Program Goals and ObjectivesProgram Goals and Objectives
MSHA’s Overall GoalsTo…
Advance the current state-of-the-practice geophysical technologies for detecting mine voids
ToTo……Accurately & economically
detect underground mine voids
Overall Program Objectives
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Objectives ContinuedObjectives Continued……
Definition: Old mine works vs.
Mine voids
Old mine works: Identify the general location/boundary of the UG workings
Mine voids: Identify the location of mine opening/entries, and pillars
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Presentation FocusPresentation Focus
Engineering ProblemProgram Goals and ObjectivesGeophysical Methodology – Field InvestigationsVoid ConfirmationGeophysical Technologies Performance EvaluationsConclusions and Recommendations
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• Surface and borehole geophysical methods:– 3-D high resolution seismic (HRS) using P-waves (HRPW)
and S-waves (HRSW)– Crosshole tomography (XHT)– Crosshole guided waves– Reverse vertical seismic profiling (RVSP)– Borehole sonar mapping
Geophysical MethodologyGeophysical Methodology
• Demonstration site:– Known abandoned coal mine adjacent to an active UG
room-and-pillar mine, Georgetown, IL
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Geophysical Methods Geophysical Methods –– An OverviewAn Overview
Basic Concept of the RVSP and HRS Techniques
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Site DescriptionSite Description
Geologic Setting Thickness of Material
in FtUnconsolidated Clay with Gravel Tan or BuffUnconsolidated Silt with Gravel Red or BrownUnconsolidated Silt with Gravel Med GrayUnconsolidated Sand with Gravel - LargeUnconsolidated Silt with Gravel Med GraySandstone - Med. Gray Sandy Shale - Med Gray Shale - Dark Gray
Danville Coal Seam # 7 (No Mining ~ 140 Ft Deep) 3.70Sandy Claystone - Med Gray Sandstone- Med Gray LimestoneSandstone- Med Gray Sandstone, Limey Med Gray with Nodules Sandy Shale - Med Gray Shale - Med Gray with Coal Streaks
Herrin Coal Seam # 6 (Target Zone ~ 233-235 Ft Deep) 6.80Limey Sandy ClaystoneSandy Claystone - Med Gray Limey Claystone - Med Gray - NodulesBlack Shale with Coal Streaks
Springfield Coal Seam # 5 ( No Mining ~ 253 Ft Deep) 0.80Limey Claystone - Med Gray - NodulesSandy Shale - Med Gray Shale - Dark Gray Black Limey ShaleSandy Shale - Med Gray
Total Drill Depth 320.00
89.30
13.20
66.20
30.00
110.00
Subsurface Strata Above and Below the Herrin Coal Seam #6
Gla
cial
M
ater
ial
Ove
rbur
den
Mat
eria
l 23
3 ft
Und
erly
ing
Mat
eria
l 80.
2 ft
Upper Coal Seam
Target Coal Seam
Lower Coal Seam
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Grid Location of HRSW and HRPW 3-D Reflection Surveys
HRS Data AcquisitionHRS Data Acquisition
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HRS Data AcquisitionHRS Data Acquisition
Georgetown Rd
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Data Analysis and InterpretationAnomalous Coal Response from P-wave
Geophysical Methodology Geophysical Methodology -- HRSHRS
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• Provided consistent data quality throughout the survey
• Obtained clear reflections from the Herrin #6 coal seam
• Imaged the general location of the old mine works
• Inadequate to identify mine voids (rooms/entries, pillar)
Geophysical Methodology Geophysical Methodology –– HRSHRS
HR primary P-wave 3-D (HRPW):
Conclusions…
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• Obtained some reflections from Herrin #6 coal seam
• The deployment of two vibrator sources were still insufficient to compensate for energy loss
• Provided limited information on the old mine works
Geophysical Methodology Geophysical Methodology –– HRSHRS
HR shear S-wave 3-D (HRSW):
Conclusions
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Geophysical Methodology Geophysical Methodology –– XHT/GWXHT/GW and and RVSPRVSP
Borehole Location Overlaid HRS Image
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Geophysical Methodology Geophysical Methodology –– Boreholes DrillingBoreholes Drilling
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Geophysical Methodology Geophysical Methodology -- RVSPRVSP
RVSP Data Analysis and InterpretationSeismic Amplitudes from RVSP Profiles along the Target Zone
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Peak Seismic Amplitudes at Target Zone Overlain on Historical Mine Map
Geophysical Methodology Geophysical Methodology -- RVSPRVSP
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Geophysical Methodology Geophysical Methodology -- RVSPRVSP
Peak Seismic Amplitudesat Target Zone fromNS #6 to NS #4
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Presentation FocusPresentation Focus
Engineering ProblemProgram Goals and ObjectivesGeophysical Methodology – Field InvestigationsVoid ConfirmationGeophysical Technologies Performance EvaluationsConclusions and Recommendations
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Boreholes Layout Basedon RVSP Results andHistorical Mine Map
Void ConfirmationVoid Confirmation
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Drilling along NS Mains and Sonar Mapping
Void ConfirmationVoid Confirmation
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Void Confirmation Void Confirmation –– Sonar Mapping Field ResultsSonar Mapping Field Results
Conf NS#4
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Void Confirmation Void Confirmation –– Sonar InterpretationsSonar Interpretations
Sonar Void Models Overlay Historical Mine Map
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Presentation FocusPresentation Focus
Engineering ProblemProgram Goals and ObjectivesGeophysical Methodology – Field InvestigationsVoid ConfirmationGeophysical Technologies Performance EvaluationsConclusions and Recommendations
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Criterion HRPW HRSW XHT GuidedWaves RVSP Sonar
Mapping*
Ability to LocateMine Works/Voids Fair Fair Poor Poor Good n/a
Resolution Poor Poor Poor Very Poor Very Good Excellent
Depth ofInvestigation Good Poor Good Good Good Very Good
AnticipatedRepeatability Good Fair Good Fair Good Very Good
Robustness underVariousGeologic/SurfaceConditions
Fair Poor Fair Fair Good Very Good
Cost High Very High Medium Low Medium Medium
Void Contents Poor Good Poor Poor Good Very Good
*Sonar mapping can only be used in a borehole that has intersected a water-filled void in the mine.
Performance EvaluationPerformance Evaluation
Performance Evaluation of Geophysical Methods
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Have these geophysical technologies met the overall project objective...
Performance EvaluationPerformance Evaluation
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NO
Partially
YESYES
Performance EvaluationPerformance Evaluation
…..……. XHT and guided waves
…………HRPW/HRSW
…….…..RVSP
Objective Select the most accurate and cost-effective method…!
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Presentation FocusPresentation Focus
Engineering ProblemProgram Goals and ObjectivesGeophysical Methodology – Field InvestigationsVoid ConfirmationGeophysical Technologies Performance EvaluationsConclusions and Recommendations
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The geophysical technologies demonstration at the The geophysical technologies demonstration at the site has verified the effectiveness of the.site has verified the effectiveness of the.……
RVSPRVSP
WhenComplemented by Sonar or Laser Mapping
Combined with Engineering Practices – the most viable geophysical method to…
Accurately and Economically Detect Mine Voids
Conclusions and RecommendationsConclusions and Recommendations
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Proposed RVSP Geophysical/Geotechnical Investigations for Commercial and Residential
Development
Where to go from here
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RVSP Proposed Methodology RVSP Proposed Methodology
A systematic approach – integrating 2-D and/or 3-D RVSP geophysical investigations with subsidence engineering evaluation for optimum foundation design…
Geophysics RVSP Subsurface Investigation:• Identify old mine works• Identify mine voids
Engineering GeophysicsSubsurface Characterization in terms of:• Subsidence evaluation• Void detection evaluation
Engineering Evaluation
Engineering Analysis:• Geotechnical evaluation• Foundation system evaluation and risk assessment• Engineering decision
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Schematic of Recommended RVSP Survey for Mine Void Detection
RVSP Proposed Methodology RVSP Proposed Methodology
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RVSP Investigation
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Questions