Advanced Geotechnical Methods for Exploration: The A-GaME

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Advanced Geotechnical Methods for Exploration:The A-GaME

Bring It!

Benjamin S. Rivers, P.E.FHWA- Resource Center

64Th Alabama Transportation ConferenceFebruary 10th, 2021

Center for Accelerating Innovation

What are the Advanced Geotechnical Methods in Exploration?

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The A-GaME is a toolbox of underutilized subsurface exploration tools that will assist with:• Assessing risk and variability in site

characterization• Optimizing subsurface exploration programs• Maximizing return on investment in project

delivery

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The A-GaME’s Mission

Mitigate risks to project schedule and budget, and improve reliability by optimizing geotechnical site characterization using proven, effective exploration methods and practices.

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Risk

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Source: FHWASource: Ohio DOT

Source: ALDOT

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Risk

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Source: Florida DOT

Source: Kentucky Transportation Cabinet

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Benefit of Upfront Site Investigation Investment

6Source: NCHRP Synthesis 484 - Influence of Geotechnical Investigation and Subsurface Conditions on Claims, Change Orders, and Overruns (After Figure 1)

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MODOT Approach for Relating Design Reliability to Variability. Example Shown: Tip resistance – shafts in clay

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COV of Mean Undrained Shear Strength, COVsu

Bridges on Minor RoadsBridges on Major RoadsMajor Bridges (<$100 million)Major Bridges (>$100 million)

Source: Missouri DOT

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Mainstream Effective Underutilized MethodsCPT - Cone Penetration Test

SCPT - Seismic Cone Penetration Test

ER - Electrical Resistivity

IP - Induced Polarization

SP - Self Potential

MWD - Measurement While Drilling

Seismic: Refraction

Seismic: Reflection

Seismic: FWI - Full Waveform Inversion

Seismic: SASW - Spectral Analysis of Surface

Waves

Seismic: Tomography

Seismic: Downhole

Seismic: Crosshole

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TDEM - Time-Domain Electromagnetic

FDEM - Frequency-Domain Electromagnetic

VLFEM - Very Low Frequency Electromagnetic

OTV - Optical Televiewers

ACT - Acoustic Televiewers

GPR - Ground Penetrating Radar

MicroGravity

PMT - Pressuremeter Test

DMT - Flat Plate Dilatometer Test

Rock Discontinuities from Photogrammetry

Pore-water pressure from Field Piezometers

Suspension Logging

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Site Characterization – Current Practice

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Total Volume Tested or Sampled < 0.01% (typically)

To Scale

Boring/CPT LocationsBorings: Typ. SPT every 5 feet; 18 inch of Sampling

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Site Characterization – Bringing your A-GaME

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Source: Florida DOT

• 6-Mile Section

• 1-day Field Testing

• ½-day Processing

Confirm conditions

Concentrate additional investigation where most valuable

Soft Soils Likely

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Sheet Pile EndSheet Pile Start

769 770 771 772 773

DRIVEN PILE DRILLED PILES

SHEET PILE EXTENT

Depth and location of sheeting & king piles

Geophysics for final designApplying geophysics to pile design/layout

Source: MNDOT

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Seismic Refraction – Top of Bedrock

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Source: Jeff Reid, Hager-Richter

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Mainstream Effective Underutilized MethodsCone Penetration Testing (CPTu/SCPTu)• More reliable

parameters than from conventional SPT

• Small strata changes easily discernable

• Pore-water pressure measurements

• Shear-wave measurements with SCPTu

• 3-10 times faster than conventional drilling

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Source: FHWA

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Televiewers – Optical and Acoustic (OTV/ATV)• High-resolution, 360o, GIS,

spatially oriented rock drillhole images

• Continuous• In-place rock structure and

condition• Eliminates difficult oriented

coring• Independent of core quality

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Mainstream Effective Underutilized Methods

Courtesy of Jeff Reid, Hager-Richter Assoc.

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Mainstream Effective Underutilized MethodsMeasurement While Drilling (MWD)• Continuous

profile• Discernable

stratigraphic and material changes

• Rock or Soil• Standardized in

Europe ISO 22476-15

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• Drilling equipment requirements• Measuring system requirements

MWD Equipment Requirements

(modified after Jean Lutz S.A., 2020) Slide Courtesy of Anahita Modiriasari, 2020

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Most Basically, MWD provides…• Continuous quantitative

drilling record• Means to assess site

variability• QC/QA value

Source: Harry Moore (Retired TN DOT)

Courtesy of Liz Smith, Terracon

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(Gui et al., 2002)

Immediate Applications• Karst Features• Detecting Boulders, Lenses, Bedrock

Interfaces• Characterization of Piedmont

Residuum and PWR• Stratification and material

identification (contrasting)

Source: FHWA

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Continuing Work Needed to…Understand interdependencies while maintaining production:• Between drilling

parameters• Bit types and size• Drilling methods –

Including HSA

Correlate to engineering index parameters

(Reiffsteck et al., 2018)

Quantitative analysisMeasuring rock strength while drilling shafts socketed into Florida limestone

Examples of MWD Investigations in Geotechnical Engineering

(Rodgers et al., 2018)Slide Courtesy of Anahita Modiriasari, 2020

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A-GaME: What’s Next?In-The-Works• User Groups• Virtual Demos/Workshops/Deep-Dive Webinars (in partnership

with A-GaMEr DOTs, DFI, Industry)• A-GaME Web Platform (in partnership with DFI)

• Archived “A-GaME Winter Webinar Series” Recorded Webinars

• MWD Implementation Document• Geophysics Webtool• Case-Histories/References/Resources• User-Group Links

• DIGGS Implementation (in partnership with GI)• Look Up AASHTO PP 102

• AASHTO Manual on Subsurface Investigation (AASHTO COMP TS1b)

• Influence of COV in LRFD (AASHTO COBS T-15)• Stop-Gap Standards of Practice (collaboration with DFI, GI,

EEGS)

A-GaME e-News New!

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Kaye Chancellor Davis, Thank You for Your Leadership!

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Questions

Benjamin S. Rivers, FHWA Resource Centerbenjamin.rivers@dot.gov404-562-3926