Monitoring the Threat of Sinkhole Formation US 18, Cerro Gordo Co., - - PowerPoint PPT Presentation

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Monitoring the Threat of Sinkhole Formation US 18, Cerro Gordo Co., - - PowerPoint PPT Presentation

Dec 08, 2022 625 likes •1.08k views

Monitoring the Threat of Sinkhole Formation US 18, Cerro Gordo Co., Iowa Using TDR Kevin M. O'Connor, Ph.D., P.E., GeoTDR Matthew Trainum, Iowa DOT, Office of Design 16 th Annual Technical Forum for Geohazards Impacting Transportation in

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Monitoring the Threat

  • f Sinkhole Formation

US 18, Cerro Gordo Co., Iowa Using TDR

Kevin M. O'Connor, Ph.D., P.E., GeoTDR Matthew Trainum, Iowa DOT, Office of Design

16th Annual Technical Forum for Geohazards Impacting Transportation in Appalachia Knoxville, TN August 2016

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Site Location and Conditions

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Sinkholes in Iowa

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2004

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EB inside

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EB outside

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EB outside ditch

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2004 Investigation

A geophysical investigation, to determine the cause of the problem and propose options for remediation, included a Ground Penetrating Radar Survey, a Resistivity Survey, and a Soil Survey (drilling program). No voids were identified beneath or within a couple meters of the pavement.

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2004 2005

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Outside ROW - South

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2004 2005 2008

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Decision +

 In 2009, a project was designed for letting

that would install a double reinforced inlay, including shoulders, for the designated area of concern on US 18 in Cerro Gordo County, Iowa.

 In addition to the inlay, the installation of

a Time Domain Reflectometry System (TDR) was chosen as a real-time monitoring device for the formation of voids/ sinkholes under the roadway.

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TDR Principle

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Cables can be grouted into boreholes or trenches to monitor deformation

TDR Cable Tester Crimp In Cable Expansive Cement Grout

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Activity up to Present Time

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crimps abrasion Cable shear would produce same reflection as a crimp Ground movement would fracture grout then cable deformation occurs

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Consistent and persistent response on all eight cables Abrasion not Shear Deformation of Cables

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Limited Correlation Among TDR, Geophysics, Drilling, and Sinkholes STA 248+75

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Eastbound STA 248+75

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In Nov 2011 and Jan 2012 exploratory drilling and geophysics did not find voids below pavement

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TIMING – new activity develops between September and March 2011, 2012, 2013, 2014, 2015, 2016

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Possible Causes

 Ground Movement

– Little or no indication of shear – Movement must cause abrasion

 Soil or Grout Shrinkage

– Requires sufficient shrinkage to cause abrasion

 Frost Heave

– Timing of TDR activity does not entirely coincide with period when frost is deepest

 Gnawing Animals

– IS THIS EVEN A POSSIBILTY??

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Additional Evidence of Burrowing

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Recent TDR Activity STA 252+02

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STA 252+02

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0.003 mm/day

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Current Status

 The persistence and consistency indicate

valid data

 The cause of cable abrasion is currently

indeterminate

 Even with this uncertainty, can still detect

cable deformation… so monitoring continues

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Questions for You

 The cause of cable abrasion is currently

indeterminate

 Has anyone seen precursor burrowing by

animals in karst areas?

 Can you suggest other causes?  Why limited to Sept-March?

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Real Time Monitoring with Time Domain Reflectometry (TDR)

Kevin M. O'Connor, Ph.D., P.E. GeoTDR, Inc. Westerville, Ohio www.geotdr.com