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Submitted by: Chaz Weaver, P.E. VDOT and Jim Sheahan, P.E. HDR Engineering, Inc

Research Needs Statement Installation of Micropile Foundations in Karst Topography. Submitted by: Chaz Weaver, P.E. VDOT and Jim Sheahan, P.E. HDR Engineering, Inc. General Background FHWA-NHI-05-039 (December,2005) “ Micropile Design and Construction”;

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Submitted by: Chaz Weaver, P.E. VDOT and Jim Sheahan, P.E. HDR Engineering, Inc

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  1. Research Needs Statement Installation of Micropile Foundations in Karst Topography Submitted by:Chaz Weaver, P.E. VDOT and Jim Sheahan, P.E. HDR Engineering, Inc

  2. General Background • FHWA-NHI-05-039 (December,2005) “Micropile Design and Construction”; • AASHTO LRFD Bridge Design Specifications 5th Edition, 2010, Section 10.9; • et al (ISM and other resources)

  3. Possible Applications of Micropiles • Restricted Access/Headroom or A Remote Area; • Support System Close to Existing Structure; • Supplemental Support For An Existing Structure (e.g. Settlement Control); • Difficult Ground Conditions (e.g., karst, mines, boulders, uncontrolled fill); • Risk of Liquefaction From Pile Driving; • Need To Minimize Vibration And/Or Noise; • Need To Reduce Or Eliminate Spoil At Hazardous Or Contaminated Sites • As Alternate Deep Foundation Type, Especially Where Piles Penetrate Rock; • Where Spread Footings Are Feasible but There Is Potential For Erosion or Scour

  4. Drilled Shafts/Micropiles [Bond Zone] [Bond Zone]

  5. Micropile Design • Per AASHTO Section 10.9 • Special Features for Karst • Case through voids and check for buckling • Anticipate Variability and Adjust, if needed • -Room for additional piles in the pattern, if necessary • Design for Redundancy, and Adjust, if needed • - Resistance Factor <AASHTO = 0.70

  6. QA/QC >>Pre-Construction • Contractor and Employee qualifications; • Performance Criteria (location, orientation, size, cross section, capacity); • Equipment List; • Installation Plan; • Grout Mix Design; • Load Test Procedures including calibration information; • Materials Disposal Plan; • Remedial Action Plan for Problems • Pre-Construction Meeting to Review Subsurface Conditions/Procedures/Installation Plan/etc.

  7. QA – During Construction Contractor Set Up Drilling Reinforcement Grouting Post Installation

  8. Submissions Required • Installation Records for each micropileinstalled: • (Minimum Information) • -drilling log with penetration rates (length/minute) • -materials encountered • -final tip elevation • -total micropile length • -description of unusual behavior/conditions • -grout quantity pumped • -pile materials and dimensions • -compliance with tolerances

  9. Load Testing and QC Methods • Load Testing (Axial Compression) • Static (ASTM) • Dynamic (Statnamic, GRLApple, et al) • QC Field Test Methods • Downhole Camera • Pile Integrity Testing (PIT)

  10. Research Proposal • Review available literature on the use of micropiles in karst and summarize design methods including consideration of variability and voids as well as specifications and procedures used to verify assumption during installation. • Review field documentation procedures including logging for drilling and documentation of grout volumes placed. • Review load testing procedures available and QC methods. • Develop specifications including QA/QC procedures for micropile construction on VDOT projects, particularly in karst topography. • Develop training program for design and construction staff that results in understanding of micropile design and construction QA/QC prodecures

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