TRC1803 Mapping Subsurface Conditions for Transportation - - PowerPoint PPT Presentation

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TRC1803 Mapping Subsurface Conditions for Transportation - - PowerPoint PPT Presentation

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TRC1803 Mapping Subsurface Conditions for Transportation Applications Clinton M. Wood 1 , PhD PE 1 Department of Civil Engineering, The University of Arkansas, Fayetteville, USA. 2018 TRC Meeting Hot Springs, AR; 17 May, 2018 1 Arkansas

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TRC1803 Mapping Subsurface Conditions for Transportation Applications

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Clinton M. Wood1, PhD PE

1Department of Civil Engineering, The University of Arkansas, Fayetteville, USA.

2018 TRC Meeting Hot Springs, AR; 17 May, 2018

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Arkansas Department of Transportation (ARDOT) Unexpected subsurface conditions (soft layers on slopes or bedrock) Expensive change

  • rders and time and cost
  • verruns or slope

stability issues on transportation projects

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Better mapping of subsurface conditions maybe possible using geophysical methods

  • Drilling and Sampling only

provides information at discrete locations.

  • Geophysical methods can

provide a more continuous image

  • f the subsurface.
  • This more complete image can be

used to inform slope stability remediation designs and bedrock cut requirements.

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Project Objectives

  • Identify AHTD project sites which could benefit from geophysical testing.
  • Develop a proposed field investigation plan for each site and perform testing using

various geophysical methods.

  • Analyze collected field data to determine accuracy, advantages, benefits, cost, and

limitations of each geophysical method for specific tasks.

  • Recommend a system for purchase.
  • Conduct field trials on ARDOT sites to develop best practices and sample datasets for the

equipment.

  • Conduct slope stability analyses on sites using geophysical and other data from the

tested slope stability site.

  • Produce project deliverables and provide training.
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Task 1: Identification of project sites, collection of data, and analysis of data.

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Task 1: Identification of project sites, collection of data, and analysis of data.

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Task 1: Identification of project sites, collection of data, and analysis of data.

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Task 1: Identification of project sites, collection of data, and analysis of data.

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Slope Stability Site near Sand Gap, AR

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Task 1: Identification of project sites, collection of data, and analysis of data.

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Slope Stability Site near Sand Gap, AR (Hwy 7)

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Task 2: Develop a proposed field investigation plan for each site and perform testing using various geophysical methods.

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Methods used for Geophysical Testing

  • 1. Multi‐Channel Analysis of Surface Waves (MASW)

I. With Rayleigh Waves II. With Love Waves

  • 2. Seismic Refraction
  • 3. Capacitively Coupled Resistivity (CCR)
  • 4. Electrical Resistivity Tomography (ERT) (Sand Gap
  • nly)
  • 5. Horizontal to Vertical Spectral Ratio (HVSR)
  • 6. Ground Penetrating Radar (GPR)
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Task 2: Develop a proposed field investigation plan for each site and perform testing using various geophysical methods.

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Sand Gap Slope Stability

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Task 2: Develop a proposed field investigation plan for each site and perform testing using various geophysical methods.

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Sand Gap Slope Stability

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Surface Wave Testing (MASW)/Seismic Refraction

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Receivers (24 total)

Laptop and Geode seismograph

Array Length (46 m) Source Locations Vertical Geophone on Landstreamer Strike Plate Sledgehammer (3‐5 Averages) Strike Beam

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Resistivity Testing CCR

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Receivers Transmitter GPS Unit Laptop Dipole Cable Dipole Length (5‐10 m)

Rope Length (2.5‐40 m)

Receivers Dipole Cables Transmitter Controller

Rope Length

Transmitter Dipole Length

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Resistivity Testing ERT

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SuperSting Control Box Pin and Electrode Cable

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Ground Penetrating Radar Testing

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Antennas Computer

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Horizontal to Vertical Spectral Ratio Testing

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Sensor Recorder

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Preliminary Results for Hardy Site (Love Wave MASW)

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Section A

BH 155+00 Soil Bedrock

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Preliminary Results for Hardy Site (Rayleigh Wave MASW)

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BH 155+00 Soil Bedrock

Section A

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Preliminary Results for Hardy Site (CCR)

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100 200 300 400 500 600 700 800 900 120 140 160

Section A

Soil Bedrock BH 155+00

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Preliminary Results for Hardy Site (GPR)

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Preliminary Results for Hardy Site

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10 20 30 40 50 60 Error index value (%)

Love HVSR Phase-Love Rayleigh Phase-Rayleigh P-wave refraction CCR

Comparison of methods to Borehole logs along the Alignment

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Final Thoughts

  • Geophysical methods can provide a rapid means of mapping subsurface conditions.
  • Each geophysical methods has strengths and limitations which make them more useful for

certain applications.

  • Based on preliminary results, the geophysical methods can provide an accurate and continuous

estimate of bedrock depth.

  • Future work includes completing data analysis and comparison of results and methods.
  • Providing recommendation regarding the most appropriate method.
  • Completing the Tasks for Year 2 of the project.
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Questions?