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 Department of Transportation (ARDOT) Unexpected subsurface conditions (soft layers on slopes or bedrock) Expensive change orders and time and cost overruns or slope stability issues on transportation projects TRC 1803 2
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 of the subsurface. • This more complete image can be used to inform slope stability remediation designs and bedrock cut requirements. TRC 1803 3
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. TRC 1803 4
Task 1: Identification of project sites, collection of data, and analysis of data . TRC 1803 5
Task 1: Identification of project sites, collection of data, and analysis of data . TRC 1803 6
Task 1: Identification of project sites, collection of data, and analysis of data . TRC 1803 7
Task 1: Identification of project sites, collection of data, and analysis of data . Slope Stability Site near Sand Gap, AR TRC 1803 8
Task 1: Identification of project sites, collection of data, and analysis of data . Slope Stability Site near Sand Gap, AR (Hwy 7) TRC 1803 9
Task 2: Develop a proposed field investigation plan for each site and perform testing using various geophysical methods. TRC 1803 10
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 only) 5. Horizontal to Vertical Spectral Ratio (HVSR) 6. Ground Penetrating Radar (GPR) TRC 1803 11
Task 2: Develop a proposed field investigation plan for each site and perform testing using various geophysical methods. Sand Gap Slope Stability TRC 1803 12
Task 2: Develop a proposed field investigation plan for each site and perform testing using various geophysical methods. Sand Gap Slope Stability TRC 1803 13
Surface Wave Testing (MASW)/Seismic Refraction Sledgehammer Source (3‐5 Averages) Locations Array Length (46 m) Receivers Laptop and Strike Geode (24 total) Plate seismograph Vertical Geophone on Landstreamer Strike Beam TRC 1803 14
Resistivity Testing CCR Transmitter Rope Length Receivers Rope Dipole Cable Length (2.5‐40 m) GPS Unit Dipole Length (5‐10 m) Laptop Transmitter Dipole Cables Transmitter Dipole Length Controller Receivers TRC 1803 15
Resistivity Testing ERT SuperSting Pin and Control Box Electrode Cable TRC 1803 16
Ground Penetrating Radar Testing Computer Antennas TRC 1803 17
Horizontal to Vertical Spectral Ratio Testing Recorder Sensor TRC 1803 18
Preliminary Results for Hardy Site (Love Wave MASW) BH 155+00 Soil Section A Bedrock TRC 1803 19
Preliminary Results for Hardy Site (Rayleigh Wave MASW) BH 155+00 Soil Section Bedrock A TRC 1803 20
Preliminary Results for Hardy Site (CCR) 160 BH 155+00 Soil Section A Bedrock 140 120 900 800 700 600 500 400 300 200 100 TRC 1803 21
Preliminary Results for Hardy Site (GPR) TRC 1803 22
Preliminary Results for Hardy Site Comparison of methods to Borehole logs along the Alignment 60 Love HVSR Phase-Love 50 Rayleigh Error index value (%) Phase-Rayleigh P-wave refraction 40 CCR 30 20 10 0 TRC 1803 23
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. TRC 1803 24
Questions? TRC 1803 25
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